Adsorption-controlled growth windows for semiconducting GaSe and ferroelectric Ga2Se3 by molecular beam epitaxy

Gallium selenide (GaSe) is a layered semiconductor with potential applications for single photon emission and ultrathin field effect transistors. GaSe has only a 2.4% lattice mismatch with the ferroelectric material Ga2Se3, suggesting the possibility of epitaxial ferroelectric Ga2Se3 gates grown on GaSe. However, the phase boundaries between these materials during epitaxial synthesis is not well understood. Here we map the phase formed for GaSe and Ga2Se3 films grown by molecular beam epitaxy on GaAs (111)B substrates, as a function of Se/Ga flux ratio and sample temperature. We observe broad windows of adsorption-controlled growth for both compounds, and compare the regions of stability to the bulk Ellingham diagrams. Using a combination of magnetotransport, Raman spectroscopy, and transmission electron microscopy, we identify regions within the single phase windows for which the transport is optimized. Our work is an essential step towards controlling phase purity for GaSe and Ga2Se3, respectively, and for future devices based on heterostructures that combine these materials.