Physical Properties of Zinc-Tin-Oxide Thin Films Deposited on Sapphire Substrates by an Rf-Magnetron Sputtering Method

Abstract

SnO2-doped ZnO (ZTO) films were prepared on a c-planed sapphire substrate by using an rf-magnetron sputtering system at 350 degrees C, and physical and optical properties were investigated. Samples were prepared by sputtering the targets made with ZnO:SnO2 as varying the ratio from 100: 0 to 70: 30. For the samples made with ZnO: SnO2 ratio of 70: 30, the films transformed to an amorphous phase from the wurtzite structure. With increasing the SnO2 contents from 0 to 30%, we noted the followings; the root mean square values of the surface roughness decreased from 10.56 to 0.44 nm, the electrical resistivity values increased from 6.54x10(-3) to 4.83x10(-2) Omega cm, carrier concentration values decreased from 5.46x10(19) to 2.94x10(18) cm(-3), and the Hall mobility values significantly increased from 0.057 to 70.58 cm(2)Ns. The average value of the optical transmittance in the visible-light range was 80-85%. For the films having less than 10% of SnO2 showed a red-shift in absorption edges toward longer wavelengths, while the amorphous films exhibit a blue-shift toward a shorter wavelength. 3.2 eV band gap energy and high optical transmittance values of ZTO films demonstrate that SnO2-doped ZnO films can be used as good conducting oxides.