Impurities in 4H and 6H SiC crystals, characterized by thermoluminescence and thermally stimulated conductivity

Thermoluminescence (TL) and thermally stimulated conductivity (TSC) of 4H and 6H SiC crystals were measured and discussed in the framework of very simple models (consisting of one species of trap and recombination center), to determine the ionization energies of involved impurities. Comparing the obtained values with ionization energies of the ground doping (Hall effect) shows that either the ground doping or the compensation (if more shallow) is the thermally emptied trap. Additionally we studied the thermoluminescence as a function of the excitation wavelength to obtain the energy for charge transfer at the impurity. An excitation energy between 1.65 and 1.9 eV is necessary to recharge the impurity in n-type and p-type 6H SiC crystals. The spectra of thermoluminescence are compared with spectra of stationary photoluminescence at different temperatures.