Session DD: Oxide Semiconductor Heterojunction Diodes

8:20 AM DD1, Ultraviolet Photodetectors with Novel Oxide Thin Films: Shizuo Fujita1; Takumi Ikenoue1; Naoki Kameyama1; Takayoshi Oshima1; 1Kyoto University A variety of wide band gap oxide semiconductors, which are recognized as stable and environmental-friendly materials, can meet various demands for detectable wavelength, sensitivity, cost, and endurance of ultraviolet photodetectors, in contrast to III-nitride semiconductors which always needs high-cost and dangerous sources for their growth. In this presentation, we report several oxide semiconductors we have developed as the materials for ultraviolet photodetectors. Ga2O3 possesses large band gap of 4.8 eV (258 nm), which is suitable for UV-C photodetectors. HIgh quality Ga2O3 substrates allow the Schottky-type photodetectors using high-resistive layers formed on the substrates by thermal annealing in oxygen atmosphere. The photodetector exhibited the photoresponsivity of 0.037 A/W at 250 nm with the external quantum efficiency of 18 %. The photodetector was capable of detecting solar-blind light of as weak as 1 nW/cm2 from the flame in normal room lighting. Robust properties of Ga2O3 against defect generation have allowed hundred-hours operation without noticeable degradation as a power monitor for a low-pressure mercury lamp (254nm, 40 mW/cm2). A SnO2 semiconductor, whose band gap is about 4 eV (310 nm), is desirable for UV-B photodetectors. Molecular beam epitaxy (MBE) and thermal annealing resulted in high resistive (5×106 Ωcm) SnO2 layers on sapphire substrates. Forming interdigital Au/Ni electrodes on the SnO2 layer, the sample operated as a UV-B photodetector with the photoresponsivity of 0.023 A/W at 290 nm with the external quantum efficiency of 10%. Oxide semiconductors can be grown by low-cost and solution-based growth techniques, which allow simple fabrication process and inexpensive devices. With the ultrasonic spray mist chemical vapor deposition where safe and inexpensive sources can be used in a simple system, Schottky-type photodetectors of PEDOT:PSS/ZnMgO were successfully fabricated on glass substrates using metal mask patterning. In spite of the low cost and low power consumption processes for the device fabrication, the photodetectors exhibited reasonably high photoresponsivity, for example, 0.074 A/W at 320 nm with the external quantuim efficiency of 36.5%. The cutoff wavelengths were tunable between 370 and 300 nm by the Mg concentrations in ZnMgO. We believe that oxide semiconductors can be key materials for the photodetectors of ultraviolet light of a variety of wavelengths and intensity.