Photoelectrical Parameters of a PVT Grown Bulk 15R-SiC Crystal at Different Stages of Growth

Abstract

The electronic quality of a Physical Vapour Transport (PVT) grown 15R-SiC crystal at different stages of growth was assessed by time-resolved optical pump-probe techniques. The measured differential transmittivity (DT) kinetics for the layers corresponding to the initial, middle and final stages of growth revealed clear differences in the decay of the DT signal, indicating a decreasing concentration of traps at the later stages of the crystal growth. The estimated trap concentration in the initial layer was NT ≈ 1019 cm-3, while it decreased down to less than 2×1018 cm-3 in the top layer. The injection dependence of the diffusion coefficient at room temperature confirmed the gradual decrease of NT in the layers corresponding to later stages of growth. Accordingly, the bipolar diffusion coefficient in the middle and the top layer was Da ≈ 2 cm2/s, while Da = 0.9 cm2/s was measured in the layer closest to the seed.