The Study Of Mircrostructural And Optical Properties Of Ti-doped And Fe_Ti Co-doped ZnO Thin Films

ZnO is a Ⅱ-Ⅳ semiconductor compounds with wide and direct band gap (about-3.37eV), excellent chemical, thermal stability, specific electrical, and a large exciton binding energy of60meV. Usually ZnO has hexahedron wurtzite structure at the air condition. Due to its unique properties, it has become a very popular material. ZnO have been extensively researched in recent years for the breadth of their technological applications, such as UV absorption, optoelectronic devices, transparent conductive film, and acoustic-wave devices and so on. Furthermore, ZnO is the most favorable material because of its abundance in nature, relatively low cost, good stability in hydrogen plasma process, and non-toxicity. Therefore, there is a considerable interest in understanding the microstructure and optical properties of doped ZnO films, which will give more chance for potential applications.The pure ZnO film, Ti-doped ZnO (ZnO:Ti) and Fe-Ti co-doped ZnO thin films with (100) preferred orientation are deposited successfully on glass and silicon(Si) substrate using radio frequency (RF) reactive magnetron sputtering technique. The crystalline and optical properties of thin films were investigated by the X-ray diffraction (XRD), scanning electron microscope (SEM), fluorescence spectrometer (PL) and ultraviolet visible (UV-Vis) spectrophotometer. The results are summarized as follows:The XRD measurements revealed that all the films had hexagonal wurtzite type structure with a strong (100) preferential orientation and relatively weak (002),(101), and (110) peaks on glass substrates. It was found that the intensity of the (100) diffraction peaks was strongly dependent on the Ti doping concentration. And the full width at half-maximum (FWUM) of (002) diffraction peaks constantly changed at various Ti contents, which decreased first and then increased, reaching a minimum of about0.378at1.43at.%Ti. The morphologies of ZnO:Ti films with1.43at.%Ti showed a denser texture and better smooth surface. All the films were found to be highly transparent in the visible wavelength region with an average transmittance over90%. Compared with Eg=3.219eV for pure ZnO film, all the doping samples exhibited a blue-shift of Eg. It can be attributed to the incorporation of Ti atoms and raising the concentration of carriers. Five emission peaks located at412,448,486, 520, and550nm were observed from the photoluminescence spectra measured at room temperature and the origin of these emissions was discussed.The pure ZnO film and Ti-doped ZnO (ZnO:Ti) thin films with (100) preferred orientation are deposited successfully on silicon(Si) substrate using radio frequency (RF) reactive magnetron sputtering technique. The effect of different Ti doping concentration on the microstructural and optical properties of ZnO:Ti thin films are investigated by X-ray diffraction (XRD) and photoluminescence (PL). As the results shown, all of the films have hexagonal wurtzite type structure with obvious (100) preferential orientation, and the thin film texture coefficient TC(100) increase sharply with adding2%of Ti doping, which indicates that Ti impurities can influence crystallinzation orientation degree of ZnO films. Compare with pure ZnO thin films, the full width at half-maximum (FWHM) of (100) diffraction peak of ZnO:Ti thin films widen and the intensity of (100) diffraction peak decrease, and the quality of crystallization of thin films decline. With different Ti doping concentration on ZnO film s, we find its correspondingly changes in the luminescence.Then study on the microstructure and optical properties of ZnO:Ti film s (1%Ti) prepared on a glass substrate with the different post-annealing temperature and different annealing time. The XRD measurements revealed that all the films show a strong (100) preferential orientation peaks on glass substrates, and the intensity of diffraction peaks decreased with the increase of annealing temperature, and the quality of crystallization of thin films are deteriorated. Unannealed ZnO:Ti film has a high transmittance and up to90%. Found that the transmittance decreased after annealing at300℃, ZnO:Ti films transmittance increase when the annealing temperature increase at400℃,500℃. The ZnO:Ti films with annealing at500℃for1h shows a lower diffraction peaks intensity, the degree of crystallinity has decreased, the surface has more large agglomerated particles, uneven grain from the SEM figure. After500℃annealing for2h, the intensity of diffraction peaks increase compare with unannealled ZnO:Ti films, the quality of the annealing ZnO:Ti film increase and has a more uniform flat surface.Finally, we discuss the microstructure and photoluminescence properties of Fe-Ti co-doped ZnO films at the different oxygen pressure ratio. The results show that the two atoms of Fe-Ti co-doped ZnO film are obtained and express that has a non-polar surface growth mode of (100), while the diffraction peak is weaker, indicate that Fe and Ti together into ZnO lattice, ZnO crystal structure distorted seriously. Fe-Ti co-doped ZnO films shows a poor crystallinity. When the oxygen pressure ratio at6:10seem the Fe-Ti co-doped ZnO films with more defect states, and give a high intrinsic defects concentration, which lead to that luminescent properties and microstructure of ZnO were improved.