Chromium compensated gallium arsenide detectors for X-ray and γ-ray spectroscopic imaging

Semi-insulating GaAs material of 500 μm thickness grown using the Liquid Encapsulated Czochralski (LEC) method has been compensated with chromium to produce high resistivity single crystals suitable for spectroscopic imaging applications. Results are presented for the performance of three small pixel detectors each with 80×80 pixels on a 250 μm pitch, fabricated with metal contacts and bonded to a spectroscopic imaging ASIC. Current-voltage measurements demonstrated a material resistivity of 2.5×109 Ω cm at room temperature. At an optimised bias voltage, the average energy resolution at 60 keV (FWHM) was in the range 2.8-3.3 keV per pixel. An analysis of the voltage dependent X-ray spectroscopy suggests that the electron mobility lifetime (μτe) for each detector is in the range 2.1-4.5×10−5 cm2 V−1. The spectroscopic imaging capability of the detectors is also demonstrated in X-ray absorption spectroscopy measurements.