Channeling contrast microscopy of epitaxial lateral overgrowth of ZnO/GaN films

Abstract

As a wide band gap (3.37 eV) semiconductor, ZnO is of great interest for applications in opto- and nano-electronics, as technologies of synthesis for ZnO layers are developed. It has been reported that the blue-UV generation can be realized in ZnO thin-films, ZnO whiskers, p-type ZnO films and thin-film diode structures at room temperature. Zinc oxide crystal of high quality with a reduced number of crystal defects can be grown on a sapphire substrate. The density of dislocations can be decreased by orders of magnitude using epitaxial lateral overgrowth (ELO), which employs a SiO2 mask layer to act as a stop layer for dislocations in so called wing areas. Rutherford Backscattering Spectrometry (RBS) is a powerful tool for the quantitative characterization of the depth profile and the crystallinity of such structures, and channeling contrast microscopy (CCM), which employs a focused ion beam in order to obtain laterally resolved channeling yield data, is ideally suited to determine micro structural characteristics, (e.g. defect densities, tilts in lattice planes, strain) of such samples. Here we report results from proton channeling contrast measurements of laterally overgrown ZnO thin films. The results show that high crystal quality ZnO films can be grown using the ELO method. Cross-sectional scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and CCM are used to study the morphology and microstructure of the ELO ZnO films. © 2007 Elsevier B.V. All rights reserved.