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InGaN/GaN double heterostructures and multiquantum wells (MQWs) have been successfully developed since more than 20 years for LED lightning applications. Recent developments show that state-of-the-art LEDs benefit from artificially generated V-pit defects. However, the control of structural and chemical properties plays a tremendous role. In this paper, we report on the lateral distribution of V-pit defects and photoluminescence of InGaN/GaN MQWs grown on thick GaN on patterned sapphire substrates. The synchrotron-based scanning X-ray diffraction microscopy technique K-map was employed to locally correlate these properties with the local tilt, strain, and composition of the InGaN/GaN MQW. Compositional fluctuation is the main factor for the variation of photoluminescence intensity and broadening. In turn, V-pit defects align along small-angle grain boundaries and their strain fields are identified as a reason for promoting the InGaN segregation process on a microscale.

Integration of functional oxides on Si substrates could open a pathway to integrate diverse devices on Si-based technology. Oxygen vacancies (Vo(··)) can strongly affect solid state properties of oxides, including the room temperature ferromagnetism (RTFM) in diluted magnetic oxides. Here, we report a systematical study on the RTFM of oxygen vacancy engineered (by Pr(3+) doping) CeO2 epitaxial thin films on Si substrates. High quality, mixed single crystalline Ce1-xPrxO2-δ (x = 0-1) solid solution films were obtained. The Ce ions in CeO2 with a fluorite structure show a Ce(4+)-dominant valence state in all films. The local crystal structures of the films were analyzed in detail. Pr doping creates both Vo(··) and PrO8-complex defects in CeO2 and their relative concentrations vary with the Pr-doping level. The RTFM properties of the films reveal a strong dependence on the relative Vo(··) concentration. The RTFM in the films initially increases with higher Pr-doping levels due to the increase of the F(+) center (Vo(··) with one occupied electron) concentration and completely disappears when x > 0.2, where the magnetic polaron concentration is considered to decline below the percolation threshold, thus long-range FM order can no longer be established. We thus demonstrate the possibility to directly grow RTFM Pr-doped CeO2 films on Si substrates, which can be an interesting candidate for potential magneto-optic or spintronic device applications.