Molecular dynamics studies of InGaN growth on nonpolar (112¯0) GaN surfaces

Abstract

We have performed direct molecular dynamics (MD) simulations of heteroepitaxial vapor deposition of $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$ films on nonpolar $(11\overline{2}0)$ wurtzite-GaN surfaces to investigate strain relaxation by misfit-dislocation formation. The simulated growth is conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN substrate. We apply time-and-position-dependent boundary constraints to affect the appropriate environments for the vapor phase, the near-surface solid phase, and the bulklike regions of the growing layer. The simulations employ a newly optimized Stillinger-Weber In-Ga-N system interatomic potential wherein multiple binary and ternary structures are included in the underlying density-functional theory and experimental training sets to improve the treatment of the In-Ga-N related interactions. To examine the effect of growth conditions, we study a matrix of 63 different MD-growth simulations spanning seven $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$-alloy compositions ranging from $x=0.0$ to $x=0.8$ and nine growth temperatures above half the simulated melt temperature. We found a composition dependent temperature range where all kinetically trapped defects were eliminated, leaving only quasiequilibrium misfit and threading dislocations present in the simulated films. Based on the MD results obtained in this temperature range, we observe the formation of interfacial misfit and threading dislocation arrays with morphologies strikingly close to those seen in experiments. In addition, we compare the MD-observed thickness-dependent onset of misfit-dislocation formation to continuum-elasticity-theory models of the critical thickness and find reasonably good agreement. Finally, we use the three-dimensional atomistic details uniquely available in the MD-growth histories to directly observe the nucleation of dislocations at surface pits in the evolving free surface.