Negative magnetoresistance of compensatedn-type GaAs at 77° K temperature

Abstract

The magnetoresistance of strongly compensatedn-type GaAs doped with Cr and O has been measured at 77°K temperature. The electron concentrations of the samples were between 3.8×1017 and 1.6×1018 cm−3 at room temperature. In low magnetic fields negative magnetoresistance was observed at liquid nitrogen temperature. The characteristics of this anomalous negative magnetoresistance were shown to be very similar to those observed at liquid He temperatures in heavily doped semiconductors. In weak fields the negative magnetoresistance was proportional to the square of the magnetic field, and showed saturation in the magnetic field range of 4000–6000 G. To account for the observed effects it was postulated that metal-like impurity band conduction is the dominant mechanism of the charge carrier transport in our samples. The observed features of the negative magnetoresistance are shown to be consistent with the model of scattering of electrons in the impurity band by localized magnetic moments. For the average value of the localized magnetic moments a value of the order of 2–3 Bohr magneton was deduced from the experimental data. It is shown that the strong compensation may play an important role in the formation of impurity band at 77°K temperature and above it.