Showing papers on "Quantum well published in 2021"

Two-dimensional Ruddlesden–Popper layered perovskite solar cells based on phase-pure thin films

Abstract: Two-dimensional Ruddlesden–Popper layered metal-halide perovskites have attracted increasing attention for their desirable optoelectronic properties and improved stability compared to their three-dimensional counterparts. However, such perovskites typically consist of multiple quantum wells with a random well width distribution. Here, we report phase-pure quantum wells with a single well width by introducing molten salt spacer n-butylamine acetate, instead of the traditional halide spacer n-butylamine iodide. Due to the strong ionic coordination between n-butylamine acetate and the perovskite framework, a gel of a uniformly distributed intermediate phase can be formed. This allows phase-pure quantum well films with microscale vertically aligned grains to crystallize from their respective intermediate phases. The resultant solar cells achieve a power conversion efficiency of 16.25% and a high open voltage of 1.31 V. After keeping them in 65 ± 10% humidity for 4,680 h, under operation at 85 °C for 558 h, or continuous light illumination for 1,100 h, the cells show <10% efficiency degradation. Two-dimensional Ruddlesden–Popper layered metal-halide perovskites show better performance over three-dimensional versions, but are typically based on quantum wells with random width distribution. Liang et al. show that introducing molten salt spacers gives phase-pure quantum wells and improved solar cell performance.

Distribution control enables efficient reduced-dimensional perovskite LEDs.

Abstract: Light-emitting diodes (LEDs) based on perovskite quantum dots have shown external quantum efficiencies (EQEs) of over 23% and narrowband emission, but suffer from limited operating stability1. Reduced-dimensional perovskites (RDPs) consisting of quantum wells (QWs) separated by organic intercalating cations show high exciton binding energies and have the potential to increase the stability and the photoluminescence quantum yield2,3. However, until now, RDP-based LEDs have exhibited lower EQEs and inferior colour purities4–6. We posit that the presence of variably confined QWs may contribute to non-radiative recombination losses and broadened emission. Here we report bright RDPs with a more monodispersed QW thickness distribution, achieved through the use of a bifunctional molecular additive that simultaneously controls the RDP polydispersity while passivating the perovskite QW surfaces. We synthesize a fluorinated triphenylphosphine oxide additive that hydrogen bonds with the organic cations, controlling their diffusion during RDP film deposition and suppressing the formation of low-thickness QWs. The phosphine oxide moiety passivates the perovskite grain boundaries via coordination bonding with unsaturated sites, which suppresses defect formation. This results in compact, smooth and uniform RDP thin films with narrowband emission and high photoluminescence quantum yield. This enables LEDs with an EQE of 25.6% with an average of 22.1 ±1.2% over 40 devices, and an operating half-life of two hours at an initial luminance of 7,200 candela per metre squared, indicating tenfold-enhanced operating stability relative to the best-known perovskite LEDs with an EQE exceeding 20%1,4–6. The efficiency and operating lifetimes of perovskite light-emitting diodes is improved by using a fluorinated triphenylphosphine oxide additive to control the cation diffusion during film deposition and passivate the surface.

High-power portable terahertz laser systems

Abstract: Terahertz (THz) frequencies remain among the least utilized in the electromagnetic spectrum, largely due to the lack of powerful and compact sources. The invention of THz quantum cascade lasers (QCLs) was a major breakthrough to bridge the so-called ‘THz gap’ between semiconductor electronic and photonic sources. However, their demanding cooling requirement has confined the technology to a laboratory environment. A portable and high-power THz laser system will have a qualitative impact on applications in medical imaging, communications, quality control, security and biochemistry. Here, by adopting a design strategy that achieves a clean three-level system, we have developed THz QCLs (at ~4 THz) with a maximum operating temperature of 250 K. The high operating temperature enables portable THz systems to perform real-time imaging with a room-temperature THz camera, as well as fast spectral measurements with a room-temperature detector. GaAs-based terahertz quantum cascade lasers emitting around 4 THz are demonstrated up to 250 K without a magnetic field. To elevate the operation temperature, carrier leakage channels are reduced by carefully designing the quantum well structures.

Ultra-high-quality two-dimensional electron systems

Abstract: Two-dimensional electrons confined to GaAs quantum wells are hallmark platforms for probing electron–electron interactions. Many key observations have been made in these systems as sample quality has improved over the years. Here, we present a breakthrough in sample quality via source-material purification and innovation in GaAs molecular beam epitaxy vacuum chamber design. Our samples display an ultra-high mobility of 44 × 106 cm2 V–1 s–1 at an electron density of 2.0 × 1011 cm–2. These results imply only 1 residual impurity for every 1010 Ga/As atoms. The impact of such low impurity concentration is manifold. Robust stripe and bubble phases are observed, and several new fractional quantum Hall states emerge. Furthermore, the activation gap (Δ) of the fractional quantum Hall state at the Landau-level filling (ν) = 5/2, which is widely believed to be non-Abelian and of potential use for topological quantum computing, reaches Δ ≈ 820 mK. We expect that our results will stimulate further research on interaction-driven physics in a two-dimensional setting and substantially advance the field. Source-material purification and optimized vacuum chamber design lead to a breakthrough in GaAs sample quality.

Lead-Free Organic-Perovskite Hybrid Quantum Wells for Highly Stable Light-Emitting Diodes.

Abstract: Two-dimensional perovskites that could be regarded as natural organic-inorganic hybrid quantum wells (HQWs) are promising for light-emitting diode (LED) applications. High photoluminescence quantum efficiencies (approaching 80%) and extremely narrow emission bandwidth (less than 20 nm) have been demonstrated in their single crystals; however, a reliable electrically driven LED device has not been realized owing to inefficient charge injection and extremely poor stability. Furthermore, the use of toxic lead raises concerns. Here, we report Sn(II)-based organic-perovskite HQWs employing molecularly tailored organic semiconducting barrier layers for efficient and stable LEDs. Utilizing femtosecond transient absorption spectroscopy, we demonstrate the energy transfer from organic barrier to inorganic perovskite emitter occurs faster than the intramolecular charge transfer in the organic layer. Consequently, this process allows efficient conversion of lower-energy emission associated with the organic layer into higher-energy emission from the perovskite layer. This greatly broadened the candidate pool for the organic layer. Incorporating a bulky small bandgap organic barrier in the HQW, charge transport is enhanced and ion migration is greatly suppressed. We demonstrate a HQW-LED device with pure red emission, a maximum luminance of 3466 cd m-2, a peak external quantum efficiency up to 3.33%, and an operational stability of over 150 h, which are significantly better than previously reported lead-free perovskite LEDs.

Distance Dependence of Förster Resonance Energy Transfer Rates in 2D Perovskite Quantum Wells via Control of Organic Spacer Length.

Abstract: Two-dimensional (2D) semiconductors are attractive candidates for a variety of optoelectronic applications owing to the unique electronic properties that arise from quantum confinement along a single dimension. Incorporating nonradiative mechanisms that enable directed migration of bound charge carriers, such as Forster resonance energy transfer (FRET), could boost device efficiencies provided that FRET rates outpace undesired relaxation pathways. However, predictive models for FRET between distinct 2D states are lacking, particularly with respect to the distance d between a donor and acceptor. We approach FRET in systems with binary mixtures of donor and acceptor 2D perovskite quantum wells (PQWs), and we synthetically tune distances between donor and acceptor by varying alkylammonium spacer cation lengths. FRET rates are monitored using transient absorption spectroscopy and ultrafast photoluminescence, revealing rapid picosecond lifetimes that scale with spacer cation length. We theoretically model these binary mixtures of PQWs, describing the emitters as classical oscillating dipoles. We find agreement with our empirical lifetimes and then determine the effects of lateral extent and layer thickness, establishing fundamental principles for FRET in 2D materials.

Pressure Sensor Based on Quantum Well-structured Photonic Crystal

Abstract: In the present communication, the strain sensitive quantum well-structured photonic crystal has been utilized to realize a pressure sensor device. The quantum well-structure in one dimensional photonic crystal opens a channel into the photonic bandgap. The channel can be tuned with the refractive index of material, which depends on parameter, i.e. pressure. This tunability of the channel with the applied pressure is used in high pressure sensor application. The proposed sensor can work in the range between 0 and 6 GPa corresponding to wavelength range 1509–1550 nm. The proposed sensor has a high quality factor, sensitivity and figure of merit (FOM) as ~ 105, 6.74 nm/GPa, 872.43 /GPa, respectively.

Excitons bound by photon exchange

Abstract: In contrast to interband excitons in undoped quantum wells, doped quantum wells do not display sharp resonances due to excitonic bound states. The effective Coulomb interaction between electrons and holes in these systems typically leads to only a depolarization shift of the single-electron intersubband transitions1. Non-perturbative light–matter interaction in solid-state devices has been investigated as a pathway to tuning optoelectronic properties of materials2,3. A recent theoretical work4 predicted that when the doped quantum wells are embedded in a photonic cavity, emission–reabsorption processes of cavity photons can generate an effective attractive interaction that binds electrons and holes together, leading to the creation of an intraband bound exciton. Here, we spectroscopically observe such a bound state as a discrete resonance that appears below the ionization threshold only when the coupling between light and matter is increased above a critical value. Our result demonstrates that two charged particles can be bound by the exchange of transverse photons. Light–matter coupling can thus be used as a tool in quantum material engineering, tuning electronic properties of semiconductor heterostructures beyond those permitted by mere crystal structures, with direct applications to mid-infrared optoelectronics. Electrons and holes in doped quantum wells cannot form bound states from usual Coulomb interaction. However, when the system is embedded in a cavity, the exchange of photons provides an effective attraction, leading to the creation of bound excitons.

Swapping of orbital angular momentum states of light in a quantum well waveguide

Abstract: We study the effect of orbital angular momentum transfer between optical fields in a semiconductor quantum well waveguide with four energy levels in a closed-loop configuration via four-wave mixing. The waveguide is driven by two strong control fields and two weak probe fields. We consider three different cases for the light-matter interaction in order to efficiently exchange optical vortices. In the first two cases, the system is initially prepared in either a lower electromagnetically induced transparency or a coherent population trapping state, while the last case prepares the system in an upper state, enabling to induce the electron spin coherence. We find that for appropriate parameters and via the spin coherence effect, the efficiency of four-wave mixing is much higher in the quantum well waveguide. Working in the electron spin coherence regime, we then study the light-matter interaction under the situation where only one of the control fields has an optical vortex. The orbital angular momentum of the vortex control beam can be efficiently transferred to a generated probe field via the spin coherence. We also show that the spatially dependent optical effects of the waveguide can be strongly modified by the electron spin coherence.

Effects of intense laser field and position dependent effective mass in Razavy quantum wells and quantum dots

Abstract: Using the effective mass and parabolic band approximations, we investigated the position-dependent effective mass and non-resonant intense laser field effects on the first and third-order corrections of the absorption and relative changes of the refraction index coefficients for intersubband transition in Razavy-like quantum wells. Calculations have been extended to the spherical Razavy-like quantum dots electronic structure. We have shown that depending on the combinations of the Razavy-like potential parameters, the quantum wells can evolve from parabolic confinement in an isolated quantum well to a configuration of two coupled quantum wells. We have shown that in general the transition energies (dipole matrix elements) between the ground state and the first excited state: i) are decreasing (increasing) functions of M-parameter, ii) are increasing (decreasing) functions of A-parameter, iii) they increase (decrease) when considering the position-dependent effective mass effects, and iv) are increasing (decreasing) functions of the intense laser field parameter. In the case of the optical absorption and relative changes in the refractive index coefficients, we have shown blueshifts or redshifts by changing the A-, M-, and α0-parameters and by considering the effects of the position-dependent effective mass. In spherical quantum dots, we have shown that with an appropriate value of A- and M-parameters the system can evolve from a spherical quantum dot with infinite parabolic potential.

Ultrafast Quantum-Well Photodetectors Operating at 10 μm with a Flat Frequency Response up to 70 GHz at Room Temperature

Abstract: III–V semiconductor mid-infrared photodetectors based on intersubband transitions hold great potential for ultra-high-speed operation up to several hundreds of GHz. In this work we exploit a ∼350 n...

Auger-Assisted Electron Transfer between Adjacent Quantum Wells in Two-Dimensional Layered Perovskites.

Abstract: Two-dimensional (2D) layered perovskites are naturally formed multiple quantum-well (QW) materials, holding great promise for applications in many optoelectronic devices. However, the further use of 2D layered perovskites in some devices is limited by the lack of QW-to-QW carrier transport/transfer due to the energy barrier formed by the insulating ligands between QWs. Herein, we report an Auger-assisted electron transfer between adjacent QWs in (CmH2m+1NH3)2PbI4 2D perovskites particularly with m = 12 and 18, where the electron energy barrier (Eb) is similar to the QW band gap energy (Eg). This Auger-assisted QW-to-QW electron transfer mechanism is established by the observation of a long-lived and derivative-like transient absorption feature, which is a signature of the quantum confined Stark effect induced by the electron-hole separation (thus an internal electric field) between different QW layers. Our finding provides a new guideline to design 2D perovskites with an optically tunable QW-to-QW charge transport property, advancing their applications in optoelectronics and optical modulations.

Designs of InGaN Micro-LED Structure for Improving Quantum Efficiency at Low Current Density.

Abstract: Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density. Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

InAs/GaAs quantum dot single-section mode-locked lasers on Si (001) with optical self-injection feedback

Abstract: Silicon based InAs quantum dot mode locked lasers (QD-MLLs) are promising to be integrated with silicon photonic integrated circuits (PICs) for optical time division multiplexing (OTDM), wavelength division multiplexing (WDM) and optical clocks. Single section QD-MLL can provide high-frequency optical pulses with low power consumption and low-cost production possibilities. However, the linewidths of the QD-MLLs are larger than quantum well lasers, which generally introduce additional phase noise during optical transmission. Here, we demonstrated a single section MLL monolithically grown on Si (001) substrate with a repetition rate of 23.5 GHz. The 3-dB Radio Frequency (RF) linewidth of the QD-MLL was stabilized at optimized injection current under free running mode. By introducing self-injection feedback locking at a feedback strength of -24dB, the RF linewidth of MLL was significantly narrowed by two orders of magnitude from 900kHz to 8kHz.

Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors.

Abstract: Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of ∼2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects. Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices. Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes. Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors. In fact, the 2D morphology of the GaS flakes intrinsically minimizes the distance between the photogenerated charges and the surface area at which the redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious for standard solid-state configurations. Consequently, PEC-type 2D GaS photodetectors display a relevant UV-selective photoresponse. In particular, they attain responsivities of 1.8 mA W-1 in 1 M H2SO4 [at 0.8 V vs reversible hydrogen electrode (RHE)], 4.6 mA W-1 in 1 M Na2SO4 (at 0.9 V vs RHE), and 6.8 mA W-1 in 1 M KOH (at 1.1. V vs RHE) under 275 nm illumination wavelength with an intensity of 1.3 mW cm-2. Beyond the photodetector application, 2D GaS-based PEC-type devices may find application in tandem solar PEC cells in combination with other visible-sensitive low-band-gap materials, including transition-metal monochalcogenides recently established for PEC solar energy conversion applications.

InGaN-Based microLED Devices Approaching 1% EQE with Red 609 nm Electroluminescence on Semi-Relaxed Substrates

Abstract: In this paper, we report the successful demonstration of bright InGaN-based microLED devices emitting in the red spectral regime grown by metal organic chemical vapor deposition (MOCVD) on c-plane semi-relaxed InGaN substrates on sapphire. Through application of an InGaN/GaN base layer scheme to ameliorate high defect density and maintain appropriate lattice constant throughout the growth, high-In quantum wells (QWs) can be grown with improved crystal quality. Improvement to the design of the growth scheme also yields higher power output resulting in an increase to the external quantum efficiency (EQE). Combined, these two improvements allow for an 80 × 80 μm2 microLED device emitting at 609 nm to achieve 0.83% EQE. Furthermore, the true In content of the QW is measured using atomic probe tomography (APT) to confirm the improved In incorporation during high temperature active region growth. These developments represent advancement toward the realization of bright, highly efficient red III-nitride LEDs to be used in RGB applications under one material system.

InAs/InP Quantum Dash Semiconductor Coherent Comb Lasers and their Applications in Optical Networks

Abstract: We report on the design, growth, and fabrication of InAs/InP quantum dash (QD) gain materials and their use in lasers for optical network applications. A noise performance comparison between QD and quantum well (QW) Fabry–Perot (F-P) lasers has been made. By using the QD gain material we have successfully developed and assembled C-band coherent comb laser (CCL) modules with an electrical fast feedback loop control system to ensure a targeted mode frequency spacing. The frequency spacing was maintained within ±100 ppm and the operation wavelengths locked on the desired ITU grid within 0.01 nm over a period of several months. We also investigated a 25-GHz C-band QD CCL with an external cavity self-injection feedback locking (SIFL) system to reduce the optical linewidth of each individual channel to below 200 kHz in the wavelength range from 1537.55 nm to 1545.14 nm. The RF mode beating signal 3-dB bandwidth was also reduced from 9 kHz to approximately 500 Hz with this SIFL system. These QD CCLs with ultra-low relative intensity noise (RIN), ultra-narrow optical linewidth, and ultra-low timing jitter are excellent laser sources for multi-terabit optical networks. Using a 34.2 GHz QD CCL we demonstrate 10.8 Tbit/s (16QAM 48 × 28 GBaud PDM) coherent data transmission over 100 km of standard single mode fiber (SSMF) and 5.4 Tbit/s (PAM-4 48 × 28 GBaud PDM) aggregate data transmission capacity over 25 km of SSMF with error-free operation.

High Power and Narrow Vertical Divergence Laser Diodes With Photonic Crystal Structure

Abstract: High power and narrow vertical divergence lasers for the 980 nm wavelength range based on the photonic crystal (PC) structure are investigated. The structure of the PC layers and the position of the quantum well (QW) are optimized through mode analysis, which to maximize the output power of the PC laser. A broad area (BA) laser with $300~\mu $ m width and 4 mm cavity length yields 41.8 W output with far-field divergence angles of 16.5° in lateral and 16.8° in vertical at full width at half maximum (FWHM) under continuous-wave (CW) 48 A operating current at 5 °C.

Self-Resonant Microlasers of Colloidal Quantum Wells Constructed by Direct Deep Patterning.

Abstract: Here, the first account of self-resonant fully colloidal μ-lasers made from colloidal quantum well (CQW) solution is reported. A deep patterning technique is developed to fabricate well-defined high aspect-ratio on-chip CQW resonators made of grating waveguides and in-plane reflectors. The fabricated waveguide-coupled laser, enabling tight optical confinement, assures in-plane lasing. CQWs of the patterned layers are closed-packed with sharp edges and residual-free lifted-off surfaces. Additionally, the method is successfully applied to various nanoparticles including colloidal quantum dots and metal nanoparticles. It is observed that the patterning process does not affect the nanocrystals (NCs) immobilized in the attained patterns and the different physical and chemical properties of the NCs remain pristine. Thanks to the deep patterning capability of the proposed method, patterns of NCs with subwavelength lateral feature sizes and micron-scale heights can possibly be fabricated in high aspect ratios.

Engineering a Robust Flat Band in III-V Semiconductor Heterostructures

Abstract: Electron states in semiconductor materials can be modified by quantum confinement. Adding to semiconductor heterostructures the concept of lateral geometry offers the possibility to further tailor the electronic band structure with the creation of unique flat bands. Using block copolymer lithography, we describe the design, fabrication, and characterization of multiorbital bands in a honeycomb In0.53Ga0.47As/InP heterostructure quantum well with a lattice constant of 21 nm. Thanks to an optimized surface quality, scanning tunnelling spectroscopy reveals the existence of a strong resonance localized between the lattice sites, signature of a p-orbital flat band. Together with theoretical computations, the impact of the nanopatterning imperfections on the band structure is examined. We show that the flat band is protected against the lateral and vertical disorder, making this industry-standard system particularly attractive for the study of exotic phases of matter.

Multi-band SWIR-MWIR-LWIR Type-II superlattice based infrared photodetector

Abstract: Type-II InAs/GaSb superlattices (T2SLs) has drawn a lot of attention since it was introduced in 1970, especially for infrared detection as a system of multi-interacting quantum wells. In recent years, T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process, which elevated the performances of T2SL-based photo-detectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). As a pioneer in the field, center for quantum devices (CQD) has been involved in growth, design, characterization, and introduction of T2SL material system for infrared photodetection. In this review paper, we will present the latest development of bias-selectable multi-band infrared photodetectors at the CQD, based on InAs/GaSb/AlSb and InAs/InAs1-xSbx type-II superlattice.

Strongly Quantum-Confined Blue-Emitting Excitons in Chemically Configurable Multiquantum Wells.

Abstract: Light matter interactions are greatly enhanced in two-dimensional (2D) semiconductors because of strong excitonic effects. Many optoelectronic applications would benefit from creating stacks of atomically thin 2D semiconductors separated by insulating barrier layers, forming multiquantum-well structures. However, most 2D transition metal chalcogenide systems require serial stacking to create van der Waals multilayers. Hybrid metal organic chalcogenolates (MOChas) are self-assembling hybrid materials that combine multiquantum-well properties with scalable chemical synthesis and air stability. In this work, we use spatially resolved linear and nonlinear optical spectroscopies over a range of temperatures to study the strongly excitonic optical properties of mithrene, that is, silver benzeneselenolate, and its synthetic isostructures. We experimentally probe s-type bright excitons and p-type excitonic dark states formed in the quantum confined 2D inorganic monolayers of silver selenide with exciton binding energy up to ∼0.4 eV, matching recent theoretical predictions of the material class. We further show that mithrene's highly efficient blue photoluminescence, ultrafast exciton radiative dynamics, as well as flexible tunability of molecular structure and optical properties demonstrate great potential of MOChas for constructing optoelectronic and quantum excitonic devices.

Highly-efficient electrically-driven localized surface plasmon source enabled by resonant inelastic electron tunneling

Abstract: On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability. However, the major barrier to the demonstrated IET-based SP sources is their low SP excitation efficiency due to the fact that elastic tunneling of electrons is much more efficient than inelastic tunneling. Here, we remove this barrier by introducing resonant inelastic electron tunneling (RIET)—follow a recent theoretical proposal—at the visible/near-infrared (NIR) frequencies and demonstrate highly-efficient electrically-driven SP sources. In our system, RIET is supported by a TiN/Al2O3 metallic quantum well (MQW) heterostructure, while monocrystalline silver nanorods (AgNRs) were used for the SP generation (localized surface plasmons (LSPs)). In principle, this RIET approach can push the external quantum efficiency (EQE) close to unity, opening up a new era of SP sources for not only high-performance plasmonic circuitry, but also advanced optical sensing applications. On-chip circuits based on plasmonic systems are a promising potential technology. Here the authors present efficient, on-chip, localized plasmonic excitation based on resonant inelastic electron tunneling with metallic quantum well junction.

Effects of applied external fields on the nonlinear optical rectification, second, and third harmonic generation in a quantum well with exponentially confinement potential

Abstract: In the present study, the nonlinear optical rectification (NOR), second harmonic generation (SHG), and third harmonic generation (THG) coefficients in GaAs/GaAlAs quantum well (QW) with exponentially confinement potential were theoretically analyzed for different applied static electric and magnetic fields as well as the non-resonant intense laser field (ILF). In addition, the effect of adjustable physical parameters ( $$\upeta $$ and $$\upkappa $$ ) on the optical properties was also investigated. The subband energy levels and their corresponding envelope wave functions of an electron confined in a QW with exponentially confinement potential are calculated by diagonalization method within the framework of effective mass and single parabolic band approximations. The analytical expressions of the NOR, SHG, and THG are obtained using compact density matrix approach via iterative method. The numerical results show that the applied external fields and physical parameters have a great effect on the optical characteristics of the considered system. In particular, we have found the applied external fields have a significant effect on the position and magnitude of resonant peaks of NOR, SHG, and THG.

Theoretical investigation of linear and nonlinear optical properties in an heterostructure based on triple parabolic barriers: Effects of external fields

Abstract: In this work, we have investigated theoretically the impact of intense laser, electric and magnetic fields on the linear and nonlinear optical properties of a quantum well heterostructure containing triple parabolic barriers (GaAs/AlGaAs). Within the framework of the effective-mass and parabolic band approximations, we have computed the confined lowest energy levels and their corresponding densities of probability, through the use of a finite difference technique to solve the corresponding differential equation. Besides, we evaluate the total optical absorption (TOACs) and relative refractive index change (RRICs) coefficients. The obtained findings show that an increase of the intensity of the intense laser field produces a blue shift at first and then a red shift of the TOACs and RRICs. A specific value of the laser field separating the two kinds of signal displacements is outlined. Contrarily to the intense laser field, an increment of the external static electric and magnetic fields induces only a blue shift in the variation of the TOACs and RRICs. In addition, we have discussed in detail the variation of diagonal and non-diagonal matrix elements which are responsible on the variation of the amplitudes of the TOACs and RRICs. We think that the obtained results can be useful in the design of new device's generation employed in optoelectronic domain.