Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

TL;DR

This study uses kinetic Monte Carlo simulations to explore how surface orientation affects atomic-scale growth mechanisms in GaN homoepitaxy, revealing the influence of surface anisotropy on morphology and growth modes.

Contribution

It introduces a simulation approach comparing c- and m-plane GaN growth, highlighting the role of step edge energy anisotropy in island morphology and growth mode boundaries.

Findings

Elongated islands on m-plane are due to step edge energy anisotropy.

Growth mode boundaries depend on temperature and growth rate.

Island spacing follows a power-law with growth rate.

Abstract

The surface orientation can have profound effects on the atomic-scale processes of crystal growth, and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane ${(0 0 0 1)}$ and m-plane ${(0 1 \overline{1} 0)}$ surfaces are compared. We present a reciprocal space analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers, and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. Island nucleation spacing obeys a power-law dependence on growth rate, with exponents of -0.24 and -0.29 for m- and c-plane, respectively.