Proceedings Article | 9 October 2024
KEYWORDS: Sensors, Gallium nitride, Diodes, X-rays, Semiconductors, X-ray detectors, Crystals, Solids, Signal to noise ratio, Gamma radiation
As semiconductor radiation detectors, detectors with high sensitivity at high energy, such as cadmium telluride (CdTe), which we have reported for many years, have been mainly developed, but CdTe has a K-edge and its attenuation coefficient at low energy, around 30 keV or lower, becomes small. there is a need for semiconductor detectors made of other materials that can be used for low-energy applications such as mammography. We propose gallium nitride (GaN) as a new semiconductor detector material, aiming at a useful detector in the low-energy region targeting 17.5 keV, where characteristic x-rays are generated. GaN has also been studied for LED and power devices, and its excellent charge transfer characteristics have been demonstrated in practical applications. In order to investigate the feasibility of GaN as a semiconductor material for radiation detectors, we fabricated pn-type and pin-type GaN detectors and evaluated their current-voltage characteristics, capacitance-voltage characteristics, and x-ray response characteristics. From the results, diode characteristics were confirmed for both structures. However, the frequency dependence of the capacitance-voltage characteristics of the pn-type detector suggested that the pn-type detector had many internal defects in the crystal. In both structures, the detected current increased with x-ray irradiation, and the current increased linearly in the range of the measured dose rate. In the alpha-ray detection measurement at an incident energy of 3.6 MeV, the pin-type detector was found to be sensitive to alpha rays. However, the pn-type detector did not detect the pulse because the pulse was buried by fluctuations due to leakage current and thermal noise. It was also shown that the pin-type detector must have a small dark current to make gamma-ray detection measurements with low energy. The results show the feasibility of GaN as a semiconductor material for radiation detectors, and both the pn-type and pin-type detectors exhibit linear current increase in the x-ray response characteristics measurements, suggesting the feasibility of GaN as a storage-type x-ray detector. In addition, the pin-type detector showed pulses of alpha-rays, suggesting the feasibility of a photon-counting type detector for gamma-rays in the future.
