Ultrafast bulk carrier recombination transients in n-type and semi-insulating 4H-SiC crystals

Carrier recombination influences the performance of SiC-based optoelectronic devices, and carrier recombination via traps is one of the limiting factors of carrier lifetime. In this work, we utilized transient absorption spectroscopy with near-homogeneous carrier distribution to evaluate ultrafast bulk carrier recombination in conductive (n-type) nitrogen-doped and semi-insulating (SI) vanadium-doped 4H-SiC wafers. Compared to n-type 4H-SiC, a pronounced modulation of transient absorption was observed in SI 4H-SiC, resulting from an additional decay process subsequent to intraband recombination (2-3 ps) caused by carrier trapping of V^3+/4+ deep acceptors. The carrier-trapping lifetime (∼16 ps) was three orders of magnitude faster than that via N-doping and/or inherent defects. With a simplified model and global analysis, the carrier recombination mechanisms and lifetimes in 4H-SiC were determined unambiguously.