Delivered by Ingenta to: Guest User IP : 117.206.112.244 Sun, 06 Jun 2010 15:45:23 Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America RESEARCH ARTICLE Advanced Science Letters Vol. 3, 319–322, 2010 Nanocrystalline Mg Doped ZnO Dilute Magnetic Semiconductor Prepared by Chemical Route R. Chandramohan 1 ∗ , J. Thirumalai 1 , T. A. Vijayan 1 , S. Valanarasu 3 , S. Elhil Vizhian 1 , M. Srikanth 1 , and V. Swaminathan 2 ∗ 1 Department of Physics, Sree Sevugan-Annamalai College, Devakottai 630303, India 2 School of Materials Science and Engineering, Nanyang Technical University, Singapore-637 798, Singapore 3 Department of Physics, Ananda College, Devakottai 630303, India This paper reports on the comparative investigation of ZnO and Mg doped ZnO (MZO) dilute magnetic semi- conducting thin films prepared by chemical bath deposition. The films were characterized for their structural properties, optical and morphological studies. The films were polycrystalline in nature with hexagonal phase having (002) preferential orientation. The typical grain size were also estimated and found to be of an average of 200 nm. It was found that Mg doping into ZnO, modulated a shift in optical band gap of the MZO films in the UV region of 3.22 eV. The films exhibit ferromagnetic properties for magnesium doping concentration of 2 at%. 1. INTRODUCTION Dilute magnetic semiconductor (DMS) has recently been a major focus of magnetic semiconductor; intense research is being tar- geted towards spintronics material 1 such as spin transistor, spin LED, non-volatile memory, optical switches and logic devices. 2 3 Earlier III-V DMS’s were reported whose Curie temperatures were quite low. 4 It is highly essential to find a solution to enhance the transition temperature of DMS to above room temperature. 5 Diet et al. reported a theoretical model of DMS materials can have a curie temperature above room temperature. 6 Subsequently, sufficient experimental data and models were available on transi- tion metals doped ZnO ferromagnetic material 7 as suitable DMS candidate for spintronics. 8 Even many magnetic materials such as Co, Fe, and Ni were doped into ZnO lattices, but the mecha- nism of magnetism is decisiveness. 9 The main aim of the present work is to prepare non magnetic cations doped nanocrystalline ZnO thin films as dilute magnetic semiconductor. The remarkable properties of ZnO are its wide direct-band gap of 3.37 eV, the binding energy of the exciton of ZnO (60 meV) which makes it an excellent material for excitonic devices. 10 Mg being the lightest metal its addition is expected to reduce the weight of the devices and make more flexible in spinning. Recently it has been demonstrated that doping with Cadmium reduces the band gap of ZnO and doping with magne- sium (Mg) widens. 11 Mg doped ZnO (MZO) film is one of the promising dilute magnetic semiconductor (DMS) besides being an alternatives to ITO (Indium tin oxide) thin films. The Mg doping enhances the band gap and is suitable for designing ∗ Authors to whom correspondence should be addressed. ZnO waveguides and FET applications. Zinc is a cheap and abundant raw material, and magnesium doping enhances its sta- bility in a reducing atmosphere, and has comparable electri- cal and optical properties. 12 Because of the addition of Mg the magnetic properties are added and hence they find extensive applications in spintronics. 13 MZO coatings exhibit high trans- parency, low resistivity and these coatings are suitable for fabri- cating transparent electrodes in solar cells, gas sensors, MEMS and ultrasonic oscillators. The opto-electrical property of MZO thin films has been modified by thermal treatment in a reducing atmosphere 14 for films grown by sputtering technique. Synthe- sis of 5% Mg doped ZnO thin films by pulsed laser deposi- tion have been reported to understand the effect of doping in optical and electronic properties. 15 16 Different techniques such as chemical vapor deposition, 17 magnetron sputtering, 18 spray pyrolysis, 19 sol–gel, 20 and molecular beam epitaxy, 21 have been used for deposition of zinc oxide films on various substrates. The chemical bath deposition (CBD) technique is an open-bath wet-chemical method that has been extensively employed for the synthesis of metal oxide thin films. 22 The ease with which the deposition can be made and the reproducibility of the method to produce doped oxide films in any laboratory make this method quite attractive. 23 24 While the solgel method with double dip- ping has produced highly oriented thin films of Li, Mg doped ZnO thin films by Liu et al., 25 they have introduced a spin in the dipped films using spin coating set up to spread the films over substrate. In the method used in this work no spinning is required as the dehydrogenation of the films is done using a dip in hot water. The magnetic properties of the Mg:ZnO thin films Adv. Sci. Lett. Vol. 3, No. 3, 2010 1936-6612/2010/3/319/004 doi:10.1166/asl.2010.1129 319