Characterization of intra-bandgap defect states through leakage current analysis for optimization of 4H-SiC photoconductive 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 switches 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. A second system measures the transient discharge of a charged capacitor bank through the material. Due to power dissipation concerns, the second system is used for currents higher than 0.1 mA. Voltage/current measurements in this region (>0.1 mA) are of interest due to the information concerning defect states near the conduction band. These shallow defect states are detrimental to switching performance while offering little benefit to voltage hold-off. From the combined data of these two systems, characteristics of the defect states are extracted and presented. We further elucidate the effect of contact annealing temperature on shallow trap levels in electron-beam irradiated material (2*10¹⁸ 1/cm²).