Shallow and deep levels in n-type 4H-SiC

Abstract

The nitrogen levels in 4H‐SiC have been determined using thermal admittance spectroscopy. The values of E_c−0.053 eV for nitrogen at the hexagonal site and E_c−0.10 eV for nitrogen at the quasicubic site agree with those reported using other techniques. The deep levels in 4H‐SiC were studied using optical admittance spectroscopy. The optical admittance spectrum showed, besides the conductance peak corresponding to band to band transitions, four other conductance peaks. These peaks correspond to photoexcitation of carriers from the defect levels to the conduction band. It is inferred from a comparison with 6H‐SiC that the conductance peak b4 is due to excitation of electrons from the vanadium donor at E_c−1.73 eV. The photoconductance build up transients of the E_c−1.73 eV level are described fully by one exponential term. This suggests that only one center contributed to the observed conductance. The decay kinetics of persistent photoconductance due to the E_c−1.73 eV level follow the stretched exponential form. The potential barrier against recapture of photoexcited carriers was determined to be 18 meV for the vanadium donor level in 4H‐SiC.