Pulsed laser reactive ablation of (0001)-textured ZnO optical waveguiding films on alpha-SiO2

Using Zn targets in a 100 Pa oxygen ambient at substrate temperatures of 275-425 degrees C, completely (0001)-textured ZnO thin films have been deposited on (0001)-oriented alpha-SiO2 substrates by the pulsed laser reactive ablation technique. The effects of deposition parameters on the microstructures of the films have been analysed. The full-width-at-half-maximum (FWHM) 2 theta angle of the (0002) X-ray reflection reached its minimum of 0.320 degrees for the ZnO films grown at substrate temperatures between 325 and 375 degrees C. The films proved to be dense, smooth, transparent and colourless. Thick lamina-like grains were observed in the ZnO films by scanning electron microscopy. The reflective indices of the films vs. wavelength calculated from the measured oscillated optical transmittance were close to those of bulk ZnO crystal. The band gap of the piezoelectric semiconductor ZnO was estimated as 3.28 eV. Favourable optical waveguiding properties of the films have been demonstrated by the observation of sharp m-lines from the transverse electric (TE) modes excited by the prism-coupling method.