Semiconductor Quantum Wells Research Articles

Elevating the performance of quantum well infrared detectors at 12.55 μm with an all-dielectric scheme

Improving the signal-to-noise ratio of infrared photodetectors is a primary goal especially for those operating in the long wavelength range. Optical design in the sub-wavelength scale provides a feasible routine toward this purpose, previous efforts mainly concentrated on integrating metallic antennas and plasmonic cavities with light absorption materials like semiconductor quantum wells (QWs). This study presents an all-dielectric way that can profit the electrical and photoelectric performance of detector concurrently. By fabricating the multiple QWs into linked micro-pillar arrays, the device yields 2.3 times enhanced responsivity at 12.55 μm relative to that of the 45° mesa counterpart, meanwhile the dark current density is found to decrease by 5.7-fold at −2.5 V and 50 K. These help to elevate the background-limited infrared photodetection (BLIP) temperature of the micro-pillar array QW photodetector by 4.0 K.

Optimization of slow light under EIT in semiconductor multiple quantum wells

Optimization of slow light under EIT in semiconductor multiple quantum wells

Enhanced response over wavelength range of 7–12 µm for quantum wells in asymmetric micro-pillars

Efficient coupling in broad wavelength range is desirable for wide-spectrum infrared light detection, yet this is a challenge for intersubband transition in semiconductor quantum wells (QWs). High-Q cavities mostly intensify the absorption at peak wavelengths but with shrinking bandwidth. Here, we propose a novel approach to expand the operating spectral range of the Quantum Well Infrared Photodetectors (QWIPs). By processing the QWs into asymmetric micro-pillar array structure, the device demonstrates a substantial enhancement in spectral response across the wavelength from 7.1 µm to 12.3 µm with guided mode resonance (GMR) effects. The blackbody responsivity is then increased by 3 times compared to that of the 45° polished edge-coupled counterpart. Meanwhile, the dark current density remains unchanged after the deep etching process, which will benefit the electrical performance of the detector with reduced volume duty ratio. In contrast to the symmetric micro-pillar array that contains simple resonance mode, the detectivity of QWIP in asymmetric pillar structure is found to be improved by 2-4 times within the range of 9.5 µm to 15 µm.

The effect of pressure on the thermodynamic properties of hydrogenic impurity in the GaAs semiconductor quantum well

ABSTRACT Studying the thermodynamic properties of hydrogen impurity in low-dimensional nanostructures under high-pressure environment is crucial for understanding the optical property and thermal excitation behaviour of semiconductor material. Here, we extensively explore the effect of pressure on thermodynamic properties, specifically, the average energy, free energy, entropy, and heat capacity of one-dimensional (1-D) hydrogenic impurity in GaAs semiconductor quantum well. Our findings reveal some novel phenomenon in the thermodynamic properties of hydrogenic impurity as pressure increases in the GaAs quantum well. Remarkably, at a constant temperature, both the average energy and free energy of hydrogenic impurity decrease as pressure rises, while entropy increases with increasing pressure. Intriguingly, the heat capacity shows distinct behaviour with varying pressure for different sizes of the quantum well. For very small size of the quantum well, the heat capacity increases with increasing pressure. However, for larger size of the quantum wells, the variation of heat capacity with pressure becomes irregular, showing a changeover from an increase to a decrease in response to increasing pressure. This research presents a pioneering method that employs pressure as a versatile tool for modulating the thermodynamic properties of hydrogenic impurity states in the nanostructures, and has some guidance for the preparation and synthesis of semiconductor devices.

Amplification and excitation of surface plasmon polaritons via four-wave mixing process

We suggest a scheme for the excitation and amplification of surface plasmon polaritons (SPPs) along the interface between metal and semiconductor quantum well (SQW), employing a four-wave mixing (FWM) process. The SQW consists of four-level asymmetric double quantum wells that exhibit quantum interference effects, which leads to the coupler-free excitation of SPPs. In our proposed system, the inherent losses of SPPs are compensated by introducing gain through the FWM process, resulting in a significant enhancement in the propagation length and penetration depth of SPPs. We further analyze the effect of gain on the long-range and short-range SPPs and observe that the propagation distance and lifetime of both types of SPPs are increased.

Half-quantized Hall states with C=3/2 exited by chiral photons

The topology of Hilbert space in semiconductor quantum wells (QW) can become non-trivial when excited by an electromagnetic wave. It means the quasi-energy bands acquire a nonzero integer Floquet-Chern number even if QW is trivial in the equilibrium. We analyze electron-photon interaction in the Floquet state and identify dynamical quantum phases characterized by half-quantized Floquet-Chern numbers. The non-integer topology depends on which equilibrium state is exposed to illumination. Trivial III-V semiconductor QW's such as AlGaAs and AlGaN, being resonantly illuminated, generate the dynamical index |CF|=1/2, similar to a gapless quantum anomalous semimetal (QAS) in equilibrium. Excitation of 2D topological insulator CdHgTe reveals |CF|=3/2 - the index stemmed exclusively from interaction with chiral photons. Comparing results obtained in continuous and full-Brillouin zone (BZ) models, we conclude that high-momentum regions in BZ contribute to the dynamical half-quantized topology. Results indicate that by manipulating parameters of external force, one can bring inverted-gap QW into a non-equilibrium state with a high topological non-integer charge |CF|=3/2. We present the phase diagram, which includes all dynamical states of non-trivial topology.

Phase-sensitive large Kerr nonlinearity in semiconductor quantum wells

This paper presents a comprehensive investigation on Kerr nonlinearity in a three-level semiconductor quantum well (SQW) superlattice and validates the existence of large Kerr nonlinearity of the order of [Formula: see text] in the vicinity of an electromagnetically induced transparency (EIT) window. The Kerr nonlinearity is found to vary with the relative phase of the applied optical fields, and by selecting suitable relative phases, an enhanced Kerr nonlinearity can be obtained. The results may find significant applications in optoelectronic and photonic devices.

Laser-field-mediated Rashba and Dresselhaus spin–orbit control in GaInAs/AlInAs quantum wells

For more possibilities in exploring the spin–orbit (SO) control in two-dimensional (2D) semiconductor quantum wells, we resort to the laser field by constructing a generic model including both the axial and transverse field components relative to the well-growth direction, with the axial one primarily modifying the structural potential of the well and the transverse one mainly altering the electron density of states and so the Hartree potential. For GaInAs/AlInAs quantum wells with two-subband occupation, we obtain the full scenario of the laser-field response of the Rashba and Dresselhaus SO couplings, including both the intrasubband (αν and βν with ν = 1,2 denoting the subband index) and intersubband (η and Γ) types, by solving the Poisson–Schrödinger equations. Remarkably, for the Dresselhaus coupling, which is insensitive to the electrical manipulation, we demonstrate that it can be substantially tuned by the laser field and unified SO control of different subbands is possible, suggesting that the optical manner is an effective supplement to the electrical means. Moreover, symmetric (α1=−α2) and selective (α1=0, α2≠0) control of the Rashba coupling of different subbands are also observed with the interplay of the two laser components, which are desirable for the realization of skyrmion lattice and the suppression of spin relaxation of given subbands. Besides, for the intersubband coupling, the Rashba term η is optically tunable while the Dresselhaus term Γ is basically immune to the laser field, i.e., selective control of the intersubband coupling by virtue of optical means. These diverse laser-field-mediated SO features offer exciting possibilities in incorporating 2D quantum wells for new applications in the field of spintronics.

Maximizing Four-Wave Mixing in Four-Subband Semiconductor Quantum Wells with Optimal-Shortcut Spatially Varying Control Fields

In the present article, we derive optimal spatially varying control fields, which maximize the four-wave mixing efficiency in a four-subband semiconductor asymmetric double quantum well, following analogous works in atomic systems. The control fields coherently prepare the medium, where a weak probe pulse is propagated and eventually converted to a signal pulse at the output. The optimal fields, which maximize the conversion efficiency for a given propagation length, are obtained by applying optimal control theory to a simplified form of propagation equations but are tested with numerical simulations using the full set of Maxwell–Schrödinger equations, which accurately describe the propagation of light pulses in the medium. For short propagation distances, the proposed optimal scheme outperforms a simpler spatially changing control protocol that we recently studied, while for larger distances, the efficiency of both protocols approaches unity. The present work is expected to find application in frequency conversion between light beams, conversion between light beams carrying orbital angular momentum, and nonlinear optical amplification.

Resonant Tunnelling and Intersubband Optical Properties of ZnO/ZnMgO Semiconductor Heterostructures: Impact of Doping and Layer Structure Variation.

ZnO-based heterostructures are up-and-coming candidates for terahertz (THz) optoelectronic devices, largely owing to their innate material attributes. The significant ZnO LO-phonon energy plays a pivotal role in mitigating thermally induced LO-phonon scattering, potentially significantly elevating the temperature performance of quantum cascade lasers (QCLs). In this work, we calculate the electronic structure and absorption of ZnO/ZnMgO multiple semiconductor quantum wells (MQWs) and the current density-voltage characteristics of nonpolar m-plane ZnO/ZnMgO double-barrier resonant tunnelling diodes (RTDs). Both MQWs and RTDs are considered here as two building blocks of a QCL. We show how the doping, Mg percentage and layer thickness affect the absorption of MQWs at room temperature. We confirm that in the high doping concentrations regime, a full quantum treatment that includes the depolarisation shift effect must be considered, as it shifts mid-infrared absorption peak energy for several tens of meV. Furthermore, we also focus on the performance of RTDs for various parameter changes and conclude that, to maximise the peak-to-valley ratio (PVR), the optimal doping density of the analysed ZnO/Zn88Mg12O double-barrier RTD should be approximately 1018 cm-3, whilst the optimal barrier thickness should be 1.3 nm, with a Mg mole fraction of ~9%.

Observation of large spin-polarized Fermi surface of a magnetically proximitized semiconductor quantum well

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.

Engineering Semi-Reversed Quantum Well Photocatalysts for Highly-Efficient Solar-to-Fuels Conversion.

Semiconductor quantum wells (QWs) exhibit high charge-utilization efficiency for light-emitting applications due to their strong charge confinement effect. Inspired by this effect, herein, this work proposes a new idea to significantly improve the photo-generated charge separation for attaining a highly-efficient solar-to-fuels conversion process through "semi-reversing" the conventional QWs to confine only the photo-generated electrons. This electron confinement-improved charge separation is implemented in the well-designed model of the CdS/TiO2/CdS semi-reversed QW (SRQW) structure. The latter is fabricated by selectively assembling CdS quantum dots (QDs) onto the {101} facets (ultra-thin edge regions) of the TiO2 nanosheets (NSs). Upon light excitation, the photo-generated electrons of SRQW can be confined on the TiO2-{101} facets in the vicinity of the CdS/TiO2 hetero-interface. Thereby, the continuous multi-electron injection to the adsorbed reactants on the interfacial active-sites is significantly accelerated. Thus, the CdS/TiO2/CdS SRQW exhibits ≈35.7 and ≈56.0-fold enhancements on the photocatalytic activities for water and CO2 reduction, respectively, compared to those of pure TiO2. Correspondingly, its CH4-product selectivity is increased by ≈180%. This work provides a novel charge separation mechanism, which is of great importance for the design of the next-generation quantum-sized photocatalysts for solar-to-fuels conversion.

Combined effects of temperature and confinement on the Shannon entropy of two-dimensional hydrogenic impurity states in the GaAs semiconductor quantum well

Understanding the quantum properties of two-dimensional (2-D) hydrogenic impurity states in the GaAs quantum well is essential for their applications in the semiconductor devices. Here, we report the combined effects of temperature and quantum confienment on the Shannon entropy of 2-D hydrogenic impurity states in the GaAs quantum well. First, by calculating the position and momentum space Shannon entropy (Sr and Sp), as well as the Shannon entropy sum (St), for the hydrogenic impurity states in the GaAs quantum well at room temperature, we show fascinating quantum confinement properties in the two conjugated spaces. Then, the effects of temperature on the Shannon entropy for different hydrogenic impurity states are examined and compared. Intriguingly, we discover that the Shannon entropy sum exhibits the property of translation invariance under the influence of temperature. Finally, with the radius of the quantum well fixed at a constant, we observe that the value of the Shannon entropy for a given quantum state is highly sensitive to the variations in temperature. While the size of circular quantum well is constrained by design parameters, such as the fabrication process and intended application, temperature adjustment emerges as a viable means to control the quantum properties of 2-D hydrogenic impurities in the quantum well. This research presents a pioneering method that employs temperature as a versatile tool for modulating the Shannon entropy of hydrogenic impurity states in the quantum well, and has potential applications in the field of semiconductor physics, material physics, chemical physics, etc.

Efficient optical nonreciprocity based on four-wave mixing effect in semiconductor quantum well

Optical nonreciprocity has been a popular research topic in recent years. Semiconductor quantum wells (SQWs) play a key role in many high-performance optoelectronic devices. In this paper, we propose a theoretical scheme to achieve nonmagnetic optical nonreciprocity based on the four-wave mixing effect in SQW nanostructures. Using the experimentally available parameters, the nonreciprocal behavior of the probe field in forward direction and backward direction is achieved through this SQW, where both nonreciprocal transmission and nonreciprocal phase shift have high transmission rates. Furthermore, by embedding this SQW nanostructure into a Mach-Zender interferometer, a reconfigurable nonreciprocal device based on high transmission nonreciprocal phase shift that can be used as an isolator or a circulator, is designed and analyzed. The device can be realized as a two-port optical isolator with an isolation ratio of 92.39 dB and an insertion loss of 0.25 dB, and as a four-port optical circulator with a fidelity of 0.9993, a photon survival probability of 0.9518 and a low insertion loss with suitable parameters. Semiconductor media have the advantages of easier integration and tunable parameters, and this scheme can provide theoretical guidance for implementing nonreciprocal and nonreciprocal photonic devices based on semiconductor solid-state media.

The shape complexity of hydrogenic impurity state in the Ga1 − χAlχN semiconductor quantum well

The shape complexity of hydrogenic impurity state in the Ga1 − χAlχN semiconductor quantum well

A particular behavior of levels energy evolution and theoretical study of the quantum probability distribution in GaAs/AlGaAs asymmetric stepped semiconductor quantum wells for terahertz optoelectronics

The study of the evolution of the energy levels as a function of the step layer’s width Lw2 in an asymmetric stepped quantum well AlxGa1-xAs/GaAs/AlyGa1-yAs/AlxGa1-xAsx=24%,y=14%, revealed a particular behavior, marked by the presence of plateaus within certain deep well’s width, Lw2, ranges. We initially computed the eigenenergies and eigenfunctions by numerically solving the Schrödinger equation. This was done within the effective mass and envelope function approximation, taking into account the influence of non-parabolicity. To explain the origin of the plateaus and their impact on intersubband transition energies, we determined the distribution of the probability density of the presence of the electron in each region of the stepped quantum well. The results of these calculations demonstrated that the electron's probability density is higher in the step well than in the deep one, particularly for electrons with energy levels above 113.47 meV. This elevation in probability density exhibits maximum values that remain nearly constant within specific Lw2 domains, providing an explanation for the observed energy plateaus. Such plateaus allow more energy tunability and thus open up additional possibilities for applications in the THz domain either in the linear or nonlinear optics.

Optical, magnetic, and transport properties of two-dimensional III-nitride semiconductors (AlN, GaN, and InN) due to acoustic phonon scattering.

In this paper, the magneto-optical transport (MOT) properties of III-nitride Pöschl-Teller quantum well (QW) semiconductors, including AlN, GaN, and InN, resulting from the acoustic phonon interaction are thoroughly investigated and compared by applying the technique of operator projection. In particular, a comparison is made between the Pöschl-Teller QW results and the square QW ones. The findings demonstrate that the MOT properties of III-nitride QW semiconductors resulting from acoustic phonon scattering are strongly influenced by the quantum system (QS) temperature, applied magnetic field, and QW width. When the applied magnetic field and QS temperature increase, the absorbing FWHM in AlN, GaN, and InN increases; on the other hand, it diminishes when the QW's width increases. The absorbing FWHM in GaN is smaller and varies slower compared with AlN; inversely, it is larger and varies faster compared with InN. In other words, the absorbing FWHM in AlN is the largest and the smallest in InN. Compared to the square QW in AlN, GaN, and InN, the absorbing FWHMs in the Pöschl-Teller QW vary more quickly and have greater values. The absorbing FWHMs resulting from the acoustic phonon interaction in III-nitrides are strongly dependent on the nanostructure's geometric shape and parameters. Our findings provide useful information for the development of electronic devices.

Bilinear magnetoresistance in 2DEG with isotropic cubic Rashba spin–orbit interaction

Bilinear magnetoresistance has been studied theoretically in 2D systems with isotropic cubic form of Rashba spin–orbit interaction. We have derived the effective spin–orbital field due to current-induced spin polarization and discussed its contribution to the unidirectional system response. The analyzed model can be applied to the semiconductor quantum wells as well as 2DEG at the surfaces and interfaces of perovskite oxides.

Identification of electronic dimensionality reduction in semiconductor quantum well structures

Two-dimensional (2D) systems, such as high-temperature superconductors, surface states of topological insulators, and layered materials, have been intensively studied using vacuum-ultraviolet (VUV) angle-resolved photoemission spectroscopy (ARPES). In semiconductor films (heterostructures), quantum well (QW) states arise due to electron/hole accumulations at the surface (interface). The quantized states due to quantum confinement can be observed by VUV-ARPES, while the periodic intensity modulations along the surface normal (kz) direction of these quantized states are also observable by varying incident photon energy, resembling three-dimensional (3D) band dispersion. We have conducted soft X-ray (SX) ARPES measurements on thick and ultrathin III-V semiconductor InSb(001) films to investigate the electronic dimensionality reduction in semiconductor QWs. In addition to the dissipation of the kz dispersion, the SX-ARPES observations demonstrate the changes of the symmetry and periodicity of the Brillouin zone in the ultrathin film as 2D QW compared with these of the 3D bulk one, indicating the electronic dimensionality reduction of the 3D bulk band dispersion caused by the quantum confinement. The results provide a critical diagnosis using SX-ARPES for the dimensionality reduction in semiconductor QW structures.

Nonlinear parametric generation in a four-level inverted-type quantum well nanostructure

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.