Adsorption-Controlled Epitaxy and Twin Control of $\gamma$-GaSe on GaAs (111)B

TL;DR

This study maps the adsorption-controlled growth window of GaSe on GaAs (111)B, revealing phase boundaries, polytype control, and twinning phenomena using molecular beam epitaxy, with implications for optoelectronic material synthesis.

Contribution

It systematically establishes the adsorption-controlled growth window for GaSe and investigates twin formation and polytype control during epitaxy.

Findings

Phase boundaries align with Ellingham diagram predictions

Higher temperatures reduce mosaicity and surface roughness

Growth temperature influences twin formation and domain orientation

Abstract

The III-Se layered semiconductors, including InSe and GaSe, are promising optoelectronic materials due to their relatively high electron mobilities at room temperature, nonlinear optical responses, ferroelectricity, self-passivated van der Waals surfaces, and ability to alloy and synthesize heterostructures for bandgap engineering. Adsorption control is a widely utilized strategy for controlling the stoichiometry and phase formation of these materials; however, the bounds of the adsorption-controlled growth window for GaSe have not been systematically established. Additionally, challenges with control over polytype and twinning remain. Here, we use molecular beam epitaxy to experimentally map the adsorption-controlled growth window of GaSe films on vicinal GaAs (111)B substrates. The observed phase boundaries show qualitative agreement with Ellingham diagram predictions. All films crystallize in the $\gamma$ ($R3m$) polytype. Increasing growth and annealing temperature leads to decreased mosaicity measured by x-ray rocking curve and smoother surfaces measured by atomic force microscopy, at the expense of a transition from singly oriented $\gamma$ to twinned $\gamma$ with $60\degree$ rotated domains.