Influence of carrier freeze-out on SiC Schottky junction admittance

Incomplete impurity ionization is investigated in the case of nitrogen dono rs and aluminum and boron accepters in 4H and 6H SiC. We calculate the degr ee of ionization for these impurities residing on different lattice sites i n a broad temperature range and for different impurity concentrations. It i s shown that the degree of carrier freeze-out is significant in heavily N-d oped 6H SiC and in Al- and B-doped SiC. Using the general Schottky junction admittance model we calculate the temperature and frequency dependencies o f the junction admittance in the case when impurity ionization by the appli ed ac bias is present. It is shown that admittance frequency dispersion may be significant at room temperature in the case of N- and B-doped SiC. Fina lly, we calculate the Schottky junction capacitance as a function of the ap plied de bias and simulate the doping profile, using the capacitance-voltag e data. The calculated profile is shown to deviate from the actual impurity concentration profile if the impurity ionization time constant is comparab le with the ac bias period, which is so for Nand B-doped SiC with certain v alues of the impurity activation energy and capture cross-section.