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

A study of the carrier transport mechanism, the charge collection efficienc y and the energy resolution has been carried out on semi-insulating GaAs X- ray detectors realised on substrates with concentrations of acceptor dopant s N-a, varying from 10(14) to 10(17) cm(-3). The electron collection effici ency (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 te mperature, the best collection efficiency (95%) and the best energy resolut ion (13.7 keV FWHM) for 59.5 keV X-rays of the Am-241 source, have been ach ieved with the less doped detectors (N-1 - 10(14) cm(-3)). The concentratio ns 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 E CE values. This behaviour strongly supports the hypothesis that the EL2 def ects play a main role in the compensation of the material and in the limita tion of the detection properties. (C) 2000 Published by Elsevier Science B. V. All rights reserved.