PERFORMANCES OF SI GAAS DETECTORS FABRICATED WITH IMPLANTED OHMIC CONTACTS

The slow component of the output pulse of Semi-Insulating (SI) Gallium Arsenide (GaAs) particle detectors, which affects charge collection e fficiency (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 electr ic field all the way to the ohmic contact, making difficult to disting uish between the effect of the non-active part of the detector and tha t of trapping/detrapping. To do that, we have carefully analyzed the o utput signals of SI GaAs detectors, operated below and above V-d and i rradiated with Am-241 alpha particles. When the detector is biased bel ow V-d the output signals are affected also by the non-active part of the detector itself, while, when the detector is operated above V-d, t he output signals are only affected by trapying/detrapping of charge c arriers. We found that trapping/detrapping is only relevant for the ho le contribution to the signal. Trapping/detrapping effects are in agre ement with the characteristics of deep levels present in the detectors as analyzed by means of PICTS (Photo Induced Current Transient Spectr oscopy) and P-DLTS (Photo Deep Level Transient Spectroscopy).