| ZnO, as a new generation of wide direct band-gap semiconductor, has larger exciton binding energy (60 meV), better chemical stability, lower growth temperature etc, compared with ZnSe and GaN. ZnO is a kind of promising material used to prepare UV lighting emitting diodes and diode lasers. Especially in January 2005, the stable and reliable p-type ZnO thin films, and ZnO homostructural p-i-n junctions were successfully prepared by Tohoku University. Meanwhile, the violet electroluminescence from the junctions was realized at room-temperature, which attracting wide attention of researchers. However, applicable ZnO light emitting devices have not been fabricated yet.The ZnO film growths were performed using a home-made atmospheric pressure MOCVD system. The ZnO: H thin films were grown on sapphire substrates (c-Al2O3) and the behaviors of hydrogen in ZnO: H thin films were investigated. Meanwhile, the growths of ZnO thin films on silicon substrates were also studied.ZnO: H thin films were prepared by adding a little of H2 gas in the reaction gas when depositing ZnO films using atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) with carrier gas of nitrogen. Zn(C2O5)2 (DEZn) and H2O were used as Zn and O precursors, respectively. The full widths at half maximum (FWHM) of the (002) and (102) omega rocking curves of ZnO: H films were 166arcsec and 293arcsec, respectively, which were smaller than the ZnO films undoped with hydrogen, indicating the improvement of crystal quality of ZnO:H films by adding hydrogen in reaction gas. The room temperature photoluminescence (PL) spectra showed that there was a strong ultraviolet (UV) emission at 380nm Meanwhile, a strong hydrogen-related bound exciton peak (I4) at 3.363eV and its two electron satellite (TES) at 3.331eV could be observed in the low temperature PL spectra measured at 10K. UV-visible spectroscopy showed hydrogen acts as donor which provide free electrons and increase the electron concentration. The oxygen-hydrogen local vibrational mode in ZnO:H films were observed in IR spectroscopy at room temperature. In addition, the effect of annealing temperature on thermal-stability of hydrogen in ZnO: H films and the structural properties of ZnO:H films were investigated. XRD results showed annealing could decrease the density of defects in films and improve the quality of ZnO:H films. By observing the change of intensity of I4 peak in low-temperature photoluminescence spectra at 10 K and the intensity of O-H band in IR spectra at room temperature during the annealing process, the thermal stability of hydrogen in ZnO:H films was investigated. These results showed that the intensity of I4 peak and O-H band would decrease with the annealing temperature increasing, indicating the hydrogen would evolve out of ZnO:H films annealed at high temperature. Finally, the influence of growth temperature on hydrogen incorporation in ZnO films was investigated by changing the growth temperature. The low-temperature photoluminescence spectra showed that it is difficult for hydrogen to incorporate into ZnO thin films grown at high temperatures (900℃) even in the hydrogen-present ambient.Highly c-axis oriented ZnO thin films were grown on Si (111) substrates by atmospheric-pressure metalorganic chemical vapor deposition. It is the first time that a thin titanium layer is applied as the initial buffer layer to protect the Si surface from oxidation and reduce the lattice mismatching between Si substrates and ZnO thin films. The thickness of Ti buffer layer was 2 nm approximately. The effect of the initial thin Ti buffer layers on the quality of ZnO thin films was studied with X-ray diffraction (XRD), interference microscopy, scanning electron microscopy (SEM) and photoluminescence (PL). The results showed that the ZnO thin film grown on Ti/Si (111) template was highly c-axis oriented and had good photoluminescence properties. These measurements indicate that the quality of ZnO thin films can be improved by introducing the initial thin Ti buffer layers. Meanwhile, the effects of zinc precursors and the thickness of ZnO low-temperature buffer layer on the growth of ZnO thin films on Ti/Si templates were studied. The results indicated that DEZn was the superior zinc precursor for the MOCVD growth of ZnO compared with DMZn. The most suitable buffer layer thickness was obtained.Finally, ZnO thin films were growth on the Ag/Si(111) templates by AP-MOCVD. Zn(C2H5)2 (DEZn) and H2O were used as Zn and O procursors, respectively. The effect of the growth conditions on the properties of ZnO films was investigated by adjusting the substrate temperature, growth rate and the flux of DEZn during growth of low-temperature ZnO buffer layer. The results showed that the metal Ag is an effective initial layer for the growth of high-quality ZnO films on Si(111) substrates.This work was supported by the 863 project (contract No. 2003AA302160) and China foundation for development of electronic information technology.
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