Analysis of the influence of defect evolution on the performance and damage of 4H-SiC photoconductive semiconductor switches

This study investigated the failure mechanism of a series-connected structured photoconductive semiconductor switches (PCSSs) made of vanadium-doped 4H-SiC. For a long time, SiC PCSSs have face reliability issues in high-voltage and high-repetition-frequency environments. Degradation and breakdown mechanisms were analyzed using a combination of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and current deep-level transient spectroscopy (I-DLTS). The vertical 4H-SiC PCSS in the series-connected structure failed after 9686 triggering pulses with a 532 nm Q-switched Nd: YAG laser with a DC voltage bias of 35 kV. The SEM and EDS showed a through-ablation channel through the substrate and connecting the electrodes, and a large amount of carbon accumulation was found inside the through-ablation channel. The I-DLTS test found that deep-level defects changed, in particular, defects associated with carbon vacancies Z1/2 and a newly formed defect DT2 near 410 K, indicating that high-speed electron collisions and defect accumulation can lead to lattice reorganization. This work highlights the effect of defects on device performance and the role of defect dynamics in impact ionization detrapping in device failure. It provides insights into improving PCSS performance in high-voltage applications. The link between defect behavior and device lifetime is also further investigated.