Study Of Preparation And Characteristics Of Metal-Doped V₂O₅ Thin Films By Reactive Magnetron Co-Sputtering

Vanadium oxide is an important functional material and has attracted widespread attention due to its good physical and chemical properties. Vanadium pentoxide (V2O5) with a layered structure is the most stable phase in the V-0 system. Furthermore, it is a wide band gap n-type semiconductor exhibiting good chemical and thermal stability. Metal-doped V2O5 thin films will be widely used in more areas, because of significant changes in the optical and electrical properties induced by metal doping.V2O5 thin films are deposited on Si (100) and glass substrates by means of direct current (DC) reactive magnetron sputtering method and the layered structured film sample is obtained by changing deposition parameters. It is indicated from X-ray diffraction (XRD) patterns that the V2O5 films are amorphous when the temperature of substrates is too high or not heated, and the film preferred orientation will change from (710) to (001) with the increase of the value of O2/Ar+O2and working pressure. The surface morphology of V2O5 thin films is characterized by scanning electronic microscope (SEM). It is found that the V2O5 thin films have about 0.5-0.8 μm rod-like crystal grains. The structure of the film is further investigated by Raman spectroscopy. The Raman peak of the V2O5 films at 145 cm-1 indicates that the film with the layered structure is obtained. X-ray photoelectron spectroscopy (XPS) testing shows the composition of single V2O5 phase in the thin films. The square resistance of about 13.4-108 KΩ/□ is obtained by using four-probe method. It can be applied to the micro uncooled bolometer. The optical properties of the film are measured by ultraviolet visible near infrared (UV-VIS-NIR) spectrophotometer. It is shown that the high transmittancee of 50% in the visible region and the optical band gap of 1.7 eV are obtained.Ti, Zn, and Co-doped V2O5 thin films are prepared on different substrates by radio frequency (RF) and DC reactive co-sputtering, respectively. The metal doping makes the diffraction peaks intensity increase and the diffraction peaks move to the lower angle. In addition, the other diffraction peaks corresponding to V2O3 (104) plane of the films deposited on the silicon substrate are observed with the doping. The grain size of the films is about 28.6-157.6 nm. The new diffraction peaks corresponding to VO2 (111) plane of the films deposited on the glass substrate are observed with the doping. The grain size of the films is about 15.7-20.5 nm. The SEM images show that the large clusters are formed due to the combination of grains. Raman spectra show that the Raman peak of the films moves to low frequency. The Raman peak intensity of Ti-doped V2O5 films is lower than that of Zn-doped V2O5 films, which shows the films have better crystallinity. There are VO2, ZnO and CO3O4 forms in the Ti, Zn, Co-doped V2O5 films, respectively. The square resistance of the metal-doped films is decreased, and is about 9.8-36.6 KΩ/□. The highest optical transmittance of 53% is obtained in the visible light range for Ti-doped V2O5 films. The lowest optical transmittance of 40% is obtained for Co-doped V2O5 films. The room temperature ferromagnetism of the Co doped V2O5 films tested by vibrating sample magnetometer (VSM) is increased with the increase of the doping sputtering power.The undoped and doped films deposited on Si substrates are annealed under 800 ℃ for an hour. After annealing, the structure, composition and resistance of the films are changed. The valence state of the V is reduced and the square resistance of the films becomes larger.