We have measured the dc electrical resistance of partially compensated (5–50 %) ion-implanted Si:P,B (both n and p type), over the temperature range 0.05–30 K. The temperature behavior is consistent with the prediction of the model for variable-range hopping (VRH) with a Coulomb gap ρ(T)=${\mathrm{\rho }}_0$exp(${\mathit{T}}_0$/T${)}^{1/2}$ over a temperature range 6.5<${\mathit{T}}_0$/T<24. We observe deviations from this behavior at our high- and low-temperature extremes. In the low-temperature region, the resistivities show a stronger temperature dependence than the Coulomb-gap model prediction. The high-temperature deviation appears consistent with a transition from Coulomb-gap VRH to Mott VRH.

• Received 17 March 1993

DOI:https://doi.org/10.1103/PhysRevB.48.2312