Measurements of optical cross sections of the carbon vacancy in 4H-SiC by time-dependent photoelectron paramagnetic resonance

Abstract

Time-dependent photoinduced electron paramagnetic resonance measurements have been made on high purity semi-insulating 4H-SiC to develop a more complete understanding of the optical transitions of the positively charged carbon vacancy VC+. The single defect model originally proposed is given validity by demonstrating that the time dependence of the photoinduced changes in VC+ may be fitted by a first order kinetic process. In addition, the photon energy dependence of the optical cross sections for capture and emission of electrons from VC+ is extracted by incorporating both processes into one expression for charge transfer. The data are interpreted by considering the role of the electronic density of states as well as participation of phonons. Analysis assuming only phonon participation yields thermal and optical energies of 1.6 and 2.15 eV, respectively, for charge transitions between VC+ and one of the band edges. Charge transfer between VC+ and the opposite band edge is associated with a thermal and an optical energy of 1.9 and 2.45 eV, respectively. An upper limit for the Franck–Condon shift of 0.55 eV is extracted from the difference between the thermal and optical energies.