Effects of discharge power on the structural and optical properties of TGZO thin films prepared by RF magnetron sputtering technique

Abstract

The transparent semiconductors of Ti and Ga-incorporated ZnO (TGZO) thin films were prepared by radio frequency (RF) magnetron sputtering onto glass substrates. The effects of discharge power on the physical properties of thin films are studied. Experimental results show that all nanocrystalline TGZO thin films possess preferential orientation along the (002) plane. The discharge power significantly affects the crystal structure and optical properties of thin films. When the discharge power is 200 W, the TGZO thin film has the optimal crystalline quality and optical properties, with the narrowest full width at half-maximum (FWHM) of 1.76×10 -3 rad, the largest average grain size of 82.4 nm and the highest average transmittance of 84.3% in the visible range. The optical gaps of thin films are estimated by the Tauc's relation and observed to increase firstly and then decrease with the increase of the discharge power. In addition, the optical parameters, including refractive index, extinction coefficient, dielectric function and dissipation factor of the thin films, are determined by optical characterization methods. The dispersion behavior of the refractive index is also analyzed using the Sellmeier's dispersion model.Ga-doped ZnO (GZO) is a promising transparent semiconductor film material for applications as transparent electrodes in photovoltaic cells (PVCs) [1] , random access memory (RAM) [2] , superficial acoustic waves [3] , touch screens [4] and gas sensitive devices. Besides high conductivity and optical transmittance in the visible region, the GZO thin films have a lot of advantages, such as non-toxicity, low cost, high abundance and high stability under hydrogen plasma, compared with Sn-doped In 3 O 2 (ITO) thin films. For the preparation of GZO thin films, there are many deposition techniques currently in use, for example, direct-current (DC) magnetron sputtering, radio frequency (RF) magnetron sputtering [5][6][7] , hydrothermal process [8] , molecular beam epitaxy, reactive plasma deposition and pulsed laser ablation (PLA). Among all these methods, conventional RF magnetron sputtering is promising in preparing transparent semiconductor GZO thin films, due to the low cost of the source materials, the high growth rates and the simplicity of the growth process required.In the present study, the transparent semiconductor thin films of Ti-doped GZO (TGZO) were deposited on glass substrates by RF magnetron sputtering technique at different discharge powers. The structural, optical and dielectric properties of the deposited films are studied in detail.Commercial plane glasses (CSG Holding Co., Ltd.) were cut into 30 mm×30 mm plates and used as substrates in this experiment. Prior to their use, the glass substrates were successively washed in an ultrasonic bath with acetone, alcohol and deionized (DI) water, each for 12 min, and then dried in a high-purity nitrogen gas jet. The TGZO transparent semiconductor films were deposited on the previously cleaned glass substrates by RF magnetron sputtering system (KDJ...