X-ray absorption spectroscopy and Eu 3+ -emission characteristics in GaAs/SnO 2 heterostructure
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X‑ray absorption spectroscopy and Eu3+‑emission characteristics in GaAs/SnO2 heterostructure Cristina F. Bueno1 · Aline Y. Ramos2 · Aude Bailly2 · Eric Mossang2 · Luis V. A. Scalvi1 Received: 17 March 2020 / Accepted: 16 August 2020 © Springer Nature Switzerland AG 2020
Abstract X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are used for investigating heterostructure samples of GaAs/SnO2. XANES data are used for analyzing the local organization around Eu in the heterostructure formed by GaAs and Eu-doped SnO2. The differences between the XANES data for these samples and data obtained for Eu-doped S nO2 thin films, deposited on glass substrate, are assumed as responsible for the differences in the photoluminescence (PL) spectra concerning the Eu3+ emission, since films deposited on glass substrate do not present E u3+ PL transitions until the annealing temperature is rather high. E u3+ emission is explored using two different excitation sources: 350 nm from a K r+ laser (above S nO2 energy bandgap) and 488 nm from an A r+ laser (below 3+ SnO2 bandgap energy). The existence of more organized regions around the Eu site observed for the heterostructure surface may be associated with the E u3+ luminescent emission. The main and secondary features in the XANES show that there are differences in the average local Eu environment for the SnO2: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. Keywords Tin dioxide · Gallium arsenide · Heterostructure · Electro-optical properties
1 Introduction There is currently great interest in semiconductor oxides and their heterostructures due to their potential applications in spintronic devices [1], photocatalysis [2], lightemitting diodes, lasers [3] and solar cells [4]. Tin dioxide (SnO2) is one of the most used semiconductor oxides, related to outstanding properties such as high transparency in the visible range, high reflectivity in the infrared [5] and high n-type free carrier concentration [6], even in the undoped form, which may lead to a high conductivity when electron scattering phenomena are prevented. Doped SnO2 thin films are used as transparent electrodes in several systems: perovskite solar cells [7], lithium-ion
batteries [8] and organic photovoltaic cells [9]. The interest in doping semiconductor oxides with rare-earth (RE) ions has increased considerably, due to its radiative emissions over a large wavelength range, which allows several types of applications such as LEDs, displays, telecommunications, analytical sensors and biomedical images [10]. Its properties depend on the location of the rare-earth ion incorporation within the crystalline lattice of the matrix [11]. X-ray absorption near edge structure (XANES) is the features up to 50 eV
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