Synthesis and Properties of Ga x Mn 1-x N films
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Synthesis and Properties of GaxMn1-xN films R. Zhang, Y. Y. Yu, X. Q. Xiu, Z. L. Xie, S. L .Gu, B. Shen, Y. Shi, and Y. D. Zheng Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Science and Technology, and Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China ABSTRATCT Mn-doped GaN films were grown by hydride vapor phase epitaxy(HVPE). structural measurements show that Mn may substitute Ga atoms in the GaN lattice. Ferromagnetism is observed in these HVPE grown Mn-doped GaN films, which may come from the GaxMn1-xN phase in the films. INTRODUCTION Diluted magnetic semiconductors (DMS) are promising for developing novel devices based on spin-polarized transport or spin injection into semiconductors [1][2]. III–V DMS became more and more important since the discovery of the carrier induced ferromagnetism in (In, Mn)As[3] and (Ga,Mn)As[4]. However, the highest reported Tc of the (In, Mn)As is 25K and Tc of (Ga, Mn)As is around 170 K, much lower than the practical environmental temperature. It is necessary to find new DMS materials with higher Tc. GaN has wide band gap energy of 3.39 eV and has been considered as one of the most excellent host materials for preparing DMS materials. Dietl et al. predicted GaxMn1-xN has a high-Tc up to above room temperature on the basis of a mean field model[5]. Calculations of the electronic structure of 3d-transition-metal doped GaN and investigations of the stability of the ferromagnetic state lead to a conclusion that V, Mn and Cr doped GaN are possible candidates for room temperature DMS[6]. Kronik et al.[7] found that Mn 3d and N 2p hybridization results in an impurity band that makes the material half metallic and therefore ideal for spin injection. It seems that the GaxMn1-xN is preferable to (Ga,Mn)As not only because of its higher Curie temperature, but also because its band structure is much more suitable for spin injection. It is difficult to fabricate a uniform GaxMn1-xN alloy film. Mn prefers octahedral bonding with N, whereas Ga prefer tetrahedral bonding. In the case of alloy growth, Mn metal vapor pressure is about 100 times greater than Ga metal [8].Many experimental efforts have been reported regarding the preparation and magnetic properties of GaxMn1-xN layers. Several groups reported GaxMn1-xN growth using molecular beam expiatory (MBE) with radio frequency (RF)[9] [10], Electron cyclotron resonance (ECR), plasma [11] and ammonia for nitrogen source[12]. It was also reported that Ga1-xMnxN had been fabricated using Mn ions implantation technique[13] and ammonothermal method[14,15]. Microcrystalline GaxMn1-xN samples grown by ammonothermal method showed a paramagnetic behavior[14, 15]. Overberg et al. [10] reported that GaN films doped with 7 at.%
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Mn by MBE are ferromagnetic with a low Tc from 10 to 25 K. Theodoropoulou et al. [13] have shown that p-type GaN films, grown by metalorganic chemical vapor deposition (MOCVD) on an α-Al2O3 substrate, implanted with 3–5 at.% Mn are ferromagnetic up to 250
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