Structural and surface characterizations of 2D β-In₂Se₃/3D β-Ga₂O₃ heterostructures grown on c-Sapphire substrates by molecular beam epitaxy

Integrating two-dimensional (2D) layered materials with wide bandgap β-Ga₂O₃ has unveiled impressive opportunities for exploring novel physics and device concepts. This study presents the epitaxial growth of 2D β-In₂Se₃/3D β-Ga₂O₃ heterostructures on c-Sapphire substrates by plasma-assisted molecular beam epitaxy. Firstly, we employed a temperature-dependent two-step growth process to deposit Ga₂O₃ and obtained a phase-pure (2¯01) β-Ga₂O₃ film on c-Sapphire. Interestingly, the in-situ reflective high-energy electron diffraction (RHEED) patterns observed from this heterostructure revealed the in-plane ‘b’ lattice constant of β-Ga₂O₃ ~ 3.038Å. In the next stage, for the first time, 2D In₂Se₃ layers were epitaxially realized on 3D β-Ga₂O₃ under varying substrate temperatures (T_sub) and Se/In flux ratios (R_VI/III). The deposited layers exhibited (00l) oriented β-In₂Se₃ on (2¯01) β-Ga₂O₃/c-Sapphire with the epitaxial relationship of [112¯0] β-In₂Se₃ || [010] β-Ga₂O₃ and [101¯0] β-In₂Se₃ || [102] β-Ga₂O₃ as observed from the RHEED patterns. Also, the in-plane ‘a’ lattice constant of β-In₂Se₃ was determined to be ~ 4.027Å. The single-phase β-In₂Se₃ layers with improved structural and surface quality were achieved at a T_sub ~ 280 °C and R_VI/III ~ 18. The microstructural and detailed elemental analysis further confirmed the epitaxy of 2D layered β-In₂Se₃ on 3D β-Ga₂O₃, a consequence of the quasi-van der Waals epitaxy. Furthermore, the β-Ga₂O₃ with an optical bandgap (E_g) of ~ 5.04 eV (deep ultraviolet) when integrated with 2D β-In₂Se₃, E_g ~ 1.43eV (near infra-red) can reveal potential applications in the optoelectronic field.