Structural and optical properties of ZnO films deposited by magnetron sputtering at room temperature

Subject of study. This study investigates nanocrystalline ZnO films deposited on glass and flexible substrates for applications in solar energy and transparent, flexible electronics. Aim of study. The aim is to determine the optimal radio-frequency (RF) magnetron sputtering power to achieve a homogeneous crystalline structure with low surface roughness during ZnO film deposition. Method. ZnO films were deposited by RF magnetron sputtering of a ceramic target in an oxygen-free environment at room temperature. The films were characterized using scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and spectrophotometry. Main results. The deposition rate of ZnO films increased linearly with sputtering power under oxygen-free, room-temperature conditions. The films exhibited a nanocrystalline structure with a dominant (002) diffraction peak, characteristic of the hexagonal ZnO lattice, and a preferred crystallite growth orientation perpendicular to the substrate surface. Increasing the sputtering power from 25 W to 100 W increased the grain size from 12.8 nm to 35.7 nm and surface roughness from 2.8 nm to 11.4 nm. The films showed ∼90% transmittance in the visible range and an optical bandgap of 3.27–3.28 eV. XPS confirmed the chemical composition of the ZnO films. Practical significance. The optimal sputtering power in an oxygen-free environment at room temperature was determined to be 75 W, yielding films with a relatively smooth surface and uniform nanocrystalline structure. These properties are promising for efficient separation of photogenerated electron–hole pairs and charge-carrier transport to electrodes in solar-cell structures, including those on flexible substrates.