Zinc Nitride Films by Reactive Sputtering of Zn in N 2 -Containing Atmosphere
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Zinc Nitride Films by Reactive Sputtering of Zn in N2-Containing Atmosphere Nanke Jiang1, Daniel G. Georgiev1 , Ahalapitiya H. Jayatissa2 and Ting Wen2 1 Department of Electrical Engineering and Computer Science, University of Toledo, Toledo, OH 43606, U.S.A. 2 Department of Mechanical, Industrial and Manufacturing Engineering, University of Toledo, Toledo, OH 43606, U.S.A. ABSTRACT Fabrication, microstructure, chemical bonding and composition, and optical properties of zinc nitride films are investigated in this work. The films were deposited by reactive magnetron rf sputtering of zinc in N 2 -Ar ambient. Based on X-ray diffraction data, the as-deposited films are polycrystalline with cubic zinc nitride structure and (400) preferred orientation. Well defined Zn-N, N-N, as well as Zn-O and H-O bonding configurations are revealed by X-ray photoelectron spectroscopy data. The as-deposited films are found to be almost-stoichiometric and contain only a small fraction of oxygen. A direct band gap of 1.5 eV is obtained by using the photon energy dependence of the optical absorption of the films. This result is confirmed independently by spectroscopic ellipsometry. INTRODUCTION Zinc nitride (Zn3N2) is a promising material for electronic and optoelectronic applications [1-4], as well as photovoltaic and sensor applications, offering additional advantages such as environment-friendly processing and potentially low fabrication cost. Zn3N2 powder was first synthesized by Juza and Hahn [5] in 1940. Zinc nitride films were first prepared by Kuriyama et al. [6] in 1993. Since then, different methods have been used to prepare zinc nitride films: reactive sputtering [2,7-9], chemical vapor deposition [1], and electrochemical processes [10]. However, there are still many challenges in the preparation of high-quality zinc nitride. Reproducibility, film stability, chemical composition control, and undesired oxidation of films are some of the problems with this material. Zinc nitride remains a relatively new material and its physical properties are not well studied or understood. The values of some important parameters are not certain, and some vary over a large range, depending on either the structure/morphology, or the preparation method or techniques for characterization. This is especially true for the energy band gap, the data for which vary from 1.06 to 3.4 eV with a direct band gap or 2.11 to 2.81 eV with indirect band gap [11]. In this work, which is in progress, zinc nitride films were fabricated by reactive sputtering of Zn in Ar+N2 atmosphere. The nitrogen concentrations in the sputtering gas mixture and the substrate temperatures are the deposition parameters which were varied. The microstructure, morphology and optical properties of the films were studied, and the effects of the deposition conditions on the crystallinity and the energy band gap were investigated. Information about the chemical bonding configurations within the films and at their surface was obtained as well. We discuss data on only three samples, represent
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