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.

Exciton Condensation in Bilayer Quantum Hall Systems

Abstract: The condensation of excitons, bound electron-hole pairs in a solid, into a coherent collective electronic state was predicted more than 50 years ago. Perhaps surprisingly, the phenomenon was first observed in a system consisting of two closely spaced parallel two-dimensional electron gases in a semiconductor double quantum well. At an appropriate high magnetic field and low temperature, the bilayer electron system condenses into a state resembling a superconductor, only with the Cooper pairs replaced by excitons consisting of electrons in one layer bound to holes in the other. In spite of being charge neutral, the transport of excitons within the condensate gives rise to several spectacular electrical effects. This article describes these phenomena and examines how they inform our understanding of this unique phase of quantum electronic matter.

Coherent dynamics of radiatively coupled quantum-well excitons.

Abstract: The optical response of radiatively coupled semiconductor multiple-quantum-well structures is investigated theoretically. It is shown that the transverse optical field leads to a coupling of exciton states within each well which causes a radiative decay and a mixing of excitonic resonances. Simultaneously, the field-induced long-ranged coupling between different wells leads to collective effects that are very sensitive to the detailed geometry of the structure. For a quantum-well spacing equal to an integer multiple of half the optical wavelength inside the medium, it is predicted that the collective effects cause a stimulated decay of electronic excitations that should be observable in either transmission or reflection geometry. On the other hand, in a quarter wavelength structure, the light-induced coupling causes an interwell energy transport and a splitting of the excitonic resonances, that should be observable as quantum beats in the time-resolved transmitted or reflected signal.

Optical polarization characteristics of ultraviolet (In)(Al)GaN multiple quantum well light emitting diodes

Abstract: The polarization of the in-plane electroluminescence of (0001) orientated (In)(Al)GaN multiple quantum well light emitting diodes in the ultraviolet-A and ultraviolet-B spectral range has been investigated. The intensity for transverse-electric polarized light relative to the transverse-magnetic polarized light decreases with decreasing emission wavelength. This effect is attributed to rearrangement of the valence bands at the Γ-point of the Brillouin zone with changing aluminum and indium mole fractions in the (In)(Al)GaN quantum wells. For shorter wavelength the crystal-field split-off hole band moves closer to the conduction band relative to the heavy and light hole bands and as a consequence the transverse-magnetic polarized emission becomes more dominant for deep ultraviolet light emitting diodes.

Emission properties of nanolasers during the transition to lasing

Abstract: This review addresses ongoing discussions involving nanolaser experiments, particularly those related to thresholdless lasing or few-emitter devices. A quantum-optical (quantum-mechanical active medium and radiation field) theory is used to examine the emission properties of nanolasers under different experimental configurations. The active medium is treated as inhomogeneously broadened semiconductor quantum dots embedded in a quantum well, where carriers are introduced via current injection. Comparisons are made between a conventional laser and a nanolaser with a spontaneous emission factor of unity, as well as a laser with only a few quantum dots providing the gain. It is found that the combined exploration of intensity, coherence time, photon autocorrelation function and carrier spectral hole burning can provide a unique and consistent picture of nanolasers in the new regimes of laser operation during the transition from thermal to coherent emission. Furthermore, by reducing the number of quantum dots in the optical cavity, a clear indication of non-classical photon statistics is observed before the single-quantum-dot limit is reached. Nanolasers operate in a regime distinctly different to that of conventional lasers, and a consistent model of nanolasing physics is needed. Whereas conventional lasers are characterized by a marked intensity jump at the onset of lasing, micro- and nanocavity lasers with well-developed three-dimensional optical mode confinement can have a vanishing small intensity jump approaching thresholdless behavior. Weng Chow from Sandia National Laboratories in the United States, with colleagues Frank Jahnke and Christopher Gies from the University of Bremen in Germany, has reviewed recent nanolaser experiments and developed a model based on quantum-optical theory to examine photon statistics in the different operational regime of nanolasers compared with conventional lasers. The results dispute the notation of thresholdless lasing and suggests the emergence of non-classical photon statistics for few-atom or few-quantum-dot active regions.

Demonstration of a 320×256 two-color focal plane array using InAs/InGaAs quantum dots in well detectors

Abstract: We report the demonstration of a two-color infrared focal plane array based on a voltage-tunable quantum dots-in-well (DWELL) design. The active region consists of multiple layers of InAs quantum dots in an In0.15Ga0.85As quantum well. Spectral response measurements yielded a peak at 5.5μm for lower biases and at 8–10μm for higher biases. Using calibrated blackbody measurements, the midwavelength and long wavelength specific detectivity (D*) were estimated to be 7.1×1010cmHz1∕2∕W(Vb=1.0V) and 2.6×1010cmHz1∕2∕W(Vb=2.6V) at 78 K, respectively. This material was processed into a 320×256 array and integrated with an Indigo 9705 readout chip and thermal imaging was achieved at 80 K.