Characterization of mid-bandgap defect states in 4H-SiC for optimization of SiC photoconductive semiconductor switches

A method of characterizing mid-bandgap defect states in high purity semi-insulating 4H-SiC through leakage current analysis for optimization of SiC photoconductive semiconductor switches, PCSS, is presented. The method utilizes two custom IV curve tracer systems to measure leakage currents through the material under various voltage/current conditions. The first system is used under low current conditions and is capable of measurements from 0 to 45 kV at currents ranging from 0 to 3 mA with pA resolution. While voltage/current measurements in the region > 0.1 mA are of primary interest for quantifying defect states near the conduction band, standard IV measurements become difficult due to excessive power dissipation in the PCSS. Hence, a second system operating in transient mode is used for currents higher than 0.1 mA. This system measures the transient discharge of a charged capacitor through the PCSS, allowing for high current measurements while subjecting the material to high power dissipation for only a short period of time (milliseconds). It is the goal to extract from the combined data of these two systems characteristics of the defect states (concentration, energy level).