A defect relaxation model for the carbon vacancy in SiC

Deep level intrinsic defects in high purity semi-insulating SiC play in important role in electrical compensation necessary to achieve high resistivity. We use a constant light intensity approach to steady-state photo-electron paramagnetic resonance (EPR) and time-dependent photo-EPR to study the ionization cross sections and relaxation energies of the well-studied defect, the positively charged carbon vacancy, V$_{c}^{+}$. As-grown 4H-SiC samples with room temperature resistivity of 10$^{10}$ Ohm-cm were studied at 4 K and 80 K. The shape of the absorption curve for V$_{c}^{+}$, as revealed by the steady state measurements, has a peak at 2.3 eV and photo-threshold at 1.8 eV. We interpret the difference between these two values as a structural relaxation upon release of an electron from the defect to conduction band. Consistently, preliminary time-dependent measurements reveal a Franck-Condon transition at 2.3 eV for release of an electron from the defect to the conduction band, and a second Franck-Condon transition at an energy greater than 1.3 eV for capture of electron at the defect from the valence band. The difference of no more than 1 eV may be interpreted as a relaxation energy, consistent with the interpretation of steady-state data. The details of the experimental approach and the formulation of the relaxation model will be presented.