RESUMEN
We have studied in this work the effect of increasing structural disorder on the persistent luminescence of a Cr3+ doped zinc gallate spinel. This disorder was introduced by progressive substitution of Zn2+ by Mg2+ ions, and was studied by photoluminescence, X-ray diffraction, extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy. It was found that increasing the Mg/Zn substitution decreases the number of Cr3+ in undistorted sites and increases the number of Cr3+ with neighbouring antisite defects and with neighbouring Cr3+ ions (referred to as Cr clusters), which in turn decreases the intensity of persistent luminescence. Both XANES and EPR spectra could be simulated by a linear combination of Cr3+ spectra with three types of Cr3+ environments. The increasing disorder was found to be correlated with a decrease of the average Cr-O bond length and a decrease of crystal field strength experienced by Cr3+ ions.
RESUMEN
We propose a simple sample preparation technique of x-ray absorption fine structure (XAFS) for its application to the individual layer of practical compound semiconductor devices. An epitaxial lift-off process enables the investigation of pure uppermost thin epitaxial layer without containing information of the bottom-side layers as well as substrate. The plain procedure offers smooth thin film with desired thickness preserving its crystallographic structure, suitable for the measurement. We carry out XAFS measurements for 2.0 and 0.2 microm thick GaAs epitaxial layer at transmission and fluorescence mode, respectively. Clear extended-XAFS oscillation is obtained, and the radial distribution function of which deduces accurate first nearest-neighbor Ga-As bond length to be 2.46 A for both the samples. That shows the feasibility of the proposed technique for the analysis of the precise atomic configurations of thin film semiconductors.
