Abstract
The evolution of the strain state as a function of layer thickness of (0001) oriented ZnO epitaxial films grown by pulsed-laser deposition on Si (111) substrates with a thin oxide Y <sub>2</sub> O <sub>3</sub> buffer layer was investigated by high resolution X-ray diffraction (XRD). The ZnO layers experience a tensile strain, which gradually diminishes with increasing layer thickness. Regions with a nearly strain-free lattice develop as the layer thickness exceeds a critical value and are correlated with the emergence of the <1120> oriented crack channels. The influence of the biaxial strain to the vibrational and optical properties of the ZnO layers were also studied by micro-Raman, optical reflectance, and photoluminescence. The deformation-potential parameters, a <sub>λ</sub> and b <sub>λ</sub> , of the E <sub>2</sub> (high) phonon mode are determined to be -740.8 ± 8.4 and -818.5 ± 14.8 cm <sup>-1</sup> , respectively. The excitonic transitions associated with the FX <sub>A</sub> , FX <sub>B</sub> , and D°X <sub>A</sub> emissions and the A-exciton binding energy all show linear dependence on the in-plane strain with a negative slope. © 2012 The Royal Society of Chemistry.