X-ray absorption spectroscopy and Eu-emission characteristics in GaAs/SnO heterostructure

X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are used for investigating heterostructure samples of GaAs/SnO. XANES data are used for analyzing the local organization around Eu in the heterostructure formed by GaAs and Eu-doped SnO. The differences between the XANES data for these samples and data obtained for Eu-doped SnO thin films, deposited on glass substrate, are assumed as responsible for the differences in the photoluminescence (PL) spectra concerning the Eu emission, since films deposited on glass substrate do not present Eu PL transitions until the annealing temperature is rather high. Eu emission is explored using two different excitation sources: 350 nm from a Kr laser (above SnO energy bandgap) and 488 nm from an Ar laser (below SnO bandgap energy). The existence of more organized regions around the Eu site observed for the heterostructure surface may be associated with the Eu luminescent emission. The main and secondary features in the XANES show that there are differences in the average local Eu environment for the SnO:Eu isolated thin films and heterostructures, being more organized in the latter. Electrical characterization evidences that the portion of the resistivity reduction that corresponds to photo-ionized intrabandgap states is responsible for the persistent photoconductivity phenomenon in the heterostructures.