Adsorption-controlled epitaxy and twin control of <i>γ</i> -GaSe on GaAs (111)B

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 γ (R3m) polytype. Increasing growth and annealing temperature leads to decreased mosaicity measured by an x-ray rocking curve and smoother surfaces measured by atomic force microsocopy, at the expense of a transition from singly oriented γ to twinned γ with 60° rotated domains.