Anisotropic effective mass and scattering of electrons in mismatched heteroepitaxial films

InP layers grown epitaxially on silicon substrates show a pronounced anisot ropy of the transverse magnetoresistance. We use this effect to study the e nsuing anisotropy of the effective mass and scattering mechanisms of electr ons. We investigated samples with an electron concentration from 7 x 10(16) to 9.6 x 10(17) cm(-3) at temperatures ranging from 4.2 to 30 K in magneti c fields of up to 15 T. The sample with the lowest electron concentration s howed 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 effec tive mass and of the Dingle temperature. We quantitatively ascribe differen ces from the bulk values to biaxial mechanical strain, distorting the Fermi sphere of bulk material to an ellipsoid. We assume that the observed aniso tropies are due to a preferential orientation of crystal defects as a resul t of differences in the thermal expansion coefficient of the InP film and t he Si substrate. (C) 1999 American Institute of Physics. [S0021-8979(99)068 07-3].