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

raw data corresponding to https://arxiv.org/abs/2603.06845 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 () 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 to twinned with $60\degree$ rotated domains.