Paramagnetic Centers and Dopant Excitation in Crystalline Silicon Carbide

Impurities, point defects, and dopant excitation in SiC have been examined by electron paramagnetic resonance (EPR). The pervasive nitrogen n-type dopant was found to show a substantial photo-enhancement, not due to generation of carrier pairs. Aluminum in Al-doped SiC showed a strong EPR signal below 4 K, which disappeared as the sample was warmed to 10 K, because of the onset of impurity band conduction. The Al EPR signal intensity depends on the degree of compensation. Boron EPR appeared in samples where excess Al counteracts the compensation of B ions by N dopant. Hydrogen plasma anneal at 250 °C partially passivated Al; however, extended heating in vacuum, expected to depassivate, actually further decreased the Al signal. Abrasion damage produced a featureless, isotropic signal suggestive of the bulk damage signal in Si, indicating dangling C or Si orbitals. An oxide interface signal, in analogy to P_b of oxidized Si, was not isolated; the observed signal included a damage-like line.