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.
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.
An oxide semiconductor of -Ga 2 O 3 has a natural solar-blind sensitivity due to its large bandgap of 4.8 eV. To evaluate its potential, a flame detector was fabricated using its conductive single crystal substrate applying a simple method without epitaxy and vacuum processes. The structure is a poly(3,4-ethylene dioxythiophene) complex with polystyrene sulfonic acid (PEDOT-PSS) Schottky contact/a semi-insulating layer of -Ga 2 O 3 /n-type region of -Ga 2 O 3 /an In ohmic contact. The spectral response of the detector exhibited a large 250-to-300-nm rejection ratio of 1:5 Â 10 4 and an external quantum efficiency of 18% at 250 nm. The device successfully detected a flame by distinguishing 1.5 nW/cm 2 solar-blind light from the flame under a strong fluorescent lamp illumination without any visible-cut filters. This result encourages the fabrication of practical -Ga 2 O 3 -based flame detectors.
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