Photosensitive electron paramagnetic resonance spectra in semi-insulating4HSiC crystals

Abstract

Photosensitive electron paramagnetic resonance (EPR) investigations of unintentionally doped, semi-insulating (s.i.) 4H–SiC have been made at 37 GHz and 77 K including photoexcitation and photoquenching experiments. In the dark the EPR spectrum consists of a low intensity line due to boron on the cubic lattice site and an EPR line with isotropic g factor $g_{\parallel }{=g}_{\perp }=\mathrm{2.0025.}\mathrm{}$ During illumination with ultraviolet light the EPR lines due to boron on the hexagonal site and nitrogen on the cubic site appear and persist after the illumination is removed, showing very small recombination rates of photocreated electrons and holes at $T=77\mathrm{}\mathrm{K}.$ During and after illumination with sub-band gap, visible light an additional, previously unreported, line, $I_p,$ appears with $g_{\parallel }=2.0048\mathrm{}$ and $g_{\perp }=\mathrm{2.0030.}\mathrm{}$ Studies of the spectral dependencies of the photoquenching process in 4H–SiC after excitation with above band gap light suggest that the $I_P$ line is due to the as yet unidentified deep level located at $E_C-1.1\mathrm{eV},$ which pins the Fermi level in this sample. A model for trapping and recombination in semi-insulating 4H–SiC without detectable concentrations of vanadium is presented.