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Y8.5.1

Optical Properties of Mn-doped GaN O. Gelhausen1, E. Malguth1,3, M. R. Phillips1, E. M. Goldys2, M. Strassburg3,4, A. Hoffmann3, T. Graf5, M. Gjukic5 and M. Stutzmann5 1 Microstructural Analysis Unit, University of Technology, Sydney, Broadway, NSW 2007 Australia 2 Division of Information and Communication Sciences, Macquarie University, North Ryde, NSW 2109, Australia 3 Institute for Solid-State-Physics, Technical University Berlin, 10623 Berlin, Germany 4 Department of Physics and Astronomy, Georgia State University, Atlanta, GA-30303, USA 5 Walter Schottky Institute, Technical University Munich, 85748 Garching, Germany ABSTRACT Molecular beam epitaxy-grown GaN with different Mn concentrations (5-23 x 1019 cm-3) and codoped with Si were investigated by cathodoluminescence (CL) spectroscopy and optical transmission measurements. In the GaN:Mn, an intense absorption peak at 1.414 +/- 0.002 eV was observed. This peak was attributed to an internal 5T2
5E transition of the deep neutral Mn3+ state since its intensity scaled with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm-3 had three effects on the emission spectrum: (i) the donor bound exciton at 3.460 eV was reduced by more than one order of magnitude, (ii) the donor-acceptor-pair band at 3.27 eV was completely quenched and (iii) the yellow luminescence centered at 2.2 eV was the strongly decreased. The latter two effects were attributed to a reduced concentration of VGa. In the infrared spectral range, three broad, Mn-doping related CL emission bands centered at 1.01 ± 0.02 eV, 1.09 ± 0.02 eV and 1.25 ± 0.03 eV were observed. These bands might be related to deep donor complexes, which are generated as a result of the heavy Mn-doping, rather than internal transitions at the Mn atom. INTRODUCTION Transition metals in GaN have been studied in detail for more than 10 years [1], but regained attraction recently due to potential application for growth of high-resistivity GaN substrate material and for dilute magnetic semiconductors (DMS) showing ferromagnetic behaviour above room temperature [2]. GaN doped with Mn is a possible candidate for spintronics applications since a Curie temperature above room temperature has been reported [3,4]. However, a viable spintronics device needs to support carrier-mediated ferromagnetism so that spin-polarised charge carriers may be injected into a nonmagnetic semiconductor [5]. Recent reports indicate that the Mn2+ acceptor level is located deep in the GaN band gap and not effective-mass-like as in GaAs:Mn [6], suggesting that carrier-mediated ferromagnetism in GaN:Mn is rather unlikely [7]. Optical studies represent one approach to identify the nature of deep levels, which are generated by the introduction of Mn in GaN. In this study, low temperature optical absorption measurements and cathodoluminescence (CL) spectroscopy were carried out to investigate the optical characteristics of GaN:Mn and GaN:Mn:Si layers. The aim of this work was to improve the understanding of how th