Growth Conditions Effect on the Structure and Optical Properties of ZnO Thin Films Synthesized by rf Magnetron Sputterin
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Growth Conditions Effect on the Structure and Optical Properties of ZnO Thin Films Synthesized by rf Magnetron Sputtering Luis Angelats-Silva1, Maharaj. S. Tomar2, Oscar Perales-Perez3, Sundiram P. Singh3 and Segundo Jáuregui-Rosas1 1
Departamento Académico de Física, Universidad Nacional de Trujillo - Perú. Department of Physics, University of Puerto Rico, Mayagüez, PR00681-9016 USA. 3 Department of Engineering Science & Materials, University of Puerto Rico, Mayagüez, PR00680-9044 USA. 2
ABSTRACT We report a systematic study of the influence of the target-substrate distance and rf power on the structural and optical properties of ZnO thin films grown by rf magnetron sputtering in Ar atmosphere from ZnO sputtering target. Sharp (002) peak showed by XRD indicates a c-axis crystalline growth of ZnO films. Growth rate remained almost constant for short target-substrate distances. However, the grain size increases with the rf power decreasing the compressive stress in ZnO films. As-grown ZnO films have average transmittance more than 80% in the visible region. Optical bandgap (Eg) increases from 3.18 to 3.27 eV as increase the target-substrate distance probably due to low stress compression in ZnO films. In addition, when rf power is above 100 W, the optical band gap increases as increase of the stress compression. INTRODUCTION ZnO thin films, with a wide band gap energy (Eg = 3.37 eV), has attracted considerable attention to be used as a transparent and conduction electrode material for various electronic devices such as solar cells, electroluminescence displays, etc. [1]. ZnO thin films have been synthesized using a variety of deposition techniques, such as metal organic chemical-vapor deposition (MOCVD) [2], pulsed-laser deposition (PLD) [3,4], and molecular-beam epitaxy (MBE) [5]. One of the deposition techniques mostly used is magnetron sputtering [6-8]. The fundamental difference between magnetron sputtering as a plasma process and thermally excited thin-film preparation methods (evaporation, chemical deposition methods) is the much higher energy input into the growing film [9-10]. Magnetron sputtering technique is characterized by the following advantages: low substrate temperatures, good adhesion of films on substrates, high deposition rates, very good thickness uniformity and high density of the films [11]. However, many articles report about the influence of deposition parameters such as substrate to target distance, rf power, substrate temperature on the structural and optical properties of ZnO films [11-15]. In this paper we investigate the growth conditions such as substrate to target distance and rf power on structural and optical properties of ZnO films synthesized onto glass by rf magnetron sputtering. EXPERIMENTAL DETAILS The magnetron sputtering used in this work has a configuration on-axis with two magnetron sputter guns at angle of 65° respect to the plane of target as shown in the figure 1. The
sputtering ZnO (purity 99.99%) target used in this study was acquired to SCM, Inc. In ord
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