Simulations of molecular beam epitaxy growth of GaAs
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Simulations of molecular beam epitaxy growth of GaAs Z. Zhang, B. G. Orr Physics Department The University of Michigan Ann Arbor, MI 48109-1120
Abstract Numerical simulations have been performed for generic III-V MBE growth. The key aspects of the simulation include two deposited species one volatile and the second with high surface mobility. Simulations reproduce the experimentally observed adatom concentrations for GaAs and show that smooth surfaces are produced for films deposited with a substrate temperature in a crossover regime between kinetically limited and entropically roughened growth.
Numerical simulations play an ever increasing role in our understanding of thin film growth. Molecular beam epitaxy (MBE) growth has been numerically modeled for many years by a number of practitioners.(1, 2, 3, 4, 5) In each of these studies certain details, or processes, present in the real experimental system have been omitted so that the most general and important features of the model can be studied. For III-V MBE growth it has become standard in many simulations to eliminate to some degree certain details such as: crystal structure, surface reconstruction, and vertical adatom diffusion. Even the multiple elemental components of the system are sometimes reduced to a single species. There are of course often justifications for leaving out such details and the agreement with experiment in many cases has been very good. In fact, it has become quite common to see numerically simulated images or videos of surfaces and believe that we have captured the essential growth dynamics. In this letter we will question the degree to which this is true and suggest a very different surface dynamics that is counter the traditional paradigm for III-V MBE growth. The conventional model for III-V MBE growth is based on a single component solid-onsolid (SOS) model.(6) The lattice is usually square and since researchers are typically only interested in relatively smooth surfaces adatom diffusion along the infrequent vertical sides of surface structure is ignored. These approximations set limits to the length scales that the simulations should be able to accurately reproduce. We will make these same approximations in this work as well. The central difference between our model and a conventional one is the explicit treatment of the two component species during the deposition. It is important to note that we are not the first group to explicitly treat the bi-component nature of the growth. The early paper by Ghaisas and Madhukar presented simulations examining the surface reactions necessary to explicitly treat the P5.3.1
molecular nature of As2 and its decomposition.(1) More recently Itoh et. al. considered in detail the effects of the As stabilized 2 X 4 surface reconstruction of the dynamics of island nucleation and growth.(5) Our work takes a different approach to the inclusion of both growth species then these. We have tried to make the fewest alterations to the standard SOS model and yet capture the new surface dynamics that multiple g
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