Glancing-incidence X-ray analysis of ZnO thin films and ZnO/ZnMgO heterostructures grown by laser-MBE

In this paper, we report on glancing-incidence X-ray analysis (GIXA) of ZnO thin films, ZnO/ZnMgO and ZnO/Au heterostructures grown by laser molecular beam epitaxy (L-MBE) on c-plane Al₂O₃ substrates. The surface and interface sensitivity of X-ray reflectivity (XRR) has been exploited to evaluate the surfaces and interfaces of ZnO-based structures. The presence of smooth interfaces is responsible for the observation of intensity oscillation in XRR, which is well correlated to the clear Pendellosung fringes in high-resolution X-ray diffraction (HRXRD) measurements. In addition, the simulation of XRR data yields reliable and precise information of the layer thickness, the surface and interface roughness of each layer. The correlation of a smooth surface and high optical and structural quality is substantiated by time-integrated photoluminescence (TIPL) and XRD measurements of ZnO/ZnMgO heterostructure and ZnO thin films. The intense exciton-related emission, in contrast to a negligible deep-level radiation and the high c-axis orientation of ZnO films, indicates good optical and structural properties due to the superior surface and interface quality of our samples.