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 Ga 0.97 Cr 0.03 N and a substrate growth temperature of ∼1050 K. Ion channeling experiments show that ∼90% of Cr sits substitutionally on the cation site. The highest measured magnetization was 1.8μ B /Cr atom (∼60% of the expected moment from band theory for ideal material) with the Curie temperature over ∼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 AlN 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. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)