Influence of contacts and substrate on semi-insulating GaAs detectors

It is commonly observed, that semi-insulating GaAs detectors show leakage current densities between 1 and several 100 nA/mm(2). Also the breakdown voltage of those surface barrier detectors varies between 100 and 270 V for 200 mu m thick devices. Moreover, the charge collection efficiency for alpha particles shows a strong correlation with the leakage current density of the detector. The presented measurements show, that the leakage current density is primarily determined by the substrate resistivity and not by the Schottky contact parameters.