GaAs devices with vertical and planar structures for optically activated high-voltage switching

A class of semi-insulating gallium arsenide diodes has been manifactured and tested, with a Schottky contact and a special ohmic contact on the back, which can be operated in reverse bias well above 5 V/mu m were leakage currents are in the 1-10 mu A range (for 3 mm diodes). Preliminary measurements show their feasibility as PhotoConductive Semiconductor Switches (PCSS). At fixed high-voltage bias, the current drawn by this device can be increased at least by two orders of magnitude, by illuminating the diode with low-intensity near-infrared light. The resulting change in resistance can be used in order to switch off (DC mode) the high voltage either in a series or a parallel load configuration. Measurements are reported for 3 mm diameter GaAs diodes, 0.2 mm thick, as for: current-voltage characteristics, current increase upon illumination with a 880 nm LED, linearity of photocurrent vs. illumination level. In addition to these diodes with vertical structure, special GaAs switches with a planar structure have been developed and tested at 670 nm with a focused laser diode beam; they are made of a 0.2 mm substrate and a series of two Schottky contacts facing each other on the same side of the substrate. The planar structures enable multiple independent switches on the same substrate, each one being able to withstand a voltage bias as high as 700 V with typical leakage currents below 20 nA, and in addition, they may provide a photocurrent/dark current gain as high as 10(6). Both types of devices can be activated either locally or remotely, e.g. with illumination via single or multiple optical fibers, thus providing a special type of PCSS for optically controlled high-voltage DC switching. We plan to use devices of this type in high-energy physics experiments, specifically, in order to control remotely the high-voltage bias of microstrip gas chambers.