RF Sputtered ITO Thin Film with Improved Optical Property
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RF Sputtered ITO Thin Film with Improved Optical Property Kousik Midyaa*, Abhishek Sharmaa, Anil Kottantharayila, Subhabrata Dharb a
Dept. of Electrical Engineering, bDept. of Physics; IIT Bombay, India, e-mail: [email protected]
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Abstract: In this study indium tin oxide (ITO) thin films have been deposited by RF sputtering technique on quartz substrate. In all cases, the substrate was heated during deposition. Thin film deposited under various process conditions, shows characteristic XRD reflection corresponding to the (222) crystal orientation. Transmittance of the film has been measured for the wavelength range from 190 to 3300 nm. Average transmittance of 84.4%, 90.2% and 85.3% for wavelengths up to 800 nm, 2500 nm and 3300 nm respectively has been obtained. The resistivity in this case is found to be as low as ~10 × 10-4 Ω-cm. Our study is focused on controlling the resistivity of the deposited film, without compromising transmittance in the near infra red (NIR) region of the spectrum. Substrate heating during deposition is found to result in films with grains which are oriented in (222) direction predominantly. Moreover, the average grain size is increased with subsequent annealing. It has been observed that though the transmittance for the samples doesn’t vary substantially upon annealing the resistivity decreases by several factors. Keywords: RF Magnetron Sputtering; ITO; Structure; Electrical properties; Optical properties --------------------------------------------------------------------------------------------------------------------------------------------
1. Introduction Indium Tin Oxide (ITO) is an n-type degenerate semiconductor, which electrically behaves like a semimetal but has a high optical transmittance. Due to such unique combination of electrical and optical properties, ITO has been widely used in different optoelectronic devices such as solar cells, optical coatings etc. High transmittance in infra red (IR) region can increase efficiency of dye-sensitized solar cell and IR emission devices. ITO thin films, deposited by different techniques, have been studied by several authors [1-4]. Most of the reports focused on optical property of ITO films in the visible range [3-5]. However, there are few reports showing transmittance of these films in visible as well as in NIR region. Some studies have shown that the transmittance of ITO thin film falls sharply after around 1400 nm [6-8], while, others have shown good transmittance of the film beyond 1400 nm even with low resistivity [9-11]. Benoy et al., have demonstrated ITO films deposited by reactive evaporation with thickness of 80 nm and transmittance of ~ 85% upto 2600 nm and resistivity of 3.3 × 10-2 Ω-cm [9]. As thickness was increased to enhance the conductivity of the film, transmittance decreased sharply. Abd. ElRaheem et al., have studied properties of ITO films deposited on glass and SiO2 coated g
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