This paper describes the heteroepitaxial growth of high-quality alpha-phase gallium oxide (α-Ga2O3) on a sapphire substrate without a buffer layer via the hydride vapor phase epitaxy method. Here, compressive strain arising from the difference in lattice constants between the substrate and α-Ga2O3 is relieved near the interface, resulting in a high crystal quality of 32.72 arcsec (full width at half maximum value) in the high-resolution x-ray diffraction 2θ scan spectrum. Subsequently, the fabricated hetero α-Ga2O3-based photodetector with a metal–semiconductor–metal structure operating under ultraviolet radiation in the C-band (UVC) demonstrates a high UVC responsivity of 5 × 102 A W−1 and a high visible blindness of 8.14 × 104 at 235 nm. The photodetector utilizes photogenerated holes trapped near the interface of the metal electrode, inducing amplified electron current flow. The developed hetero α-Ga2O3-based UVC photodetector can be used to detect early signs of fire, flames, or corona discharge in visible light environments for social and industrial safety applications.

Undoped epitaxial films of α-Ga₂O₃ were grown on basal plane sapphire substrates by halide vapor phase epitaxy (HVPE) in three different modes: standard HVPE, HVPE with constant flow of Ga and pulsed supply of O₂ (O₂-control growth regime), and with constant flow of O₂ and pulsed delivery of Ga (Ga-control growth fashion). The best crystalline quality as judged by x-ray symmetric and asymmetric reflection half-widths and by atomic force microscopy morphology profiling was obtained with the O₂-control deposition, and these results appear to be the best so far reported for α-Ga₂O₃ films. All grown α-Ga₂O₃ epilayers were high-resistivity n-type, with the Fermi level pinned near E_c − 1 eV deep traps. Photoinduced current transient spectra also showed the existence in standard HVPE samples and samples grown under the O₂-control pulsed growth conditions of deep hole traps with levels near E_v + 1.4 eV whose density was suppressed in the Ga-control pulsed HVPE samples. The levels of the dominant deep traps in these α-Ga₂O₃ samples are close to the position of dominant electron and hole traps in well documented β-Ga₂O₃ crystals and films.

α-Ga2O3, with an ultra-high energy bandgap of 5.1 eV, is an attractive material for applications in solar-blind photodetectors and high-power electronics. We fabricated an α-Ga2O3 metal-semiconductor-metal (MSM) interdigitated solar-blind photodetector, where an epitaxial α-Ga2O3 thin film was grown on a sapphire substrate using a hydride vapor-phase epitaxy technique. Excellent optoelectronic device properties including high responsivity (4.24 × 104 A/W), detectivity (1.77 × 1011 Jones), and external quantum efficiency (2.07 × 105) were demonstrated in response to ultraviolet (UV) C wavelength. Under sunlight, the α-Ga2O3 MSM photodetector exhibited stable solar-blind sensitivity to UVC wavelength without interference from the incoming solar spectrum. Our work proposes that α-Ga2O3 has great potential as a next-generation high-performance solar-blind photodetector.

A compact self-powered solar-blind UV-C photodiode was demonstrated using an ultra-wide bandgap (UWBG) α-Ga₂O₃ thin film as a wavelength-selective absorber layer. The UWBG-based Schottky junction architecture renders the use of low-performance and bulky solar-blind UV bandpass filters unnecessary. High-quality α-Ga₂O₃ thin films with a thickness of 1.25 µm were grown on a (0001) sapphire substrate via the halide vapor-phase epitaxy technique. The self-powered solar-blind UV-C photodetector based on the Ni/α-Ga₂O₃ Schottky junction exhibited excellent responsivity (1.17 × 10⁻⁴ A/W), photo-to-dark current ratio (1.12 × 10⁵), and reproducibility, as well as fast rise/decay characteristics without persistent photoconductivity upon exposure to UV-C radiation (254 nm wavelength). The relationship between light intensity (I) and photocurrent (P) was modeled by I ∼ P^0.69, indicating the high-quality of the halide vapor-phase epitaxy-grown α-Ga₂O₃ thin film. Upon exposure to natural sunlight, the fabricated solar-blind photodetector showed excellent solar blindness with sensitivity to UV-C radiation and did not require an external power source. Therefore, this UWBG α-Ga₂O₃ thin-film Schottky barrier photodiode is expected to facilitate the development of a compact and energy-independent next-generation UV-C photodetector with solar blindness.