Temperature dependence of structural and optical properties of ZnO films grown on Si substrates by MOCVD

Growth of ZnO films on Si (111) substrates has been carried out at temperatures ranging from 300 to 475 degrees C by metal organic chemical vapor deposition (MOCVD) technique. A multilayer-tower structure was observed for the film deposited at 300 degrees C. For the films deposited at higher temperatures, nanorods accompanied with nanotubes were observed. The X-ray diffraction measurement shows that the film deposited at 425 degrees C has better crystalline quality than the others. Ultraviolet (UV) band edge emissions peaked at 3.27 eV with a full-width at half-maximum (FWHM) of 113-136 meV were observed for all of the films at room temperature. Low-temperature photoluminescence (PL) spectra at 3.5 K are dominated by neutral donor-bound excitons ((DX)-X-0) and donor-acceptor pair (DAP) emission. For the films deposited at lower temperature, a deep level emission peaked at 2.80 eV were observed. Temperature dependence of PL shows that the free exciton emission increases with increasing temperature and eventually dominates the PL spectra for the temperature higher than 80 K. Time-resolved PL were carried out at room temperature and 77 K. For the film deposited at 425 degrees C, the decay times of DAP and (DX)-X-0 at 77K were 293 and 389ps, respectively, while that of the band edge emission was 190ps at room temperature. (c) 2006 Elsevier B.V. AH rights reserved.