Effects of the crystallite mosaic spread on integrated peak intensities in 2θ-ω measurements of highly crystallographically textured ZnO thin films

Abstract

We report x-ray diffraction (2θ-ω and rocking curve) and transmission electron microscopy measurements on crystallographically textured ZnO thin films of varying thicknesses and crystallite mosaic spread deposited by pulsed laser deposition on Si. The integrated areas of the (0002) ZnO reflections in 2θ-ω mode do not scale with film thickness and in some cases show discrepancies of two orders of magnitude compared to expectations based solely on sample thicknesses. Intensity differences of this type are regularly used in the literature as indications of differences in sample crystallinity or crystal quality. However transmission electron microscopy data of our samples show no evidence of amorphous deposits or significantly varying crystal quality in different films. X-ray rocking curves of these samples do show substantial variations in the mosaic spread of crystallites in the ZnO films which are the origin of the differences in integrated areas of the (0002) ZnO reflections in 2θ-ω measurements. We outline a generally applicable model to treat the 2θ-ω mode peak intensities which shows good agreement with the experimental data (to within an order of magnitude) and which is much simpler than utilizing a full reciprocal space map approach to understand the x-ray diffraction data. We conclude that the normalized integrated intensity of the (0002) ZnO reflection in highly crystallographically textured ZnO thin films is strongly dependent on the rocking curve width in addition to the film thickness and the use of such intensities in isolation as measures of the thin film crystallinity or crystal quality, without reference to the rocking curve width, is likely to be misleading when making judgments of such aspects of the thin film structure