Effect of RF power on the optical, electrical, mechanical and structural properties of sputtering Ga-doped ZnO thin films

We present the influences of radio-frequency (RF) power on the optical, electrical, mechanical, and structural properties of Ga-doped zinc oxide (GZO) thin films by RF magnetron sputtering at room temperature. GZO thin films were grown on unheated glass and silicon substrates using radio-frequency (RF) magnetron sputtering method with different RF powers (from 60 W to 160 W). The optical properties of the GZO thin film were determined by a UV-vis spectrophotometer. The residual stress in GZO films were measured by a home-made Twyman-Green interferometer with the fast Fourier transform (FFT) method. The surface roughness of GZO films were measured by a microscopic interferometry. The microstructure, composition and crystal orientation of the GZO films were determined by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). This paper revealed that the optical, electrical, mechanical, and structural properties of GZO thin film are subject to the RF power. For the optical spectrum measurement, an average optical transmittance in the visible region of the spectra of 85% was obtained. For the characteristic measurements, all the GZO thin films deposited by RF magnetron sputtering have compressive stress at different RF powers. A minimum residual stress of 0.24 GPa is found at the RF power of 140 W. A four-point probe method was used to measure the resistivity of the GZO thin films with different powers, the results indicate that the resistivity increases with increasing of RF power. In addition, the root-mean-square (RMS) surface roughness of GZO thin films slightly increases as the RF power is increasing. We have also compared the results with the relevant literatures.