Sign of Hall coefficient in nearest-neighbor hopping conduction in heavily Al-doped p-type 4H-SiC

Abstract

We have observed negative Hall coefficients [RH(T)] in a nearest-neighbor hopping (NNH) conduction region in epilayers of heavily Al-doped or Al–N co-doped p-type 4H-SiC grown on n-type 4H-SiC substrates by CVD or in wafers of heavily Al–N co-doped p-type 4H-SiC fabricated by solution growth. We propose a simple physical model to explain the sign of RH(T) in NNH conduction. According to this model, RH(T) becomes positive when the Fermi level (EF) is higher than the Al acceptor level (EAl), that is, the Fermi–Dirac distribution function f(EAl) is greater than 0.5, whereas RH(T) becomes negative when EF is lower than EAl, which occurs at low temperatures. Because the dominant conduction mechanisms in heavily Al-doped or Al–N co-doped p-type 4H-SiC with Al concentrations on the order of 1019 cm−3 are band and NNH conduction at high and low temperatures, respectively, the proposed model can explain why RH(T) becomes negative at low temperatures.