Structural and optical properties of in situ Eu-doped ZnCdO/ZnMgO superlattices grown by plasma-assisted molecular beam epitaxy

In situ Eu-doped {ZnCdO/ZnMgO} superlattices (SLs) with varying ZnCdO and ZnMgO sublayer thicknesses were deposited using plasma-assisted molecular beam epitaxy. The impact of Eu doping in ZnCdO quantum wells on the structural and optical properties of the superlattices was examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), cathodoluminescence (CL) combined with scanning electron microscopy (SEM), temperature-dependent photoluminescence (PL), photoluminescence excitation (PLE), and UV-Vis spectroscopy. High-resolution cross-sectional TEM images and SIMS depth profile measurements confirmed the high quality of the as-grown {ZnCdO/ZnMgO} periodic structures. XRD analysis indicated a single-phase ZnO wurtzite structure in the samples. The CL spectra of both as-grown and annealed {ZnCdO/ZnMgO}₂₂ SLs doped with Eu exhibited a dominant near-edge peak, alongside a broad band attributed to deep-level emissions. Characteristic emission peaks corresponding to the transitions of Eu³⁺ ions were observed. Furthermore, the intensity of red luminescence increased after annealing at 700 °C; however, further increases in annealing temperature led to a decrease in intensity. Analysis of the CL spectra revealed that native defects play a role in energy transfer from the ZnCdO host matrix to the Eu³⁺ ions.