Contact Effects in Light Activated GaAs Switches.

The purpose of this work was to examine the effects of various tyes of contacts on the switching behavior of a light-triggered power switch. The switch was constructed from a homogeneous wafer of chromium-doped gallium arsenide the contacts were either ohmic, non-ohmic, or Schottky barriers. These were formed on the wafer in two geometries both contacts on one side, and one contact spacings were used to permit the effects of the location of the existing laser pulse to be studied. A high voltage power supply zero to 20 kV was employed as the bias supply. A NdYAG laser, in the pulsed mode, was used to trigger the switch, which was mounted on a cold finger cooled to near liquid nitrogen temperature. Cooling reduced the dark current to manageable values less than 1 micro A, and also reduced the avalanche breakdown voltage. The results of the measurements indicate that ohmic contacts produced more reliable switching than the non-ohmic or Schottky contacts, inasmuch as the shape of the output current pulse was better, and the number of pulses which the switches could sustain before the pulse shape deteriorated was greater, for the ohmic contacts. Surface discharge between the one-sided contacts obscured any differences in switching characteristics which might have depended on the location of the pulsed light excitation, so that no correlation between position and behavior could be obtained.