16 kV, 75 kHz, 50% Duty Cycle, SiC Photonic Based Bulk Conduction Power Switch Development

A transconductance-like behavior similar to that of junction semiconductor devices is observed in photonically excited wide bandgap (WBG) semi-insulating material without a junction. This property offers the possibility of power electronic devices capable of virtually unlimited voltage and current carrying capability due to intrinsic electrical isolation of the controlling voltage from the switched high voltage. A proof of concept experiment demonstrated the transconductance-like property in burst mode switching to >16 kV, 50% duty cycle, and 75 kHz. Our eventual goal is to combine the light source, optics and the WBG material to form a compact module that is functionally equivalent to junction power electronic devices. In this paper, we present the background, our generalized approach for implementing photoconductive switching for potential applications to high repetition rate (>50 kHz), high voltage (>15 kV) power switching, our associated material measurements, and our path forward to multi-10s of ampere devices.

High Voltage Wide Bandgap Photoconductive Switching

High gain photoconductive switching using Si and GaAs was studied previously for pulsed high voltage switching. A laser is used to generate charge carriers within the material to render the bulk conductive. We have begun the study of photoconductive switching using wide bandgap materials. These materials appear to operate in a non-high gain mode and the on resistance can be directly controlled with the laser intensity over many decades. It is presently believed that the conduction mechanism may be due to (a) excitation of deep states or (b) multi-photon pumping of carriers from the valance band. We present the study of the physics processes and development of a device operating at >20-kV.