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Metalorganic chemical vapor deposition was used to study InGaAs/GaAs quantum dots, for optoelectronic applications.

Results are presented of an analysis of nanoscale compositional fluctuations in InGaAs/GaAs quantum wires.

A new study investigates GaN/AlGaN quantum wells characterized by different structural and strain distribution parameters.

Spatially resolved near-field luminescence in ZnCdSe/ZnSe quantum wells was sued to individually resolve excitons localized at compositional potential fluctuations.

Research was conducted to prove that accurate analytic solutions are present when the amplitude of the relevant Fourier components of the surface profiles is much smaller than the corresponding wavelengths. A proposed method offers a solution of the elasticity problem for any surface profile. Due to the simplicity and flexibility of the method, it is well suited for engineering a vast range of nanostructures.

Researchers investigated the role of exciton localization in the radiative process through observation of transient photoluminescence in GaAs V-shaped quantum wires in relation to temperature. They observed that low temperatures are accompanied by exciton localization, that there are free-exciton polariton transitions at mid-range temperatures below 100 K, and that thermal activated nonradiative recombination processes occur at temperatures above 120 K. Analysis of the transient luminescence thus provides a simple method for determining exciton localization and localization centre density.

The structural and optical characteristics of quaternary In0.52Ga0.18Al0.30As layers grown by molecular beam epitaxy were investigated using high resolution x-ray diffraction, absorption, photoluminescence and photoreflectance spectroscopy. The results showed that several transitions related to impurities and a free exciton feature were present, indicating that the exciton binding energy was smaller than predicted.

The optical and structural characteristics of ternary alloy AlxGa1-xAs/AlAs multiple-quantum-well structures were investigated. The results showed that the direct energy gap was proportional to the AlAs mole fraction and the band offset ratio was determined by the composition of the alloy. In addition, exciton absorption bleaching occurred in the material.

Research describing the photopersistance and phototransport properties of GaN/AlGaN multiple quantum wells is presented. In particular observations of yellow luminescence, indicating the existence of defects, are examined.

We present a study of the structural and optical properties of a heterostructure emitting in the midinfrared. The structure consists of monolayerlike InSb quantum wells inserted in an InAs/GaSb superlattice (SL) matrix. X-ray diffraction and transmission electron microscopy analyses show a high structural quality of the structure. A strong emission line with a peak energy near 0.30 eV (3.5 μm) is observed from the monolayerlike InSb. In order to identify the physical origin of this transition, excitation density and temperature dependent photoluminescence experiments have been performed on samples with different nominal InSb thicknesses and SL designs. The experimental results suggest a type II band alignment, with electrons localized in the conduction miniband of the InAs/GaSb SL matrix and holes localized in the monolayerlike InSb. This assignment is supported by the shift of InSb layer emission to lower energies when the SL design is changed, and by tight-binding calculations. [ABSTRACT FROM AUTHOR]

A quantum dot (QD) microcavity emitting around 1.3 μm at room temperature is studied by photoreflectance (PR) and photoluminescence. The temperature dependence of the PR spectra line shape and amplitude allows determining the tuning condition of the quantum dot ground state transition with the cavity mode. Our study suggests a way to find the exciton energy when the distinct QD features are hidden by the broadening of the QD dielectric function in combination with the relatively narrow cavity-mode width. [ABSTRACT FROM AUTHOR]

The optical properties of multilayer InAs/InGaAs quantum dots (QDs) with different GaAs barrier thicknesses have been investigated. The photoluminescence (PL) intensity is found to increase with increasing GaAs barrier thickness. For thicknesses larger than 40 nm the PL intensity increases linearly with the number of the QD layers, with a considerable narrowing of the full width at half maximum (from 33 to 26 meV for active regions consisting of three QD layers). This growth protocol has been applied to laser structures containing stacked InAs/InGaAs QD layers. The broad area processed devices exhibit a modal gain as high as 30 and 41 cm-1 for structures embedding five and seven QD layers, respectively, which corresponds to 6 cm-1 per QD layer. The internal quantum efficiency and the transparency current density per QD layer were approximately 70% and 10 A/cm2, respectively, for both structures. [ABSTRACT FROM AUTHOR]

We have studied the optical properties of different thienyl-S,S-dioxide oligothiophenes under strong excitation. No stimulated emission is observed in neat films due to singlet-singlet bimolecular annihilation. The bimolecular recombination constant is quantified from a rate equation model in the limit of constant annihilation rate. We demonstrate that tunable stimulated emission in the range 490–660 nm, due to optical gain with an estimated cross section of the order of σg≈10-17 cm2, can be obtained by blending the active molecule with small quantities of inert polycarbonate poly(bisphenol-A-carbonate) (PC). The presence of amplified spontaneous emission (ASE) for a PC:active molecule relative concentration as small as 1:500 suggests that the polycarbonate role is to reduce the intermolecular diffusion rate rather than to isolate the active molecules. Moreover, for higher PC content, a continuous decrease of the bimolecular quenching role is observed. These results demonstrate that the absence of stimulated emission in neat films is not necessarily due to intrinsic molecular properties, as strong ASE can be obtained by slightly modifying the molecule interaction during the deposition process. This approach could allow a considerable extension of the number of molecules showing stimulated emission for organic laser applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9 × 10[sup 10] to 0.6 × 10[sup 10] cm[sup -2] as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 µm with the excited state transition wavelength of around 1.3 µm has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 µm but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%. [ABSTRACT FROM AUTHOR]

Thermal stain causes splitting of light- and heavy-hole excitons in the excitonic states of GaAs/Al(x)Ga(1-x)As multiple quantum wells. The splitting is temperature dependent and is related to varying thermal expansion coefficient of the quantum wells that weakens the tensile strain of the components in the GaAs layers during optical analysis.

Room temperature-induced emission in optically pumped narrow ZnSe/ZnSxSe1-x multiple-quantum-well structures was investigated. The results showed that the structures featured an optical excitation threshold of 300 kW per square centimeter at 300 K. At low temperature, an unsaturated gain coefficient of theorder of 5 x 10 squared was observed.

A combination of transmission electron microscopy and time-resolved photoluminescence techniques is employed to study the structural, as well as the optical properties of the vertically stacked triple InAs dot-in-well structure. The discussed quantum dots are shown to be bound to each other by the phenomenon of electronic coupling.

Presents a study that investigated the correlation between the structural and optical properties of polydispersed quantum dots in glass matrix. Method of the study; Results and discussion; Conclusion.

Presents the results of a study which investigated the radiative recombination processes of the free-carrier plasma confined in Ga[0.47]In[0.53]As/Al[sub0.48]In[sub0.52]As multiple-quantum well structures on indium phosphide substrate. Adaptation of space-resolved luminescence; Theoretical analysis of the optical gain spectra; Discussion on the low-excitation-intensity experiments.

A systematic study of the effect of growth parameters on the structural and optical properties in InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy is presented. The dot is significantly reduced as the growth rate decreases while the island size becomes larger.

The effect of quantum mechanical coupling on the optical properties of vertically stacked V-groove quantum wires are studied by means of photoluminescence and photoluminescence-excitation spectroscopy. The experimental results are analyzed by a simple theoretical model based on an analytical procedure.

We have studied the influence of difference growth conditions on the two-dimensional to three-dimensional growth mode transition for a specific class of InGaAs/GaAs quantum dots (QDs) optimized for applications to optical devices operating around 1.3 μm (In content xapprox. 0.5). The dots are grown by low-pressure metalorganic chemical vapor deposition on GaAs substrates. We demonstrate that the critical layer thickness corresponding to optimized single-QD layer structures (i.e., with reduced wetting layer thickness and high uniformity) can be controlled by kinetic effects. The optimized growth conditions allow us to grow six-layers stacked QD structures as active material for the fabrication of a light emitting devices operating around 1.3 μm at room temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]