SI-GaAs detectors with epitaxial junction

High leakage currents and incomplete charge collection limit the performance of detectors obtained from bulk semiinsulating (SI) GaAs. In this contest, a crucial role is played by the electron limiting contact. We have investigated the effect of an epitaxial p-type layer deposited on the semi-insulating substrate in place of the usual Schottky contact. Electrical characterization evidences an effect of the p-layer only at low voltages, but radiation detection experiments show an improvement of the charge collection efficiency, which is function of the doping level of the p-layer. In particular both alpha and chi irradiations give evidence of gain mechanisms in the collected charge. From these results, the strong relation between the structure of the electron-blocking interface and the charge collection properties of these detectors comes out.