Ultra-wide bandgap semiconductor of β-Ga2O3 and its research progress of deep ultraviolet transparent electrode and solar-blind photodetector

Gallium oxide (Ga2O3), with a bandgap of about 4.9 eV, is a new type of ultra-wide bandgap semiconductor material. The Ga2O3 can crystallize into five different phases, i.e. a, alpha, beta, gamma, delta and epsilon-phase. Among them, the monoclinic beta-Ga2O3 (space group: C2/m) with the lattice parameters of alpha = 12.23 angstrom, beta = 3.04 angstrom, c = 5.80 angstrom, and beta = 103.7 degrees has been recognized as the most stable phase. The beta-Ga2O3 can be grown in bulk form from edge-defined film-fed growth with a low-cost method. With a high theoretical breakdown electrical field (8 MV/cm) and large Baliga's figure of merit, the beta-Ga2O3 is a potential candidate material for next-generation high-power electronics (including diode and field effect transistor) and extreme environment electronics [high temperature, high radiation, and high voltage (low power) switching]. Due to a high transmittance to the deep ultraviolet-visible light with a wavelength longer than 253 nm, the beta-Ga2O3 is a natural material for solar-blind ultraviolet detection and deep-ultraviolet transparent conductive electrode. In this paper, the crystal structure, physical properties and device applications of Ga2O3 material are introduced. And the latest research progress of beta-Ga(2)O(3 )in deep ultraviolet transparent conductive electrode and solar-blind ultraviolet photodetector are reviewed. Although Sn doped Ga2O3 thin film has a conductivity of up to 32.3 S/cm and a transmittance greater than 88%, there is still a long way to go for commercial transparent conductive electrode. At the same time, the development history of beta-Ga2O3 solar-blind ultraviolet photodetectors based on material type (nanometer, single crystal and thin film) is described in chronological order. The photodetector based on quasi-two-dimensional beta-Ga2O3 flakes shows the highest responsivity (1.8 x 10(5) A/W). The photodetector based on ZnO/Ga2O3 core/shell micron-wire has a best comprehensive performance, which exhibits a responsivity of 1.3 x 10(3) A/W and a response time ranging from 20 mu s to 254 nm light at -6 V. We look forward to applying the beta-Ga2O3 based solar-blind ultraviolet photodetectors to military (such as: missile early warning and tracking, ultraviolet communication, harbor fog navigation, and so on) and civilian fields (such as ozone hole monitoring, disinfection and sterilization ultraviolet intensity monitoring, high voltage corona detection, forest fire ultraviolet monitoring, and so on).