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.

Long-wavelength semiconductor lasers

Abstract: A semiconductor laser wherein a wide range of laser emission wavelengths can be obtained by varying the composition of monocrystalline alloys employed as semiconductor material. The semiconductor structure comprises on a monocrystalline indium phosphide substrate of a predetermined conductivity type successive epitaxial layers consisting of a first confinement layer of the same conductivity type, an active layer having the formula (Gax Al1-x)0.47 In0.53 As where x is within the range of 0 to 0.27, and a second confinement layer of opposite conductivity type. The confinement layers are composed of either InP or a ternary alloy Al0.47 In0.53 As or a quaternary alloy Gax' Al1-x' Asy' Sb1-y' where x' and y' are chosen so that the material should have a predetermined crystal lattice and an energy gap of greater width than the substrate material.

Optical bistability in a three-level semiconductor quantum-well system

Abstract: Optical bistable behavior in a unidirectional ring cavity (or a Fabry–Perot cavity) containing a semiconductor quantum well, described as a three-level ladder-type system with similar transition energies, has been studied The system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence The threshold for switching to upper branch of the bistable curve is found to be reduced due to the presence of quantum interference Such system can be used for making efficient and fast all-optical switching devices

Helical edge and surface states in HgTe quantum wells and bulk insulators

Abstract: The quantum spin Hall (QSH) effect is the property of a new state of matter which preserves time reversal, has an energy gap in the bulk, but has topologically robust gapless states at the edge. Recently, the QSH state has been theoretically predicted and experimentally observed in HgTe quantum wells [B. A. Bernevig et al., Science 34, 1757 (2006); M. Konig et al., ibid. 318, 766 (2007)]. In this work, we start from realistic tight-binding models and demonstrate the existence of the helical edge states in HgTe quantum wells and calculate their physical properties. We also show that three-dimensional HgTe is a topological insulator under uniaxial strain and show that the surface states are described by single-component massless relativistic Dirac fermions in $2+1$ dimensions. Experimental predictions are made based on the quantitative results obtained from realistic calculations.

Selective quantum-well intermixing in GaAs-AlGaAs structures using impurity-free vacancy diffusion

Abstract: Impurity-free vacancy disordering (IFVD) using SiO/sub 2/ and SrF/sub 2/ dielectric caps to induce selective quantum-well (QW) intermixing in the GaAs-AlGaAs system is studied. The intermixing rate of IFVD was found to be higher in n-i-p and intrinsic than in p-i-n structures, which suggests that the diffusion of the Group III vacancy is not supported in p-type material. Single-mode waveguides have been fabricated from both as-grown and bandgap-tuned double-quantum-well (DQW) laser samples. Propagation losses as low as 8.5 dB cm/sup -1/ were measured from the bandgap-tuned waveguides at the lasing wavelength of the undisordered material, i.e., 860 nm. Simulation was also carried out to study the contribution of free-carrier absorption from the cladding layers, and the leakage loss induced by the heavily p-doped GaAs contact layer. It was found that the leakage loss contributed by the GaAs cap layer is significant and increases with wavelength. Based on IFVD, we also demonstrate the fabrication of multiple-wavelength lasers and multichannel wavelength division multiplexers using the one-step "selective intermixing in selected area" technique. This technique enables one to control the degree of intermixing across a wafer. Lasers with bandgaps tuned to five different positions have been fabricated on a single chip. These lasers showed only small changes in transparency current, internal quantum efficiency, or internal propagation loss, which indicates that the quality of the material remains high after being intermixed. Four-channel wavelength demultiplexers based on a waveguide photodetector design have also been fabricated. Photocurrent and spontaneous emission spectra from individual diodes showed that the absorption edge was shifted by different degrees due to the selective degree of QW intermixing. The results obtained also imply that the technique can be used in the fabrication of broad-wavelength emission superluminescent diodes.

Quantum cascade laser with plasmon‐enhanced waveguide operating at 8.4 μm wavelength

Abstract: A unipolar cascade laser operating at 8.4 μm wavelength is reported. The structure, grown by molecular beam epitaxy in the AlInAs/GaInAs material system, contains a 25‐stage coupled‐quantum‐well active region. The waveguide design is optimized to enhance optical confinement and reduce losses associated with the interface plasmon mode, by taking advantage of the dispersion of the refractive index of the contact layer near the plasma frequency. The peak optical power is 30 mW and the threshold current density 2.8 kA/cm2, at a heat‐sink temperature of 100 K and the highest operating temperature is 130 K. The slope efficiency at 100 K is ∼0.1 W/A, corresponding to a differential quantum efficiency of 5.4% per stage. This work, combined with previous results on shorter wavelength quantum cascade lasers, demonstrates that the wavelength of these new light sources can be tailored over a wide range by changing the active layers’ thicknesses using the same materials.