Low-temperature transition from band conduction to nearest-neighbor hopping conduction in heavily Al-doped 4H-SiC epilayers

Abstract Holes that are thermally excited from Al acceptors into the valence band contribute to band conduction, while an equal number of charge carriers participate in nearest-neighbor hopping (NNH) between Al acceptor sites. Because the mobility associated with NNH conduction is much lower than that of band conduction, the resistivity for NNH conduction, ρNNH(T), is expected to be significantly higher and therefore unobservable. Nevertheless, we have observed ρNNH(T) experimentally at low temperatures in heavily Al-doped 4H-SiC. This behavior can be explained by assuming the presence of localized states between the acceptor level and the valence band maximum.