Negative Hall Factor of Acceptor Impurity Hopping Conduction in p-Type 4H-SiC

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Experimental data obtained from temperature-dependent Hall-effect measurements on Al-doped p-type 4H-SiC samples, which exhibit an anomalous sign reversal of the Hall coefficient to negative at low temperatures, are analyzed on the basis of a previously proposed impurity hopping conduction model. According to the small-polaron theory for the nonadiabatic case, the activation energy E3 for the drift mobility of nearest-neighbor hopping is deduced, taking into account the temperature dependence of the preexponential factor. Existing models for the sign of the Hall coefficient are critically examined. It is shown that the anomalous sign reversal of the Hall coefficient can be well explained by assuming a hopping Hall factor in the form AH3=(kBT/J3)exp(KHE3/kBT) with a negative sign of J3.