High resolution kinetic Monte Carlo simulation of InAs(001)
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Introduction
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The conceptual simplicity of molecular beam epitaxy makes it an interesting subject for theoretical investigation
of crystal growth. MBE allows a sufficient control of substrate temperature and flux. Only simple chemistry of
the constituents of the grown crystal are involved.
The complex behavior of zincblende III-V semiconductor surfaces hinders a complete determination the atomistic
growth processes by experimental techniques. The large experimental parameter space including temperature, both
independent fluxes of group III and V elements as well as variations in the substrate (for instance GaAs or InAs,
singular or vicinal surface) makes optimizing in experiment difficult. Stability of surface reconstructions is
influenced by independent adjustable fluxes and temperature. Reconstructions directly influence growth mode through
change in microscopic growth processes.
Reliable microscopic modeling tools are necessary for deeper understanding of growth on the atomic scale. Predictive
capability of ab initio density functional theory based simulation would allow to develop new growth techniques
independent from experimental apparatus.
High resolution kinetic Monte-Carlo simulation
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We developed a kinetic Monte-Carlo simulation for growth of InAs(001). Based on extensive calculations employing
ab initio density functional theory a parameterized many-body expansion for the total surface energy used in the
model is developed. Its accuracy is tested at an independent set of DFT calculations and found to be in the order
of the accuracy of the DFT calculations itself. Therefore, the equilibrium behavior if the kinetic Monte Carlo
simulation parameter free. It reproduces the energetics of the DFT reconstruction phase diagram within the a2(2x4)-b2(2x4)
stability region.
Thermodynamic equilibrium
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The reconstruction phase diagram of InAs(001) predicts the two reconstructions a2(2x4) and b2(2x4) to be stable
at temperature T=0 K. At finite temperature it is found that both reconstructions coexist without phase separation
and do not exhibit a phase transition. The following figures compare simulation results with atomic resolution
scanning tunneling graphs for annealed surfaces at different temperatures. The density of the As-dimers in the
top rows is used for quantitative comparison. The As-density is 0.5 monolayer for the perfect b2(2x4) and 0.25 monolayer for the a2(2x4).
Experimental and simulated results agree over a wide range of temperature and As-flux values.
Growth kinetics
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We compare results of the kinetic Monte-Carlo simulation with experimental results in the low coverage. Identical
growth conditions are used including temperature, group III flux, and group V flux. A qualitative agreement is
found for surface morphology. Island densities are in agreement within a order of magnitude.
Based on these results we were able to clarify a possible atomic mechanism leading to a counterintuitive reduced
island density with increasing As-pressure observed experimentally. The increase in As-flux leads to the reduction
of an effective In adatom density that is responsible for nucleation. From standard nucleation theory follows then
a reduced island density.
Results
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Literature
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F. Grosse and M.F. Gyure, Ab initio-based modeling of III-V semiconductor surfaces: Thermodynamic equilibrium and growth kinetics on atomic scales, Phys. Rev. B66, 075320 (2002). PDF or Link to Journal
F. Grosse, W. Barvosa-Carter, J. J. Zinck, M.F. Gyure, Atomistics of III-V
semiconductor surfaces: The role of group V pressure, Conference proceedings NA-MBE, Providence, RI submitted to
JVST 20 (3) 1178-1181 (2002) PDF
F. Grosse, W. Barvosa-Carter, J.J. Zinck, and M.F. Gyure. Submitted to Phys. Rev. B.Microscopic mechanisms of surface phase transitions on InAs(001), Phys. Rev. B66, 075321 (2002). PDF or Link to Journal
F. Grosse, W. Barvosa-Carter, M. Wheeler, J.J. Zinck, and M.F. Gyure, Arsenic Flux Dependence of Island Nucleation
on InAs(001), Phys. Rev. Lett. 89, 116102 (2002). PDF or Link to Journal
Related pages
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Stability of Surface Reconstructions on InAs(001)