Low Temperature MOCVD Synthesis of High-Mobility 2D InSe

2D indium selenide (InSe) is a layered semiconductor with high electron mobility and a tunable band gap ranging from 1.25 eV in the bulk to 2.8 eV in the monolayer limit. However, growing phase-pure InSe remains challenging due to the complex indium-selenium (In-Se) phase diagram. This complexity and the sensitivity of chemical precursors to growth conditions make it difficult to control which In-Se phase forms during synthesis during, e.g., metal-organic chemical vapor deposition (MOCVD). MOCVD is considered the most promising approach for growing InSe, as it enables wafer-scale, uniform, and controllable deposition-key requirements for device integration. We present a systematic investigation of InSe synthesis on c-plane sapphire substrates at low temperatures. By varying Se/In precursor ratio and growth temperature, we create a phase diagram that covers In-rich, equal stoichiometric, and Se-rich In_xSe_y phases. Raman spectroscopy and atomic force microscopy, supported by energy dispersive X-ray spectroscopy and scanning transmission electron microscopy, reveal formation conditions of 2D InSe. The epitaxial alignment is verified by in-plane X-ray diffraction. Samples grown under optimized conditions exhibit a strong optical absorption in the visible range and especially a comparably high electron mobility, underlining the potential of the MOCVD-grown material for future applications.