Minority-site occupancy of transition metals in dilute magnetic semiconductors.

In a dilute magnetic semiconductor (DMS), magnetic atoms (or impurities) replace a few percent of the atoms of an otherwise non-magnetic semiconductor. For almost two decades, the co-existence of ferromagnetism and semiconducting behavior in some DMS materials has generated fundamental new physics and enabled the study of phenomena of interest for spin electronics (spintronics). However, despite such intense research, DMS materials are still far from understood. Some of the open questions are at the very genesis of the DMS magnetism: the position (site) of the magnetic impurities in the host lattice. In general, it is easy to determine the lattice site occupied by the majority of the impurities. It is far more difficult to identify lattice sites occupied by minority fractions which can, nevertheless, dramatically affect the magnetic behavior. Part of this project consists of investigating such effects using a unique combination of emission channeling and X-ray absorption fin e structure spectroscopies. Minority-site fractions are closely linked to a perhaps even more important question: Is there a fundamental reason why ferromagnetism in DMS is only observed well below room temperature, or can the current limits be overcome through manipulation of the impuritys lattice location? In the other part of this project we will seek an answer for this question, by exploring the use of ion irradiation under carefully designed conditions to manipulate the impuritys lattice location.

Keywords:GaAs, ZnO, DMS, Lattice location, GaMnAs, Ion implantation, GaN