Comparative Study of Compensated Wide Band Gap Photo Conductive Switch Material for Extrinsic Mode Operations

The material properties of semi insulating 6H-SiC and GaN have been analyzed in terms of their applications as a photoconductive switch at high bias conditions. Both the switches have similar button type geometry and have been analyzed for breakdown, photocurrent profile, rise and fall time. The laser power and duration for initiating conduction in both the PCSS were the same except for the wavelength, which was selected to provide sufficient energy for carrier generation in the switches. Analysis show that both GaN and SiC have good capability as a PCSS material in terms of such parameters as current conduction, hold-off and risetime, with Fe compensated GaN having a moderate advantage in terms of rise time and off-state hold-off properties. The presence of traps in both the compensated materials types plays a role in the switch performance. The trap parameters such as capture cross section, concentration limit the maximum voltage to which the PCSS can be pulse charged. In GaN, due to its high capture cross sections, the voltage is limited to a maximum of 41 kV while it is 38 kV for SiC. The rise and fall time for GaN is also better as compared to SiC. In the simulation studies, ohmic contact was assumed. In laboratory applications the conduction current magnitude at the charging and on-state of the PCSS are limited by the damage of the switch electrodes and bulk material. The higher thermal conductivity of SiC compared to GaN must also be considered at higher power operations.