Showing papers on "Quantum well published in 1994"

The quantum hydrodynamic model for semiconductor devices

Abstract: The classical hydrodynamic equations can be extended to include quantum effects by incorporating the first quantum corrections These quantum corrections are $O( {\hbar ^2 } )$ The full three-dimensional quantum hydrodynamic (QHD) model is derived for the first time by a moment expansion of the Wigner–Boltzmann equation The QHD conservation laws have the same form as the classical hydrodynamic equations, but the energy density and stress tensor have additional quantum terms These quantum terms allow particles to tunnel through potential barriers and to build up in potential wellsThe three-dimensional QHD transport equations are mathematically classified as having two Schrodinger modes, two hyperbolic modes, and one parabolic mode The one-dimensional steady-state QHD equations are discretized in conservation form using the second upwind methodSimulations of a resonant tunneling diode are presented that show charge buildup in the quantum well and negative differential resistance (NDR) in the current-v

Preparation, characterization, and photophysics of the quantum dot quantum well system cadmium sulfide/mercury sulfide/cadmium sulfide

Abstract: The synthetic procedure, the characterization, and some photophysical properties of a quantum dot quantum well (QDQW) system are described in detail. The novel structures prepared via wet chemical methods consist of a core of size-quantized CdS and a well of 1-3 monolayers of HgS capped by 1-5 monolayers of CdS acting as the outermost shell. Additionally, theoretical calculations based on the effective mass approximation appropriate to describe the 1s-1s electronic transition of the composite particles are presented

Near-Field Spectroscopy of the Quantum Constituents of a Luminescent System

Abstract: Luminescent centers with sharp (<0.07 millielectron volt), spectrally distinct emission lines were imaged in a GaAs/AIGaAs quantum well by means of low-temperature near-field scanning optical microscopy. Temperature, magnetic field, and linewidth measurements establish that these centers arise from excitons laterally localized at interface fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus opens a rich area of physics involving quantum resolved systems.

Sharp-line photoluminescence and two-photon absorption of zero-dimensional biexcitons in a GaAs/AlGaAs structure.

Abstract: Using a micron-sized photoluminescence (PL) probe enables us to study single islandlike interface defects of a thin GaAs/AlGaAs quantum well. The bound exciton ground state locally emits a distinct sharp line. With increasing excitation of this quantum dot level additional transition lines emerge at lower energy. They are attributed to localized biexciton states. The biexciton correlation energy is about 4 meV. A distinct two-photon resonant absorption peak of the biexciton ground state is observed in PL excitation spectroscopy. Its linewidth is only about 30 \ensuremath{\mu}eV. The spectra and their polarization properties are discussed on the basis of a discrete level scheme and the Pauli exclusion principle.

Quantum-dot quantum well CdS/HgS/CdS: Theory and experiment.

Abstract: An extended theoretical approach for calculating the 1s-1s electronic transition in spherically layered semiconductor quantum dots is presented. The extension over the common effective-mass approximation includes the implementation of the Coulomb interaction and finite potential wells at the particle boundaries. The calculations are carried out for the quantum-dot quantum well CdS/HgS/CdS and compared to recently available experimental results. The wave functions of electrons and holes spreading over the entire structure and the probabilities of presence in the different layers, as well as outside the structure in the surrounding dielectric water, are presented.

Low threshold voltage vertical-cavity lasers fabricated by selective oxidation

Abstract: Novel vertical-cavity surface emitting lasers fabricated using selective oxidation to form a current aperture under a top monolithic distributed Bragg reflector mirror are reported. Large cross-sectional area lasers (259 µm2) exhibit threshold current densities of 150 A/cm2 per quantum well and record low threshold voltage of 1.33 V. Smaller lasers (36 µm2) possess threshold currents of 900 µA with maximum output powers greater than 1 mW. The record performance of these oxidised vertical-cavity lasers arises from the low mirror series resistance and very efficient current injection into the active region.

Semiconductor-Laser Physics

Abstract: 1. Semiconductor Laser Diodes 2. Basic Concepts 3. Free-Carrier Theory 4. Coulomb Effects 5. Many-Body Gain 6. Band Mixing and Strain in Quantum Wells 7. Semiclassical laser Theory 8. Multimode Operation 9. Quantum Theory of the Laser 10. Propagation Effects 11. Beyond Quasiequilibrium Theory, Appendices A-e, Index

High-performance uncooled 1.3-/spl mu/m Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP strained-layer quantum-well lasers for subscriber loop applications

Abstract: Design considerations for fabricating highly efficient uncooled semiconductor lasers are discussed. The parameters investigated include the temperature characteristics of threshold current, quantum efficiency, and modulation speed. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP material system instead of the conventional Ga/sub x/In/sub 1-x/As/sub y/P/sub 1-y//InP material system. To reduce the transparency current and the carrier-density-dependent loss due to the intervalence-band absorption, strained-layer quantum wells are chosen as the active layer. Experimentally, 1.3-/spl mu/m compressive-strained five-quantum-well lasers and tensile-strained three-quantum-well lasers were fabricated using a 3-/spl mu/m wide ridge-waveguide laser structure. For both types of lasers, the intrinsic material parameters are found to be similar in magnitude and in temperature dependence if they are normalized to each well. Specifically, the compressive-strained five-quantum-well lasers show excellent extrinsic temperature characteristics, such as small drop of 0.3 dB in differential quantum efficiency when the heat sink temperature changes from 25 to 100/spl deg/C, and a large small-signal modulation bandwidth of 8.6 GHz at 85/spl deg/C. The maximum 3 dB modulation bandwidth was measured to be 19.6 GHz for compressive-strained lasers and 17 GHz for tensile-strained-lasers by an optical modulation technique. The strong carrier confinement also results in a small k-factor (0.25 ns) which indicates the potential for high-speed modulation up to 35 GHz. In spite of the aluminum-containing active layer, no catastrophic optical damage was observed at room temperature up to 218 mW for compressive-strained five-quantum-well lasers and 103 mW for tensile-strained three-quantum-well lasers. For operating the compressive-strained five-quantum-well lasers at 85/spl deg/C with more than 5 mW output power, a mean-time-to-failure (MTTF) of 9.4 years is projected from a preliminary life test. These lasers are highly attractive for uncooled, potentially low-cost applications in the subscriber loop. >

Nonparabolicity and a sum rule associated with bound-to-bound and bound-to-continuum intersubband transitions in quantum wells

Abstract: A sum rule for electronic intersubband transitions has been derived following Kane's model, beyond the quadratic dispersion relations The sum rule takes into account the effects of nonparabolicity and the different effective masses in the well and barrier materials; it depends on the property of the ground state of the system and, as such, on the shape of the potential The boundaries of the validity of matrix element computations are also discussed in the case where only the conduction band is included Experimental results are presented for bound-to-bound and bound-to-continuum intersubband transitions in various types of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{Ga}}_{\mathit{y}}$${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$As quantum well systems (single wells, coupled wells and quantum wells with Bragg confinement); the agreement with theory is excellent In the last section of the paper, the effect of the electric field on the sum rule is investigated

Condensation of indirect excitons in coupled AlAs/GaAs quantum wells.

Abstract: The photoluminescence of excitons confined in an electric field tunable coupled AlAs/GaAs quantum well has been investigated at $T\ensuremath{\ge}350$ mK and magnetic fields $H\ensuremath{\le}14$ T. In the indirect regime where electrons and holes are separated both in real and in $k$ space, the magnetic field was found to result in (i) a strong change of both the photoluminescence intensity and decay time which is attributed to anomalies in the exciton transport and (ii) an appearance of a huge broad band noise in the photoluminescence intensity which is evidence for exciton condensation.

Quantum dots formed by interface fluctuations in AlAs/GaAs coupled quantum well structures.

Abstract: We report about optical experiments on electric field tunable AlAs/GaAs coupled quantum well structures in the regime of the electric field induced \ensuremath{\Gamma}-X transition. Using the energetically tunable X-point state in the AlAs layer as an internal energy spectrometer and charge reservoir we are able to map out the electronic states in the neighboring GaAs quantum well in great detail. In spatially resolved and bias voltage dependent photoluminescence experiments we find sets of extremely narrow emission lines below the fundamental band gap energy of the GaAs quantum well. The new emission lines are shown to originate from natural quantum dots which are formed by well width fluctuations of the GaAs quantum well.

Time‐resolved optical characterization of InGaAs/GaAs quantum dots

Abstract: We report on the optical characterization of the strained InGaAs/GaAs quantum dots (QDs). The temperature dependence of the photoluminescence (PL) indicates that the onset energy of the thermal quenching in ∼20‐nm‐diam QDs is enhanced by a factor of ∼2 as compared to a quantum well (QW), due to the additional confinement. At low temperature, an increased carrier lifetime is observed for the QDs as compared to a reference QW (880 vs 330 ps). The carrier lifetime in the QDs was found to be independent of the temperature for T<30 K. In addition to this different dynamics of the localized excitons, we find that in the steady state PL and PL excitation, there is virtually no overlap between the emission and the absorption energies.

Band-structure engineering in strained semiconductor lasers

Abstract: The influence of both compressive and tensile strain on semiconductor lasers and optical amplifiers is reevaluated in the light of recent experimental and theoretical work. Strain reduces the three-dimensional symmetry of the lattice and helps match the wave functions of the holes to the one-dimensional symmetry of the laser beam. It can also decrease the density of states at the valence band maximum and so reduce the carrier density required to reach threshold. These two effects appear to adequately explain the TE and TM gain in compressive and tensile structures, including polarization-independent amplifiers, the behavior of visible lasers and the improved frequency characteristics of InGaAs/GaAs lasers. In 1.5 /spl mu/m InGaAsP/InP lasers phonon-assisted Auger recombination appears to remain the dominant current path and can explain why the temperature sensitivity parameter to remains >

Progress in long-wavelength strained-layer InGaAs(P) quantum-well semiconductor lasers and amplifiers

Abstract: The progress in long-wavelength compressively and tensile-strained InGaAs(P) quantum-well semiconductor lasers and amplifiers is reviewed. By the application of grown-in strain, the device performance is considerably improved such that conventional bulk and unstrained quantum-well active-layer devices are outperformed, while a high reliability is maintained. >

Study of the two‐dimensional–three‐dimensional growth mode transition in metalorganic vapor phase epitaxy of GaInP/InP quantum‐sized structures

Abstract: Ga0.5In0.5P/InP quantum‐sized structures, grown by metalorganic vapor phase epitaxy, have been optically characterized by photoluminescence, cathodoluminescence, and photoluminescence excitation spectroscopy. Additional structural information has been obtained by atomic force microscopy. We find that the two‐dimensional layer‐by‐layer growth mode is limited to the growth of 1‐ML‐thick and, in part, 2‐ML‐thick quantum wells. The transition towards three‐dimensional Stranski–Krastanow island growth occurs before the second monolayer of InP is completed. To further study the dynamics of the island formation, growth interruptions were introduced between the InP deposition and the subsequent growth of the upper GaInP barrier. The two types of coherent islands show a quantum confinement in vertical direction, corresponding to about 2‐ and 3‐ML‐thick and about 9‐ and 10‐ML‐thick InP strained quantum wells.

Quantum beats of electron Larmor precession in GaAs wells.

Abstract: We observe quantum beats in the time-resolved photoluminescence of GaAs quantum wells in a magnetic field perpendicular to the growth direction. These beats originate from Larmor precession of electron spins and show a coherence time of 500 ps, which is much longer than the optical dephasing time of 7 ps. The long coherence time allows us to determine the electron Land\'e g factors with an accuracy better than 1%.

Silicon oxide resonant tunneling diode structure

Abstract: A resonant tunneling diode (400) made of a silicon quantum well (406) with silicon oxide tunneling barriers (404, 408). The tunneling barriers have openings (430) of size smaller than the electron wave packet spread to insure crystal alignment through the diode without affecting the tunneling barrier height, and the openings (430) have an irregular (nonperiodic) shape.

Formation of GaAs ridge quantum wire structures by molecular beam epitaxy on patterned substrates

Abstract: A ridge quantum wire structure has been successfully fabricated on a patterned (001) GaAs substrate by first growing a (111)B facet structure with a very sharp ridge and then depositing a thin GaAs quantum well on its top. Electron microscope study has shown that a GaAs wire with the effective lateral width of 17–18 nm is formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that one of the luminescence lines comes from the wire region at the ridge and its blue shift (∼60 meV) agrees with the quantum confined energy calculated for the observed wire structure.

Molecular‐beam epitaxy growth of quantum dots from strained coherent uniform islands of InGaAs on GaAs

Abstract: The two‐ (2D) to three‐dimensional (3D) growth mode transition during the initial stages of growth of highly strained InxGa1−xAs on GaAs is used to obtain quantum dot structures. Transmission electron micrographs (TEM) reveal that when the growth of InxGa1−xAs is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of InGaAs result. Size distribution measurements from TEM images indicate that these dots are less than 300 A in diameter and remarkably uniform. A phase diagram is constructed, showing the growth conditions under which these strained coherent uniform dots form. Photoluminescence from layers containing these dots is observed and correlated with growth conditions and with structural data obtained from TEM images. We observe that the photoluminescence emitted from the dots and an underlying reference quantum well are nearly equal, indicating a high quantum efficiency for these quantum dots.

Coupled semiconductor microcavities

Abstract: The coupled semiconductor microcavity is a system in which there are three oscillators, two photonic and one electronic (quantum well excitons). It develops three strongly coupled modes which allow a wide design range for a variety of optoelectronic applications. The MBE grown structure is comprised of two λ sized GaAs cavities containing InxGa1−xAs quantum wells, separated by a common mirror. Reflectivity measurements show both two coupled photon mode behavior and three coupled mode behavior, i.e., two photon and one exciton, depending on the relative position of the exciton resonance.

Ultrafast 1.55‐μm photoresponses in low‐temperature‐grown InGaAs/InAlAs quantum wells

Abstract: Doping with Be was found to be very effective for shortening of carrier lifetime in InGaAs/InAlAs multiple quantum wells (MQWs) grown at low temperature by molecular beam epitaxy. The MQW materials have carrier lifetimes controllable from a few tens of picoseconds to 1 ps in the 1.55‐μm wavelength region, coupled with a large optical nonlinearity due to an excitonic feature, implying applicability to ultrafast optical devices in the fiber‐optic communication. The carrier lifetime was measured by a time‐resolved pump‐probe method using an optical source based on a 1.535‐μm semiconductor laser. We also investigated the resistivity, carrier density, and Hall mobility in the MQWs.

Optical spectroscopy of a GaAs/AlGaAs quantum wire structure using near-field scanning optical microscopy

Abstract: We report the first spectroscopic study using a low temperature near‐field scanning optical microscope. We have studied an array of GaAs/AlGaAs cleaved edge overgrowth quantum wires. The three luminescence peaks originate from different structures in the sample: The (001)‐oriented multiple quantum wells, the (110)‐oriented single quantum well, and the quantum wires. The linewidth of the quantum wire emission is related to roughness in the (110)‐oriented single quantum well. Quenching of the multiple quantum wells and single quantum well emission near the quantum wires is attributed to diffusion of photoexcited carriers into the wires.

Low threshold half-wave vertical-cavity lasers

Abstract: Data are presented characterising half-wavelength vertical-cavity surface-emitting lasers defined by a native-oxide ring in which the native oxide is 200 A from the single quantum well. The lowest threshold is achieved with a 2 µm square active region, with a minimum threshold current of 91 µA continuous-wave at room temperature.

Quantum Well Intersubband Transition Physics and Devices

Abstract: Detector Applications.- Random Scattering Optical Couplers for Quantum Well Infrared Photodetectors.- Performance of Grating Coupled AlGaAs/GaAs Quantum Well Infrared Detectors and Detector Arrays.- Novel Grating Coupled and Normal Incidence III-V Quantum Well Infrared Photodetectors with Background Limited Performance at 77 K.- Background Limited 128x128 GaAs/AlGaAs Multiple Quantum Well Infrared Focal Plane Arrays.- Imaging Performance of LWIR MiniBand Transport Multiple Quantum Well Infrared Focal Plane Arrays.- Modeled Performance of Multiple Quantum Well Infrared Detectors in IR Sensor Systems.- GaAs/AlGaAs QWIPs vs. HgCdTe Photodetectors for LWIR Applications.- Detector Physics.- The Physics of Emission-RecomBination in Multiquantum Well Structures.- Physics of Single Quantum Well Infrared Photodetectors.- A Three-color Voltage TunaBle Quantum Well IntersuBBand Photodetector for Long Wavelength Infrared.- Multi ? Controlled Operation of Quantum Well IR Detectors Using Electric Field Switching and Rearrangement.- Infrared Hot-Electron Transistor Design Optimization.- 16 ?m Infrared Hot Electron Transistor.- Long Wavelength ?c=18?m Infrared Hot Electron Transistor.- A Novel Transport Mechanism for Photovoltaic Quantum Well IntersuBBand Infrared Detectors.- IntersuBBand Stark-Ladder Transitions in MiniBand-Transport Quantum-Well Infrared Detectors.- CO2-Laser Heterodyne Detection with GaAs/AlGaAs MQW Structures.- IntersuBBand Transition Experimental.- IntersuBBand ABsorption in n-Type Si and Ge Quantum Wells.- IntersuBBand Transitions in p-Type SiGe/Si Quantum Wells for Normal Incidence Infrared Detection.- Large Energy IntersuBBand Transitions in High Indium Content InGaAs/AlGaAs Quantum Wells.- Applications of High Indium Content InGaAs/AlGaAs Quantum Wells in the 2-Detector Applications.- Random Scattering Optical Couplers for Quantum Well Infrared Photodetectors.- Performance of Grating Coupled AlGaAs/GaAs Quantum Well Infrared Detectors and Detector Arrays.- Novel Grating Coupled and Normal Incidence III-V Quantum Well Infrared Photodetectors with Background Limited Performance at 77 K.- Background Limited 128x128 GaAs/AlGaAs Multiple Quantum Well Infrared Focal Plane Arrays.- Imaging Performance of LWIR MiniBand Transport Multiple Quantum Well Infrared Focal Plane Arrays.- Modeled Performance of Multiple Quantum Well Infrared Detectors in IR Sensor Systems.- GaAs/AlGaAs QWIPs vs. HgCdTe Photodetectors for LWIR Applications.- Detector Physics.- The Physics of Emission-RecomBination in Multiquantum Well Structures.- Physics of Single Quantum Well Infrared Photodetectors.- A Three-color Voltage TunaBle Quantum Well IntersuBBand Photodetector for Long Wavelength Infrared.- Multi ? Controlled Operation of Quantum Well IR Detectors Using Electric Field Switching and Rearrangement.- Infrared Hot-Electron Transistor Design Optimization.- 16 ?m Infrared Hot Electron Transistor.- Long Wavelength ?c=18?m Infrared Hot Electron Transistor.- A Novel Transport Mechanism for Photovoltaic Quantum Well IntersuBBand Infrared Detectors.- IntersuBBand Stark-Ladder Transitions in MiniBand-Transport Quantum-Well Infrared Detectors.- CO2-Laser Heterodyne Detection with GaAs/AlGaAs MQW Structures.- IntersuBBand Transition Experimental.- IntersuBBand ABsorption in n-Type Si and Ge Quantum Wells.- IntersuBBand Transitions in p-Type SiGe/Si Quantum Wells for Normal Incidence Infrared Detection.- Large Energy IntersuBBand Transitions in High Indium Content InGaAs/AlGaAs Quantum Wells.- Applications of High Indium Content InGaAs/AlGaAs Quantum Wells in the 2-7 ?m Regime.- Spectroscopy of Narrow MiniBands in the Continuum of Multi Quantum Wells.- IntersuBBand ABsorption in Strongly Coupled Superlattices: MiniBand Dispersion, Critical Points, and Oscillator Strengths.- Electronic Quarter-Wave Stacks and Bragg Reflectors: Physics of Localized Continuum States in Quantum Semiconductor Structures.- Modulation of the Optical ABsorption By Electric-Field-Induced Quantum Interference in Coupled Quantum Wells.- Phase Retardation and Induced Birefringence Related to IntersuBBand Transitions in Multiple Quantum Well Structures.- The Interaction of Photoexcited e-h Pairs with a Two Dimensional Electron Gas Studied By IntersuBBand Spectroscopy.- Photoinduced IntersuBBand Transitions in GaAs/AlGaAs Asymmetric Coupled Quantum Wells.- Far Infrared Spectroscopy of IntersuBBand Transitions in Multiple Quantum Well Structures.- OBservation of IntersuBBand Transitions in Asymmetric ?-Doped GaAs, InSB, and InAs Structures.- Effects of Coupling on IntersuBBand Transitions.- On Some Peculiarities of IntersuBBand ABsorption in Semiconductor Quantum Wells.- The Relative Strengths of InterBand and IntersuBBand Optical Transitions: Breakdown of the Atomic Dipole Approximation for InterBand Transitions.- Optical Transitions and Energy Level Ordering for Quantum Confined Impurities.- SuBBand Structures of Superlattices under Strong In-Plane Magnetic Fields.- IntersuBBand Relaxation.- Temperature Dependent IntersuBBand Dynamics in n-Modulation Doped Quantum Well Structures.- Ultrafast Dynamics of Electronic Capture and IntersuBBand Relaxation in GaAs Quantum Well.- Structure-Dependent Electron-Phonon Interactions.- Nonlinear Phenomena.- Second Harmonic Generation in p-Type Quantum Wells.- Resonant Harmonic Generation Near 100?m in an Asymmetric DouBle Quantum Well.- Second Harmonic Generation in GaAs-AlAs and Si-SiGe Quantum Well Structures.- Non-Resonant Two-Photon ABsorption in Quantum Well Infrared Detectors.- Optical Saturation of IntersuBBand Transitions.- Novel Phenomena.- Use of Classically Free QuasiBound States for Infrared Emission.- Evidence for LWIR Emission Using IntersuBBand Transitions in GaAs/AlGaAs MQW Structures.- Fast Data Coding Using Modulation of InterBand Optical Properties By IntersuBBand ABsorption in Quantum Wells.- Theory of Terahertz Generation due to Quantum Beats in Quantum Wells.- Far-Infrared Study of an Antenna-Coupled Quantum Point Contact.- Control of Electron Population By IntersuBBand Optical Excitation in a Novel Asymmetric DouBle Quantum Well Structure.

Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection

Abstract: The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 /spl mu/m low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5. >

Structural and optical properties of self‐assembled InGaAs quantum dots

Abstract: A one step method for the production of quantum dots is presented. The method exploits the mismatch strain of molecular beam epitaxy (MBE) deposited InGaAs on GaAs to induce a transition from the two‐dimensional growth mode to the three‐dimensional (Stranski–Krastanow) growth mode. The cluster size is limited to quantum dimensions by precisely controlling the amount of InGaAs that is deposited in order to cause the growth mode transition. Very narrow lateral size distributions with standard deviations of 14% on the dot area have been obtained. Smooth MBE growth of GaAs over these clusters produces a layer of quantum dots, whose high quality and uniformity has been observed with transmission electron microscopy, atomic force microscopy, and photoluminescence (PL). The quantum dot PL intensity is enhanced compared to a reference quantum well. Resonances in photoluminescence excitation (PLE) spectra suggest that the density of states in these dots has minima close to zero between the quantum states, as expec...

Monolithic strained‐InGaAsP multiple‐quantum‐well lasers with integrated electroabsorption modulators for active mode locking

Abstract: Active mode locking by monolithic lasers with integrated electroabsorption modulators using strained‐InGaAsP multiple quantum wells is described. The electroabsorption modulator acts as a short optical gate when a sinusoidal voltage is driven at a deep bias point. Pulse widths as short as 2 ps have been obtained at a repetition rate of 16.3 GHz for a 2.5‐mm‐long monolithic laser.

Type II heterojunctions in the GaInAsSb/GaSb system

Abstract: This article reviews the pioneering investigations of the luminescence and photoelectric phenomena in type II heterojunctions based on the GaInAsSb/GaSb system. This system is remarkable because it is possible to create and study heterojunctions with both staggered and broken-gap alignment, depending on the alloy composition. Type II heterojunctions differ from type I in the existence of adjacent dual quantum wells for electrons and holes on both sides of the interface. Simultaneous confinement of electrons and holes in these wells causes unique optical and electrical properties of such heterojunctions and greatly modifies the characteristics of optoelectronic devices. The review considers the photo- and electroluminescence spectra of GaInAsSb/GaSb heterojunctions with staggered band alignment. The importance of tunnelling-assisted transitions through the interface in the radiative recombination of confined carriers is shown. The influence of these transitions on the structure and polarization characteristics of the luminescence spectra is considered. A new mechanism of photocurrent gain in isotype n-N heterojunctions due to hole confinement at the type II interface is discussed. Unusual asymmetric electrical properties of type II heterojunctions with broken-gap band alignment are demonstrated and discussed in connection with their energy band diagrams. Novel in light sources and photodetectors for the 1.6-4.7 mu m spectral range based on the GaInAsSb/GaSb system are briefly reviewed.