Characterization of bulk crystals of transition metal doped ZnO for spintronic applications
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Characterization of bulk crystals of transition metal doped ZnO for spintronic applications M. H. Kane1, R. Varatharajan3, Z. C. Feng2, S. Kandoor1, J. Nause3, C. Summers1, I. T. Ferguson2,* 1 ) Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 2 ) Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 3 ) Cermet, Inc., Atlanta, GA * [email protected] ABSTRACT In this work, we report on the material properties of ZnO doped with Mn, Co, and Fe grown by a modified melt growth technique. X-ray diffraction measurements show that transition metals can be incorporated on Zn sites; an increase in the lattice parameter is apparent with increasing doping level. UV-visible transmission and reflectance measurements have also been performed. Absorption bands in the visible regime are distinctive to the individual transition metal dopants. A noticeable shift in the optical band edge has been observed from these Mn/Co/Fe-doped ZnO crystals in comparison with the undoped material. ZnO may also provide a suitable platform for the incorporation of transition metal elements through high temperature near equilibrium growth processes; however, further work is required in order to employ these materials for spintronic applications. INTRODUCTION ZnO has a wide and direct band gap of 3.36 eV at room temperature and an exciton binding energy of 60 meV which is higher than that of GaN of 28 meV. It is a promising material for blue-UV light emitting devices and also a possible candidate as substrate for the growth of III-nitrides. ZnO doped with transition metal elements has attracted interest for applications in the field of spintronics. Theoretical predictions and some experimental results have indicated that it is a promising room temperature ferromagnetic semiconductor. There is, however, more work needed to elucidate the mechanism of ferromagnetism in these materials and develop them for device applications. Considerable effort has been devoted to exploiting both the spin and charge properties of the electron for the next generation of electronic devices. Such ‘spintronic’ devices would have numerous applications in next-generation electronics such as novel electro-magneto-optical devices [1,2], and quantum computers [3]. In order for these spintronic devices to be realized, there is a need to develop a new class of materials that can adequately support spin storage and transfer. Ferromagnetic III-V and II-VI semiconductors show much promise in that regard, and they can be easily integrated into existing semiconductor technology. The previously studied and widely characterized II-VI and III-V ferromagnetic semiconductors, such as Ga1-xMnxAs and In1-xMnxAs, all exhibit Curie temperatures well below room temperature [4,5]. For practical spintronic device applications, however, stable and sufficiently robust ferromagnetism will be required to persist to room temperature (>300 K). The current interest in ZnO and other wideband gap semiconductors for spintronic applications w
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