Factors affecting minimum on-state resistance of SiC photoconductive semiconductor switch

Two photoconductive semiconductor switches(PCSSs) were fabricated using V-doped semi-insulating 6H-SiC transverse-cut wafer with different dark resistivities. A series of photoconductive experiments with different bias voltages and different triggering laser energies were done on the two samples. The experimental results indicate that, the sample with higher dark resistivity can endure much higher bias voltage, and the maximum bias voltage are elevated from 4.2 kV for the sample with lower dark resistivity to 32 kV for the sample with higher dark resistivity. However, the sample with higher dark resistivity has higher on-state resistance of k level, at least one order-of-magnitude higher than that of the sample with lower dark resistivity, less than 100 . Carrier mobilities and lifetimes were estimated by comparing laser waveforms and photo-current waveforms. In comparison with GaAs-PCSSs, the extremely low carriers lifetime and mobility are found to be the reasons for the high on-state resistance of SiC-PCSSs. Then an improved V:6H-SiC PCSS was fabricated and measured. The maximum working voltage is 10 kV, the photocurrent is 90 A, and the on-state performanceis elevated greatly.