Impurity conduction and minimum metallic conductivity in n-type InP subjected to a magnetic field

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Abstract
Low-temperature conduction has been studied for two n-type InP crystals with impurity concentrations of 6·6 × 1015 cm−3 and 1·2 × 1016 cm−-3. The electrical resistivity and Hall coefficient were measured from 100 K down to liquid-helium temperatures and in magnetic fields up to 7·5 T. According to the Mott eriterion, these samples are located on the insulating side of the metal–nonmetal (MNM) transition. The different conduction processes with activation energies (ϵ1, ϵ2, ϵ3) were observed for each sample when the magnetic field and temperature were varied. The variations of activation energies ϵ1 and ϵ2 with magnetic field are found to be very similar; they are described satisfactorily by the hydrogenic model of Fenton and Haering (1967), taking account of the strong effect of screening of the impurity potential. Attention is drawn to the minimum metallic conductivity which appears for each sample, and excellent agreement is found between experiment and the values of the minimum metallic conductivity deduced from the Mott analysis.