Edge-Dependent Step-Flow Growth Mechanism in $\beta$-Ga$_{2}$O$_{3}$ (100) Facet at the Atomic Level

TL;DR

This study uncovers the atomic-level step-flow growth mechanism of $eta$-Ga$_{2}$O$_{3}$ (100) facet using machine-learning molecular dynamics and DFT, revealing how adatom mobility and step barriers influence film quality.

Contribution

It provides the first detailed atomic-level understanding of the step-flow growth mechanism of $eta$-Ga$_{2}$O$_{3}$ (100) facet, highlighting the role of adatoms and Ehrlich-Schwoebel barriers.

Findings

Ga adatoms and Ga-O pairs are key for surface migration.

Asymmetric barriers suppress double-steps and hillocks.

Misfit towards [00$ar{1}$] does not cause twin boundaries.

Abstract

Homoepitaxial step-flow growth of high-quality $\beta$-Ga$_{2}$O$_{3}$ thin films is essential for the advancement of high-performance Ga$_{2}$O$_{3}$-based devices. In this work, the step-flow growth mechanism of $\beta$-Ga$_{2}$O$_{3}$ (100) facet is explored by machine-learning molecular dynamics simulations and density functional theory calculations. Our results reveal that Ga adatoms and Ga-O adatom pairs, with their high mobility, are the primary atomic species responsible for efficient surface migration on the (100) facet. The asymmetric monoclinic structure of $\beta$-Ga$_{2}$O$_{3}$ induces a distinct two-stage Ehrlich-Schwoebel barrier for Ga adatoms at the [00$\overline{1}$] step edge, contributing to the suppression of double-step and hillock formation. Furthermore, a miscut towards [00$\overline{1}$] does not induce the nucleation of stable twin boundaries, whereas a miscut towards [001] leads to the spontaneous formation of twin boundaries. This research provides meaningful insights not only for high-quality $\beta$-Ga$_{2}$O$_{3}$ homoepitaxy but also the step-flow growth mechanism of other similar systems.