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 proce ss 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 implanta tion, both natural and thermal oxidation may also result in lifetime reduct ion due to enhanced surface losses. Moreover, a long-term stability test ha s revealed a substantial degradation of lifetime characteristics, consisten t with a spontaneous surface oxidation and slow relaxation of SiO2/SiC inte rface states. We show that for common film thickness < 100 mum, the effecti ve lifetime is dominated by surface leakage, which is found, generally, to be higher in 4H compared to 6H-SiC. (C) 2001 American Institute of Physics.