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Wurtzite ScxAl1−xN/GaN (x = 0.13–0.18) multi-quantum wells grown by molecular beam epitaxy on c-plane GaN are found to exhibit remarkably strong and narrow near-infrared intersubband absorption in the technologically important 1.8–2.4 μm range. Band structure simulations reveal that, for GaN wells wider than 3 nm, the quantized energies are set by the steep triangular profile of the conduction band caused by intrinsic polarization fields. As a result, the intersubband transition energies provide unique and direct access to essential ScAlN polarization parameters. Measured infrared absorption indicates that the spontaneous polarization difference of the presumed lattice-matched Sc0.18Al0.82N/GaN heterostructure is smaller than the theoretically calculated value. The intersubband transition energies are relatively insensitive to the barrier alloy composition indicating negligible variation of the net polarization field in the probed 0.13–0.18 Sc composition range. [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]

The polarized photoluminescence emitted on the edge of a series of aluminum‐rich (Al,Ga)N‐AlN quantum wells (QWs) grown by molecular beam epitaxy on AlN templates deposited by metal organic chemical vapor deposition on c‐plane sapphire is measured. The contrast and the principal axis of the emission diagrams for 2 nm‐thick (Al,Ga)N QWs grown for aluminum compositions between 40% and 90% are studied. The light is emitted on the edge of the QWs at wavelengths going from 280 nm down to 209 nm. The emission diagram, a change from oblate to prolate with respect to the in‐plane orientation, for an aluminum composition is found to occur around 72%, that is, at an emission wavelength of about 235 nm. The orientations and shapes of the edge‐emission diagrams indicate that the fluctuations of the composition of the (Al,Ga)N confining layer are deep enough for producing intravalence band mixings. This property, that acts in concert with the built‐in strain and quantum‐confined Stark effect, contributes to the anisotropy of the light emission when the aluminum composition reaches 60–70%, that is, for an emission wavelength of 260–235 nm. [ABSTRACT FROM AUTHOR]

In this paper, we study the localization of an electron in a binary quantum system formed by a pair of quantum dots (QDs). The traditional theoretical consideration of such systems is limited to the symmetrical case when QDs in such double quantum dot (DQD) are assumed identical in all respects. In this paper, we model the effects of breaking QD similarities in a DQD by studying two-dimensional (2D) DQDs as a double quantum well (DQW). This is done by solving the Schrödinger equation, with parameters chosen to describe an InAs/GaAs heterostructure. We calculate the energy spectrum of the electron confinement and the spectral distribution of localized/delocalized spatial states. Both symmetric and asymmetric QW shapes are considered and their effects are compared. The effects of symmetry breaking are explained within the framework of the two-level system theory. We delineate the QW weak and strong coupling cases in DQW. In particular, we show that the coherence in ideal DQW is unstable in the case of a weak QW coupling. Within the framework of the proposed approach, a charge qubit realized on a DQD is discussed and, as an example, a qubit based on an almost ideal DQD is proposed. [ABSTRACT FROM AUTHOR]

Deep ultraviolet light-emitting diodes (DUV LEDs) typically suffer from strong parasitic absorption in the p-epitaxial layer and rear metal contact/mirror. This problem is exacerbated by a substantial portion of the multiple quantum well (MQW) emissions having a strong out-of-plane dipole component, contributing to emission in widely oblique directions outside the exit cone of the front semiconductor emitting surface. To address this, we propose an architecture that leverages such a heavily oblique angular emission profile by utilizing spaced-apart or scattered volume emitter micropixels that are embedded in a low-index dielectric buffer film with a patterned top surface. This approach achieves high light extraction efficiency at the expense of enlarging the effective emission area, however, it does not require a high-index (e.g., sapphire) substrate or a lens or a nanotextured epi for outcoupling purposes. Hybrid wave and ray optical simulations demonstrated a remarkable larger than three to sixfold increase in light extraction efficiency as compared to that of a conventional planar LED design with a sapphire substrate depending on the assumed epi layer absorption, pixel size, and ratio of light emission area to the MQW active area. An extraction efficiency three times greater than that of a recent nanotextured DUV LED design was also demonstrated. This architecture paves the way for DUV LEDs to have a plug efficiency comparable to that of mercury lamps while being significantly smaller. [ABSTRACT FROM AUTHOR]

In this study, we introduce an innovative semiconductor quantum well (SQW) nanostructure, which exhibits a unique four-level configuration arranged in an inverted Y-shape. This configuration enables interaction with three laser fields and demonstrates the intriguing nonlinear phenomenon of parametric generation. Our investigation delves into a wide range of parametric conditions, aiming to understand the profound impact of various system parameters on the generation and propagation of new light fields within this groundbreaking nanostructure. By employing a combination of analytical and numerical methods, we not only reveal the potential for precise manipulation of coherence among energy levels but also showcase its practical implications — high-efficiency and tunability in the parametric generation process. This pioneering scheme represents a significant advancement in the field of SQW structures, bridging the gap between theoretical exploration and practical application. Our findings promise exciting prospects for the development of novel light sources and optical devices based on SQW structures, thereby pushing the boundaries of what is achievable in various applications and setting new standards for the state-of-the-art in this domain. [ABSTRACT FROM AUTHOR]

InAs quantum wells (QWs) are promising material systems due to their small effective mass, narrow bandgap, strong spin–orbit coupling, large g-factor, and transparent interface to superconductors. Therefore, they are promising candidates for the implementation of topological superconducting states. Despite this potential, the growth of InAs QWs with high crystal quality and well-controlled morphology remains challenging. Adding an overshoot layer at the end of the metamorphic buffer layer, i.e., a layer with a slightly larger lattice constant than the active region of the device, helps to overcome the residual strain and provides optimally relaxed lattice parameters for the QW. In this work, we systematically investigated the influence of overshoot layer thickness on the morphological, structural, strain, and transport properties of undoped InAs QWs on GaAs(100) substrates. Transmission electron microscopy reveals that the metamorphic buffer layer, which includes the overshoot layer, provides a misfit dislocation-free InAs QW active region. Moreover, the residual strain in the active region is compressive in the sample with a 200 nm-thick overshoot layer but tensile in samples with an overshoot layer thicker than 200 nm, and it saturates to a constant value for overshoot layer thicknesses above 350 nm. We found that electron mobility does not depend on the crystallographic directions. A maximum electron mobility of 6.07 × 105 cm2/Vs at 2.6 K with a carrier concentration of 2.31 × 1011 cm−2 in the sample with a 400 nm-thick overshoot layer has been obtained. [ABSTRACT FROM AUTHOR]

This study investigates the kinetic properties of both symmetrical and asymmetrical multilayer and nano-sized semiconductor structures. We develop a theoretical framework using various models and mathematical methods to solve the Schrödinger matrix equation for a system of electrons, taking into account the Bastard condition, which considers the difference in the effective masses of current carriers in adjacent layers. We analyze tunnel-coupled electronic states in quantum wells separated by a narrow tunneltransparent potential barrier. Our findings provide insights into the electronic properties of semiconductor structures, which are crucial for applications in micro- or nanoelectronics and other areas of solid-state physics. [ABSTRACT FROM AUTHOR]

Piezotronic devices have attracted a great deal of attention due to their potential applications in self-powered tactile sensing, nano-device memory, human-electronic interface, etc. As the size of piezotronic devices shrinks, some interesting quantum effects begin to appear. In this paper, we establish a theory oriented to the engineering application of piezoelectric semiconductors, called quantum-corrected phenomenological (QCP) theory, by coupling the density-gradient theory and the linear piezoelectricity theory through Gauss's law. For numerical verification, we specifically studied the electromechanical behaviors in GaN/AlGaN heterostructure quantum wells (QWs) with both infinite and finite barrier height. The results of electron density, electric potential, and quantum potential are provided, and their dependence on the doping density, the applied stress, and the Al mole fraction is investigated. Some interesting quantum effects are revealed, and their influencing mechanisms are well investigated from a macroscopic perspective. Not only do the conclusions drawn in this paper enrich the fundamental understanding of the piezotronic effect in a QW structure, but also the proposed QCP theory can serve as a valuable tool for future device engineering. [ABSTRACT FROM AUTHOR]

We present a theoretical analysis of mid-infrared radiative recombination in InAs/GaSb superlattices (SLs). We employ a semi-analytical plane wave expansion method in conjunction with an 8-band k ⋅ p Hamiltonian to compute the SL electronic structure, paying careful attention to the identification and mitigation of spurious solutions. The calculated SL eigenstates are used directly to compute spontaneous emission spectra and the radiative recombination coefficient B . We elucidate the origin of the relatively large B coefficients in InAs/GaSb SLs which, despite the presence of spatially indirect (type-II-like) carrier confinement, are close to that of bulk InAs and compare favourably to those calculated for mid-infrared type-I pseudomorphic and metamorphic quantum well structures having comparable emission wavelengths. Our analysis explicitly quantifies the roles played by carrier localisation (specifically, partial delocalisation of bound electron states) and miniband formation (specifically, miniband occupation and optical selection rules) in determining the magnitude of B and its temperature dependence. We perform a high-throughput optimisation of the room temperature B coefficient in InAs/GaSb SLs across the 3.5–7 μ m wavelength range, quantifying the dependence of B on the relative thickness of the electron-confining InAs and hole-confining GaSb layers. This analysis provides guidance for the growth of optimised SLs for mid-infrared light emitters. Our results, combined with the expected low non-radiative Auger recombination rates in structures having spatially indirect electron and hole confinement, corroborate recently observed high output power in prototype InAs/GaSb SL inter-band cascade light-emitting diodes. [ABSTRACT FROM AUTHOR]

The magnetic proximity effect (MPE) attracts much attention as a promising way for introducing ferromagnetism into a nonmagnetic electron-transport channel. Although the range of MPE is generally limited to the interface, it is extended to several tens of nm in high-quality semiconductor bilayers consisting of a nonmagnetic quantum well (QW) and an underlying ferromagnetic semiconductor (FMS) layer. To elucidate the mechanism of this long-range MPE, it is essential to observe the magnetically proximitized electronic structure of the nonmagnetic semiconductor. Here, by investigating the Shubnikov - de Haas oscillations in nonmagnetic n-type InAs QW / FMS (Ga,Fe)Sb bilayers, we successfully observe the spin-polarized Fermi surface of the InAs QW. The spontaneous spin-splitting energy in the conduction band of the InAs QW reaches 18 meV when applying a negative gate voltage. This large and gate-tunable spin-polarized Fermi surface of a magnetically proximitized InAs QW provides an ideal platform for novel spintronic and topological devices. Narrow-gap semiconductors with gate-controllable spin-splitting provide an ideal platform for novel spintronic and topological devices. The authors observe a large spontaneous spin-splitting energy, reaching 18 meV and widely tunable by a gate voltage, in an InAs quantum well that is magnetically proximitized by a ferromagnetic semiconductor (Ga,Fe)Sb. [ABSTRACT FROM AUTHOR]

This study investigates the shape complexity of hydrogenic impurity states in the Ga1 − χAlχN semiconductor quantum well for the first time. The shape complexity is calculated for a specific hydrogenic impurity state in both position and momentum spaces (C[r] and C[p]) through the utilization of Shannon entropy and averaging electron probability density. The results demonstrate that the Shannon entropy and the average electron probability density vary monotonically with the quantum well width. However, the shape complexity exhibits extreme points, and their physical source is discussed in detail. Furthermore, the impact of doping Al element on the shape complexity of the hydrogenic impurity in the Ga1 − χAlχN quantum well is examined. The investigation demonstrates that the changes in C[r] or C[p] with the quantum well width exhibit similarity for different contents of the doping Al element, indicating a scaled invariance of shape complexity under translation. However, for a fixed width of the quantum well, the shape complexity of hydrogenic impurity state in the Ga1 − χAlχN quantum well is highly sensitively to the Al element content. As the shape complexity plays a crucial role in quantifying the disorder of a quantum system, our findings indicate that we can control the internal disorder of hydrogenic impurity in the semiconductor quantum well by adjusting the well size and doping element content. Our study provides some theoretical guidance for the study of the internal disorder of hydrogenic impurity in semiconductor quantum well and has certain applications in semiconductor material manufacturing and synthesis. [ABSTRACT FROM AUTHOR]

In this work, the influence of light on the temperature dependence of transverse magnetoresistance oscillations is studied. A generalized mathematical expression that calculates the temperature and light dependence of the quasi-Fermi levels of small-scale p-type semiconductor structures in a quantizing magnetic field is derived. New analytical expressions have been found to represent the temperature dependence of transverse differential magnetoresistance oscillations in dark and light situations, taking into account the effect of light on the oscillations of the Fermi energy of small-scale semiconductor structures. A mathematical model has been developed that determines the light dependence of the second-order derivative of the transverse magnetoresistance oscillations of p-type semiconductors with quantum wells by magnetic field induction. A new theory is proposed, which explains the reasons for the significant shift of the differential magnetoresistance oscillations along the vertical axis measured in the experiment for dark and light conditions. [ABSTRACT FROM AUTHOR]

For a long time, researchers in nanochemistry have been exploring ways to create 3D structures using cross‐linked nanoparticles, such as lyogels and aerogels. In the present work, how simple modifications to the nanoparticle surface can be used to influence the resulting structure in a targeted manner is demonstrated. Specifically, positively charged surface ligands containing amine groups are compared to negatively charged ligands typically used, containing carboxylic acid groups, to generate network structures using different gelation agents. By utilizing bridging through S2− ions, a network structure of anisotropic CdSe/CdS nanorods is generated, packing them side by side at the nanoscopic level. The resulting structures exhibit improved fluorescence properties comparable to those of tip‐to‐tip connected networks but without harsh conditions for the nanoparticle surfaces. This innovative new method of gelation using S2− ions can achieve adequate photoluminescence quantum yields as well as prolonged fluorescence lifetimes compared to other network structures. [ABSTRACT FROM AUTHOR]

The ongoing miniaturization of semiconductor devices renders charge‐carrier transport along interfaces increasingly important. The characteristic length scales in state‐of‐the‐art semiconductor technology span only a few nanometers. Consequently, charge‐carrier transport inevitably occurs directly at interfaces between adjacent layers rather than being confined to a single material. Herein, charge‐carrier diffusion is systematically studied in prototypical active layer systems, namely, in type‐I direct‐gap quantum wells and in type‐II heterostructures. The impact of internal interfaces is revealed in detail as charge‐carrier diffusion takes place much closer to or even across the internal interfaces in type‐II heterostructures. Type‐I quantum wells and type‐II heterostructures exhibit comparable diffusion rates given similar inhomogeneous exciton linewidths. Consequently, the changes in the structural quality of the interfaces are responsible for changes in diffusion and charge‐carrier transport along interfaces rather than the existence of the interfaces themselves. [ABSTRACT FROM AUTHOR]

We employed the selective-area-epitaxy technique using metalorganic chemical vapor deposition to fabricate and study samples of semiconductor heterostructures that incorporate highly strained InGaAs quantum wells (980–990 nm emission wavelength). Selective area epitaxy of InGaAs quantum wells was performed on templates that had a patterned periodic structure consisting of a window (where epitaxial growth occurred) and a passive mask (where epitaxial growth was suppressed), each with a width of 100 µm for every element. Additionally, a selectively grown potential barrier layer was included, which was characterized by an almost parabolic curvature profile of the surface. We conducted a study on the influence of the curvature profile of the growth surface on the optical properties of InGaAs quantum wells and the spatial distribution of composition in an ultrawide window. Our results showed that, under fixed selective-area-epitaxy conditions, the composition of the InxGa1−xAs and the wavelength of the quantum-well emission changed across the width of the window. Our study demonstrates that increasing the curvature profile of the growth surface of highly strained quantum wells leads to a transition in the photoluminescence wavelength distribution profile across the window, from quasi-parabolic to inverted parabolic. [ABSTRACT FROM AUTHOR]

Herein, the possibility of creating a noncascade intersubband midinfrared injection laser based on HgCdTe with a minimum number of quantum wells is analyzed. An error‐tolerant laser structure with three quantum wells that is insensitive to the variations in the quantum well thickness is proposed. The calculations predict a modal gain of 35 cm−1 at the wavelength of approximately 9.2 μm at 77 K and the operating temperature up to 125 K. [ABSTRACT FROM AUTHOR]

InAs quantum wells (QWs) are promising material systems due to their small effective mass, narrow bandgap, strong spin–orbit coupling, large g-factor, and transparent interface to superconductors. Therefore, they are promising candidates for the implementation of topological superconducting states. Despite this potential, the growth of InAs QWs with high crystal quality and well-controlled morphology remains challenging. Adding an overshoot layer at the end of the metamorphic buffer layer, i.e., a layer with a slightly larger lattice constant than the active region of the device, helps to overcome the residual strain and provides optimally relaxed lattice parameters for the QW. In this work, we systematically investigated the influence of overshoot layer thickness on the morphological, structural, strain, and transport properties of undoped InAs QWs on GaAs(100) substrates. Transmission electron microscopy reveals that the metamorphic buffer layer, which includes the overshoot layer, provides a misfit dislocation-free InAs QW active region. Moreover, the residual strain in the active region is compressive in the sample with a 200 nm-thick overshoot layer but tensile in samples with an overshoot layer thicker than 200 nm, and it saturates to a constant value for overshoot layer thicknesses above 350 nm. We found that electron mobility does not depend on the crystallographic directions. A maximum electron mobility of 6.07 × 105 cm2/Vs at 2.6 K with a carrier concentration of 2.31 × 1011 cm−2 in the sample with a 400 nm-thick overshoot layer has been obtained.

Quantum well systems based on semiconductors with the wurtzite crystalline structure have found widespread applications in photonics and optoelectronic devices, such as light-emitting diodes, laser diodes, or single-photon emitters. In these structures, the radiative recombination processes can be affected by (i) the presence of strain and polarization-induced electric fields, (ii) quantum well thickness fluctuations and blurring of a well–barrier interface, and (iii) the presence of dislocations and native point defects (intentional and unintentional impurities). A separate investigation of these phenomena is not straightforward since they give rise to similar effects, such as a decrease of luminescence efficiency and decay rate, enhancement of the Stokes shift, and strong blueshift of the emission with increasing pump intensity. In this Perspective article, we review the usefulness of measurements of the quantum well luminescence as a function of the hydrostatic pressure for both scientific research and the development of light-emitting technologies. The results presented here show that high-pressure investigations combined with ab initio calculations can identify the nature of optical transitions and the main physical factors affecting the radiative efficiency in quantum well systems. Finally, we will discuss an outlook to the further possibilities to gain new knowledge about the nature of recombination processes in quantum wells using high-pressure spectroscopy. [ABSTRACT FROM AUTHOR]

Real-time monitoring of room-temperature exciton photoluminescence (PL) while irradiated with ultrafast laser excitations (UV and infrared) in long alkyl-chain based (C12H25NH3)2PbI4 inorganic–organic hybrid semiconductors is presented. These naturally self-assembled 2D hybrid structures show strong room-temperature Mott-type excitons confined within the lowest inorganic bandgap, which are highly sensitive to structural phase flips. Under both one-photon (E1PA ≥ Eg) and two-photon (2E2PA ≥ Eg) laser excitations, the exciton PL of unstable phase-II appears initially, and with prolonged laser exposure, the PL peak switches to a new stable blueshifted phase-I peak position. This exciton phase flip demonstrates different laser-induced structural deformations in inorganic quantum wells (PbI6 extended network) associated with orthorhombic (phase-I) and monoclinic (phase-II) unit cells. One-photon absorption induced PL shows the various time dynamics of laser exposure depending on laser characteristics (continuous wave and ultrashort pulsed lasers), mostly influenced by localized heating, ablation effects, and third-order nonlinear effects such as saturation of linear absorption and exciton–exciton annihilation. However, in two-photon absorption induced PL, the near infrared laser excitation reveals the redshifted crumpled excitons from the deeper depth of the sample, which are induced by multiphoton absorption and avalanche ionization. A series of systematic linear and nonlinear steady-state and time-resolved PL studies are presented. A simplified kinetic model further provides an understanding of the real-time evolution of laser-induced excitons and their related phase flips. These laser-induced exciton phase flips and linear and nonlinear optical probing open a new avenue for novel functional properties and nonlinear absorption–based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Colloidal quantum wells (CQWs) have emerged as a promising class of gain material in various optical feedback configurations. This is due to their unique excitonic features arising from their 1D quantum confinement. However, existing methods for integrating CQW onto microresonators will cause low laser quality due to uneven CQW coating. To overcome this, the use of liquid‐interface kinetically driven self‐assembly is proposed to coat ultrathin, close‐packed layers of colloidal CdSe/Cd1−xZnxS core/shell CQWs between 7 and 14 nm onto the surface of silica microsphere cavities. The fabricated CQW‐whispering‐gallery‐mode microlasers possess a commendable high quality (Q) factor of 13 000 at room temperature. Stable single‐mode lasing output is demonstrated through evanescent field coupling between a CQW‐coated microsphere and a thin uncoated microfiber in a 2D‐3D microcavity configuration. These promising results highlight the suitability of the liquid‐interface kinetically driven self‐assembly method for realizing ultrathin CQW‐coated microlasers and its high compatibility for integrating colloidal nanocrystals onto complex 3D microstructures for future miniaturized colloidal optoelectronic and photonic applications. [ABSTRACT FROM AUTHOR]

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices relies on surface gates which impose strong limitations on the maximum distance from the surface where the confining electrostatic potentials can be engineered. Surface gates also introduce strain fields which cause imperfections in the semiconductor crystal structure. Another way to create confining electrostatic potentials inside semiconductors is by means of light and photosensitive dopants. Light can be structured in the form of perfectly parallel sheets of high and low intensity which can penetrate deep into a semiconductor and, importantly, light does not deteriorate the quality of the semiconductor crystal. In this work, we employ these important properties of structured light to form metastable states of photo-sensitive impurities inside a GaAs/AlGaAs quantum well structure in order to create persistent periodic electrostatic potentials at large predetermined distances from the sample surface. The amplitude of the light-induced potential is controlled by gradually increasing the light fluence at the sample surface and simultaneously measuring the amplitude of Weiss commensurability oscillations in the magnetoresistivity. [ABSTRACT FROM AUTHOR]

Two-dimensional topological insulators have attracted much attention for potential application to quantum computers on the basis of a new principle. Semiconductor composite quantum wells, in which electrons and holes are confined in separate layers, can serve as two-dimensional topological insulators when their layer structure is optimized. We describe time-resolved measurements of ambipolar plasmon transport in both the electron and hole regimes separately using a single device. This technique will pave the way for investigations of charge and spin dynamics in two-dimensional topological insulators. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamics of a vertically emitting micro-cavity operated in the Gires–Tournois regime that contains a semiconductor quantum-well and that is subjected to strong time-delayed optical feedback and detuned optical injection. Using a first principle time-delay model for the optical response, we disclose sets of multistable dark and bright temporal localized states coexisting on their respective bistable homogeneous backgrounds. In the case of anti-resonant optical feedback, we identify square-waves with a period of twice the round-trip in the external cavity. Finally, we perform a multiple time scale analysis in the good cavity limit. The resulting normal form is in good agreement with the original time-delayed model. [ABSTRACT FROM AUTHOR]

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine‐tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice‐mismatched substrates is a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, it is shown that the van der Waals epitaxy of 2D GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heteroepitaxy is applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. [ABSTRACT FROM AUTHOR]

Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na2KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics. [ABSTRACT FROM AUTHOR]

The effect of thermally generated equilibrium carrier distribution on the vacancy generation, recombination, and mobility in a semiconductor heterostructure with an undoped quantum well is studied. A different rate of thermally generated equilibrium carriers in layers with different band gaps at annealing temperatures forms a charge-carrier density gradient along a heterostructure. The nonuniform spatial distribution of charged vacancy concentration that appears as a result of strong dependence in the vacancy formation rate on the local charge-carrier density is revealed. A model of vacancy-mediated diffusion at high temperatures typical for post-growth annealing that takes into account this effect and dynamics of nonequilibrium vacancy concentration is developed. The change of atomic diffusivity rate in time that follows on the of spatial vacancy distribution dynamics in a model heterostructure with quantum wells during a high-temperature annealing at fixed temperatures is demonstrated by computational modeling. [ABSTRACT FROM AUTHOR]

The last decade has witnessed extensive breakthroughs and significant progress in atomically flat two-dimensional (2D) semiconductor nanoplatelets (NPLs) in terms of synthesis, growth mechanisms, optical and electronic properties and practical applications. Such NPLs have electronic structures similar to those of quantum wells in which excitons are predominantly confined along the vertical direction, while electrons are free to move in the lateral directions, resulting in unique optical properties, such as extremely narrow emission line width, short photoluminescence (PL) lifetime, high gain coefficient, and giant oscillator strength transition (GOST). These unique optical properties make NPLs favorable for high color purity light-emitting applications, in particular in light-emitting diodes (LEDs), backlights for liquid crystal displays (LCDs) and lasers. This review article first introduces the intrinsic characteristics of 2D semiconductor NPLs with atomic flatness. Subsequently, the approaches and mechanisms for the controlled synthesis of atomically flat NPLs are summarized followed by an insight on recent progress in the mediation of core/shell, core/crown and core/crown@shell structures by selective epitaxial growth of passivation layers on different planes of NPLs. Moreover, an overview of the unique optical properties and the associated light-emitting applications is elaborated. Despite great progress in this research field, there are some issues relating to heavy metal elements such as Cd2+ in NPLs, and the ambiguous gain mechanisms of NPLs and others are the main obstacles that prevent NPLs from widespread applications. Therefore, a perspective is included at the end of this review article, in which the current challenges in this stimulating research field are discussed and possible solutions to tackle these challenges are proposed. [ABSTRACT FROM AUTHOR]

High-power, broad-area, semiconductor lasers are attractive sources for material processing, aerospace, and laser pumping. The design of the active region is crucial to achieve the required high power and electro-optical conversion efficiency, since the temperature significantly affects the performance of the quantum well, including the internal quantum efficiency and mode gain. In this work, the temperature effects on the active region of a 808 nm high-power semiconductor laser were investigated theoretically and experimentally. The simulations were performed with a Quasi-3D model, which involved complete steady-state semiconductor and carrier confinement efficiency combined with a new mathematical method. The critical aluminum content of the quantum barrier was proposed and the relationship between temperature and various loss sources was disclosed in the temperature range of 213 to 333 K, which provides a reliable reference for the design of epitaxial structures of high-power semiconductor lasers in different operating conditions. Subsequently, the optimized epitaxial structure was determined and used to fabricate standard laser bar chips with a cavity length of 2 mm. The experimental electro-optical conversion efficiency of 71% was demonstrated with a slope efficiency of 1.34 W/A and an injection current of 600 A at the heatsink temperature of 223 K. A record high electro-optical conversion efficiency of 73.5% was reached at the injection current of 400 A, while the carrier confinement efficiency was as high as 98%. [ABSTRACT FROM AUTHOR]

We have studied two-dimensional absorption and gain spectrum in an asymmetric semiconductor triple-coupled-quantum-well (TCQW) nanostructure. Four subband transitions are coupled by using four coherent fields in a close-loop configuration to introduce cross-Kerr effect and four-wave-mixing (FWM) induced nonlinearity in achieving nonlinear absorption and gain profiles. Position-dependent absorption and gain are obtained by applying one, or two coherent fields in a variety of standing wave configurations including superposed field configuration in the standing-wave regime. In addition to the control parameters like Rabi frequency and detuning, the specialty of the model is to employ double-controlled spatial phase-coherence guided by the FWM-induced phase and the phases introduced by the standing wave formation. Our results highlight the high-precision electron localization in spatial domain. The evolution of spatially modulated gain without inversion may be a substitute for obtaining gain from a traditional quantum cascade laser. The importance of the present work is to find its application in designing electro-optic modulators in semiconductor nanostructures in near future. [ABSTRACT FROM AUTHOR]

We examine how the weak excitation regime of a quantum well confined in a semiconductor microcavity (SM) influences the dynamics of quantum coherence and the total phase. We analyze the impact of the physical parameters on different quantumness measures, and illustrate their numerical results. We show that the amount of the coherence and total phase in the SMs for multi-photon excitation can be improved and controlled by the strength of the field, exciton-photon coupling, cavity dissipation rate, and excitonic spontaneous emission rate. We illustrate how the fidelity varies depending on the physical parameters. These results might have far-reaching ramifications not just in quantum information processing and optics, but also in physics at large. [ABSTRACT FROM AUTHOR]

The effect of enhancement of the electron concentration in the near-surface quantum well owing to a resonant tunneling between the semiconductor and the metal is analyzed theoretically. The range of parameters (acceptor concentration and insulator thickness) wherein such an electron-supplying mechanism becomes plausible is defined. Generally, the supply effect can be expected for a doping between (5-6)×1018 and (2-3)×1019 cm-3, e.g., for the SiO2/p+-Si(1019 cm-3) structures with the oxide thickness exceeding ~3 nm. The electron density provided due to a resonant tunneling can reach rather high values (~1012 cm-2 and more). Consequently, the quasi-Fermi level in the well is substantially shifted approaching that of the semiconductor bulk. However, a deformation of the band diagram due to electron charge in the quantum well in the regimes close to activation of a resonant transport is small. [ABSTRACT FROM AUTHOR]

We studied spin dephasing processes in GaAs/AlGaAs multiple quantum wells (MQWs) grown on a semi-insulating (110)-oriented GaAs substrate using the time-resolved Kerr rotation (TRKR) technique. The TRKR spectra gives the electron g-factor in MQWs, as well as the spin dephasing time (SDT) for electron spins within the sample plane. The electron g-factor shows a strong two-fold anisotropy, while the in-plane SDT remains almost isotropic. The anisotropy of the electron g-factor increases monotonically with the spread of more electron wave functions into the AlGaAs barrier. The two-fold symmetry of the electron g-factor is discussed with a phenomenological model based on spin splitting of energy bands caused by spin-orbit coupling. [ABSTRACT FROM AUTHOR]

Hot carriers are a critical issue in modern photovoltaics and miniaturized electronics. We present a study of hot electron energy relaxation in different two-dimensional electron gas (2DEG) structures and compare the measured values with regard to the dimensionality of the semiconductor formations. Asymmetrically necked structures containing different types of AlGaAs/GaAs single quantum wells, GaAs/InGaAs layers, or bulk highly and lowly doped GaAs formations were investigated. The research was performed in the dark and under white light illumination at room temperature. Electron energy relaxation time was estimated using two models of I-V characteristics analysis applied to a structure with n-n+ junction and a model of voltage sensitivity dependence on microwave frequency. The best results were obtained using the latter model, showing that the electron energy relaxation time in a single quantum well structure (2DEG structure) is twice as long as that in the bulk semiconductor. [ABSTRACT FROM AUTHOR]

The In1−xGaxAsyP1−y submicron wires with adjustable wavelengths directly grown by metalorganic chemical vapor deposition on a V-groove-patterned Si (001) substrate are reported in this paper. To ensure the material quality, aspect ratio trapping and selective area growth methods are used. By changing the parameters in the epitaxy process, we realize the adjustment of the material energy band of In1−xGaxAsyP1−y submicron wires. By further optimizing the growth conditions, we realize high-quality submicron wires. The morphology of the submicron wires is characterized by scanning electron microscopy and transmission electron microscopy. Through high-resolution X-ray diffraction measurement, it is disclosed that the lattice of the optimized In1−xGaxAsyP1−y part matches that of InP. A PL spectrum test shows that the PL spectrum peak is from 1260 nm to 1340 nm. The In1−xGaxAsyP1−y can be used as a well material or barrier material in a quantum well, which would promote the development of silicon-based lasers. [ABSTRACT FROM AUTHOR]

Quantum optomechanical system serves as an interface for coupling between photons and phonons via radiation pressure. We theoretically investigate the optical response of a hybrid optomechanical system that contains a single undoped semiconductor quantum well inside a cavity as well as a thin dielectric movable membrane in the middle, quadratically coupled to the cavity photons. We find that in the presence of both quadratic optomechanical coupling and exciton–cavity field coupling, two additional absorption dips appear in the output field spectrum of the probe field as compared to a standard quadratic optomechanical system which gives only two-phonon optomechanical induced transparency and optomechanical induced absorption phenomena with probe field detuning. This is due to the formation of the dressed state mediated by the single-photon state and the exciton mode. Furthermore, we have shown that the optical transmission of the probe field at these two absorption dips can be controlled by a number of parameters present in the system like exciton–cavity field coupling strength, decay rate of exciton as well as the mean number of thermal phonons- in the environment. We also explore the possibility of slow light in this absorption regime due to exciton–photon coupling. Our study shall provide a method to control the propagation of light in quadratic hybrid optomechanical system containing semiconductor nanostructures. [ABSTRACT FROM AUTHOR]

This research paper discusses an analytical approach to designing the active region of light emitting diodes to enhance its performance. The layers in the active region were modified and the effects of changing the width of quantum well and barrier layers in a multiquantum light emitting diode on the output power and efficiency have been investigated. Also, the ratio of the quantum well width to the B layer width was calculated and proposed in this research paper. The study is carried out on two different LED structures. In the first case, the width of the quantum well layers is kept constant while the width of the B layers is varied. In the second case, both the quantum well and B layer widths are varied. Based on the simulation results, it has been observed that the LED power efficiency increases considerably for a given quantum well to B layers width ratio without increasing the production complexity. It is also seen that for a desired power efficiency the width of quantum well should be between 0.003 µm and 0.006 µm, and the range of B width (height) should be 2.2 to 6 times the quantum well width. The proposed study is carried out on the GaN-AlGaN-based multi-quantum well LED structure, but this study can be extended to multiple combinations of the semiconductor structures. [ABSTRACT FROM AUTHOR]

Understanding and controlling the nonlinear optical properties and coherent quantum evolution of complex multilevel systems out of equilibrium is essential for the new semiconductor device generation. In this work, we investigate the nonlinear system properties of an unbiased quantum cascade structure by performing two-dimensional THz spectroscopy. We study the time-resolved coherent quantum evolution after it is driven far from equilibrium by strong THz pulses and demonstrate the existence of multiple nonlinear signals originating from the engineered subbands and find the lifetimes of those states to be in the order of 4–8 ps. Moreover, we observe a coherent population exchange among the first four intersubband levels during the relaxation, which have been confirmed with our simulation. We model the experimental results with a time-resolved density matrix based on the master equation in Lindblad form, including both coherent and incoherent transitions between all density matrix elements. This allows us to replicate qualitatively the experimental observations and provides access to their microscopic origin.

Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near- and mid-infrared applications, particularly in 1.55 µm optical communication systems. Incorporating dilute amounts of bismuth (Bi) into GaAs reduces the effective bandgap rapidly, while significantly increasing the spin-orbit-splitting energy. Additional incorporation of dilute amounts of nitrogen (N) helps to attain lattice matching with GaAs, while providing a route for flexible bandgap tuning. Here we present a study of the electronic bandstructure and optical gain of the lattice matched GaNx-BiyAs1-x-y/GaAs quaternary alloy quantum well (QW) based on the 16-band k⋅p model. We have taken into consideration the interactions between the N and Bi impurity states with the host material based on the band anticrossing and valence band anticrossing model. The optical gain calculation is based on the density matrix theory. We have considered different lattice matched GaNBiAs QW cases and studied their energy dispersion curves, optical gain spectrum, maximum optical gain, and differential gain and compared their performances based on these factors. The thickness and composition of these QWs were varied in order to keep the emission peak fixed at 1.55 µm. The well thickness has an effect on the spectral width of the gain curves. On the other hand, a variation in the injection carrier density has different effects on the maximum gain and differential gain of QWs of varying thicknesses. Among the cases studied, we found that the 6.3 nm thick GaN3Bi5.17As91.83 lattice matched QW was most suited for 1.55 µm (0.8 eV) GaAs-based photonic applications. [ABSTRACT FROM AUTHOR]

The search for exotic new topological states of matter in widely accessible materials, for which the manufacturing process is mastered, is one of the major challenges of the current topological physics. Here we predict higher order topological insulator state in quantum wells based on the most common semiconducting materials. By successively deriving the bulk and boundary Hamiltonians, we theoretically prove the existence of topological corner states due to cubic symmetry in quantum wells with double band inversion. We show that the appearance of corner states does not depend solely on the crystallographic orientation of the meeting edges, but also on the growth orientation of the quantum well. Our theoretical results significantly extend the application potential of topological quantum wells based on IV, II–VI and III–V semiconductors with diamond or zinc-blende structures. [ABSTRACT FROM AUTHOR]

2D halide perovskite‐like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to lasing. To date, the most studied families of such low‐dimensional halide perovskite‐like compounds are Ruddlesden–Popper, Dion–Jacobson, and other phases that can be derived from 3D halide perovskites by slicing along different crystallographic directions, which leads to the spatially isotropic corner‐sharing connectivity type of metal‐halide octahedra in the 2D layer plane. In this work, a new family of hybrid organic–inorganic 2D lead halides is introduced, by reporting the first example of the hybrid organic–inorganic post‐perovskite 3‐cyanopyridinium lead tribromide (3cp)PbBr3. The post‐perovskite structure has unique octahedra connectivity type in the layer plane: a typical "perovskite‐like" corner‐sharing connectivity pattern in one direction, and the rare edge‐sharing connectivity pattern in the other. Such connectivity leads to significant anisotropy in the material properties within the inorganic layer plane. Moreover, the dense organic cation packing results in the formation of 1D fully organic bands in the electronic structure, offering the prospects of the involvement of the organic subsystem into material's optoelectronic properties. The (3cp)PbBr3 clearly shows the 2D quantum size effect with a bandgap around 3.2 eV and typical broadband self‐trapped excitonic photoluminescence at temperatures below 200 K. [ABSTRACT FROM AUTHOR]

In this study, the influence of exciton spins relaxation (ESR) on spatial evolution of amplification without population inversion in a four-level GsAs multiple quantum wells is discussed theoretically. The role of propagation distance on absorption, dispersion and group index of weak probe light in the presence and absence of ESR is then analyzed. It is found that exciton spin relaxation (spin decoherence) which resulted from many-particle interaction in semiconductors have essential roles to adjusting the absorption and dispersion properties of weak probe light. Moreover, it is realized that the propagation distance in the presence of ESR can lead to switching between subluminal and superluminal light propagation. Our study provides a suitable treatment for the next generation of all-optical systems in semiconductor nanostructures. [ABSTRACT FROM AUTHOR]

The physics of interacting nuclear spins in solids is well interpreted within the nuclear spin temperature concept. A common approach to cooling the nuclear spin system is adiabatic demagnetization of the initial, optically created, nuclear spin polarization. Here, the selective cooling of 75As spins by optical pumping followed by adiabatic demagnetization in the rotating frame is realized in a nominally undoped GaAs/(Al,Ga)As quantum well. The lowest nuclear spin temperature achieved is 0.54 μK. The rotation of 6 kG strong Overhauser field at the 75As Larmor frequency of 5.5 MHz is evidenced by the dynamic Hanle effect. Despite the presence of the quadrupole induced nuclear spin splitting, it is shown that the rotating 75As magnetization is uniquely determined by the spin temperature of coupled spin-spin and quadrupole reservoirs. The dependence of heat capacity of these reservoirs on the external magnetic field direction with respect to crystal and structure axes is investigated. The manipulation of spin degree of freedom allows the exploration of novel phenomena at the nanoscale. The authors achieved unprecedented submicroKelvin temperatures in the spin system of nuclei embedded in low dimensional semiconductors. A result that opens the way to the investigation of spin-spin interactions and exotic spin-ordered phases. [ABSTRACT FROM AUTHOR]

Dry etching damage and compositional fluctuation of GaN-based semiconductors and alloys are major issues to overcome to improve device fabrication processes and performance. Electron energy-loss spectroscopy (EELS) in a transmission electron microscope is a useful method for studying these phenomena because it can analyze the elemental composition and chemical bond states of a sample with high spatial resolution. However, because these various components of information are superposed in an EELS spectrum, the analysis has to be performed carefully. This requires multivariate statistical techniques, such as principal component analysis (PCA), to process the large amounts of data extracted from EELS. Herein we apply PCA to N-K core and In-M4,5 core edge EELS spectra to study the degree of ion-beam etching damage of GaN and the composition of GaInN ternary alloy quantum wells. Two data pretreatment procedures prior to the PCA analysis were examined to assess their comparative practical usefulness. The differential-based pretreatment method for PCA was useful when the shape of the EELS core edge structure was changed, whereas the power-law subtraction-based pretreatment method was useful when the intensity of the EELS core edge structure was variable. [ABSTRACT FROM AUTHOR]

Superfluidity has been predicted and now observed in a number of different electron-hole double-layer semiconductor heterostructures. In some of the heterostructures, such as GaAs and Ge-Si electron-hole double quantum wells, there is a strong mismatch between the electron and hole effective masses. We systematically investigate the sensitivity to unequal masses of the superfluid properties and the self-consistent screening of the electron-hole pairing interaction. We find that the superfluid properties are insensitive to mass imbalance in the low density BEC regime of strongly-coupled boson-like electron-hole pairs. At higher densities, in the BEC-BCS crossover regime of fermionic pairs, we find that mass imbalance between electrons and holes weakens the superfluidity and expands the density range for the BEC-BCS crossover regime. This permits screening to kill the superfluid at a lower density than for equal masses. [ABSTRACT FROM AUTHOR]