Magnetoresistance in low-temperature grown molecular-beam epitaxial GaAs

Abstract

Conductivity, Hall effect as well as “physical” and “geometrical” magnetoresistances were measured at 290–440 K in molecular-beam epitaxial GaAs layers grown at 200–400 °C. The experimental data were analyzed taking into account the combined band and hopping conductance regime. Positive hopping magnetoresistance parameters (Δρ/ρ0B2)h≈10−4 T−2 and hopping Hall mobilities lower than 1×10−4 m2 V−1 s−1 were determined in the as-grown layers. A transverse-to-longitudinal hopping magnetoresistance ratio of about 2, consistent with hopping transport theories, was obtained. In the annealed layer grown at 200 °C (J200a) the band mobility determined from the geometrical magnetoresitance (GMR) mobility was found to be significantly higher than the band Hall mobility. It is related to a mixed band conductivity regime with the hole concentration p exceeding the electron one n. The difference between GMR and Hall mobilities decreases with increasing growth temperature as far as a typical single-carrier band conductivity regime (n>p) is present in the layer grown at 400 °C. In contradiction to the layers grown at higher temperatures, the J200a layer showed the opposite (positive) sign of the hopping Hall coefficient as well as the largest hopping magnetoresistance parameter (≈3×10−2 T−2).