Study on Photoelectric Efficiency and Failure Mechanism of High Purity 4H-SiC PCSS

The article focuses on photoelectric efficiency ( ${E}_{\text {pe}}$ ) and failure mechanism of vertical high purity semi-insulating (HPSI) 4H-SiC photoconductive semiconductor switches (vPCSSs) at high voltage and low optical energy. The effects of ${E}_{\text {pe}}$ on illumination strategies and storage capacitances are investigated in pulse forming line (PFL) storage circuits and capacitor storage circuits, respectively. A 532-nm laser with 90- $\mu \text{J}$ energy and a 500-ps pulsewidth is applied. In the PFL storage circuit, the ${E}_{\text {pe}}$ of side-illuminated vPCSS (vPCSS2) is at least 20 times higher than that of top-illuminated vPCSS (vPCSS1). In the capacitor storage circuit, the ${E}_{\text {pe}}$ of vPCSS2 increases and then begins to saturate with the increase of the storage capacitor. The critical storage capacitor is 250 pF. In the 500-pF capacitor storage circuit, the peak output voltage and output power of vPCSS2 at 11 kV are up to 5.2 kV and 540 kW, respectively. The power gain is 4.77 dB. The different illumination strategies result in diverse failure mechanisms. The hold-off voltage of vPCSS1 is higher than that of vPCSS2. A greater cause for vPCSS1 failure is a high local field of about 1.2 MV/cm at 18 kV. Due to a longer optical length and a field increase at the electrode edge, the vPCSS2 breakdown is caused by a high current density at the left electrode edge. A 2-D device simulation shows the maximum current density of vPCSS2 about 7000 A/cm2 at 11 kV.