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Two‐dimensional organic–inorganic hybrid perovskites (OIHPs) with alternating structure of the organic and inorganic layers have a natural quantum well structure. The difference of dielectric constants between organic and inorganic layers in this structure results in the enhancement of dielectric confinement effect, which exhibits a large exciton binding energy and hinders the separation of electron‐hole pairs. Herein, a strategy to reduce the dielectric confinement effect by narrowing the dielectric difference between organic amine molecule and [PbBr6]4− octahedron is put forward. The Ethanolamine (EOA) contains hydroxyl groups, resulting in the positive and negative charge centers of O and H non‐overlapping, which generated a larger polarity and dielectric constant. The reduced dielectric constant produces a smaller exciton binding energy (71.03 meV) of (C2H7NO)2PbBr4 ((EOA)2PbBr4) than (C8H11N)2PbBr4 ((PEA)2PbBr4 (156.07 meV), and promotes the dissociation of electrons and holes. The increasing of lifetime of photogenerated carrier in (EOA)2PbBr4 are proved by femtosecond transient absorption spectra. Density functional theory (DFT) calculations have also indicated that the small energy shift of the total density of states (DOS) between the C/H/N and the Pb/Br in (EOA)2PbBr4 favors the separation of electrons and holes. In addition, this work demonstrates the application of (PEA)2PbBr4 and (EOA)2PbBr4 in the field of photocatalytic CO2 reduction. [ABSTRACT FROM AUTHOR]

It is reported that the solvent environment exerts a significant influence on the property of perovskite precursor solution and resultant film, which is more pronounced in more complex low‐dimensional perovskites. Four solvent additives with varying basicity are introduced to instigate a tug‐of‐war among bonding interactions, thereby exploring the systematic effect of the solvent environment on the growth of quantum wells and the photoelectric properties of the resultant low‐dimensional perovskite films. A governing principle that diverges significantly from those previously documented for three‐dimensional perovskites is elucidated in low‐dimensional perovskites. When coordination interactions predominate in the solvent environment, the emergence of a two‐dimensional GA2PbI4 transitional phase is fostered to facilitate subsequent transformation into the desirable ACI phase, and the perovskite crystallization kinetics is retarded to improve the film quality. Hence, the highest power conversion efficiency (PCE) of 22.73% is obtained for GA(MA)nPbnI3n+1 (n = 5) based solar cells with a p‐i‐n structure. The PCE achieved in this work is a record among the reported low‐dimensional perovskite solar cells. [ABSTRACT FROM AUTHOR]

We demonstrate scalable ultra-strong light–matter coupling with intersubband polaritons in a truly harmonic confining potential. The harmonicity grants immunity from electron–electron interactions, a protection guaranteed by the Kohn theorem, allowing the intersubband transition frequency to be lowered while keeping the light–matter interaction strength constant. In principle, this procedure permits increasing the relative coupling strength (η = ΩRabi/ω12) at will. We measure a record low intersubband transition at 1.24 THz and a lower polaritonic mode at 920 GHz, below the barrier of 1 THz. The system exhibits a η ratio of 0.24, fully in the ultra-strong coupling regime, and remains stable up to 78 K. This approach is valuable for future non-adiabatic quantum electrodynamic experiments at long wavelengths. [ABSTRACT FROM AUTHOR]

Quantum well AlGaN/AlN/GaN high electron mobility transistor (HEMT) devices are a unique kind of semiconductor device that make use of a heterostructure made up of layers of different materials. In this study, the operational characteristics and performance optimization of HEMT devices, with a specific emphasis on the behavior of three‐quantum‐well (3QW) HEMT devices, are explored. The impact of gate voltage is explored and is observed that higher gate voltages result in lower pinch‐off voltages and higher saturation drain currents. In these findings, valuable insights for optimizing circuit designs and ensuring dependable operation across a range of electronic applications are offered. In addition, In this study, the device's ability to detect changes in gate voltage and its nonlinear characteristics is emphasized, providing valuable information for improving the device's performance. Additionally, the benefits of HEMT devices with negative threshold voltages are explored. Devices utilizing AlGaN/AlN/GaN structures demonstrate exceptional performance characteristics, such as rapid switching capabilities, high energy efficiency, and low noise performance, making them well suited for a wide range of scientific and technological applications. Finally, when comparing a QW HEMT device at different drain bias conditions (Vd = 1 V and Vd = 5 V), noticeable variations suggesting improved performance with higher drain bias. [ABSTRACT FROM AUTHOR]

Understanding quantum systems is of significant importance for assessing the performance of quantum hardware and software, as well as exploring quantum control and quantum sensing. An efficient representation of quantum states enables realizing quantum state tomography with minimal measurements. In this study, we propose an alternative approach to state tomography that uses tensor network representations of mixed states through locally purified density operators and employs a classical data postprocessing algorithm requiring only local measurements. Through numerical simulations of one-dimensional pure and mixed states and two-dimensional pure states up to size 8 × 8, we demonstrate the efficiency, accuracy, and robustness of our proposed methods. Experiments on the IBM and Quafu Quantum platforms complement these numerical simulations. Our study opens avenues in quantum state tomography for two-dimensional systems using tensor network formalism. Quantum state tomography is a fundamental tool for assessing the performance of quantum hardware and plays a crucial role in advancing quantum information processing. The authors present a method based on tensor network representations and local measurements, demonstrating accuracy and efficiency in characterizing noisy quantum states. [ABSTRACT FROM AUTHOR]

The construction of miniaturized light-emitting diodes (LEDs) with high external quantum efficiency (EQE) at room temperature remains a challenge for on-chip optoelectronics. Here, we demonstrate microsized LEDs fabricated by a dry-transfer van der Waals (vdW) integration method using typical layered Ruddlesden-Popper perovskites (RPPs). A single-crystalline layered RPP nanoflake is used as the active layer and sandwiched between two few-layer graphene contacts, forming van der Waals LEDs (vdWLEDs). Strong electroluminescence (EL) emission with a low turn-on current density of ~20 pA μm-2 and high EQE exceeding 10% is observed at room temperature, which sets the benchmark for the EQE of vdWLEDs ever recorded. Such efficient EL emission is attributed to the inherent multiple quantum well structure and high photoluminescence quantum yield (~35%) of RPPs and a low charge injection barrier of ~0.10 eV facilitated by the Fowler-Nordheim tunneling mechanism. These findings promise a scalable pathway for accessing high-performance miniaturized light sources for on-chip optical optoelectronics. [ABSTRACT FROM AUTHOR]

In our quest to understand the generation of cosmological perturbations, we face two serious obstacles: we do not have direct information about the environment experienced by primordial perturbations during inflation, and our observables are practically limited to correlators of massless fields, heavier fields and derivatives decaying exponentially in the number of e-foldings. The flexible and general framework of open systems has been developed precisely to face similar challenges. Building on previous work, we develop a Schwinger-Keldysh path integral description for an open effective field theory of inflation, describing the possibly dissipative and non-unitary evolution of the Goldstone boson of time translations interacting with an unspecified environment, under the key assumption of locality in space and time. Working in the decoupling limit, we study the linear and interacting theory in de Sitter and derive predictions for the power spectrum and bispectrum that depend on a finite number of effective couplings organised in a derivative expansion. The smoking gun of interactions with the environment is an enhanced but finite bispectrum close to the folded kinematical limit. We demonstrate the generality of our approach by matching our open effective theory to an explicit model. Our construction provides a standard model to simultaneously study phenomenological predictions as well as quantum information aspects of the inflationary dynamics. [ABSTRACT FROM AUTHOR]

Red micro-light-emitting diodes (μ-LEDs) with AlGaInP/GaInP multiple quantum wells are fabricated with an oxide perimeter region to control the current injection path. When the values of the external quantum efficiency (EQE) of the 30 μm-size μ-LED with the oxide perimeter region are compared with those of the device without the oxide perimeter region, an improvement as high as 40% is observed at current densities <80 A/cm2. From the finite-difference time-domain simulation of the light-extraction efficiency (LEE), which shows that the LEE of the device with the oxide perimeter region is ∼12% smaller than that of the device without the oxide perimeter region, it can be seen that the increased EQE is attributed to the improvement of the internal quantum efficiency (IQE). Since the oxide perimeter region limits the current paths to the sidewalls of the μ-LED chips, the nonradiative recombination via sidewall defects is considered suppressed, resulting in the improvement of the IQE. The oxidation of the AlGaAs layer utilized in this work is easy to implement and accurately controllable, suitable for mass-production of high-efficiency red μ-LEDs for display applications. [ABSTRACT FROM AUTHOR]

Ultraviolet photodetectors (UPDs) based on low‐dimensional halide perovskites have undergone rapid development. Here, regulation of the electronic configuration of low‐dimensional hybrid perovskites are reported via organic cations for self‐powered UPDs. For the first time, it is determine that the rational design of organic cation phenyl alkylammonium can effectively prevent phonon scattering thus increasing charge carrier extraction in low dimensional lead chlorine perovskite thin‐films. As a result, the exciton‐binding energy can be reduced to 62.91 meV in (PMA)2PbCl4 perovskite films with a charge‐carrier mobility of 0.335 cm2 V−1 s−1. The fabricated (PMA)2PbCl4‐based self‐powered UPDs has achieved a high detectivity of 6.32 × 1013 jones with a low noise current of 0.35 pA Hz−1/2 under zero bias. A further demonstration of images with high UV to visible light rejection ratio under weak‐light illumination of 70 nW cm−2 highlights the feasible potential application of low‐dimensional perovskite. [ABSTRACT FROM AUTHOR]

Spherical quantum wells (SQWs) have proven to be excellent materials for suppressing Auger recombination due to their expanded confinement volume. However, research on the factors and mechanisms of their high-intensity optical properties, such as multiexciton properties and third-order optical nonlinearities, remains incomplete, limiting further optimization of these properties. Here, a series of CdS/CdSe (xML)/CdS SQWs with varying CdSe layer thicknesses were prepared. The modulation effects of CdSe shell variations on the PL properties, defect distribution, biexciton binding energy, and third-order optical nonlinearities of the SQWs were investigated, and their impact on the material's multiexciton properties was further analyzed. Results showed that the typical CdS/CdSe(3ML)/CdS sample exhibited a large volume-normalized two-photon absorption cross-section (18.17 × 102 GM/nm3) and favorable biexciton characteristics. Optical amplification was observed at 12.4 μJ/cm2 and 1.02 mJ/cm2 under one-photon (400 nm) and two-photon (800 nm) excitation, respectively. Furthermore, different amplified spontaneous emission spectra were observed for the first time under one/two-photon excitation. This phenomenon was attributed to thermal effects overcoming the biexciton binding energy. This study provides valuable insights for further optimizing multiexciton gain characteristics in SQWs and developing optical gain applications. [ABSTRACT FROM AUTHOR]

In this study, the influence of temperature and hydrostatic pressure on impurity states in InxGa1-xAs/GaAs quantum wells (QWs) with different shapes, including square, parabolic, and V-shaped, was investigated using the effective mass envelope function approximation and the plane wave expansion method. The results demonstrate that an increase in temperature leads to a decrease in the energy of the impurity states, while an increase in hydrostatic pressure causes the impurity state energy to rise. It was observed that the effect of hydrostatic pressure on the impurity states is more significant than that of temperature. Furthermore, the impact of temperature and hydrostatic pressure varies depending on the shape of the QWs. Additionally, as the In composition increases, the impurity states exhibit a gradual increasing trend. [ABSTRACT FROM AUTHOR]

Quantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits. [ABSTRACT FROM AUTHOR]

Numerical and analytical results of a study of the single-particle entropy of a quasi-two-dimensional electron gas with allowance for the nonparabolicity of the dispersion are presented. The dependence of the single-particle entropy on the chemical potential of the gas at and far from the resonance points is analysed. It is shown that at low temperatures, the nonparabolicity of the band gives a small correction to the single-particle entropy. Both at and far from the resonance point, this correction is proportional to the product of the nonparabolicity coefficient and temperature α T. The influence of the broadening of the size quantization levels on the single-particle entropy is estimated numerically. The results obtained are presented for different temperatures of the degree of nonparabolicity of the conduction band and the magnitude of broadening. [ABSTRACT FROM AUTHOR]

This paper reports on a monolithically integrated gallium arsenide (GaAs)-based photonic integrated circuit platform for wavelengths around 1064 nm. Enabled by spatially selective quantum well removal and two-step epitaxial growth, it supports on-chip gain as well as passive waveguides. In addition, shallow- and deep-etched waveguides are realized. The former result in waveguide losses of less than 2 dB/cm, while the latter enable compact integrated waveguide components. To demonstrate the performance of the platform, racetrack ring resonators based on deep-etched Euler bends and shallow-etched directional couplers are realized, achieving high intrinsic quality factors of 2.6 × 105 and 3.2 × 105 for the fundamental TE and TM mode, respectively. To demonstrate the use of these resonators, ring-resonator-coupled lasers are fabricated, resulting in one-sided output powers of up to 14 mW and single-mode operation with 40 dB side-mode suppression. The successful integration of ring resonators on a GaAs-based active/passive photonic integrated circuit platform paves the way for the realization of fully monolithic, widely tunable, and narrow linewidth ring-resonator-coupled laser sources. [ABSTRACT FROM AUTHOR]

This paper explores the propagation loss in waveguides on directly bonded InP/Si substrates, using numerical simulations to understand the effect of voids within the waveguide structure. Using COMSOL Multiphysics, we developed a model to simulate light propagation, focusing on how void characteristics such as diameter and angle influence the propagation loss. Our findings reveal a correlation between void dimensions and the increased threshold current density in separate confinement heterostructure multiple quantum well laser diodes, thereby providing insights into optimizing waveguide design for enhanced laser performance on InP/Si substrates. This research underscores the critical role of substrate bonding quality in minimizing internal losses and improving device efficiency. [ABSTRACT FROM AUTHOR]

The impact of delta-doping modulation and electric field influence within a nanostructure consisting of three GaAs quantum wells (QWs) separated by AlGaAs barriers was investigated. The quantized energy levels, Fermi energy, wavefunctions, self-consistent potential, and electron density distribution were evaluated by a self-consistent solution of the Schrödinger and Poisson equations using the finite element method within the FEniCS project in Python. The results indicate that increasing the electric field reduces energy levels and Fermi energy. In addition, the delta-doping position and electric field significantly affect the self-consistent potential and electron density distribution. This study provides a possibility to tailor optical properties, such as the linear absorption coefficient and photoluminescence, by adjusting geometrical and non-geometrical parameters, including donor density, enhancing the functionality of doped QWs in designing high electron mobility transistors. [ABSTRACT FROM AUTHOR]

A type I InAs(Sb)/InAsPSb strain engineered multiple quantum wells light emitting diodes system has been demonstrated. Tensile InAsPSb quantum barriers with a high degree of band offset (∆EC = 116–123 meV, ∆EV = 193–250 meV) were used to compensate for the high compressive strain of the InAs(Sb) quantum wells. The structure was grown on the n+-InAsxP1−x metamorphic buffer with a high degree of relaxation (98%), low surface roughness (0.69 nm), and low dislocation density. Through careful strain engineering design, the compressive strain of InAs(Sb) reaches 0.57%–1.52% without strain relaxation. The incorporation of Sb into the multiple quantum wells not only reduces the bandgap but also improves the interface quality by acting as an effective surfactant. Structural analysis reveals superior quality in InAsSb/InAsPSb multiple quantum wells compared to InAs/InAsPSb multiple quantum wells, demonstrating significantly reduced interface roughness and suppression of the Stranski–Krastanov growth mode. Room temperature electroluminescence measurements show a tunable emission wavelength ranging from 2.7 to 3.3 μm, accompanied by a narrow full width at half maximum value of 45 meV. Photoluminescence analysis indicates that the internal quantum efficiency of InAsSb/InAsPSb multiple quantum wells is 5.5%, which is 7 times higher than that of InAs/InAsPSb. [ABSTRACT FROM AUTHOR]

We discuss the electrical properties of molecular beam epitaxy (MBE) grown, modulation doped, Ge1− x Sn x quantum well devices. A consequence of the epitaxial growth process is that electronic disorder is introduced even in modulation doped quantum well structures and electrical transport properties that are characteristic of a high level of disorder are apparent. MBE growth of this material also results in the surface segregation of elemental β -Sn in the way that has been observed utilizing other epitaxial growth methods. A thermally activated, p-type mobility is a clear feature of the electrical properties with generally temperature independent hole densities ∼1012 cm−2 from the measured Hall effect and coming from the modulation doping. We present a discussion of Hall effect measurements in this disordered regime. The percolation carrier density in MBE modulation doped GeSn is in the region of ∼1 × 1012 cm−2 although Hall measurements in this regime are difficult to quantify when the resistivity >(h / e 2). In this notation h is Planck's constant and e is the unit of charge. Conductivities (σ) as low as ∼0.028 × (e 2/ h) × square can be measured in the four-contact ac configuration and the temperature dependence indicates a mobility edge in these p-type devices below ∼2 × 1012 cm−2. At lower temperatures (<∼1 K) the presence of a Coulomb gap can be determined using dc transport, constant voltage measurements where small ac current excitation is not available experimentally. This two-contact configuration can determine σ down to ∼10−6 × (e 2/ h), deep into the localization regime, revealing a hopping conductivity dominated system. We discuss the relevance of these electrical properties for MBE grown GeSn devices. [ABSTRACT FROM AUTHOR]

HgTe has been considered to be one of the most versatile topological materials. Depending on the in‐plane strain, Weyl and Dirac semi‐metal, as well as topological insulator phases, are feasible. Here, for the first time it is reported, that an InAs:S substrate promotes an initial 2D growth of a ZnTe thin layer and subsequent high crystalline quality ZnTe/CdTe superlattices serve as a smooth and continuous virtual substrate for the growth of (Cd,Hg)Te/HgTe/(Cd,Hg)Te heterostructures with unstrained quantum well HgTe (topological insulator) and compressively strained bulk HgTe (Weyl semimetal) by molecular beam epitaxy. Compared with the superlattices previously grown on GaAs substrates, the quantum well and bulk heterostructures exhibit homogeneous surfaces with root mean square roughnesses of 0.88–0.93 nm, which is three times lower than those observed for 3D islands (2.7–3.4 nm) on GaAs substrates. Additionally, magnetotransport measurements confirm high electronic quality and demonstrate that the S‐doped InAs substrate can be used as an effective back gate. These results manifest a (big) step forward toward the improvement of micro‐ and nanometer‐sized top‐ and back‐gated device fabrication on topological materials. [ABSTRACT FROM AUTHOR]

This study compared the photoluminescence (PL) stabilities of formamidinium (FA) and methylammonium (MA) in lead iodide perovskite quantum dots (QDs). To exclude other factors, such as size and purity, that may affect stability, MAPbI3 and FAPbI3 QDs with nearly identical sizes (~10.0 nm) were synthesized by controlling the ligand concentration and synthesis temperature. Transmission electron microscopy images and X‐ray diffraction patterns confirmed homogeneous single‐phase perovskite structures. Additionally, the bandgaps and sizes of the synthesized QDs closely matched those of the infinite quantum well model, which guaranteed that the photostability was solely caused by the different organic molecules in the two QDs. We analyzed the PL peak centers and full‐width at half maximum of the QDs for 32 days. The enhanced stability of FAPbI3 was found to be caused by the nearly zero redshift (1.615 eV) of its PL peak, in contrast to the redshift (1.685→1.670 eV) of MAPbI3. [ABSTRACT FROM AUTHOR]

The optical properties of wurtzite violet InGaN/GaN coupled quantum well (QW) structures are experimentally studied using photoluminescence (PL) and electroluminescence (EL) spectroscopy. Two emission peaks, referred to as Peak H and Peak L, are observed in both PL and EL spectra, due to the ground state splitting induced by the well coupling. Experimental PL and EL results reveal that coupled QWs show different optical responses due to the different variation in the electric field inside the QW structure. Since the direction of the polarization electric field of the as-grown well/barrier layers is different, the external electric field applied by electrodes can change the energy band alignment between the well and the barrier layers, thus adjusting the coupling between the wells. Our results provide relevant information to improve our understanding of the optical properties of InGaN/GaN QWs and to develop novel optoelectronic devices. [ABSTRACT FROM AUTHOR]

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K). [ABSTRACT FROM AUTHOR]

We demonstrated GaN-based resonant tunneling diode (RTD) oscillators employing monolithic microwave integrated circuits. The GaN-based RTDs with a GaN quantum well and AlN double barriers were grown on freestanding c-plane semi-insulating GaN substrates using metal–organic chemical vapor deposition. The circuit components, including an RTD, a coplanar waveguide, a metal–insulator–metal capacitor, and shunt resistors, were monolithically fabricated on the GaN substrate. The circuits oscillated at a fundamental frequency of 17 GHz, which closely matched an estimated frequency using a three-dimensional electromagnetic simulator and a circuit simulator. This study contributes to the advancement of semiconductor high-frequency devices for millimeter wave and terahertz applications. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) perovskite solar cells (PSCs) exhibit better stability compared with three‐dimensional PSCs. However, fundamental questions remain over the chemical phase space in the 2D perovskite framework. Here, phase distribution of alternating cations in the interlayer space 2D perovskite (GA(MA)nPbnI3n+1) is regulated by using potassium salt to control the assembly behavior of colloidal particles and manage the growth of quantum well. The strong affinity between the spacer cation and sulfonate can slow down the intercalation of organic spacer cations to provide a time window for the insertion of MA+, which is conducive to forming high n phase to facilitate the charge transportation. During the crystallization process, potassium salt is extruded to the grain boundary and produce a passivation effect. In this case, the ion migration channels and inlet of water and oxygen are cut off, which is beneficial for the stability of PSCs. A power conversion efficiency of 20.90% is obtained in this work, to the best knowledge, which is the highest PCE for all reported GA(MA)3Pb3I10 perovskite and the large‐area device (1.01 cm2) shows a high efficiency of 18.73 %. Besides, the devices deliver good humidity stability. [ABSTRACT FROM AUTHOR]

Highly efficient and spectrally pure single photon sources are desirable in fundamental studies of quantum physics and in many varied applications like in quantum metrology and quantum cryptography. 2D semiconductor colloidal quantum wells (CQWs) are quite appropriate as nanoscale photon sources because of their giant oscillator strengths and large absorption cross sections. The integration of such sources with dielectric metasurfaces exhibiting narrow resonances provides an excellent platform for highly efficient light‐matter interactions and the development of on‐chip light sources with high spectral purity. Here details on the use of capillary filling method are reported to achieve photonic coupling of CQWs to a metasurface resonator (MSR) featuring a square‐lattice geometry of holes on a slab‐waveguide to achieve strongly enhanced and almost spectrally pure emission of ≈3% of the original out‐of‐plane emission line‐width of the quantum emitters at room temperature. Long‐range exciton‐mediated photon transport facilitated by in‐plane slab waveguide modes is demonstrated and a theoretical basis to explain all the experimental data including that in terms of the MSR‐modified Lamb shifts and Purcell decays is provided. The results demonstrate a new platform with emergent photonic properties and suggest possibility of their use in on‐chip photonic quantum information processing. [ABSTRACT FROM AUTHOR]

In this paper five enhancement‐mode monolithically integrated white‐light High electron mobility transistors‐light emitting diodes (HEMT‐LED) structures are proposed and simulated to obtain maximum light intensity, drain current Id and maximum trans‐conductance gm. In first four HEMT‐LED structures white light is generated by combining inbuilt yellow and blue lights and in fifth proposed structure the white light is generated with the combination of inbuilt red, green and blue lights. The InGaN quantum wells (QWs) are inserted in to e‐mode ITO/p‐GaN gate HEMT structures and the desired wavelength of light spectrums are generated by changing the in content (mole fraction), to obtain inbuilt white light. Among five proposed structures one shows Maximum Id‐max of 925 mA and maximum gm of 250 mS, which is significantly higher than any HEMT‐LED structures reported before. All the proposed structures are simulated in Silvaco TCAD software. [ABSTRACT FROM AUTHOR]

Shubnikov–de Haas oscillations and magneto-intersubband oscillations of the magnetoresistance in structures with single HgTe quantum wells with a width of 10−18 nm have been experimentally investigated. The conduction band spectrum in these arrays is split by the spin–orbit interaction. This leads to beats in the Shubnikov−de Haas oscillations and gives rise to low-frequency magneto-intersubband oscillations. The mutual positions of the antinodes of the Shubnikov−de Haas oscillations and the peaks in the magneto-intersubband oscillations are unusual: at low magnetic fields, they are opposite to theoretical predictions. The measurements in high magnetic fields, at which the relative amplitude of Shubnikov–de Haas oscillations exceeds 0.2–0.3, show a change in the mutual positions of the antinodes of the Shubnikov–de Haas oscillations and the peaks in low-frequency oscillations. Numerical calculations and additional measurements at different temperatures suggest that the observed effects are due to magnetic-field-induced oscillations of the Fermi level. [ABSTRACT FROM AUTHOR]

The present study examines the electronic and optical properties of Rosen-Morse quantum wells, which exhibit hyperbolic and exponential potential profiles, subjected to intense laser fields and electric fields. Calculations are performed within the framework of the effective mass and parabolic band approximations. To determine the eigenvalues of electrons confined in these potentials, the diagonalization method was employed, utilizing orthonormal base functions that are solutions of an infinite square quantum well. To calculate the total absorption coefficient, including linear and nonlinear terms for transitions between the lowest two energy levels, a combination of the standard density matrix formalism and the perturbation expansion method was employed. Our results indicate that intense laser field is a valuable tool for controlling the confinement potential of low-dimensional systems, enabling the appropriate tuning of these systems. While the electric field applied only to symmetrical structures breaks the symmetry and causes the peaks in the absorption spectrum to shift to red, a blue shift of the absorption peaks was achieved with the combined effect of the selected geometric shapes of the quantum wells and the electric field. Therefore, it is hoped that the obtained results will provide important improvements in device applications with a suitable choice of both fields and structure parameters. [ABSTRACT FROM AUTHOR]

This work will explore the generations of quantum nonlocalities (as entanglement, Bellnonlocality, and steerability) for two quantum wells (excitons) in dissipative microcavities containing a linear optical medium. An optical fiber links the microcavities. The generated two‐exciton nonlocalities are explored by using Bell inequality, steering inequality, and entanglement of formation. For initial correlated and uncorrelated states, the ability of the excitation–photon–fiber interactions to produce new generation and robustness of the two‐exciton nonlocality is investigated under the effects of the couplings of the exciton–photon and fiber–photon interactions as well as of the dissipations and the optical susceptibility. It is found that increasing the optical susceptibility enhances the regularity and amplitudes, reduces the frequencies of two‐exciton nonlocality dynamics, and supports dissipation degradations. For the initial uncorrelated state, decreasing the difference between the exciton–photon and fiber–photon couplings enhances the generations of the nonlocalities. For the initial correlated state, increasing the exciton–photon and fiber–photon couplings enhances the nonlocality conservation. For open microcavites, increasing the exciton–photon and fiber–photon couplings and the difference between them supports the nonlocality degradations resulting from the external environment dissipations. [ABSTRACT FROM AUTHOR]

This study presents a quantum well model using the transfer matrix technique to analyze the charge transfer characteristics of nanostructure sequences in both DNA and superlattices. The unconfined state, or unbound state, above the quantum well is used to investigate carrier behaviors in a semiconductor nanostructure. These analytical approaches can be extended to enhance the understanding of charge transfer in DNA nanostructures with periodic and aperiodic sequences. Experimental validation was conducted through photoreflectance spectroscopy on nanostructures within the semiconductor superlattices. Furthermore, the study's findings were compared with earlier research by Li et al. on the thermoelectric effect and its dependence on molecular length and sequences in single DNA molecules. The results showed agreement, offering novel insights into charge transfer and transport in DNA nanostructures across various sequence types. [ABSTRACT FROM AUTHOR]

This work presents an analysis and design of the two barrier-quantum well asymmetric spacer tunnel layer (QW-ASPAT) diodes for implantable rectenna circuits application. The RF and DC characteristic of a 10×10 μm² QW-ASPAT devices based on GaAs and In0.53Ga0.47As platform was simulated and extracted by using SILVACO atlas software. The highest extracted curvature coefficient, kv value of the both QW-ASPAT devices at zero bias was about 33V-1 compared with the standard structure GaAs/InGaAs was about 13V-1. The effects of changing in the thickness of the thin AlAs-barrier, the well width, and the spacer layer are fully investigated on the non-linear relationship between current and voltage of these diodes. A CV simulation was carried out, and it was found that the addition of the quantum-well layer between spacers and barrier reduced the junction capacitance of the QW-ASPAT device when compared with standard devices. The cut-off frequency of the proposed QW-GaAs and QW-InGaAs devices are 26GHz and 46GHz respectively. Finally, we conclude that the QW-ASPAT device is the best structure and can be used for microwave rectifiers in the miniaturized integrated rectenna systems. [ABSTRACT FROM AUTHOR]

Site- and polarity-controlled core–shell InGaN/GaN nanorod LED structures were grown by metal organic vapor phase epitaxy on Si(111). Scanning transmission electron microscope images reveal uniform multiple quantum wells on polarization-free sidewalls. Spatially resolved photoluminescence mapping on a single nanorod demonstrates that the emission at 3.0 eV stems from the polarization-free m-plane, which is supported by a fast recombination lifetime of ∼490 ps at low temperatures. Quasi-resonant laser excitation demonstrates predominant radiative recombination at low excitation densities, whereas at high excitation densities, the efficiency is lowered by Auger recombination and/or carrier leakage. [ABSTRACT FROM AUTHOR]

The misfit dislocation formation related to plastic strain relaxation in Si or Ge quantum well layers in SiGe heterostructures for spin qubits tends to negatively affect the qubit behaviors. Therefore, it is essential to understand and then suppress the misfit dislocation formation in the quantum well layers in order to achieve high-performance qubits. In this work, we studied the misfit dislocation propagation kinetics and interactions by annealing the strained Si or Ge layers grown by molecular beam epitaxy. The annealing temperatures are from 500 to 600 °C for Si layers and from 300 to 400 °C for Ge layers. The misfit dislocations were investigated by electron channeling contrast imaging. Our results show that the misfit dislocation propagation is a thermally activated process. Alongside, the blocking and unblocking interactions during misfit dislocations were also observed. The blocking interactions will reduce the strain relaxation according to theoretical calculation. These observations imply that it is possible to suppress the misfit dislocation formation kinetically by reducing the temperatures during the SiGe heterostructure epitaxy and post-epitaxy processes for developing well-functional SiGe-based spin qubits. [ABSTRACT FROM AUTHOR]

Hybrid ferromagnet–semiconductor systems possess new outstanding properties, which emerge when bringing magnetic and semiconductor materials into contact. In such structures, the long-range magnetic proximity effect couples the spin systems of the ferromagnet and semiconductor on distances exceeding the carrier wave function overlap. The effect is due to the effective p–d exchange interaction of acceptor-bound holes in the quantum well with d-electrons of the ferromagnet. This indirect interaction is established via the phononic Stark effect mediated by the chiral phonons. Here, we demonstrate that the long-range magnetic proximity effect is universal and observed in hybrid structures with diverse magnetic components and potential barriers of various thicknesses and compositions. We study hybrid structures consisting of a semimetal (magnetite Fe3O4) or dielectric (spinel NiFe2O4) ferromagnet and a CdTe quantum well separated by a nonmagnetic (Cd,Mg)Te barrier. The proximity effect is manifested in the circular polarization of the photoluminescence corresponding to the recombination of photoexcited electrons with holes bound to shallow acceptors in the quantum well induced by magnetite or spinel itself, in contrast to interface ferromagnet in case of metal-based hybrid systems. A nontrivial dynamics of the proximity effect is observed in the studied structures due to recombination-induced dynamic polarization of electrons in the quantum well. It enables the determination of the exchange constant Δexch ≈ 70 μeV in a magnetite-based structure. The universal origin of the long-range exchange interaction along with the possibility of its electrical control offers prospects for the development of low-voltage spintronic devices compatible with existing solid-state electronics. [ABSTRACT FROM AUTHOR]

In highly doped semiconductor quantum wells (QWs), electrons populate various energy states from different subbands and, therefore, several optical intersubband transitions (ISBTs) can occur simultaneously. Coulomb coupling between these ISBTs gathers the strength of all the individual transitions and concentrates all the oscillator strength in a single collective excitation: the multisubband plasmon (MSP). MSPs are an excellent platform for the study of collective and exotic effects in semiconductors and for the demonstration of novel device concepts. Indeed, the high electronic densities involved in the collective excitation greatly enhance the coupling strength and enable the ultra-strong coupling regime between MSPs and either optical modes in a cavity or phonons in the semiconductor. In this Perspectives paper, after addressing the basic physics of MSPs and the state of the art, we outline the most promising paths for the research community in this topic from the point of view of basic physics, material platforms, and applications of MSPs. [ABSTRACT FROM AUTHOR]

We consider the problem of analyzing spin-flip qubit gate operation in the presence of Random Telegraph Noise (RTN). Our compressive approach is the following. By using the Feynman disentangling operators method, we calculate the spin-flip probability of qubit driven by different kinds of composite pulses, e.g., Constant pulse (C-pulse), Quantum Well pulse (QW-pulse), and Barrier Potential pulse (BP-pulse) in the presence of RTN. When composite pulses and RTN act in the x-direction and z-direction respectively, we calculate the optimal time to achieve perfect spin-flip probability of qubit. We report that the highest fidelity of spin-flip qubit can be achieved by using C-pulse, followed by BP-pulse and QW-pulse. For a more general case, we have tested several pulse sequences for achieving high fidelity quantum gates, where we use the pulses acting in different directions. From the calculations, we find that high fidelity of qubit gate operation in the presence of RTN is achieved when QW-pulse, BP-pulse, and C-pulse act in the x-direction, y-direction, and z-direction, respectively. We extend our investigations for multiple QW and BP pulses while choosing the C-pulse amplitude constant in the presence of RTN. The results of calculation show that 98.5 % fidelity can be achieved throughout the course of RTN that may be beneficial for quantum error correction. [ABSTRACT FROM AUTHOR]

A photovoltaic device fabricated with conventional zincblende materials can use the Type-II quantum well structure, which spatially separates electrons and holes, to reduce their recombination rate. In order to obtain higher power conversion efficiency, it is desirable to preserve more energetic carriers by engineering a phonon "bottleneck," a mismatch between the gaps in the well and barrier phonon structure. Such a mismatch leads to poor phonon transport and therefore prevents energy from leaving the system in the form of heat. In this paper, we perform a superlattice phonon calculation to verify the "bottleneck" effect and build on this a model to predict the steady state of the hot electrons under photoexcitation. We describe the electrons and phonons with a coupled Boltzmann equation system and numerically integrate it to get the steady state. We find that inhibited phonon relaxation does lead to a more out-of-equilibrium electron distribution and discuss how this might be enhanced. We examine the different behaviors obtained for various combinations of recombination and relaxation rates and their experimental signatures. [ABSTRACT FROM AUTHOR]

Efficiency droop at high current densities is a problem for InGaN-based light-emitting diodes (LEDs), especially for conventional c-plane devices. The large internal electric fields in c-plane quantum wells (QWs) lead to an increase in the active region carrier density (n), causing the electrical efficiency droop onset to occur at low current densities. Here, we present an approach to reduce the internal electric fields (Eint) in c-plane QWs by placing doped p-type and n-type GaN barriers close to the QW. The reduced Eint also allows a thick QW active region design, which helps to lower n to further reduce the droop. The concept of using doped barriers to control Eint is explained using theory and device simulations. Following that, multiple series of thick single QW (SQW) LEDs were grown and characterized. Key parameters in the epitaxial design such as the doping levels and the relative position of the doped barriers were systematically studied and optimized. By using optimized doped barriers and a thick SQW, c-plane LEDs with a low-efficiency droop of 14% at 300 A/cm2 [with respect to the peak external quantum efficiency (EQE)] and a high peak EQE of 49% were demonstrated. [ABSTRACT FROM AUTHOR]

Trench defects, resulting in low emission efficiency in green and longer spectrum ranges, are widely observed in III-nitride alloy multiple quantum wells (MQWs), particularly in those with high indium content. There is a lack of understanding of the atomic formation mechanism of trench defects; however, it is crucial to the efficiency of devices. Here, we provided a thermodynamic analysis through first-principles calculations based on the density functional theory combined with experimental confirmation to reveal the atomic formation mechanism of trench defects in the InGaN MQWs system. The In-rich region is easy to form and induces basal plane stacking faults (BSFs) at the interface between the InGaN quantum well and the GaN quantum barrier (QB). The boundary between BSF and non-BSF regions exhibits a much slower growth rate due to the formation of homoelementary bonds, resulting in a V-shaped groove shape. Based on high-angle annular dark field scanning transmission electron microscopy, we observe the trench defects originating from the thick GaN QB layer due to the formation of closed-loop V-shaped grooves and the BSF. Besides, the cathodoluminescence measurements show that the InGaN QW within the defect has excess indium and poor crystal quality. [ABSTRACT FROM AUTHOR]

III-V lasers based on self-assembled quantum dots (QDs) have attracted widespread interest due to their unique characteristics, including low threshold current density (Jth), low sensitivity to backreflections, and resistance to threading dislocations. While most work to date has focused on 1.3 μm InAs/GaAs QDs, InP QDs have also aroused interest in lasers emitting at visible wavelengths. Molecular beam epitaxy (MBE) enables the growth of high-density InP/AlGaInP QDs on exact (001)-oriented GaAs substrates but requires a relatively low substrate temperature of <500 °C. The low substrate temperature used for phosphide growth in MBE leads to degraded optical properties and makes post-growth annealing a crucial step to improve the optical quality. Here, we report the exceptional thermal stability of InP/AlGaInP QDs grown using MBE, with up to 50× improvement in room temperature photoluminescence intensity with the optimization of annealing temperature and time. We also demonstrate the room temperature pulsed operation of InP multiple quantum dot (MQD) lasers on GaAs (001) emitting close to 735 nm with Jth values of 499 A/cm2 after annealing, a factor of 6 lower than their as-grown counterparts and comparable to such devices grown by MOCVD. In0.6Ga0.4P single quantum well (SQW) lasers on GaAs (001) also exhibit a substantial reduction in Jth from 340 A/cm2 as-grown to 200 A/cm2 after annealing, emitting at 680 nm under pulsed operation conditions. This work shows that post-growth annealing is essential for realizing record-performance phosphide lasers on GaAs grown by MBE for applications in visible photonics. [ABSTRACT FROM AUTHOR]

Ternary semiconductors such as InGaN thin films, quantum wells, and superlattices commonly exhibit alloy fluctuations that become increasingly pronounced with higher In-content. The thickness fluctuations of quantum wells and their thin cap-layers further introduce nanoscale inhomogeneities that alter the potential landscape. In this work, we present a combined theoretical and experimental study of InGaN single quantum wells with thin GaN cap-layers to unravel the influence of cap-layer thickness, compositional inhomogeneity, and thickness fluctuations on their electronic and optical properties. A pronounced spectral shift of quantum well emission for thin cap-layers between 1 and 10 nm is observed by micro-photoluminescence spectroscopy. The origin of this shift is explained by calculations of electronic band profiles and probability density overlap of carriers in the quantum well. The impact of alloy fluctuations and homogeneity for different cap-layer thicknesses is studied on both the microscale and nanoscale using UV micro-Raman scattering and tip-enhanced Raman spectroscopy (TERS). On the microscale, the alloy composition as determined by micro-Raman mapping appears very homogeneous except for the thinnest 1 nm cap-layer where small fluctuations are visible. On the nanoscale, TERS reveals local fluctuations on a 20–30 nm length scale. The influence of the cap-layer thickness on the TERS spectra is discussed regarding both the nanoscale homogeneity and the depth resolution of the near-field Raman scattering technique. Our results demonstrate the capabilities of TERS to resolve nanoscale thickness fluctuations and compositional inhomogeneities in ultra-thin semiconductor layers, even when they are buried by thin cap-layers with thicknesses below 10 nm. [ABSTRACT FROM AUTHOR]

Silicon photonics is a promising technology for the fabrication of dense photonic chips, thanks to the very mature silicon industry. The direct epitaxial growth of III–V lasers on silicon is one of the main challenges for the realization of compact and robust mid-infrared sensors based on photonic integrated circuits. The crystal defects arising from this heteroepitaxial growth affect the laser performance and, therefore, need to be mitigated but also studied to better understand their impact on the laser operation. Here, we studied the effect of threading dislocations on laser performance by comparing the series of GaSb-based diode lasers grown on native GaSb and Si substrates with different numbers of quantum wells (nQW) in their active zones. As expected, the laser threshold currents are higher in the case of diode lasers on Si, and they rapidly vary with nQW. Still, the lowest threshold current densities are achieved with nQW = 1 for both substrates. With the help of a theoretical gain model, we attribute these results to the fact that dislocations create non-radiative recombination but do not introduce additional optical losses. This work allows a better understanding of the origin of performance degradation and the decision to be made regarding the heterostructure design. [ABSTRACT FROM AUTHOR]

Quasi‐2D perovskites have attracted significant attention because of their environmental robustness and superior long‐term stability compared with their 3D counterparts. However, they typically consist of a mixture of multiple quantum wells with different optoelectrical properties, which degrades the electronic properties and hinders further electronic applications. Here, to challenge this issue, a surface p‐doping strategy involving the introduction of a thiophene‐containing polymer onto the surface of quasi‐2D tin perovskites is reported. The tin ions in the perovskites effectively interact with the sulfur atoms in the thiophene moieties, thereby generating hole carriers and inducing p‐doping. The resulting doped quasi‐2D perovskites exhibit excellent surface crystallinity, lower trap density, and enhanced charge carrier transport capability along the perovskite semiconductor channels. Consequently, the doped quasi‐2D tin perovskite‐based transistors exhibit a high field‐effect mobility of 53 cm2V−1s−1 (7 cm2V−1s−1 for the control device) and an outstanding on/off ratio (>107), together with superior operational stability. [ABSTRACT FROM AUTHOR]

An isotopically enriched 28Si/SiGe undoped heterostructure is a promising platform for Si-based qubits due to the long coherence time by reducing 29Si isotopes with non-zero nuclear spins. Carriers in the buried Si quantum well (QW) of the Si/SiGe heterostructures could tunnel to the oxide/Si interface, increasing charge noise and leading to charge instability. In this work, we investigate the tunneling effects on carrier distribution and transport properties in an isotopically enriched 28Si/SiGe undoped heterostructure and its transient characteristics by controlling the hold time of gate biasing under different drain biases. By holding the gate bias for a longer time, the drain is reduced since more carriers in the buried QW tunnel to the oxide interface. Furthermore, under a larger drain bias, more carriers can move across the Si/SiGe heterojunction to the oxide interface and are trapped, resulting in a stronger current reduction, which is explained by a lucky electron model. [ABSTRACT FROM AUTHOR]

The inner barrier in stepped quantum wells, which embrace an intrinsic structural inversion asymmetry (SIA), offers more possibilities for the multi-band spin–orbit (SO) control. By varying the inner band offset δ , which adjusts the quantum confinement for electrons and also the SIA, we reveal that both the Rashba ( α ν ) and Dresselhaus ( β ν ) SO coeffcients of the two subbands exhibit contrasting dependence on δ. Also, α 1 and α 2 may have opposite signs, depending on the value of δ. By fine tuning the inner offset, there may even exist a scenario in which α 2 identically vanishes but α 1 is finite, offering a knob on how to subband-selectively suppress spin relaxation induced by SO coupling. In addition, by resorting to an external gate V g , we reveal that in the regime of α 1 and α 2 having opposite signs, their magnitudes also vary with V g in an opposite manner. This, together with the engineered inner barrier of stepped wells, will facilitate flexible spin manipulation. Finally, the interband SO couplings, which depend on the spatial overlap of wave functions of distinct subbands and the corresponding parities, are also discussed. [ABSTRACT FROM AUTHOR]

This paper explores the optical limiting (OL) characteristics of an input probe field within a closed-loop asymmetric coupled quantum well (ACQW) system. Our research reveals that the application of Terahertz (THz) coupling laser fields can induce the OL behavior within the THz domain in the ACQW. The study demonstrates that revers saturable absorption arises through cross-Kerr nonlinearity, contributing to the emergence of OL behavior. Additionally, it is shown that the self-defocusing is induced concurrently within the system, further enhancing nonlinear refractive OL effects. Furthermore, it is revealed that the properties of induced OL can be manipulated by adjusting the characteristics of the applied fields. The discovered outcomes hold potential utility in safeguarding sensors and detectors operating within the THz band. [ABSTRACT FROM AUTHOR]

The hole transport and the carrier distribution in AlGaN-based far-ultraviolett (UVC) light emitting diodes (LEDs) emitting around 233 nm was investigated. Temperature-dependent electroluminescence measurements on dual wavelength AlGaN multiple quantum well (MQW) LEDs show a strong shift in the spectral power distribution from 250 to 233 nm with decreasing temperature. Comparing experimental data with simulation shows that the hole mobility and the electron to hole mobility ratios have a significant influence on the carrier injection efficiency (CIE) and that the change in the spectral power distribution is originating from a change in the hole distribution in the MQWs. Poor hole injection and charge carrier confinement in the AlGaN MQW active region was identified as one of the main reasons for the low CIE in far-UVC LEDs. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr (VI)) is a heavy metal that is distributed globally and poses a significant threat to the environment through various mechanisms. It can react with soil and water, leading to severe environmental damage. In this study, the toxicity of Cr (VI) was investigated by analyzing two major cyanobacteria species, Nostoc commune and Anabaena variabilis, commonly found in soil along with their consortia. The findings revealed that the toxicity mechanisms of Cr (VI) differed in individual monocultures, with Cr (VI) competing with various components. However, when the cyanobacteria species were combined, i.e., in consortia, they demonstrated an impressive retention of their functioning even in Cr (VI) concentration at 10 ppm. The study also concluded that non-photochemical quenching played a critical role in minimizing Cr (VI) toxicity. Furthermore, the research examined the role of the S-cycle in the process. The quantum yield of electron flux revealed that the Cr (VI) was competing with Qa in A. variabilis and with Qb in N. commune, albeit the photosystem dysfunction is only visible in the latter. The mechanism seemed to be quantum tunneling alteration because of the Cr (VI) having different energized quantum wells. The consortia proved to be behaving in a better manner as compared to the control. Overall, this study reveals the mode of toxicity of Cr (VI) in these two important cyanobacterial strains as well as it also discusses the mechanism of tolerance of consortia against Cr (VI) toxicity. [ABSTRACT FROM AUTHOR]

Gaussian potentials serve as a valuable tool for the comprehensive modeling of short‐range interactions, spanning applications from Nuclear Physics to the artificial confinement of electrons within quantum dots. This study focuses on examining the lowest states within Gaussian wells, with particular emphasis on the weakly bound regime. The analysis delves into the asymptotic behavior of the exact wave function at both small and large distances, motivating the development of a few parametric Ansatz which is locally accurate and yields to a fast convergent basis set. To validate its efficacy, we assess its convergence rate using a toy model of Nuclear Physics, specifically for Deuteron. Furthermore, we employ the expansion of the energy close to the threshold to derive an analytical formula for the binding energy of the Deuteron whose accuracy improves as the effective parameter approaches the critical. To conclude our study, we test the ability of our Ansatz to describe relativistic corrections into a quantum dot and its performance as an orbital in the exploration of the electronic structure of a two‐electron quantum dot. [ABSTRACT FROM AUTHOR]