Anisotropic effective mass and scattering of electrons in mismatched heteroepitaxial films

Abstract

InP layers grown epitaxially on silicon substrates show a pronounced anisotropy of the transverse magnetoresistance. We use this effect to study the ensuing anisotropy of the effective mass and scattering mechanisms of electrons. We investigated samples with an electron concentration from 7×1016 to 9.6×1017 cm−3 at temperatures ranging from 4.2 to 30 K in magnetic fields of up to 15 T. The sample with the lowest electron concentration showed an anisotropic negative magnetoresistance which we attribute to weak localization. This allows the characteristic times for inelastic scattering (coherence time) and for spin–orbit interaction to be determined. For the InP layers on Si of higher electron concentration we measured for the first time Shubnikov-de Haas oscillations, showing again anisotropy of the effective mass and of the Dingle temperature. We quantitatively ascribe differences from the bulk values to biaxial mechanical strain, distorting the Fermi sphere of bulk material to an ellipsoid. We assume that the observed anisotropies are due to a preferential orientation of crystal defects as a result of differences in the thermal expansion coefficient of the InP film and the Si substrate.