Showing papers on "Quantum dot laser published in 1998"

1.3 μm room-temperature GaAs-based quantum-dot laser

Abstract: Room-temperature lasing at the wavelength of 1.31 μm is achieved from the ground state of an InGaAs/GaAs quantum-dot ensemble. At 79 K, a very low threshold current density of 11.5 A/cm2 is obtained at a wavelength of 1.23 μm. The room-temperature lasing at 1.31 μm is obtained with a threshold current density of 270 A/cm2 using high-reflectivity facet coatings. The temperature-dependent threshold with and without high-reflectivity end mirrors is studied, and ground-state lasing is obtained up to the highest temperature investigated of 324 K.

GaAs/AlxGa1−xAs quantum cascade lasers

Abstract: A unipolar injection quantum cascade (QC) laser grown in an AlGaAs/GaAs material system by molecular beam epitaxy, is reported. The active material is a 30 period sequence of injectors/active regions made from Al0.33Ga0.67As/GaAs-coupled quantum wells. For this device a special waveguide design, which complies with a GaAs heavily doped substrate and very short Al0.90Ga0.10As cladding layers, has been optimized. At a heat-sink temperature of 77 K, the laser emission wavelength is 9.4 μm with peak optical power exceeding 70 mW and the threshold current density is 7.3 kA/cm2. The maximum operating temperature is 140 K. This work experimentally demonstrates the general validity of QC laser principles by showing laser action in a heterostructure material different from the one used until now.

Quantum dot heterostructures: Fabrication, properties, lasers (Review)

Abstract: In the present review we summarize original results where 1) we have experimentally discovered a novel class of spontaneously ordered nanostructures, namely equilibrium arrays of threedimensional, coherently strained islands on crystal surfaces; 2) we have developed a theory of spontaneous formation of semiconductor nanostructures in heteroepitaxial systems; 3) we have experimentally demonstrated the existence of a novel class of semiconductor heterostructures, namely perfect quantum dots having an atom-like energy spectrum; we have performed a detailed investigation of the optical properties of quantum dots; 4) we have fabricated quantum dot-based injection lasers demonstrating unique charactristics, namely high-temperature stability of the threshold current and ultra-high material gain.

Short wavelength (λ∼3.4 μm) quantum cascade laser based on strained compensated InGaAs/AlInAs

Abstract: Growth of quantum cascade lasers based on strain-compensated InxGa1−xAs/InyAl1−yAs and operating at a wavelength shorter than 4 μm is reported. Pulsed mode operation of these lasers up to T=280 K is reported with a high T0. Continuous wave powers as high as 120 mW are reported at cryogenic temperatures (15 K).

Silicon single-electron quantum-dot transistor switch operating at room temperature

Abstract: We fabricated a silicon single-electron quantum-dot transistor, which showed drain current oscillations at room temperature. These oscillations are attributed to electron tunneling through a single silicon quantum dot inside a narrow wire channel. Analysis of its current–voltage characteristic indicates that the energy level separation is about 110 meV and the silicon dot diameter is about 12 nm.

Spontaneous Emission Spectrum in Double Quantum Dot Devices

Abstract: A double quantum dot device is a tunable two-level system for electronic energy states. A dc electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.

Resonant tunneling in quantum cascade lasers

Abstract: Experimental evidence that in quantum cascade lasers electron injection into the active region is controlled by resonant tunneling between two-dimensional subbands is discussed. A quantitative analysis is carried out using an equation for the current density based on a tight-binding approximation. Electron injection into the active region is optimized when the current density is limited by the lifetime of the excited state of the laser transition. In this regime, quasi-equilibrium is reached between the population of the injector ground state and that of the excited state of the laser transition characterized by a common quasi-Fermi level. The design of the injector depends on the selected laser active region; in particular, the choice of physical parameters, such as doping concentration and injection barrier thicknesses, is in general different for vertical or diagonal transition lasers. The paper concludes with an investigation of the transport properties at threshold and its dependence on stimulated emission; a relationship between the differential resistance above threshold and the value of the slope efficiency is deduced.

Study of lasing action based on Förster energy transfer in optically pumped organic semiconductor thin films

Abstract: We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold (1 μJ/cm2), and long operational lifetime (>106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of >106 pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 A and is tr...

Semiconducting polymer distributed feedback lasers

Abstract: We have fabricated photopumped distributed feedback lasers by spin-casting thin films of the semiconducting polymer poly(2-butyl, 5-(2′-ethyl-hexyl)-1,4-phenylenevinylene) over gratings in silicon oxide. The lasers have two modes that each have a linewidth of 0.2 nm. The lasing wavelength was tuned from 540 to 583 nm by adjusting the period of the gratings.

Carrier dynamics in type-II GaSb/GaAs quantum dots

Abstract: The optical properties and dynamics of charge carriers in self-organized arrays of type-II (staggered band lineup) GaSb/GaAs quantum dots are studied. Interband absorption from type-II quantum dots is evidenced; the energetic positions of quantum dot absorption peaks coincide with those apparent in photoluminescence spectra. (Sb,As) intermixing with an antimony diffusion length of about 1 nm is found to make an important contribution to the observed transition energies. Dipole layer formation and quantum dot state filling contribute to the luminescence blueshift with increasing excitation density. The recombination rate of electrons with localized holes drastically depends on the average carrier density. When several carriers are localized at each dot, decay time constants around 5 ns, quite similar to type-I systems, are observed. Individual, spatially indirect excitons decay with much larger time constants close to 1 \ensuremath{\mu}s. The decay time of quantum dot luminescence is independent of the temperature in the measured range $Tl~65\mathrm{K}$ as expected for zero-dimensional excitons.

1.3-μm continuous-wave lasing operation in GaInNAs quantum-well lasers

Abstract: A 1.3-/spl mu/m continuous wave lasing operation is demonstrated, for the first time, in a GaInNAs quantum-well laser at room temperature. This lasing performance is achieved by increasing the nitrogen content (up to 1%) in GaInNAs quantum layer. It is thus confirmed that this type of laser is suitable for use as a light source for optical fiber communications.

Optical, Electronic, and Structural Properties of Uncoupled and Close-Packed Arrays of InP Quantum Dots

Abstract: Solid films consisting of close-packed arrays of InP quantum dots have been prepared by slowly evaporating colloidal solutions of InP quantum dots. The diameters of the quantum dots were controlled to be between about 30 to 60 A; size-selective precipitation yielded a size distribution of about 10% about the mean diameter. The arrays show regions of hexagonal order, as well as disordered regions. Oxide layers can form irreversibly on the quantum dot surface and limit the effectiveness of the size-selective precipitation. Photoluminescence spectra obtained from close-packed films of InP quantum dots formed from quantum dots with a single mean diameter and from a mixture of two quantum dot sizes show that energy transfer occurs from the photoexcited smaller quantum dots to the larger quantum dots. The efficiency of this energy transfer process is high.

Electroluminescence efficiency of 1.3 μm wavelength InGaAs/GaAs quantum dots

Abstract: Data are presented characterizing the spectral emission and the electroluminescence efficiency dependence on growth conditions of 1.3 μm wavelength InGaAs/GaAs quantum dots. We show that highly efficient 1.3 μm room temperature electroluminescence can be achieved with only ten total deposited monolayers with an averaged In content of 50%. Atomic force microscopy shows that the 1.3 μm wavelength quantum dots form with a density of ∼1.3×1010 cm−2.

Characteristics of InGaAs quantum dot infrared photodetectors

Abstract: A quantum dot infrared photodetector (QDIP) consisting of self-assembled InGaAs quantum dots has been demonstrated Responsivity of 325 mA/W at 92 μm was obtained for nonpolarized incident light on the detector with a 45° angle facet at 60 K The QDIPs exhibit some unique electro-optic characteristics such as a strong negative differential photoconductance effect and blueshift of the response peak wavelength

Emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers

Abstract: A study of the emission spectra and mode structure of InAs/GaAs self-organized quantum dot lasers is presented. In contrast to conventional bulk or quantum well lasers, the number of lasing modes increases above threshold. This behavior is shown to be consistent with carriers localized in noninteracting dots and a resultant inhomogeneously broadened gain spectrum. The lasing spectra are found to have a complicated form with groups of longitudinal modes separated by nonlasing spectral regions and lasing occurring via a number of different lateral modes. These characteristics are discussed in terms of the spatially discrete nature of the quantum dots.

Photon-spin controlled lasing oscillation in surface-emitting lasers

Abstract: We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time.

InGaAs/GaAs quantum dot lasers

Abstract: InGaAs quantum dots (QDs) grown by strained-layer epitaxy on GaAs can accommodate more In than planar growth and present an interesting approach for realizing GaAs-based laser diodes that operate in the 1.1 to 1.3 /spl mu/m wavelength range. Although QD emission wavelengths as long as 1.3 /spl mu/m have been reported, lasing in edge-emitting devices has been limited to wavelengths just over 1.0 /spl mu/m. Recently, we found that for optimized growth conditions, QD electroluminescence efficiency at 1.3 /spl mu/m is comparable to good InGaAs quantum wells emitting at 0.98 /spl mu/m. In particular, the use of separate and alternating sub-monolayer depositions increases the emission wavelength to 1.3 /spl mu/m and leads to high electroluminescence efficiency, while keeping the total In content of the deposited material to a minimum to avoid excessive strain. We describe the influence of growth method on the formation and emission characteristics of self-assembled InGaAs/GaAs QDs and describe device characteristics from edge emitting lasers using these QD active regions.

Continuous-wave and high-power pulsed operation of index-coupled distributed feedback quantum cascade laser at λ≈8.5 μm

Abstract: High performance index-coupled quantum cascade distributed feedback (QC-DFB) lasers operating at λ≈8.5 μm are reported. Reliable dynamic single-mode emission with a side mode suppression ratio ⩾30 dB is obtained. The continuous single-mode tuning range is 140 nm. In pulsed operation a record high peak output power of 60 mW at 300 K is achieved. We further report on the first continuous-wave QC-DFB lasers. These devices display an output power of 10 mW at 120 K.

Observation of confinement-dependent exciton binding energy of GaN quantum dots

Abstract: The photoluminescence emission peak energy of GaN quantum dots was observed to shift to higher energy with decreasing quantum dot size. This effect was found to be a combination of a blueshift from the confinement-induced shift of the electronic levels and a redshift from the increased Coulomb energy induced by a compression of the exciton Bohr radius. From this observation, absolute values of the exciton binding energy as a function of quantum dot size are determined.

Near-room-temperature mid-infrared interband cascade laser

Abstract: A 25-stage interband cascade laser with a W active region and a third hole quantum well for the suppression of leakage current has exhibited lasing in pulsed mode up to 286 K. A peak output power of 160 mW/facet and a slope efficiency of 197 mW/A per facet (1.1 photons per injected electron) were measured at 196 K. Above 200 K, the characteristic temperature was higher (T0=53 K) and the threshold current densities lower than for a previously reported W interband cascade laser without the third hole quantum well.

High-power λ≈8 μm quantum cascade lasers with near optimum performance

Abstract: Quantum cascade (QC) lasers emitting at λ≈8 μm with a power performance equal to short-wavelength (λ≈5 μm) QC lasers are reported. The device improvement is mainly achieved by a design of the injector/relaxation region, which at laser threshold allows resonant carrier injection between the ground state of the preceding and the upper laser level of the subsequent active region. In pulsed operation a peak output power of 1.3 W per facet has been measured at 100 K. At room temperature a record peak power of 325 mW and a record slope efficiency of 180 mW/A have been measured. In continuous-wave operation the maximum power at 30 K was 510 mW per facet and still 200 mW per facet at 80 K. The high values of the output power and slope efficiency demonstrate the validity of the cascading scheme, in which electrons above threshold generate one photon per each active region they successively traverse.

Uniform quantum-dot arrays formed by natural self-faceting on patterned substrates

Abstract: Of the approaches currently under investigation for the fabrication of functional III–V semiconductor nanostructures, self-organized growth mechanisms and directed growth on patterned substrates have yielded quantum wires and dots with the best structural and electronic properties1. In patterned growth, high densities of structures are difficult to obtain; self-organization, on the other hand, can provide densely packed structures with good crystal quality, but generally offers limited control over nanostructure uniformity and spatial position. In the case of quantum dots, non-uniformity of size and shape is clearly undesirable, as the resulting structures will exhibit a broad range of electronic and optical properties, effectively smearing out the sought-for zero-dimensional behaviour of the dot ensemble. Here we demonstrate a method for improving size uniformity, while maintaining a high density of quantum dots, that combines elements of both self-organization and patterning. The photoluminescence spectrum of the resulting ordered arrays of quantum dots is dominated by a single sharp line, rather than the series of sharp lines that would indicate transitions in quantum dots of different sizes2,3,4,5,6,7.

Modification of InAs quantum dot structure by the growth of the capping layer

Abstract: InAs quantum dots inserted at the middle of a GaAs quantum well structure have been investigated by transmission electron microscopy and scanning transmission electron microscopy. We find that the growth condition of the overlayer on the InAs dots can lead to drastic changes in the structure of the dots. We attribute the changes to a combination of factors such as preferential growth of the overlayer above the wetting layers because of the strained surfaces and to the thermal instability of the InAs dots at elevated temperature. The result suggests that controlled sublimation, through suitable manipulation of the overlayer growth conditions, can be an effective tool to improve the structure of the self-organized quantum dots and can help tailor their physical properties to any specific requirements of the device applications. (C) 1998 American Institute of Physics.

Electric-field effects on excitons in quantum dots

Abstract: Using low-temperature microphotoluminescence spectroscopy we have investigated the effect of a lateral electric field on quantum dot excitons trapped by monolayer width fluctuations in a narrow quantum well. We observe a redshift of the ground state and several excited states, when a lateral field is applied. This Stark shift is reduced when the dot is populated with several excitons that screen the electric field. The lines broaden increasingly at high fields, which is attributed to field-induced lateral tunneling out of the dot.

Fabrication and room-temperature characterization of a silicon self-assembled quantum-dot transistor

Abstract: A quantum-dot transistor based on silicon self-assembled quantum dots has been fabricated The device shows staircases and oscillations in the drain current at room temperature These data are interpreted as due to single electron tunneling through the dots located in the shortest current path between the source and the drain electrodes The dot size calculated from the data is ∼7 nm, which is consistent with the size of the self-assembled dots incorporated in the transistor

A multiwavelength semiconductor laser

Abstract: Many systems, such as atoms and molecules in gas mixtures, dye solutions and some solid-state materials, can exhibit simultaneous laser action at several wavelengths as a result of the excitation of several optical transitions1. But semiconductor lasers are usually monochromatic because the electronic levels are distributed in continuous energy bands2. In order to achieve simultaneous lasing at several well-separated wavelengths, researchers have proposed3 combining different semiconductors with distinct bandgap energies in the active material. However, the difficulty of pumping different regions and of absorption of the shorter-wavelength light could be resolved only by using separated multiple resonators or by multisection injection devices4,5,6,7. Here we report the realization of a single artificial semiconductor material with distinct optical transitions, which permits simultaneous multiwavelength laser action at mid-infrared wavelengths (6.6, 7.3 and 7.9 µm). This is achieved by tailoring the electronic states and electron relaxation times in the material, which is a superlattice layered structure. The laser has potential applications in sensors for trace-gas analysis.

Temperature dependence of the threshold current density of a quantum dot laser

Abstract: Detailed theoretical analysis of the temperature dependence of threshold current density of a semiconductor quantum dot (QD) laser is given. Temperature dependences of the threshold current density components associated with the radiative recombination in QDs and in the optical confinement layer (OCL) are calculated. Violation of the charge neutrality in QDs is shown to give rise to the slight temperature dependence of the current density component associated with the recombination in QD's. The temperature is calculated (as a function of the parameters of the structure) at which the components of threshold current density become equal to each other. Temperature dependences of the optimum surface density of QD's and the optimum thickness of the OCL, minimizing the threshold current density, are obtained. The characteristic temperature of QD laser T/sub o/ is calculated for the first time considering carrier recombination in the OCL (barrier regions) and violation of the charge neutrality in QDs. The inclusion of violation of the charge neutrality is shown to be critical for the correct calculation of T/sub o/. The characteristic temperature is shown to fall off profoundly with increasing temperature. A drastic decrease in T/sub o/ is shown to occur in passing from temperature conditions wherein the threshold current density is controlled by radiative recombination in QD's to temperature conditions wherein the threshold current density is controlled by radiative recombination in the OCL. The dependences of T/sub o/ on the root mean square of relative QD size fluctuations, total losses, and surface density of QDs are obtained.

Lasing with low threshold current and high output power from columnar-shaped InAs/GaAs quantum dots

Abstract: Lasers with a new type of quantum dot achieve low threshold current and high output power. By supplying a small amount of InAs and GaAs alternately on GaAs substrates, dots with high uniformity and high emission efficiency were self-assembled. The lasers exhibited a threshold current of 5.4 mA, a current density of 160 A/cm/sup 2/, and an output power of 110 mW at room temperature.

Effect of matrix on InAs self-organized quantum dots on InP substrate

Abstract: InAs self-organized quantum dots in In0.53Ga0.47As and In0.52Al0.48As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition.

Self-assembled semiconductor structures: electronic and optoelectronic properties

Abstract: Strained epitaxy has been shown to produce pyramidal-shaped semiconductor dot structures by single-step epitaxy. The very high density of these dots (approaching per wafer) and their ever improving uniformity suggest that these features could have important applications in future microelectronics. Understanding the structural and electronic properties of these quantum dots is therefore of great importance. In this paper, we examine some of the physics controlling the performance of devices that could be made from such structures. The self-assembled quantum dots are highly strained and we will examine the strain tensor in these quantum dots using a valence force-field model. In this paper we will address the following issues: (1) What is the general nature of the strain tensor in self assembled quantum dots? (2) What are the electron and hole spectra for InAs-GaAs quantum dots? (a) What are the important intersubband radiative and nonradiative scattering processes in the self assembled quantum dots? In particular, we will discuss how the electron-phonon interactions are modified in the quantum dot structures. Consequences for uncooled intersubband devices such as lasers, detectors, and quantum transistors will be briefly discussed.