A vertical-type Schottky photodetector based on a (100)-oriented β-Ga2O3 substrate has been fabricated with simple processes of thermal annealing and vacuum evaporation. The photodetector exhibited a rectification ratio higher than 106 at ±3 V, and showed deep-ultraviolet-light detection at reverse bias. The spectral response showed solar-blind sensitivity with high photoresponsivities of 2.6–8.7 A/W at wavelengths of 200–260 nm. These values were 35–150 times higher than those derived assuming the internal quantum efficiency to be unity. This fact is attributed to the carrier multiplication occurring in the highly resistive surface region that is subject to a high internal electric field of about 1.0 MV/cm at the reverse bias of 10 V.

We fabricated β-Ga2O3 photodiodes with a Au Schottky contact on a single crystal substrate and investigated the effect of postannealing on the electrical and optical properties of the photodiodes. The ideality factor improved to near unity by annealing at temperatures above 200 °C; however, the reverse leakage current remained nearly unchanged. The responsivity in the wavelength region below 260 nm was enhanced dramatically by a factor of more than 102 after annealing at 400 °C resulting in maximum responsivity of 103 A/W, accompanied with a contrast ratio of about six orders of magnitude between the responsivities at 240 and 350 nm.

PACS 72.80. Jc, 78.66.Li, 81.10.Fq Transparent conductive Sn-doped β-Ga 2 O 3 single crystal with high crystallinity was successfully fabricated as a substrate for the growth of GaN-based compounds. Sn-doped β-Ga 2 O 3 single crystals were grown using a floating zone (FZ) method, and the properties of electrical conductivity, optical transmittance, and crystallinity were characterized to optimize the growth condition. It was found that these properties are controlled by the Sn doping concentration, and the specimen for 32 ppm Sn-doped β-Ga 2 O 3 single crystal was optimized to satisfy these properties simultaneously, i.e. the substrate with the internal optical transmittance of above ~85 % in the visible region, the electrical resistivity of 4.27×10 -2 Ωcm, the carrier density of 2.26×10 18 cm -3 , and the FWHM of X-ray rocking curve of 43 arcsec was obtained.