Application of excite-probe techniques for determination of surface, bulk and nonlinear recombination rates in cubic SiC

Non-equilibrium carrier dynamics was studied in a free-standing 160 μm thick 3C-SiC wafer using time-resolved differential transmittivity (DT), differential reflectivity (DR), and light induced transient grating (LITG) techniques. To enable investigation of carrier recombination and diffusion features in the middle part of the wafer, a wedge-shaped strip was prepared by polishing out the most-defective part of the wafer on the substrate side. Measurements of DT and DR decay kinetics on both sides of the wedged sample and their numerical fitting provided bulk lifetimes of 180 ns in the middle part and 60 ns in the edge part (∼50 μm thick subsurface region). On the as-grown side, the surface recombination velocity was equal to 3 × 103 cm/s. Carrier diffusivity, determined by LITG technique, and recombination rate were found injection-dependent. The low-injection value of diffusion length, LD = 8 μm, was found the longest in the middle part of the wafer, while at high injections it decreased to 1 μm due to an impact of Auger recombination with a coefficient, C = (4 ± 1) × 10−32 cm6/s. The 2.7 times lower diffusion length value in the edge part was explained by an impact of point defects to the carrier lifetime and diffusivity.