Influence of temperature on the energy resolution of sensors based on HR GaAs:Cr

HR GaAs:Cr is a well known material, used for room-temperature X-ray detector applications. While GaAs:Cr detectors have typically shown good performance at 25${}^{\circ }$C, there may be benefits of running the detector at lower temperatures where leakage currents are lower. The aim of this study was to evaluate the energy resolution across the temperature range $-{10}^{\circ }$C to 30${}^{\circ }$C which is easily achievable using compact electrical cooling solutions. Using HR GaAs:Cr detectors that were flip-chip-bonded to STFC's PIXIE ASIC, it was possible to measure the spectroscopic performance of the material as a function of temperature. Both HR GaAs:Cr sensors were of 500 μm thickness and mobility-lifetime products measured at room temperature comprised $0.5\cdot {10}^{-4}$ and $1.7\cdot {10}^{-4}$ cm${}^2$V${}^{-1}$ for sensors dated from 2016 and 2018, respectively. Using an ${}^{241}$Am sealed source, pulse height spectra were measured for pixel arrays with pitches of 250 and 500 μm for temperatures in the range -10${}^{\circ }$C to 30${}^{\circ }$C. By varying the operating voltage of the detectors it was also possible to study the variation in the charge transport properties of the HR GaAs:Cr over the same temperature range.