Growth and doping of (Ga,Mn)N epitaxial films

Gerd Kunert 1Sylwia Dobkowska 2Tian Li 3Carsten Kruse 1Alberta Bonanni 3Jörg Grenzer 4Johannes V. Borany 4Wiktor Stefanowicz 2Maciej Sawicki 2Tomasz Dietl 2,5Detlef Hommel 1

1. University of Bremen, Institute of Solid State Physics, P.O. Box 330440, Bremen 28334, Germany
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. Institut für Halbleiter und Feskörperphysik, Johannes Kepler Universität (FKP-JKU), Altenbergerstr. 69, Linz 4040, Austria
4. Institute of Ion Beam Physics and Materials Research, Helmholtz Zentrum Dresden Rossendorf (HZDR), Bautzner Landstrasse 400, Dresden 01328, Germany
5. Japan Science and Technology Agency, Semiconductor Spintronics Project (ERATO), al. Lotników 32/46, Warszawa 02-668, Poland

Abstract
Owing to the lack of band carriers, and to the highly localized nature of electrons residing on Mn, (Ga,Mn)N has been classified as dilute magnetic insulator, where spin-spin interactions proceed via short ranged superexchange coupling [1,2]. In the case of compensated samples, in which Mn2+ prevails, this interaction is antiferromagnetic [1], like in Mn-based II-VI dilute magnetic semiconductors (DMSs). However, in high quality weakly compensated epilayers that contain merely Mn3+ ions, the superexchange acquires a ferromagnetic character [1,2,4], leading to Curie temperatures below 10 K [2,4], as predicted a time ago for Cr doped II-VI DMSs [5] and widely studied by first principle methods [6].

In this work we report on the growth of (Ga,Mn)N films by molecular beam epitaxy (MBE) which show the highest ever reported for any DMS (to our knowledge) field-induced magnetization M(H) [7]. It reaches 150 emu/cm3 at 70 kOe, to be compared the value of 90 emu/cm3 attained in (Ga,Mn)As [8]. Sapphire substrates and MOVPE GaN buffers have been employed. According to high resolution x-ray diffraction (HRXRD) investigations, the films show a linear dependence of the c-lattice parameter on the amount of Mn incorporated (figure 1). Reciprocal space maps reveal that the layers are fully strained. Furthermore, according to high resolution transmission electron microscopy (HRTEM) measurements there are no secondary crystalline phases in these samples. The magnitudes of the Mn concentrations xeff provided by SQUID measurements have been cross-checked by secondary ions mass spectroscopy (SIMS). For a more detailed analysis of the crystalline structure of the layers, Rutherford backscattering (RBS) studies have been performed along the (0001)-direction. It has been found that the signal in the channelling mode drops to 3 % of its magnitude in the random mode, which is among the lowest values reported for GaN and, thus, confirms the high structural quality of the (Ga,Mn)N layers.
For achieving high Curie temperature the inclusion of carriers in GaMnN is essential. Therefore codoping experiments have been performed on GaMnN layers with Mg as well as Si as dopands. Additional Mg shifts the fermi-level to lower energies and surpresses the inclusion of Mn as seen in figure 2. Additional Si-doping, can in contrast increase the fermi-level, and therefore the amount of Mn incorporated.


References

1 A. Bonanni et al., Phys. Rev. B, 84, 3 (2011).

2 M. Sawicki et al., Phys. Rev. B, 85, 20 (2012).

3 E. Sarigiannidou et al., Phys. Rev. B, 74, 041306 (2006).

4 J. Blinowski et al., Phys. Rev. B 53, 9524 (1996).

5 K. Sato et al., Rev. Mod. Phys. 82, 1633 (2010), and references therein.

6 G. Kunert et al., Appl. Phys. Lett. 101, 022413 (2012).

7 D. Chiba et al., Appl. Phys. Lett. 90, 122503 (2007).

Figure 1: Change of c-lattice parameter with Mn content, determined by different methods. Measurements belonging to the same sample are marked by a dashed rectangle.

Figure 2: A shift in the fermi-level by Si- or Mg-doping leads to a significant change in the Mn concentrations incorporated under the same growth conditions.

 

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Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 2, by Gerd Kunert
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-15 17:04
Revised:   2013-07-22 11:32