Single-Crystalline All-Oxide α-γ-β Heterostructures for Deep-Ultraviolet Photodetection

Recent advancements in gallium oxide (Ga₂O₃)-based heterostructures have allowed optoelectronic devices to be used extensively in the fields of power electronics and deep-ultraviolet photodetection. While most previous research has involved realizing single-crystalline Ga₂O₃ layers on native substrates for high conductivity and visible-light transparency, presented and investigated herein is a single-crystalline β-Ga₂O₃ layer grown on an α-Al₂O₃ substrate through an interfacial γ-In₂O₃ layer. The single-crystalline transparent conductive oxide layer made of wafer-scalable γ-In₂O₃ provides high carrier transport, visible-light transparency, and antioxidation properties that are critical for realizing vertically oriented heterostructures for transparent oxide photonic platforms. Physical characterization based on X-ray diffraction and high-resolution transmission electron microscopy imaging confirms the single-crystalline nature of the grown films and the crystallographic orientation relationships among the monoclinic β-Ga₂O₃, cubic γ-In₂O₃, and trigonal α-Al₂O₃, while the elemental composition and sharp interfaces across the heterostructure are confirmed by Rutherford backscattering spectrometry. Furthermore, the energy-band offsets are determined by X-ray photoelectron spectroscopy at the β-Ga₂O₃/γ-In₂O₃ interface, elucidating a type-II heterojunction with conduction- and valence-band offsets of 0.16 and 1.38 eV, respectively. Based on the single-crystalline β-Ga₂O₃/γ-In₂O₃/α-Al₂O₃ all-oxide heterostructure, a vertically oriented DUV photodetector is fabricated that exhibits a high photoresponsivity of 94.3 A/W, an external quantum efficiency of 4.6 × 10⁴%, and a specific detectivity of 3.09 × 10¹² Jones at 250 nm. The present demonstration lays a strong foundation for and paves the way to future all-oxide-based transparent photonic platforms.