Performances of SI GaAs detectors fabricated with implanted ohmic contacts

Abstract

The slow component of the output pulse of Semi-Insulating (SI) Gallium Arsenide (GaAs) particle detectors, which affects charge collection efficiency (cce), has been generally attributed to trapping/detrapping effects. However, most of the detectors analyzed in the literature can only be operated below the voltage v d necessary to extend the electric field all the way to the ohmic contact, making difficult to distinguish between the effect of the non-active part of the detector and that of trapping/detrapping. To do that, we have carefully analyzed the output signals of SI GaAs detectors, operated below and above v d and irradiated with 241Am a particles.When the detector is biased below v d the output signals are affected also by the non-active part of the detector itself, while, when the detector is operated above Vd , the output signals are only affected by trappingldetrapping of charge carriers. We found that trappingldetrapping is only relevant for the hole contribution to the signal. Trapping/detrapping effects are in agreement with the characteristics of deep levels present in the detectors as analyzed by means of PICTS (Photo Induced Current Transient Spectroscopy) and P-DLTS (Photo Deep Level Transient Spectroscopy).

Optical Beam Induced Current Investigations of Particle Detectors

“…Indeed, due to their very low free charge carrier concentration n 10 7 cm À3 , for many years Schottky diodes fabricated on SI GaAs were assumed to be fully depleted, even at zero bias voltage. The ohmic contacts have been realized on the whole back surface of the wafers by implanting Si ions [9]. It was also found that the depletion layer width W does not increase with the square root law valid for Schottky junctions on semiconducting materials, even if no identity of opinions on the functional relationship between W with biasing V a was reached for a long time.…”

Monte Carlo simulation of the induced signal in semi-insulating GaAs detectors

“…For the case of ␣ particles ͑5.48 MeV͒, the presence of plasma effects due to the high density of generated pairs (10 18 cm Ϫ3 ) ͑Ref. 9 On the basis of the above simulations, we provide a microscopic interpretation of measured charge signals. 8 This delay is not of primary interest in the present letter where we mostly focus on long-time-scale effects ͑above 10 ns͒.…”

Recent results on GaAs detectors

“…The improved ohmic contact was realised by annealing a multi-layer titaniumpalladium-germanium metal contact. Alenia SpA have fabricated diodes with an ion-implanted ohmic contact which allow a bias many times V f d to be applied [4].…”