Compensation of p-type doping in Al-doped 4H-SiC

One of the major challenges of 4H-silicon carbide (4H-SiC) is that the preparation of low resistivity p-type 4H-SiC single crystals lags seriously behind that of low resistivity n-type 4H-SiC single crystals, hindering the development of important 4H-SiC power devices such as n-channel insulated gate bipolar transistors. In particular, the resistivity of p-type 4H-SiC single crystals prepared through the physical vapor transport technique can only be lowered to around 100 m Omega cm. One of the key causes is the incomplete ionization of the p-type dopant Al with an ionization energy similar to 0.23 eV. Another factor is the compensating effect. It cannot simply assume nitrogen (N) is the sole compensatory center, since the number of the compensating center is larger than the concentration of N doping. In this work, we systematically investigate the compensation of native defects and self-compensation in Al-doped 4H-SiC. It is found that the positively charged carbon vacancies ( V-C(2+)) are also the dominant compensating centers in Al-doped 4H-SiC. When the Al concentration is in the range of 10(16)-10(19) cm(-3), the concentration of holes is lower by one order of magnitude than the Al concentration because of the compensation of V-C(2+). As the Al concentration exceeds 10(20) cm(-3), the concentration of holes is only in the order of magnitude of 10(19) cm(-3) owing to the dominant compensation of V-C(2+) and supplementary self-compensation of interstitial Al ( Al-i(3+)). We propose that the passivation of V-C(2+) as well as quenching is effective to enhance the hole concentration of Al-doped 4H-SiC.