Influence of nitrogen incorporation on structural, electronic and magnetic properties of Ga 12x Mn x As R. Kling * , A. Ko ¨ der, W. Schoch, S. Frank, M. Oettinger, W. Limmer, R. Sauer, A. Waag Abteilung Halbleiterphysik, Universita ¨t Ulm, Albert-Einstein-Allee 45, 89081 Ulm, Germany Received 26 August 2002; accepted 31 August 2002 by E.L. Ivchenko Abstract For spin injection, detection and manipulation, diluted magnetic semiconductors are interesting materials. GaMnAs is one of these candidates, though the ferromagnetism occurs only at temperatures below 110 K. In order to possibly increase the Curie temperature, nitride based III –V semiconductors have been proposed. Here, we report results on the structural, magnetic and electronic properties of Ga 12x Mn x N y As 12y . In GaMnNAs, the valence band maximum is supposed to increase in energy with N concentration, and since Mn is a relative deep acceptor with an activation energy of 110 meV, this would lead to a reduction of the activation energy and hence to a higher doping level. GaMnNAs thin films have been grown by low-temperature molecular- beam epitaxy. We present experimental data on the transport properties of this compound, indicating that it is ferromagnetic at low nitrogen concentrations. Samples with higher N concentration show a decrease of the Curie temperature or even no ferromagnetism at all and a high ohmic resistance compared to GaMnAs reference layers. This is most probably due to a compensation of the holes, which are needed for the ferromagnetic coupling. q 2002 Published by Elsevier Science Ltd. PACS: 75.50.Pp; 73.50.Jt; 72.80.Ey; 81.05.Ea Keywords: A. DMS; A. GaMnNAs; D. Curie temperature; D. Spintronics 1. Introduction In the past few years the ternary compound GaMnAs has attracted a lot of interest as it combines conventional III–V semiconductor technology with magnetic properties of the Mn ions [1,2]. Diluted magnetic semiconductors (DMS) are now under intense investigation for spin injection, spin manipulation and spin detection. In a mean field based theory on DMS by Dietl et al., Curie temperatures for various Mn containing semiconductor compounds have been calculated [3]. According to these calculations, a general trend towards higher Curie temperatures for Mn doped semiconductors is seen for materials with lighter elements, originating from a stronger p – d hybridization and the reduction of the spin-orbit coupling. One of these compounds is GaMnN with [Mn] ¼ 5% which should have a Curie temperature of about 400 K assuming that high p- type (, 3.5 £ 10 21 cm 23 ) doping is possible. As high p-type doping is problematic in GaN, our approach in order to investigate nitrogen containing DMS has been to incorpor- ate N into GaMnAs leading to the new quaternary compound GaMnNAs. This material is interesting in various respects. First it is well known that the incorporation of N into GaAs changes the band structure substantially, causing a reduction of the band gap [4] and hence in general changing the position of deep impurity states relative to the band edges. The change of the valence band and conduction band edges as a function of N concentration are plotted in Fig. 1 [5], together with the deep Mn acceptor level. Since this acceptor level is far from being a hydrogen like level, we assume here that its energetic position does not change with nitrogen content in GaNAs. As can be seen qualitatively from the figure, there is a crossover of the position of the Mn acceptor level and the GaNAs valence band. This crossover occurs at a nitrogen concentration of approximately 7%. The maximum N concentration reported 0038-1098/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S0038-1098(02)00483-0 Solid State Communications 124 (2002) 207–210 www.elsevier.com/locate/ssc * Corresponding author. Tel.: þ49-7315-0261-21; fax: þ 49- 7315-0261-08. E-mail address: rainer.kling@physik.uni-ulm.de (R. Kling).