Investigation of Semi-Insulating Gallium Arsenide Photoconductive Photodetectors

The structure and working mechanism of a photoconductive photodetector are compared with a p(+)-i-n(+) (PIN) photodiode and a metal-semiconductor-metal (MSM) photodetector which is regarded as two back-to-back Schottky barrier photodiodes. Because a photoconductive photodetector has the features of high critical field strength, especially no junction capacitance and no dead zone, it has the main merits of high signal-noise ratio, ultrafast response and high quantum efficiency. We fabricate two photoconductive photodetectors in a lateral configuration on a semi-insulating (SI) gallium arsenide (GaAs) wafer, which wavelength range of response is from UV to 1.73 mu m due to two-photon absorption. It is shown by the volt-ampere characteristics curve that the dark leakage current of 30-mu m-gap SI GaAs photoconductive photodetector at a bias field of 66 V/cm is less than 1.2 mu A. Our experiment has demonstrated that SI GaAs photoconductive photodetectors are noteworthily superior to high-speed Si PIN photodetectors to measure ultrashort pulse lasers with the properties of ultrafast response, ultrawide spectral range, high signal-noise ratio and ease of fabrication.