Temperature dependence of commercial 4H-SiC UV Schottky photodiodes for X-ray detection and spectroscopy

Two commercial-off-the-shelf (COTS) 4H-SiC UV photodiodes have been investigated for their suitability as low-cost high temperature tolerant X-ray detectors. Electrical characterisation of the photodiodes which had different active areas (0.06 mm2 and 0.5 mm2) is reported over the temperature range 0 °C to 140 °C together with measurements of the X-ray photocurrents generated when the detectors were illuminated with an 55Fe radioisotope X-ray source. The 0.06 mm2 photodiode was also investigated as a photon counting spectroscopic X-ray detector across the temperature range 0 °C to 100 °C. The depletion widths (at 120 V reverse bias) of the two diodes were found to be 2.3 µm and 4.5 µm, for the 0.06 mm2 and 0.5 mm2 detectors respectively, at 140 °C. Both devices had low leakage currents (<10 pA) at temperatures ≤40 °C even at high electric field strengths (500 kV/cm for 0.06 mm2 diode; 267 kV/cm for 0.5 mm2 diode). At 140 °C and similar field strengths (514 kV/cm for 0.06 mm2 diode; 269 kV/cm for 0.5 mm2 diode), the leakage currents of both diodes were <2 nA (corresponding to leakage current densities of 2.4 µA/cm2 and 0.3 µA/cm2 for each diode respectively). The results demonstrated that both devices could function as current mode detectors of soft X-rays at the temperatures <80 °C and that when coupled to a low noise charge sensitive preamplifier, the smaller diode functioned as a photon counting spectroscopic X-ray detector at temperatures ≤100 °C with modest energy resolution (1.6 keV FWHM at 5.9 keV at 0 °C; 2.6 keV FWHM at 5.9 keV at 100 °C). Due to their temperature tolerance, wide commercial availability, and the radiation hardness of SiC, such detectors are expected to find utility in future low-cost nanosatellite (cubesat) missions and cost-sensitive industrial applications.