Transition Metal-Doped ZnO: A Comparison of Optical, Magnetic, and Structural Behavior of Bulk and Thin Films
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Transition Metal-Doped ZnO: A comparison of Optical, Magnetic, and Structural Behavior of Bulk and Thin Films William E. Fenwick1, Matthew H. Kane1,2, Zaili Fang1, Tahir Zaidi1, Nola Li1, Varatharajan Rengarajan3, Jeff Nause3, and Ian T. Ferguson1,2 1 School of Electrical and Computer Engineering, Georgia Institute of Technology, 778 Atlantic Dr., Atlanta, GA, 30332-0250 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0245 3 Cermet, Inc., 1019 Collier Rd., Atlanta, GA, 30318
ABSTRACT Transition metal-doped ZnO bulk crystals and thin films have been investigated to determine the effects of transition metal incorporation on optical, magnetic, and structural properties of ZnO. A modified melt growth technique was used to grow bulk Zn1-xMnxO, Zn1-xCoxO, and Zn1-xFexO. Optical transmission measurements show an apparent shift in absorption edge with increasing transition metal incorporation. Raman spectroscopy also shows increasing lattice disorder with increasing transition metal concentration. ZnO thin films doped with Ni, Co, and Gd were grown by metalorganic chemical vapor deposition (MOCVD). While the Co-doped thin films showed antiferromagnetic behavior, magnetic hysteresis was observed in the Ni-doped and Gd-doped thin films. Structural quality was verified with X-ray diffraction (XRD), and optical properties were investigated using room temperature photoluminescence (PL) and optical transmission measurements. Properties of ZnO:TM bulk crystals and thin films are compared and used to discuss possible origins of ferromagnetism in these materials. INTRODUCTION Zinc oxide (ZnO) has shown promise recently as a novel material for use in optoelectronic devices because of its wide bandgap (3.37eV) and high exciton binding energy (~60meV). These properties make it a useful material in applications such as surface acoustic wave devices, gas sensors, and UV emitters and detectors. Another possible application of ZnO-based materials is in spintronic devices. Recent predictions of room-temperature ferromagnetism in both GaN and ZnO-based dilute magnetic semiconductors (DMS) have focused a significant amount of attention on these materials systems. [1,2] However, the origin of ferromagnetism in these materials remains unclear and must be investigated further in order to realize the potential of these materials systems for room-temperature spintronic devices. Transition metal-doped ZnO II-VI semiconductors have been of interest due to their unique properties and promise in various applications [3]. Specifically, transition metal-doped ZnO has been grown by several different techniques, including pulsed laser deposition (PLD) [4], molecular beam epitaxy (MBE)[5], and metal organic chemical vapor deposition (MOCVD)[6]. MOCVD growth is desirable because of its flexibility and its scalability, which allows for the development of a commercially viable device technology. Non-equilibrium growth techniques such as MOCVD allow for the incorporation of dopants in higher conc
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