Optical characterization of excess carrier lifetime and surface recombination in 4H/6H–SiC

The high-injection lifetime and surface recombination parameters have been investigated in as-grown 4H and 6H–SiC epilayers subjected to various process treatments. A depth-resolved optical transient absorption technique was utilized to evaluate the influence of film thickness and surface treatment on carrier lifetime. We demonstrate that besides polishing and ion implantation, both natural and thermal oxidation may also result in lifetime reduction due to enhanced surface losses. Moreover, a long-term stability test has revealed a substantial degradation of lifetime characteristics, consistent with a spontaneous surface oxidation and slow relaxation of SiO2/SiC interface states. We show that for common film thickness <100 μm, the effective lifetime is dominated by surface leakage, which is found, generally, to be higher in 4H compared to 6H–SiC.