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InAs QDs (InA + qd)
Selected AbstractsFunctionalized Self-Assembled InAs/GaAs Quantum-Dot Structures Hybridized with Organic MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Miaoxiang Chen Abstract Low-dimensional III,V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress-free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule,QD systems by grafting various types of air-stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider-bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non-radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620,nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule,QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications. [source] Self-organized InAs quantum dots grown in a V-groove InGaAs quantum wirePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2007Chang-Sik Son Abstract Self-organized InAs quantum dots (QDs), by the Stranski,Krastanow mode, have been grown by using low-pressure metalorganic chemical vapor deposition on V-groove GaAs substrates. By adjusting the flow rate of AsH3 during the growth of InAs QDs, a one dimensional InAs QD array was successfully formed along the [01] direction only at the bottom of V-grooves. No QDs were observed on the sidewalls and the surface of the mesa top. The InAs QDs took on an oval shape. They were spatially well-isolated along the [01] direction with a line density of 3 × 103 cm,1. These low-density InAs QDs are expected to be used in areas of quantum information and quantum computing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of deep levels at GaAs/GaAs and GaAs/InAs interfaces grown by MBE-interrupted growth techniquePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007M. Kaniewska Abstract In order to find the origin of crystalline defects occurring in the preparation of InAs/GaAs quantum dots (QDs), their appearance was tracked through three different sample types designed as Schottky diodes. Specimens with a GaAs cap layer on a GaAs buffer layer as well as with an InAs wetting layer without QDs were grown by molecular beam epitaxy (MBE) using the interrupted growth technique. Deep level transient spectroscopy (DLTS) was used for comparison with structures containing InAs QDs. It was found that two main levels with thermal activation energies of 0.14,0.16 eV and 0.46,0.52 eV from the conduction band edge, respectively, are grown-in defects, which are characteristic of the growth interrupted interface occuring under an excess of As. Both these levels together with an additional level at 0.10,0.12 eV found in the InAs wetting layer structures were also present in those with QDs, probably resulting from strain or In penetration. All three defects were agglomerated close to the interface created by the interrupted growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of photoluminescence spectra of self-assembled InAs/GaAs quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003F.J. Manjón Abstract Photoluminescence (PL) measurements have been performed in InAs/GaAs self-assembled quantum dots (QDs) under high excitation conditions at low temperatures and under high hydrostatic pressures up to 10 GPa. Mechanically polished samples for high pressure experiments exhibited PL emission from the QD ground state but not from the excited states. Instead, a new broad band is observed in the energy range of the first excited state, which is tentatively attributed to emission from smaller dots formed during the mechanical thinning of the sample. With increasing pressure we found a similar blue shift for the PL maxima of the QD ground state (65 meV/GPa) and of the new broad band (69 meV/GPa). These pressure coefficients are 20% and 40% lower than those reported for dots of less than half the height as in our case and for the wetting layer, respectively. Our results point to a systematic reduction of the pressure coefficient of the InAs QDs with the increase of the dot height. [source] Time-resolved photoluminescence of type-II InAs/GaAs quantum dots covered by a thin GaAs1,xSbx layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2009Yu-An Liao Abstract We investigate carrier lifetimes of InAs/GaAs quantum dots (QDs) covered by a thin GaAs1,xSbx layer by time-resolved photoluminescence (PL). Both the power dependent PL peak shift and the longer decay time confirm the type-II band alignments. Different recombination paths have been identified by temperature dependent measurements. At low temperatures, the long-range recombination with holes trapped in the GaAsSb layer is significant, resulting in non-single-exponential decays. The short-range recombination with holes confined in the band-bending region surrounding the InAs QDs is important at higher temperatures. The variation in decay time across the ground-state and the temporal PL peak redshift further confirm the localization of holes in the GaAsSb layer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Deterministic self-organization: Ordered positioning of InAs quantum dots by self-organized anisotropic strain engineering on patterned GaAs (311)BPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2009E. Selçuk Abstract Laterally ordered InGaAs quantum dot (QD) arrays, InAs QD molecules, and single InAs QDs in a spot-like periodic arrangement are created by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice (SL) templates on planar GaAs (311)B substrates in molecular beam epitaxy. On shallow- and deep-patterned substrates the respectively generated steps and facets guide the self-organization process during SL template formation to create more complex ordering such as periodic stripes, depending on pattern design. Here we demonstrate for patterns such as shallow- and deepetched round holes and deep-etched zigzag mesas that the self-organized periodic arrangement of QD molecules and single QDs is spatially locked to the pattern sidewalls and corners. This extends the concept of guided self-organization to deterministic self-organization. Absolute position control of the QDs is achieved without one-to-one pattern definition. This guarantees the excellent arrangement control of the ordered QD molecules and single QDs with strong photoluminescence emission up to room temperature, which is required for future quantum functional devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improved luminescence efficiency of InAs quantum dots grown on atomic terraced GaAs surface prepared with in-situ chemical etchingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009Yasuhiro Idutsu Abstract Observation of the enhanced luminescence efficiency of InAs quantum dots (QDs) grown on atomically controlled GaAs surfaces is reported. With the trisdimethylaminoarsenic (TDMAAs) in-situ surface etching process, formation of atomic steps and terraces on GaAs surfaces were clearly observed. InAs QDs grown on the processed GaAs surfaces showed the clear dependence of QDs size, density and optical characteristics on the surface properties, i.e., the increase of the QDs height and diameter the decrease of the QDs density. About 6-times enhancement of photoluminescence efficiency which has the peak around 1550-nm wavelength was observed by growing InAs QDs on atomically controlled GaAs surfaces. This is due to the migration enhancement of InAs during thegrowth the QDs. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Contactless electroreflectance and photoluminescence of InAs quantum dots with GaInNAs barriers grown on GaAs substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007M. Motyka Abstract InAs quantum dots (QDs) with GaInNAs barriers grown on (001) GaAs substrate by molecular beam epitaxy have been studied by contactless electroreflectance (CER) and photoluminescence (PL) spectroscopies. It has been observed that the overgrowth of self-organized InAs QDs with GaInNAs layers effectively tunes the QD emission to the 1.3 ,m spectral region. In case of PL spectra only one peak related to QD emission has been observed. In the case of CER spectra, in addition to a CER feature corresponding to the QD ground state, a rich spectrum of CER resonances related to optical transitions in InAs/GaInNAs/GaAs QW has been observed. It has been concluded that the application of GaInNAs instead InGaAs leads to better control of emission wavelength from InAs QDs since strains in GaInNAs can be tuned from compressive to tensile. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] InAs quantum dot formed on GaNAs buffer layer by Metalorganic Chemical Vapor DepositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006R. Suzuki Abstract We investigated MOCVD grown InAs QDs on a GaNAs buffer layer. Distribution uniformity and shape of QDs on buffer layers were characterized for different nitrogen (N) compositions from 0% to 2%. It was found that the distribution of QDs on a GaNAs buffer layer became more uniform than that on a GaAs and the coalescence of QDs was suppressed. Increase of the aspect ratio (diameter/height) was also observed by increase of N composition. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] InAs quantum dots on GaAs substrates with InGaAs strain reducing layer for long wavelength emissionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003S. Saravanan Abstract InAs QDs on GaAs substrates were grown by molecular beam epitaxy (MBE). The dot density and properties were studied by atomic force microscopy (AFM). The low temperature photoluminescence (PL) characteristics of InAs QDs with different cap layers are discussed. The results suggest that InAs QDs covered by two InGaAs layers with different indium composition have long wavelength emission without much reduction in the PL intensity. [source] Optical properties of InAs/InP quantum dot stack grown by metalorganic chemical vapor depositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003Heedon Hwang Abstract The 5-layer InAs quantum dot (QD) stack was grown on an (001) InP substrate by low pressure-metalorganic chemical vapor deposition. 40 nm InP spacer layers were inserted between the InAs QDs. The integrated intensity of the photoluminescence peak at 300 K was over 12% of that at 10 K. Far-infrared absorption peaks were observed at 819 cm,1 (101.64 meV) and 518 cm,1 (64.08 meV) from this structure at room temperature by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Raman analysis showed that the peak at 819 cm,1 was attributed to a plasmon related peak in the n-type InP substrate. The absorption peak at 518 cm,1 was regarded as a peak related with intersubband transition in the InAs QDs, suggesting that room temperature operating quantum dot devices may be fabricated. [source] High quality InAs quantum dots covered by InGaAs/GaAs hetero-capping layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2003R. Ohtsubo Abstract Self-assembled InAs quantum dots with high performance were fabricated by molecular beam epitaxy via Stranski,Krastanov growth mode and InGaAs/GaAs hetero-capping growth. The size and shape of the dots were modified during the first GaAs capping layer, which plays an important role of a reduction in the inhomogeneous broadening. In particular, when the substrate temperature of the GaAs capping layer was 450,°C, the PL linewidth decreased to less than 20,meV. In order to reduce the residual strain in the InAs QDs and the capping layer, the InGaAs capping layer was additionally grown on the InAs dots covered by the first GaAs capping layer. As a result, the presented InGaAs/GaAs hetero-capping layer induced strong photoluminescence (PL) intensity, narrow PL linewidth and 1.3,,m light emission at room temperature. [source] | ||||||||||