Wide-bandgap oxide semiconductors Ga₂O₃ and ZnO have garnered significant attention due to their exceptional optoelectronic properties and thermo-chemical stability. This study innovatively integrates a ZnO quaternary alloy (BeZnOS) with Ga₂O₃ to construct a novel BeZnOS/Ga₂O₃ heterojunction ultraviolet photodetector. By leveraging the synergistic band modulation via isovalent ion (Be²⁺/S^2-) co-doping in ZnO, we aim to enhance the photogenerated carrier separation and transport efficiency through optimized heterojunction band alignment, ultimately developing a high-performance self-driven deep-UV photodetector. This work provides new insights into ZnO bandgap engineering and establishes a materials foundation for developing high-performance, all-oxide-based deep-ultraviolet photodetectors.

The heterostructure thin films were synthesized via pulsed laser deposition (PLD) using KrF excimer laser ablation (λ=248 nm) on c-plane sapphire substrates. Ceramic targets of BeZnOS and Ga₂O₃ were prepared by solid-state sintering at 1200 ℃ under argon atmosphere. Prior to deposition, substrates underwent rigorous cleaning in acetone, ethanol, and deionized water (15 min each) followed by N₂ drying. BeZnOS films were grown at 700 ℃ with 2 Pa O₂ partial pressure and 350 mJ laser energy, while Ga₂O₃ layers were selectively deposited through a shadow mask at 650 ℃ (2 Pa O₂, 250 mJ). Post-growth in situ annealing was performed at 550 ℃ (20 Pa O₂, 20 min) to optimize crystallinity. Device fabrication was completed by depositing Pt (high-work-function) and Al (low-work-function) electrodes through magnetron sputtering (100 W, 1.5 Pa Ar) to form Pt/BeZnOS/Ga₂O₃/Al architectures with 200 μm×200 μm contacts.

Comprehensive structural and optoelectronic characterizations were conducted using high-resolution X-ray diffraction (XRD), UV-Vis-NIR transmission spectroscopy, field-emission scanning electron microscopy with energy-dispersive spectroscopy (FESEM/EDS), and X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS). These techniques systematically analyzed crystalline phase purity, optical bandgaps, elemental distribution profiles, and energy band configurations. A Omni-λ 3027 setup consisting of Keithley 2635 digital source meter, probe station, electromagnetic shielding dark box, monochromator, 150 W xenon lamp and phase-locked amplifier, was utilized to measure the optoelectronic performances of the photodetector.

Structural characterization via high-resolution XRD confirmed phase-pure hexagonal wurtzite BeZnOS and monoclinic β-Ga₂O₃ film. Optical transmission spectrum revealed dual absorption edges, corresponding to direct bandgaps of 3.30 (BeZnOS) and 4.50 eV (Ga₂O₃) via Tauc analysis. Cross-sectional FE-SEM demonstrated layer thicknesses of 212 nm (BeZnOS) and 165 nm (Ga₂O₃), while EDS mapping confirmed elemental stratification with well-defined heterointerfaces. The fabricated Pt/BeZnOS/Ga₂O₃/Al photodetector exhibits pronounced rectifying behavior (rectification ratio: 1.72×10²) and achieved self-powered operation at zero bias. Notably, dual spectral response peaks emerged in the UVC and UVA regions, with a peak responsivity of 23.5 mA/W at 240 nm and a corresponding specific detectivity of 2.3×10¹¹ Jones. The device further demonstrated rapid response kinetics (rise time τ_r = 0.09 s; decay time τ_d = 0.10 s). These exceptional characteristics originate from the synergistic coupling of built-in electric fields: 1) the type-II band alignment at the BeZnOS/Ga₂O₃ heterojunction (ΔE_C = 1.9 eV, ΔE_V = 0.7 eV), and 2) the Schottky barrier at the Pt/BeZnOS interface. This dual-field configuration drives efficient spatial separation of electrons and holes, reducing recombination and enhancing photocurrent generation. Additionally, the photoresponse characteristics of the device exhibit significant intensity dependence: under weak illumination, it demonstrates higher responsivity but slower response speed, whereas under strong illumination, it shows lower responsivity yet faster response speed. This phenomenon primarily originates from the carrier saturation effect in deep-level trap states, whereby high light intensity saturates the trap centers, thereby suppressing the persistent photoconductivity (PPC) relaxation process.

This work successfully demonstrates a high-performance self-driven deep-UV photodetector based on an engineered BeZnOS/Ga₂O₃ heterojunction, achieving high sensitivity (R_{240 nm} = 23.5 mA/W, D* = 2.3×10¹¹ Jones) and fast response (τ_r/τ_d=0.09 s/0.10 s) at zero bias. The fabricated heterojunction forms a type-II band alignment, which directionally couples with the built-in electric field of the Pt/BeZnOS Schottky junction to generate an enhanced composite field. This synergistic configuration significantly promotes the separation and transport of photogenerated carriers, ultimately enabling high-sensitivity and rapid-response self-powered operation. The innovative dual-junction synergistic modulation strategy demonstrates significant potential for advancing self-driven optoelectronic devices.