The structural, electronic, and optical properties of β-Ga₂O₃with oxygen vacancies are studied by employing first-principles calculations based on density function theory. Based on the defects formation energies, we conclude the oxygen vacancies are most stable in their fully charge states. The electronic structures and optical properties of β-Ga₂O₃are calculated by Generalized Gradient Approximation + U formalisms with the Hubbard U parameters set 7.0 eV and 8.5 eV for Ga and O ions, respectively. The calculated bandgap is 4.92 eV, which is consistent with the experimental value. The static real dielectric constants of the defective structures are increased compared with the intrinsic one, which is attributed to the level caused by the Ga-4s states in the bandgap. Extra peaks are introduced in the absorption spectra, which are related to Ga-4s and O-2p states. Experimentally, β-Ga₂O₃films are deposited under different O₂volume percentage with ratio-frequency magnetron sputtering method. The measured results indicate that oxygen vacancies can induce extra emission peaks in the photoluminescence spectrum, the location of these peaks are close to the calculated results. Extra O₂can increase the formation energies of oxygen vacancies and thus reduce oxygen vacancies in β-Ga₂O₃.

Solar-blind photodetectors have received increasing attention due to their widely applications in military and civil aspects. However, most of the photodetectors exhibit low detection ability for weak ultraviolet light signal, and the forewarning of weak ultraviolet radiation is important for the immune system of humans. Herein, the self-powered photodetector based on $\beta $ -Ga ₂ O ₃ /NiO heterojunction with an ultralow dark current (1.09 nA at −15 V) has been fabricated, and the synthesized platinum (Pt) nanoparticles (NPs) are used for surface modification of the device. The obtained devices with Pt NPs exhibit a large ${I}_{\text {photo}}/{I}_{\text {dark}}$ ratio of 9153, an excellent detectivity of $4.2\times 10^{9}$ Jones, an ultrahigh linear dynamic range of 79 dB, and a high responsivity of 4.27 mA/W, with respective enhancements over 4476%, 2220%, 71.7%, and 2442% compared to the pristine device, respectively. These results indicated that the device has the excellent ability for weak ultraviolet light signal detection, and the enhanced performance can be attributed to the Pt NPs, which can remarkably enhance the generation of photogenerated carriers via the formation of the local electric field and the local surface plasmon resonance effect. The experiment provides an effective method for fabricating high-performance solar-blind photodetector.

Self-powered photodetectors working in solar-blind region (below 280 nm) have attracted growing attention due to their wide applicability. Monoclinic Ga₂O₃ (β-Ga₂O₃) with excellent merits and a wide bandgap (4.9 eV) is regarded as a good candidate for solar-blind photodetector application. Self-powered photodetectors generally based on homo/heterojunction suffer from a complex fabrication process and slow photoresponse because of the interface defects and traps. Herein, we demonstrated a fabrication and characterization of a self-powered metal-semiconductor-metal (MSM) deep-ultraviolet (DUV) photodetector based on single crystal β-Ga₂O₃. The self-powered property was realized through a simple one-step deposition of an asymmetrical pair of Schottky interdigital contacts. The photocurrent and responsivity increase with the degenerating symmetrical contact. For the device with the most asymmetric interdigital contacts operated at 0 V bias, the maximum photocurrent reaches 2.7 nA. The responsivity R_λ, external quantum efficiency EQE, detectivity D*, and linear dynamic range LDR are 1.28 mA/W, 0.63, 1.77 × 10¹¹ Jones, and 23.5 dB, respectively. The device exhibits excellent repeatability and stability at the same time. Besides, the device presents a fast response speed with a rise time of 0.03 s and a decay time of 0.08 s. All these results indicate a promising and simple method to fabricate a zero-powered DUV photodetector.