Effects of Field-Dependent Trapping and Detrapping on the Responses of Compensated GaAs Photoconductive Switches

In this paper, the response of a semi-insulating gallium arsenide photoconductive switch used in high-power microwave generation has been analyzed through experiment and simulation. The switch characteristics as a result of trapping and detrapping phenomena during a transient are studied. Analysis show that field-enhanced capture at high field locations during the onstate creates a temporary reservoir of trapped charge at different pockets in the device. Release of trapped charge and the subsequent injection of carriers from the contacts to maintain charge neutrality helps maintain conduction, which persists even after the laser pulse until all charges are transferred across the device. A model has been presented which can explain such phenomena as lock-on effect, persistent conductivity, and low-power requirement during transients. This phenomenon is unique to semi-insulating gallium arsenide and is primarily due to field-enhanced trapping and could be applicable to other materials that have similar characteristics