Highly doped semiconductor nanocrystals are of high interest for applications such as mid-infrared plasmonic sensors. The expected controllable free carrier concentration in the 1019-1021 cm-3 range renders these nano-structures a great alternative to metal-based nanoparticles. We report on the fabrication of heavily phosphorus-doped Ge nanocrystals embedded in a GeO2 matrix which support a plasmonic response in the mid-infrared. Germanium nanocrystals were obtained by disproportionation of substoichiometric germanium oxide films induced by thermal annealing. Doped thin films were prepared under ultrahigh vacuum by simultaneous electron-beam assisted evaporation of GeO2 and evaporation of phosphorus from a GaP decomposition source. Samples were studied by transmission electron microscopy, Raman spectroscopy, and infrared absorption spectroscopy. The spectroscopic analysis carried out on samples annealed at above 400 degrees C evidences vibrational bands related to the dielectric matrix and a narrow contribution attributed to collective oscillations of electrons located in Ge nanocrystals. Based on the Mie theory and the Drude model, the mobility and the free charge carrier density were extracted from the simulation of the plasmonic response and were close to 1000 cm2.V-1.s-1 and 2 & times; 10 1 9 cm-3 , respectively. These results demonstrate the potential of these materials for applications in the mid-infrared range.

GaN-based spin light-emitting diodes (spin-LEDs) are attractive for realizing room-temperature spin-controlled light emission in efficient, color-tunable devices. In this work, we demonstrate spin injection in a GaN spin-LED fabricated on a Si substrate using wafer-bonding technology. An inverted n-i-p LED structure with n-type GaN on top facilitates the injection of spin-polarized electrons from a ferromagnetic Au/Co/MgO spin-injector layer grown by molecular beam epitaxy. At room temperature, an electroluminescence circular polarization of approximately 8% is measured under an applied 1 T out-of-plane magnetic field in a surface-emitting geometry. After considering contributions from the Zeeman effect and magnetic circular dichroism, about 6% circular polarization is attributed to the pure spin injection into GaN. This work is focused on the detailed structural and interface characterization of the spin-LED and allows to understand its spin and optoelectronic properties. These results highlight the potential of GaN-based spin-optoelectronic devices compatible with Si platforms.

We investigate the growth, the microstructure and the thermal stability of Ge:P thin films prepared by co- evaporation of Ge and P in ultra-high vacuum. Ex-situ annealing of Ge:P thin films containing up to 45 at% of Pat temperatures close to 500 degrees C leads to the formation of GeP, which crystallizes in a monoclinic structure with space group C2/m. Microstructural investigations show that GeP thin films are polycrystalline with typical grain sizes in the micrometer range. High resolution imaging gives clear evidence that the GeP films are lamellar with an atomic structure in good agreement with a monoclinic structure. When annealing at temperatures larger than 530 degrees C, only pure crystalline Ge remains in the films. Thermal desorption spectroscopy measurements show that P desorption occurs for annealing temperatures above 500 degrees C. For annealing temperatures larger than 530 degrees C, GeP is decomposed and P atoms diffuse towards the surface prior to effusion. A detailed analysis based on the theory of Eyring allows us to determine both the activation energy for P diffusion as well as the P diffusion coefficient in Ge:P thin films.

Quantum well (QW) states formed in a double-barrier magnetic tunnel junction (DMTJ) enable the coherent resonant tunneling of electrons. This phenomenon is significant for both the fundamental understanding of quantum transport and the development of advanced functionalities in spintronic devices. Careful engineering of the structural and chemical disorders at the QW/barrier interface is essential to maintain strong electron phase coherence, thereby ensuring reliable conductance oscillations in DMTJ. In this study, we systematically investigate the influence of interfacial disorders and band structure on QW-induced conductance oscillations in epitaxial Fe/MgAlOx/Fe (QW)/MgAlOx/Co/Fe DMTJs grown by molecular beam epitaxy. It is found that the amplitude of QW oscillations is reduced to one-third due to chemical disorders caused by the incorporation of 2-4 monolayers of Co at the Fe (QW)/MgAlOx interface. In contrast, structural disorder induced by the incorporation of a single Fe monolayer completely suppresses the oscillations. In addition, the QW oscillation depends on the available majority Delta(1) states of the injecting electrons at the Fermi level (E-F) with k(//) = 0 from the upper electrode. Replacing the Fe upper electrode with Fe4N, which lacks a majority of Delta(1) states at E-F, significantly reduces the oscillation amplitude. Instead, using the bcc Co upper electrode, which possesses majority Delta(1) states, results in no change in QW oscillation. Our findings highlight the critical role of interfacial disorder and band structure in QW-induced conductance oscillations, advancing the development of spin-dependent quantum resonant tunneling applications.

Controlling the intensity of emitted light and charge current is the basis of transferring and processing information 1 . By contrast, robust information storage and magnetic random-access memories are implemented using the spin of the carrier and the associated magnetization in ferromagnets 2 . The missing link between the respective disciplines of photonics, electronics and spintronics is to modulate the circular polarization of the emitted light, rather than its intensity, by electrically controlled magnetization. Here we demonstrate that this missing link is established at room temperature and zero applied magnetic field in light-emitting diodes 2 – 7 , through the transfer of angular momentum between photons, electrons and ferromagnets. With spin–orbit torque 8 – 11 , a charge current generates also a spin current to electrically switch the magnetization. This switching determines the spin orientation of injected carriers into semiconductors, in which the transfer of angular momentum from the electron spin to photon controls the circular polarization of the emitted light 2 . The spin–photon conversion with the nonvolatile control of magnetization opens paths to seamlessly integrate information transfer, processing and storage. Our results provide substantial advances towards electrically controlled ultrafast modulation of circular polarization and spin injection with magnetization dynamics for the next-generation information and communication technology 12 , including space–light data transfer. The same operating principle in scaled-down structures or using two-dimensional materials will enable transformative opportunities for quantum information processing with spin-controlled single-photon sources, as well as for implementing spin-dependent time-resolved spectroscopies.

Integrating tunneling magnetoresistance (TMR) effect in memristors is a long-term aspiration because it allows to realize multifunctional devices, such as multi-state memory and tunable plasticity for synaptic function. However, the reported TMR in different multiferroic tunnel junctions is limited to 100%. This work demonstrates a giant TMR of -266% in La0.6Sr0.4MnO3(LSMO)/poly(vinylidene fluoride)(PVDF)/Co memristor with thin organic barrier. Different from the ferroelectricity-based memristors, this work discovers that the voltage-driven florine (F) motion in the junction generates a huge reversible resistivity change up to 106% with nanosecond (ns) timescale. Removing F from PVDF layer suppresses the dipole field in the tunneling barrier, thereby significantly enhances the TMR. Furthermore, the TMR can be tuned by different polarizing voltage due to the strong modification of spin-polarization at the LSMO/PVDF interface upon F doping. Combining of high TMR in the organic memristor paves the way to develop high-performance multifunctional devices for storage and neuromorphic applications.

We investigate the growth of Au/FexNy/MgO trilayers on GaAs(001) substrates by plasma-assisted molecular beam epitaxy. The optimization of the growth conditions made it possible to obtain the compound of stoichiometric Fe4N. Microstructural studies show that Fe4N forms 3D islands at the initial stages of growth. As the Fe4N thickness increases, a columnar growth sets in leading to a strong texturing and to the formation of grains having the same crystallographic orientation. The growth is epitaxial with the relationship GaAs (001) [110]//MgO (001) [110]//Fe4N (001) [110]//Au (012) [0-32]. A chemical analysis at the nanoscale reveals that the interfaces are rather sharp with a limited interdiffusion. Magnetic characterizations show that a trilayer containing a 1-nm-thick Fe4N layer is already ferromagnetic. The easy magnetization axis is in-plane independent of the Fe4N layer thickness (from 1 to 6 nm). This study shows the potential to use Fe4N as a spin injector for spin-optoelectronic applications.

Highly doped semiconductor nanocrystals are of great interest for applications in nanophotonics and appear as an exciting alternative for infrared plasmonics with detection and identification of molecules, covering applications in biology, medicine, air quality control, sanitary control, and safety issues. Among the main parameters that influence optical properties and plasmonic response, the nanocrystal size plays a major role. In this work, we report on the influence of the silicon nanocrystal size on the localized surface plasmon resonance obtained in n-type Si nanocrystals embedded in a silicon dioxide matrix. The size control of phosphorus-doped Si nanocrystals was achieved by using a (SiO/SiO2) multilayer architecture. In this study, the nanocrystal diameter is varied from 7 to 16 nm, while the P content is kept constant at 0.9 atom %. Here, we demonstrate that the mid-infrared plasmonic absorption exhibits both a redshift and broadening as the nanocrystal diameter decreases from 16 to 7 nm. The plasmonic response was successfully modeled in the framework of Mie theory, considering the Drude model and size-dependent scattering of free carriers. The redshift of the plasmon is explained not only by size-dependent scattering but also by size-dependent doping efficiency. Both charge carrier mobilities and free carrier densities are found to vary between 17 and 28 cm2 V-1 s-1 and between 1.89 x 1020 and 2.6 x 1020 cm-3, respectively. In this work, we shed light on the key role of the Si/SiO2 interface that needs to be optimized to reach plasmonic properties in very small nanocrystals that could support quantum plasmonics.

A sign-reversible tunneling magnetoresistance (TMR) bestows an extra control freedom to design TMR-based spintronic devices for developing spin-logic applications. Here, we demonstrate a large sign reversal of TMR in an epitaxial Fe/MgAlOx/Fe4N magnetic tunnel junction (MTJ) controlled by the bias voltage. At room temperature (RT), the TMR is measured as large as -26.7% (-38% under optimistic definition) at V = +0.45 V, and it changes the sign to be +3.2% at V = -0.6 V. The TMR sign-reversal effect is doubled compared to those of the Fe/MgO/Fe4N MTJs, which is attributed to the better lattice mismatch between Fe4N and MgAlOx as well as less N diffusion inside the tunneling barrier. First-principles calculations reveal that the change of the TMR sign originates from different symmetry-dependent tunneling channels between Fe and Fe4N electrodes under opposite bias voltages. The Fe/MgAlOx/Fe4N MTJ with voltage-controllable TMR signs and relatively large TMR ratios at RT will promote the development of versatile and reprogrammable spin-logic applications.

As building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily phosphorus-doped SiO/SiO2 multilayers in an ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 atom %, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 atom %, i.e., well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles are observed for P contents exceeding 4 atom % in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3-6 mu m range. A core-shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm2 V-1 s-1 and 2.3 x 1020 cm-3, respectively. This results in a dopant activation rate of about 8%.

Disordered topological insulator (TI) films have gained intense interest by benefiting from both the TI's exotic transport properties and the advantage of mass production by sputtering. Here, we report on the clear evidence of spin-charge conversion (SCC) in amorphous Gd-alloyed BixSe1-x (BSG)/CoFeB bilayers fabricated by sputtering, which could be related to the amorphous TI surface states. Two methods have been employed to study SCC in BSG (tBSG = 6-16 nm)/CoFeB(5 nm) bilayers with different BSG thicknesses. First, spin pumping is used to generate a spin current in CoFeB and detect SCC by the inverse Edelstein effect (IEE). The maximum SCC efficiency (SCE) is measured to be as large as 0.035 nm (IEE length λIEE) in a 6 nm thick BSG sample, which shows a strong decay when tBSG increases due to the increase of BSG surface roughness. The second method is THz time-domain spectroscopy, which reveals a small tBSG dependence of SCE, validating the occurrence of a pure interface state-related SCC. Furthermore, our angle-resolved photoemission spectroscopy data show dispersive two-dimensional surface states that cross the bulk gap until the Fermi level, strengthening the possibility of SCC due to the amorphous TI states. Our studies provide a new experimental direction toward the search for topological systems in amorphous solids.

Understanding the polarization switching mechanisms at play in ferroelectric materials is crucial for their exploitation in electronic devices. The conventional centrosymmetric reference structure-based mechanism which accounts for ferroelectricity in most of the usual displacive ferroelectric materials is too energy-demanding for some newly diagnosed ferroelectric materials such as the Ga2-xFexO3 (0.8 < x < 1.4) compounds. Some alternative theoretical propositions have been made and need experimental confirmation. A dual-scale electron microscopy study is performed on thin films of the Ga0.6Fe1.4O3 multiferroic compound. A wide scale precession-assisted electron diffraction tomography study first allows the determination of the structure the compound adopts in thin films, and even permits the refinement of the atomic positions within this structure. Cationic mobility is suggested for two of the atomic positions through the existence of extra electronic density. A local in situ high resolution scanning transmission electron microscopy study then allows confirming these mobilities by directly spotting the cationic displacements on successively acquired images. The whole study confirms an unconventional switching mechanism via local domain wall motion in this compound.

Dielectric films have played a vital role in the development of micro‐ and nanoelectronic devices over the past decades. However, the stability of current dielectrics under extreme high‐temperature conditions is still a major shortcoming to be overcome. Herein, the successful fabrication of high‐quality amorphous ternary AlBN dielectric films on n++GaN substrates by pulsed laser deposition (PLD) at room temperature (25 ± 2 °C) is reported. Systematic characterizations on the morphology, structure, chemical composition, and band offsets properties of the fabricated films reveal that both as‐deposited and 800 °C postdeposition annealing (PDA) thin films are amorphous and exhibit good physical and electrical properties. Large band offsets (>2.0 eV), high dielectric constants (>10), and low leakage currents are achieved in both cases. Furthermore, the leakage current density in the Au/AlBN/n++GaN junctions of 800 °C PDA thin films is reduced by approximately one order of magnitude compared with those of as‐deposited thin films. The demonstration of these excellent properties indicates that the amorphous AlBN dielectric thin films are promising candidates for integrated dielectric layers in electronic devices for harsh environment applications.

This work reports on the influence of phosphorous atoms on the phase separation process and optical properties of silicon nanocrystals (Si-NCs) embedded in phosphorus doped SiO/SiO2 multilayers. Doped SiO/SiO2 multilayers with different P contents have been prepared by co-evaporation and subsequently annealed at different temperatures up to 1100 °C. The sample structure and the localization of P atoms were both studied at the nanoscale by scanning transmission electron microscopy and atom probe tomography. It is found that P incorporation modifies the mechanism of Si-NC growth by promoting the phase separation during the post-growth-annealing step, leading to nanocrystal formation at lower annealing temperatures as compared to undoped Si-NCs. Hence, the maximum of Si-NC related photoluminescence (PL) intensity is achieved for annealing temperatures lower than 900 °C. It is also demonstrated that the Si-NCs mean size increases in the presence of P, which is accompanied by a redshift of the Si-NC related emission. The influence of the phosphorus content on the PL properties is studied using both room temperature and low temperature measurements. It is shown that for a P content lower than about 0.1 at%, P atoms contribute to significantly improve the PL intensity. This effect is attributed to the P-induced-reduction of the number of non-radiative defects at the interface between Si-NCs and SiO2 matrix, which is discussed in comparison with hydrogen passivation of Si-NCs. In contrast, for increasing P contents, the PL intensity strongly decreases, which is explained by the growth of Si-NCs reaching sizes that are too large to ensure quantum confinement and to the localization of P atoms inside Si-NCs.

A perpendicularly magnetized spin injector with a high Curie temperature is a prerequisite for developing spin optoelectronic devices on two-dimensional (2D) materials working at room temperature (RT) with zero applied magnetic field. Here, we report the growth of Ta/CoFeB/MgO structures with large perpendicular magnetic anisotropy (PMA) on full-coverage monolayer (ML) molybdenum disulfide (MoS2). A large perpendicular interface anisotropy energy of 0.975 mJ/m2 has been obtained at the CoFeB/MgO interface, comparable to that observed in magnetic tunnel junction systems. It is found that the insertion of MgO between the ferromagnetic (FM) metal and the 2D material can effectively prevent the diffusion of the FM atoms into the 2D material. Moreover, the MoS2 ML favors a MgO(001) texture and plays a critical role in establishing the large PMA. First-principles calculations on a similar Fe/MgO/MoS2 structure reveal that the MgO thickness can modify the MoS2 band structure, from a direct band gap with 3ML-MgO to an indirect band gap with 7 ML-MgO. The proximity effect induced by Fe results in splitting of 10 meV in the valence band at the Γ point for the 3ML-MgO structure, while it is negligible for the 7 ML-MgO structure. These results pave the way to develop RT spin optoelectronic devices based on 2D transition-metal dichalcogenide materials.

We report on the fabrication of an organic multiferroic tunnel junction (OMFTJ) based on an organic barrier of the Poly(vinylidene fluoride) (PVDF):Fe3O4 nanocomposite. By adding Fe3O4 nanoparticles into the PVDF barrier, we found that the ferroelectric properties of the OMFTJ are considerably improved compared to those with a pure PVDF barrier. This can lead to tunneling electroresistances of about 450% at 10K and 100% at room temperature (RT), which are much higher than those of the pure PVDF based device (70% at 10K and 7% at RT). OMFTJs based on the PVDF:Fe3O4 nanocomposite could open new functionalities in smart multiferroic devices via the interplay of the magnetism of nanoparticles with the ferroelectricity of the organic barrier.