Study of Structural and Optoelectronic Properties of ZnO Codoped with Ca and Mg

ZnO codoped with Ca and Mg in various proportions was prepared by a chemical method and annealed at 600？C. The structural and optical properties of these oxide samples were systematically studied by XRD, SEM, EDS, and PL spectrometer. XRD pattern shows a hexagonal wurtzite structure. The size of particle as shown by XRD machine and calculated by Scherer’s formula is found in the nano range. The formation of particles showed that they were polycrystalline. Due to larger ionic and covalent radii of Ca than those of Zinc, a lattice deformation occurs with the development of strain field. New phases were observed in XRD pattern of few samples ZnO-2.2 and ZnO-2.4. SEM micrograph shows the formation of nanoparticles. EDS study confirms the codoping of ZnO with Ca and Mg. Optical properties like photoluminescence emission showed a blue shift in peak wavelength. General conductivity and photoconductivity were found high in samples containing certain proportion of Ca and Mg in comparison with pure ZnO. 1. Introduction Zinc Oxide has attracted a lot of research interest due to its enormous potential for application in a variety of optoelectronic and electronic devices. The main advantages of ZnO for optoelectronic applications are its large exciton binding energy [60？mev], wide band gap energy of 3.2？ev at room temperature, and the existence of well developed bulk and epitaxial growth processes. ZnO can be prepared by an easy and cheap chemical method. It is nonpoisonous; so it can be used widely. ZnO thin films are used as transparent electrodes in photovoltaic cell in place of expensive Indium Tin Oxide [1]. ZnO nanowires have also been investigated as gas sensors [2, 3]. ZnO is suitable for UV detection by using its photoconduction properties [3]. ZnO normally forms in the hexagonal (wurtzite) crystal structure with and . The Zn atoms are tetrahedrally coordinated with four O atoms where the d-electrons of Zn hybridize with the p-electrons of O. Layers occupied by Zinc atoms alternate with layers occupied by Oxygen atoms. Presence of free electrons in undoped ZnO has been attributed to Zn interstitials and Oxygen vacancies [4]. The intrinsic defect levels that lead to n-type doping lie approximately 0.01 to 0.05？ev below the conduction band. The photoluminescence study of ZnO reflect the intrinsic direct band gap, a strongly bound exciton state, and the gap states due to point defects [4]. Visible emissions in violet blue, green, and red orange range in case of ZnO are due to transitions between self-activated centers formed by doubly ionized Zinc Vacancy and