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 x_eff 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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