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We investigate experimentally and theoretically the impact of valence band mixing and spectrum of confined states on the polarization of light emitted from or absorbed by GaAs/AlGaAs semiconductor quantum dots and quantum wires with tailored heterostructure potential. In particular, such nanostructures with parabolic-profile confinement potentials, realized by organometallic vapor phase epitaxy inside pyramidal pits, served as model systems for the study. Different degrees of linear polarization (DOLP) of emitted light, depending on the confinement potential profile, the specific excitonic transition, and the level of excitation, are observed. A theoretical model shows that, besides the impact of valence band mixing, the overlap of conduction and valence band wavefunctions as well as state occupation probability and broadening of transitions determine the DOLP. The conclusions are useful for the design of quantum light emitters with controlled polarization properties. [ABSTRACT FROM AUTHOR]

We present results on the polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs) grown in inverted tetrahedral pyramids. The emitted light was detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry, in addition to the standard top-emission geometry. Whereas the in-plane linear polarization was isotropic, as a consequence of the high symmetry of the system, we found a strong polarization anisotropy of the edge-emitted light revealing QD states of predominantly heavy- or light-hole character. By temperature control of the charge state, several neutral and charged light-hole like exciton complexes were identified. In particular, a biexciton showing a twofold radiative recombination path, leading to two nearly perpendicularly polarized emission multiplets, was identified. These results are also of technological relevance for any design of optoelectronic QD-integrated devices. [ABSTRACT FROM AUTHOR]

The observation and the interpretation of line splitting in photoluminescence and cathodoluminescence spectra of GaAs/AlGaAs V-groove quantum wires (QWRs) are reported. The QWR emission line splits into two peaks whose intensities oscillate systematically along the axis of the wire. Combining atomic force microscopy and cathodoluminescence measurements, we show a clear correlation between the surface topography of the V-groove and the individual peak intensities. We elucidate the relationship between the V-groove sidewall roughness and the shape at its bottom, and explain their impact on the QWR formation using a two-dimensional growth model accounting for self-limited growth in each V-groove domain. The influence of the long-range substrate roughness on the QWR spectral features is thus clarified. The study provides guidelines for improving QWR uniformity in order to achieve near-ideal model systems for one-dimensional semiconductors. [ABSTRACT FROM AUTHOR]

An analytical model of thermal and electrical characteristics of vertical cavity surface emitting lasers (VCSELs) and VCSEL arrays is presented. The model is based on analytical expressions for the thermal resistance and for the I-V curve of the devices and incorporates only a few macroscopic parameters. It accounts for three-dimensional current and heat flows and provides thermo-electrical self-consistency. Good agreement between the model’s predictions and the measured characteristics of InGaAs/AlGaAs VCSEL arrays is obtained. [ABSTRACT FROM AUTHOR]

We report sub-meV (as low as 0.6 meV) low-temperature photoluminescence linewidth and high low-temperature electron mobility (μ∼1-1.5×106 cm2/Vs) of GaAs quantum wells in AlGaAs barriers grown by standard metalorganic vapor phase epitaxy. These records values are achieved by epitaxial growth on (100) slightly misoriented substrates [<=0.6 degrees off-(100) GaAs substrates] in combination with a high V/III ratio for AlGaAs growth. Such small misorientations are sufficient to drastically modify the optical and transport properties as well as the growth mode and surface morphologies of both GaAs and AlGaAs epitaxial layers, allowing greater interface quality and reduced impurity incorporation. The quantum wells so obtained show optical properties comparable to high-quality samples grown by molecular beam epitaxy. In addition, the slight misorientation considerably reduces the impact of substrate temperature on electron mobility, which allows achieving high values of μ within a much broader range of growth temperatures. [ABSTRACT FROM AUTHOR]

We present experimental evidence that at room temperature the main coupling mechanism between an n-type δ-doping region and an adjacent plane of dots is energy-conserving electron-electron scattering, in which a hot electron in the δ-doping region transfers energy to a deeply confined electron in that region and relaxes to the quantum dot. We demonstrate that at room temperature the increased capture cross section due to electron-electron scattering considerably enhances the injection into the quantum dots with a certain size and thus reduces the phonon bottleneck in quantum dot assemblies for the quantum dots that interact with the δ-doping region. We identify different temperature-dependent injection schemes by comparing the photoluminescence of dilute and dense assemblies with the corresponding photoluminescence of similar structures including n-type δ-doping regions adjacent to the dots’ plane. [ABSTRACT FROM AUTHOR]

A general method for nondestructive mapping of three-dimensional surfaces, particularly useful in cases where the surface is composed of a large array of identical depressions, is presented. The sample is first marked with a uniform flux of particles, which then act as isotropic sources of some detectable radiation. By measuring the emitted radiation from several directions, it is possible to reconstruct the surface using a parametrization coupled with a least squares fit procedure. As an example, we report on the experimental implementation of the algorithm to arrays of micron-scale inverted pyramids etched in GaAs substrates, using a particular sequence of alpha emitting atoms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have examined the crystallographic structure of GaAs/InP interfaces obtained by wafer fusion following different procedures. Plan-view and cross-sectional transmission electron microscopy reveal that the interface is not only composed of a regular array of two sets of edge dislocations and is more complex than generally supposed. If a twist is created due to misalignment of the two substrates, the dislocations are not edge dislocations but also have a screw component. Dislocations for which the Burgers vectors have a component normal to the interface are also present. Those dislocations probably result from steps and some of them accommodate the tilt between the two substrates. Inclusions and voids as well as a low number of volume dislocations are present in all the samples. The observed volume dislocation density near the interface lies in the 10[sup 5]–10[sup 7] cm[sup -2] range and these volume dislocations may be associated with thermal mismatch. The origin of all these defects is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A high-power InAs quantum dot (QD) vertical-external-cavity surface-emitting laser emitting at 1.5 μm is reported. The active region employs 20 layers of high-density Stranski–Krastanow InAs quantum dots on an InP substrate. The QD density and emission wavelength were independently adjusted by employing a double-cap growth sequence. Optimization of the spacer layer thickness and strain compensation rendered possible nucleation of a relatively high number of QD layers per antinode of the electromagnetic standing wave, which in turn enabled a high output power continuous wave operation of about 2.2 W. The operation wavelength could be tuned over 60 nm, taking advantage of the broadband gain characteristic of QD media. [ABSTRACT FROM AUTHOR]

Details a study which performed an atomic force microscopy (AFM) imaging of semiconductor nanostructures. Preparation of the study samples; Limitations and sources of error in AFM imaging process; Results and discussion.

We fabricated and studied a system comprising four site-controlled semiconductor quantum dots (QDs) embedded in a linear photonic crystal membrane cavity. The excellent position control and small spectral broadening permit coupling of the emission of all four QDs to the same photonic cavity modes. This is corroborated by co-polarization of the QD and cavity emission lines, as well as reduction in decay time, both with characteristic dependence on QD-cavity energy detuning. Scaling up to larger QD systems is discussed. [ABSTRACT FROM AUTHOR]

Exciton and cavity mode (CM) dynamics in site-controlled pyramidal quantum dots (QDs), integrated with linear photonic crystal membrane cavities, are investigated for a range of temperatures and photo-excitation power levels. The absence of spurious multi-excitonic effects, normally observed in similar structures based on self-assembled QDs, permits the observation of effects intrinsic to two-level systems embedded in a solid state matrix and interacting with optical cavity modes. The coupled exciton and CM dynamics follow the same trend, indicating that the CM is fed only by the exciton transition. The Purcell reduction of the QD and CM decay times is reproduced well by a theoretical model that includes exciton linewidth broadening and temperature dependent non-radiative processes, from which we extract a Purcell factor of 17±5. For excitation powers above QD saturation, we show the influence of quantum wire barrier states at short delay time, and demonstrate the absence of multiexcitonic background emission. [ABSTRACT FROM AUTHOR]

Two site-controlled quantum dots (QDs) were integrated in a photonic crystal molecule (PCM) formed by L3 nanocavities. A statistical analysis of the coupled cavity modes demonstrated the formation of bonding and anti-bonding delocalized PCM states. Excitonic transitions belonging to each QD were identified by scanning micro-photoluminescence spectroscopy. Co-polarization of the QDs photoluminescence with the coupled cavity modes provides evidence for the simultaneous coupling of two spatially separated QDs to the same PCM mode. [ABSTRACT FROM AUTHOR]

Exciton recombination dynamics in tailored-potential, site-controlled AlGaAs quantum wires (QWRs) are studied. Time-resolved photoluminescence spectra evidence exciton localization inweakly disordered "uniform" QWRs, whereas deterministic bandgap grading is shown to suppresslocalization and promote exciton drift along the potential gradient. Measured exciton transit timesbetween two quantum dot probes placed at opposite ends of the potential gradient yield the effective1D exciton mobility as >1300 cm²/(eVs). [ABSTRACT FROM AUTHOR]

The impact of optical disorder on photon propagation in long Ln photonic crystal cavities is investigated using spectrally resolved imaging, group index measurements, and selective mode excitation with site-controlled quantum dots. Mobility and diffusive edges, separating localized, diffusive, and dispersive regimes, are consistently identified. In situ probing of the photonic modes demonstrates the low impact of disorder in the dispersive regime and the transition to phase-distorted modes in the diffusive regime. The analysis yields criteria for designing photonic crystal waveguides for efficient single photon transport. [ABSTRACT FROM AUTHOR]

We present a detailed study of biexciton complexes formed in single, site-controlled pyramidal GaInAs/GaAs quantum dots (QDs). By using power dependent measurements and photon correlation spectroscopy, we identify the excitonic transitions of a large number of pyramidal QDs, exhibiting both positive and negative biexciton binding energies. Separation of charges within the QD, caused by piezoelectric fields, is believed to be responsible for the positive to negative crossover of the biexciton binding energy with increasing QD size. In particular, QDs exhibiting vanishing biexciton binding energies are evidenced, with potential applications in quantum information processing. [ABSTRACT FROM AUTHOR]

GaInAsN quantum dots (QDs) were grown in inverted pyramids on a patterned (111)B GaAs surface. Incorporation of N in the active structure is attested to by a significant (∼80 meV) redshift of the photoluminescence spectrum of the QDs. Influence of the capillarity effect on the N incorporation is evidenced by comparing the redshift in the QD emission to that of its quantum wire (QWR) barriers. The significant increase in the inhomogeneous broadening of the InGaAsN QD arrays as compared to similar InGaAs QDs is explained by the large influence of a small number of N atoms and their configuration within the QD on its effective bandgap and confinement energy. [ABSTRACT FROM AUTHOR]

Site-controlled InGaAsN quantum wires (QWRs) emitting at 1.3 μm at room temperature were grown on V-grooved GaAs substrates by modulated-flux metallorganic vapor phase epitaxy. The nonplanar substrate template is shown to enhance the nitrogen uptake, evidenced by a redshift in photoluminescence wavelength twice larger for the QWRs than for the adjacent quantum well regions. The mechanism of this increase in nitrogen incorporation efficiency, achieved without degradation in optical properties, is explained by the extended gradient of In content at the step-rich QWR interfaces. [ABSTRACT FROM AUTHOR]

Carrier transport and capture paths via barriers of different dimensionality in AlGaAs/GaAs quantum wire (QWR)/quantum dot (QD) heterostructures, grown in inverted pyramids, are studied by photoluminescence (PL) spectroscopy. Evidence for thermally activated diffusion related to potential disorder in the QWR barriers and thermionic emission of carriers from the QD into the QWR barrier is observed in temperature dependent PL spectra. Similar activation energies for the thermionic emission are derived from the continuous-wave and time-resolved PL spectroscopy. [ABSTRACT FROM AUTHOR]

We investigated the composition and optical properties of GaInAsN/GaAs single quantum wells (QWs) grown on vicinal-(001) GaAs substrates using metallorganic vapor phase epitaxy with modulated nitrogen-precursor flux. A significant enhancement in N incorporation and photoluminescence efficiency is achieved with such optimized QW structures. Possible mechanisms of the observed increase in N uptake and reduction in defect density, related to the substrate vicinality, are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate engineering of carrier states in the conduction band (CB) and valence band (VB) of site-controlled InGaAs/GaAs quantum dots (QDs) grown into pyramidal recesses, by controlling their shape, size, and composition. QDs with CB level separation ranging from ∼15 to 70 meV are obtained, useful in applications based on intraband transitions, e.g., QD photodetectors and QD cascade lasers. Moreover, by varying the aspect ratio and composition of the QDs we are able to switch the polarization of the dominant interband transition, a feature of interest for producing single photon emitters and QD amplifiers with prescribed polarization states [ABSTRACT FROM AUTHOR]

Measuring the turn-on delay of diode lasers provides useful information on carrier recombination dynamics, particularly Auger recombination, essential for their design for high-speed modulation and power-efficient performance. Here we present a rigorous, comprehensive relationship between the time delay and the Auger recombination coefficient. We demonstrate the application of this formulation by extracting this coefficient for AlGaInAs/InP quantum wells incorporated in long-wavelength vertical-cavity surface-emitting lasers. [ABSTRACT FROM AUTHOR]

The diffusivity of photogenerated electron-hole pairs in weakly disordered GaAs/AlGaAs V-groove quantum wires was measured using a photoluminescence (PL) time-of-flight technique. It is shown that the electron-hole pair diffusion is thermally activated above about 50 K. Exciton localization is observed in micro-PL (μPL) spectra at low temperature. A reduction in the Stokes shift is found to accompany the increase in the diffusion coefficient. Nevertheless, localization-related features in the μPL spectra disappear at intermediate temperatures, before measurable diffusion occurs. [ABSTRACT FROM AUTHOR]

Significant reduction in inhomogeneous broadening of GaAs/AlGaAs V-groove quantum wires (QWRs) is achieved by growing them on vicinal (001) GaAs substrates misaligned by several degrees with respect to the [formula] groove direction. Low temperature photoluminescence spectra exhibit QWR linewidths as low as 3.7 meV for subband separation of 41 meV and 3 meV for subband separation of 27 meV. Atomic force microscopy evidences a change in the growth dynamics as compared with QWRs made on exact (001) GaAs substrates. The impact of the different growth dynamics on the wire interface structure is discussed. [ABSTRACT FROM AUTHOR]

The authors demonstrate the deterministic coupling between a single, site-controlled InGaAs/GaAs pyramidal quantum dot (QD) and a photonic crystal membrane cavity defect. The growth of self-ordered pyramidal QDs in small (300 nm base side) tetrahedral recesses etched on (111)B GaAs substrates was developed in order to allow their integration within the thin GaAs membranes. Accurate (better than 50 nm) positioning of the QD with respect to the optical cavity mode is achieved reproducibly owing to the site control. Coupling of the dot emission with the cavity mode is evidenced in photoluminescence measurements. The deterministic positioning of the pyramidal QDs and the control of their emission spectrum opens the way for devices based on QDs integrated with coupled nanocavities. [ABSTRACT FROM AUTHOR]

It is demonstrated that n-type δ-doped resonant tunneling double quantum well (QW) lasers operated close to resonance exhibit an extremely low transparency current density of 14 A/cm2 per QW. This suggests that the threshold current is almost identical to that of the best reported single QW device without δ doping and yet the modal gain is almost double. The low transparency current density is mainly due to the enhanced coupling between the QWs. [ABSTRACT FROM AUTHOR]

We present experiments and an accompanying theory for the growth modes during metalorganic vapor-phase epitaxy on vicinal GaAs(001). Our theory is based on a model that takes account of deposition, diffusion, and dissociation of molecular precursors, and the diffusion and step incorporation of atoms released by the precursors. The experimental conditions for island nucleation and growth, step flow, and step bunching are reproduced by this model, with the step bunching instability caused by the difference in molecular dissociation from above and below step edges. [ABSTRACT FROM AUTHOR]

The character of the hole states in a pyramidal GaAs/AlGaAs quantum dot-in-dot (DiD) heterostructure is shown to be controllable by tailoring the confinement potential shape. The change in ground valence band state from heavy hole like to light hole like is demonstrated by side-view polarization resolved photoluminescence measurements. The experimental findings are supported by three-dimensional numerical model calculations. The results are applicable for polarization control in quantum dot photonic devices. [ABSTRACT FROM AUTHOR]

The inhomogeneous broadening in the luminescence spectra of ordered arrays of pyramidal GaAs/AlGaAs semiconductor quantum dots (QDs) was studied as a function of the dot size. Dot arrays with inhomogeneous broadening as small as 4.1 meV and a corresponding ground state to first excited state transition separation of 28 meV were obtained. By evaluating the QD energy levels using a multiband k·p model, the authors estimated that the observed inhomogeneous broadening corresponds to dot height fluctuations of about 1–2 ML across the array. [ABSTRACT FROM AUTHOR]

The authors demonstrate electrically controlled mode switching and beam steering in separate-contact photonic crystal heterostructures implemented with two-dimensional arrays of coupled vertical-cavity surface-emitting lasers. Two weakly coupled, lasing photonic crystal domains are switched in and out of mutual coherence by controlling the injected currents. Switching of the transverse lasing mode is accompanied by corresponding variations in the far-field pattern and the emission wavelength. Proper adjustment of the driving currents also allows steering of the beam of the ensemble of coupled lasers. [ABSTRACT FROM AUTHOR]

Integration of a site-controlled semiconductor V-groove quantum wire (QWR) into a photonic-crystal (PhC) membrane microcavity is reported. Reproducible coupling of the QWR emission to a mode of the PhC cavity is evidenced by the narrower linewidth, higher intensity, and variation with temperature and PhC parameters of the QWR line. Finite difference time domain simulations of the cavity are employed for identifying the observed mode. The presented PhC-QWR coupled structures are promising for achieving very low-threshold lasers and for studies of one-dimensional photon-exciton coupled systems. [ABSTRACT FROM AUTHOR]

Exciton transfer between two parallel GaAs V-groove quantum wires or two planar quantum wells separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence and photoluminescence excitation spectroscopy. It is found that the transfer is strongly reduced between the widely spaced quantum wires as compared with quantum wells. This observation is supported by model calculations, which yield strong dimensionality dependence of the photon-exchange transfer. [ABSTRACT FROM AUTHOR]

The spatial coherence and the optical phase distribution across a two-dimensional (2D) photonic crystal implemented with coupled arrays of vertical cavity surface emitting lasers (VCSELs) are experimentally characterized. This is achieved by performing Young’s interference experiments between pairs of array elements using a spatial light modulator arrangement. In contrast to far-field measurements that provide information only on the global spatial coherence, this approach can yield full mapping of the complex degree of spatial coherence. Examples of such analysis are presented for nominally uniform one-dimensional and 2D arrays of coupled VCSELs and possible mechanisms of the observed coherence degradation are discussed. [ABSTRACT FROM AUTHOR]

The authors present a polarization-resolved photoluminescence study of single semiconductor quantum dots (QDs) interconnected to quantum wires, measured both in a top geometry, and in a less conventional cleaved-edge geometry. Strong polarization anisotropy is revealed for all observed transitions, and it is deduced that closely spaced QD hole states exhibit nearly pure heavy-or light-hole character. These effects are attributed to the large aspect ratio of the dot shape. [ABSTRACT FROM AUTHOR]

Optical transitions associated with all three linear polarization directions were investigated in single GaAs V-groove quantum wires of different wire thicknesses. This was accomplished by combining absorption measurements in V-groove waveguide geometry with surface-excited photoluminescence excitation spectroscopy. The observed transitions were identified with the aid of model calculations. It is shown that excitonic intersubband coupling should be accounted for in order to explain the optical transitions associated with confined light-hole-like states. The results are relevant for the design of efficient quantum wire waveguide modulators and lasers. [ABSTRACT FROM AUTHOR]

We report the observation and theory of the morphological evolution of vicinal (001) ridges on V-grooved GaAs surfaces during metal organic vapor-phase epitaxy. The pattern of the nonplanar substrate induces unusual ordering of monatomic steps, different from the free step flow observed on a nonpatterned vicinal surface. The step edges develop profiles that kinetic Monte Carlo simulations reveal are determined by the width of the ridges between neighboring V grooves and the kinetics of interfacet mass migration between the ridge and the bounding sidewalls of the V groove. [ABSTRACT FROM AUTHOR]

We investigate the embedded interfaces of GaAs/AlGaAs quantum wells grown by metal organic vapor phase epitaxy on slightly (<1°)-misoriented (001) substrates using selective etching and atomic force microscopy. Depending on the substrate misorientation, we observe different growth modes at the embedded interfaces, which are directly correlated to the photoluminescence linewidth. We show that the narrowest linewidth is obtained on 0.2°-off (001) substrates for which the heterointerfaces consist of atomically smooth narrow terraces. [ABSTRACT FROM AUTHOR]

We demonstrate efficient, regulated single-photon operation from site-controlled InGaAs quantum dots (QDs) grown on a prepatterned substrate. Under nonresonant optical excitation, carriers trapped at structural or compositional defects of the adjacent nanostructures led to a degradation of the single-photon statistics from a QD. When the QD was excited quasiresonantly, single photons were emitted and a nearly complete suppression of multiphoton emission was achieved, making these QDs promising candidates for effective solid-state single-photon sources. [ABSTRACT FROM AUTHOR]

We demonstrate control of the confined-state energies of semiconductor quantum dots (QDs) grown on prepatterned substrates. The InGaAs/AlGaAs QDs self-order at the apex of self-limiting, inverted pyramids whose locations are fixed by lithography. The confinement energy in the dots is systematically varied across the substrate by changing the pattern of the pyramid array in their vicinity. The resulting energy- and site-controlled QDs show systematic and reproducible shifts of their emission wavelengths as well as antibunched photon emissions from confined single excitons. Such QDs should be useful for applications in quantum information processing and quantum communication devices, e.g., multiple-wavelength single-photon emitters. [ABSTRACT FROM AUTHOR]

We have optimized the molecular-beam epitaxy growth conditions of self-organized InAs/GaAs quantum dots (QDs) to achieve a low density of dots emitting at 1300 nm at low temperature. We used an ultralow InAs growth rate, lower than 0.002 ML/s, to reduce the density to 2 dots/μm2 and an InGaAs capping layer to achieve longer emission wavelength. Microphotoluminescence spectroscopy at low-temperature reveals emission lines characteristic of exciton-biexciton behavior. We also study the temperature dependence of the photoluminescence, showing clear single QD emission up to 90 K. With these results, InAs/GaAs QDs appear as a very promising system for future applications of single photon sources in fiber-based quantum cryptography. [ABSTRACT FROM AUTHOR]

Single-photon correlation and microphotoluminescence spectroscopy are employed to characterize the emission from disordered InGaAs/AlGaAs quantum wires grown in inverted tetrahedral pyramids. Recombinations of neutral and charged excitons, localized by wire potential fluctuations, are identified. Antibunched photon emission is observed from both excitonic species that are shown to recombine at the same disordered wire site. This demonstrates the use of single-photon correlation spectroscopy for obtaining spatial information on optical processes in nanostructures. [ABSTRACT FROM AUTHOR]

We investigated theoretically the effects of the one-dimensional barriers on the electronic states in a quantum dot grown on a nonplanar substrate. These peculiar barriers drastically modify the confined carrier wave functions and their energies. Connecting the quantum wire to the pyramidal quantum dot leads to an enhancement in the ground to first excited state separation energy and a simultaneous large reduction of the energy size sensitivity. [ABSTRACT FROM AUTHOR]

We report on the growth and optical properties of homogeneous, dense arrays of site-controlled, single GaAs/AlGaAs quantum dot (QD) heterostructures with periodicities as small as 300 nm. The samples were grown by organometallic chemical vapor deposition on (111)B GaAs substrates containing dense inverted pyramid recess patterns prepared by electron beam lithography and wet chemical etching. Low-temperature microphotoluminescence spectra of the samples show distinct luminescence from the QDs with 1–3 meV linewidth. Low-temperature cathodoluminescence spectrally resolved images reveal uniform emission energy within an ensemble of 900 QDs. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied the uniformity of site-controlled, pyramidal InGaAs/AlGaAs semiconductor quantum dots (QDs) grown by organometallic chemical vapor deposition on prepatterned substrates. The inhomogeneous broadening of the QD ground state emission has been determined to be 7.6 meV by statistical single QD photoluminescence spectroscopy on a set of 120 individual QD structures. Taking into account the ground-to-excited state separation of 55 meV, such a small value has not yet been observed in QD systems where other growth mechanisms are employed. Moreover, a high reproducibility of the sharp QD emission features in the single exciton regime has been observed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the fabrication of a quantum-dot light-emitting diode (QD-LED), exhibiting electroluminescence from a single, self-formed QD obtained by epitaxial growth on pyramidal recess patterns. Moreover, selective carrier injection through a submicron metal contact and a 20-nm-wide self-formed low potential vertical channel connected to the QD active area is demonstrated, resulting in enhanced injection efficiency. The developed fabrication process offers full flexibility to control the number and position of the emitters down to a single QD in a micron-size compact LED. This makes this system an ideal candidate for efficient, electrically driven single-photon sources for quantum information applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High internal quantum efficiency (∼60%), narrow linewidth (as narrow as 14 meV) exciton emission at room temperature has been obtained using strained InGaAs V-groove quantum wire (QWR) light-emitting diodes (LEDs). The high efficiency is achieved with the aid of selective carrier injection through self-ordered A1GaAs vertical quantum wells (VQWs), where the VQWs are separated from the InGaAs QWRs by thin GaAs spacer layers in order to reduce nonradiative recombination and inhomogeneous alloy broadening. Evidence for excitonic recombination in these LEDs up to RT is provided by measurements of the emission energy shifts at high magnetic fields. [ABSTRACT FROM AUTHOR]