Recent progress towards the development of ferromagnetic nitride semiconductors for spintronic applications

This article describes progress towards producing prototype magnetoelectronic structures based on III-N semiconductor materials. We focus on the materials properties connected with the key physical phenomena underlying potential spintronic devices: producing, injecting, transporting, manipulating and detecting spin-polarized electron populations. Our experiments have shown that the maximum magnetic moment is realized for a composition of Ga0.97Cr0.03N and a substrate growth temperature of similar to 1050 K. Ion channeling experiments show that similar to 90% of Cr sits substitutionally on the cation site. The highest measured magnetization was 1.8 mu(B)/Cr atom (similar to 60% of the expected moment from band theory for ideal material) with the Curie temperature over similar to 900 K. This strongly suggests a link between the Cr-Ga impurity band and ferromagnetism and suggests that a double-exchange-like mechanism is responsible for the ferromagnetic ordering. The transport properties of spin-polarized charge carriers were modeled theoretically taking into account both the Elliott-Yafet and the D'yakonov-Perel' scattering mechanisms. We include the spin-orbit interaction in the unperturbed Hamiltonian and treat scattering by ionized impurities and phonons as a perturbation. Our numerical calculations predict two orders of magnitude longer electron spin relaxation times and an order of magnitude shorter hole spin relaxation times in GaN than in GaAs. First-principles electronic structure calculations predict that efficient spin injection can be achieved using a ferromagnetic GaN: Cr electrode in conjunction with an AN tunnel barrier. In this structure, the electrode is found to be half-metallic up to the interface and is thus a candidate for high-efficiency magnetoelectronic devices. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.