  Two-dimensional (2D) indium monoselenide (InSe) has attracted significant
attention as a III-VI two-dimensional semiconductor (2D) with a combination of
favorable attributes from III-V semiconductors as well as van der Waals 2D
transition metal dichalcogenides. Nevertheless, the large-area synthesis of
phase-pure 2D InSe remains unattained due to the complexity of the binary In-Se
system and the difficulties in promoting lateral growth. Here, we report the
first polymorph-selective synthesis of epitaxial 2D InSe by metal-organic
chemical deposition (MOCVD) over 2 inch diameter sapphire wafers. We achieve
thickness-controlled, layer-by-layer epitaxial growth of InSe on c-plane
sapphire via dynamic pulse control of Se/In flux ratio. The layer-by-layer
growth allows thickness control over wafer scale with tunable optical
properties comparable to bulk crystals. Finally, the gate-tunable electrical
transport suggests that MOCVD-grown InSe could be a potential channel material
for back-end-of-line integration in logic transistors with field-effect
mobility comparable to single-crystalline flakes.
