Statistical Property Of Random Surface Of ZnO Thin Filmprepared By RF Magnetron Sputtering

ZnO is a II-VI compound semiconductor with a wide direct bandgap of 3.3 eV at room temperature, exciton binding energy of 60meV. Its lattice parameters are a=0.3249nm and c=0.5206nm. Due to their excellent physical and chemical properties, ZnO films have many realized and potential applications such as surface acoustic wave devices, planar optical waveguides, piezoelectric devices, etc. In this work, the films were prepared using RF reactive magnetron sputtering technique. For various applications, highly preferred c-axis orientation of ZnO films is usually important. Uniform and compact ZnO films with the highly preferred c-axis orientation and the high transmittance in visible region can be prepared by magnetron sputtering under optimized condition. It is the most investigated and widely used method. ZnO thin films and their morphology properties have attracted a lot of attention recently due to their potential applications in photonic materials. The surface morphology is one of the key features controlling mechanical and optical characteristics of the thin film. For example, the demagnetizing fields of thin magnetic films change as the interface roughness changes, and the electrical conductivity of thin metal films depends on surface roughness. However, the surface height of a thin film is a random walk with respect to the position vector which makes it so hard to describe the surface morphology precisely by using a mathematical function. Some statistical functions with the corresponding parameters, such as height auto-correlation function, have been proposed to describe the random film surface. In this paper, ZnO thin films are deposited on quartz glass and silicon substrates using the reactive radio-frequency (RF) magnetron sputtering method under different deposition pressure. The residual pressure, before deposition, was about 4.5×10-4Pa.The RF power was at 120 W, and the depositions were carried out with an oxygen-argon mixture gas under the sputtering pressures of 0.5Pa and 0.7Pa, respectively. Gas flow meters controlled precisely the flow rates of oxygen and argon at 4 SCCM and 16 SCCM, and SCCM denotes standard cubic centimeters per minute. The sputtering times were 2 hours for the depositions of ZnO film on quartz glass and silicon substrates, respectively. An atomic force microscope (AFM) is taken to measure the surface morphologies of the ZnO thin films. This paper engaged in the research work of the influences of different growth conditions on features of ZnO thin films in several aspects, especially in the impacts of different substrates and growth temperatures, respectively. A method for characterizing the morphology property of ZnO film surface with Gaussian correlation is investigated. The parameters of root-mean-square roughness w and lateral correlation lengthζare introduced in Gaussian model to describe the correlation properties of the random film surfaces. The surface morphologies of the film surface are scanned by an atomic force microscopy. The height auto-correlation functions and root-mean-square roughness are obtained by using the numerical calculus method. Carried on the fitting with the Gaussian function to the height auto-correlation function data, the lateral correlation lengths are extracted to describe the statistical properties of ZnO thin film in mathematics with other parameters.