Tuning the bandgap of ZnO by substitution with Mn 2C , Co 2C and Ni 2C S. Venkataprasad Bhat, F.L. Deepak * Chemistry and Physics of Materials Unit and CSIR Centre of Excellence in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore 560064, India Received 21 April 2005; accepted 27 May 2005 by C.N.R. Rao Available online 14 June 2005 Abstract ZnO doped with Mn 2C , Co 2C and Ni 2C have been prepared by the decomposition of acetate solid solutions. Electronic absorption spectroscopy has been used to measure the bandgaps of the doped ZnO samples and the variation of the bandgap with dopant concentration has been examined. q 2005 Elsevier Ltd. All rights reserved. PACS: 75.50.Ky; 75.50.Pp; 78.20.Ke; 82.30.Hk Keywords: A. Dilute magnetic semiconductors (DMS); B. Chemical synthesis; D. Optical properties 1. Introduction Zinc oxide, a II–VI semiconductor, is a well-known piezoelectric and electro-optic material with wide direct band gap (3.3 eV) and large exciton binding energy. ZnO is now being considered as a potential material for a wide range of applications such as opto electronic and lumines- cent devices as well as chemical sensors. Extensive studies have been carried out to modify the properties of ZnO for different applications [1]. Doping with transitional metal elements leads to many interesting properties of ZnO. Currently, much experimental and theoretical research is focused on dilute magnetic semiconductors (DMS) based on ZnO doped with transition metal ions such as Mn and Co, since the predicted room temperature ferromagnetism in the DMS may be useful in spintronics. Ferromagnetism in Mn and Co doped ZnO is not established and there are many contradictory experimental observations [2]. It appears nearly certain that without the introduction of additional carriers, ZnO cannot be rendered ferromagnetic by doping with Mn and Co [3]. However, the ternary nature of the DMS provides a possibility of tuning band parameters by varying the composition of the material. Thus, doping of ZnO with transition elements such as Mn, Co, and Ni offers a viable means of tuning the band gap. A linear variation in the bandgap with composition is expected on the basis of the virtual crystal approximation (VCA). DMS materials are known to show a deviation from the linear dependence in the form of band gap bowing as in ZnMnSe and CdMnS [4,5]. The observed dip in the band gap has been theoretically explained as a manifestation of strong exchange interaction present between d electrons of Mn, and the s and p electrons of the host matrix. This strong exchange interaction between d electrons of the magnetic transition metal ions and the sp carriers is a most distinctive feature of DMS. Although the exchange interaction is especially important in the presence of an external magnetic field H, in certain cases it can manifest at HZ0. A similar effect of sp–d exchange interaction on the band gap has been reported in Mn doped ZnO from the previous studies. Fukumura et al. [6] and Jung et al. [7] report an overall blue-shift in the band gap with increase in Mn concentration Solid State Communications 135 (2005) 345–347 www.elsevier.com/locate/ssc 0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2005.05.051 * Corresponding author. E-mail address: leonard@jncasr.ac.in (F.L. Deepak).