Impurity Conduction At Low Compensation Levels In Zn-Doped Inp

We report on the impurity-conduction measurements, in the strong-localization regime, for p-type Zn-doped InP epilayers with low compensation levels. Both Hall-transport and magnetoresistance measurements were carried out. Variable-range hopping was present in all samples below 5 K, where Mott's full expression for the conductivity was found to give an excellent description of the data, with consistency between the theoretical predictions for the activation energies and the corresponding experimental values. Above 5 K, nearest-neighbor hopping was observed in all samples and was found to be consistent with a model by Efros and Shklovskii, provided that the effects of an enhancement of the dielectric constant at high doping levels were included. An unusual saturation of the low-temperature conductivity was observed in the purest epilayers. For layers with a low level of compensation, such an effect has been predicted by Shklovskii and Yanchev. However, their theory could only provide a qualitative explanation of our results.