Raman Scattering and Carrier Diffusion Study in Heavily Codoped 6H-SiC Layers

Abstract

Thick 6H-SiC epilayers were grown using the fast sublimation method on low-offaxis substrates. They were co-doped with N and B impurities of 1019 cm-3 and (4·1016–5·1018) cm-3 concentration, respectively. The epilayers exhibited donor–acceptor pair (DAP) photoluminescence. The micro-Raman spectroscopic study exposed a compensated n-6H-SiC epilayer of common quality with some 3C-SiC inclusions. The compensation ratio of B through 200 m thick epilayer varied in 20-30% range. The free carrier diffusivity was studied by transient grating technique at high injection level. The determined ambipolar diffusion coefficient at RT was found to decrease from 1.15 cm2 /s to virtually 0 cm2 /s with boron concentration increasing by two orders.