Irradiation of optically activated SI-GaAs high-voltage switches with low and high energy protons

Semi-Insulating Gallium Arsenide (SI-GaAs) devices have been tested for radiation hardness with 3--4 MeV or 24 GeV proton beams. These devices can be operated in dc mode as optically activated electrical switches up to 1 kV. Both single switches (vertical Schottky diodes) and multiple (8) switches (planar devices) have been studied, by analyzing their current-voltage (I-V) reverse characteristics in the dark and under red light illumination, both before and after irradiation. The authors propose to use them in the system of high-voltage (-600 V) switches for the microstrip gas chambers for the CMS experiment at CERN. Low energy protons (3--4 MeV) were used in order to produce a surface damage below the Schottky contact; their fluence (up to 2.6 x 1015 p/cm2) gives a high-dose irradiation. The high energy proton irradiation (energy: 24 GeV, fluence: 1.1 x 1014 p/cm2) reproduced a ten years long proton exposure of the devices in CMS experiment conditions. For low energy irradiation, limited changes of the I-V curves in the dark have been observed, with at most a fourfold increase of the leakage current; after exposure, however, the breakdown voltage decreases significantly. For high energy irradiation, the authors observed--for the vertical Schottky diodes biased at -600 V--an increase of the leakage current and a reduction of the photocurrent after irradiation, with respect to pre-irradiation conditions. For these diodes, the reduction of the photocurrent/dark current ratio was 25:1. At the same proton energy, an analogous behavior was shown by the planar devices, but after irradiation the current gain may reduce over three orders of magnitude