Process And Their Optical And Electrical Properties Of Rf Sputtered Aluminum Doped Zno Thin Films

Zinc oxide (ZnO) is an important wide band gap (Eg=3.37eV) semiconductor material, its exciton binding energy is 60meV. These characters make it expected to be applied in the ultraviolet optoelectronic devices which can be operated at room temperature. Although, AZO thin films also have been fabricated for conducting transmission application in the previous work, the Al3+ concentration was always below 10 atomic percent (at.%), which put a strict limitation on the optical band-gap shift to deeper ultraviolet range as using in deeper UV LD and LED purpose. Therefore, further studies on heavy doped AZO thin films and relative phenomena are important! In order to study heavy-doped AZO thin film, we researched three topics in this paper mainly:1. ZnO thin films were prepared by RF sputtering method on the Si substrates in order to get the best process conditions. Then the Al-doped ZnO (AZO) thin films with different Al3+ concentration (2at%,5at%,10at%.15at%,20at%,30at% and 40at%) were prepared on Si and quart substrates. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscope (XPS) were used to characterize the crystalline structure, orientation and surface morphology of the AZO thin film. It was revealed that wurtzite structure with (002) orientation AZO thin films were obtained at Al concentration below 15 atomic percent (at%). As the Al concentration above 15at%, the thin films did not fully crystallize.2. Photoluminescence spectrum was acquired in a SHIMADZU fluorespectrometer at room temperature. The shape of all the spectra was featured by a strong emission near UV and a defect-related deep level emission in visible region. Two new emission peaks occurred at 351nm and 313nm when the Al doping above 15at% from the Photoluminescence spectrum, and the peaks shifted towards the shorter wavelengths with increasing the Al concentration.3. Ultraviolet-visible (UV-vis) spectrometer was used to measure the optical properties of the AZO thin film. It was found that their optical transmittance was over 85% in the visible region with a sharp fundamental absorption edge. Optical band-gap of the films is increased, depending on the Al doped concentration, from 3.34eV for un-doped ZnO film to 4.6eV for 30at% Al doping.4. The electrical properties of the AZO thin films were studied. A minimum resistivity of 3.4×10^-4Ω.cm was obtained at a doping concentration of 2at%; while the maximum 1.3×10⁷Ω.cm at a doping concentration of 30at%.