Optical properties of transition metal (Mn, Fe and V) doped Zinc Oxide ceramics and thin films
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Optical properties of transition metal (Mn, Fe and V) doped Zinc Oxide ceramics and thin films Neha Awasthi, P. Bhattacharya and R.S. Katiyar Department of Physics, University of Puerto Rico, San Juan PR-00931.
ABSTRACT Transition metal doped (Mn, Fe and V) ZnO ceramics and their thin films were prepared by pulsed laser deposition on glass substrates. The ceramic targets did not show any additional phase formation from XRD measurement, except for high Fe concentrations. Optical absorption showed sub-band gap absorption for Mn doping. The band gap was shifted by 0.06 eV for V doped ZnO as concentration was increased to 10%. Micro Raman spectra showed some defect induced modes for all the transition metals doped ZnO ceramics. In V doped ZnO ceramics there was two phonon induced resonance Raman scattering with increase in dopant concentrations. Raman spectra for thin films did not show any significant additional modes for Mn and Fe. However V doped ZnO thin films showed an additional mode for concentration ≥5 %. INTRODUCTION Dilute magnetic semiconductors (DMS) involve charge and spin degrees of freedom in a single material and are extensively investigated for potential applications in spintronics1. This field exists between the magnetism and electronics of semiconductors. Among these, II-IV semiconductors have an advantage, where the concentration of charge and spin can be controlled independently by changing the concentrations of dopant elements, injecting carriers and transition metal (TM) element respectively2. One of the extensively studied materials is p-type Ga1xMnxAs for spintronic related device applications. The Curie temperature for this material is much below room temperature1. To achieve practical device application it is important to increase Tc above room temperature. Several theoretical predictions have raised the possibility of ferromagnetism above room temperature in 3d TM doped ZnO3. Zinc Oxide (ZnO) is a wide band gap semiconductor (3.3 eV) with a large exciton binding energy (60meV) and has potential for room temperature ferromagnetism. With large electron mass, 0.3me (me: bare electron mass), it is expected to exhibit a strong magnetic interaction between the mobile carriers and the localized magnetic ions. It is a good choice for forming transparent ferromagnetic material4. In this work, we investigated the optical properties of TM doped ZnO. The ceramic targets and thin films of TM doped ZnO have been characterized using X-ray diffraction, optical absorption and micro Raman spectroscopy.
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EXPERIMENT ZnO thin films with different concentrations (1,3,5,10 %) of Mn, Fe and V were deposited on glass slides using pulsed laser ablation technique. Targets for laser ablation were prepared using conventional powder processing method with high purity ZnO, Mn2O3, Fe2O3 and V2O5 powders. The constituent powders were taken in stoichiometric amounts and ball milled for 24 h. Dry powders were calcined at 800 ºC for 4 hours. Polyvinyl alcohol (5%) was used as binder and steric acid as lubrican
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