Study On Preparation And Properties Of Novel Transparent Conductive CuAlO₂Thin Films

As a p-type wide direct band gap oxide semiconductor without intentional doping, delafossite CuAlO2with especial optical and electrical properties, has become the best semiconductor materials for the fabrication of transparent oxide optoelectronic device. CuAlO2also offers a whole range of applications in microelectronics, photoelectronics and magnetoelectronics due to the discovery of other properties, such as stability in high temperature, resistance to radiation and environment friendly. In recent years, CuAlO2has been attracting many attentions due to its potential technological applications.In this paper, CuAlO2films with exceed Al volume fraction of1%～5%were prepared by RF magnetron sputtering on silicon and quartz glass using a sintered CuAlO2ceramic target. The microstructure, composition, surface morphology, surface roughness, optical and wetting properties of films were characterized by X-ray diffractometer, energy dispersive X-ray spectroscopy, scanning electron microscope,3D profilometer, ultraviolet-visible spectrophotometer and contact angle apparatus, respectively. The influence of Al components and annealing condition on the microstructure, composition, surface morphology, optical and wetting properties of films were studied.The results show that CuAlO2film annealed under ambient atmosphere at1173K for4h is delafossite structure with diffraction peaks at2θ=31.63,36.66,52.84and66.82°related to the (006),(101),(107)and(1010) planes of CuAlO2, respectively. Along with CuAlO2phase the annealed film exhibits impurity (511) phase of Al2O3, and the surface roughness is23.9nm.After annealing, the microstructure of CuAlO2film changes from amorphous to Cu-Al-0phase, and surface roughness increases due to the formation of crystal grain. Average transmittance and reflectance of CuAlO2films decrease from60%and15%to40%and10%, respectively. The average refractive index turns2.1into1.5, and direct and indirect band gap of the film reduce from3.86and1.56eV to3.50and1.37eV. With the adding of Al component, the average transmittance of the film first increase then decrease, while the average reflectance, absorption coefficient coefficient, refractive index, extinction coefficient, direct and indirect band gap of CuAlO2film first decrease then increase. All are caused by the variation of crystal structure and surface roughness. CuAlO2film changes from hydrophobicity to hydrophily after annealing, and water contact angle (WCA) of the annealed film increases from31.1°to70.5°. Studies of the influence of UV exposure on wetting behavior of the as-deposited CuAlO2films have shown that WCA reduce quickly under UV exposure in2h.The higher the light source energy is, the faster the reduction of WCA is. Exposure for long time (>2h), WCA fluctuates and becomes stable.The main innovations of the paper are as follows:1. The influence of Al components on the microstructure, composition, surface morphology, optical and wetting properties of films was studied.3%Al-CuA102film was obtained with maximum transmittance of60%and minimum reflectance of9.7%.2. Surface wettability and photo-induced wetting properties of CuAlO2films have been studied, and the corresponding mechanisms have been analyzed.