Spectral Characterization of Persistent Photo Conductance in SiC

Abstract

The transient photo response of 4H-and 6H-SiC specimens at various wavelengths has been studied using Optical Admittance Spectroscopy. Differences in the transient response were found for excitation and recombination for different specimens in both polytypes. The results indicate that optical excitation of charge carriers to the conduction band is a single transition, but recombination of free carriers from the conduction band is a process that may involve multiple transitions to the ground state mediated by deep centers in the material. Similarities in the persistent photo conductance after excitation from deep centers, and after excitation at above bandgap energies, suggest that carriers from the conduction band can drop through deep centers on the way to the valence band. Annealing studies also indicate that stoichiometry can play a significant role in the PPC effect.