Polarization dependence of absorption in strongly vertically coupled InAs/GaAs quantum dots for two-color far-infrared photodetector

Strongly vertically coupled InAs/GaAs quantum dots (QDs) with modulation doping are investigated, and polarization dependence of two-color absorptions was observed. Analysis of photoluminescence (PL) and absorption spectra shows that s-polarized absorptions at. 10.0 and 13.4 mu m, stem from the first excited state E-1 and the second excited state E-2 in the QDs to the bound state E-InGaAs in the InGaAs spacer, respectively, whereas p-polarized absorptions at 10.0 and 8.2 mu m stem from the first excited state E-1 and the ground E-g in the QDs to the bound state E-InGaAs in the InGaAs spacer, respectively. These measurements illustrate that transitions from excited states are more sensitive to normal incidence, which are very important in designing QD infrared detector. (C) 2007 Elsevier B.V. All rights reserved.

Evolution of surface morphology and photoluminescence characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

Evolution of surface morphology and optical characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are investigated by atomic force microscopy (AFM) and photoluminescence (PL). After deposition of 16 monolayers (ML) of In0.5Ga0.5As, QDs are formed and elongated along the [110] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.

GaAs-Based Metamorphic Long-Wavelength InAs Quantum Dots Grown by Molecular Beam Epitaxy

A bilayer stacked InAs/GaAs quantum dot structure grown by molecular beam epitaxy on an In0.05Ga0.95As metamorphic buffer is investigated. By introducing a InGaAs Sb cover layer on the upper InAs quantum dots (QDs) layers, the emission wavelength of the QDs is extended successfully to 1.533 mu m at room temperature, and the density of the QDs is in the range of 4 x 10(9) -8 x 10(9) cm(-2). Strong photoluminescence (PL) intensity with a full width at half maximum of 28.6 meV of the PL spectrum shows good optical quality of the bilayer QDs. The growth of bilayer QDs on metamorphic buffers offers a useful way to extend the wavelengths of GaAs-based materials for potential applications in optoelectronic and quantum functional devices.

Carrier channels of multimodal-sized quantum dots: A surface-mediated adatom migration picture

This paper focuses on the study of carrier channels of multimodal-sized quantum dots formed on patterned substrate by a rate-equation-based model. Surface-mediated indium adatom migration is revealed by a direct comparison between quantum dot wetting layer, which acts as carrier channel, formed on a flat substrate and on a patterned substrate. For the assessment of suitability, the carrier channel of the dot-in-well structure has also been studied by the present model, and the transition energies of the carrier channel (e.g., InGaAs quantum well) obtained from theoretical simulation agree fairly well with those obtained from the reflectance measurements.

Double hydrogenic impurities in double quantum dots

The ground states and degree of entanglement of double hydrogenic impurities in a pair of vertically stacked InGaAs/GaAs quantum dots are studied with a proposed diagonalization technique. It is found that at short barrier widths, the entanglement is small due to the coupling between the intra- and interdot orbitals. At large barrier widths, large entanglement occurs.

Influence of dislocation stress field on distribution of quantum dots

InAs quantum dots (QDs) were grown on In0.15Ga0.85As strained layers by molecular beam epitaxy on GaAs (0 0 1) substrates. Atomic force microscopy and transmission electron microscopy study have indicated that In0.15Ga0.85As ridges and InAs QDs formed at the inclined upside of interface misfit dislocations (MDs). By testifying the MDs are mixed 60 degrees dislocations and calculating the surface stress over them when they are 12-180 nm below the surface, we found the QDs prefer nucleating on the side with tensile stress of the MDs and this explained why the ordering of QDs is weak when the InGaAs layer is relatively thick. (c) 2006 Elsevier B.V. All rights reserved.

Temperature dependence of surface quantum dots grown under frequent growth interruption

We grow InGaAs quantum dot (QD) at low growth rate with 70 times insertion of growth interruption in MBE system. It is found that because of the extreme growth condition, QDs exhibit a thick wetting layer, large QD height value and special surface morphology which is attributed to the enhanced adatom surface diffusion and In-segregation effect. Temperature dependence of photoluminescence measurement from surface QD shows that this kind of QD has good thermal stability which is explained in terms of the presence of surface oxide. The special distribution of QD may also play a role in this thermal character. (c) 2006 Elsevier B.V. All rights reserved.

Growth of InAs quantum dots on vicinal GaAs (100) substrates by metalorganic chemical vapor deposition and their optical properties

The growth of InAs quantum dots on vicinal GaAs (100) Substrates was systematically studied using low-pressure metalorganic chemical vapor deposition (MOCVD). The dots showed a clear bimodal size distribution on vicinal substrates. The way of evolution of this bimodal size distribution was studied as a function of growth temperature, InAs layer thickness and InAs deposition rate. The optical properties of dots grown on vicinal substrates were also studied by photoluminescence (PL). It was found that, compared with dots on exact substrates, dots on vicinal substrates had better optical properties such as a narrower PL line width, a longer emission wavelength, and a larger PL intensity. (c) 2006 Elsevier B.V. All rights reserved.

Time-resolved photoluminescence spectra of self-assembled InAs/GaAs quantum dots

Two types of InAs self-assembled Quantum dots (QDs) were prepared by Molecular beam epitaxy. Atomic force microscopy (AFM) measurements showed that, compared to QDs grown on GaAs substrate, QDs grown on InGaAs layer has a significantly enhanced density. The short spacing (several nanometer) among QDs stimulates strong coupling and leads to a large red-shift of the 1.3 mu m photoluminescence (PL) peak. We study systematically the dependence of PL lifetime on the QDs size, density and temperature (1). We found that, below 50 K, the PL lifetime is insensitive to temperature, which is interpreted from the localization effects. As T increases, the PL lifetime increases, which can be explained from the competition between the carrier redistribution and thermal emission at higher temperature. The increase of carriers in QDs migrated from barriers and wetting layer (WL), and the redistribution of carriers among QDs enhance the PL lifetime as T increases. The thermal emission and non-radiative recombination have effects to reduce the PL lifetime at higher T. As a result, the radiative recombination lifetime is determined by the wave function overlapping of electrons and holes in QDs, and QDs with different densities have different PL lifetime dependence on the QDs size. (c) 2005 Elsevier B.V. All rights reserved.

Size evolution and optical properties of self-assembled InAs quantum dots on different matrix

InAs quantum dots have been grown by solid source molecular beam epitaxy on different matrix to investigate the effect on the structure and optical properties. High density of 1.02 x 10(11) cm(-2) of InAs islands on In0.15Ga0.85As and In0.15Al0.85As underlying layer has been achieved. Atomic force microscopy and photoluminescence spectra show the size evolution of InAs islands on In0.15Ga0.85As underlying layer. A strong 1.3 mum photoluminescence from InAs islands on In0.15Ga0.85As underlying layer and with InGaAs strain-reduced layer has been obtained. Single-mirror light emitting diode structures with InAs quantum dots capped by InGaAs grown on InGaAs layer as active layer were fabricated and the corresponding radiative efficiency was deduced to be as high as 20.5%. Our results provide important information for optimizing the epitaxial structures of 1.3 mum wavelength quantum dots devices. (C) 2003 Elsevier B.V. All rights reserved.

Role of different cap layers tuning the wavelength of self-assembled InAs/GaAs quantum dots

We have investigated the effect of different cap layers on the photoluminescence (PL) of self-assembled InAs/GaAs quantum dots (QDs). Based upon different cap layers, the wavelength of InAs QDs can be tuned to the range from 1.3 to 1.5 mum. An InAlAs and InGaAs combination layer can enlarge the energy separation between the ground and first excited radiative transition. GaAs/InAs short period superlattices (SLs) make the emission wavelength shift to 1.53 mum. The PL intensity of InAs QDs capped with GaAs/InAs SLs shows an anomalous increase with increasing temperature. We attribute this to the transfer of carriers between different QDs.

The evolution of InAs/InAlAs/InGaAlAs quantum dots after rapid thermal annealing

We have studied how the optical properties of InAs self-assembled quantum dots (QDs) grown on GaAs substrate are affected when depositing an InAlAs/InGaAs combination overgrowth layer directly on it by rapid thermal annealing (RTA). The photoluminescence measurement demonstrated that the InAs QDs experiences an abnormal variation during the course of RTA. The model of transformation of InAs-InAlAs-InGaAlAs could be used to well explain the phenomena. (C) 2003 Elsevier Science B.V. All rights reserved.

Effects of seed dot layer and thin GaAs spacer layer on the structure and optical properties of upper In(Ga)As quantum dots

The structure and optical properties of In(Ga)As with the introduction of InGaAlAs or InAlAs seed dot layers are investigated. The area density and size homogeneity of the upper InGaAs dots are efficiently improved by the introduction of a buried layer of high-density dots. Our explanation for the realization of high density and size homogeneity dots is presented. When the GaAs spacer layer is too thin to cover the seed dots, the upper dots exhibit some optical properties like those of a quantum well. By analyzing the growth dynamics, we refer to this kind of dot as an empty-core dot. (C) 2003 American Institute of Physics.

Surface morphology and optical property of 1.3 mu m In0.5Ga0.5As/GaAs self-organized quantum dots grown by MBE

Surface morphology and optical properties of 1.3 mum self-organized InGaAs/GaAs quantum dots structure grown by molecular beam epitaxy have been investigated by atomic force microscopy and photoluminescence measurements. It has been shown that the surface morphology evolution and emission wavelengths of InGaAs/GaAs QDs can be controlled effectively via cycled monolayer deposition methods due to the reduction of the surface strain. Our results provide important information for optimizing the epitaxial parameters for obtaining 1.3 mum long wavelength emission quantum dots structures. (C) 2002 Elsevier Science B.V. All rights reserved.

Structure and optical properties of upper In(Ga)As quantum dots on a different seed layer with a thin GaAs spacer layer

The structure and optical properties of In(Ga)As grown with the introduction of InGaAlAs or InAlAs seed dots layers are investigated. The area density and size homogeneity of the upper InGaAs dots are efficiently improved with the introduction of a layer of high-density buried dots. When the GaAs spacer layer is too thin to cover the seed dots, the upper dots exhibit the characterization of a quantum well. By analyzing the growth dynamics, we refer to it as an empty-core structure dot. (C) 2002 Elsevier Science B.V. All rights reserved.