Mn charge states in GaMnN as a function of Mn concentration and co-doping
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Mn charge states in GaMnN as a function of Mn concentration and co-doping Enno Malguth1,2, Axel Hoffmann1, Wolfgang Gehlhoff1, Matthew H. Kane3, and Ian T. Ferguson3 1 Institut für Festkörperphysik, Technische Universität Berlin, Berlin, 10623, Germany 2 Microstructural Analysis Unit, University of Technology Sydney, Sydney, 2007, Australia 3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0245 ABSTRACT In the context of the pursuit of a dilute magnetic semiconductor for spintronic applications, a set of GaMnN samples with varying Mn concentration and Si or Mg co-doping was investigated by optical and electron spin resonance spectroscopy. The results clearly demonstrate how the charge state of Mn is changed between 2+, 3+ and 4+ by Mg and Si codoping. For p-type GaMnN we show that the introduction of the Mn3+/4+ donor can be compensated by Mg co-doping lowering the Fermi energy below the Mn3+/4+ level. While our results are in agreement with the hypothesis that the infrared photoluminescence appearing in GaMnN upon Mg doping originates from Mn4+, an unambiguous proof is still to be presented. Under this assumption, our measurements show that the Mn4+ center must be excited via an extra-center process at 2.54 eV.
INTRODUCTION The development of semiconductor based spintronic devices requires a ferromagnetic spin-coupling at room temperature in a dilute magnetic semiconductor (DMS). Theoretical models predict a great potential to achieve this goal for p-type doped GaMnN [1]. In order to purposefully design such a DMS, the following issues need to be clarified: (1) the charge state of Mn found in n- and p-type GaN, i.e., the position of the acceptor and donor levels formed by Mn within the band gap, (2) the electronic structure of the respective charge states, (3) details on the incorporation of Mn into the host lattice (site, strain, complex formation). In this work we address these issues by means of optical and magnetic studies on GaMnN samples with varying Mn concentrations and co-doping. A general problem of achieving p-type GaMnN is the fact that the Mn3+/4+ donor level is believed to be found within the band gap compensating p-type doping [2]. This is supported by the observation of a structured luminescence band that occurs around 1 eV in Mg co-doped GaMnN and that is attributed to the internal 4T2(F) —4T1(F) transition of Mn4+[3]. However to our knowledge, there is no unambiguous proof of this assignment. According to Ref. [3] the numerous zero phonon lines (ZPL's) of the emission feature are the result of different defect complexes involving Mn4+ and probably Mg. While some of our results are in good agreement with this interpretation others are rather difficult to explain. While discussing our results on this luminescence we need to take into account that it might originate from a different defect than Mn4+.
On the contrary, Mn3+ in GaN is well established [4-6]. The 5D ground state of the d4 ion is split by the tetrahedral crystal field into a
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