Structure and Composition of ZnO Films Prepared by Radio-Frequency Magnetron Sputtering

Zinc oxide (ZnO) films prepared on quartz-glass substrates using radio-frequency magnetron sputtering have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and photoluminescence (PL). Crystal structure of ZnO films were dependent on the sputtering condition; argon (Ar) gas pressure and target-substrate distance. The XRD results indicated that the peak intensity of (002)-orientation increases with increasing Ar gas pressure and target-substrate distance. The SEM images showed a pillar structure formed in films with high (002)-orientation. The film composition determined by AES results was ZnxO1-x from x=0.482 to 0.501. The optical band gap of 3.25-3.29 eV and the visible transmittance of greater than 80 % were obtained. The PL spectrum with the peak at 620 nm was observed in highly crystallized films. In contrast, non-crystalline films did not show the PL spectrum in the range of 400 to 900 nm. It is clarified that the product of Ar gas pressure (P) and target-substrate distance (D) was strongly related to the film structure. Well crystallized films were obtained at the P·D above 0.4 Torr·mm. It was concluded that the pillar structure of the film could be formed when energy of sputter-particles decreased to the surface migration energy.