Performance of bulk semi-insulating GaAs-based sensor and its comparison to Si-based sensor for Timepix radiation camera

Nowadays, pixelated detectors based on Timepix readout chip play important role in various fields of science and research like particle physics, advanced spectrometry and especially X-ray imaging for medical and material purposes. Present work is focused on the evaluation of the 350 μm thick prototype (semi-insulating) SI GaAs sensor performance and its comparison to 300 μm thick Si sensor that was chosen as a reference. Both sensors consist of 256 × 256 pixels matrix with pixel pitch of 55 μm. We performed flat field illumination to test the pixel homogeneity and found out that the response of GaAs sensor is less homogeneous in terms of number of counts across the sensor compared to Si sensor. The imaging performance was tested using two samples of different absorption strength, specifically one less-absorbing sample and one more-absorbing sample. We found out that our fabricated SI GaAs sensor shows better imaging performance than Si sensor in case of imaging more-absorbing sample and vice versa. This is due to different prevalent detection efficiency regions. The spatial resolution was determined to be 8.73 lp/mm and 8.25 lp/mm for GaAs and Si sensor, respectively. Also, spectrometric measurements were carried out and results show that Si sensor has about 2 times higher energy resolution in comparison with SI GaAs sensor.