Effects of photon irradiation on the time response of diamond photodetectors

Radiation hardness, mass and power budget constraints as well as high detection efficiency are strong requirements for detectors devoted to space applications. Progress in material deposition and device fabrication technologies presently makes diamond photoconductors the most sensitive among deep ultraviolet photodetectors, but still some problems, related to the signal response dynamic and reproducibility, prevent such devices from a full exploitation. The aim of our work is to study the effects of photon irradiation on the time response of detectors based on single crystal diamonds. The improved performance of these deep ultraviolet photo-conductors enables the analysis of effects that are usually hidden by the persistence of the photocurrent and by excess charge trapping-detrapping at defects. Negligible or reduced impact of the persistence of photocurrent makes possible the analysis of the signal response time evolution in consecutive photocurrent transient. In this paper, a deep ultraviolet detector based on a 300-μm thick high-pressure high-temperature 1b-type single crystal diamond was irradiated with photons in the spectral region around the band gap energy corresponding to 110-250 nm spectral range. Photocurrent transients at different energies were measured in vacuum. The results show that current transient shapes and the time response depend on the energy and probably on the irradiation intensity. A possible explanation of this behaviour is discussed.