Sign of Hall coefficient in nearest-neighbor hopping conduction in heavily Al-doped p-type 4H-SiC
Hideharu Matsuura, Akinobu Takeshita, Atsuki Hidaka, Shiyang Ji, Kazuma Eto, Takeshi Mitani, Kazutoshi Kojima, Tomohisa Kato, Sadafumi Yoshida, Hajime Okumura
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 10 19 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.