Effect of the initial thin Ti buffer layers on the quality of ZnO thin films grown on Si(111) substrates by MOCVD

Highly cc-axis oriented ZnO thin films were grown on Si(111) substrates by atmospheric-pressure metal-organic 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 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). For the ZnO thin film employing the initial thin Ti buffer layer, only (002) and (004) peaks were observed in the XRD spectrum and the FWHM of XRD rocking curves of ZnO(002) was 1.54∘, indicating that the ZnO thin film grown on Ti/Si(111) template was highly cc-axis oriented. The microscopic images showed regular hexagonal columns and uniform grains in the ZnO thin film. Meanwhile, a strong and sharp ultraviolet (UV) excitonic emission at 379 nm (3.27 eV) dominated the room-temperature photoluminescence (PL) spectrum without obvious emission related deep level defects and free exciton emission with a shoulder at the bound-exciton peak was observed at 10 K. These measurements indicate that the quality of ZnO thin films can be improved by introducing initial thin Ti buffer layers.