Reappraisal of Conduction and Hall Effect Due to Impurity Hubbard Bands in Weakly Compensated n‐GaAs

Abstract

A Hubbard‐band model is used for analyzing the low‐temperature data of Hall‐effect measurements on weakly compensated n‐GaAs samples with donor concentrations ND less than 1016 cm−3. In the model, not only the bottom Hubbard band formed from the neutral donor states but also the top Hubbard band formed from the negatively charged donor states is taken into account. Nearest‐neighbor hopping (NNH) or Efros‐Shklovskii (ES) variable‐range hopping (VRH) is assumed for conduction in the bottom Hubbard band, depending on ND, while NNH is assumed for conduction in the top Hubbard band. For the sample with ND = 1.3 × 1015 cm−3, it is shown that the Hall mobility is dominated by NNH in the top Hubbard band in the temperature range of 4–15 K while it is dominated by NNH in the bottom Hubbard band below 3 K. For this sample, it is also shown that the absolute value of the Hall coefficient is dominated by the contribution from the top Hubbard band around its peak at 4.4 K. For the samples with ND in the range of 2.7–9 × 1015 cm−3, on the other hand, it is shown that there hardly exists the temperature range in which the conduction in the top Hubbard band dominates.