Inhomogeneity of Minority Carrier Lifetime in 4H-SiC Substrates

The minority carrier lifetimes in lightly N-doped n-type and V-doped semi-insulating 4H-SiC crystals were measured by microwave photo-conductance decay method. The resistivity mapping of the n-type 4H-SiC wafer lightly doped with nitrogen was examined by contactless resistivity measurement system to reveal the relationship between minority carrier lifetime and resistivity. Combining with the Raman spectroscopy and theoretical analysis of the nonequilibrium carrier recombination mechanism, it was found that the inhomogeneity of minority carrier lifetime in n-type 4H-SiC wafer was caused by inhomogeneous distribution of nitrogen concentration and the minority carrier lifetime was inversely proportional to the majority carrier concentration. It was also found that the minority carrier lifetime of V-doped semi-insulating 4H-SiC crystal was lower by one order of magnitude than that of N-doped n-type wafer. Second ion mass spectroscopy was used to examine the impurity concentration in different regions of V-doped semi-insulating 4H-SiC. It confirmed that the inhomogeneity of minority carrier lifetime originated from the inhomogeneous distribution of electrically active impurity concentration.