Non-Equilibrium Carrier Diffusion and Recombination in Semi-Insulating PVT Grown Bulk 6H-SiC Crystals

Abstract

We applied a non-degenerate four wave mixing (FWM) technique to investigate carrier generation, diffusion and recombination processes in PVT-grown semi-insulating wafers of 6H-SiC at 300 K. The resistivity of samples, cut from different places of a boule as well as from different boules, varied in range from a few ⋅cm up to 1010 ⋅cm. Interband excitation (at 355 nm) and below bandgap excitation (at 532 nm) allowed to study dynamics of the bipolar plasma and the contribution of deep levels to carrier generation and recombination. The nonequilibrium carrier lifetime was shorter in the samples of higher resistivity, in accordance with the increasing density of deep levels. The bipolar plasma diffusion in high-resistivity samples (~109 ⋅cm) provided the value of the diffusion coefficient D = 4.4 cm2/s and hole mobility μh = (88 ± 6) cm2/Vs.