Influence of Deposition Temperature on Properties of Multilayered Gallium Doped Zinc Oxide Films Prepared by DC Magnetron Sputtering Technique

Abstract

Multilayered transparent conducting films based on ZnO: Ga were deposited onto glass substrate
by DC magnetron sputtering technique. The films were prepared from alloy (Zn: Ga) and ceramic
(ZnO: Ga) targets with gallium composition of 3 at% and 4 at%, respectively. Crystal structure and
phase analysis were measured using X-ray diffractometer (XRD). The XRD structural analysis
results indicated that all multilayered films were polycrystalline with (002) orientation slightly
shifted of diffracting angles due to gallium dopant concentrations as increase in the deposition
temperatures. The films were hexagonal wurtzite structure, having preferred growth orientation in
c-axis perpendicular to the substrate surface. The cross section micrographs imaging and elemental
composition of multi-layered ZnO: Ga films were studied by Scanning Electron Microscopy (SEM)
and Energy Dispersive X-ray spectroscopy (EDX), respectively. The films' surface morphology
and grain size approximations were studied by Atomic Force Microscopy (AFM) operated in the
tapping mode. Grain size approximations observed in atomic force microscopy scans were
confirmed by Debye Scherrer's formula. Optical transmittance and electrical properties of multilayered
films were studied using the UV-VIS spectrophotometer and Ecopia HMS-3000 Hall
Effect measurement equipment. Film deposited at substrate temperature of 270 °C showed the best
desired results of structural, optical and electrical properties. The film has optical transmittance of
over 91% and the lowest resistivity of 1.8  10–4 Ω-cm corresponding to the highest carrier
concentration of 4.8  1021 cm-3 and Hall mobility of 7.5 cm2 /Vs were obtained. The film’s band
gaps of 3.6 eV and extinction coefficient of 0.43 were computed empirically, while refractive
index of 1.75 was calculated by Swanepoel’s envelope method from the transmittance spectra. The
increase of the films optical band gap arises from among other factors Ga doping concentration
and increase of deposition temperatures.

Keywords: ZnO: Ga; DC Magnetron Sputtering; Swanepoel’s Envelope Method; Thin Films