Structure, morphology and properties of Fe-doped ZnO films prepared by facing-target magnetron sputtering system

We have prepared a series of ZnO films with various concentrations of Fe dopant by using facing-target magnetron sputtering system and investigated their structure, morphology, optical properties and magnetic properties by means of the X-ray diffraction, Raman spectrometer, X-ray photoelectron spectroscopy, scanning electron microscope, UV-vis spectrophotometer, spectrofluorophotometer and vibrated sample magnetometer, respectively. The results showed Fe was in 2+ valence state in film. With increasing the concentration of Fe dopant the crystal quality deteriorated gradually and an increasing compressive stress occurred in ZnO films. All the grains grew with a columnar form along the [0 0 2] direction and the average size of grains decreased monotonically as the concentration of Fe dopant increased. The calculated results indicated that the band gap of films decreased with the increment of the concentration of Fe dopant, which resulted in the red-shift of violet emission peak. Moreover, the intensity of violet emission peak increased with the increment of Fe concentration because of the interface trap existing in depletion regions located at the ZnO grains boundaries. When the concentration of Fe dopant was smaller than 0.028, the films exhibited paramagnetic properties while the films displayed weak ferromagnetic properties when the concentration of Fe dopant increased to 0.041.