Electrical Properties of Heavily Al-Doped 4H-SiC

We investigate the temperature-dependent resistivity ( ρ ( T )) and Hall coefficient ( R H ( T )) of heavily Al-doped 4H-SiC and discuss the underlying conduction mechanisms. The sign of R H ( T ) changes from positive to negative in nearest-neighbor hopping (NNH) and variable-range hopping (VRH) conduction, whereas it is positive in band conduction because Al-doped 4H-SiC is a p-type semiconductor. We propose a general physical model to explain why R H ( T ) in hopping conduction becomes negative at low temperatures, which is applicable to both NNH and VRH conduction. Moreover, we elucidate why the activation energy for negative R H ( T ) becomes similar to that of ρ (T) in NNH conduction.