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Giant Stark effect in coupled quantum wells: Analytical model
摘要： Coupled quantum wells have been proposed as candidates for highly polarizable structures due to their near-degenerate and dipole-coupled electronic states. Hence, many interesting applications in linear and nonlinear optics can be envisioned. We analyze this proposal considering a simple structure with a delta-function barrier separating the wells. While very substantial Stark shifts are certainly predicted for this geometry, perturbative estimates based on polarizabilities (and hyperpolarizabilities) fail beyond a critical ?eld strength that depends inversely on the barrier. Hence, a giant Stark effect due to near-degenerate states is invariably limited by a small critical ?eld. Our analytical (hyper) polarizability expressions are applied to ?nd quantitative Stark shifts for GaAs quantum wells and transition-metal dichalcogenide bilayers. The predicted Stark shifts and critical ?elds agree with the ?eld dependence observed in a range of available experiments.
关键词： Stark effect,hyperpolarizability,GaAs,transition-metal dichalcogenide bilayers,polarizability,coupled quantum wells
更新于2025-09-23 15:19:57
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Increased radiative recombination of AlGaN-based deep ultraviolet laser diodes with convex quantum wells
摘要： An AlGaN-based deep ultraviolet laser diode with convex quantum wells structure is proposed. The advantage of using a convex quantum wells structure is that the radiation recombination is significantly improved. The improvement is attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes, which results in an increased hole injection efficiency and a decreased electron leakage into the p-type region. Particularly, comparisons with the convex quantum barriers structure and the reference structure show that the convex quantum wells structure has the best performance in all respects.
关键词： AlGaN,radiation recombination,convex quantum wells,electron leakage,deep ultraviolet laser diode,hole injection efficiency
更新于2025-09-23 15:19:57
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Ultrathin Plasmonic Tungsten Oxide Quantum Wells with Controllable Free Carrier Densities
摘要： We report the colloidal synthesis of ~3 tungsten-oxygen (W-O) layer thick (~1 nm), two-dimensional (2D) WO3-x nanoplatelets (NPLs) (x ~ 0.55 — 1.03), which display tunable near-infrared localized surface plasmon resonances (LSPR) spectra and high free electron density (Ne) that arises predominantly from their large shape factor. Importantly, the W to O composition ratios inferred from their LSPR measurements show much higher percentage of oxygen vacancies than those determined by X-ray diffraction analysis, suggesting that the aspect ratio of ultrathin WO3-x NPLs is the key to producing an unprecedentedly large Ne, although synthesis temperature is also an independent factor. We find that NPL formation is kinetically controlled, whereas thermodynamic parameter manipulation leads to Ne as high as 4.13 X 1022 cm-3, which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. The unique structural properties of 2D nanomaterials along with the high Ne of WO3-x NPLs provide an attractive alternative to plasmonic noble metal nanostructures for energy conversions.
关键词： Ultrathin Plasmonic Tungsten Oxide,Quantum Wells,Colloidal Synthesis,Localized Surface Plasmon Resonances,Free Carrier Densities
更新于2025-09-23 15:19:57
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Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells
摘要： n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.
关键词： quantum wells,THz spectroscopy,group IV epitaxy,intersubband transitions,silicon–germanium heterostructures
更新于2025-09-23 15:19:57
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Effect of Interface State Density of the AlGaN Electron Blocking Layer/GaN Barrier Layer in InGaN Blue Light-Emitting Diodes
摘要： Herein, two kinds of blue InGaN light-emitting diodes (LEDs) were compared in order to understand the effect of the strain originating from two different sapphire substrates. One of the LED types was grown on a patterned sapphire substrate (PSS), and the other was grown on a conventional sapphire substrate (CSS). The internal strains biased on InGaN quantum wells were compared by studying the time-resolved photoluminescence and the electroreflectance. Through analysis of the dynamic capacitance dispersion measurements, the relation between the trap states and trap density of the AlGaN electron blocking layer/GaN barrier interface above the InGaN quantum wells can be understood in great detail. The trapped charges of the CSSs have faster response times than those of the PSSs; this is attributed to the stronger piezo-field, which induces the AlGaN EBL/GaN barrier interface trap states to be effectively located at shallower levels from the conduction band.
关键词： Strain,Patterned sapphire substrate,InGaN quantum wells
更新于2025-09-23 15:19:57
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Study on Optical Properties and Waveguide Structure Optimization of Semiconductor Lasers with InGaAs Quantum Well
摘要： InGaAs quantum wells (QWs) are grown on GaAs substrates by metal-organic chemieal vapor deposition (MOCVD). Sample grown on substrates (100) oriented 2° off towards <111> exhibits relatively high photoluminescence (PL) intensity and narrow full-width at half-maximum (FWHM). Increasing growth rate leads to the enhancement of PL intensity and decrease of FWHM. Asymmetric waveguide layers are applied to reduce the confinement factor of base mode and increase the loss of higher-order mode.
关键词： MOCVD,waveguide structure,photoluminescence,InGaAs quantum wells,semiconductor lasers
更新于2025-09-23 15:19:57
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Comparative Analysis of Injection Microdisk Lasers Based on InGaAsN Quantum Wells and InAs/InGaAs Quantum Dots
摘要： The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μ m with different active regions, notably, InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages.
关键词： nitrogen-containing semiconductors,quantum dots,quantum wells,microlaser
更新于2025-09-19 17:13:59
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The model and stress analysis of self-doping SiGe/Si multi-quantum wells applied in uncooled infrared focal plane array
摘要： Silicon-germanium multi-quantum wells (MQWs) ?lm is a promising sensitive material with high temperature coe?cient of resistance (TCR). This paper focuses on solving the stress problem of uncooled infrared focal plane array caused by intrinsic stress of MQWs ?lms. First of all, the paper presents the accurate TCR model of MQWs, which is more consistent with the actual situation especially when the Fermi level enters the valence band. The energy bands distributions and each sub-band wavefunction of MQWs were calculated. The critical thickness analysis about epitaxial growth ?lm was carried out for solving intrinsic stress of MQWs ?lm, which leads to the deformation of pixel structure in the fabrication processes. The paper calculated the maximum ?lm stress in completely strain state and derived the buckling of the bolometer. Tri-layer structure was applied in support beam design for the deformation compensation. The self-doping MQWs ?lm was epitaxial growth on silicon substrate with bu?er layer to overcome the lattice slips in experiments. The bolometer was fabricated and released without visible deformation utilizing the compensation methods. The ohmic-contact problems and signals were also mentioned in the paper. The thermal conductivity and capacity were calculated by means of thermal response experiments without infrared radiation.
关键词： Multi-quantum wells,Intrinsic stress,Uncooled infrared focal plane array
更新于2025-09-19 17:13:59
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Surface-plasmon-enhanced LED based on multilayer gratings and core-shell Ag/SiO <sub/>2</sub> nanoparticles
摘要： This paper proposes a novel GaN-based LED with nano-grating structure based on surface plasmons. This structure mainly contains n-GaN, multiple quantum wells and p-GaN, Ag–SiO2 grating, core–shell Ag/SiO2 nanoparticle and ITO triangular grating. The basic principle of the light emitting characteristics of LED is described in detail. The COMSOL software is used to analyse properties and optimise parameters based on the ?nite element method. The radiated intensity, absorbed intensity and electric ?eld distribution are obtained. The results indicate that this structure has a higher luminous ef?ciency with the luminous intensity increased to about 58.59 times compared with the ordinary structure and about 3.94 times compared with the reference structure, and can enhance the internal quantum ef?ciency and the external quantum ef?ciency of the LED simultaneously.
关键词： light-emitting diode,quantum wells,grating,surface plasmons
更新于2025-09-19 17:13:59
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Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models
摘要： n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an experimental case study, we have epitaxially grown samples consisting of two asymmetric coupled quantum wells forming a three-level system, which we optically pump with a free electron laser. The benchmark quantity selected for model testing purposes is the saturation intensity at the 1→3 intersubband transition. The numerical quantum model prediction is in reasonable agreement with the experiments and therefore outperforms the discrete-energy-level analytical model, of which the prediction of the saturation intensity is off by a factor 3.
关键词： silicon–germanium heterostructures,intersubband photoluminescence,optical pumping,intersubband transitions,electron–phonon interaction,infrared spectroscopy,quantum wells,free electron laser,terahertz quantum cascade laser
更新于2025-09-16 10:30:52