| Summary: | 碩士 === 國立交通大學 === 電子物理系 === 90 === Interdigitated ultraviolet photoconductive detectors, conventional metal-semiconductor-metal (MSM) photodetectors, and transparent-electrode MSM photodetectors were successfully fabricated on n-GaN wafers. Photo response on wavelength (spectral responsivity), chopper frequency (ac response) and bias voltage (dc response) had been extensively investigated. Responsivity spectra of all type detectors had sharp edge at wavelength around 364 nm, and dropped with a tail in wavelength greater than 364 nm, which is equivalent to the energy gap of GaN. Ac response of photoconductive detectors and MSM photodetectors decayed with the increasing chopping frequency, indicating a large excess carrier lifetime. Optical quenching effect was observed on the responsivity spectra for the photoconductive detectors illuminated simultaneously with He-Ne laser (6328nm). Acceptor-like deep levels trapping the holes was attributed to the main effect to large carrier lifetime and optical quenching phenomenon. Photoconductive detectors, conventional MSM photodetectors, and transparent-electrode MSM photodetectors have maximum dc responsivity (with detection wavelength of 325 nm) of 82.4A/W at 0.5V, 2.47A/W at 8V, and 3.29A/W at 8V, respectively. For the large excess carrier lifetime, photoconductive gain effect was ascribed to the resulting photocurrent amplification for these three type photodetectors.
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