Electrical and Optical Properties of Defects in N-Type 4h-Sic

Several n-type 4H-SiC samples grown by the physical vapor transport technique were studied using both thermal and optical admittance spectroscopy. The ionization energy ED for nitrogen donors in 4H-SiC was determined to be 0.053 eV and 0.10 eV below the conduction band. This agrees reasonably well with the values of 0.052 eV and 0.092 eV determined by IR absorption measurements. It is believed that EC-0.053 eV is the ionization energy of the nitrogen atom occupying the hexagonal site (h). The 0.10 eV activation energy has been attributed to the nitrogen atoms occupying the cubic sites(k).The optical admittance studies reveal five conductance peaks. One of these corresponds to the band-to-band transitions from which the bandgap of 3.41 eV was determined at 40K. The other four conductance peaks correspond to transitions from defect levels to the conduction band. These defects are located at EC-1.73 eV, EC-1.18 eV, EC-0.87 eV, and EC-0.72 eV.