Simple physical model for the sign of the Hall coefficient in variable-range hopping conduction in heavily Al-doped p-type 4H-SiC

We observe negative Hall coefficients ( R H ( T )) in the variable-range hopping (VRH) conduction region for heavily Al-doped p-type 4H-SiC. We have proposed a simple physical model in which the difference between the density of hopping sites for holes and the density of hopping sites for electrons under a magnetic field determines the sign of R H ( T ), and explained the negative R H ( T ) in nearest-neighbor hopping (NNH) conduction. Based on our proposed model for NNH conduction, here we propose a model in which R H ( T ) becomes positive when the density of localized states ( g ( E )) around the Fermi level ( E F ) increases with increasing energy ( E ), whereas R H ( T ) becomes negative when g ( E ) around E F decreases with increasing E . In heavily Al-doped p-type 4H-SiC where g ( E ) around E F is considered to decrease with increasing E , the proposed model can explain why R H ( T ) becomes negative in the VRH conduction region.