The structural, electronic, and optical properties of β-Ga2O3 with 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-Ga2O3 are 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-Ga2O3 films are deposited under different O2 volume 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 O2 can increase the formation energies of oxygen vacancies and thus reduce oxygen vacancies in β-Ga2O3.
Self-powered photodetectors working in solar-blind region (below 280 nm) have attracted growing attention due to their wide applicability. Monoclinic Ga 2 O 3 (β-Ga 2 O 3) 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-Ga 2 O 3. 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 × 10 11 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 zeropowered DUV photodetector.
In this study, β-Ga2O3 thin films were directly deposited on sapphire substrates by radio-frequency magnetron sputtering. The effects of post-annealing temperature and oxygen concentration during sputtering on the structural and optical properties of the films were investigated in detail. The results indicated that the crystalline quality of the films improved with increasing post-annealing temperature. When 1 vol. % oxygen was included in the deposition process, β-Ga2O3 film displayed the best crystalline quality, the band gap and atomic ratios of O to Ga of the film were increased, and the content of oxygen vacancies in the film was effectively lowered. These results revealed an effective, convenient method to prepare high-quality β-Ga2O3 thin films.
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