Monolithic Integration of 2D GaSe/3D β-Ga2O3 Mixed-Dimensional Heterostructures on c-Sapphire Substrates by Molecular Beam Epitaxy

In this study, we explore the heteroepitaxial growth and characteristics of 2D GaSe/3D β-Ga₂O₃ mixed-dimensional (MD) heterostructures on c-Sapphire substrates by using molecular beam epitaxy (MBE). The β-Ga₂O₃ film, synthesized in the initial stage, exhibited high crystallinity, serving as a suitable template for subsequent GaSe growth. In situ reflection high-energy electron diffraction (RHEED) provided critical insights into the nucleation dynamics of 2D GaSe on 3D β-Ga₂O₃/c-Sapphire under varying epitaxial conditions. High-resolution X-ray diffraction (HR-XRD) and Raman spectroscopy further confirmed the successful monolithic integration of these MD heterostructures, exhibiting high uniformity with large surface coverage. Notably, the Ga pretreatment on the 3D β-Ga₂O₃/c-Sapphire template prior to GaSe growth effectively stabilized the surface through Se passivation, promoting uniform 2D layer growth at 425 °C compared to the nontreated counterpart. This approach preserved the integrity of the 2D/3D heterointerface, as validated by microstructural analysis. Unlike strain-free exfoliated GaSe films, the epitaxial growth in this study allowed for tunable band-edge energy attributed to the strain induced in the films by modification of the growth temperature. The resulting MD heterojunction, formed between 2D GaSe (with near band-edge emission ∼1.81 eV grown at 480 °C) and 3D β-Ga₂O₃ (∼4.96 eV), demonstrates significant potential for next-generation optoelectronic devices.