Topic
Quantum well
About: Quantum well is a research topic. Over the lifetime, 44627 publications have been published within this topic receiving 674023 citations. The topic is also known as: QW & quantum potential well.
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TL;DR: In this article, the existence of massless fermion states in a graphene quantum well has been investigated by means of analytical and numerical calculations, showing an unusual quasilinear dependence on the momentum parallel to the QW: their number depends on the wave vector and is constrained by electron-hole conversion in barrier regions.
Abstract: We report the existence of confined massless fermion states in a graphene quantum well (QW) by means of analytical and numerical calculations. These states show an unusual quasilinear dependence on the momentum parallel to the QW: their number depends on the wave vector and is constrained by electron-hole conversion in the barrier regions. An essential difference with nonrelativistic electron states is a mixing between free and confined states at the edges of the free-particle continua, demonstrated by the direction-dependent resonant transmission across a potential well.
224 citations
TL;DR: With far-infrared spectroscopy, coupling between electron quantum dots becomes visible in the electronic excitation spectrum and gated GaAs-AlGaAs quantum wells that enable field-effect tuning of the coupling between adjacent dots are employed.
Abstract: With far-infrared spectroscopy, coupling between electron quantum dots becomes visible in the electronic excitation spectrum. We employ gated GaAs-AlGaAs quantum wells that enable field-effect tuning of the coupling between adjacent dots. For noninteracting quantum dots in a magnetic field we observe the characteristic edge- and bulk-mode spectrum.. The coupling of dots is reflected by a branching of the bulk mode into a cyclotron-resonance-like and a magnetoplasmonlike mode and a splitting of the edge mode. The latter is caused by formation of new edge orbits embracing two adjacent dots.
224 citations
TL;DR: In this article, a relaxation oscillation frequency was found to increase three times in a 50 A In0.9Ga0.1As/In0.52Al0.48As QW structure compared with that in a GaAs/Al 0.4Ga 0.6As Qw structure for the undoped case.
Abstract: Lasing characteristics of strained quantum well (QW) structures such as InGaAs/AlGaAs on GaAs and InGaAs/InAlAs on InP were analyzed by taking into account the band mixing effect in the valence band. A relaxation oscillation frequency fr, which gives a measure of the upper modulation frequency limit, was found increased three times in a 50 A In0.9Ga0.1As/In0.52Al0.48As QW structure compared with that in a 50 A GaAs/Al0.4Ga0.6As QW structure for the undoped case. One of the main factors for this improved frequency bandwidth is attributed to the reduced subband nonparabolicity as well as the reduced valence‐band density of state in the strained QW structure. The corresponding lasing threshold current is one order of magnitude smaller than that of the GaAs/AlGaAs QW structure. With a p doping in the QW the fr value increases, and the 3 dB cutoff frequency of about 90 GHz will be expected with an acceptor concentration of 5×1018 cm−3 in the In0.9Ga0.1As/In0.52Al0.48As QW.
224 citations
TL;DR: The general guiding principles for designing DQW structures with optimum excitonic properties are established, and ZnSe is found to be one of the most promising candidates for the barrier material of the GaAs D QW.
Abstract: Excitonic and nonlinear-optical properties of dielectric quantum-well (DQW) structures are investigated theoretically. A DQW is a quantum well sandwiched by barrier materials with a smaller dielectric constant and a larger band gap than the well material. The fundamental physics determining the excitonic properties in a DQW, i.e., exciton binding energy, exciton oscillator strength, and nonlinear-optical response, are clarified. The most important mechanisms for enhancing the excitonic properties are quantum-confinement effect, mass-confinement effect, and dielectric-confinement effect. Quantum confinement increases the spatial overlap between an electron and a hole as a result of the potential well confinement, and it enhances oscillator strength. Mass confinement is based on the penetration of the carrier wave function into barrier layers with a heavier effective mass than the well layer. It increases the exciton reduced mass and hence the exciton binding energy. Dielectric confinement arises from the reduction of the effective dielectric constant of the whole system due to the penetration of the electric field into the barrier medium having a smaller dielectric constant than the well and enhances the Coulomb interaction between the electron and hole. On the basis of these analyses, the general guiding principles are established for designing DQW structures with optimum excitonic properties. Various practical examples of DQW's are examined with respect to the lattice-constant matching, the difference in the dielectric constant, and the difference in the carrier effective masses. ZnSe is found to be one of the most promising candidates for the barrier material of the GaAs DQW.
224 citations
TL;DR: In this paper, a surface-emitting semiconductor laser has been passively mode-locked in an external cavity incorporating a semiconductor saturable absorber mirror, with a repetition rate variable around 4.4 GHz.
Abstract: A surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs-GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22-ps full-width at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz.
223 citations