Carrier Removal in Electron Irradiated 4H and 6H SiC

A strong reduction of the free carrier concentration has been observed in both 4H and 6H n-type SiC as a result of MeV-electron irradiation. Samples irradiated with a sufficiently high dose experience complete compensation of carriers. Irradiation with even higher doses reveals the same result, i.e. no conversion to p-type which occurs in silicon irradiated with high doses has been found. The dose required for complete loss of carrier response is higher for 6H than 4H material. Furthermore, the free carrier concentration depends on both measurement temperature and frequency and recovers after annealing. The results strongly suggest that deep acceptor levels in the upper half of the band gap are the main cause for the removal of free carriers rather than deactivation of the nitrogen donors as found in ion-irradiated samples, which is in agreement with previous findings on proton-irradiated 4H- and 6H-SiC[8]. © (2009) Trans Tech Publications, Switzerland.