Nondestructive Evaluation of Photoelectrical Properties of a PVT Grown Bulk 15R-SiC Crystal

Abstract

Investigation of excess carrier dynamics in a 15R-SiC bulk layer grown by physical vapour transport (PVT) on 15R-SiC substrate has been carried out using pump-probe techniques: an interband carrier injection by a picosecond laser pulse and measuring the induced absorption and diffraction of a probe beam. For this task, differential transmittivity (DT) and light induced transient grating (LITG) techniques were used. Room temperature carrier lifetime varied in the 3 ns 8 ns range at excess carrier densities above ΔN0= 7×1017cm-3and was ascribed to the recovery time of optically recharged carrier traps, and their activation energy ofEa= 75 meV was determined. The presence of recharged traps caused the injection-dependence of the diffusion coefficientD, whereby its value dropped below 0.1 cm2/s at ΔN0< 1×1018cm-3and gradually increased up to 0.7 cm2/s at higher injections. At elevated temperatures (300 K < T < 700 K), when the traps are thermally activated, the diffusivity increased up to ~ 1.5 cm2/s and was independent on ΔN0. The overgrown layer parameters were comparable to those of the used 15R PVT seed.