MOCVD Growth of Covalent and 2D Ga–Se: A Raman Microscopy-Based Phase Validation

Two-dimensional (2D) materials like gallium selenide (GaSe) hold great promise for optoelectronic devices. GaSe, in particular, features a thickness-dependent bandgap tunable from red to the ultraviolet region. Gallium sesquiselenide (Ga ₂ Se ₃ ), a related phase with a direct bandgap and a lattice constant closely matched to silicon, can also be grown, making it suitable for integration. To achieve phase-pure growth, constructing a detailed phase diagram is essential. We report wafer-scale synthesis of GaSe and Ga ₂ Se ₃ via metal-organic chemical vapor deposition (MOCVD), systematically varying growth temperature (450–600°C) and the selenium-to-gallium partial pressure ratio. Raman spectroscopy confirmed phase formation, while AFM, SEM, and HAADF-STEM revealed morphology and epitaxy. Ga ₂ Se ₃ formed micron-scale three-dimensional islands and epitaxial films with antiphase domains on GaP/Si, whereas GaSe grew as faceted ⟨111⟩-oriented sheets. Photoluminescence and cathodoluminescence showed direct transitions at 1.34 eV for Ga ₂ Se ₃ and 1.89 eV for GaSe. These results demonstrate controlled MOCVD synthesis of phase-pure GaSe and Ga ₂ Se ₃ , highlighting their potential for silicon-based optoelectronics.