mbelab.bib
@article{beaton2010,
author = {D.A. Beaton and R.B. Lewis and M. Masnadi-Shirazi and T. Tiedje},
title = {{Temperature dependence of hole mobility in GaAs$_{1-x}$Bi$_x$ alloys}},
publisher = {AIP},
year = {2010},
journal = {J. Appl. Phys.},
volume = {108},
number = {8},
eid = {083708},
numpages = {4},
pages = {083708},
keywords = {gallium arsenide; gallium compounds; Hall mobility; hole mobility; III-V semiconductors; impurities; phonons; semiconductor growth},
url = {http://link.aip.org/link/?JAP/108/083708/1},
doi = {10.1063/1.3493734},
abstract = {The Hall mobility of holes has been measured in GaAs grown at low temperatures and in GaAs$_{1-x}$Bi$_x$ alloys for Bi concentrations x ranging from 0.94\% to 5.5\%. The hole mobility is found to decrease with increasing Bi content. The temperature dependence of the mobility in the $25$ to $300~$K range is fit with a combination of phonon scattering, ionized impurity scattering, and Bi related scattering. The hole scattering cross-section for an isolated Bi impurity is estimated to be $0.2~$nm$^2$. The temperature independent mobility at the highest Bi concentration (x = 5.5\%), is interpreted as being limited by scattering from Bi clusters.}
}
@article{Kumaran2010:Epitaxial,
author = {Raveen Kumaran and Thomas Tiedje and Scott E. Webster and Shawn Penson and Wei Li},
journal = {Opt. Lett.},
keywords = {Laser materials; Rare-earth-doped materials; Thin films},
number = {22},
pages = {3793--3795},
publisher = {OSA},
title = {{Epitaxial Nd-doped $\alpha$-(Al$_{1-x}$Ga$_x$)$_2$O$_3$ films on sapphire for solid-state waveguide lasers}},
volume = {35},
year = {2010},
doi = {10.1364/OL.35.003793},
url = {http://ol.osa.org/abstract.cfm?URI=ol-35-22-3793},
abstract = {Single crystal aluminum-gallium-oxide films have been grown by
molecular beam epitaxy (MBE) in the corundum phase. Films of the
(Al$_{1-x}$Ga$_x$)$_2$O$_3$ alloys doped with neodymium have
favorable properties for solid state waveguide lasers, including a
high thermal conductivity sapphire substrate and a dominant emission
peak in the 1090-1096~nm wavelength range. The peak position is
linearly correlated to the unit cell volume, which is dependent on
film composition and stress. Varying the Ga-Al alloy composition
during growth will enable the fabrication of graded index layers for
tunable lasing wavelengths and low scattering losses at the
interfaces.}
}
@article{Webster2010:Structural,
author = {S.E. Webster and R. Kumaran and S. Penson and T. Tiedje},
journal = {J. Vac. Sci. Technol. B},
volume = {28},
number = {3},
pages = {C3A20--C3A23},
year = {2010},
publisher = {AIP},
title = {Structural analysis of thin epitaxial {Y$_2$O$_3$} films on sapphire},
url = {http://link.aip.org/link/?JVB/28/C3A20/1},
doi = {10.1116/1.3368608},
abstract = {High structural quality yttrium oxide films have been grown on R-plane sapphire by molecular beam epitaxy. X-ray diffraction measurements showed clear pendellosung fringes and sharp peaks. X-ray measurements indicate that the films grow nearly perfectly up to a critical thickness with x-ray peak widths as low as 7 arc sec. This critical thickness increases with decreasing growth rate up to 7 nm at 10 nm/h. The optimal growth temperature was found to be 800 $^{\circ}$C. Evidence of short range (<10 nm) surface diffusion is presented.}
}
@article{imhof:131115,
author = {Sebastian Imhof and Angela Thranhardt and Alexej Chernikov and Martin Koch and Niko S. Koster and Kolja Kolata and Sangam Chatterjee and Stephan W. Koch and Xianfeng Lu and Shane R. Johnson and Dan A. Beaton and Thomas Tiedje and Oleg Rubel},
collaboration = {},
title = {Clustering effects in {Ga(AsBi)}},
publisher = {AIP},
year = {2010},
journal = {Appl. Phys. Lett.},
volume = {96},
number = {13},
eid = {131115},
numpages = {3},
pages = {131115},
keywords = {gallium arsenide; III-V semiconductors; Monte Carlo methods; photoluminescence},
url = {http://link.aip.org/link/?APL/96/131115/1},
doi = {10.1063/1.3374884},
abstract = {The photoluminescence from a Ga(AsBi) sample is investigated as a function of pump power and lattice temperature. The disorder-related features are analyzed using a Monte Carlo simulation technique. A two-scale approach is introduced to separately account for cluster localization and alloy disorder effects. The corresponding characteristic energy scales of 11 and 45 meV are deduced from the detailed comparison between experiment and simulation.}
}
@article{Li2010:Optical,
author = {Wei Li and Scott E. Webster and Raveen Kumaran and Shawn Penson and Thomas Tiedje},
journal = {Applied Optics},
volume = {49},
number = {4},
pages = {586--591},
year = {2010},
publisher = {OSA},
title = {Optical wave propagation in epitaxial {Nd:Y$_2$O$_3$} planar waveguides},
url = {http://www.opticsinfobase.org/abstract.cfm?URI=ao-49-4-586},
doi = {10.1364/AO.49.000586},
abstract = {Optical wave propagation in neodymium-doped yttrium oxide (Nd:Y$_2$O$_3$) films grown on R-plane sapphire substrates by molecular beam epitaxy has been studied by the prism coupler method. The measurements yield propagation loss data, the refractive index, and the dispersion relation. The refractive index of the Nd:Y$_2$O$_3$ at 632.8 nm is found to be 1.909, and the lowest propagation loss measured is 0.9 +/- 0.2 cm$^{-1}$ at 1046 nm with a polymethyl methacrylate top cladding layer on a film with 6 nm root mean square surface roughness. The loss measurements suggest that the majority loss of this planar waveguide sample is scatter from surface roughness that can be described by the model of Payne and Lacey [Opt. Quantum Electron.26, 977 (1994)].}
}
@article{Kumaran2009:Epitaxial,
doi = {10.1364/OL.34.003358},
author = {Raveen Kumaran and Scott E. Webster and Shawn Penson and Wei Li and Thomas Tiedje and Peng Wei and Francois Schiettekatte},
journal = {Optics Letters},
keywords = {Laser materials; Rare-earth-doped materials; Thin films},
number = {21},
pages = {3358--3360},
publisher = {OSA},
title = {Epitaxial neodymium-doped sapphire films, a new active medium for waveguide lasers},
volume = {34},
year = {2009},
url = {http://ol.osa.org/abstract.cfm?URI=ol-34-21-3358},
abstract = {Epitaxial films of neodymium-doped sapphire have been grown by
molecular beam epitaxy on R, A and M-plane sapphire substrates. The
emission spectrum features sharp lines consistent with single site
doping of the Nd$^{3+}$ ion into the host crystal. This material is
believed to be a non-equilibrium phase, inaccessible by conventional
high temperature growth methods. Neodymium-doped sapphire has a
promising lasing line at 1096~nm with an emission cross section of
11.9$\times$10$^{-19}$~cm$^2$, similar to the 1064~nm line of
Nd:YVO$_4$.}
}
@article{Lu2009:Composition,
doi = {10.1063/1.3191675},
author = {Xianfeng Lu and D.A. Beaton and R.B. Lewis and T. Tiedje and Yong Zhang},
journal = {Appl. Phys. Lett.},
volume = {95},
pages = {041903},
publisher = {AIP},
title = {Composition dependence of photoluminescence of {GaAs$_{1-x}$Bi$_x$} alloys},
year = {2009},
url = {http://link.aip.org/link/APPLAB/v95/i4/p041903/s1},
abstract = {Room temperature photoluminescence (PL) spectra have been measured for GaAs$_{1-x}$Bi$_x$ alloys with Bi concentrations in the 0.2\%-10.6\% range. The decrease in the PL peak energy with increasing Bi concentration follows the reduction in bandgap computed from density functional theory. The PL peak energy is found to increase with PL pump intensity, which we attribute to the presence of shallow localized states associated with Bi clusters near the top of the valence band. The PL intensity is found to increase with Bi concentration at low Bi concentrations, peaking at 4.5\% Bi.}
}
@article{Beaudoin1999:Bandedge,
title = {Bandedge absorption of {GaAsN} films measured by the photothermal deflection spectroscopy},
journal = {Journal of Crystal Growth},
volume = {311},
number = {7},
pages = {1662--1665},
year = {2009},
doi = {10.1016/j.jcrysgro.2008.11.068},
url = {http://www.sciencedirect.com/science/article/B6TJ6-4V0MV7G-7/2/51abc86ddfd0ce64b10dbd7c4ec1c4ef},
author = {M. Beaudoin and I.C.W. Chan and D. Beaton and M. Elouneg-Jamroz and T. Tiedje and M. Whitwick and E.C. Young and J.F. Young and N. Zangenberg},
keywords = {A1. Characterization},
keywords = {A3. Molecular beam epitaxy},
keywords = {B1. Nitrides},
keywords = {B2. Semiconducting III-V materials},
abstract = {The optical absorption of GaAsN films grown by molecular beam epitaxy on GaAs substrates is measured using the mirage effect photothermal deflection spectroscopy (PDS). The PDS spectra were fitted with a modified Fernelius model, which takes into account multiple reflections within the GaAsN layer and GaAs substrate. This allowed the extraction of bandedge parameters for a series of GaAsN films with N content varying from 0.24\% to 1.4\% N. All films show a clear Urbach absorption edge with a composition-dependent bandgap consistent with literature and Urbach slope parameters roughly 3 times larger than GaAs values.}
}
@article{Lewis2008:GaAsBi_LED,
title = {{GaAs$_{1-x}$Bi$_x$} light emitting diodes},
journal = {Journal of Crystal Growth},
volume = {311},
pages = {1872--1875},
year = {2009},
url = {http://www.phas.ubc.ca/mbelab/papers/GaAsBi_LED.pdf},
author = {R.B. Lewis and D.A. Beaton and Xianfeng Lu and T. Tiedje},
abstract = {GaAs$_{1-x}$Bi$_x$ light emitting diodes have been grown and characterized. The p-i-n structure uses a 100 nm intrinsic layer with a central 50 nm GaAs$_{1-x}$Bi$_x$ light emitting layer with 1.8 \% bismuth. The diodes showed peaks in the electroluminescence (EL) emission at 987 nm from the GaAs$_{1-x}$Bi$_x$ and 870nm from the GaAs. The wavelength of the peak in the EL from the GaAs$_{1-x}$Bi$_x$ was independent of temperature in the range 100-300 K while the GaAs peak shifted with temperature as expected. Photoluminescence measurements on the same p-i-n structure show temperature dependence of the peak wavelength similar to the temperature dependence of GaAs.}
}
@article{Kumaran2008:Molecular,
title = {Molecular beam epitaxy growth of neodymium-doped yttrium aluminum perovskite},
journal = {Journal of Crystal Growth},
volume = {311},
number = {7},
pages = {2191--2194},
year = {2009},
doi = {10.1016/j.jcrysgro.2008.11.044},
url = {http://www.sciencedirect.com/science/article/B6TJ6-4TYJV4P-6/2/b438c41999c460f54b629b7a706863fd},
urlpdf = {http://www.physics.ubc.ca/mbelab/papers/kumaran2009_jcrygrow.pdf},
author = {R. Kumaran and S.E. Webster and S. Penson and Wei Li and T. Tiedje},
keywords = {Al. Crystal structure},
keywords = {A1. Heat transfer},
keywords = {A3. Molecular beam epitaxy},
keywords = {B1. Oxides},
keywords = {B1. Perovskites},
keywords = {B1. Rare-earth compounds},
abstract = {Epitaxial neodymium-doped yttrium aluminum perovskite
(Nd:YAlO3) has been grown by plasma-assisted molecular beam epitaxy on
R-plane sapphire at . The substrates were annealed in air at to
generate atomically ordered surfaces. Structural and optical
characterization was performed using X-ray diffraction and
photoluminescence. Emission spectra identical to that from bulk
crystalline Nd:YAlO3 were obtained.}
}
@article{ciatto2008:spatial,
author = {G. Ciatto and E. C. Young and F. Glas and J. Chen and R. Alonso Mori and T. Tiedje},
title = {Spatial correlation between {B}i atoms in dilute {G}a{A}s$_{1-x}${B}i$_x$: From random distribution to {B}i pairing and clustering},
journal = {\prb},
volume = 78,
pages = 035325,
url = {http://www.physics.ubc.ca/mbelab/papers/PhysRevB_78_035325.pdf},
doi = {10.1103/PhysRevB.78.035325},
year = 2008,
abstract = { We use x-ray absorption spectroscopy to investigate the
local structure around {B}i atoms in {G}a{A}s$_{1-x}${B}i$_x$ layers
grown on {G}a{A}s as a function of {B}i concentration in
order to detect short-range order. We find that static
disorder in the {B}i next-nearest-neighbor interatomic
distances dramatically increases when the {B}i
concentration is increased. At 1.2\% {B}i concentration,
the {B}i atoms are randomly distributed whereas at 1.9\%,
they tend to form next-nearest-neighbor pairs. When
the {B}i concentration rises to 2.4\%, our results
suggest that some of the {B}i atoms form small {B}i
clusters. Such strong deviations from a random
distribution are likely to play an important role in
the occurrence of the giant optical bowing recently
measured in this alloy. }
}
@article{franceur20098:Bi,
author = {S. Francoeur and S. Tixier and E. Young and T. Tiedje and A. Mascarenhas},
title = {{B}i isoelectronic impurities in {G}a{A}s},
journal = {\prb},
volume = 77,
pages = 085209,
url = {http://www.physics.ubc.ca/mbelab/papers/PhysRevB_77_085209.pdf},
doi = {10.1103/PhysRevB.77.085209},
year = 2008,
abstract = { {G}a{A}s$_{1-x}${B}i$_{x}$ is a mixed-anion semiconductor
alloy. In the {A}s-rich regime 0.4\% x 4 \% ,
isovalent {B}i creates a series of bound states but
this alloy nonetheless exhibits properties
characteristic of regular semiconductors. The dual
impurity-alloy character can be tuned by varying the
temperature. Below 100 K, multiple {B}i bound states
appear at low energy in the luminescence
spectrum. These states are associated with the
pseudo-donor potential created by isovalent {B}i
impurities. Taking into consideration the
concentration regime at which these bound states are
observed, they likely involve excitons bound to
clusters composed of a few substitutional {B}i atoms,
indirectly implying that the isolated {B}i state is
resonant with the valence band. At ambient
temperature, these localized states are strongly
suppressed and luminescence from the band edges is
measured. The important {B}i-induced atomic disorder
creates a strong intraband coupling resulting in an
important reduction of the band gap for a relatively
small alloy concentration. These results on a
pseudodonor isoelectronic alloy are reminiscent of the
better known pseudoacceptor {G}a{A}s{N}, but offer a
complementary view of this intriguing and yet little
understood class of alloys.}
}
@article{flugel2007:E,
author = {B. Fluegel and A. Mascarenhas and A. J. Ptak and S. Tixier and E. C. Young and T. Tiedje},
title = {E$_+$ transition in {G}a{A}s$_{1-x}${N}$_x$ and {G}a{A}s$_{1-x}${B}i$_x$ due to isoelectronic-impurity-induced perturbation of the conduction band
},
journal = {\prb},
volume = 76,
pages = 155209,
url = {http://www.physics.ubc.ca/mbelab/papers/PhysRevB_76_155209.pdf},
doi = {10.1103/PhysRevB.76.155209},
year = 2007,
abstract = { An above-band-gap transition E$_+$ is experimentally
observed in the dilute {G}a{A}s$_{1-x}${B}i$_x$
alloy. Precise measurements at very low dilutions are
made of the above-band-gap transition E$_+$ that is
observed in {G}a{A}s$_{1-x}${N}$_x$, making it
possible to compare the behavior of the different
isoelectronic traps {B}i and {N} in the common host
{G}a{A}s with respect to their perturbation to the
host electronic structure. We suggest that the origin
of the E$_+$ level observed in {G}a{A}s is not the
isolated isoelectronic impurity level {N}$_x$, as is
presumed in the band-anticrossing model, but rather
the isoelectronic-impurity-induced perturbation of the
conduction band L$^c_6$}
}
@article{pettinari2008:Influence,
author = {G. Pettinari and A. Polimeni and M. Capizzi and J. H. Blokland and P. C. M. Christianen and J. C. Maan and E. C. Young and and T. Tiedje},
title = {Influence of bismuth incorporation on the valence and conduction band
edges of {G}a{A}s$_{1-x}${B}i$_{x}$},
journal = {\apl},
volume = 92,
pages = 262105,
url = {http://www.physics.ubc.ca/mbelab/papers/ApplPhysLett_92_262105.pdf},
doi = {10.1063/1.2953176},
year = 2008,
abstract = {We investigate the electronic properties of
{G}a{A}s$_{1-x}${B}i$_x$ by photoluminescence at
variable temperature (T = 10-430 K) and high magnetic
field (B = 0-30
T). {I}n{G}a{A}s$_{0.981}${B}i$_{0.019}$, localized
state contribution to PL is dominant up to 150 K. At T
= 180 K the diamagnetic shift of the free-exciton
states reveals a sizable increase in the carrier
effective mass with respect to {G}a{A}s. Such an
increase cannot be accounted for by an enhanced
localized character of the valence band states,
solely. Instead, it suggests that also the Bloch
states of the conduction band are heavily affected by
the presence of bismuth atoms.}
}
@article{lu2008:Effect,
author = {X. Lu and D.A. Beaton and R.B. Lewis and T. Tiedje and M.B. Whitwick},
title = {Effect of molecular beam epitaxy growth conditions on the {B}i content of {G}a{A}s$_{1-x}${B}i$_x$},
journal = {\apl},
volume = 92,
pages = 192110,
url = {http://www.physics.ubc.ca/mbelab/papers/Xianfeng_APL.pdf},
doi = {10.1063/1.2918844},
year = 2008,
abstract = {We describe how the {B}i content of
{G}a{A}s${1-x}${B}i$_x$ epilayers grown on {G}a{A}s
can be controlled by the growth conditions in molecular
beam epitaxy. Nonstandard growth conditions are
required because of the strong tendency for {B}i to
surface segregate under usual growth conditions for
{G}a{A}s. A maximum {B}i content of 10\% is achieved
at low substrate temperature and low arsenic pressure,
as inferred from x-ray diffraction measurements. A
model for bismuth incorporation is proposed that fits
a large body of experimental data on {B}i content for a
wide range of growth conditions. Low growth rates are
found to facilitate the growth of bismide alloys with
a low density of {B}i droplets.}
}
@article{whitwick2008:LinSmoothing,
author = {M.B. Whitwick and T. Tiedje and Tian Li},
title = {Linear Smoothing of {G}a{A}s(100) During Epitaxial Growth on Rough Substrates},
journal = {\jcg},
volume = 310,
pages = {3192--3196},
doi = {doi:10.1016/j.jcrysgro.2008.03.019},
url = {http://www.physics.ubc.ca/mbelab/papers/Whitwick2008LinearSmoothing.pdf},
year = 2008,
abstract = { The smoothing of weakly roughened {G}a{A}s (100) substrates is measured with elastic light scattering during homoepitaxial growth of {G}a{A}s buffer layers. The smoothing measurements are used to determine the coefficient of the linear term in the continuum growth equation for {G}a{A}s, as a function of growth rate and temperature. The temperature and growth rate dependence are in good agreement with theoretical predictions from an atomistic description of the growth process. The density of atomic steps on the surface, which is a key parameter in the continuum growth equation, is measured independently using atomic force microscopy. The linear smoothing coefficients computed from the experimental values for the step density, are found to be in good agreement with the smoothing rates measured with light scattering. These experiments provide experimental support for the continuum growth model that has been derived analytically from basic atomic level phenomena in epitaxial film growth. }
}
@article{tiedje2008:bisnfriends,
author = {T. Tiedje and E. C. Young and A. Mascarenhas},
title = {Growth and Properties of the Dilute Bismide Semiconductor {G}a{A}s$_{1-x}${B}i$_{x}$ a Complementary Alloy to the Dilute Nitrides},
journal = {\ijn},
volume = {},
pages = {},
url = {http://www.physics.ubc.ca/mbelab/papers/bismide_review.pdf},
year = {2008},
abstract = {In this review we describe the growth and properties
of the dilute bismide semiconductor alloy
{G}a{A}s$_{1-x}${B}i$_{x}$ and show how its properties are
in certain respects complementary to the dilute
nitride alloy, {G}a{N}$_y${A}s$_{1-y}$. Like the dilute
nitrides the dilute bismides show a giant band gap
bowing effect in which a small concentration of the
alloying element has a disproportionate effect on the
band gap, however in the case of the bismide the band
gap reduction is associated with an increase in the
energy of the valence band maximum (VBM) rather than a
reduction in the energy of the conduction band minimum
(CBM). Under standard {G}a{A}s growth conditions {B}i acts
as a surfactant with associated improvements in
surface quality. In order to incorporate {B}i, growth
temperatures below 400$^o$C are used with {A}s$_{2}$/{G}a
flux ratios close to unity. The electron mobility of
{G}a{A}s is only weakly affected by {B}i alloying, in
contrast to the dilute nitrides where the electron
mobility decreases rapidly with N alloying. {B}i
alloying also produces a giant bowing effect in the
spin orbit splitting in the valence band. Strong room
temperature photoluminescence is observed. Prospects
for future device applications of this new compound
semiconductor alloy are discussed.}
}
@article{tiedje2008:tsf,
author = {T. Tiedje and A. Ballestad},
collaboration = {},
title = {Atomistic Basis for Continuum Growth Equation: Description of Morphological Evolution of {G}a{A}s During Molecular Beam Epitaxy
},
year = {2008},
publisher = {Elsevier B.V.},
journal = {\tsf},
volume = {516},
number = {12},
pages = {3705-3728},
keywords = {molecular beam epitaxy; thin film; gallium arsenide;III-V
semiconductors; gallium compounds;semiconductor growth;
kinetic monte carlo;solid on solid;continuum growth equation;scanning probe;
light scattering;adatom transport;downhill migration;stable growth},
url = {http://www.physics.ubc.ca/mbelab/papers/TSFarticle.pdf},
doi = {10.1016/j.tsf.2007.11.015},
abstract = { This review brings together experimental data on surface
shape evolution during epitaxial growth of {G}a{A}s with
kinetic Monte Carlo simulations of a solid-on-solid
model and numerical solutions of a continuum growth
equation derived from an adatom transport
equation. Scanning probe and light scattering
measurements of the surface morphology of {G}a{A}s, grown
by molecular beam epitaxy, on planar as well as
patterned (100) substrates are reviewed. We show that
the experimental data can be described by a stable
continuum growth equation that is mixed- order in the
spatial derivatives, with an Edwards-Wilkinson type
linear term, together with a conservative nonlinear
term. The stable growth equation is derived from two
coupled rate equations, one of which describes the
transport of adatoms on the surface and the other
describes the rate of change of surface height due to
adatom incorporation into the surface at step
edges. In this analysis, we assume that there is a
combination of an Ehrlich-Schwoebel barrier and/or an
incorporation barrier at step edges that favor a net
downhill migration of adatoms across step edges, with
the consequence that the growth model, like the
experimental system, is stable, meaning that
undulations in the surface tend to smooth out during
growth. The coefficients in the growth equation depend
on the growth rate and the density of steps on the
surface. The continuum description of the
morphological evolution is tested by comparisons to
computer experiments consisting of kinetic Monte Carlo
simulations of a solid-on-solid model. The methods
used in this analysis of {G}a{A}s epitaxy are expected to
be broadly applicable to other materials that exhibit
stable epitaxial growth. }
}
@article{karaiskaj2007:hiresphoto,
author = {D. Karaiskaj and A. Mascarenhas and J. F. Klem and K. Volz and W. Stolz and M. Adamcyk and T. Tiedje},
title = { High spectral and spatial resolution photoluminescence
experiments on excitons bound to nitrogen pairs in
{G}a{A}s },
year = {2007},
journal = {\prb},
volume = {76},
number = {},
pages = {125209},
keywords = {thin film; gallium arsenide;III-V semiconductors; gallium compounds;nitrogen;
semiconductor growth;photoluminescence;confocal microscopy},
url = {http://www.physics.ubc.ca/mbelab/papers/PRBsingleN-2.pdf},
abstract = { High resolution PL spectroscopy was performed on high
quality bulk {G}a{A}s, lightly doped with the nitrogen
isoelectronic impurity. The shallowest nitrogen pair
bound exciton center labeled as X1 revealed in total
six transitions, including transitions which had not
been observed previously. The photoluminescence lines
from a small ensemble of nitrogen centers showed
polarization depen- dent intensity. High spectral
resolution PL spectroscopy was combined with confocal
spectroscopy experiments performed on a {G}a{A}s:{N}/Al{G}a{A}s
heterostructure. The high spatial resolution achieved
by this technique enables us to localize and examine
individual nitrogen bound excitons. Similar spectral
structure and polarization dependence was observed for
individual {N}-pair centers in {G}a{A}s. Both techniques
support the C2v symmetry of such isoelectronic
impurity centers. The comparison between the PL
spectra from an ensemble of nitrogen pairs and
individual centers demonstrate the ability of the
single impurity technique to lift the orientational
degeneracy. }
}
@article{zangenberg2007:plasma,
author = {N. Zangenberg and D. A. Beaton and T. Tiedje and S. Tixier
and M. Adamcyk and R. Kumaran and J. A. MacKenzie
and E. Nodwell and E. C. Young and G. I. Sproule},
collaboration = {},
title = {Molecular beam epitaxy growth of the dilute nitride {G}a{A}s$_{1-x}${N}$_{x}$ with a helical resonator plasma source},
publisher = {AVS},
year = {2007},
journal = {Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films},
volume = {25},
number = {4},
pages = {850--856},
keywords = {molecular beam epitaxial growth; gallium arsenide; III-V
semiconductors; gallium compounds; wide band gap
semiconductors; plasma materials processing;
photoluminescence; semiconductor growth;
semiconductor epitaxial layers},
url = {http://www.physics.ubc.ca/mbelab/papers/JVA_plasma.pdf},
doi = {10.1116/1.2748800},
abstract = { Dilute nitride semiconductors of composition
{G}a{A}s$_{1-x}${N}$_{x}$ ($0.0017<$x$<0.0115$) are grown
by plasma-assisted molecular beam epitaxy with a
helical resonator plasma source for active
nitrogen. The plasma source is self-starting at the
operating pressure and can be operated at two
different frequencies for which the emission
spectrum is dominated by {N}$_{2}$ molecules or by {N}
atoms. For the same power the molecular-rich mode is
found to produce a higher flux of active
nitrogen. After extended operation the plasma tube
becomes contaminated with {A}s which reduces the flux
of active nitrogen and creates a below band gap
emission band in the photoluminescence of the
{G}a{A}s$_{1-x}${N}$_{x}$. For the clean discharge tube no
difference is observed in the photoluminescence for
samples grown in the molecule-rich or atom-rich
mode. }
}
@article{Robin2007:y2o3,
author = {I. C. Robin and R. Kumaran and S. Penson and S. E. Webster and T. Tiedje and A. Oleinik},
title = {Structure and photoluminescence of {Nd:Y$_2$O$_3$} grown by molecular beam epitaxy},
journal = {Optical Materials},
volume = {30},
year = {2008},
pages = {835--838},
doi = {10.1016/j.optmat.2007.03.003},
abstract = {Crystalline yttrium oxide films have been grown on
Si (001) and sapphire (0001) substrates by
molecular beam epitaxy using molecular oxygen and
thermal evaporation of yttrium. Neodymium doped
films showed strong room temperature
photoluminescence from the rare earth ions. The
dependence of luminescence intensity on neodymium
concentration was studied and a maximum was
estimated to occur at 2 at.\% assuming complete
neodymium incorporation. The structural properties
of the films were characterized using X-ray
diffraction.},
keywords = {Oxide thin films; Rare-earth doped oxides; Planar waveguides},
url = {http://www.sciencedirect.com/science/article/B6TXP-4NHD95S-1/2/3f3df445e401f6f1a917813f77d73bd0}
}
@article{Young2007:bismuth,
author = {E.C. Young and M.B. Whitwick and T. Tiedje and D. Beaton},
title = {{B}ismuth incorporation in {G}a{A}s$_{1-x}${B}i$_{x}$ grown by molecular beam epitaxy with in-situ light scattering},
journal = {\pssc},
volume = {4},
pages = {1707--1710},
url = {http://www.physics.ubc.ca/mbelab/papers/PSSc_ecyoung_Sept06.pdf},
year = {2007},
abstract = {The dilute bismide semiconductor
{G}a{A}s$_{1-x}${B}i$_{x}$ is an interesting new
semiconductor alloy with novel properties and
potential device applications. Like the dilute
nitride alloy {G}a{A}s$_{1-x}${N}$_{x}$, the dilute
bismide shows a giant bandgap bowing effect. {B}i
alloying primarily affects the states in the
vicinity of the top of the va-lence band rather than
the bottom of the conduction band as in the case of
{N} alloying. MBE growth of dilute bismides requires
low growth temperatures (320-390C) and near
stochiometric group III/V ratios, due to the strong
tendency of {B}i to surface segregate under usual {G}a{A}s
growth conditions. Optimal growth conditions are
close to conditions that produce {B}i and/or {G}a
droplets. In-situ light scattering is found to be a
useful tool for defining growth conditions that do
not produce droplets on the surface}
}
@article{Fluegel2006:giant,
author = {B. Fluegel and S. Francoeur and A. Mascarenhas and S. Tixier and E.C. Young and T. Tiedje},
title = {Giant spin-orbit bowing in {G}a{A}s$_{1-x}${B}i$_{x}$},
journal = {\prl},
year = {2006},
volume = {97},
pages = {067205},
url = {http://www.physics.ubc.ca/mbelab/papers/prl_fluegel_aug06.pdf},
abstract = {We report a giant bowing of the spin-orbit
splitting energy $\Delta_{o}$ in the dilute
{G}a{A}s$_{1-x}${B}i$_{x}$alloy for {B}i concentrations
ranging from 0\% to 1.8\%. This is the first
observation of a large relativistic correction to
the host electronic band structure induced by just a
few percent of isoelectronic doping in a
semiconductor material. It opens up the possibility
of tailoring the spin-orbit splitting in
semiconductors for spintronic applications.}
}
@article{Cooke2006:electron,
author = {D.G. Cooke and E.C. Young and F.A. Hegmann and T. Tiedje},
title = {Electron mobility in dilute {G}a{A}s bismide and nitride alloys measured by time-resolved terahertz spectroscopy},
journal = {\apl},
year = {2006},
volume = {89},
pages = {122103},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Cooke_Sept06.pdf},
abstract = {We report time-resolved terahertz spectroscopy
measurements of the electronic transport properties
of dilute {G}a{A}s bismide and nitride alloys. The
electron mobility for {G}a{A}s$_{1-y}${B}i$_{y}$ (y =
0.84\%) extracted from Drude fits to the transient
complex conductivity was ~2800 cm$^{2}$/Vs at a
carrier density of 2.7 x 10$^{18}$ cm$^{-3}$, close
to the mobility of 3300 cm/$^{2}$Vs measured for
{G}a{A}s at a similar carrier density. The electron
mobility did not decrease significantly for {B}i
concentrations up to 1.4\% . In contrast, the
{G}a{N}$_{x}${A}s$_{1-x}$ (x = 0.84\%) and
{G}a{N}$_{x}${A}s$_{1-x-y}${B}i$_{y}$ (x = 0.85\%, y =
1.4\%) films exhibited non-Drude behavior with
severely reduced electron mobility and suppressed
conductivity at low frequencies indicative of
carrier localization.}
}
@article{Ballestad2006:nonlinear,
author = {A. Ballestad and T. Tiedje},
title = {Emergence of Macroscopic Structure from Atomistic Dynamics in Epitaxial Film Growth},
volume = 74,
pages = 153405,
journal = {\prb},
year = {2006},
url = {http://www.physics.ubc.ca/mbelab/papers/PhysRevB_74_153405.pdf},
abstract = {A nonlinear differential equation is derived for
the surface shape evolution in epitaxial growth,
from a transport equation for the adatoms. A
negative Ehrlich-Sch{\"o}bel barrier is assumed to
be present at atomic steps favouring downhill
migration of adatoms. Expressions for the
coefficients in the growth equation are obtained in
terms of the deposition rate, step density, step
edge potential barrier and the adatom release rate
from step edges. The analytical model is found to
be in good agreement with a kinetic Monte Carlo
simulation of a solid-on-solid model, which includes
the same physical phenomena.}
}
@article{Karaiskaj:Ultra,
author = {D. Karaiskaj and A. Mascarenhas and M. Adamcyk and E.C. Young and T. Tiedje},
title = {Ultra narrow photoluminescence transitions of nitrogen cluster
bound excitons in dilute {G}a{A}s{N}},
journal = {\prb},
year = {2006},
url = {http:/www.physics.ubc.ca/mbelab/papers/PhysRevB_74_035208.pdf},
abstract = {High resolution photoluminescence spectroscopy on
heavily doped {G}a{A}s:{N} reveals the existence of
excitons bound to a nitrogen cluster. The observed
transitions are exceedingly sharp, similar to those
observed for excitons bound to nitrogen pairs in
high quality {G}a{A}s with the narrowest transition
being only 94 ueV. Moreover, several other features
can be observed originating most likely from phonon
replicas of the nitrogen pair bound excitons and
higher order clusters. However, the main transitions
which dominate the photoluminescence spectra are
thought to originate from excitons bound to a three
nitrogen cluster. The sharp photoluminescence
features are superimposed on a broad luminescence
band indicating a strong perturbation induced by
nitrogen atoms to the host {G}a{A}s lattice. The number
of the allowed transitions and their polarization
dependence provide important information about the
arrangement of the nitrogen atoms in the cluster.}
}
@article{Weilmeir:Optical,
author = {M.K. Weilmeier and K.M. Colbow and T. Tiedje and T. Van Buuren and Li Xu},
title = {A new optical measurement technique for semiconductor substrates in molecular beam epitaxy.},
journal = {\cajp},
pages = {422--426},
url = {http://www.physics.ubc.ca/mbelab/papers/CJPv69p422.pdf},
year = {1990},
abstract = {A new optical temperature measurement technique
for use in molecular beam epitaxy is demonstrated
with {G}a{A}s substrates. The temperature of the
semiconductor is inferred from its band gap, which
is measured by the diffuse reflectivity of the
substrate that is textured on the back surface. The
method has a sensitivity of better than 2C and an
absolute accuracy limited by the accuracy with which
the band gap is known as a function of temperature.
It was found to be necessary to calibrate the
measurement technique with a thermocouple in contact
with the sample in order to achieve satisfactory
accuracy at high temperatures. Measurements of the
optical absorption edge of {G}a{A}s, show that the slope
of the Urbach edge is independent of temperature
from room temperature to 450C.}
}
@article{Tiedje2006:Radiation,
author = {T. Tiedje and K.A. Mitchell and B. Lau and A. Ballestad and E. Nodwell},
title = {Radiation Transport Model for Ablation Hollows on Snowfields},
journal = {\jgres},
url = {http://www.physics.ubc.ca/mbelab/papers/Tiedje_et_al_JGR_2006.pdf},
year = {2006},
abstract = {The ablation hollows or ''suncups'' that form on the surface of snowfields in summer are
a wonderful example of pattern formation in nature. Suncups reduce the albedo of the snow and
set a characteristic length for interaction of wind with the snowpack. They also contain
information about the properties of the snow and its ablation rate, that could be extracted if we
had a more quantitative understanding of how suncups form. A mathematical model is proposed
that explains the shape, size and dynamical behavior of suncups in terms of the interaction of
solar radiation with the snowpack. Using a perturbation method, we derive a non-linear partial
differential equation for the time dependent shape of the snow surface from an approximate
physical model for the interaction of solar radiation with snow. The resulting equation, which is
similar to the Kuramoto-Sivashinsky equation in fluid mechanics, has a characteristic length and
amplitude. We find expressions for the characteristic size of suncups in terms of the spectrally
averaged diffusion length of solar radiation in snow. The model correctly describes the shape of
suncups, with their spatially ordered patterns of parabolic valleys and V-shaped ridges. It is also
in remarkably good agreement with the observed length scales and growth rates. Depending on
the relative values of the coefficients of the nonlinear terms in the differential equation, the
suncup patterns can be either stationary in time, or chaotic.}
}
@article{Young2005:Strain,
author = {E.C. Young and A.N. Koveshnikov and S. Tixier and K.L.
Kavanagh and T. Tiedje},
title = {Strain relaxation by <100> misfit dislocations in dilute
nitride {I}n{G}a{A}s{N}/{G}a{A}s quantum wells},
journal = {\pssa},
volume = {},
number = {3-4},
pages = {2849--2857},
url = {http://www.physics.ubc.ca/mbelab/papers/PSSa_ECYoung_Nov05.pdf},
year = {2005},
abstract = {The effect of dilute {N} alloying and {B}i surfactant growth
on strain relaxation in highly strained {I}n{G}a{A}s single quantum well (QWs) was
investigated by using high resolution X-ray diffraction (HRXRD) and
transmission electron microscopy (TEM). Dilute nitride {I}n{G}a{N}{A}s
QWs of varying thickness, constant lattice mismatch 1.7\%, were grown by
molecular beam epitaxy on oriented {G}a{A}s (001) substrates. Some samples were
exposed to a flux of {B}i surfactant during the growth procedure, which acts to
enhance the {N} incorporation, increase the optical emission, and create
smoother interfaces. The QWs were
observed to relax through the formation of pure edge-type, misfit dislocations
aligned with in-plane <100> directions. These were found to be directly
associated with degradation in the optical emission, however,1\% {N} addition,
with or without {B}i surfactant, did not have a detectable effect on the
critical thickness nor the rate of this relaxation mechanism.}
}
@article{Young2005:Bismuth,
author = {E.C. Young and S. Tixier and T. Tiedje},
title = {Bismuth surfactant growth of the dilute nitride {G}a{N}$_x${As}$_{1-x}$},
journal = {\jcg},
volume = {279},
number = {3-4},
pages = {316--320},
url = {http://www.physics.ubc.ca/mbelab/papers/JoCG_ECYoung_June05.pdf},
year = {2005},
abstract = {The presence of a bismuth surfactant is found to increase
the nitrogen incorporation in the dilute nitride {G}a{N}x{A}s$_{1-x}$ by as much as 60\%
during growth by molecular beam epitaxy. Films with nitrogen concentrations
in the 0.4-0.95\% range were grown using an RF plasma source for nitrogen.
The {B}i surface coverage is inferred from reflection high energy electron
diffraction as a function of {B}i flux and substrate temperature, and the
nitrogen content is obtained by high-resolution x-ray diffraction. At
constant substrate temperature the nitrogen content is found to increase with
{B}i coverage, which has the form of a Langmuir isotherm when plotted as a
function of {B}i flux.}
}
@article{Seong2005:Bi-induced,
author = {M.J. Seong and S. Francoeur and S. Yoon and A. Mascarenhas and S. Tixier and M. Adamcyk and T. Tiedje},
title = {{B}i-induced vibrational modes in {G}a{A}s{B}i},
journal = {\sm},
volume = {37},
pages = {394},
url = {http://www.physics.ubc.ca/mbelab/papers/SM_Seong_2005.pdf},
year = {2005},
abstract = {We have studied {G}a{A}s$_{1-x}${B}i$_x$ (up to $x \sim$ 3\%) using Raman scattering with two different polarization configurations. Two {B}i-induced phonon modes are observed at $\sim$186~cm$^{-1}$ and $\sim$214~cm$^{-1}$ with increasing Raman intensity as the {B}i concentration increases. By comparing Raman selection rules for the observed {B}i-induced phonon modes with those for the substitutional {N} vibrational mode ({G}a{N} mode) in {G}a{A}s{N}, the phonon mode at $\sim$214~cm$^{-1}$ is identified as originating from substitutional {B}i at the {A}s site in {G}a{A}s{B}i.}
}
@article{Ballestad2005:Nonlinear,
author = {A. Ballestad and B. Lau and J.H. Schmid and T. Tiedje},
title = {Nonlinear Growth in {G}a{A}s Molecular Beam Epitaxy},
journal = {\mrssp},
volume = {859E},
pages = {JJ9.6.1},
url = {http://www.physics.ubc.ca/mbelab/papers/MRSSP_Ballestad_v859EpJJ9-6-1.pdf},
year = {2005},
abstract = {We investigate experimentally and
computationally the nonlinear replication of surface shapes during
epitaxial growth. Experimental measurements of surface shapes
consisting of atomic force microscope (AFM) images of epitaxially
grown {G}a{A}s are compared with surface shapes computed from continuum
growth equations with a conservative or a non-conservative nonlinear
term. Both the non-conservative and the conservative nonlinear terms
are found to be consistent with the experiments, although the
conservative nonlinearity is preferred on physical grounds. Kinetic
Monte Carlo (KMC) simulations cover a wider range of spatial
frequencies, which enables the two different nonlinear terms to be
distinguished. In this case, the observed surface shapes are
consistent with the conservative nonlinearity.}
}
@article{Tixier2005:Band,
author = {S. Tixier and S.E. Webster and E.C. Young and T. Tiedje and S. Francoeur and A. Mascarenhas and P. Wei and F. Schiettekatte},
title = {Band gaps of the dilute quaternary alloys {G}a{N}$_x${A}s$_{1-x-y}${B}i$_y$ and {G}a$_{1-y}${I}n$_y${N}$_x${A}s$_{1-x}$},
journal = {\apl},
volume = {86},
pages = {112113},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Tixier_v86p112113.pdf},
year = {2005},
abstract = {We report strong band gap photoluminescence at room temperature in dilute quaternary {G}a{N}$_x${A}s$_{1-x-y}${B}i$_y$ alloys ($x$<1.6\%,$y$<2.6\%) grown by molecular beam epitaxy. The band gap of the alloy can be approximated by the band gap of {G}a{A}s minus the reduction in gap associated with the effects of {N} and {B}i alloying individually. A one-parameter method for fitting the composition dependence of the band gaps of dilute quaternary semiconductor alloys is proposed which is in excellent agreement with data for {G}a$_{1-y}${I}n$_y${N}$_x${A}s$_{1-x}$.}
}
@article{Wei2004:Ion,
author = {P. Wei and S. Tixier and M. Chicoine and S. Francoeur and A. Mascarenhas and T. Tiedje and F. Schiettekatte},
title = {Ion Beam Characterization of {G}a{A}s$_{1-x-y}${N}$_{x}${B}i$_{y}$ Epitaxial Layers},
journal = {\nimb},
volume = {219-220},
pages = {671},
url = {http://www.physics.ubc.ca/mbelab/papers/NIMB_Wei_v219-220_p671.pdf},
year = {2004},
abstract = {Incorporation of {B}i in {G}a{A}s$_{1-x}${N}$_{x}$ epitaxial layers represents a
significant interest as {B}i compensates the lattice parameter reduction cased by the {N}
incorporation while contributing to the reduction of the band gap energy.
{G}a{A}s$_{1-x-y}${N}$_{x}${B}i$_{y}$ epitaxtial layers were grown on {G}a{A}s wafers by molecular beam
epitaxy. The quality of the films as well as the concentration and lattice location of {B}i
and {N} were characterized by the channeling Rutherford backscattering spectrometry and
nuclear reaction analysys using 2 and 3.72 MeV He beams, respectively. The amount of
nitrogen in the film was measured by means of the ${}^{14}${N}($\alpha$, p)$^{17}$O
endothermic nuclear reaction and elastic recoil detection. The results indicate that
high quality epitaxial layers were obtained, with $y = 1.8\%$ {B}i incorporated into the
layer. Angular scan along the main axes showed no strain in the film and indicated that
most of the {B}i atoms are located at substitutional sites. Nitrogen lattice incorporation
is more difficult to establish because of the presence of {B}i in t he layer, but we
estimate the substitutional fraction to be $71 +/- 6\%$.}
}
@article{Ballestad2004:Comment,
author = {Anders Ballestad and Thomas Tiedje and Jens Schmid},
title = {Comment on '{T}ransient {E}volution of {S}urface {R}oughness on {P}atterned {G}a{A}s(001) {D}uring {H}omoepitaxial {G}rowth'},
journal = {\prl},
volume = {93},
pages = {159604},
url = {http://www.physics.ubc.ca/mbelab/papers/PRL_159601_2004.pdf},
year = {2004},
abstract = {Kan {\it et al.}~[1] recently published intriguing experimental
evidence that patterned {G}a{A}s surfaces are subject to a non-monotonic
amplitude decay during epitaxial growth. They compared the temporal
evolution of their surface shapes with calculations based on four
continuum growth models, including the KPZ equation, and found that
none of them could reproduce the amplitude evolution, nor the shape of
the experimental surfaces. We do not agree with their attempt to
extend these conclusions to the much lower amplitude morphology
($~\lesssim 3^\circ$ surface slope) that we studied earlier, in which
KPZ behavior was observed~[2].
}
}
@article{Ruck2004:Filled,
author = {B. J. Ruck and A. Koo and U. D. Lanke and F. Budde and H. J. Trodahl and G. V. M. Williams and A. {B}ittar and J. B. Metson and E. {N}odwell and T. Tiedje and A. Zimina and S. Eisebitt},
title = {Filled and empty states of disordered {G}a{N} studied by {X}-ray absoption and emission},
journal = {\jap},
year = {2004},
volume = 96,
issue = 6,
pages = {3571--3573},
url = {http://www.physics.ubc.ca/mbelab/papers/JAP_Ruck_2004.pdf},
abstract = {X-ray absorption and emission spectroscopies are used to
study the effects of short-ranged ordering on the electronic states
of disordered {G}a{N}. Nanocrystalline samples with crystallites as
small as 3nm exhibit an electronic structure resembling a broadened
version of that in crystalline {G}a{N}. The electronic structure is even
more heavily broadened in amorphous {G}a{N} films containing oxygen
impurities or excess gallium. The oxygen containing films show an
additional peak in the density of states just above the conduction
band edge, and a downward shift of the valence band edge. The
signature of molecular nitrogen trapped within the films is evident
in both the absorption and emission spectra.}
}
@article{Schmid2004:SurfacePattern,
author = {Jens H. Schmid and Tom Tiedje and Richard Mar and Anders Ballestad},
title = {Surface Pattern Transfer in {G}a{A}s with Molecular Beams of {Cl}$_2$ },
journal = {\prb},
year = {2004},
volume = 70,
pages = {045315},
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Schmid_2004.pdf},
abstract = {The time evolution of surface gratings on {G}a{A}s(001)
during maskless thermal Cl$_2$ etching is investigated using atomic
force microscopy and real-time measurements of diffracted light
intensity. The decay of the grating depends strongly on its
orientation with respect to the crystal axes. The pattern transfer can
be altered significantly by using a directional molecular beam of
Cl$_2$ instead of exposure to a nondirectional low-pressure gas
phase. In particular, if the molecular beam is incident on the sample
from an off-normal direction, the grating shape develops a strong
asymmetry. A numerical model consisting of two coupled partial
differential equations for the surface height and the concentration of
chlorine on the surface is in good quantitative agreement with the
observed shape evolution. The model includes the effects of the
crystal anisotropy of the etch rate, spatial inhomogeneity of the
Cl$_2$ flux to the surface, and surface diffusion of the
chlorine. Fits of the model to the surface shapes allow us to
determine the diffusion length of chlorine on {G}a{A}s(001) to be on the
order of 50 nm at 200 $^{\circ}$C.}
}
@article{Ballestad2004:PredictingGaAs,
author = {Anders Ballestad and Thomas Tiedje and Jens Schmid and Ben Ruck and Martin Adamcyk},
title = {Predicting {G}a{A}s Surface Shapes During {MBE} Regrowth on Patterned Substrates},
journal = {\jcg},
volume = {271},
number = {1-2},
pages = {13--21},
url = {http://www.physics.ubc.ca/mbelab/papers/JOCG_Ballestad_2004.pdf},
year = {2004},
abstract = {We have developed a continuum model based on two coupled
differential equations that explains the complex surface shapes
observed in epitaxial regrowth on micron scale gratings. This model
describes the dependence of the surface morphology on film thickness
and growth temperature in terms of a few simple atomic scale processes
including adatom diffusion, step-edge attachment and detachment, and a
net downhill migration of surface adatoms. The continuum model reduces
to the linear part of the Kardar-Parisi-Zhang equation with a flux
dependent smoothing coefficient in the long wavelength limit.
}
}
@article{Nodwell2004:TightBinding,
author = {Eric Nodwell and Martin Adamcyk and Anders Ballestad and Thomas Tiedje and Sebastien Tixier and Scott E. Webster and Erin C. Young and Alex Moewes and E. Z. Kurmaev and Tony van Buuren},
title = {Tight-binding model for the x-ray absorption and emission spectra of dilute {G}a{N}$_x${A}s$_{1-x}$ at the nitrogen {K} edge},
journal = {\prb},
year = {2004},
volume = 69,
pages = {155210--155213},
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Nodwell_2004.pdf},
abstract = {X-ray absorption and fluorescence spectra have been measured at the
nitrogen {K}-edge of dilute {G}a{N}$_{x}${A}s$_{1-x}$ alloys. The x-ray
spectra are in good agreement with a $sp^3s^*$ tight-binding model
in which nitrogen is included in a supercell configuration and
the disorder in the nitrogen distribution is neglected. A strong
peak in the x-ray absorption spectrum is interpreted as a nitrogen
resonant state in the conduction band rather than as an
electron-hole exciton. The tight-binding calculation is also in good
agreement with the observed nitrogen concentration dependence of the
optical bandgap.}
}
@article{Rogers1996:Binding,
author = {D. Rogers and Thomas Tiedje},
title = {Binding Energies of Hydrogen to the {Si}(111) 7x7
Surface by Statistical Scanning Tunneling Microscopy},
journal = {\prb},
volume = 53,
number = 20,
pages = {R13227--R13230},
month = may,
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Rogers_Tiedje_1996.pdf},
year = 1996,
abstract = {The equilibrium distribution of hydrogen chemisorbed to adatoms on Si~111! 737 surfaces has been determined by counting the occupied adatom sites in scanning-tunneling-microscope images of hydrogen-treated Si surfaces. From the distribution of the chemisorbed hydrogen, we are able to determine the relative binding energies of hydrogen to the four different symmetry adatoms.}
}
@article{Pinnington1999:Real,
author = {Thomas Pinnington and Y. Levy and Jim A. MacKenzie and
Thomas Tiedje},
title = {Real Time Monitoring of {I}n{A}s/{G}a{A}s Quantum Dot
Growth Using Ultraviolet Light Scattering},
journal = {\prb},
volume = 60,
number = 23,
pages = {15901--15909},
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Pinnington_1999.pdf},
year = 1999,
abstract = {We present real-time measurements of surface structure evolution during quantum dot growth in {I}n{A}s/{G}a{A}s grown by molecular-beam epitaxy. The measurements were made using an ultraviolet light-scattering technique in which the 254 nm line of a mercury lamp is used as the light source. This technique provides sensitivity to roughness on lateral lengthscales as low as 154 nm for our setup. Using this technique, we can detect the onset of quantum dot formation in this system, as indicated by reflection high-energy electrondiffraction measurements. The continuous increase in the scattering signal after the dots have formed, is explained in terms of diffusion-limited growth and ripening of the large islands that coexist with the quantum dots.}
}
@article{Rogers1997:Scanning,
author = {Rogers, D. and Tiedje, Thomas},
title = {Scanning Tunneling Microscopy and Low Energy Electron
Diffraction Study of the Formation of a (3x(3R30o
Reconstruction on the Hydrogen Etched {S}i(111) 1X1
Surface},
journal = {\jvstb},
volume = 15,
number = 5,
pages = {1641--1646},
month = sep,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Rogers_Tiedje_1997.pdf},
year = 1997,
abstract = {The Si~111! 737 surface is exposed at room temperature to atomic hydrogen and studied with scanning tunneling microscopy ~STM! and low energy electron diffraction ~LEED! in ultrahigh vacuum. For increasing exposures, the LEED pattern of the surface changes in well defined steps to a 131 pattern. The STM images of the 131 surface appear rough and disordered. The 131 pattern and rough surface are consistent with an etching of several surface layers by the atomic hydrogen. Heating the 131 surface to 560 °C and cooling to room temperature produces a surface with a )3)R30° LEED pattern. The STM images of this surface are consistent with a distribution of adatoms on an ideal Si~111! surface. Further heating results in a 737 surface.}
}
@article{vanBuuren1993:Photoelectron,
author = {Tony van Buuren and Thomas Tiedje and J. R. Dahn and
B. M. Way},
title = {Photoelectron spectroscopy measurements of the band
gap in porous silicon},
journal = {\apl},
volume = 63,
number = 21,
pages = {2911--2913},
month = nov,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_VanBuuren_Tiedje_1993.pdf},
year = 1993,
abstract = {Photoemission and x-ray absorption spectroscopy show that both the conduction and valence bands of porous silicon are shifted relative to the bands for bulk silicon, as expected in the quantum confinement model for the optical properties of porous silicon. The shift in the valence band is larger than the shift in the conduction band and proportional to it, with a proportionality constant that is consistent with effective mass theory. No oxygen is detected in the as-prepared porous silicon.}
}
@article{Pacradouni1996:Guided,
author = {V. Pacradouni and R. Morin and M. Kanskar and Jeff F.
Young and Shane R. Johnson and Thomas Tiedje},
title = {Guided Mode Dispersion Near the Band Edge of
{I}n{G}a{A}s/{A}l{G}a{A}s/{G}a{A}s Single Quantum Well {GRINSCH}
Waveguides},
journal = {\jap},
volume = 80,
number = 10,
pages = {6039--6044},
month = nov,
url = {http://www.physics.ubc.ca/mbelab/papers/JAPL_Pacradouni_Tiedje_1996.pdf},
year = 1996,
abstract = {High resolution Fabry Perot fringe spacing measurements are used to determine the group index dispersion of TE and TM polarized modes in single quantum well {I}n{G}a{A}s/Al{G}a{A}s/{G}a{A}s graded index separate confinement heterostructure waveguides. The TE mode data, over a ;175 nm range below the quantum well band gap, is compared with model calculations of guided mode dispersion using existing empirical formulas for the index dispersion of Alx{G}a12x{A}s and {G}a{A}s, and different phenomenological expressions for the TE index dispersion of the {I}n{G}a{A}s quantum well. A satisfactory fit is obtained when the quantum well is modeled as a two-dimensional set of equal strength oscillators with a constant density of states, plus a single 1S excitonic level.}
}
@article{Adamcyk1998:Diffusion,
author = {Martin Adamcyk and M. Beaudoin and I. Kelson and Y.
Levy and Thomas Tiedje},
title = {Diffusion Studies of {R}a and {P}b in {G}a{A}s by the
Alpha-Particle Energy Loss Method},
journal = {\jap},
volume = 84,
number = 11,
pages = {6003--6006},
month = dec,
url = {http://www.physics.ubc.ca/mbelab/papers/JAPL_Adamcyk_1998.pdf},
year = 1998
}
@article{Eisebitt1997:Soft,
author = {S. Eisebitt and S. N. Patitsas and Thomas Tiedje and
Tony van Buuren and J. Luning and J.E. Rubensson and W.
Eberhardt},
title = {Soft {X}-ray Fluorescence of Porous Silicon:
Electronic Structure of {S}i Nanostructures},
journal = {\el},
volume = 37,
number = 2,
pages = {133--138},
month = jan,
url = {http://www.physics.ubc.ca/mbelab/papers/EURO_Eisebitt_1997.pdf},
year = 1997,
abstract = {The electronic structure of porous Si is investigated using soft X-ray fluorescence spectroscopy. Significant changes are observed as compared to bulk Si, which we interpret as due to altered electronic structure in the Si nanostructures. By imposing standing wave boundary conditions on the valence band wave functions, we calculate the fluorescence spectrum for thin Si sheets of different orientations. For a (100)-oriented sheet, the calculation is in good agreement with the experimental spectra, suggesting that the nanostructure in porous Si is predominantly in the form of thin Si (100)-type sheets.}
}
@article{Pinnington1997:Effect,
author = {Thomas Pinnington and Christian Lavoie and Thomas
Tiedje},
title = {Effect of Growth Conditions on Surface Roughening of
Relaxed {I}n{G}a{A}s on {G}a{A}s},
journal = {\jvstb},
volume = 15,
number = 4,
pages = {1265--1269},
month = jul,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Pinnington_1997.pdf},
year = 1997,
abstract = {We report elastic light scattering measurements of the surface morphology of strained {I}nx{G}a1 x{A}s on {G}a{A}s, grown by molecular beam epitaxy at different growth temperatures and {I}n contents. During strain relaxation through formation of interfacial misfit dislocations, the surface of the film roughens in response to inhomogeneous surface strains produced by the interfacial misfit dislocations. The time dependence of this roughening is modeled by an Edwards Wilkinson equation in which the deposition flux noise is neglected and the inhomogeneous surface stress is the only driving term.}
}
@article{Lavoie1995:Relationship,
author = {Christian Lavoie and Thomas Pinnington and Eric
Nodwell and Thomas Tiedje and R. S. Goldman and Karen
L. Kavanaugh and J. L. Hutter},
title = {Relationship Between In-Situ Surface Morphology and
Strain Relaxation During Growth of {I}n{G}a{A}s Strained
Layers},
journal = {\apl},
volume = 67,
number = 25,
pages = {3744--3746},
month = dec,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Lavoie_1995.pdf},
year = 1995,
abstract = { The relationship between the surface morphology and
strain relaxation is explored in strained {I}n$_x${G}a$_{1-x}${A}s
layers grown on {G}a{A}s by molecular beam epitaxy. \emph{In situ}
light scattering, detected simultaneously along [110] and
[1 -1 0], reveals an asymmetric surface roughening which is
consistent with \emph{ex situ} scanning force
microscopy. Transmission electron microscopy shows that strain
relaxation by misfit dislocation formation occurs before the
surface roughening is detected, for {I}n$_{0.18}${G}a$_{0.82}${A}s films
grown at 490°C.}
}
@article{Beaudoin1997:Optical,
author = {M. Beaudoin and A. J. G. de{V}ries and Shane R.
Johnson and H. Laman and Thomas Tiedje},
title = {Optical Absorption Edge of Semi-insulating {G}a{A}s
and {I}n{P} at High Temperatures},
journal = {\apl},
volume = 70,
number = 26,
pages = {3540--3542},
month = jun,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Beaudoin_deVries_1997.pdf},
year = 1997,
abstract = {The temperature dependences of the optical absorption edges of semi-insulating {G}a{A}s and {I}n{P} have been measured from room temperature to 905 °C and 748 °C, respectively, with accuracies of 61 °C at room temperature and 65 °C at 900 °C. The temperature dependence of the optical absorption edge is adequately reproduced by an Einstein model although the Varshni model gives an improved fit to the band gap. Finally, the widths of the absorption edges are correlated with ionicity.}
}
@article{Lavoie1996:Indium,
author = {Christian Lavoie and Thomas
Pinnington and Thomas Tiedje and J. L. Hutter and G. Soerensen and
R. Streater},
title = {Indium-Induced Smoothing of {G}a{A}s Films
During {MBE} Growth},
journal = {\cajp},
volume = 74,
pages = {S47--S53},
url = {http://www.physics.ubc.ca/mbelab/papers/CJP_Lavoie_Pinnington_1996.pdf},
year = 1996,
abstract = {A new technique is reported for
obtaining a smooth growth surface during molecular beam epitaxy
growth of {G}a{A}s on (001) {G}a{A}s substrates. The smoothing is achieved
by exposing the surface to an indium flux during growth of the {G}a{A}s
buffer layer at high substrate temperature (590$^\circ$C). In situ
light scattering shows a dramatic reduction in surface roughness
along the [110] direction during this process, consistent with ex
situ scanning force microscopy measurements on the films, which
reveal atomically flat terraces oriented along the <110>
directions. The surface reconstruction shifts from (2$\times$4) to
(4$\times$2) under the indium flux as revealed by reflection
high-energy electron diffraction. The sticking coefficient of the
indium as determined by secondary-ion mass spectroscopy is less than
10\%. We attribute the observed effects to a transition from group V
to group III termination, induced by surface segregation of the
nonincorporated indium.}
}
@article{Konsek1997:Selective,
author = {R. Konsek and Robin J. N. Coope and T. P. Pearsall and
Thomas Tiedje},
title = {Selective Surface Modifications with a Scanning
Tunneling Microscope},
journal = {\apl},
volume = 70,
number = 14,
pages = {1846--1848},
month = apr,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Konsek_1997.pdf},
year = 1997,
abstract = {A combination scanning tunneling microscope ~STM! and scanning electron microscope has been used to selectively pattern and image Si~111! and Si~001! surfaces in a SEM chamber. Both positive and negative STM tip polarities produce marks on the surface with linewidths as small as 20 nm. We have transferred these patterns to the silicon substrate via selective wet chemical etching. We demonstrate a well-defined voltage threshold for patterning at negative tip bias. The modifications are consistent with a model based on hydrogen depassivation and electric field mediated deposition. The physical mechanism for positive tip bias patterning is shown to be different than that for negative bias. At positive bias, the patterning is consistent with selective surface contamination.}
}
@article{Eisebitt1998:Speckle,
author = {S. Eisebitt and A. Karl and R. Scherer and W.
Eberhardt and Martin Adamcyk and Thomas Tiedje and C.
Pistonesi},
title = {Speckle with Soft {X}-rays: A Demonstration},
journal = {\srn},
volume = 11,
year = 1998
}
@article{Ritchie1997:Semiconductor,
author = {S. Ritchie and Shane R. Johnson and Christian Lavoie
and J. A. Mackenzie and Thomas Tiedje and R. Streate},
title = {Semiconductor Substrate Cleaning and Surface
Morphology in Molecular Beam Epitaxy},
journal = {\ss},
volume = 374,
pages = {418--426},
url = {http://www.physics.ubc.ca/mbelab/papers/SS_Ritchie_1997.pdf},
year = 1997
}
@article{Adamcyk2000:Effect,
author = {Martin Adamcyk and Thomas Pinnington and Anders
Ballestad and Thomas Tiedje},
title = {Effect of the Starting Surface on the Morphology of
{MBE} Grown {G}a{A}s},
journal = {\mseb},
volume = 75,
number = 2,
pages = {153--156},
url = {http://www.physics.ubc.ca/mbelab/papers/cmrs_99_complete_paper.pdf},
year = 2000,
abstract = {In this paper, we study the homoepitaxial growth of {G}a{A}s by molecular beam epitaxy on substrates that have different pre-growth roughness due to the method of removing the native oxide. The evolution of the surface roughness of 1µm thick {G}a{A}s films grown at 553°C was monitored in real time using ultraviolet light scattering, and compared with ex situ atomic force microscopy measurements of the power spectral density (PSD) of the surface morphology. The PSD at a spatial frequency of 2 µm-1, is approximately three orders of magnitude larger for films grown on thermally cleaned substrates than for films grown on substrates cleaned with atomic hydrogen. No mounding indicative of unstable growth was observed in the films cleaned with atomic hydrogen.}
}
@article{Sfigakis2000:Near,
author = {F Sfigakis and P. Paddon and V. Pacradouni and Martin
Adamcyk and Christine Nicoll and A. R. Cowan and Thomas
Tiedje and Jeff F. Young},
title = {Near Infrared Refractive Index of Thick, Laterally
Oxidized {Al{G}a{A}s} Cladding Layers},
journal = {\jlwt},
volume = 18,
number = 2,
year = 2000
}
@article{Tixier1999:Electron,
author = {Sebastien Tixier and Y. Zheng and Thomas Tiedje and G.
Cooper and C. Brion},
title = {Electron Momentum Spectroscopy of Surfaces},
journal = {\srl},
volume = 6,
number = 5,
pages = {579--584},
year = 1999
}
@article{Eisebitt1996:Quantum,
author = {S. Eisebitt and J. Luning and J. E. Rubensson and Tony
van Buuren and S. N. Patitsas and Thomas Tiedje and M.
Berger and R. Arens-Fischer and S. Frohnhoff and W.
Eberhardt},
title = {Quantum Confinement Effects in the Soft {X}-ray
Fluoresence Spectra of Porous Silicon Nanostructures},
journal = {\ssc},
volume = 97,
number = 7,
pages = {549--552},
url = {http://www.physics.ubc.ca/mbelab/papers/SSCOMM_Eisebitt_Tiedje_1996.pdf},
year = 1996
}
@article{Schmid2002:Kinetic,
author = {Jens H. Schmid and Anders Ballestad and Ben J. Ruck
and Martin Adamcyk and Thomas Tiedje},
title = {Kinetic Roughening of {G}a{A}s(001) during Thermal
{Cl}$_2$ Etching},
journal = {\prb},
volume = 65,
number = 20,
pages = {155315},
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_jens_2002.pdf},
year = 2002,
abstract = {The surface morphology of Cl2-etched {G}a{A}s001! is measured as a function of etch time by atomic force microscopy and elastic light scattering. A flat surface is found to become rougher during the etch whereas a textured substrate becomes smoother. We have numerically simulated this behavior. It is found that the evolution of surface roughness at length scales between 50 nm and 5 mm can be described with excellent accuracy by a continuum equation for the surface height h( t), which is given by dh/dt5 n2h 2l/2(h)22K4h1 h, where his a random noise input.}
}
@article{Schmid2003:Surface,
author = {Jens H. Schmid and Richard Mar and Thomas Tiedje},
title = {Surface Pattern Evolution during Thermal
{Cl}$_2$ Etching of {G}a{A}s(001)},
journal = {\apl},
volume = 82,
number = 25,
pages = {4549-4551},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_jens_2003.pdf},
year = 2003,
abstract = {The evolution of one- and two-dimensional surface gratings during maskless thermal Cl$_{2}$ etching of {G}a{A}s is investigated using atomic force microscopy. It is found that the limiting factor for pattern transfer is the anisotropy of the etch rate with respect to crystal orientation. A simple numerical model based on an interpolation of measured etch rates is presented that can be used to calculate the evolution of surface patterns.}
}
@article{Adamcyk2002:Comparison,
author = {Martin Adamcyk and Jens H. Schmid and Thomas Tiedje and A. Koveshnikov and A. Chaboun and V. Fink and Karen L. Kavanagh},
title = {Comparison of Strain Relaxation in {I}n{G}a{A}s{N} and {I}n{G}a{A}s Thin Films},
journal = {\apl},
volume = 80,
number = 23,
pages = {4357-4359},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Martin_2002.pdf},
year = 2002,
abstract = {We compare the strain relaxation of {I}n0.08{G}a0.92{A}s and {I}n0.12{G}a0.88{A}s0.99N0.01 epitaxial thin films grown on {G}a{A}s (001) by elemental-source molecular-beam epitaxy. The epilayers we studied were essentially identical in their compressive lattice mismatch (0.6260.02\%), and thickness (600 nm). The strain state of the samples was determined by in situ substrate curvature monitoring, and by ex situ x-ray diffraction and plan-view transmission electron microscopy. We observe a slower rate of strain relaxation, and a 25\% higher residual strain in the nitride. This is attributed to the presence of nitrogen interstitials in the {I}n{G}a{A}s{N} epilayers and/or to the higher nitrogen bond strengths.}
}
@article{Tixier2003:Surfactant,
author = {Sebastien Tixier and Martin Adamcyk and Erin C. Young and Jens H. Schmid and Thomas Tiedje},
title = {Surfactant Enhanced Growth of {G}a{N}{A}s and {I}n{G}a{N}{A}s Using Bismuth},
journal = {\jcg},
volume = 251,
number = {1-4},
pages = {449-454},
url = {http://www.physics.ubc.ca/mbelab/papers/jocg_seb_2003.pdf},
year = 2003,
abstract = {Dilute nitride {G}a{N}{A}s thin films and {I}n{G}a{N}{A}s single quantum wells (QWs) have been grown by molecular beam epitaxy with a concurrent bismuth flux. {B}i does not incorporate into the films and acts as a surfactant. Atomic force microscopy images reveal that, at sufficiently high bismuth flux, step flow growth occurs in {G}a{N}0.004{A}s0.996 even at substrate temperatures as low as 460C. This results in an order of magnitude decrease in the surface roughness. A similar smoothing effect is obtained when growing {G}a{A}s and Al{G}a{A}s thin films with bismuth. Furthermore, {B}i is found to enhance the incorporation of nitrogen into {G}a{N}{A}s. The peak photoluminescence intensity from an {I}n0.26{G}a0.74{N}0.011{A}s0.989 QW is increased by more than a factor of two with the surfactant. We conclude that {B}i reduces the incorporation of defects and/or impurities in the dilute {G}a{N}{A}s based alloys.}
}
@article{Tixier2003:Molecular,
author = {Sebastien Tixier and Martin Adamcyk and Thomas Tiedje and S. Francoeur and A. Mascarenhas and Peng Wei and F. Schiettekatte},
title = {Molecular Beam Epitaxy Growth of {G}a{A}s{B}i},
journal = {\apl},
volume = 82,
number = 14,
pages = {2245-2247},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Seb_2003.pdf},
year = 2003,
abstract = {{G}a{A}s$_{12x}${B}i$_x$ epilayers with bismuth concentrations up to x53.1\% were grown on {G}a{A}s by molecular beam epitaxy. The {B}i content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that {G}a{A}s{B}i is pseudomorphically strained to {G}a{A}s but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of {G}a{A}s{B}i to the hypothetical zincblende {G}a{B}i alloy gives 6.3360.06 Å. Room-temperature photoluminescence of the {G}a{A}s{B}i epilayers is obtained and a significant redshift in the emission of {G}a{A}s{B}i of ;84 meV per percent {B}i is observed.}
}
@article{Francoeur2003:Band,
author = {S. Francoeur M.-J. Seong and A. Mascarenhas and Sebastien Tixier and Martin Adamcyk and Thomas Tiedje},
title = {Band {G}ap of {G}a{A}s$_{1-x}${B}i$_{x}$, 0http://www.physics.ubc.ca/mbelab/papers/APL_Francoeur_2003.pdf},
year = 2003,
abstract = {The band gap of {G}a{A}s{B}i epitaxial layers as a function of bismuth concentration up to 3.6\% is determined. The optical transitions were measured by modulated electroreflectance. The energy of the band gap decreases at a linearized rate of 88 meV/\% {B}i, or 83 meV/\% {B}i for the heavy hole to conduction band transition for {G}a{A}s{B}i strained to {G}a{A}s. The valence-band splitting increases faster than that of {G}a{A}s under similar compressive strain whereas the temperature dependence of the observed {G}a{A}s{B}i transitions is similar to that of {G}a{A}s.}
}
@article{Kaiser2003:Determining,
author = {C. Kaiser and Yuval Levy and Thomas Tiedje and Jeff F. Young},
title = {Determining the profile of textured membranes by the alpha particle energy loss method},
journal = {\apl},
volume = 80,
number = 14,
pages = {2607-2609},
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Christina_2002.pdf},
year = 2002,
abstract = {Alpha particle energy loss (AEL) spectroscopy was used to characterize a 5 mm pitch grating of silicon bars on a silicon dioxide membrane. Comparison of the data with simulated spectra shows that the angle of nonvertical grating sidewalls are readily quantified by AEL. The potential of AEL for distinguishing undercut and overcut etch profiles is assessed.}
}
@article{Sadeghi2000:Multilevel,
author = {S. M. Sadeghi and Jochen Meyer and Thomas Tiedje and Mario Beaudouin},
title = {Multilevel Infrared Coupling of Excitons in Quantum-Well Semiconductors},
journal = {\jqe},
volume = 36,
number = 11,
pages = {1267-1271},
url = {http://www.physics.ubc.ca/mbelab/papers/IEEE_JQE_Sadeghi_2000.pdf},
year = 2000,
abstract = {}
}
@article{Adamcyk1999:Coherent,
author = {Martin Adamcyk and S. Eisebitt and A. Karl and
Christine Nicoll and Thomas Pinnington and R. Scherer
and Thomas Tiedje and W. Eberhardt},
title = {Coherent Soft {X}-ray Scattering from {I}n{P} Islands on
a Semiconductor Substrate},
journal = {\jvstb},
volume = 17,
number = 4,
pages = {1728-1732},
month = jul,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Adamcyk_1999.pdf},
year = 1999,
abstract = {Coherent soft x-ray scattering experiments from a semiconductor sample consisting of {I}n{P} islands on a smooth semiconductor substrate are described. The soft x-ray scattering was performed with 266 eV photons produced by an undulator source. Using a position sensitive detector, we are able to detect diffusely scattered x rays in the vicinity of the specular reflection, with an in-plane momentum transfer of up to 6 mm21. Using Huygens Fresnel theory and atomic force microscope images of the surface structure, we simulated the scattering assuming a finite lateral coherence length for the incident radiation. The lateral coherence length of the incident beam was found to be 20 mm from a fit to the observed diffraction pattern from a pinhole. The effect of changes in the surface morphology on the speckle pattern was simulated to explore the potential of coherent soft x-ray scattering for the study of surface structure dynamics.}
}
@article{Beaudoin1997:Insitu,
author = {M. Beaudoin and Jim A. MacKenzie and Thomas Pinnington
and S. Ritchie and Thomas Tiedje and Z. Gelbart and U.
Giesen and I. Kelson and Y. Levy and A. J. SpringThorpe
and R. Streater},
title = {In situ Thickness Measurements in Molecular Beam
Epitaxy Using Alpha Particle Energy Loss},
journal = {\sct},
volume = {94-95},
pages = {374--378},
url = {http://www.physics.ubc.ca/mbelab/papers/SCT_Beaudoin_1997.pdf},
year = 1997
}
@article{Johnson1994:Factors,
author = {Shane R. Johnson and Christian Lavoie and Eric Nodwell
and Thomas Tiedje and Jim A. MacKenzie},
title = {Factors affecting the temperature uniformity of
semiconductor substrates in molecular-beam epitaxy},
journal = {\jvstb},
volume = 12,
number = 2,
pages = {1225--1228},
month = mar,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Johnson_Lavoie_Nodwell_1994.pdf},
year = 1994
}
@article{Kavanaugh1997:InSitu,
author = {Karen L. Kavanaugh and R. S. Goldman and Christian
Lavoie and B. Leduc and Thomas Pinnington and Thomas
Tiedje and D. Klug and J. Tse},
title = {In-situ Detection of Misfit Dislocations by Light
Scattering},
journal = {\jcg},
volume = 174,
pages = {550-557},
url = {http://www.physics.ubc.ca/mbelab/papers/JOCG_Kavanaugh_1997.pdf},
year = 1997
}
@article{Ritchie1999:Growth,
author = {S. Ritchie and M. Beaudoin and Thomas Tiedje and
Thomas Pinnington},
title = {Growth on {I}n{P} Islands on {L}a{F}$_3$/{I}n{P}(111){B}
Heterostructures by Molecular Beam Epitaxy},
journal = {\jjap},
volume = 38,
pages = {L192--L194},
year = 1999
}
@article{Adamcyk2000:Surface,
author = {Martin Adamcyk and S. Eisebitt and A. Karl and
Christine Nicoll and Thomas Pinnington and R. Scherer
and Thomas Tiedje and W. Eberhard},
title = {Surface Roughness and Resonant Scattering Effects in
Soft {X}-ray Speckle from Random Semiconductor
Interfaces},
journal = {\srl},
volume = 6,
pages = {1121--1128},
issue = 6,
year = 2000
}
@article{Perovic1995:FEG,
author = {D. D. Perovic and M. R. Castell and A. Howie and
Christian Lavoie and Thomas Tiedje and J. S. W. Cole},
title = {{FEG} {SEM} Imaging of Compositional and Doping Layer
Semiconductor Superlattices},
journal = {\um},
volume = 58,
pages = {104--113},
url = {http://www.physics.ubc.ca/mbelab/papers/ULTRA_Perovic_Tiedje_1995.pdf},
year = 1995
}
@article{Adamcyk2000:Smoothing,
author = {Martin Adamcyk and Anders Ballestad and Thomas
Pinnington and Thomas Tiedje and M. Davies and Yan Feng},
title = {Smoothing of Textured {G}a{A}s Surfaces During Molecular
Beam Epitaxy Growth},
journal = {\jvstb},
volume = 18,
number = 3,
pages = {1488--1492},
month = may,
url = {http://www.physics.ubc.ca/mbelab/papers/JVB01488.pdf},
year = 2000,
abstract = {The surface morphology of homoepitaxial {G}a{A}s layers grown by molecular beam epitaxy on random and periodically textured substrates has been measured by atomic force microscopy and elastic light scattering. The random texture was obtained by thermal evaporation of the surface oxide and the periodic texture consisted of one-dimensional grating patterns fabricated by holographic lithography. The time evolution of the surface morphology was simulated numerically with a nonlinear growth equation that includes deposition noise and anisotropy in the surface diffusion. The surface of the random substrate develops shallow mounds as the large amplitude initial texture smooths out, an effect that has previously been attributed to unstable growth.}
}
@article{Johnson1995:Temperature,
author = {Shane R. Johnson and Thomas Tiedje},
title = {Temperature Dependence of the {U}rbach Edge in {G}a{A}s},
journal = {\jap},
volume = 78,
number = 9,
pages = {5609--5613},
url = {http://www.physics.ubc.ca/mbelab/papers/JAPL_Johnson_Tiedje_1995.pdf},
year = 1995,
abstract = {The temperature dependence of the optical-absorption edge (Urbach edge) of {G}a{A}s is measured in semi-insulating and n-type {G}a{A}s (n=2X 10 cmm3) over the temperature range from room temperature to 700 C. Both the optical absorption and the temperature are measured using a diffuse reflectance technique. The characteristic energy of the exponential absorption edge is found to increase linearly with temperature, from 7.5 meV at room temperature to 12.4 meV at 700 C, for semi-insulating {G}a{A}s. The temperature dependent part of the width of the Urbach edge for semi-insulating {G}a{A}s is six times smaller than predicted by the standard theory where the edge width is proportional to the phonon population.}
}
@article{Rahmim2001:Interference,
author = {Arman Rahmim and Sebastien Tixier and Thomas Tiedje and
S. Eisebitt and M. Loergen and R. Scherer and
W. Eberhardt and J. Luening and A. Scholl},
title = {Interference between Magnetism and Surface Roughness
in Coherent Soft X-ray Scattering},
journal = {\prb},
volume = 65,
number = 23,
pages = {235421},
year = 2002,
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Rahmim_Tixier_2002.pdf},
abstract = { In coherent soft x-ray scattering from magnetically
ordered surfaces there are contributions to the scattering from
the magnetic domains, from the surface roughness, and from the
diffraction associated with the pinhole aperture used as a
coherence filter. In the present work, we explore the interplay
between these contributions by analyzing speckle patterns in
diffusely scattered x-rays from the surface of magnetic thin
films. Magnetic contrast from the surface of antiferromagnetically
ordered $LaFeO_{3}$ films is caused by magnetic linear dichroism
in resonant x-ray scattering. The samples studies possess two
types of domains with their magnetic orientations perpendicular to
each other. By tuning the x-ray energy from one of the two
Fe-$L_{3}$ resonant absorption peaks to the other, the relative
amplitudes of the x-ray scattering from the two domains is
inverted which results in speckle pattern changes. A theoretical
expression is derived for the intensity correlation between the
speckle patterns with the magnetic contrast inverted and not
inverted. The model is found to be in good agreement with the
x-ray-scattering observations and independent measurements of the
surface roughness. An analytical expression for the correlation
function gives an explicit relation between the change in the
speckle pattern and the roughness, and magnetic and aperture
scattering. Changes in the speckle pattern are shown to arise from
beating of magnetic scattering with the roughness scattering and
diffraction from the aperture. The largest effect is found when
the surface roughness scatter is comparable in intensity to the
magnetic scatter. }
}
@article{Tiedje1992:Role,
author = {Thomas Tiedje and K. M. Colbow and Y. Gao and J. R.
Dahn and J. N. Reimers and D. C. Houghton},
title = {Role of {C}oulomb repulsion in 4f orbitals in
electrical excitation of rare-earth impurities in
semiconductors},
journal = {\apl},
volume = 61,
number = 11,
pages = {1296--1297},
month = sep,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Tiedje_Colbow_1992.pdf},
year = 1992,
abstract = {The role of the on-site Coulomb repulsion energy in the electrical excitation of rare-earth ions by minority carrier injection in semiconductors is examined. Resonant photoemission measurements of the interfacial electronic energy level alignment in {N}dF,/silicon heterojunctions show that the large Coulomb repulsion energy of the atomic-like 4f orbitals prevents the direct excitation of the 4f levels by either electron or hole capture.}
}
@incollection{Young1999:Photonic,
author = {Jeff F. Young and P. Paddon and V. Pacradouni and
Thomas Tiedje and Shane R. Johnson},
title = {Photonic Lattices in Semiconductor Waveguides},
booktitle = {Future Trends in Microelectronics: Off the Beaten Path},
publisher = {Wiley Interscience},
editor = {S. Luryi and J. Xu and A. Zaslavsky},
address = {New York},
year = 1999
}
@article{DeCorby1997:Elimination,
author = {R.G. DeCorby and R.I. MacDonald and M. Beaudoin and
Thomas Pinnington and Thomas Tiedje and F. Gouin},
title = {Elimination of Low Frequency Gain in {I}nAl{A}s/{I}n{G}a{A}s
Metal Semiconductor Metal Photodetectors by Silicon
Nitride Passivation},
journal = {\jem},
volume = 26,
pages = {L25},
year = 1997
}
@article{Ballestad2001:Simulation,
author = {Anders Ballestad and Ben J. Ruck and Jens H. Schmid
and Martin Adamcyk and Eric Nodwell and Christine
Nicoll and Thomas Tiedje},
title = {Surface morphology of {G}a{A}s during molecular beam
epitaxy growth: comparison of experimental data with
simulations based on continuum growth equations},
journal = {\prb},
volume = 65,
number = 20,
pages = {205302},
year = 2002,
url = {http://www.physics.ubc.ca/mbelab/papers/PRB_Ballestad_Ruck_2002.pdf},
abstract = {Using atomic force microscopy and in situ elastic light scattering we show that the surface of molecular beam epitaxy MBE! grown {G}a{A}s tends towards an equilibrium roughness independent of the initial condition, as predicted by kinetic roughening theory. Two separate continuum growth equations are consistent with the observed equilibrium roughness, namely, the Kardar-Parisi-Zhang KPZ! equation ]h/ ]t5 n2h1(l/2) 3(h)21 h, where h is the surface height and h represents nonconservative noise, and the MBE equation ]h/ ]t52 k4h2(L/2)2(h)21 hc , where hc represents conservative noise. These equations represent different physical smoothing mechanisms, so to distinguish between them we have numerically solved both equations. A novel geometric implementation of the nonlinear terms avoids instabilities associated with stiffness of the equations. We find that the time and length scale dependence of the smoothing of initially rough substrates is consistent with the KPZ equation but not the MBE equation. {A}s the growth temperature is increased the coefficient n increases relative to l, but the KPZ description remains valid over the entire measured temperature range of 550 600 °C. Reducing the {A}s overpressure increases the anisotropy of the surface morphology. We provide a physical interpretation of the KPZ equation in which the incorporation rate of mobile adatoms on the surface is governed by evaporation/condensation type dynamics. These results provide important insight into the MBE growth mechanism of {G}a{A}s.}
}
@article{Beaudoin1998:Film,
author = {M. Beaudoin and Martin Adamcyk and Z. Gelbart and U.
Giesen and I. Kelson and Y. Levy and J. Mackenzie and
Thomas Tiedje},
title = {Film Thickness and Composition Monitoring During
Growth by Molecular Beam Epitaxy Using Alpha Particle
Energy Loss},
journal = {\apl},
volume = 72,
number = 25,
pages = {3288--3290},
month = jun,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Beaudoin_Adamcyk_1998.pdf},
year = 1998,
abstract = {The a-particle energy loss method ~AEL! has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For {I}n{P} and {G}a{A}s substrates recoil implanted with a-particle emitters, we have been able to measure thickness and composition of deposited {G}a{A}s, Al{G}a{A}s and {I}n{G}a{A}s in real time. The AEL method yields in situ real time results comparable in accuracy to those obtained by ex situ scanning electron microscope and high-resolution x-ray diffraction measurements.}
}
@article{Coope1997:Surface,
author = {Robin J. N. Coope and Thomas Tiedje and S. L. Konsek
and T. P. Pearsall},
title = {Surface Modification and Imaging of {H}-Passivated
{Si} with a Combined Scanning Tunneling and {SEM}},
journal = {\um},
volume = 68,
pages = {257-266},
url = {http://www.physics.ubc.ca/mbelab/papers/ULTRA_Coope_1997.pdf},
year = 1997
}
@article{Kelson1997:Applicability,
author = {I. Kelson and Y. Levy and D. Racah and E. Redmard and
M. Beaudoin and Thomas Pinnington and Thomas Tiedje and
U. Giesen},
title = {The Applicability of Implanted $\alpha$-Sources to
Thickness and Stoichiometry Measurements of Thin Films},
journal = {\jphd},
volume = 30,
pages = {131--136},
url = {http://www.physics.ubc.ca/mbelab/papers/JPD_Kelson_1997.pdf},
year = 1997,
abstract = {A method for determining both the thickness and the average stoichiometry of thin films is presented. The method is based on implanting radioactive -sources in the substrate prior to layer growth and measuring the energy loss of the -particles as they traverse the layer. Information about the stoichiometry is obtained through the comparison of the energy loss of -particles of different initial energies. Experimental examples for the utilization of this method are presented, in which Sb was grown on Si substrates, {G}a{A}s, {I}n{A}s and Al{A}s on {G}a{A}s and YBCO on YSZ. The experimental precision which can be expected using the method is discussed, together with specific scenarios in which it could be advantageously applied.}
}
@article{Ballestad2001:Evidence,
author = {Anders Ballestad and Ben J. Ruck and Martin Adamcyk
and Thomas Pinnington and Thomas Tiedje},
title = {Evidence from the Surface Morphology for Nonlinear
Growth of Epitaxial {G}a{A}s Films},
journal = {\prl},
volume = 86,
number = 11,
pages = {2377--2380},
month = mar,
url = {http://www.physics.ubc.ca/mbelab/papers/PRL002377.pdf},
year = 2001,
day = 12,
abstract = {The mesoscale morphology of homoepitaxial {G}a{A}s surfaces is explained with an anisotropic and nonlinear Kardar-Parisi-Zhang (KPZ) model in which adatoms are incorporated into the film from a metastable surface layer. Evaporation-condensation between the film and the metastable layer is proposed as the microscopic physical origin of the KPZ description, as well as of the excess noise observed in the power spectral density. The parabolic mounds observed experimentally in films grown on rough substrates are in good agreement with the surface shape expected from the solution of the KPZ equation in the large amplitude limit.}
}
@inproceedings{Schmid2001:CL2,
author = {Jens H. Schmid and Martin Adamcyk and Jim A. MacKenzie
and Ben J. Ruck and Thomas Tiedje},
title = {Cl$_2$-Etching and {MBE}-Regrowth for {G}a{A}s/{A}l{O}$_x$
Photonic Crystals},
booktitle = {Mat. Res. Soc. Symp. Proc.},
volume = 637,
pages = {E4.4},
url = {http://www.physics.ubc.ca/mbelab/papers/MRSfall2000.pdf},
year = 2001,
abstract = {We propose a new method for fabricating high index contrast gratings made of gallium arsenide ({G}a{A}s) and aluminum oxide (AlOx) buried in {G}a{A}s based waveguide structures. A central part of this method is a UHV-compatible thermal chlorine etch and MBE-regrowth on etched {G}a{A}s and Alx{G}a1-x{A}s. We describe results on surface roughness evolution during the etch obtained by in-situ elastic light scattering. These measurements allow us to determine the process parameters that lead to a smooth etched surface on which we demonstrate successful regrowth.}
}
@article{vanBuuren1991:Oxide,
author = {Tony van Buuren and M. K. Weilmeier and I. Athwal and
K. M. Colbow and Jim A. MacKenzie and Thomas Tiedje and
P. C. Wong and K. A. R. Mitchell},
title = {Oxide Thickness effect and surface roughening in the
desorption of the oxide from {G}a{A}s},
journal = {\apl},
volume = 59,
number = 4,
pages = {464--465},
month = jul,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_VanBuuren_Tiedje_1991.pdf},
year = 1991,
abstract = {The temperature for thermal desorption of the gallium oxide from {G}a{A}s is shown to increase linearly with oxide thickness. In addition, we show by diffuse light scattering that highly polished {G}a{A}s substrates roughen during the oxide desorption. These results are interpreted in terms of a model in which the oxide evaporates inhomogeneously.}
}
@article{Eisebitt1998:Resonant,
author = {S. Eisebitt and J. Luning and J.E. Rubensson and W.
Settels and A. Eberhard and S. Patitsas and Thomas
Tiedje},
title = {Resonant Inelastic Soft {X}-ray Scattering at the {Si}
{L}-3 edge: Experiment and Theory},
journal = {\jesrp},
volume = 93,
number = {N1-3},
pages = {245--250},
year = 1998
}
@inproceedings{Cody1997:Learning,
author = {G. D. Cody and Thomas Tiedje},
title = {A Learning Curve Approach to Projecting Cost and
Performance for Photovoltaic Technologies},
booktitle = {Proc. SPIE},
pages = 3138,
year = 1997
}
@article{Johnson1997:Effect,
author = {Johnson, Shane R. and Tiedje, Thomas},
title = {Effect of Substrate Thickness, Back Surface Texture,
Reflectivity, and Thin Film Interference on Optical
Band-Gap Thermometry},
journal = {\jcg},
volume = {175/176},
pages = {273--280},
url = {http://www.physics.ubc.ca/mbelab/papers/JOCG_Johnson_Tiedje_1997.pdf},
year = 1997
}
@article{Eisebitt1996:Soft,
author = {S. Eisebitt and J. Luning and J. E. Rubesson and Tony
van Buuren and S. N. Patitsas and Thomas Tiedje and M.
Berger and R. Arens-Fischer and S. Frohnhoff and W.
Eberhardt},
title = {Soft {X}-ray Emission of Porous Silicon Nanostructures},
journal = {\jesrp},
volume = 79,
pages = {135--138},
url = {http://www.physics.ubc.ca/mbelab/papers/JESRP_Eisebitt_1996.pdf},
year = 1996
}
@article{Johnson1993:Semiconductor,
author = {Shane R. Johnson and Christian Lavoie and Thomas
Tiedje},
title = {Semiconductor substrate temperature measurement by
diffuse reflectance spectroscopy in molecular beam
epitaxy},
journal = {\jvstb},
volume = 11,
number = 3,
pages = {1007--1010},
month = may,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Johnson_1993.pdf},
year = 1993
}
@article{Beaudoin1999:Insitu,
author = {M. Beaudoin and Martin Adamcyk and Y. Levy and J.A.
MacKenzie and S. Ritchie and Thomas Tiedje and Z.
Gelbart and U. Giesen and I. Kelson},
title = {In-situ Real Time Monitoring of Thickness and
Composition in {MBE} Using Alpha Particle Energy Loss},
journal = {\jcg},
volume = {201/202},
pages = {26--30},
url = {http://www.physics.ubc.ca/mbelab/papers/JOCG_Beaudoin_1999.pdf},
year = 1999,
abstract = {The \alpha-particle energy loss method (AEL) has been implemented in situ to monitor film thickness and composition during growth of {G}a{A}s, {I}n{P} and LaF3 based materials by molecular beam epitaxy (MBE). {I}n the AEL method, a ^{228}Th source is used to recoil implant a 5 mm diameter region of the surface of the wafers with the \alpha-emitter daughter isotope ^{224}Ra prior to growth. The implanted nuclei decay with a half life of 3.7 days through a sequence of daughters which emit alpha particles at di!erent energies. Deposition on the surface causes the emission lines to be shifted to lower energies due to energy loss in the film. For substrates marked with a low activity (~ 30 kBq; similar to activity of smoke detectors) we are able to measure film thickness with +/- 6 nm uncertainty and growth rate with +/-0.01 nm/s uncertainty in real time. By measuring the relative growth rates of the di!erent materials, AEL also allows us to infer the composition of a ternary layer film as well as the sticking coefficients rates directly at different growth temperatures.}
}
@article{Kanskar1997:Two,
author = {M. Kanskar and P. Paddon and V. Pacradouni and R.
Morin and A. Busch and Jeff F. Young and Shane R.
Johnson and Jim A. MacKenzie and Thomas Tiedje},
title = {Two Dimensional Photonic Lattice in an Air-Bridged
Semiconductor Waveguide},
journal = {\apl},
volume = 70,
number = 11,
pages = {1438--1440},
month = mar,
url = {http://www.physics.ubc.ca/mbelab/papers/APL_Kanskar_1997.pdf},
year = 1997,
abstract = {An air-bridged, 120-nm-thick semiconductor slab with a two-dimensional ~2D! square array of through holes on a 480 nm pitch ~L! was fabricated using selective wet etching techniques. The second order photonic resonances of the structure were studied by comparing broadband optical scattering data with numerical solutions of Maxwell s equations. Features observed in these spectra over a 1200 cm21 range, near 9500 cm21, indicate that the 2D texture splits the energy degeneracy of slab modes with propagation constants 62p/L,0\% and 0,62p/L\% by as much as 14\%.}
}
@inproceedings{Levy1999:Insitu,
author = {Y. Levy and Anders Ballestad and M. Davies and Y. Feng
and I. Kelson and W. Mandeville and V. Pacradouni and
Al Schmalz and Thomas Tiedje and Jeff F. Young},
title = {In-Situ Etch Rate Measurements by Alpha-Particle
Energy Loss},
booktitle = {Proceedings, Spring MRS},
year = 1999
}
@article{Adamcyk2001:Faceting,
author = {Martin Adamcyk and Sebastien Tixier and Ben J. Ruck
and Jens H. Schmid and Thomas Tiedje and V. Fink and M.
Jeffries and D. Karaiskaj and Karen L. Kavanaugh and M.
Thewalt},
title = {Faceting Transition in Epitaxial Growth of Dilute
{G}a{N}$_x${A}s$_{1-x}$ Films on {G}a{A}s},
journal = {\jvstb},
volume = 19,
number = 4,
pages = {1417--1421},
month = jul,
url = {http://www.physics.ubc.ca/mbelab/papers/JVSTB_Adamcyk_2001.pdf},
year = 2001,
abstract = {An abrupt transition to a 111\% faceted growth mode is observed in molecular-beam-epitaxy growth of dilute {G}a{N}x{A}s12x (x,0.05) films on ~100! {G}a{A}s substrates. The faceted growth mode is favored by high growth temperatures, high nitrogen content, and high arsenic flux. The best electronic quality material, as measured by low-temperature photoluminescence, was obtained at high growth temperatures and high arsenic flux without exceeding the threshold for facet formation. The nitrogen content was found to be insensitive to the arsenic flux.}
}
@article{Mak1994:Carbon,
author = {A. Mak and Shane R. Johnson and Christian Lavoie and
Jim A. MacKenzie and Thomas Tiedje},
title = {Carbon filament source for p-type doping in molecular
beam epitaxy},
journal = {\jvstb},
volume = 12,
number = 3,
pages = 1407,
month = may,
year = 1994
}
@article{Pinnington1997:Surface,
author = {Thomas Pinnington and Thomas Tiedje and Christian
Lavoie and B. Haveman and Eric Nodwell},
title = {Surface Morphology Dynamics in Strained Epitaxial
{I}n{G}a{A}s},
journal = {\prl},
volume = 79,
pages = 1698,
url = {http://www.physics.ubc.ca/mbelab/papers/prl96.pdf},
year = 1997,
abstract = {Elastic light scattering has been used to measure the time evolution of the power spectrum of the surface morphology of strained {I}n{G}a{A}s layers during growth. From a combination of and {G}a1 xed scattering angle measurements during growth and variable scattering angle measurements after growth, we are able to determine both the time and spatial frequency dependence of the power spectral density during relaxation of the strained lms via mis t dislocations. The data are t with an Edwards-Wilkinson model, for which the surface morphology is driven by inhomogeneous surface strains.}
}
@article{Cody1996:Learning,
author = {G. Cody and T. Tiedje},
title = {A Learning Curve Approach to Projecting Cost and Performance in Thin Film Photovoltaic},
journal = {Mat. Res. Symp. Proc. J},
url = {http://www.physics.ubc.ca/mbelab/papers/pvlearn.pdf},
year = {1996}
}