PERFORMANCE OF A NEW OHMIC CONTACT FOR GAAS PARTICLE DETECTORS

In recent papers, we have investigated, within the context of the RD-8 experiment, the behaviour as a function of bias of the active region of particle detectors made by Alenia SpA on semi-insulating liquid enc apsulated Czochralski gallium arsenide: the active region width depend s linearly on the bias voltage. The diodes were found to break down as soon as the field reached the back ohmic contact. This suggested that the ohmic contact was injecting holes into the diode, therefore we ha ve decided to develop a new, non-injecting, non-alloyed ohmic contact. This new contact allows us to go far beyond, five times, the voltage bias necessary to have a fully active detector. The higher voltage rea ched by the detectors helps us improve the charge collection efficienc y, up to more than 95% for alphas and more than 90% for beta (mips) pa rticles and X-rays, giving a more stable operation of the detectors. F or the first time we can explore the characteristics of a GaAs detecto r beyond the voltage needed for it to be completely active.