Investigation on the photocurrent tailof vanadium-compensated 4H–SiC for microwave application

Vanadium-compensated semi-insulating 4H–SiC photoconductive semiconductor switch (PCSS) has been a promising candidate for frequency-agile microwave generation. This application usually requires the PCSS to operate in linear mode so that a short carrier lifetime is required. However, in our experiment, some samples showed a long tail of photocurrent when illuminated with 532 nm light. To investigate the cause of the tail, we performed photocurrent tests at 532 and 1064 nm for two 4H–SiC samples with different doping. From the experimental results, we deduce that the cause is a hole trap that was not investigated previously. To verify it, we constructed a versatile transient simulation model of 4H–SiC triggered at sub-bandgap light. The model can deal with amphoteric V in steady state, the extrinsic light absorption and recombination process with more than one trap level. The simulation results agree well with the experiments. By characterizing the properties of the trap, we deduce that the unintentional doping of aluminum’s shallow acceptor level functions as the hole trap.