Magnetic Properties of GaN Layers Implanted by Mn, Cr or V.
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Magnetic Properties of GaN Layers Implanted by Mn, Cr or V. Vitaliy A. Guzenko1, Nicolas Thillosen1, Andre Dahmen1, Raffaella Calarco1, Thomas Schäpers1, Martina Luysberg2, and Lothar Houben2 1 Institute of Thin Films and Interfaces (ISG-1), Research Centre Jülich, 52425 Jülich, Germany 2 Institute of Solid State Research (IFF), Research Centre Jülich, 52425 Jülich, Germany ABSTRACT We report on magnetic properties of the GaN layers implanted with 3d transition metal ions. GaN layers grown by MOVPE on sapphire substrates, p- or n-doped, were implanted by Mn, Cr or V ions with a dose of 5×1016 cm-2 and implantation energy of 200 keV. Subsequently, a rapid thermal annealing in nitrogen atmosphere for 5 minutes at different temperatures (700°C – 1050°C) was performed. The magnetization as a function of magnetic field as well as the dependence on temperature revealed paramagnetic behavior for all samples. In addition, an antiferromagnetic coupling between implanted ions was found.
INTRODUCTION In recent years the field of spintronics has been rapidly developing and a special role has been played by diluted magnetic semiconductors (DMS), owing to their potential for future spintronic devices [1]. In comparison with conventional ferromagnets they are of advantage for an efficient electrical spin injection into semiconductors, because of the better material matching. Recently, GaN-based DMS became of great interest due to prediction of room temperature ferromagnetism in GaN:Mn by Dietl et al. [2] and other compounds (GaN:Cr and GaN:V) by Sato et al. [3]. It has been proposed that a stable ferromagnetic state in GaN:Mn (Mn concentration up to 10%), in GaN:Cr and GaN:V (at even higher impurity concentration) should be achieved. Interestingly, according to the band structure calculations by Sato et al. [3], ferromagnetic ordering, which pertains to the partial filling of the anti-bonding impurity states, in n-type GaN:V seems to be possible. Several groups have investigated the growth and properties of GaN-based DMS. However, the results show significant discrepancies, particularly regarding the magnetic properties of the layers. It has been reported on ferromagnetic [4–8] or paramagnetic [9], antiferromagnetic [10] or spin-glass [11] behavior. It is worth to be mentioned that different techniques were applied for the fabrication of GaN-based DMS: molecular beam epitaxy [9, 11], metal-organic chemical vapor deposition [4, 5], ammono-thermal technique [10], or ion implantation [6–8]. The origin of the ferromagnetism in GaN-based DMS is still far from being completely understood. Hence, the question, whether it is possible to fabricate homogeneous ferromagnetic layers without precipitation, is of particular importance. Between others one of the basic prerequisites for the realization of spintronic devices is the electrical injection of the spin-polarized current into GaN. To meet this criterion good ohmic contacts are necessary. Because of the wide band gap and strong Fermi level pinning a large Schottky barrier [12] i
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