On Photoelectrical Properties of 6H-SiC Bulk Crystals PVT-Grown on 6H- and 4H-SiC Substrates

Abstract

Free carrier lifetimes and diffusion coefficients were determined in 6H-SiC bulk crystals grown by PVT on 6H-and 4H-SiC seeds varying the temperature from 300 K to 650 K and at excess carrier densities ΔN0 from 1017 cm-3 to 1019 cm-3. Carrier generation was achieved by using a single or two-photon absorption of picosecond pulses at 351 and 532 nm, respectively. Fast and slow recombination transients revealed the decay time of free carriers and the presence of deep acceptor traps. The thermal trap activation energy Ea = 0.33 eV was determined in the 6H/4H sample and ascribed to the boron, while the presence of deeper traps is suggested in the 6H/6H sample. At room temperature and reaching conditions of trap saturation regime (ΔN0 1019 cm3), both crystals revealed the bipolar diffusion coefficient Da 4 cm2/s. For comparison, we also determined the photoelectrical parameters in commercial 6H-SiC crystals grown by the Lely and PVT techniques.