Annealing-dependent phenomena in Ga₁[-x]Mn[x]As

Abstract

There has been a great deal of recent research interest in the development of "spintronics" technology. Many potential spintronic devices will require a "spin injector" capable of producing a spin-polarized current. In particular, it would be valuable to develop a ferromagnetic semiconductor spin injector that would be compatible with semiconductor materials common to existing electronic devices. A promising candidate for such a spin-injector is Ga1-xMnxAs, due to its relatively high ferromagnetic transition temperature (TC), and its compatibility with standard GaAs. However, in order to achieve maximum TC, Ga1-xMnxAs must be carefully annealed after growth. While it has been known since 2001 that annealing can increase TC, it has not been understood until very recently exactly how annealing achieves this benefit. With the aim of better understanding the annealing process, this dissertation's primary focus is polarized neutron reflectometry experiments that examine how annealing changes the depth-dependent properties of Ga1-xMnxAs thin films. For several uncapped films, annealing is observed to significantly alter these films' chemical and magnetic depth profiles, while annealing is observed to do little to a sample capped with GaAs. These results provide evidence that annealing enhances Ga1-xMnxAs by ripping ferromagnetically disruptive Mn impurities from the crystal lattice, freeing them to migrate to the surface of the film-corroborating other recent work. ms chemical and magnetic depth profiles, while annealing is observed to do little to a sample capped with GaAs. These results provide evidence that annealing enhances Ga1-xMnxAs by ripping ferromagnetically disruptive Mn impurities from the crystal lattice, freeing them to migrate to the surface of the film-corroborating other recent work.