We report on experiments in which a spin-polarized current is injected from a GaMnAs ferromagnetic electrode into a GaAs layer through an AlAs barrier. The resulting spin polarization in GaAs is detected by measuring how the tunneling current, to a second GaMnAs ferromagnetic electrode, depends on the orientation of its magnetization. Our results can be accounted for by sequential tunneling with the nonrelaxed spin splitting of the chemical potential, that is, spin accumulation, in GaAs. We discuss the conditions on the hole spin relaxation time in GaAs that are required to obtain the large effects we observe.

Unintentionally doped (100) InP wafers were ‘‘cleaned’’ with 12 different etching procedures, either found in the current literature or adapted from Si technology. We present the results of x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering experiments together with electrical properties of Au/InP contacts realized on the same samples. We can distinguish: first, the solutions which result in a rather clean InP surface and give metal-semiconductor Au/InP diodes from those which lead to an approximately 20-Å-thick oxide layer and give metal-insulating-semiconductor structures, and second, the solutions which give electrically stable structures from those which lead to very unstable ones. Detailed electrical measurements [J-V; J(V,T); C(V,T)] have been performed on two kind of stable surfaces: on ‘‘clean’’ etched ones and on one oxidized with NH4OH-H2O2-H2O (5:1:100) solution. For the first ones, a quasi-ideal metal-semiconductor diode is found. For the oxidized surfaces, current flow is controlled by pure tunneling through the oxide layer. A correlation between surface composition evaluated with XPS and surface electrical properties has been clearly established: the electrical properties of the relatively P-rich oxides are quite unstable while the others, In rich, remain stable over several months. The composition and the nature of the various oxides are discussed.

We have used a set of complementary experimental techniques to characterize an epitaxial structure (25 nm Fe)/GaAs(001) annealed at 450 °C under ultrahigh vacuum conditions. The solid state interdiffusion leads to the formation of an epitaxial reaction layer made of Fe2As patches embedded in a Ga rich Fe3Ga2−XAsX ternary phase. The epitaxial character of this layer explains how the usually reported epitaxial growth of Fe on GaAs performed in the temperature range of 175 to 225 °C is possible in spite of the species intermixing occurring at the interface. Moreover, the observed grains of Fe2As explain the decrease of magnetization at the interface in such contact, since Fe2As is an antiferromagnetic alloy.