Interface energies of Ga2O3 phases with the sapphire substrate and the phase-locked epitaxy of metastable structures explained

TL;DR

This study uses density functional theory to analyze interface energies of Ga2O3 phases on sapphire, explaining the phase-locking phenomenon during epitaxial growth by identifying conditions favoring alpha Ga2O3 nucleation.

Contribution

It provides a fundamental understanding of metastable phase nucleation in Ga2O3 by calculating interface energies, which was previously lacking.

Findings

Alpha Ga2O3 is the preferred phase in 2D islands under certain growth conditions.

Low temperatures and high growth rates favor alpha phase nucleation.

The results explain phase-locking observed in experiments.

Abstract

Despite the extensive work carried out on the epitaxial growth of Ga2O3, a fundamental understanding of the nucleation of its different metastable phases is still lacking. Here we address the role of interface energies by Density Functional Theory calculations of alpha, beta and kappa Ga2O3 on (0001) Al2O3 substrates, and different Ga2O3 interlayers. In conjunction to surface energies and misfit strain contribution, we demonstrate that alpha Ga2O3 is the preferred phase in 2D islands, when the low growth temperatures and the high growth rates hinder 3D island nucleation. This quantitatively explains the phase-locking in Mist-CVD experiments