Effect Of Zn Buffer Layer On The Structural And Optical Properties Of ZnO Thin Films

ZnO is a new-type semiconductor with a direct wide-band-gap of 3.37eV at room temperature (RT). It has a high exciton binding energy of 60meV and hexagonal wurtzite structure at the air condition. The feasibility of using excitonic lasers of ZnO at RT has been demonstrated. It has been investigated extensively because of its interesting electrical, optical and piezoelectric properties making suitable for many applications such as light emitting diodes, photodetectors, electroluminescence, transparent conductive film, surface acoustic waves device and so on.ZnO films have been grown by various deposition methods including magnetron sputtering, pulsed laser deposition, molecular beam epitaxy, metal organic chemical vapor deposition, spray pyrolysis and sol-gel process. Magnetron sputtering method is widely used by the researchers because the equipment is simple, low cost, easy operation, high rate of deposition, the requirement of base temperature is lower and good film adhesion, its ingredients in a certain extent controllable, etc.In this thesis, we researched the effect of Zn buffer layer thickness on the structural and optical properties of ZnO films grown by RF magnetron sputtering. In this way some experimental data and the theoretical basis are provided for the application of ZnO films. The results are summarized as follows:1. ZnO thin films grown on Zn buffer layer were prepared on glass substrates by radio frequency (RF) magnetron sputtering system. Deposition time of Zn buffer layer changed from 5 min to 15 min, and the influence on the crystal structures and optical properties of ZnO thin films have been investigated. The XRD results show that the ZnO thin films with Zn buffer layer have a hexagonal wurtzite structure, and with the increase of Zn buffer layer sputtering time, the full-width at half-maximum (FWHM) for the ZnO(002) diffraction peak was decreased gradually, indicating that the crystalline quality of ZnO thin films was improved. The PL spectra show that the ZnO thin film grown on Zn buffer layer deposition duration of 15 min is the most suitable bule-light emission material. Meanwhile, a strong blue emission at 435nm dominated the room-temperature PL spectrum was mainly caused by the electron transition from the shallow donor level created by zinc interstitials to the top of the valence band, and the green emission at 530nm was mainly derived from oxygen vacancies.2. Highly c-axis oriented ZnO thin films were prepared on Si (100) substrates with various thicknesses of Zn buffer layers by RF magnetron sputtering system. The effect of the Zn buffer layer thickness on the microstructure and optical properties of ZnO thin films was studied. The full width at half maximums (FWHMs) of the ZnO (002) peaks first decreased to 0.071°when the Zn buffer deposition time reached 10 and 15 min, and then increased to 0.118°with further increasing the Zn buffer deposition time to 25 min. The grain size values of ZnO films with Zn buffer deposition time 0,10,15 and 25 min are 15.196, 11 5.344, 115.338, and 69.402 nm, respectively. The room temperature photoluminescence (PL) spectrum exhibited three dominated emission peaks located at 425 nm (2.92eV), 480 nm (2.58eV), and 525 nm (2.36eV) for all the samples annealed in oxygen ambience. The PL intensities of blue and green peaks first increased, and then decreased with increasing the Zn buffer layer deposition time.