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

Abstract

Abstract We have observed negative Hall coefficients [R H(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 R H(T) in NNH conduction. According to this model, R H(T) becomes positive when the Fermi level (E F) is higher than the Al acceptor level (E Al), that is, the Fermi–Dirac distribution function f(E Al) is greater than 0.5, whereas R H(T) becomes negative when E F is lower than E Al, 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 R H(T) becomes negative at low temperatures.