Growth and Modeling of ZnO and the Characterization of Epitaxial Thin Films by means of Synchrotron Radiation : A Comprehensive Study of Synthesis, Characterization and Modeling of Selected Model Structures

Abstract

ZnO is a promising material that recently attracts wide interest due its outstanding properties that make it suitable for applications in short wavelength optoelectronic devices, as well as high temperature electronics. Producing both large and pure single crystals of ZnO is however challenging. This study presents successful growth of up to 3 mm ZnO single crystals, grown by the chemical vapour transport method and the characterization of these crystals, using optical microscopy, X-ray diffraction and scanning electron microscopy.

The polar (0001) and (000-1) surfaces of ZnO in oxygen and zinc rich atmospheres have also been thoroughly investigated by using ab initio calculations to predict the surface structures for varying coverage of oxygen and zinc on the two different surfaces.

Finally, a method for characterizing nanometer sized thin films using a six-axis goniometer at the BM01A beam line at the ESRF in France has also been developed. The goniometer allows for high flexibility, which is useful for thin film characterization. By mounting the thin film sample like a single crystal and using X-rays with low incident angles, it has been possible to reproduce previously obtained information about the selected samples, although in more detail and in a more efficient manner, due to the high brilliance X-rays available at the synchrotron, and the large area CCD-detector accessible at the beam line.

Details about the experimental setup as well as results for a model system, a Co3O4 thin film on a α-Al2O3 substrate, will be presented among other systems of interest. Various substrates used for thin film deposition and their suitability for SXRD characterization has also been investigated, proving for instance that the phonon scattering in silicon results in broad diffuse scattering that overshadows thin film reflections and consequently complicates characterization of thin films.