Electrical Injection Research Articles

Electrically driven europium-doped GaN microdisk.

For the practical implementation of microdisk resonators as active nanophotonic devices, it is essential that they can be electrically driven. However, it is difficult to inject current in such small-scale devices without severely degrading their optical properties. We demonstrate the successful fabrication of an electrically injected microdisk based on Eu-doped GaN, in which an SiO2 spacer is used to prevent the interaction of the metal contact with the optical resonances. The microdisk shows Eu-related emission upon electrical injection and from the observed resonance peak, a cavity quality (Q)-factor of 3400 is concluded.

(Invited) Electrodeposition of Manganese Arsenides (MnxAs) as Promising Candidates in Spintronics

Spintronics is a new branch of electronics in which the spin of the electrons as well as their charge is manipulated to produce a desired outcome. Spintronic devices are particularly attractive for memory storage and magnetic sensor applications, and potentially for quantum computing where the electron spin would represent a bit of information. Nowadays many efforts are made to increase the efficiency and lower the production costs of these materials, among others the use of molecular inorganic compounds and cheap preparation techniques [1].Most of these layers are synthesized with physical and/or vapor phase techniques [2] which allow to obtain materials with a very few defects, but which are complex to manage and typically very expensive. For this reason, in this study we have searched for a way to electrochemically deposit a compound with interesting spintronic properties in the aqueous medium. In fact, electrodeposition is notoriously a very cheap, versatile and easily scalable technique.With this purpose Mn-As system was selected thanks to its good magnetic and transport properties to be used as building blocks for spin valve [3]. MnAs has potential applications in spintronics, for electrical spin injection into GaAs and Si based devices [4] and DFT simulations predict that Mn2As and Mn3As have a low magnetization saturation and a high spin polarization at the Fermi-level [5]. Starting from MnSO4 and NaAsO2 precursors solutions with various concentrations, supporting electrolytes and pH were tested.The electrochemical behaviour of the precursors was investigated with cyclic voltammetries and both potentiostatic as well as galvanostatic deposition were carried out. The deposits obtained were morphologically and compositional characterised with scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence spectroscopy (XRF), the chemical states were analysed with X-ray photoelectron spectroscopy (XPS), the crystalline structure was investigated with X-ray diffraction measurements (XRD). The preliminary magnetic and transport measurements evidence the promising properties of this deposition process to provide spinfiltering materials.The authors acknowledge Regione Toscana POR CreO FESR 2014-2020 – azione 1.1.5 sub-azione A1 – Bando 1 “Progetti Strategici di ricerca e sviluppo” which made possible the project “RAM-PVD” (CUP 3647.04032020.157000057_1225).

Regulation of flux-closure domain structures via oxygen vacancies and charged scanning probe microscopy

Manipulation of topological structures has become one of the most interesting topics in ferroelectrics through multiple excitations due to their prospective applications in electro-mechanical-optic devices. Scanning probe microscopy (SPM) has been developed as a powerful tool to manipulate the polar state in ferroic materials, in which the electric field induced by charged SPM enables dynamic coupling between the switching of the polar states and electromigration of oxygen vacancies, resulting in unknown influences of oxygen vacancy on the polar state in ferroelectric topological structures. Here, we regulate the polar state by considering oxygen vacancies and a non-uniform electric field under the charged SPM experiment for flux-closure domain structures in PbTiO3 thin films. The charged SPM probe can excite the growth of newly flux-closure domains to improve the density of topological states. In contrast, oxygen vacancies are found to suddenly prohibit the evolution of the flux-closure domain structure, when their concentration jumps to a threshold value. Our results might give guidelines to increase and stabilize the memory unit through co-modulating the electric field and ions injection in the information field.

Numerical Investigation of the Electro-Thermo Convection in an Inclined Cavity Filled with a Dielectric Fluid

The present work is a numerical analysis of electro-thermo convection, occurring in a square differentially heated cavity filled with a dielectric fluid. The cavity experiences the combined effects of viscous, electrical, and thermal forces. The equations modelling the physical problem are solved via the finite volume approach. The study focuses on the effect of cavity tilt on the fluid flow structure and thermal performance inside the enclosure under the action of an electric field. A parametric study was performed, where the tilt angle is getting varied between 0° and 90°, as well as the Rayleigh number (5000 ≤ Ra ≤ 250,000) and the electric field (0 ≤ T ≤ 800). Furthermore, the electric charge injection level C, the mobility M and the Prandtl Pr numbers were all adjusted to a value of 10. The obtained results demonstrate that the hydrodynamic and thermal fields are significantly impacted by the cavity inclination. In addition, regardless of the thermal Rayleigh’s number, high electric field values could govern fluid movement through electric forces. Electro-convection typically demonstrates an oscillating flow due to the tilting of the cavity which gives rise to a bicellular regime occupying the entire cavity. A correlation has been established to estimate heat transfer by considering various system parameters such as cavity inclination, electrical Rayleigh number, and thermal Rayleigh number.

Tissue-specific in vivo transformation of plasmid DNA in Neotropical tadpoles using electroporation.

Electroporation is an increasingly common technique used for exogenous gene expression in live animals, but protocols are largely limited to traditional laboratory organisms. The goal of this protocol is to test in vivo electroporation techniques in a diverse array of tadpole species. We explore electroporation efficiency in tissue-specific cells of five species from across three families of tropical frogs: poison frogs (Dendrobatidae), cryptic forest/poison frogs (Aromobatidae), and glassfrogs (Centrolenidae). These species are well known for their diverse social behaviors and intriguing physiologies that coordinate chemical defenses, aposematism, and/or tissue transparency. Specifically, we examine the effects of electrical pulse and injection parameters on species- and tissue-specific transfection of plasmid DNA in tadpoles. After electroporation of a plasmid encoding green fluorescent protein (GFP), we found strong GFP fluorescence within brain and muscle cells that increased with the amount of DNA injected and electrical pulse number. We discuss species-related challenges, troubleshooting, and outline ideas for improvement. Extending in vivo electroporation to non-model amphibian species could provide new opportunities for exploring topics in genetics, behavior, and organismal biology.

Defect‐Engineered Electrically‐Injected Germanium‐on‐Insulator Waveguide Light Emitters at Telecom Wavelengths

AbstractGe‐on‐insulators (GOIs) have been extensively explored as a potential platform for electronic‐photonic integrated circuits (EPICs), enabling various emerging applications. Although an efficient electrically‐injected light source is highly desirable, realizing such devices with optimal light emission efficiency remains challenging. Here, the first room‐temperature electrically‐injected Ge waveguide light emitters consisting of a lateral p–i–n homojunction on a GOI platform that can be monolithically integrated with EPICs are demonstrated. A high‐quality Ge active layer is transferred onto an insulator layer with the misfit dislocations in the Ge active layer eliminated to suppress unwanted nonradiative recombination. A 0.165% tensile strain is introduced to enhance the directness of the band structure and improve the light emission efficiency. The device comprises a waveguide structure with a significantly improved optical confinement as the optical resonator and a lateral p–i–n homojunction structure as the electrical injection structure. Under continuous‐wave electrical current injection at room temperature, enhanced electroluminescence is successfully observed at telecommunications wavelengths covering the C, L, and U bands, with improved efficiency. Theoretical analysis suggests that the quantum efficiency of Ge light emitters is dramatically affected by the defect density. These results pave the way for developing efficient, room‐temperature, electrically‐injected light emitters for next‐generation GOI‐based EPICs.

Optimal control of the part mass for the injection molding process

Injection molding is one of the most important processes to manufacture plastic goods. During the long production times, process variations might lead to a varying product quality. Therefore, in the state of the art, the machine variables of injection molding machines (e.g. the barrel temperature and the screw speed) are controlled to suppress these variations. However, the influence of changes of the raw material on the part quality cannot be systematically suppressed with state-of-the-art controllers. In this work, a novel control concept is proposed where the part mass is controlled instead of the usual machine variables. The control strategy is based on an estimation of the plastics mass in the mold. In order to account for the system nonlinearities, a model predictive control strategy is developed for both the filling and the holding-pressure phase. The feasibility and the benefits of this proposed part-mass control strategy is evaluated by a series of measurements on an electric injection molding machine.

Coherent control of mid-infrared frequency comb by optical injection of near-infrared light

We demonstrate the use of a low power near-infrared laser illuminating the front facet of a quantum cascade laser (QCL) as an optical actuator for the coherent control of a mid-infrared frequency comb. We show that with appropriate current control of the QCL comb and intensity modulation of the near-infrared laser, a tight phase lock of a comb line to a distributed feedback laser is possible with 2 MHz of locking bandwidth and 200 mrad of residual phase noise. A characterization of the whole scheme is provided, showing the limits of the electrical actuation, which we bypassed using the optical actuation. Both comb degrees of freedom can be locked by performing electrical injection locking of the repetition rate in parallel. However, we show that the QCL acts as a fast near-infrared light detector such that injection locking can also be achieved through modulation of the near-infrared light. These results on the coherent control of a QCL frequency comb are particularly interesting for coherent averaging in dual-comb spectroscopy and for mid-infrared frequency comb applications requiring high spectral purity.

Spin‐Orbit Readout Using Thin Films of Topological Insulator Sb2Te3 Deposited by Industrial Magnetron Sputtering

AbstractDriving a spin‐logic circuit requires the production of a large output signal by spin‐charge interconversion in spin‐orbit readout devices. This should be possible by using topological insulators, which are known for their high spin‐charge interconversion efficiency. However, high‐quality topological insulators have so far only been obtained on a small scale, or with large scale deposition techniques that are not compatible with conventional industrial deposition processes. The nanopatterning and electrical spin injection into these materials have also proven difficult due to their fragile structure and low spin conductance. The fabrication of a spin‐orbit readout device from the topological insulator Sb2Te3 deposited by large‐scale industrial magnetron sputtering on SiO2 is presented. Despite a modification of the Sb2Te3 layer structural properties during the device nanofabrication, a sizeable output voltage is measured that can be unambiguously ascribed to a spin‐charge interconversion process. The results pave the way for the integration of layered van der Waals materials in spin‐logic devices.

"Blue-free" orange ZnO-related light-emitting diode based on a natural interface layer of Ga2O3 and ZnGa2O4.

To fabricate a ZnO-related light-emitting diode (LED) with zero emission at blue wavelengths ("blue-free"), an ingenious strategy is employed. Specifically, for the first time to the best of our knowledge, a natural oxide interface layer, possessing remarkable visible emission potential, is introduced into the Au/i-ZnO/n-GaN metal-insulator-semiconductor (MIS) structure. The unique Au/i-ZnO/interface layer/n-GaN structure successfully eliminated the harmful blue emissions (400-500 nm) from the ZnO film, and the remarkable orange electroluminescence is mainly attributed to the impact ionization process of the natural interface layer at high electric field. It is worth mentioning that the device achieved ultra-low color temperature (2101 K) and excellent color rendering index (92.8) under electrical injection, indicating that the device could fulfill the requirements of electronic display systems and general illumination, and might even play unexpected roles in special lighting domains. The results obtained provide a novel and effective strategy for the design and preparation of ZnO-related LEDs.

Toward Nonepitaxial Laser Diodes.

Thin-film organic, colloidal quantum dot, and metal halide perovskite semiconductors are all being pursued in the quest for a wavelength-tunable diode laser technology that does not require epitaxial growth on a traditional semiconductor substrate. Despite promising demonstrations of efficient light-emitting diodes and low-threshold optically pumped lasing in each case, there are still fundamental and practical barriers that must be overcome to reliably achieve injection lasing. This review outlines the historical development and recent advances of each material system on the path to a diode laser. Common challenges in resonator design, electrical injection, and heat dissipation are highlighted, as well as the different optical gain physics that make each system unique. The evidence to date suggests that continued progress for organic and colloidal quantum dot laser diodes will likely hinge on the development of new materials or indirect pumping schemes, while improvements in device architecture and film processing are most critical for perovskite lasers. In all cases, systematic progress will require methods that can quantify how close new devices get with respect to their electrical lasing thresholds. We conclude by discussing the current status of nonepitaxial laser diodes in the historical context of their epitaxial counterparts, which suggests that there is reason to be optimistic for the future.

Carrier dynamics in blue, cyan, and green InGaN/GaN LEDs measured by small-signal electroluminescence

We study the carrier dynamics for c-plane InGaN/GaN light-emitting diodes (LEDs) with various emission wavelengths near the green gap using a small-signal electroluminescence method. The LEDs were grown by Lumileds using state-of-the-art growth conditions. Radiative and non-radiative recombination rates are numerically separated, and the carrier recombination lifetime and carrier density are obtained. Experiment shows that the causes of efficiency reduction at longer wavelength in the present structures are injection efficiency decrease, radiative recombination rate decrease, and imbalance of the increase in Auger–Meitner and radiative terms due to the interplay between the carrier–current density relationship and the quantum-confined Stark effect (QCSE). The effects of QCSE, phase-space filling, and the carrier–current density relationship on efficiency reduction at longer wavelengths are examined separately with experimental data and Schrödinger–Poisson calculations. In addition, we confirm the scaling law between Cn and Bn under electrical injection and find that the increase in carrier density at a given current density is the primary cause for lower radiative efficiency at high current density in longer wavelength LEDs. Conversely, we do not observe a significant efficiency reduction at longer wavelengths from extrinsic material degradation.

Half‐Metallic Heusler Alloy/GaN Heterostructure for Semiconductor Spintronics Devices

AbstractBecause spin‐orbit coupling in wurtzite semiconductors is relatively weak compared with that in zincblende ones, the III‐nitride semiconductor GaN is a promising material for high‐performance optical semiconductor spintronic devices such as spin lasers. For the purpose of reducing the operating power of spin lasers, it is necessary to demonstrate highly efficient electrical spin injection from a ferromagnetic material into GaN with a low‐resistance contact. Here, an epitaxial half‐metallic Heusler alloy Co2FeAlxSi1−x(CFAS)/GaN heterostructure is developed by inserting an ultrathin Co layer between the CFAS and GaN. The CFAS/n+‐GaN heterojunctions clearly show tunnel conduction with very small rectification and a low resistance‐area product of ≈3.8 kΩµm2, which is several orders of magnitude smaller than those reported in previous work, at room temperature. Nonlocal spin signals and a Hanle effect curve are observed at low temperatures using lateral spin‐valve devices with the CFAS/n+‐GaN contacts, suggesting pure spin current transport in bulk GaN. The spin transport is observed at temperatures as high as room temperature, with a high spin polarization of 0.2 at a low bias voltage less than 2.0 V. This study is expected to open a path to GaN‐based spintronic devices with highly spin‐polarized and low‐resistance contacts.

Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

AbstractThe notion of quasi‐equilibrium is central to most solar cells; however, it has been questioned in organic photovoltaics (OPVs) owing to strong energetic disorder that frustrates efficient relaxation of electrons and holes within their respective density of states (DOS). Here, modulation electroluminescence (EL) spectroscopy is applied to OPVs and it is found that the frequency response of charge transfer (CT) state EL on the high energy side of the spectrum differs from that of the low energy side. This observation confirms that static disorder contributes substantially to the linewidth of the steady‐state EL spectrum and is unambiguous proof that the distribution of CT states formed by electrical injection in the dark is not in quasi‐equilibrium. These results emphasize the need for caution when analyzing OPV cells on the basis of reciprocity models that assume quasi‐equilibrium holds, and highlight a new method to study this unusual aspect of OPV operation.

Directional Emission from Electrically Injected Exciton–Polaritons in Perovskite Metasurfaces

We present a new approach to achieving strong coupling between electrically injected excitons and photonic bound states in the continuum of a dielectric metasurface. Here a high-finesse metasurface cavity is monolithically patterned in the channel of a perovskite light-emitting transistor to induce a large Rabi splitting of ∼200 meV and more than 50-fold enhancement of the polaritonic emission compared to the intrinsic excitonic emission of the perovskite film. Moreover, the directionality of polaritonic electroluminescence can be dynamically tuned by varying the source-drain bias, which induces an asymmetric distribution of exciton population within the transistor channel. We argue that this approach provides a new platform to study strong light-matter interactions in dispersion engineered photonic cavities under electrical injection and paves the way to solution-processed electrically pumped polariton lasers.

Failure Scenario of Power Supply Due to Conducted Electric Pulse From E1 HEMP

This article presents the effects of a high amplitude conducted electromagnetic pulse on the electrical behavior of a flyback switch-mode power supply. The electromagnetic pulse is generated by a current injection platform that is able to reproduce differential or common mode parasitic currents and voltages induced by the coupling between E1 high-altitude nuclear electromagnetic pulse and a global electrical network. In this article, injections are performed in differential mode until the destruction of power supply. Current and voltage measurements have been performed around each destroyed component during the injection. Finally, these destruction tests, associated with spice simulations and component analyses, permit to build a power supply destruction scenario with the component's failures chronology modeling. This scenario is the first step in order to model the susceptibility of power supplies during an electrical pulse injection.

Electric field-driven folding of single molecules

Folding of molecules is an essential process in nature, and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations. The electric field offers a unique strategy to drive the folding of molecular conformation and to control charge transport through single molecules but remains unexplored. The single-molecule break junction technique provides access to detect the conformational changes via the monitoring of single-molecule conductance, and the electric field between two metal electrodes with nanoscale spacing can provide an extremely strong to achieve in-situ control and detection of molecular folding at the single-molecule level. Here, we use the electric field to control the single-molecule folding using the scanning tunneling microscope break junction (STM-BJ) technique. The electric fields induced folding could lead to a ∼1400% conductance change of the single-molecule junctions, and the folding/unfolding process can be in-situ switched at the scale of milliseconds. DFT calculations suggest the conformational control originates from the electric field-induced charge injection, and the formation of homoconjugated conformation with the overlapped orbitals. This work provides the first demonstration of electric field-driven molecular folding, which is essential for the understanding of molecular machines in nature and for the design of artificial molecular machines.

Electrical Resistance Tomographic by Using Current Injection and Magnetic Field Induction

A critical issue in electrical tomography is ill-posed problems due to low sensitivity. In the electric current injection method, the placement of the injection electrode on the object boundary can influence it. This condition causes the reconstruction result of parameter change far away from the boundary to be inferior in quality. Another excitation method is using magnetic field induction proposed to overcome these problems. Each reconstruction image was obtained using two methods with three types of parameter changes, that represented the edge and the center of the object position. Both reconstruction results are merged and further processed to enhance the quality of the image, based on the average value of the resistivity of each element. The results show that the final image reconstruction has a smaller root mean square error (RMSE) than the electric current injection method.

Frequency modulations due to domain dynamics in terahertz quantum cascade lasers

The light output of quantum cascade lasers is strongly affected by electric field-domain oscillations if the laser shows electrical instabilities. This can result in a substantial broadening of the emission spectrum, which is investigated here by detailed simulations for a terahertz device. We explain how the light pulsation is affected by electrical injection conditions and external capacitances. Experimental data confirm that the oscillation frequencies are not essentially affected by circuit conditions, while a large external capacitance produces almost non-observable oscillations due to stabilization of the circuit.

Bright semiconductor single-photon sources pumped by heterogeneously integrated micropillar lasers with electrical injections

The emerging hybrid integrated quantum photonics combines the advantages of different functional components into a single chip to meet the stringent requirements for quantum information processing. Despite the tremendous progress in hybrid integrations of III-V quantum emitters with silicon-based photonic circuits and superconducting single-photon detectors, on-chip optical excitations of quantum emitters via miniaturized lasers towards single-photon sources (SPSs) with low power consumptions, small device footprints, and excellent coherence properties is highly desirable yet illusive. In this work, we present realizations of bright semiconductor SPSs heterogeneously integrated with on-chip electrically-injected microlasers. Different from previous one-by-one transfer printing technique implemented in hybrid quantum dot (QD) photonic devices, multiple deterministically coupled QD-circular Bragg Grating (CBG) SPSs were integrated with electrically-injected micropillar lasers at one time via a potentially scalable transfer printing process assisted by the wide-field photoluminescence (PL) imaging technique. Optically pumped by electrically-injected microlasers, pure single photons are generated with a high-brightness of a count rate of 3.8 M/s and an extraction efficiency of 25.44%. Such a high-brightness is due to the enhancement by the cavity mode of the CBG, which is confirmed by a Purcell factor of 2.5. Our work provides a powerful tool for advancing hybrid integrated quantum photonics in general and boosts the developments for realizing highly-compact, energy-efficient and coherent SPSs in particular.