Influence of substrate on the performance of semi-insulating GaAs detectors

A study of the carrier transport mechanism, the charge collection efficiency and the energy resolution has been carried out on semi-insulating GaAs X-ray detectors realised on substrates with concentrations of acceptor dopants N-a, varying from 10(14) to 10(17) cm(-3). The electron collection efficiency (ECE) and the reverse current were found to decrease with increasing N-a, while the resistivity of the material was found to increase. At room temperature, the best collection efficiency (95%) and the best energy resolution (13.7 keV FWHM) for 59.5 keV X-rays of the Am-241 source, have been achieved with the less doped detectors (N-1 - 10(14) cm(-3)). The concentrations of ionised EL2(+), determined by optical measurements in IR regions, was shown to increase with N-a and to be quasi-inversely proportional to the ECE values. This behaviour strongly supports the hypothesis that the EL2 defects play a main role in the compensation of the material and in the limitation of the detection properties. (C) 2000 Published by Elsevier Science B.V. All rights reserved.