Reduction in Al acceptor density by electron irradiation in Al-doped 4H-SiC

The influence of electron irradiation on the hole concentration in Al-doped 4H-SiC epilayers is investigated with free carrier concentration spectroscopy (FCCS) using the temperature dependent hole concentration p(T). By 4.6-MeV electron irradiation, p(T) is reduced over the whole temperature range. Using FCCS, the densities and energy levels of acceptors or hole traps are determined. In the unirradiated and irradiated samples, similar to200 meV and similar to370 meV acceptor levels or hole-trap levels are detected. By irradiation, only the density of Al acceptors whose energy level is similar to200 meV is reduced from 6.2x10(15) cm(-3) to 8.2x10(14) cm(-3). This indicates that the main reduction in p(T) by the electron irradiation resulted from the decrease of the Al acceptor density, not from the creation of defects.