The response time of GaN photoconductive detector under various ultraviolet-radiation intensities

摘要

The persistent photoconductivity (PPC) effect was generally observed in many Ⅲ-Ⅴ compound semiconductors and it was always related to yellow luminescence. In this paper, the PPC effect in unintentionally doped GaN was investigated. The GaN photoconductive detector response time measured by changing the chopper frequency of modulator was studied under various ultraviolet-radiation intensities. The maximum value of UV intensities used in test was approximately 0.2W/m~2. Experimental results show that the response time of unintentionally doped GaN PC detector is independent of the wavelength of the ultraviolet radiation in the range of 300～365nm and it decreases with the increasing of UV radiation intensity. The longest response time getting in experiments was 7.64ms and the shortest 2.89ms. Fourier transformation and lock-in amplifier was used to reduce the noise at AC frequency of 50Hz and the results show that Fourier transformation was more effective to eliminate the low frequency noise. The experimental data fit the theoretical curve very well, better than the results reported previously. Finally, these phenomena were tried to be explained using a mechanism that minor carriers were captured by deep acceptors. The deep acceptors were deduced to be V_(Ga)-related complexes. In strong UV radiation, the photo-generated holes (minor carriers) were no longer captured by deep acceptors and the recombination opportunities with majority carriers were increased. Consequently the response time was reduced. The other possible reason was that there were metastable states which were related to Ga vacancy.