Atomistic Modeling of III-V Semiconductors: Thermodynamic Equilibrium and Growth Kinetics
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Atomistic Modeling of III-V Semiconductors: Thermodynamic Equilibrium and Growth Kinetics Frank Grosse1, William Barvosa-Carter2, Jennifer J. Zinck2, and Mark F. Gyure2 1 Department of Mathematics, University of California, Los Angeles, CA 2 HRL Laboratories, LLC, Malibu, CA. © 2001 HRL Laboratories, LLC. All Rights Reserved ABSTRACT Growth kinetics and thermodynamic equilibrium can both be determining factors at different stages of III-V semiconductor heteroepitaxy. We study their interplay, employing kinetic Monte Carlo simulations for the InAs(001) surface. The simulation contains atomistic details of both species, including the stability of different reconstructions and their kinetics. The behavior of the surface in thermodynamic equilibrium, including different reconstructions, is determined exclusively by extensive total energy calculations employing ab initio density functional theory. The continuous phase transition between the α2(2x4) and β2(2x4), predicted by theory, is confirmed by experiment. At full layer coverage, a recovery of the stable reconstruction is observed. The different time scales associated with As2 and In are discussed with respect to equilibrium and kinetics. INTRODUCTION Recent improvements in heteroepitaxy of III-V semiconductors enable nearly atomically flat interfaces between different layers. The reduction in width of some device layers down to a few atomic lattice constants on the other hand increases the effect of variations on the atomic scale. The complex behavior of III-V semiconductor surfaces makes investigation of atomic mechanisms challenging. Although many new insights into static surfaces, particularly concerning reconstructions, have been gained over the past few years, [1-4] the understanding of kinetics on the atomic scale is still in its infancy, even despite recent progress [5-7]. Because direct observation of microscopic processes is experimentally very difficult one relies on either in situ techniques like reflection high energy electron diffraction (RHEED) or photo emission (PE) that need additional interpretation to conclude microscopic morphology, or ex situ characterization with techniques like atomic resolution scanning tunneling microscopy (STM), where the surface is processed before it is investigated. The challenge for theoretical investigation is the determination of the large number of possible surface processes and their complex interplay. Although total energy calculations employing ab initio density functional theory (DFT) allow studying single processes with high accuracy [7,8], a full quantum mechanical treatment over long time scales or larger cells is not possible. These arguments suggest that computer simulations based on a combination of theory and experiment, for model construction and verification respectively, might be necessary to gain understanding in the complex dynamics of III-V semiconductors. In this paper, we describe a new methodology that combines thermodynamic equilibrium and growth kinetics within one unified model, based on extensiv
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