Miscut dependent surface evolution in the process of N-polar GaN$(000\bar 1)$ growth under N-rich condition

TL;DR

This study uses kinetic Monte Carlo simulations to analyze how substrate miscut angles influence surface morphology during N-polar GaN growth under N-rich conditions, revealing mechanisms behind surface roughening and smoothening.

Contribution

The paper introduces a two-component kinetic Monte Carlo model that explains surface evolution in N-polar GaN growth, highlighting the impact of miscut angle, temperature, and nitrogen excess.

Findings

Higher miscut angles lead to smoother surfaces.

Low gallium adatom diffusion causes surface roughening at small miscuts.

Surface smoothening occurs with increased temperature or nitrogen excess.

Abstract

The evolution of surface morphology during the growth of N-polar (000-1) GaN under N-rich condition is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2deg and 4deg. The results are compared with experimentally observed surface morphologies of (000-1) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000-1) surface where both types of atoms: nitrogen and gallium attach the surface and diffuse independently, explains that at relatively high rates of the step flow (miscut angle <2deg) the low diffusion of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4deg), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions, the growth is realized by the process of two-dimensional island nucleation and coalescence. Additionally, we show that higher crystal miscut, lower crystal growth rate or higher temperature results in similar effect of the smoothening of the surface. We show that the surface also smoothens for the growth conditions with very high N-excess. The presence of large number of nitrogen atoms changes locally mobility of gallium atoms thus providing easier coalescence of separated island.