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International audience; (Tb, Eu)–co-doped ZnO films with about 3 at.% total doping rate were grown by magnetron sputtering on Si substrate. Post annealing treatments were performed at 973–1373 K in continuous nitrogen flow to investigate the transformation of microstructural and optical characteristics by means of X-ray diffraction, transmission electron microscopy, photoluminescence and electroluminescence. For annealing temperatures lower than 1073 K, segregation of Eu and Tb was observed mainly at the film/substrate junction. For temperatures higher than 1173 K, additional phases appeared, namely, Zn2SiO4 and rare earth silicates. For the highest temperature investigated (1373 K), only silica and rare earth silicates remained in the film due to Zn evaporation. PL measurements indicated a very intense Eu emission associated with the presence of rare earth silicate inclusions. Energy transfer from Tb towards Eu was evidenced in this secondary phase. At last, based on these preliminary works, a (Tb, Eu)–co-doped ZnO/Si electroluminescent structure was produced and showed very promising results paving the way for very thin ZnO based light emitting diodes.

By using ZnO thin films doped with Ce, Tb or Eu, deposited via radiofrequency magnetron sputtering, we have developed monochromatic (blue, green and red, respectively) light emitting devices (LEDs). The rare earth ions introduced with doping rates lower than 2% exhibit narrow and intense emission peaks due to electronic transitions in relaxation processes induced after electrical excitation. This study proves zinc oxide to be a good host for these elements, its high conductivity and optical transparency in the visible range being as well exploited as top transparent electrode. After structural characterization of the different doped layers, a device structure with intense electroluminescence is presented, modeled, and electrically and optically characterized. The different emission spectra obtained are compared in a chromatic diagram, providing a reference for future works with similar devices. The results hereby presented demonstrate three operating monochromatic LEDs, as well as a combination of the three species into another one, with a simply-designed structure compatible with current Si technology and demonstrating an integrated red-green-blue emission.

ver the last few decades, significant progress has been made with inorganic materials to enable them as next generation photovoltaic materials that can fulfil the demands of green energy. Cu2ZnSn(S,Se)4stands out as a p-type absorber material due to exemption from scarce and strategic elements and its similarities with Cu2InGa(S,Se)4. Organic materials such as fullerenes and its derivatives are effective n-type semiconductors. We report the usage of n-type fullerene materials with kesterite-based absorbers in a thin film polycrystalline solar cell for the partial substitution of the CdS buffer layer with C60or C70fullerenes. Impedance measurements reveal that using C60as an interlayer increases the built-in potential, suggesting reduction in the interfacial recombination. This promotes charge conduction, resulting in an increased open circuit voltage and thus device performance.

International audience; Ce-doped SiO x N y and SiAlON matrices are promising materials for blue LED applications. The uniqueness of this approach stems from the fact that SiO x N y , as a host, combines specific properties of individual SiO x and SiN y matrices like solubility, efficient emission, 5 eV gap, with a broad excitation range from 400 nm to 500 nm of Ce 3+ ions due to the 4f-5d transitions. Furthermore, the co-doping with aluminum enhances the Ce 3+ emission. In this work, we fabricated electroluminescent devices using SiO x N y :Ce 3+ and SiAlON:Ce 3+ as active layers and investigated the resulting emission under optical and electrical excitations as a function of nitrogen, cerium and aluminum concentrations. I-V measurements were conducted to determine the SiO x N y :Ce 3+ layer electrical parameters. Charge transport through the devices obeys the Poole-Frenkel conduction mechanism. It was demonstrated that by optimizing the SiO x N y :Ce 3+ growth parameters, an improvement of electroluminescence yield can be achieved with a maximum intensity obtained for devices with cerium content of 4 at.%. Rare earth (RE) doped silicon based materials have been extensively investigated in the past few years. Various hosts were doped with Er 3+ ions that emit at 1.5 μm corresponding to the maximum transparency of silica used in telecommunications. 1 For the Ce 3+ ion, up to date, only a few studies have been reported on its electrolu-minescence (EL). 2 Among the silicon-based matrices, silica (SiO 2) and silicon nitride (Si 3 N 4) have been explored; however, each of them present certain advantages and drawbacks. In the case of silica matrices , achievement of strong RE 3+ ions emission is limited by a low excitation cross section, 3 a low RE solubility as well as RE clusters formation. 4,5 However, the main drawback limiting SiO 2 : RE 3+ light emitting applications comes from the large bandgap of the matrix (∼9 eV) resulting in low electrical conductivity. On the other hand, Si 3 N 4 with a smaller energy bandgap (4 eV) and reduced tendency of the RE to form clusters, seems to be more suitable for RE doping. 6-8 However, despite these advantages, the emission efficiency from RE 3+ ions in a nitride matrix is much lower than in silica matrix. 9 To capitalize on the RE doping advantages offered by both oxide and nitride silicon matrices, a Ce-doped SiO x N y matrix has been explored by Ramirez et al. 10 It was reported that the maximum EL peak from Ce 3+ ion shifted from 400 nm to 476 nm as function of the nitrogen concentration (i.e. the nephelauxetic effect). 10,11 Koao et al. showed that aluminum co-doping Ce-doped SiO 2 glasses lead to an enhancement of photoluminescence emission. 12 In this work, Ce-doped Si(Al)O x N y layers with a typical thickness of 50 nm were grown by sputter de-position. Photoluminescence (PL) from the SiO x N y :Ce 3+ layers and EL from this active layer were examined for device performance as a function of growth parameters and material composition. Experimental Active layer preparation.-The devices were fabricated in a few step processes. First, the Ce-doped SiO x N y active layer was grown by magnetron reactive sputtering with 8 sccm for Ar and 2 sccm for N 2 on 2-inch diameter (001) p-type silicon wafers. During the growth, the chamber base pressure was fixed at 3 mTorr and the substrate temperature was at room temperature (RT). Additional information on the growth process can be found in the following Reference 11. z Samples were deposited from CeO 2 , Al and Si targets with density of power varied from 0 to 2.1 W.cm −2 , 0.3 to 0.75 W.cm −2 and fixed at 4.5 W/cm 2 , respectively. As-deposited films were then thermally annealed in the 600°C to 1200°C temperature range for 1 h, in nitrogen atmosphere at ambient pressure. Device fabrication.-Figure 1 illustrates the typical fabricated device structure with the indicated specific layers thicknesses. The individual indium tin oxide (ITO) top electrical contacts were deposited on the SiO x N y :Ce 3+ layer by electron beam evaporation using a shadow mask having a set of circular holes with a diameter of 200 μm. In 2 O 3 /SnO 2 (90%/10%) pellets with a diameter of 1 mm or 2 mm were used as sputtering targets. An oxygen flux was maintained in the sputtering chamber during deposition cycle to prevent the formation of oxygen defects in the transparent conducting layer, which would potentially cause EL from ITO layer. The ITO layer thickness was 200 nm. The SiO x N y :Ce 3+ /ITO structure was heated up at a ramp rate of 15°C/min from RT to 600°C and annealed for 1 h in a nitrogen atmosphere at ambient pressure. The bottom metal contact, a 200-nm-thick Al layer, was deposited at RT on the back of the silicon substrate. Figure 1. Schematic layout of fabricated Al/p-Si/SiO x N y :Ce 3+ /ITO device.

This is the peer reviewed version of the following article: Lopez-Garcia, A. [et al.]. Ultrathin wide-bandgap a-Si:H-based solar cells for transparent photovoltaic applications. "Solar RRL", 1 Gener 2022, vol. 6, núm. 1, p. 2100909:1-2100909:8. , which has been published in final form at https://onlinelibrary.wiley.com/doi/full/10.1002/solr.202100909. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Herein, the fabrication of UV-blue selective transparent solar cells based on ultrathin (

In this work, the relation between the photovoltaic and resistive switching (RS) properties of metal-oxide-semiconductor devices containing Si nanocrystal (Si NC) superlattices is investigated. A first approximation concludes that the low resistance state achieved by the RS process allows for enhanced photogenerated carrier extraction when compared to the high resistance state and pristine devices. By using different current compliance values during the electroforming process, the low resistance state is further modified, improving its conductivity and the collection probability of photogenerated carriers. Conversion efficiency is enhanced by at least one and up to five orders of magnitude by applying different electroforming processes. In addition to promoting the RS properties in these devices, spectral response measurements demonstrate that Si NCs are partially responsible for the optical absorption, and that their contribution is maintained after electroforming. We thus conclude that the proposed methodology can improve the conversion efficiency of this and other multijunction solar cells or structures that also exhibit RS properties. Through RS, a dense network of conductive filaments is promoted in the insulating region, which reduces the travel distance of photocarriers for their collection., This work was financially supported by the Spanish Ministry of Economy, Industry and Competitiveness (TEC2016-76849-C2-1-R) and the German Research Foundation (ZA191/27-3 and ZA191/33-1). J.L.F. acknowledges financial support from the subprogram “Ayudas para la Formación de Profesorado Universitario” (FPU16/06257) from the Spanish Ministry of Education, Culture and Sports.

The increasing need for efficient memories with integrated functionalities in a single device has led the electronics community to investigate and develop different materials for resistive switching (RS) applications. Among these materials, the well-known Si nanocrystals (NCs) have demonstrated to exhibit RS properties, which add to the wealth of phenomena that have been studied on this model material platform. In this work, we present ZnO/Si NCs/p-Si resistive switching devices whose resistance state can be electrically read at 0 V under the application of low-power monochromatic illumination. The presented effect is studied in terms of the inner structural processes and electronic physics of the device. In particular, the creation of conductive filaments through the Si NC multilayers induces a low-resistance path for photogenerated carriers to get extracted from the device, whereas in the pristine state charge extraction is strongly quenched due to the insulating nature of the NC-embedding SiO2 matrix. In addition, spectral inspection of the generated photocurrent allowed unveiling the role of Si NCs in the reported effect. Overall, the hereby shown results pave the way to obtain memories whose RS state can be read under low-power conditions.

In the last few years, the emergence of studies concerning the resistive switching (RS) phenomenon has resulted in the finding of a large amount of materials being capable of acting as an active layer in such devices, i.e., the layer where the change in resistance takes place. Whereas the normal operation consists of the electrical readout of the modified resistance state of the device after electrical writing, electro-photonic approaches seek the involvement of light in these devices, be it either for the active Set or Reset operations or the readout. We propose in this work silicon nanocrystal multilayers (Si NC MLs) as an active material for being used in RS devices, taking advantage of their outstanding optical properties. The resistance states of Si NC MLs were obtained by electrical excitation, whose readout is carried out by electrical and electro-optical means, thanks to a distinguishable electroluminescence emission under each state. To achieve this, we report on an adequate design that combines both the Si NC MLs with ZnO as a transparent conductive oxide, whose material properties ensure the device RS performance while allowing the electro-optical characterization. Overall, such an occurrence states the demonstration of a Si NCs-based electroluminescent RS device, which paves the way for their future integration into photonic integrated circuits.

Transparent conducting oxides have excellent electrical and optical properties that can be exploited to enhance the performance of devices for a large variety of applications such as integrated optoelectronics, biosensing, light detection or resistive memories. In addition, they have also shown the ability to be integrated in silicon CMOS devices and therefore the potential for mass production. In this work, we will focus on ITO and ZnO for different application fields of integrated optoelectronics, memristors and biosensing.

International audience

The achievement of an efficient all-Si electrically-pumped light emitter is a major milestone in present optoelectronics still to be fulfilled. Silicon nanocrystals (Si NCs) are an attractive material which, by means of the quantum confinement effect, allow attaining engineered bandgap visible emission from Si by controlling the NC size. In this work, SiO2-embedded Si NCs are employed as an active layer within a light-emitting device structure. It is demonstrated that the use of an additional thin Si3N4 interlayer within the metal-insulator-semiconductor device design induces an enhanced minority carrier injection from the substrate, which in turn increases the efficiency of sequential carrier injection under pulsed electrical excitation. This results in a substantial increase in the electroluminescence efficiency of the device. Here, the effect of this Si3N4 interlayer on the structural, optical, electrical, and electro-optical properties of a Si NC-based light emitter is reported, and the physics underlying these results is discussed.

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole−Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

We report a joint experimental and theoretical study of the lattice dynamics of cubic Tb2O3. Up to 16 optical Raman‐active modes have been observed with polarized and unpolarized Raman scattering measurements on a high‐quality Tb2O3 single crystal. The measured wavenumbers have been compared with those of other rare‐earth (RE) and related sesquioxides with cubic (C‐type or bixbyite) structure. First‐principles calculations have allowed us to assign the symmetry of the experimentally observed Raman‐active modes. Additional lattice‐dynamical calculations on the related cubic RE sesquioxides Dy2O3, Gd2O3, Eu2O3, and Sm2O3 indicate that the phonon wavenumbers of the Raman‐active modes in these compounds are monotonically reduced with increasing the lattice parameter along the Dy2O3‐Tb2O3‐Gd2O3‐Eu2O3‐Sm2O3 series, thus prompting for a revision of the experimental Raman spectra of some of these compounds (mainly Eu2O3 but also Gd2O3)., This study was supported by the Spanish Ministerio de Economía y Competitividad under Projects MAT2015‐ 71070‐REDC, MAT2015‐71035‐R, MAT2016‐75586‐C4‐2‐ P/3‐P, and FIS2017‐2017‐83295‐P.

In this work, the fabrication and the structural, optical and electrical properties of Al-Tb/SiO2 nanomultilayers have been studied. The nanomultilayers were deposited by means of electron beam evaporation on top of p-type Si substrates. Optical characterization shows a narrow and strong emission in the green spectral range, indicating the optical activation of Tb3+ ions. The electrical characterization revealed conduction limited by the electrode, although trapped-assisted mechanisms can also contribute to transport. The electroluminescence analysis revealed also emission from Tb3+ ions, a promising result to include this material in future optoelectronics applications as integrated light-emitting devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was financially supported by the Spanish Ministry of Economy and Competitiveness (TEC2016-76849-C2-1-R and MAT2015-71035-R). O.B. also acknowledges the subprogram “Ayudas para Contratos Predoctorales para la Formaci on de Doctores” from the Spanish Ministry of Economy and Competitiveness for economical support.

In this work, the electroluminescence (EL) emission of zinc oxide (ZnO)/Si nanocrystals (NCs)-based light-emitting devices was studied under pulsed electrical excitation. Both Si NCs and deep-level ZnO defects were found to contribute to the observed EL. Symmetric square voltage pulses (50-μs period) were found to notably enhance EL emission by about one order of magnitude. In addition, the control of the pulse parameters (accumulation and inversion times) was found to modify the emission lineshape, long inversion times (i.e., short accumulation times) suppressing ZnO defects contribution. The EL results were discussed in terms of the recombination dynamics taking place within the ZnO/Si NCs heterostructure, suggesting the excitation mechanism of the luminescent centers via a combination of electron impact, bipolar injection, and sequential carrier injection within their respective conduction regimes.

The optical, electrical and electro-optical properties of metal-insulator-semiconductor (MIS) devices containing Si-rich silicon nitride (SRN) films are reported. The photoluminescence and optical absorption characterization evidences that optically active centers present a defective nature. As a consequence, a Poole-Frenkel type transport mechanism is considered, which is in agreement with the electrical results. The electro-optical performance of the devices has been found to be strongly modulated by the poly-Si electrode transmittance. After taking into account this contribution, EL emission has been studied, being the obtained spectra in accordance to the PL ones, which proofs that the same luminescent centers are also being excited electrically. The electrical response of the devices has been investigated under light excitation, showing induced photocurrent and photoconductivity, which makes SRN a good candidate material for photovoltaic applications.

The electro-optical properties of devices containing Si-rich silicon nitride (SRN) thin films, deposited by means of low-pressure chemical-vapor deposition (LPCVD), are studied. After optically evidencing the presence of defects in our films, a Poole-Frenkel conduction mechanism has been considered, which is in agreement with electrical experiments. We found that the poly-Si layer strongly modulates the electroluminescence and light absorption of the devices. In addition, they showed photocurrent and photoconductivity under illumination, SRN becoming a promising material for photovoltaic applications.

Fabrication and organosilane-functionalization and characterization of nanostructured ITO electrodes are reported. Nanostructured ITO electrodes were obtained by electron beam evaporation, and a subsequent annealing treatment was selectively performed to modify their crystalline state. An increase in geometrical surface area in comparison with thin-film electrodes area was observed by atomic force microscopy, implying higher electroactive surface area for nanostructured ITO electrodes and thus higher detection levels. To investigate the increase in detectability, chemical organosilane-functionalization of nanostructured ITO electrodes was performed. The formation of 3-glycidoxypropyltrimethoxysilane (GOPTS) layers was detected by X-ray photoelectron spectroscopy. As an indirect method to confirm the presence of organosilane molecules on the ITO substrates, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were also carried out. Cyclic voltammograms of functionalized ITO electrodes presented lower reduction-oxidation peak currents compared with non-functionalized ITO electrodes. These results demonstrate the presence of the epoxysilane coating on the ITO surface. EIS showed that organosilane-functionalized electrodes present higher polarization resistance, acting as an electronic barrier for the electron transfer between the conductive solution and the ITO electrode. The results of these electrochemical measurements, together with the significant difference in the X-ray spectra between bare ITO and organosilane-functionalized ITO substrates, may point to a new exploitable oxide-based nanostructured material for biosensing applications. As a first step towards sensing, rapid functionalization of such substrates and their application to electrochemical analysis is tested in this work. Interestingly, oxide-based materials are highly integrable with the silicon chip technology, which would permit the easy adaptation of such sensors into lab-on-a-chip configurations, providing benefits such as reduced size and weight to facilitate on-chip integration, and leading to low-cost mass production of microanalysis systems.

Multilayers consisting of silicon nanocrystals (Si NCs) and SiO2 are successfully fabricated by electron beam evaporation, using pure Si and SiO2 targets in an oxygen-rich atmosphere for alternately depositing silicon-rich oxide (SRO) layers and SiO2 barriers, respectively. A post-deposition annealing process is carried out at different temperatures in order to achieve the Si precipitation in the form of nanocrystals. The stoichiometry of the layers is determined by X-ray photoelectron spectroscopy, which confirms the controlled silicon oxidation in order to attain SRO layers. Transmission electron microscopy and Raman-scattering measurements confirm the presence of crystalline Si-nanoprecipitates. Photoluminescence spectra from the Si NC samples can be deconvolved into two contributions, whose dynamics suggest that two different luminescent centers are responsible for the optical emission of the samples. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, This work was financially supported by the Spanish Ministry of Economy and Competitiveness (TEC2016‐76849‐C2‐1‐R and MAT2015‐71035‐R). O.B. also acknowledges the subprogram “Ayudas para Contratos Predoctorales para la Formación de Doctores” from the Spanish Ministry of Economy and Competitiveness for economical support. J.L.F. also acknowledges the subprogram “Ayudas para la Formación de Profesorado Universitario” from the Spanish Ministry of Education, Culture and Sports for economical support.

Electron beam evaporation was employed in order to fabricate Al- and Tb-codoped Si oxide multilayers via the delta-doping approach. This methodology permits the control of the rare-earth (RE) separation along the growth direction with nanometric resolution. To investigate the control of the RE separation in the growth direction, different SiO 2 thicknesses were studied. After deposition, the samples were submitted to different annealing processes for 1 h in N 2 , at temperatures ranging from 700 to 1100 °C. Photoluminescence experiments reveal narrow emissions ascribed to Tb 3+ ions in all samples, with an intensity variation depending on the oxide thickness and annealing temperature. In addition, the incorporation of Al under different spatial configurations produced an enhancement of more than one order of magnitude in the photoluminescence intensity, in respect to the best sample without Al. Finally, time-resolved measurements were carried out in order to determine the 5 D 4 → 7 F 5 transition dynamics, obtaining a decay time of ~1.6 ms ascribed to the Tb 3+ ions.

The electroactivity of nanostructured indium tin oxide (ITO) has been investigated for its further use in applications such as sensing biological compounds by the analysis of redox active molecules. ITO films were fabricated by using electron beam evaporation at different substrate temperatures and subsequently annealed for promoting their crystallization. The morphology of the deposited material was monitored by scanning electron microscopy, confirming the deposition of either thin films or nanowires, depending on the substrate temperature. Electrochemical surface characterization revealed a 45 % increase in the electroactive surface area of nanostructured ITO with respect to thin films, one third lower than the geometrical surface area variation determined by atomic force microscopy. ITO surfaces were functionalized with a model organic molecule known as 6-(ferrocenyl)hexanethiol. The chemical attachment was done by means of a glycidoxy compound containing a reactive epoxy group, the so-called 3-glycido...

In this invited talk, we will report our latest advances in the field of nanostructured silicon-based light emitters with special emphasis in those that are rare earth doped. We have recently shown that it is possible to push external quantum efficiencies over the 10% by fine tuning the material composition and by using a new device concept that we have called hot electron engineering. Most of the rare earth amount introduced in the host material must be optically active. This can be accomplished by using a deposition method that introduces the rare earth during film growth and by a suitable passivating annealing procedure that: i) does not promote rare earth precipitation and clustering; ii) brings the rare earth to the 3+ oxidation state and iii) reduces non radiative defects. Additionally, for electroluminescent devices the matrix composition must be engineered so that it allows conduction-band transport in contrast with defective systems in which transport is hopping-like. The hot electron engineering concept relies on the fact that the rare earth excitation process in Si-based dielectric matrices proceeds mainly via impact excitation by hot electrons. Thus, devising suitable structures for which electrons can be accelerated to average energies that are resonant to the rare earth excitation energies, will improve both efficiency and maximum power emission. Additionally, driving the device with pulsed polarization and short duty cycle will improve device efficiency and lifetime. Finally, the structures must allow at the same time significant light extraction efficiency. This can be accomplished by improving the antireflective properties of the whole stack and/or by nanostructuring the ITO or polysilicon electrode. We will be show silicon oxides, nitrides and oxynitrides as hosts for the rare-earth species and, additionally, we will display the advantages and drawbacks of introducing small percentages of carbon and aluminum. The rare-earth species incorporated in those matrices are Er, Ce, Tb, Eu and Nd and their light emission efficiency depend in a complex way on matrix composition, material processing, device structure and device polarization. The simplest hot electron engineering structures are bilayers and trilayers with silicon oxide as accelerator. More complex structures like multilayers and superlattices will be also introduced and optimal designs will be proposed. Some reliability issues and potential solutions for them will be also presented. We acknowledge existing collaborations in this field with teams of the McMaster University at Hamilton (Canada), Institut de Microelectrònica de Barcelona (Spain), Nanophotonics Technology Center of Valencia (Spain), Instituto de Óptica of Madrid (Spain), Ion Beam Institute at Rossendorf (Germany), IMTEK at the University of Freiburg (Germany) and CIMAP-CNRS at Caen (France).

Charge transport and electroluminescence mechanisms in Si-rich Si oxynitride/silicon oxide (SRON/SiO2) superlattices deposited on p-type Si substrate are reported. The superlattice structures were deposited by plasma-enhanced chemical-vapor deposition and subsequently annealed at 1150 °C to precipitate and crystallize the Si excess into Si nanocrystals. The dependence of the electrical conduction on the applied voltage and temperature was found to be well described by a Poole-Frenkel transport mechanism over a wide voltage range. On the other hand, the observed dependence of the electroluminescence on the SRON layer thickness is a clear proof of quantum confinement and was attributed to an excitonic radiative recombination taking place in the confined states within the Si quantum dots. A model is proposed based on thermal hopping of electrons between the quantum dots acting as trap states (Poole-Frenkel). A correlation between carrier transport and electroluminescence has been established considering impa...

[EN] The resistive switching properties of ITO/ZnO/p-Si devices have been studied, which present well-defined resistance states with more than five orders of magnitude difference in current. Both the high resistance state (HRS) and the low resistance state (LRS) were induced by either sweeping or pulsing the voltage, observing some differences in the HRS. Finally, the charge transport mechanisms dominating the pristine, HRS, and LRS states have been analyzed in depth, and the obtained structural parameters suggest a partial re-oxidation of the conductive nanofilaments and a reduction of the effective conductive area., This work was financially supported by the Spanish Ministry of Economy and Competitiveness (Project Nos. TEC2012-38540-C02-01 and TEC2016-76849-C2-1-R). O.B. also acknowledges the subprogram "Ayudas para Contratos Predoctorales para la Formacion de Doctores" of the Spanish Ministry of Economy and Competitiveness for economical support. X.P., C.L., and C.G. are grateful to C. Frilay for his expertise in the maintenance of the sputtering kit used for the growth of the ZnO films.

Light emitting Al-Tb/SiO2 nanomultilayers (NMLs) for optoelectronic applications have been produced and characterized. The active layers were deposited by electron beam evaporation onto crystalline silicon substrates, by alternatively evaporating nanometric layers of Al, Tb, and SiO2. After deposition, all samples were submitted to an annealing treatment for 1 h in N2 atmosphere at different temperatures, ranging from 700 to 1100 °C. Transmission electron microscopy confirmed the NML structure quality, and by complementing the measurements with electron energy-loss spectroscopy, the chemical composition of the multilayers was determined at the nanoscopic level. The average composition was also measured by X-ray photoelectron spectroscopy (XPS), revealing that samples containing Al are highly oxidized. Photoluminescence experiments exhibit narrow emission lines ascribed to Tb3+ ions in all samples (both as-deposited and annealed ones), together with a broadband related to SiO2 defects. The Tb-related emission intensity in the sample annealed at 1100 °C is more than one order of magnitude higher than identical samples without Al. These effects have been ascribed to the higher matrix quality, less SiO2 defects emitting, and a better Tb3+ configuration in the SiO2 matrix thanks to the higher oxygen content favored by the incorporation of Al atoms, as revealed by XPS experiments.