441 research outputs found
Strain Relaxation in Graded InGaAs and InP Buffer Layers on GaAs (001)
We investigate compositionally graded Inxo≤x≤0.5Ga1-xAs and InP buffer layers which are prepared by molecular beam epitaxy on (001) GaAs substrate. The initial In content xo is equal to 0, 0.12, 0.18, 0.24, and 0.5 for the different samples. The In composition of the graded buffer increases linearly between xo and 0.5 with a fixed slope of 50% In-content per μm. The idea was to combine the advantage of surface flatness in homogeneous buffer layers and the reduced density of threading dislocations on the surface for graded buffer layers. The best compromise in terms of photoluminescence intensity and linewidth, electron mobility and crystal quality is achieved for xo = 0.18. For comparison to the InGaAs layers, we investigated also homogenous InP buffer layers on GaAs substrate. A strong photoluminescence peak with a linewidth of 5 meV is observed for 1 μm InP grown at 450°C applying a GaP decomposition source. The density of threading dislocations in the surface region is lower than in relaxed In0.5Ga0.5As layers but still by far not as low as for the graded buffer layers
Caracteres botânicos e agronômicos das cultivares de arroz irrigado BR/MS-1 e BR/MS-2.
bitstream/item/66077/1/CPAO-CIR.-TEC.-18-90.pd
Nonlinear evolution of surface morphology in InAs/AlAs superlattices via surface diffusion
Continuum simulations of self-organized lateral compositional modulation
growth in InAs/AlAs short-period superlattices on InP substrate are presented.
Results of the simulations correspond quantitatively to the results of
synchrotron x-ray diffraction experiments. The time evolution of the
compositional modulation during epitaxial growth can be explained only
including a nonlinear dependence of the elastic energy of the growing epitaxial
layer on its thickness. From the fit of the experimental data to the growth
simulations we have determined the parameters of this nonlinear dependence. It
was found that the modulation amplitude don't depend on the values of the
surface diffusion constants of particular elements.Comment: 4 pages, 3 figures, published in Phys. Rev. Lett.
http://link.aps.org/abstract/PRL/v96/e13610
Novel diffusion mechanism on the GaAs(001) surface: the role of adatom-dimer interaction
Employing first principles total energy calculations we have studied the
behavior of Ga and Al adatoms on the GaAs(001)-beta2 surface. The adsorption
site and two relevant diffusion channels are identified. The channels are
characterized by different adatom-surface dimer interaction. Both affect in a
novel way the adatom migration: in one channel the diffusing adatom jumps
across the surface dimers and leaves the dimer bonds intact, in the other one
the surface dimer bonds are broken. The two channels are taken into account to
derive effective adatom diffusion barriers. From the diffusion barriers we
conclude a strong diffusion anisotropy for both Al and Ga adatoms with the
direction of fastest diffusion parallel to the surface dimers. In agreement
with experimental observations we find higher diffusion barriers for Al than
for Ga.Comment: 4 pages, 2 figures, Phys. Rev. Lett. 79 (1997). Other related
publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm
Self-directed growth of AlGaAs core-shell nanowires for visible light applications
Al(0.37)Ga(0.63)As nanowires (NWs) were grown in a molecular beam epitaxy
system on GaAs(111)B substrates. Micro-photoluminescence measurements and
energy dispersive X-ray spectroscopy indicated a core-shell structure and Al
composition gradient along the NW axis, producing a potential minimum for
carrier confinement. The core-shell structure formed during the growth as a
consequence of the different Al and Ga adatom diffusion lengths.Comment: 20 pages, 7 figure
Re-entrant Layer-by-Layer Etching of GaAs(001)
We report the first observation of re-entrant layer-by-layer etching based on
{\it in situ\/} reflection high-energy electron-diffraction measurements. With
AsBr used to etch GaAs(001), sustained specular-beam intensity oscillations
are seen at high substrate temperatures, a decaying intensity with no
oscillations at intermediate temperatures, but oscillations reappearing at
still lower temperatures. Simulations of an atomistic model for the etching
kinetics reproduce the temperature ranges of these three regimes and support an
interpretation of the origin of this phenomenon as the site-selectivity of the
etching process combined with activation barriers to interlayer adatom
migration.Comment: 11 pages, REVTeX 3.0. Physical Review Letters, in press
Analytical solution of generalized Burton--Cabrera--Frank equations for growth and post--growth equilibration on vicinal surfaces
We investigate growth on vicinal surfaces by molecular beam epitaxy making
use of a generalized Burton--Cabrera--Frank model. Our primary aim is to
propose and implement a novel analytical program based on a perturbative
solution of the non--linear equations describing the coupled adatom and dimer
kinetics. These equations are considered as originating from a fully
microscopic description that allows the step boundary conditions to be directly
formulated in terms of the sticking coefficients at each step. As an example,
we study the importance of diffusion barriers for adatoms hopping down
descending steps (Schwoebel effect) during growth and post-growth equilibration
of the surface.Comment: 16 pages, REVTeX 3.0, IC-DDV-94-00
A Coupled Equations Model for Epitaxial Growth on Textured Surfaces
We have developed a continuum model 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.Comment: 11 pages, 4 figures. Submitted to the Journal of Crystal Growt
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