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Sample records for ingaas qds structures

  1. Structural, optical and photovoltaic properties of co-doped CdTe QDs for quantum dots sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Ayyaswamy, Arivarasan; Ganapathy, Sasikala; Alsalme, Ali; Alghamdi, Abdulaziz; Ramasamy, Jayavel

    2015-12-01

    Zinc and sulfur alloyed CdTe quantum dots (QDs) sensitized TiO2 photoelectrodes have been fabricated for quantum dots sensitized solar cells. Alloyed CdTe QDs were prepared in aqueous phase using mercaptosuccinic acid (MSA) as a capping agent. The influence of co-doping on the structural property of CdTe QDs was studied by XRD analysis. The enhanced optical absorption of alloyed CdTe QDs was studied using UV-vis absorption and fluorescence emission spectra. The capping of MSA molecules over CdTe QDs was confirmed by the FTIR and XPS analyses. Thermogravimetric analysis confirms that the prepared QDs were thermally stable up to 600 °C. The photovoltaic performance of alloyed CdTe QDs sensitized TiO2 photoelectrodes were studied using J-V characteristics under the illumination of light with 1 Sun intensity. These results show the highest photo conversion efficiency of η = 1.21%-5% Zn & S alloyed CdTe QDs.

  2. Structural, morphological and optical properties of PEDOT:PSS/QDs nano-composite films prepared by spin-casting

    NASA Astrophysics Data System (ADS)

    Najeeb, Mansoor Ani; Abdullah, Shahino Mah; Aziz, Fakhra; Ahmad, Zubair; Rafique, Saqib; Wageh, S.; Al-Ghamdi, Ahmed A.; Sulaiman, Khaulah; Touati, Farid; Shakoor, R. A.; Al-Thani, N. J.

    2016-09-01

    This paper describes the structural, morphological and optical properties of the nano-composite of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and quantum dots (QDs). The ZnSe and CdSe QDs have been synthesized, with the aid of Mercaptoacetic acid (MAA), by a colloidal method with an average size of ~5 to 7 nm. QDs have been embedded in PEDOT:PSS using a simple solution processing approach and has been deposited as thin films by spin coating technique. The QDs embedded PEDOT:PSS enhances the light absorption spectra of samples, prominently in terms of absorption intensity which may consequently improve sensitivity of the optoelectronic devices.

  3. InGaP-based InGaAs quantum dot solar cells with GaAs spacer layer fabricated using solid-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sugaya, T.; Takeda, A.; Oshima, R.; Matsubara, K.; Niki, S.; Okano, Y.

    2012-09-01

    We report InGaP-based multistacked InGaAs quantum dot (QD) solar cells with GaAs spacer layers. We obtain a highly stacked and well-aligned InGaAs QD structure with GaAs spacer layers in an InGaP matrix grown by solid-source molecular beam epitaxy. The photoluminescence intensity of the InGaAs QDs in the InGaP matrix increases as the number of QD layers increases, which indicates the growth of a high-quality InGaP-based multistacked InGaAs QD structure. The short-circuit current density and the conversion efficiency of the InGaP-based QD solar cells increase as the number of InGaAs QD layers increases.

  4. Fabrication of double barrier structures in single layer c-Si-QDs/a-SiOx films for realization of energy selective contacts for hot carrier solar cells

    NASA Astrophysics Data System (ADS)

    Kar, Debjit; Das, Debajyoti

    2017-01-01

    Thin films of c-Si-QDs embedded in an a-SiOx dielectric matrix forming arrays of double barrier structures have been fabricated by reactive rf-magnetron sputtering at ˜400 °C, without post-deposition annealing. The formation of larger size c-Si-QDs of reduced number density in homogeneous distribution within a less oxygenated a-SiOx matrix at higher plasma pressure introduces systematic widening of the average periodic distance between the adjacent `c-Si-QDs in a-SiOx', as obtained by X-ray reflectivity and transmission electron microscopy studies. A wave-like pattern in the J-E characteristics identifies the formation of periodic double-barrier structures along the path of the movement of charge carriers across the QDs and that those are originated by the a-SiOx dielectric matrix around the c-Si-QDs. A finite distribution of the size of c-Si-QDs introduces a broadening of the current density peak and simultaneously originates the negative differential resistance-like characteristics, which have suitable applications in the energy selective contacts that act as energy filters for hot carrier solar cells. A simple yet effective process technology has been demonstrated. Further initiative on tuning the energy selectivity by reducing the size and narrowing the size-distribution of Si-QDs can emerge superior energy selective contacts for hot carrier solar cells, paving ground for accomplishing all-Si solar cells.

  5. Spatially correlated structural and optical characterization of a single InGaAs quantum well fin selectively grown on Si by microscopy and cathodoluminescence techniques

    NASA Astrophysics Data System (ADS)

    David, S.; Roque, J.; Rochat, N.; Bernier, N.; Piot, L.; Alcotte, R.; Cerba, T.; Martin, M.; Moeyaert, J.; Bogumilowizc, Y.; Arnaud, S.; Bertin, F.; Bassani, F.; Baron, T.

    2016-05-01

    Structural and optical properties of InGaAs quantum well fins (QWFs) selectively grown on Si using the aspect ratio trapping (ART) method in 200 nm deep SiO2 trenches are studied. A new method combining cathodoluminescence, transmission electron microscopy, and precession electron diffraction techniques is developed to spatially correlate the presence of defects and/or strain with the light emission properties of a single InGaAs QWF. Luminescence losses and energy shifts observed at the nanoscale along InGaAs QWF are correlated with structural defects. We show that strain distortions measured around threading dislocations delimit both high and low luminescent areas. We also show that trapped dislocations on SiO2 sidewalls can also result in additional distortions. Both behaviors affect optical properties of QWF at the nanoscale. Our study highlights the need to improve the ART growth method to allow integration of new efficient III-V optoelectronic components on Si.

  6. Carrier dynamics of strain-engineered InAs quantum dots with (In)GaAs surrounding material

    NASA Astrophysics Data System (ADS)

    Nasr, O.; Chauvin, N.; Alouane, M. H. Hadj; Maaref, H.; Bru-Chevallier, C.; Sfaxi, L.; Ilahi, B.

    2017-02-01

    The present study reports on the optical properties of epitaxially grown InAs quantum dots (QDs) inserted within an InGaAs strain-reducing layer (SRL). The critical energy states in such QD structures have been identified by combining photoluminescence (PL) and photoluminescence of excitation (PLE) measurements. Carrier lifetime is investigated by time-resolved photoluminescence (TRPL), allowing us to study the impact of the composition of the surrounding materials on the QD decay time. Results showed that covering the InAs QDs with, or embedding them within, an InGaAs SRL increases the carrier dynamics, while a shorter carrier lifetime has been observed when they are grown on top of an InGaAs SRL. Investigation of the dependence of carrier lifetime on temperature showed good stability of the decay time, deduced from the consequences of improved QD confinement. The findings suggest that embedding or capping the QDs with SRL exerts optimization of their room temperature optical properties.

  7. Effect of deposition temperature on the structural and optical properties of CdSe QDs thin films deposited by CBD method

    SciTech Connect

    Laatar, F.; Harizi, A.; Smida, A.; Hassen, M.; Ezzaouia, H.

    2016-06-15

    Highlights: • Synthesis of CdSe QDs with L-Cysteine capping agent for applications in nanodevices. • The films of CdSe QDs present uniform and good dispersive particles at the surface. • Effect of bath temperature on the structural and optical properties of CdSe QDs thin films. • Investigation of the optical constants and dispersion parameters of CdSe QDs thin films. - Abstract: Cadmium selenide quantum dots (CdSe QDs) thin films were deposited onto glass substrates by a chemical bath deposition (CBD) method at different temperatures from an aqueous solution containing L-Cysteine (L-Cys) as capping agent. The evolution of the surface morphology and elemental composition of the CdSe films were studied by AFM, SEM, and EDX analyses. Structural and optical properties of CdSe thin films were investigated by XRD, UV–vis and PL spectroscopy. The dispersion behavior of the refractive index is described using the single oscillator Wemple-DiDomenico (W-D) model, and the physical dispersion parameters are calculated as a function of deposition temperature. The dispersive optical parameters such as average oscillator energy (E{sub o}), dispersion energy (E{sub d}), and static refractive index (n{sub o}) were found to vary with the deposition temperature. Besides, the electrical free carrier susceptibility (χ{sub e}) and the carrier concentration of the effective mass ratio (N/m*) were evaluated according to the Spitzer-Fan model.

  8. High in content InGaAs near-infrared detectors: growth, structural design and photovoltaic properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiwei; Miao, Guoqing; Song, Hang; Li, Dabing; Jiang, Hong; Li, Zhiming; Chen, Yiren; Sun, Xiaojuan

    2017-04-01

    The design of novel structural material is an effective way to improve photodetection device performance. In this paper, the fabrication and performance of high In content InGaAs detectors were investigated. Using the two-step growth method, mismatch defect was effectively inhibited even with larger lattice mismatch at the interface. Meanwhile, the spectral response can cover the entire near-infrared region at room temperature. Through experiments and simulation, the optoelectronic properties of detector with different materials in the p-region are explored, elucidating the critical role of cap material in the transport properties of carriers. Compared to the typical InP cap detector, the InAsP cap detector shows better device performance. Also the dark current mechanism is analyzed on the basis of bias-temperature relation, and the result shows that the tunneling current plays a key role at high bias or low temperature. The introduction of a novel InGaAs detector provides a potential application to the development of near-infrared detection.

  9. Widely tunable alloy composition and crystal structure in catalyst-free InGaAs nanowire arrays grown by selective area molecular beam epitaxy

    SciTech Connect

    Treu, J. E-mail: Gregor.Koblmueller@wsi.tum.de; Speckbacher, M.; Saller, K.; Morkötter, S.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G. E-mail: Gregor.Koblmueller@wsi.tum.de; Döblinger, M.

    2016-02-01

    We delineate the optimized growth parameter space for high-uniformity catalyst-free InGaAs nanowire (NW) arrays on Si over nearly the entire alloy compositional range using selective area molecular beam epitaxy. Under the required high group-V fluxes and V/III ratios, the respective growth windows shift to higher growth temperatures as the Ga-content x(Ga) is tuned from In-rich to Ga-rich InGaAs NWs. Using correlated x-ray diffraction, transmission electron microscopy, and micro-photoluminescence spectroscopy, we identify structural defects to govern luminescence linewidths in In-rich (x(Ga) < 0.4) and Ga-rich (x(Ga) > 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 < x(Ga) < 0.6) are mainly due to compositional inhomogeneities. Most remarkably, the catalyst-free InGaAs NWs exhibit a characteristic transition in crystal structure from wurtzite to zincblende (ZB) dominated phase near x(Ga) ∼ 0.4 that is further reflected in a cross-over from blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  10. In-situ atomic layer deposition of tri-methylaluminum and water on pristine single-crystal (In)GaAs surfaces: electronic and electric structures.

    PubMed

    Pi, T W; Lin, Y H; Fanchiang, Y T; Chiang, T H; Wei, C H; Lin, Y C; Wertheim, G K; Kwo, J; Hong, M

    2015-04-24

    The electronic structure of single-crystal (In)GaAs deposited with tri-methylaluminum (TMA) and water via atomic layer deposition (ALD) is presented with high-resolution synchrotron radiation core-level photoemission and capacitance-voltage (CV) characteristics. The interaction of the precursor atoms with (In)GaAs is confined at the topmost surface layer. The Ga-vacant site on the GaAs(111)A-2 × 2 surface is filled with Al, thereby effectively passivating the As dangling bonds. The As-As dimers on the GaAs(001)-2 × 4 surface are entirely passivated by one cycle of TMA and water. The presumed layerwise deposition fails to happen in GaAs(001)-4 × 6. In In0.20Ga0.80As(001)-2 × 4, the edge row As atoms are partially bonded with the Al, and one released methyl then bonds with the In. It is suggested that the unpassivated surface and subsurface atoms cause large frequency dispersions in CV characteristics under the gate bias. We also found that the (In)GaAs surface is immune to water in ALD. However, the momentary exposure of it to air (less than one minute) introduces significant signals of native oxides. This indicates the necessity of in situ works of high κ/(In)GaAs-related experiments in order to know the precise interfacial atomic bonding and thus know the electronic characteristics. The electric CV measurements of the ALD-Al2O3 on these (In)GaAs surfaces are correlated with their electronic properties.

  11. InGaAs quantum dots grown by molecular beam epitaxy for light emission on Si substrates.

    PubMed

    Bru-Chevallier, C; El Akra, A; Pelloux-Gervais, D; Dumont, H; Canut, B; Chauvin, N; Regreny, P; Gendry, M; Patriarche, G; Jancu, J M; Even, J; Noe, P; Calvo, V; Salem, B

    2011-10-01

    The aim of this study is to achieve homogeneous, high density and dislocation free InGaAs quantum dots grown by molecular beam epitaxy for light emission on silicon substrates. This work is part of a project which aims at overcoming the severe limitation suffered by silicon regarding its optoelectronic applications, especially efficient light emission device. For this study, one of the key points is to overcome the expected type II InGaAs/Si interface by inserting the InGaAs quantum dots inside a thin silicon quantum well in SiO2 fabricated on a SOI substrate. Confinement effects of the Si/SiO2 quantum well are expected to heighten the indirect silicon bandgap and then give rise to a type I interface with the InGaAs quantum dots. Band structure and optical properties are modeled within the tight binding approximation: direct energy bandgap is demonstrated in SiO2/Si/InAs/Si/SiO2 heterostructures for very thin Si layers and absorption coefficient is calculated. Thinned SOI substrates are successfully prepared using successive etching process resulting in a 2 nm-thick Si layer on top of silica. Another key point to get light emission from InGaAs quantum dots is to avoid any dislocations or defects in the quantum dots. We investigate the quantum dot size distribution, density and structural quality at different V/III beam equivalent pressure ratios, different growth temperatures and as a function of the amount of deposited material. This study was performed for InGaAs quantum dots grown on Si(001) substrates. The capping of InGaAs quantum dots by a silicon epilayer is performed in order to get efficient photoluminescence emission from quantum dots. Scanning transmission electronic microscopy images are used to study the structural quality of the quantum dots. Dislocation free In50Ga50As QDs are successfully obtained on a (001) silicon substrate. The analysis of QDs capped with silicon by Rutherford Backscattering Spectrometry in a channeling geometry is also presented.

  12. Strongly confined excitons in self-assembled InGaAs quantum dot clusters

    NASA Astrophysics Data System (ADS)

    Creasey, Megan; Li, Xiaoqin; Lee, Jihoon; Wang, Zhiming; Salamo, Gregory

    2011-03-01

    Quantum dot clusters (QDCs) consisting of regular geometric patterns of six InGaAs quantum dots (QD) are grown on a GaAs substrate using a hybrid growth method that combines droplet homoepitaxy and Stranski-Krastonov growth. These novel structures have potential applications as tunable single photon sources, entangled photon sources, or error corrected qubits - devices critical to the fields of secure optical communications and quantum computing We study the photoluminescence arising from a single cluster using both continuous wave and ultrafast spectroscopic techniques with variations in the sample temperature and excitation power. Our results suggest excitons (bound electron-hole pairs) are strongly confined within the individual QDs rather than loosely confined throughout the entire QDC. The work at Texas is supported financially by NSF, ARO, AFOSR, ONR, the Welch Foundation, and the Alfred Sloan Foundation. The work at Arkansas is supported by the NSF.

  13. Quantitative excited state spectroscopy of a single InGaAs quantum dot molecule through multi-million-atom electronic structure calculations.

    PubMed

    Usman, Muhammad; Tan, Yui-Hong Matthias; Ryu, Hoon; Ahmed, Shaikh S; Krenner, Hubert J; Boykin, Timothy B; Klimeck, Gerhard

    2011-08-05

    Atomistic electronic structure calculations are performed to study the coherent inter-dot couplings of the electronic states in a single InGaAs quantum dot molecule. The experimentally observed excitonic spectrum by Krenner et al (2005) Phys. Rev. Lett. 94 057402 is quantitatively reproduced, and the correct energy states are identified based on a previously validated atomistic tight binding model. The extended devices are represented explicitly in space with 15-million-atom structures. An excited state spectroscopy technique is applied where the externally applied electric field is swept to probe the ladder of the electronic energy levels (electron or hole) of one quantum dot through anti-crossings with the energy levels of the other quantum dot in a two-quantum-dot molecule. This technique can be used to estimate the spatial electron-hole spacing inside the quantum dot molecule as well as to reverse engineer quantum dot geometry parameters such as the quantum dot separation. Crystal-deformation-induced piezoelectric effects have been discussed in the literature as minor perturbations lifting degeneracies of the electron excited (P and D) states, thus affecting polarization alignment of wavefunction lobes for III-V heterostructures such as single InAs/GaAs quantum dots. In contrast, this work demonstrates the crucial importance of piezoelectricity to resolve the symmetries and energies of the excited states through matching the experimentally measured spectrum in an InGaAs quantum dot molecule under the influence of an electric field. Both linear and quadratic piezoelectric effects are studied for the first time for a quantum dot molecule and demonstrated to be indeed important. The net piezoelectric contribution is found to be critical in determining the correct energy spectrum, which is in contrast to recent studies reporting vanishing net piezoelectric contributions.

  14. Photoconductivity Relaxation Mechanisms of InGaAs/GaAs Quantum Dot Chain Structures

    NASA Astrophysics Data System (ADS)

    Kondratenko, Serhiy V.; Iliash, Sviatoslav A.; Vakulenko, Oleg V.; Mazur, Yuriy I.; Benamara, Mourad; Marega, Euclydes; Salamo, Gregory J.

    2017-03-01

    An experimental study of the photoconductivity time decay in InGaAs/GaAs quantum dot chain structures is reported. Different photoconductivity relaxations resulting from spectrally selecting photoexcitation of InGaAs QWR or QDs as well as GaAs spacers were measured. The photoconductivity relaxation after excitation of 650 nm follows a stretched exponent with decay constant dependent on morphology of InGaAs epitaxial layers. Kinetics with 980 nm excitation are successfully described by equation that takes into account the linear recombination involving Shockley-Read centers in the GaAs spacers and bimolecular recombination via quantum-size states of InGaAs QWRs or QDs.

  15. Hybrid semiconductor quantum dot-metal nanocrystal structures prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Urbańczyk, A.; Hamhuis, G. J.; Nötzel, R.

    2011-05-01

    We report the formation of In nanocrystals and their alignment near dilute InAs quantum dots (QDs) on GaAs (0 0 1) by molecular beam epitaxy. The In nanocrystals exhibit surface plasmon resonances in the near-infrared range, which can be matched with the emission wavelength of In(Ga)As QDs. The alignment of the In nanocrystals near the InAs QDs is due to the strain-driven migration yielding single isolated QD-metal nanocrystal pairs and isolated QD-metal nanocrystal dimer structures, representing the basic hybrid QD-metal nanocrystal plasmonic nanostructures.

  16. Carrier relaxation in (In,Ga)As quantum dots with magnetic field-induced anharmonic level structure

    NASA Astrophysics Data System (ADS)

    Kurtze, H.; Bayer, M.

    2016-07-01

    Sophisticated models have been worked out to explain the fast relaxation of carriers into quantum dot ground states after non-resonant excitation, overcoming the originally proposed phonon bottleneck. We apply a magnetic field along the quantum dot heterostructure growth direction to transform the confined level structure, which can be approximated by a Fock-Darwin spectrum, from a nearly equidistant level spacing at zero field to strong anharmonicity in finite fields. This changeover leaves the ground state carrier population rise time unchanged suggesting that fast relaxation is maintained upon considerable changes of the level spacing. This corroborates recent models explaining the relaxation by polaron formation in combination with quantum kinetic effects.

  17. Electronic coupling of single lateral strained InGaAs quantum dot molecule based on nanohole structure

    NASA Astrophysics Data System (ADS)

    Parvizi, Roghaieh

    2016-02-01

    The electronic properties of laterally coupled InGaAs/GaAs quantum dot molecule are studied theoretically under in-plane electric field. The quantum dot molecule energy spectrum and envelope functions are calculated by solving one-band effective-mass Schrödinger equation with considering strain effect by employing finite element method in three dimensions. The obtained results indicate that the electron's coupling energy strongly depends on the In mole fractions of the nanohole, such that quantum dots act as a molecule in case that In mole fractions of dots are larger than that of nanohole. It can be also observed that electrons perceive the double-dots structure composing quantum dot molecule in close distances(less than 7 nm), while the holes discern two single dots structure. The effect of an in-plane electric field on the energy spectrum is investigated and it can be demonstrated that the coupling energy can be tuned by applying a low-intensity static electric field.

  18. Investigation of polarization-selective InGaAs sensor with elliptical two-dimensional holes array structure

    NASA Astrophysics Data System (ADS)

    Wang, Wenbo; Fu, Dong; Hu, Xiaobin; Xu, Yun; Song, Guofeng; Wei, Xin

    2016-10-01

    Polarimetric imaging in infrared wavelengths have attracted more and more attention for broad applications in meteorological observations, medicine, remote sensing and many other fields. Metal metamaterial structures are used in nanophotonics in order to localize and enhance the incident electromagnetic field. Here we develop an elliptical gold Two-Dimensional Holes Array (2DHA) in which photons can be manipulated by surface plasmon resonance, and the ellipse introduce the asymmetry to realize a polarization selective function. Strong polarization dependence is observed in the simulated transmission spectra. To further understand the coupling mechanism between gold holes array and InP, the different parameters of the 2DHA are analyzed. It is shown that the polarization axis is perpendicular to the major axis of the ellipse, and the degree of polarization is determined by the aspect ratio of the ellipse. Furthermore, the resonance frequency of the 2DHA shows a linear dependence on the array period, the bandwidth of transmission spectra closely related to duty cycle of the ellipse in each period. This result will establish a basis for the development of innovative polarization selective infrared sensor.

  19. Electrostatic assembles and optical properties of Au CdTe QDs and Ag/Au CdTe QDs

    NASA Astrophysics Data System (ADS)

    Yang, Dongzhi; Wang, Wenxing; Chen, Qifan; Huang, Yuping; Xu, Shukun

    2008-09-01

    Au-CdTe and Ag/Au-CdTe assembles were firstly investigated through the static interaction between positively charged cysteamine-stabilized CdTe quantum dots (QDs) and negatively charged Au or core/shell Ag/Au nano-particles (NCs). The CdTe QDs synthesized in aqueous solution were capped with cysteamine which endowed them positive charges on the surface. Both Au and Ag/Au NCs were prepared through reducing precursors with gallic acid obtained from the hydrolysis of natural plant poly-phenols and favored negative charges on the surface of NCs. The fluorescence spectra of CdTe QDs exhibited strong quenching with the increase of added Au or Ag/Au NCs. Railey resonance scattering spectra of Au or Ag/Au NCs increased firstly and decreased latter with the concentration of CdTe QDs, accompanied with the solution color changing from red to purple and colorless at last. Experimental results on the effects of gallic acid, chloroauric acid tetrahydrate and other reagents demonstrated the static interaction occurred between QDs and NCs. This finding reveals the possibilities to design and control optical process and electromagnetic coupling in hybrid structures.

  20. High kappa Dielectrics on InGaAs and GaN: Growth, Interfacial Structural Studies, and Surface Fermi Level Unpinning

    DTIC Science & Technology

    2010-12-24

    MOSFETs and GaN MOSFETs without employing interfacial layers and surface chemical pre-treatments. We have achieved many firsts and made great impacts...hold world record high dc performances of InGaAs MOSFETs , including the drain current, peak transconductance, and peak electron mobility in the self...aligned inversion-channel In0.75Ga0.25As and In0.2Ga0.8As MOSFETs using both in-situ MBE-Al2O3/GGO and ex-situ ALD-Al2O3 gate dielectrics. The high

  1. High Dielectrics on High Carrier Mobility InGaAs Compound Semiconductors and GaN - Growth, Interfacial Structural Studies, and Surface Fermi Level Unpinning

    DTIC Science & Technology

    2010-02-19

    widely used in the Si industry for high k gate dielectrics deposition. (3) First to demonstrate oxide scaling of MBE-grown GGO on In0.2Ga0.8As to a CET...energy-band parameters at interfaces of high κ atomic- layer -deposited (ALD) oxides on GaAs and InGaAs, and first to achieve inversion-channel GaN...MOS transistors need to be operated with their oxide - III-V interfaces resembling that of SiO2- Si , namely nearly perfect passivation. Through the

  2. Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well.

    PubMed

    Tatebayashi, J; Liang, B L; Laghumavarapu, R B; Bussian, D A; Htoon, H; Klimov, V; Balakrishnan, G; Dawson, L R; Huffaker, D L

    2008-07-23

    Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4 K) time-resolved PL measurements show a decay time of [Formula: see text] ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text] ns).

  3. Structural and optical properties of In 0.5Ga 0.5As/GaAs quantum dots in an In 0.1Ga 0.9As well using repeated depositions of InAs/GaAs short-period superlattices for the application of optical communication

    NASA Astrophysics Data System (ADS)

    Song, J. D.; Choi, W. J.; Lee, J. I.; Lee, J. Y.

    2006-05-01

    We report structural and optical properties of In 0.5Ga 0.5As/GaAs quantum dots (QDs) in a 100 Å-thick In 0.1Ga 0.9As well grown by repeated depositions of InAs/GaAs short-period superlattices with atomic force microscope, transmission electron microscope (TEM) and photoluminescence (PL) measurement. The QDs in an InGaAs well grown at 510 °C were studied as a function of n repeated deposition of 1 monolayer thick InAs and 1 monolayer thick GaAs for n=5-10. The heights, widths and densities of dots are in the range of 6-22.0 nm, 40-85 nm, and 1.6-1.1×10 10/cm 2, respectively, as n changes from 5 to 10 with strong alignment along [1 -1 0] direction. Flat and pan-cake-like shape of the QDs in a well is found in TEM images. The bottoms of the QDs are located lower than the center of the InGaAs well. This reveals that there was intermixing-interdiffusion-of group III materials between the InGaAs QD and the InGaAs well during growth. All reported dots show strong 300 K-PL spectrum, and 1.276 μm (FWHM: 32.3 meV) of 300 K-PL peak was obtained in case of 7 periods of the QDs in a well, which is useful for the application to optical communications.

  4. Crosstalk study of near infrared InGaAs detectors

    NASA Astrophysics Data System (ADS)

    Li, Xue; Tang, Hengjing; Li, Tao; Fan, Cui; Shao, Xiumei; Li, Jianwei; Wei, Jun; Gong, Haimei

    2016-05-01

    Crosstalk characteristics of high density FPA detectors attract widespread attention in the application of electro-optical systems. Crosstalk characteristics of near-infrared (NIR) InGaAs photodiodes and focal plane arrays (FPAs) were studied in this paper. The mesa type detector was investigated by using laser beam induced current technique (LBIC) to measure the absorption outside the designed photosensitive area, and the results show that the excess absorption enlarges the crosstalk of the adjacent pixels. The structure optimization using the effective absorption layer between the pixels can effectively reduce the crosstalk to 2.5%. The major crosstalk components of the optimization photodiode come from the electronic signal caused by carrier lateral diffusion. For the planar type detectors, test structures were used to compare the crosstalk of different structures, and the guard ring structure shows good suppression of the crosstalk. Then the back-illuminated 32x32 InGaAs photodiodes with 30μm pitch were designed, and LBIC was used to measure its lateral diffusion of the effective carriers and fill factor of photosensitive area. The results indicate that the fill factor of detectors can reach up to 98% when the diffusion region is optimized, and the minimum response exists between two neighborhood pixels. Based on these crosstalk measurement results and optimizing structure designs, the linear InGaAs photodiodes were designed and thus the InGaAs FPA assembly was fabricated. The assembly shows higher electro-optical performance and good improvement on crosstalk. The assembly was applied in infrared imaging system and modulation transfer function (MTF) of FPA assembly was calculated to be above 0.50. The clear image based on FPA assembly was obtained.

  5. InGaAs quantum dot molecules around self-assembled GaAs nanomound templates

    SciTech Connect

    Lee, J. H.; Wang, Zh. M.; Strom, N. W.; Mazur, Yu. I.; Salamo, G. J.

    2006-11-13

    Several distinctive self-assembled InGaAs quantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplet homoepitaxy. Depending on the specific InAs monolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals.

  6. Dielectric function of InGaAs in the visible

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Sieg, R. E.; Yao, H. D.; Snyder, P. G.; Woollam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.

    1990-01-01

    Measurements are reported of the dielectric function of thermodynamically stable In(x)Ga(1-x)As in the composition range 0.3 equal to or less than X = to or less than 0.7. The optically thick samples of InGaAs were made by molecular beam epitaxy (MBE) in the range 0.4 = to or less than X = to or less than 0.7 and by metal-organic chemical vapor deposition (MOCVD) for X = 0.3. The MBE made samples, usually 1 micron thick, were grown on semi-insulating InP and included a strain release structure. The MOCVD sample was grown on GaAs and was 2 microns thick. The dielectric functions were measured by variable angle spectroscopic ellipsometry in the range 1.55 to 4.4 eV. The data was analyzed assuming an optically thick InGaAs material with an oxide layer on top. The thickness of this layer was estimated by comparing the results for the InP lattice matched material, i.e., X = 0.53, with results published in the literature. The top oxide layer mathematically for X = 0.3 and X = 0.53 was removed to get the dielectric function of the bare InGaAs. In addition, the dielectric function of GaAs in vacuum, after a protective arsenic layer was removed. The dielectric functions for X = 0, 0.3, and 0.53 together with the X = 1 result from the literature to evaluate an algorithm for calculating the dielectric function of InGaAs for an arbitrary value of X(0 = to or less than X = to or less than 1) were used. Results of the dielectric function calculated using the algorithm were compared with experimental data.

  7. Dielectric function of InGaAs in the visible

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Yao, H. D.; Snyder, P. G.; Woolam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.; Sieg, R. E.

    1990-01-01

    Measurements are reported of the dielectric function of thermodynamically stable In(x)Ga(1-x)As in the composition range 0.3 equal to or less than X = to or less than 0.7. The optically thick samples of InGaAs were made by molecular beam epitaxy (MBE) in the range 0.4 = to or less than X = to or less than 0.7 and by metal-organic chemical vapor deposition (MOCVD) for X = 0.3. The MBE made samples, usually 1 micron thick, were grown on semi-insulating InP and included a strain release structure. The MOCVD sample was grown on GaAs and was 2 microns thick. The dielectric functions were measured by variable angle spectroscopic ellipsometry in the range 1.55 to 4.4 eV. The data was analyzed assuming an optically thick InGaAs material with an oxide layer on top. The thickness of this layer was estimated by comparing the results for the InP lattice matched material, i.e., X = 0.53, with results published in the literature. The top oxide layer mathematically for X = 0.3 and X = 0.53 was removed to get the dielectric function of the bare InGaAs. In addition, the dielectric function of GaAs in vacuum, after a protective arsenic layer was removed. The dielectric functions for X = 0, 0.3, and 0.53 together with the X = 1 result from the literature to evaluate an algorithm for calculating the dielectric function of InGaAs for an arbitrary value of X (0 = to or less than X = to or less than 1) were used. Results of the dielectric function calculated using the algorithm were compared with experimental data.

  8. Effect of growth temperature and quantum structure on InAs/GaAs quantum dot solar cell.

    PubMed

    Park, M H; Kim, H S; Park, S J; Song, J D; Kim, S H; Lee, Y J; Choi, W J; Park, J H

    2014-04-01

    InGaAs-capped InAs quantum dots (QDs) and InAs QDs were adopted for the study of the effects through growth temperature and the band structure of InAs QDs on the performance of GaAs-based QD solar cell. It has been shown that the defects due to low temperature growth resulted in the decrease of Voc, Jsc and external quantum efficiency for GaAs bulk solar cell and QD embedded solar cells. It has been also found that InAs QDs act as defects by trapping photo-generated carries which affect the carrier transport in QD solar cell. The QD solar cell with InGaAs-capped InAs QDs showed higher performance than the QD solar cell with only InAs QDs. Such result has been explained by photo-generated carrier trapping and tunneling through InGaAs QW state in InGaAs-capped InAs QDs.

  9. Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

    NASA Astrophysics Data System (ADS)

    Ananth, Devanesan Arul; Rameshkumar, Angappan; Jeyadevi, Ramachandran; Jagadeeswari, Sivanadanam; Nagarajan, Natarajan; Renganathan, Rajalingam; Sivasudha, Thilagar

    2015-03-01

    Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs-rutin conjugate exhibited excellent quenching property due to the -OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of -OH group in its structure. Photolabelling of E. coli with QDs-rutin and QDs-caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs-rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.

  10. Ellipsometric study of InGaAs MODFET material

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Sieg, R. E.; Yao, H. D.; Snyder, P. G.; Woollam, J. A.; Pamulapati, J.; Bhattacharya, P. K.

    1990-01-01

    In(x)Ga(1-x)As based MODFET (modulation doped field effect transistor) material was grown by molecular beam epitaxy on semi-insulating InP substrates. Several structures were made, including lattice matched and strained layer InGaAs. All structures also included several layers of In(0.52)Al(0.48)As. Variable angle spectroscopic ellipsometry was used to characterize the structures. The experimental data, together with the calibration function for the constituent materials, were analyzed to yield the thickness of all the layers of the MODFET structure. Results of the ellipsometrically determined thicknesses compare very well with the reflection high energy electron diffraction in situ thickness measurements.

  11. Development and characterization of PCDTBT:CdSe QDs hybrid solar cell

    SciTech Connect

    Dixit, Shiv Kumar Bhatnagar, Chhavi Kumari, Anita Madhwal, Devinder Bhatnagar, P. K. Mathur, P. C.

    2014-10-15

    Solar cell consisting of low band gap polymer poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10, 30-benzothiadiazole)] (PCDTBT) as donor and cadmium selenide/zinc sulphide (CdSe/ZnS) core shell quantum dots (QDs) as an acceptor has been developed. The absorption measurements show that the absorption coefficient increases in bulk heterojunction (BHJ) structure covering broad absorption spectrum (200nm–700nm). Also, the photoluminescence (PL) of the PCDTBT:QDs film is found to decrease by an order of magnitude showing a significant transfer of electrons to the QDs. With this approach and under broadband white light with an irradiance of 8.19 mW/cm{sup 2}, we have been able to achieve a power conversion efficiency (PCE) of 3.1 % with fill factor 0.42 for our typical solar cell.

  12. Development and characterization of PCDTBT:CdSe QDs hybrid solar cell

    NASA Astrophysics Data System (ADS)

    Dixit, Shiv Kumar; Bhatnagar, Chhavi; Kumari, Anita; Madhwal, Devinder; Bhatnagar, P. K.; Mathur, P. C.

    2014-10-01

    Solar cell consisting of low band gap polymer poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) as donor and cadmium selenide/zinc sulphide (CdSe/ZnS) core shell quantum dots (QDs) as an acceptor has been developed. The absorption measurements show that the absorption coefficient increases in bulk heterojunction (BHJ) structure covering broad absorption spectrum (200nm-700nm). Also, the photoluminescence (PL) of the PCDTBT:QDs film is found to decrease by an order of magnitude showing a significant transfer of electrons to the QDs. With this approach and under broadband white light with an irradiance of 8.19 mW/cm2, we have been able to achieve a power conversion efficiency (PCE) of 3.1 % with fill factor 0.42 for our typical solar cell.

  13. Impact of La{sub 2}O{sub 3} interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks deposited by atomic-layer-deposition

    SciTech Connect

    Chang, C.-Y. Takenaka, M.; Takagi, S.; Ichikawa, O.; Osada, T.; Hata, M.; Yamada, H.

    2015-08-28

    We examine the electrical properties of atomic layer deposition (ALD) La{sub 2}O{sub 3}/InGaAs and Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La{sub 2}O{sub 3}/InGaAs interface provides low interface state density (D{sub it}) with the minimum value of ∼3 × 10{sup 11} cm{sup −2} eV{sup −1}, which is attributable to the excellent La{sub 2}O{sub 3} passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La{sub 2}O{sub 3}. In order to simultaneously satisfy low D{sub it} and small hysteresis, the effectiveness of Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks with ultrathin La{sub 2}O{sub 3} interfacial layers is in addition evaluated. The reduction of the La{sub 2}O{sub 3} thickness to 0.4 nm in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, D{sub it} of the Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs interfaces becomes higher than that of the La{sub 2}O{sub 3}/InGaAs ones, attributable to the diffusion of Al{sub 2}O{sub 3} through La{sub 2}O{sub 3} into InGaAs and resulting modification of the La{sub 2}O{sub 3}/InGaAs interface structure. As a result of the effective passivation effect of La{sub 2}O{sub 3} on InGaAs, however, the Al{sub 2}O{sub 3}/10 cycle (0.4 nm) La{sub 2}O{sub 3}/InGaAs gate stacks can realize still lower D{sub it} with maintaining small hysteresis and low leakage current than the conventional Al{sub 2}O{sub 3}/InGaAs MOS interfaces.

  14. Dimensionality of InGaAs nonlinear optical response

    SciTech Connect

    Bolton, S.R. |

    1995-07-01

    In this thesis the ultrafast optical properties of a series of InGaAs samples ranging from the two to the three dimensional limit are discussed. An optical system producing 150 fs continuum centered at 1.5 microns was built. Using this system, ultrafast pump-probe and four wave mixing experiments were performed. Carrier thermalization measurements reveal that screening of the Coulomb interaction is relatively unaffected by confinement, while Pauli blocking nonlinearities at the band edge are approximately twice as strong in two dimensions as in three. Carrier cooling via phonon emission is influenced by confinement due both to the change in electron distribution function and the reduction in electron phonon coupling. Purely coherent band edge effects, as measured by the AC Stark effect and four wave mixing, are found to be dominated by the changes in excitonic structure which take place with confinement.

  15. 320×256 InGaAs solid state low-light devices

    NASA Astrophysics Data System (ADS)

    Shi, Yan-li; Lu, Qiang; Hu, Rui; Deng, Gong-rong; Chu, Zhu-jun; Li, Long; Qian, Yao-hong; Feng, Yun-xiang

    2014-11-01

    The InGaAs devices has been chosen as new candidate of solid-state low-light devices because of advantages such as wide response wavelength, high quantum efficiency, high device performance, digitalized readout, high temperature operation, high reliability and long lifetime. It has gained vital development and application in the world. 320×256 InGaAs solid-state low-light devices has been prepared and studied, the p-i-n material structure was grown by MOCVD system. The mesa device structure was chosen and fabricated by inductively coupled plasma (ICP) method. The detector chip and CMOS readout integrated circuit was bonded by flip-chip bonding. The FPAs was packaged to Dewar which temperature could be changed by temperature controller. Both performances of single element device and focal plane arrays were studied in detail. Very simple optics lens was adopted to show the imaging of 1.064μm laser spot and hand. Study results disclose feasible material growth, devices processing and high temperature operation characteristics of InGaAs devices.

  16. n/p/n Tunnel Junction InGaAs Monolithic Interconnected Module (MIM)

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Murray, Christopher S.; Fatemi, Navid S.; Weizer, Victor

    2005-01-01

    The Monolithic Interconnected Module (MIM), originally introduced at the First NREL thermophotovoltaic (TPV) conference, consists of low-bandgap indium gallium arsenide (InGaAs) photovoltaic devices, series interconnected on a common semi-insulating indium phosphide (inP) substrate. An infrared reflector is deposited on the back surface of the substrate to reflect photons, which were not absorbed in the first pass through the structure. The single largest optical loss in the current device occurs int he heavily doped p-type emitter. A new MIM design (pat.pend.) has been developed which flips the polarity of the conventional MIM cell (i.e., n/p rather than p/n), eliminating the need for the high conductivity p-type emitter. The p-type base of the cell is connected to the n-type lateral conduction layer through a thin InGaAs tunnel junction. 0.58 eV and 0.74 eV InGaAs devices have demonstrated reflectances above 90% for wavelengths beyond the bandgap (greater than 95% for unprocessed structures). Electrical measurements indicate minimal voltage drops across the tunnel junction (less than mV/junction under 1200K-blackbody illumnination) and fill factors that are above 70% at current densities (J(sub sc)) above 8 Angstroms per square centimeters for the 0.74eV devices.

  17. Electrical and Optical Performance Characteristics of p/n InGaAs Monolithic Interconnected Modules

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Jenkins, Phillip P.; Weizer, Victor G.; Hoffman, Richard W., Jr.; Murray, Christopher S.; Riley, David R.

    1997-01-01

    There has been a traditional trade-off in ThermoPhotoVoltaic (TPV) energy conversion development between system efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A Monolithic Interconnected Module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual Indium Gallium Arsenide (InGaAs) devices series-connected on a single semi-insulating Indium Phosphide (InP) substrate. The MIMs are exposed to the entire emitter output, thereby maximizing output power density. An InfraRed (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 sq cm device consisting of eight (8) series interconnected cells. MIM devices, produced from 0.74eV InGaAs, have demonstrated V(sub infinity) = 3.2 volts, J(sub sc) = 70 mA/sq cm and a fill factor of 66% under flashlamp testing. IR reflectance measurements (greater than 2 microns) of these devices indicate a reflectivity of greater than 82%. MIM devices produced from 0.55 eV InGaAs have also been demonstrated. In addition, conventional p/n InGaAs devices with record efficiencies (11.7% AM0) have been demonstrated.

  18. Site-Controlled Growth of Single InP QDs

    SciTech Connect

    Vlasov, A. S. Mintairov, A. M.; Kalyuzhnyy, N. A.; Mintairov, S. A.; Salii, R. A.; Denisyuk, A. I.; Babunts, R. A.

    2015-08-15

    The MOVPE growth of InP/GaInP quantum dots (QDs) on GaAs substrate “defects” formed by a focused beam of Ga{sup +} ions is studied. It is shown that ordered arrays of QDs with a density of 0.25 (μm){sup −2} can be obtained in the InP/GaInP system. It is demonstrated that effective luminescence can be obtained by using two QD sheets separated by a GaAs/GaInP buffer layer.

  19. Energetics of neutral Si dopants in InGaAs: An ab initio and semiempirical Tersoff model study

    NASA Astrophysics Data System (ADS)

    Lee, Cheng-Wei; Lukose, Binit; Thompson, Michael O.; Clancy, Paulette

    2015-03-01

    A roadblock in utilizing III-V semiconductors for scaled-down electronic devices is their poor dopant activation. As a first step to unravel the dopant behavior in InGaAs, we studied the tendency for dopant formation computationally using two approaches: ab initio and semiempirical methods. We studied a number of structural possibilities, such as the impact of local sites and local and global environments. We will show that the dopant we considered here, Si, has discrete preferences for certain sites and the nature of its surroundings. Substitutional defects are clearly preferred over interstitial locations. We shall show that cation ordering has an impact on dopant energetics. Critically, for large-scale simulations of dopant diffusion in InGaAs alloys, we also present a parameterization of the Abell-Tersoff semiempirical potential for pairwise interactions between silicon atoms and each of the elements constituting InGaAs. In the absence of experimental data, reference parameters for estimating the Tersoff values were obtained using ab initio pseudopotential calculations (density functional theory and generalized gradient approximations). These sets of Tersoff parameters were optimized to describe the bulk structural properties of the mostly theoretical alloys Si-As, Si-Ga, and Si-In. We demonstrate the transferability of these parameters by predicting formation energies of extrinsic point "defects" of Si on a variety of sites in ternary InGaAs alloys with different local compositional configurations, both random and ordered. Tersoff model predictions of the extrinsic "substitution energy" of a Si dopant on a cationic lattice site were found to be independent of the composition of the dopant's second nearest neighbors, but were affected by the strain induced by a local arrangement of In and Ga cationic atoms. This finding is important since common deposition processes used to create InGaAs may lead to specifically ordered patterns within the cation sublattice.

  20. Characteristics of Monolithically Integrated InGaAs Active Pixel Image Array

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Cunningham, T. J.; Pain, B.; Lange, M. J.; Olsen, G. H.

    1999-01-01

    Switching and amplifying characteristics of a newly developed monolithic InGaAs Active Pixel Imager Array are presented. The sensor array is fabricated from InGaAs material epitaxially deposited on an InP substrate.

  1. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  2. Improvement of growing of Ge QDs by the method of liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Maronchuk, I. I.; Sanikovitch, D. D.; Cherkashin, A. S.; Nitchev, H.; Dimova-Malinovska, D.

    2017-01-01

    This paper reports on improvement of the technological conditions for nano-heteroepitaxial structures (NHES) growth with Ge quantum dots (QDs) by liquid phase epitaxial (LPE) method applying impulse cooling on the substrate (ICS) The physical and mathematic modeling of the processes of growth and the analysis of the thermodynamic status has been carried out to optimize the construction of the thermal unit, the located in it graphite cassette and of the thermal conditions. For the analysis the Solid Works Flow Simulation program is applied, which has a satisfactory accuracy of calculations of heat-transfer simulation. The analysis has revealed shortcomings in the construction of the equipment. Having in mind these results the equipment is reconstructed and new different elements of the thermal block are installed. Good agreement of the experimental and calculated temperature distribution in the process of NHES with Ge QDs growing is obtained. The grown Ge QDs have improved structure with homogeneous distribution and size and depth of the Quantum Wells. The experiments carried out show good reproducibility of the growing process confirming the correctness of the mathematic modeling.

  3. SWIR InGaAs focal plane arrays in France

    NASA Astrophysics Data System (ADS)

    Rouvié, A.; Huet, O.; Hamard, S.; Truffer, J. P.; Pozzi, M.; Decobert, J.; Costard, E.; Zécri, M.; Maillart, P.; Reibel, Y.; Pécheur, A.

    2013-06-01

    SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. The study of InGaAs FPA has begun few years ago with III-VLab, gathering expertise in InGaAs material growth and imaging technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has led to put quickly on the market a 320x256 InGaAs module. The recent transfer of imagery activities from III-VLab to Sofradir allows developing new high performances products, satisfying customers' new requirements. Especially, a 640x512 InGaAs module with a pitch of 15µm is actually under development to fill the needs of low light level imaging.

  4. Photon echoes from (In,Ga)As quantum dots embedded in a Tamm-plasmon microcavity

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Poltavtsev, S. V.; Kapitonov, Yu. V.; Vondran, J.; Yakovlev, D. R.; Schneider, C.; Kamp, M.; Höfling, S.; Oulton, R.; Akimov, I. A.; Kavokin, A. V.; Bayer, M.

    2017-01-01

    We report on the coherent optical response from an ensemble of (In,Ga)As quantum dots (QDs) embedded in a planar Tamm-plasmon microcavity with a quality factor of approximately 100. Significant enhancement of the light-matter interaction is demonstrated under selective laser excitation of those quantum dots which are in resonance with the cavity mode. The enhancement is manifested through Rabi oscillations of the photon echo, demonstrating coherent control of excitons with picosecond pulses at intensity levels more than an order of magnitude smaller as compared with bare quantum dots. The decay of the photon echo transients is weakly changed by the resonator, indicating a small decrease of the coherence time T2 which we attribute to the interaction with the electron plasma in the metal layer located close (40 nm) to the QD layer. Simultaneously we see a reduction of the population lifetime T1, inferred from the stimulated photon echo, due to an enhancement of the spontaneous emission by a factor of 2, which is attributed to the Purcell effect, while nonradiative processes are negligible, as confirmed from time-resolved photoluminescence.

  5. Synthesis of CdTe QDs/single-walled aluminosilicate nanotubes hybrid compound and their antimicrobial activity on bacteria

    NASA Astrophysics Data System (ADS)

    Geraldo, Daniela A.; Arancibia-Miranda, Nicolás; Villagra, Nicolás A.; Mora, Guido C.; Arratia-Perez, Ramiro

    2012-12-01

    The use of molecular conjugates of quantum dots (nanocrystalline fluorophores) for biological purposes have received much attention due to their improved biological activity. However, relatively, little is known about the synthesis and application of aluminosilicate nanotubes decorated with quantum dots (QDs) for imaging and treatment of pathogenic bacteria. This paper describes for a first time, the use of single-walled aluminosilicate nanotubes (SWNT) (imogolite) as a one-dimensional template for the in situ growth of mercaptopropionic acid-capped CdTe QDs. This new nanohybrid hydrogel was synthesized by a simple reaction pathway and their enhanced optical properties were monitored by fluorescence and UV-Vis spectroscopy, confirming that the use of these nanotubes favors the confinement effects of net CdTe QDs. In addition, studies of FT-IR spectroscopy and transmission electron microscopy confirmed the non-covalent functionalization of SWNT. Finally, the antimicrobial activity of SWNT coated with CdTe QDs toward three opportunistic multi-resistant pathogens such as Salmonella typhimurium, Acinetobacter baumannii, and Pseudomonas aeruginosa were tested. Growth inhibition tests were conducted by exposing growing bacteria to CdTe QDs/SWNT hybrid compound showing that the new nano-structured composite is a potential antimicrobial agent for heavy metal-resistant bacteria.

  6. Molecualr-scale multicoordinating ligands for coating luminescent QDs and gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhan, Naiqian

    Colloidal semiconductor quantum dots (QDs) are inorganic nanocrystals that possess several unique photophysical properties, including tunable narrow emission and remarkable photo- and chemical stability. They have large surface area, and thus can be decorated with large numbers and a variety of molecular vectors. These properties combined offer a potentially superior alternative to traditional organic fluorophore for advanced applications in bio-imaging and bio-sensing. Herein, our effort has centered on developing a series of metal coordinating ligands with controllable structures to modify the QD surfaces and construct biocompatible nanocrystals. The ligand architecture accounts for several factors: (i) variable coordination number, (ii) nature of the hydrophilic moiety, polyethylene glycol (PEG) or zwitterion, and (iii) versatility of end-reactive groups including amine, azide, carboxylic acid and aldehyde. The ligand design is combined with a newly developed photoligation strategy to promote the dispersion of luminescent QDs in buffer media. The dissertation is organized in six chapters: In chapter 1, we provide a brief introduction of the basic photophysical properties of QDs and the synthesis history for growing high quality semiconductor nanocrystals. We also present some of the most effective methods reported to date to prepare aqueous QD dispersions, discuss the effective chemical coupling strategies for conjugating biomolecules, and review the recent literatures that have used QD-bioconjugates for imaging and sensing purposes. In Chapter 2, we describe a novel photoligation strategy to promote the transfer of luminescent QDs from hydrophobic to hydrophilic media using lipic acid (LA)-based ligands. We also discusse the experimental conditions, mechanismfor in-situ ligand exchange and the generosity of the method towards the diverse functionality while maintaining the optical properties of the nanocrystals. In chapter 3, we present the design and synthesis

  7. A Monolithically Integrated Receiver Front-End Comprising Ion-Implanted Lateral Interdigitated InGaAs Pin And Inp JFET Devices

    NASA Astrophysics Data System (ADS)

    Lee, W. S.; Kitching, S. A.; Bland, S. W.

    1989-11-01

    An optical receiver front-end consisting of a lateral interdigitated InGaAs PIN photodetector integrated with an InP JFET amplifier has been fabricated by selective ion implantation. The lateral interdigitated InGaAs PlN is integrated here for the first time. The advantages of the lateral detector structure are its inherently low capacitance and the simplification of the InGaAs material growth requirement to a single layer. A quasi-planar integration approach has been developed in conjunction with a two-level metallisation interconnect scheme employing polyimide as the inter-level dielectric. An optical sensitivity of -29 dBm has been measured at 560 Mbit/s and 1.3 µm wavelength.

  8. Roles of the methyl and methylene groups of mercapto acids in the photoluminescence efficiency and carrier trapping dynamics of CdTe QDs.

    PubMed

    Chandra Sekhar, M; De, Apurba; Hossain, Sk Saddam; Samanta, Anunay

    2017-01-04

    Surface protection using an appropriate ligand is essential for controlling the size, stability and luminescence properties of the quantum dots (QDs). Though 3-mercaptopropanoic acid (3-MPA) is regarded as the most suitable protecting ligand among the mercapto acids for water soluble CdTe QDs, one receives a different picture from recent studies, which report a much higher luminescence efficiency of 3-mercaptobutyric acid (3-MBA) capped QDs compared with those capped by 3-MPA and attribute the observation to the influence of the side methyl group of mercapto acids. Herein we report the luminescence properties and carrier trapping dynamics of four different, but structurally related mercapto acid capped CdTe QDs prepared using a different method. The results show that these QDs are much more fluorescent than those prepared directly in an aqueous environment and surprisingly, no enhanced luminescence for the QDs capped by mercapto acids containing a side methyl group is observed. Ultrafast pump-probe measurements confirm these results in addition to providing insight into the carrier trapping dynamics of these systems. It is shown that our findings, which appear to be in conflict with the recent literature, can be rationalized and the exact role of the side methyl group of the mercapto acids can be understood by careful analysis of the results taking into consideration the difference in the methods of preparation of the QDs in the two cases.

  9. Preparation of water soluble L-arginine capped CdSe/ZnS QDs and their interaction with synthetic DNA: Picosecond-resolved FRET study

    SciTech Connect

    Giri, Anupam; Goswami, Nirmal; Lemmens, Peter; Pal, Samir Kumar

    2012-08-15

    Graphical abstract: Förster resonance energy transfer (FRET) studies on the interaction of water soluble arginine-capped CdSe/ZnS QDs with ethidium bromide (EB) labeled synthetic dodecamer DNA. Highlights: ► We have solubilized CdSe/ZnS QD in water replacing their TOPO ligand by L-arginine. ► We have studied arginine@QD–DNA interaction using FRET technique. ► Arginine@QDs act as energy donor and ethidium bromide-DNA acts as energy acceptor. ► We have applied a kinetic model to understand the kinetics of energy transfer. ► Circular dichroism studies revealed negligible perturbation in the DNA B-form in the arg@QD-DNA complex. -- Abstract: We have exchanged TOPO (trioctylphosphine oxide) ligand of CdSe/ZnS core/shell quantum dots (QDs) with an amino acid L-arginine (Arg) at the toluene/water interface and eventually rendered the QDs from toluene to aqueous phase. We have studied the interaction of the water soluble Arg-capped QDs (energy donor) with ethidium (EB) labeled synthetic dodecamer DNA (energy acceptor) using picoseconds resolved Förster resonance energy transfer (FRET) technique. Furthermore, we have applied a model developed by M. Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (EB-DNA) molecules around the donor QDs. Circular dichroism (CD) studies revealed a negligible perturbation in the native B-form structure of the DNA upon interaction with Arg-capped QDs. The melting and the rehybridization pathways of the DNA attached to the QDs have been monitored by the CD which reveals hydrogen bonding is the associative mechanism for interaction between Arg-capped QDs and DNA.

  10. Buffer Layer Effects on Tandem InGaAs TPV Devices

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

    2004-01-01

    Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

  11. Hole transfer dynamics from QDs to tethered ferrocene derivatives

    NASA Astrophysics Data System (ADS)

    Alivisatos, A. Paul

    Quantum dots (QDs) have shown particular promise in recent years as light absorbers in solar energy conversion schemes. However, in solution junction solar devices such as QD-sensitized solar cells and photocatalytic water splitting systems, efficiencies are often limited by hole transfer from the photoexcited QD. This process is sluggish and can lead to oxidative photocorrosion of the QD material. In order to design highly efficient nanocrystal systems with hole transfer rates that outcompete these undesirable processes, a fundamental understanding of the parameters that control these rates is imperative.We have developed a model system to study charge transfer from QDs to surface bound acceptors, to fundamentally understand the charge transfer processes for QD systems, namely electronic coupling between the donor and acceptor and the thermodynamic driving force for the hole transfer process. Specifically, we examine hole transfer from the nearly spherical CdSe-core CdS-shell QDs with photoluminescence (PL) quantum yields over 80% to ferrocene derivatives bound to the QD surface via an alkane thiol linker. In this system, we mitigate the ill-defined nonradiative charge dynamic pathways that are intrinsic to native CdSe cores, and then controllably engineer on the surface charge acceptors with well-defined oxidation potentials, spatial distribution, and quantity. By Measuring the PL lifetime decay and calibrating the number of hole acceptor ligands per QD via quantitative `H NMR, we extracted the hole transfer rate per acceptor. This rate per acceptor could be varied over four orders of magnitude by changing the coupling between donor and acceptor through modulations in the CdS shell thickness and alkane chain length of the molecule. Furthermore, owning to the large number of acceptors on the surface, we achieve systems in which ~99% of the photoexcited holes are transferred to these well-defined mediators.We further mapped the relationship between the

  12. A sensitive photoelectrochemical biosensor for AFP detection based on ZnO inverse opal electrodes with signal amplification of CdS-QDs.

    PubMed

    Xu, Ru; Jiang, Yandong; Xia, Lei; Zhang, Tianxiang; Xu, Lin; Zhang, Shuang; Liu, Dali; Song, Hongwei

    2015-12-15

    In this work, ZnO inverse opals structure (IOs) based photoelectrochemical (PEC) electrode was fabricated for alpha-fetoprotein (AFP) detection. Then, the uniform CdS quantum dots (QDs) were hydrothermally synthesized, which allowed the binding of AFP and glucose oxidase (GOD) on CdS QDs, forming the AFP-CdS-GOD composite. The competitive immunosensor of AFP and the AFP-CdS-GOD composite with anti-AFP antibodies (Ab) immobilized on FTO (fluorine-doped tin oxide) /ZnO IOs electrode was successfully applied to the detection of AFP. GOD could catalyze glucose to produce hydrogen peroxide (H2O2) acting as an electron donor to scavenge photogenerated holes in the valence band of CdS QDs, reducing the recombination of electrons and holes of CdS QDs. Also the effective energy level matching between the conduction bands of CdS QDs and ZnO widened the range of light absorption, allowing for electron injection from excited CdS QDs to ZnO upon visible light irradiation, which enhanced the photocurrent. The results show that the immunosensor of AFP possesses a large linear detection range of 0.1-500 ng/ml with a detection limit of 0.01 ng/ml. It also exhibits excellent anti-interference property and acceptable stability. This work provides a promising method for achieving excellent photoelectrochemical biosensor detection of other proteins.

  13. New developments on InGaAs focal plane array

    NASA Astrophysics Data System (ADS)

    Coussement, J.; Rouvié, A.; Oubensaid, E. H.; Huet, O.; Hamard, S.; Truffer, J.-P.; Pozzi, M.; Maillart, P.; Reibel, Y.; Costard, E.; Billon-Lanfrey, D.

    2014-06-01

    SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. The recent transfer of imagery activities from III-VLab to Sofradir provides a framework for the production activity with the manufacturing of high performances products: CACTUS320 SW and CACTUS640 SW. The developments, begun at III-Vlab towards VGA format with 15μm pixel pitch, lead today to the industrialization of a new product: SNAKE SW. On one side, the InGaAs detection array presents high performances in terms of dark current and quantum efficiency. On the other side, the low noise ROIC has different additional functionalities. Then this 640×512 @ 15μm module appears as well suited to answer the needs of a wide range of applications. In this paper, we will present the Sofradir InGaAs technology, some performances optimization and the last developments leading to SNAKE SW.

  14. Developmental toxicity of CdTe QDs in zebrafish embryos and larvae

    NASA Astrophysics Data System (ADS)

    Duan, Junchao; Yu, Yongbo; Li, Yang; Yu, Yang; Li, Yanbo; Huang, Peili; Zhou, Xianqing; Peng, Shuangqing; Sun, Zhiwei

    2013-07-01

    Quantum dots (QDs) have widely been used in biomedical and biotechnological applications. However, few studies focus on the assessing toxicity of QDs exposure in vivo. In this study, zebrafish embryos were treated with CdTe QDs (4 nm) during 4-96 h post-fertilization (hpf). Mortality, hatching rate, malformation, heart rate, and QDs uptake were detected. We also measured the larval behavior to analyze whether QDs had persistent effects on larvae locomotor activity at 144 hpf. The results showed that as the exposure dosages increased, the hatching rate and heart rate of zebrafish embryos were decreased, while the mortality increased. Exposure to QDs caused embryonic malformations, including head malformation, pericardial edema, yolk sac edema, bent spine, and yolk not depleted. QDs fluorescence was mainly localized in the intestines region. The larval behavior testing showed that the total swimming distance was decreased in a dose-dependent manner. The lowest dose (2.5 nM QDs) produced substantial hyperactivity while the higher doses groups (5, 10, and 20 nM QDs) elicited remarkably hypoactivity in dark periods. In summary, the data of this article indicated that QDs caused embryonic developmental toxicity, resulted in persistent effects on larval behavior.

  15. Enhance antimicrobial activity of ZnO nanomaterial's (QDs and NPs) and their analytical applications

    NASA Astrophysics Data System (ADS)

    Wahab, Rizwan; Khan, Farheen; Lutfullah; Singh, R. B.; Khan, Asif

    2014-08-01

    The small scale nanomaterial's such as quantum dots and nanoparticles, which have unique properties studied under varying conditions. Various techniques were used in order to best understand the structure of ZnO nanoparticles and quantum dots, which inhibit the growth of Escherichia coli bacteria under dose dependent manner. The results of obtained datas were confirmed with statistical analytical methods. The linear regressive equation data obtained from UV-visible spectra, which give satisfactory results and allows to quickly and easily calculate statistical datas such as: concentration range of analytes, mean, standard deviation, variance and standard analytical error, relative standard deviation, coefficient of correlation, variance of regression line errors in the slope and the intercept, confidence limit for the slope and the intercept. Instead, validation is an important trait measure by any methods due to near to the quality of results. The proposed method validated by specificity, precision, accuracy, limit detection and quantitation. The absorption spectra of sample solution were recorded maximum absorbance for both nanoparticles (NPs) and quantum dots (QDs) at ʎmax 600 nm, this wavelength was suitable and selected for all operational analytical measurements. The size and shape of the prepared NPs and QDs were examined with sophisticated instruments such as FESEM and TEM, whereas crystallinity of the prepared materials was analyzed with X-ray diffraction pattern (XRD).

  16. Analysis of Carrier Recombination Processes in 0.6 eV InGaAs Epitaxial Materials for Thermophotovoltaic Devices

    SciTech Connect

    D Donetsky; F Newman; M Dashiell

    2006-10-30

    Minority carrier lifetime was measured by time-resolved photoluminescence (TRPL) method in sets of p-type and n-type InGaAs double heterostructures (DH) moderately doped with Zn and Te, respectively. Contributions of the radiative and non-radiative recombination terms were separated by fitting experimental data to temperature dependences of the radiative term. The latter was modeled with measured fundamental absorption spectrum and the temperature dependence of the photon recycling effect was taken into account. Different temperature dependences of radiative terms for electron and hole materials were obtained. It was concluded that in 0.6 eV Te-doped InGaAs structures the radiative recombination controls the hole lifetime at liquid nitrogen temperatures, while Auger recombination dominates at room and above room temperatures. In similar 0.6 eV InGaAs with Zn-doped active regions Shockley-Read-Hall (SRH) recombination was found dominant in a wide temperature range from liquid nitrogen to above-room temperatures. Rapid decrease of electron lifetime with decrease of excess carrier concentration was observed and attributed to recombination through partially-ionized deep donor centers. The obtained data allows for more adequate modeling of the performance and design optimization of narrow-gap photonic devices based on InGaAs Indium-rich compounds.

  17. Optical fiber amplifiers based on PbS/CdS QDs modified by polymers.

    PubMed

    Sun, Xiaolan; Xie, Libin; Zhou, Wei; Pang, Fufei; Wang, Tingyun; Kost, Alan R; An, Zesheng

    2013-04-08

    Optical fiber amplifiers based on PbS/CdS semiconductor quantum dots (QDs) modified by an amphiphilic polymer were demonstrated. Well-defined QDs and an amphiphilic copolymer were first prepared and the amphiphilic copolymer was then used to disperse the QDs into silica sol to allow uniform and reproducible incorporation of QDs into the silica coating of the optical fibers. QD-doped silica sol was deposited on the fusion tapered fiber coupler via dip-coating. A 1550 nm semiconductor light emitting diode as the signal source and a 980 nm laser diode as the pump source were injected into the fiber coupler simultaneously. Through evanescent wave excitation, a signal gain as high as 8 dB was obtained within the wavelength range between 1450 and 1650 nm. In addition, the optical fiber amplifiers based on PbS/CdS QDs showed enhanced thermal stability when compared to amplifiers based on PbS QDs.

  18. Functionalized CdSe/ZnS QDs for the detection of nitroaromatic or RDX explosives.

    PubMed

    Freeman, Ronit; Finder, Tali; Bahshi, Lily; Gill, Ron; Willner, Itamar

    2012-12-18

    Chemically modified CdSe/ZnS quantum dots (QDs) are used as fluorescent probes for the analysis of explosives, and specifically, the detection of trinitrotoluene (TNT) or trinitrotriazine (RDX). The QDs are functionalized with electron-donating ligands that bind nitro-containing explosives, exhibiting electron-acceptor properties, to the QD surface, via supramolecular donor-acceptor interactions leading to the quenching of the luminescence of the QDs.

  19. Negative differential resistance of InGaAs dual channel transistors

    NASA Astrophysics Data System (ADS)

    Sugaya, T.; Yamane, T.; Hori, S.; Komori, K.; Yonei, K.

    2006-05-01

    We demonstrate a new type of velocity modulation transistor (VMT) with an InGaAs dual channel structure fabricated on an InP (001) substrate. The dual channel structure consists of a high mobility 10 nm In0.53Ga0.47As quantum well, a 2 nm In0.52Al0.48As barrier layer, and a low mobility 1 nm In0.26Ga0.74As quantum well. The VMTs have a negative differential resistance (NDR) effect with a low source-drain voltage of 0.38 V. The NDR characteristics can be clearly seen in the temperature range of 50 to 220 K with a gate voltage of 5 V. The NDR mechanism is thought to be the carrier transfer from the high mobility to the low mobility channels. Three-terminal VMTs are favorable for applications to highfrequency, high-speed, and low-power consumption devices.

  20. Polariton condensation in a strain-compensated planar microcavity with InGaAs quantum wells

    SciTech Connect

    Cilibrizzi, Pasquale; Askitopoulos, Alexis Silva, Matteo; Lagoudakis, Pavlos G.; Bastiman, Faebian; Clarke, Edmund; Zajac, Joanna M.; Langbein, Wolfgang

    2014-11-10

    The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs{sub 0.98}P{sub 0.02} microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal space spectroscopic imaging under non-resonant optical excitation, we observe polariton condensation and a second threshold marking the onset of photon lasing, i.e., the transition from the strong to the weak-coupling regime. Condensation in a structure with suppressed photonic disorder is a necessary step towards the implementation of periodic lattices of interacting condensates, providing a platform for on chip quantum simulations.

  1. InGaAs communication photodiodes: from low to high power level designs

    NASA Astrophysics Data System (ADS)

    Achouche, M.

    2009-01-01

    While InGaAs absorption material has been used for various applications up to 1.6μm wavelength, specific designs for low level detection have become of main interest using high responsivity and low dark current detectors. By adding an avalanche multiplication layer to form an avalanche photodiode (APD) using the Separated Absorption and Multiplication (SAM) structure, one can take advantage of the very low noise properties of multiplication process in large bandgap Al(Ga)(In)As material to improve receiver sensitivity by >10dB. Under high power level injection, specific PIN structures have been developed to improve space charge effects as needed for power applications such as microwave analog photonic links. Specific designs to achieve simultaneously broad bandwidth, high responsivity, very high power saturation and high linearity will be discussed.

  2. Phase transfer of hydrophobic QDs for water-soluble and biocompatible nature through silanization

    SciTech Connect

    Yang, Ping; Zhou, Guangjun

    2011-12-15

    Graphical abstract: A facile and novel method has been developed for creating water-soluble and biocompatible CdSe/ZnS quantum dots with a small hydrodynamic diameter (less than 10 nm) via silanization. Highlights: Black-Right-Pointing-Pointer A facile and novel method has been developed for creating water-soluble and biocompatible CdSe/ZnS quantum dots (QDs) with a small hydrodynamic diameter (less than 10 nm). Black-Right-Pointing-Pointer The control of ligand exchange plays an important role to retain high fluorescence quantum yields. Black-Right-Pointing-Pointer The functional SiO{sub 2}-coated QDs were conjugated with immunoglobin G antibody by using biotin-streptavidin as linkers. Black-Right-Pointing-Pointer The QD phase transfer by silanization is a well-established method for generating biocompatible QDs. -- Abstract: A novel method has been developed for creating water-soluble and biocompatible CdSe/ZnS quantum dots (QDs) with a small hydrodynamic diameter (less than 10 nm). The silanization of the QDs was carried out by using partially hydrolyzed tetraethyl orthosilicate (TEOS) to replace organic ammine or tri-n-octylphosphine oxide on the surface of the QDs. The partially hydrolyzed 3-mercaptopropyltrimethoxysilane attached to the hydrolyzed TEOS layer on the QDs prevented the QDs from agglomeration when the QDs were transferred into water. The functional SiO{sub 2}-coated QDs were conjugated with immunoglobin G antibody by using biotin-streptavidin as linkers. The SiO{sub 2}-coated QDs exhibited the same absorption and photoluminescence (PL) spectra as those of initial QDs in organic solvents. The SiO{sub 2}-coated QDs preserved PL intensities, is colloidally stable over a wide pH range (pH 6-11). Because the mean diameter of amphiphilic polymer-coated QDs was almost 2 times of that of functional SiO{sub 2}-coated QDs, the QD phase transfer by silanization is a well-established method for generating biocompatible QDs.

  3. The toxicity and invasive effects of QDs on mung bean development

    NASA Astrophysics Data System (ADS)

    Zhai, Peng; Wang, Xiaomei; Wang, Ruhua; Huang, Xuan; Feng, Gang; Lin, Guimiao; Chen, Qiang; Xu, Gaixia; Chen, Danni

    2014-09-01

    Objective: Nowadays, the nanomaterials have been applied in every aspects of our life, including cosmetics, fresh-keeping, antisepsis and medicines. However, we know little about the toxic effects of nanoparticles towards plants. In this thesis, we synthesized quantum dots (QDs), and then toxicity and invasive effects of QDs for mung beans were investigated. Methods: We synthesised red CdTe QDs in water sphase with L-Cystein stabilizers, then prepared different concentration of QDs solution to cultivate mung bean plant, the radical length of mung beans was measured after four days every day, after 7 days, the distribution of QDs in mung bean plant was recorded under the microscopic. Results: The result showed the QDs inhibited the growth of mung beans, the higher the concentration of QDs was, the greater the inhibition effect was. After 7 days, the radicle average lengths of mung beans in different concentrations of QDs solution - blank 0.1μmol/L 0.2μmol/L 0.5 μmol/L 1 μmol/L - were 19.350+/- 0.427, 14.050+/- 0.879, 10.525+/- 0.554, 7.250+/- 0.522, 7.650+/- 0.229. The QDs mostly adhered onto the root surface and hairs. Conclusion: In conclusion, the QDs synthesized with L-cystein have effects on the growth of mung beans. However, it is necessary to do more experiments to confirm the mechanism of the toxicity effect of QDs on plants.

  4. GaAsSb-capped InAs QD type-II solar cell structures — improvement by composition profiling of layers surrounding QD

    NASA Astrophysics Data System (ADS)

    Hospodková, Alice; Vyskočil, Jan; Zíková, Markéta; Oswald, Jiří; Pangrác, Jiří; Petříček, Otto

    2017-02-01

    Type-II band alignment offers several advantages for proposed intermediate band solar cell structures. We focused on the quantum dot (QD) solar cell structures based on type-II InAs/GaAs QD layers capped with GaAsSb strain reducing layers. The GaAsSb strain reducing layers were prepared with or without graded Sb concentration. Strong enhancement of photocurrent was achieved by adding an InGaAs buffer layer under the type-II QD structure, thanks to improved electron extraction from QDs. For comparison, a structure with GaAs-capped InAs QDs was prepared, too. Properties of all structures are compared and the mechanism of carrier extraction or relaxation is discussed. Gradient of antimony concentration in a strain reducing layer (SRL) significantly improved resulting properties of solar cell structures. It is shown that in a multiple-QD structure with a GaAsSb SRL, electrons and holes have non-intersecting trajectories which prevents carrier recombination and improves the efficiency of solar cell structures. NextNano band structure calculations of different types of structures support our experimental results.

  5. Energy states, transport, and magnetotransport in diluted magnetic semiconductor (Ga, Mn)As with quantum well InGaAs.

    PubMed

    Shchurova, L Yu; Kulbachinskii, V A

    2011-03-01

    We investigate energy levels, thermodynamic, transport and magnetotransport properties of holes in GaAs structure with quantum well InGaAs delta-doped by C and Mn. We present self-consistent calculations for energy levels in the quantum well for different degrees of ionization of Mn impurity. The magnetoresistance of holes in the quantum well is calculated. We explain observed negative magnetoresistance by the reduction of spin-flip scattering on magnetic ions due to aligning of spins with magnetic field.

  6. One-pot microwave assisted approach for synthesis of CdSe/CdS core-shell quantum dots (QDs) and investigating optical properties

    NASA Astrophysics Data System (ADS)

    Molaei, M.; Bardsiri, F. Salari; Bahador, A. R.; Karimipour, M.

    2016-02-01

    In this work, CdSe QDs were synthesized using a microwave assisted method and chemical reaction between NaHSe, CdSO4 at the presence of TGA as capping molecule. Thereafter without CdSe extraction, CdS shell was grown subsequently around CdSe cores by a reaction based on the heat sensitivity of Na2S2O3 dissociation. Synthesized QDs were characterized by means of X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-Vis and photoluminescence (PL) spectroscopy. All of these analyzes confirmed formation of CdSe QDs and successfully growth of CdS shell on surface of CdSe to forming CdSe/CdS core-shell structure.

  7. Ab initio modeling of vacancies, antisites, and Si dopants in ordered InGaAs

    NASA Astrophysics Data System (ADS)

    Wang, Jingyang; Lukose, Binit; Thompson, Michael O.; Clancy, Paulette

    2017-01-01

    In0.53Ga0.47As, a III-V compound semiconductor with high electron mobility, is expected to bring better performance than silicon in next-generation n-type MOSFET devices. However, one major challenge to its wide scale adoption is the difficulty of obtaining high enough dopant activation. For Si-doped InGaAs, the best current experimental result, involving 10 min of furnace annealing at temperatures above 700 °C, yields a free electron concentration of 1.4 ×1019 cm-3, a value that still falls short of requirement for practical applications. In this paper, we investigate the origin of low dopant activation in InGaAs by calculating formation energies for a wide variety of single point defects (Si substutionals, Si tetrahedral interstitials, vacancies, and antisites) in Si-doped In0.5Ga0.5As in a CuAu-I type crystal structure. We find that (1) a high electron concentration can only be achieved under In/Ga-poor growth conditions, while As-poor conditions inhibit n-type doping; and (2) in heavily n-doped samples, cation vacancies VIn/Ga-3 contribute the most to the compensation of excess Si donors via the Si III - VIII mechanism (III = In/Ga), thus becoming the limiting factor to higher dopant activation. Under the most favorable growth conditions for n-doping, we find the maximum carrier concentration to be 5.2 ×1018 cm-3 under thermal equilibrium, within an order of magnitude of the best experimental value.

  8. Exciton delocalization and hot hole extraction in CdSe QDs and CdSe/ZnS type 1 core shell QDs sensitized with newly synthesized thiols

    NASA Astrophysics Data System (ADS)

    Singhal, Pallavi; Ghorpade, Prashant V.; Shankarling, Ganapati S.; Singhal, Nancy; Jha, Sanjay K.; Tripathi, Raj M.; Ghosh, Hirendra N.

    2016-01-01

    The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady state absorption study suggests the exciton delocalization from CdSe QDs in the presence of the thiols. However similar features were not observed in the presence of a ZnS shell over a CdSe core, instead a broadening in the excitonic peak was observed with both APT and ADPT but not with AAT. This exciton delocalization and broadening in the excitonic peak was also confirmed by ultrafast transient absorption studies. Steady state and time resolved emission studies show hole transfer from photo-excited QDs and CSQDs to the thiols. A signature of hot hole extraction was observed in transient absorption studies which was confirmed by fluorescence upconversion studies. Both hot and thermalized hole transfer rates from CdSe QDs and CdSe/ZnS CSQDs to the thiols were determined using the fluorescence up-conversion technique. Experiments with different ZnS shell thicknesses have been carried out which suggest that hole transfer is possible till 2.5 monolayer of the ZnS shell. To the best of our knowledge we are reporting for the first time the extraction of hot holes from CdSe/ZnS type I CSQDs by a molecular adsorbate.The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady

  9. Indium out-diffusion in Al{sub 2}O{sub 3}/InGaAs stacks during anneal at different ambient conditions

    SciTech Connect

    Krylov, Igor; Winter, Roy; Ritter, Dan; Eizenberg, Moshe

    2014-06-16

    Indium out-diffusion during anneal enhances leakage currents in metal/dielectric/InGaAs gate stacks. In this work, we study the influence of ambient conditions during anneal on indium out-diffusion in Al{sub 2}O{sub 3}/InGaAs structures, prior to the gate metal deposition. Using X-ray photoemission spectroscopy and time of flight secondary ions mass spectrometry, we observed much lower indium concentrations in the Al{sub 2}O{sub 3} layer following vacuum and O{sub 2} anneals compared to forming gas or nitrogen anneals. The electrical characteristics of the Ni/Al{sub 2}O{sub 3}/InGaAs gate stack following these pre-metallization anneals as well as after subsequent post metallization anneals are presented. Possible explanations for the role of the annealing ambient conditions on indium out-diffusion are presented.

  10. Comparative optical study of epitaxial InGaAs quantum rods grown with As{sub 2} and As{sub 4} sources

    SciTech Connect

    Nedzinskas, Ramūnas; Čechavičius, Bronislovas; Kavaliauskas, Julius; Karpus, Vytautas; Valušis, Gintaras; Li, Lianhe; Khanna, Suraj P.; Linfield, Edmund H.

    2013-12-04

    Photoreflectance and photoluminescence (PL) spectroscopies are used to examine the optical properties and electronic structure of InGaAs quantum rods (QRs), embedded within InGaAs quantum well (QW). The nanostructures studied were grown by molecular beam epitaxy using As{sub 2} or As{sub 4} sources. The impact of As source on spectral features associated with interband optical transitions in the QRs and the surrounding QW are demonstrated. A red shift of the QR- and a blue shift of the QW-related optical transitions, along with a significant increase in PL intensity, have been observed if an As{sub 4} source is used. The changes in optical properties are attributed mainly to carrier confinement effects caused by variation of In content contrast between the QR material and the surrounding well.

  11. InGaAs Detectors for Miniature Infrared Instruments

    NASA Technical Reports Server (NTRS)

    Krabach, T. N.; Staller, C.; Dejewski, S.; Cunningham, T.; Herring, M.; Fossum, E. R.

    1993-01-01

    In the past year, there has been substantial impetus for NASA to consider missions that are of relatively low cost as a trade off for a higher new mission launch rate. To maintain low mission cost, these missions will be of short duration and will use smaller launch vehicles (e.g. Pegasus). Consequently, very low volume, very low mass instrument (a.k.a. miniature instrument) payloads will be required. Furthermore, it is anticipated that the number of instruments flown on a particular mission will also be highly constrained; consequently increased instrument capability will also be desired. In the case of infrared instruments, focal planes typically require cooling to ensure high performance of the detectors, especially in the case of spectrometers where high D* is necessary. In this paper, we discuss the InGaAs detector technology and its potential.

  12. Numerical study of the intrinsic recombination carriers lifetime in extended short-wavelength infrared detector materials: A comparison between InGaAs and HgCdTe

    NASA Astrophysics Data System (ADS)

    Wen, Hanqing; Bellotti, Enrico

    2016-05-01

    Intrinsic carrier lifetime due to radiative and Auger recombination in HgCdTe and strained InGaAs has been computed in the extended short-wavelength infrared (ESWIR) spectrum from 1.7 μm to 2.7 μm. Using the Green's function theory, both direct and phonon-assisted indirect Auger recombination rates as well as the radiative recombination rates are calculated for different cutoff wavelengths at 300 K with full band structures of the materials. In order to properly model the full band structures of strained InGaAs, an empirical pseudo-potential model for the alloy is fitted using the virtual crystal approximation with spin-orbit coupling included. The results showed that for InxGa1-xAs grown on InP substrate, the compressive strain, which presents in the film when the cutoff wavelength is longer than 1.7 μm, leads to decrease of Auger recombination rate and increase of radiative recombination rate. Since the dominant intrinsic recombination mechanism in this spectral range is radiative recombination, the overall intrinsic carrier lifetime in the strained InGaAs alloys is shorter than that in the relaxed material. When compared to the relaxed HgCdTe, both relaxed and compressively strained InGaAs alloys show shorter intrinsic carrier lifetime at the same cutoff wavelength in room temperature which confirms the potential advantage of HgCdTe as wide-band infrared detector material. While HgCdTe offers superior performance, ultimately the material of choice for ESWIR application will also depend on material quality and cost.

  13. Aqueous synthesis and characterization of Ni, Zn co-doped CdSe QDs

    NASA Astrophysics Data System (ADS)

    Thirugnanam, N.; Govindarajan, D.

    2016-01-01

    Ni, Zn co-doped CdSe quantum dots (QDs) were synthesized by chemical precipitation method through aqueous route. The prepared QDs were characterized by X-ray diffraction (XRD) technique, UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy and high resolution transmission electron microscopy (HRTEM). XRD technique results indicate that the prepared samples have a zinc blende cubic phase. From UV-Vis absorption spectroscopy technique, the prepared samples were blue shifted with respect to their bulk counter part due to quantum confinement effect. Among different doping ratios examined, a maximum PL emission intensity was observed for CdSe:Ni(1 %):Zn(1 %) QDs. HRTEM pictures show that the prepared QDs were in spherical shape.

  14. Suppressed blinking behavior of CdSe/CdS QDs by polymer coating

    NASA Astrophysics Data System (ADS)

    Zhang, Aidi; Bian, Yannan; Wang, Jinjie; Chen, Kuiyong; Dong, Chaoqing; Ren, Jicun

    2016-02-01

    Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are mostly focused on the introduction of an inorganic shell and organic small molecule compounds. In this study, we described a ``bottom up'' approach for the synthesis of CdSe/CdS/polymer core/shell/shell QDs via the in situ one-pot polymerization approach in order to control the blinking behavior of QDs. Three monomers (dithiothreitol (DTT), phenylenediamine (PDA), and hexamethylenediamine (HDA)) were respectively used to polymerize with hexachlorocyclotriphosphazene (HCCP), and then the polyphosphazene polymers were obtained with cyclotriphosphazene as the basic macromolecular backbone. By regulating the molar ratios of the activated comonomers, we can control the blinking behavior of CdSe/CdS/polymer QDs. Under the optimal conditions, the percentage of ``non-blinking'' CdSe/CdS/polymer QDs (the ``on time'' fraction > 99% of the overall observation time) was up to 78%. The suppression mechanism was attributed to the efficient passivation of QD surface traps by the sulfhydryl or phenyl groups in the polyphosphazene polymers.Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are

  15. Characterization of NIR InGaAs imager arrays for the JDEM SNAPmission concept

    SciTech Connect

    Seshadri, S.; Cole, M.D.; Hancock, B.; Ringold, P.; Wrigley, C.; Bonati, M.; Brown, M.G.; Schubnell, M.; Rahmer, G.; Guzman, D.; Figer,D.; Tarle, G.; Smith, R.M.; Bebek, C.

    2006-05-23

    We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP. However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future astronomy applications.

  16. The Invasion and Reproductive Toxicity of QDs-Transferrin Bioconjugates on Preantral Follicle in vitro

    PubMed Central

    Xu, Gaixia; Lin, Suxia; Law, Wing-Cheung; Roy, Indrajit; Lin, Xiaotan; Mei, Shujiang; Ma, Hanwu; Chen, Siping; Niu, Hanben; Wang, Xiaomei

    2012-01-01

    The toxicity of QD has been extensively studied over the past decade. However, the potential toxicity of QDs impedes its use for clinical research. In this work, we established a preantral follicle in vitro culture system to investigate the effects of QD-Transferrin (QDs-Tf) bioconjugates on follicle development and oocyte maturation. The preantral follicles were cultured and exposed to CdTe/ZnTe QDs-Tf bioconjugates with various concentrations and the reproductive toxicity was assessed at different time points post-treatment. The invasion of QDs-Tf for oocytes was verified by laser scanning confocal microscope. Steroid production was evaluated by immunoassay. C-band Giemsa staining was performed to observe the chromosome abnormality of oocytes. The results showed that the QDs-Tf bioconjugates could permeate into granulosa cells and theca cells, but not into oocyte. There are no obvious changes of oocyte diameter, the mucification of cumulus-oocyte-complexes and the occurrence of aneulpoidy as compared with the control group. However, delay in the antrum formation and decrease in the ratio of oocytes with first polar body were observed in QDs-Tf-treated groups. The matured oocytes with first polar body decreased significantly by ~16% (from 79.6±10 % to 63±2.9 %) when the concentration of QDs-Tf bioconjugates exceeded 2.89 nmol·L-1 (P < 0.05). Our results implied that the CdTe/ZnTe QDs-Tf bioconjugates were reproductive toxic for follicle development, and thus also revealed that this in vitro culture system of preantral follicle is a highly sensitive tool for study on the reproductive toxicity of nanoparticles. PMID:22916073

  17. Electrical and Optical Performance Characteristics of 0.74-eV p/n InGaAs Monolithic Interconnected Modules

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Jenkins, Phillip P.; Weizer, Victor G.; Hoffman, Richard W., Jr.; Jain, Raj K.; Murray, Christopher S.; Riley, David R.

    1997-01-01

    There has been a traditional trade-off in thermophotovoltaic (TPV) energy conversion development between system efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A monolithic interconnected module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual indium gallium arsenide (InGaAs) cells series-connected on a single semi-insulating indium phosphide (InP) substrate. The MIM is exposed to the entire emitter output, thereby maximizing output power density. An infrared (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 sq cm device consisting of eight (8) series interconnected cells. MIM devices, produced from 0.74-eV InGaAs, have demonstrated V(sub oc) = 3.2 volts, J(sub sc) = 70 mA/sq cm, and a fill factor of 66% under flashlamp testing. Infrared (IR) reflectance measurements (greater than 2 micron) of these devices indicate a reflectivity of greater than 82%. MIM devices produced from 0.55-eV InGaAs have also been demonstrated. In addition, conventional p/n InGaAs devices with record efficiencies (11.7% AM0) have been demonstrated.

  18. [Mechanism of quantum dots facilitating Cu2+-induced hepatic L02 cells toxicity: possible trojan-horse role of QDs].

    PubMed

    Zhao, Yu-Xia; Lin, Kuang-Fei; Zhang, Wei; Miao, You-Na; Liu, Li-Li

    2010-09-01

    Concerns regarding the potential environmental impact of quantum dots (QDs) are raised for its extensive use. Understanding the influences of QDs on original environmental pollutants induced toxicity and obtaining information about the mechanism is crucial to evaluate potential ecological hazards posed by QDs. The effects of QDs on Cu2+ induced Hepatic L02 cells toxicity and the mechanisms were investigated. IC10 value of 2 microg/mL QDs and IC10-IC50 value of 2.5-20 microg/mL of CU2+ was used in this study. Firstly Luminescence emission spectrum of QDs showed 10 nm red shifts with addition of Cu2+ provide the interaction possibility of QDs and Cu2+, the further X-ray energy dispersive spectroscopy (EDX) analysis indicated binding of Cu2+ on QDs surface. Then the intracellular Cu2+ concentrations showed increase with addition of QDs, which is accompanied by loss of cell viability and morphology changes. The mechanism was therefore assumed as interaction of QDs-Cu2+ improved the intracellular Cu2+ level then cytotoxicity. QDs seemed to serve as Trojan-horse taking much more Cu2+ into cells via cheating cell membrane recognition, which imply the possible interactions with heavy metal ions will pose a significant influence on environment and human body.

  19. Fast imaging of eccrine latent fingerprints with nontoxic Mn-doped ZnS QDs.

    PubMed

    Xu, Chaoying; Zhou, Ronghui; He, Wenwei; Wu, Lan; Wu, Peng; Hou, Xiandeng

    2014-04-01

    Fingerprints are unique characteristics of an individual, and their imaging and recognition is a top-priority task in forensic science. Fast LFP (latent fingerprint) acquirement can greatly help policemen in screening the potential criminal scenes and capturing fingerprint clues. Of the two major latent fingerprints (LFP), eccrine is expected to be more representative than sebaceous in LFP identification. Here we explored the heavy metal-free Mn-doped ZnS quantum dots (QDs) as a new imaging moiety for eccrine LFPs. To study the effects of different ligands on the LFP image quality, we prepared Mn-doped ZnS QDs with various surface-capping ligands using QDs synthesized in high-temperature organic media as starting material. The orange fluorescence emission from Mn-doped ZnS QDs clearly revealed the optical images of eccrine LFPs. Interestingly, N-acetyl-cysteine-capped Mn-doped ZnS QDs could stain the eccrine LFPs in as fast as 5 s. Meanwhile, the levels 2 and 3 substructures of the fingerprints could also be simultaneously and clearly identified. While in the absence of QDs or without rubbing and stamping the finger onto foil, no fluorescent fingerprint images could be visualized. Besides fresh fingerprint, aged (5, 10, and 50 days), incomplete eccrine LFPs could also be successfully stained with N-acetyl-cysteine-capped Mn-doped ZnS QDs, demonstrating the analytical potential of this method in real world applications. The method was also robust for imaging of eccrine LFPs on a series of nonporous surfaces, such as aluminum foil, compact discs, glass, and black plastic bags.

  20. Lattice-engineered MBE growth of high-indium mole fraction InGaAs for low cost MMICs and (1.3--1.55 {micro}m) OEICs

    SciTech Connect

    Childs, T.T.; Sokolov, V.; Sullivan, C.T.

    1997-11-01

    Using molecular beam epitaxy (MBE) and lattice engineering techniques, the feasibility of combining photonic devices applicable to the 1.3 to 1.55 {micro}m wavelength range and monolithic microwave (or mm-wave) integrated circuits (MMICs) on GaAs is demonstrated. A key factor in the MBE growth is incorporation of an InGaAs active layer having an indium arsenide mole fraction of 0.35 or greater and its lattice compatibility with the underlying semi-insulating GaAs substrate. The InGaAs layer used for the photonic devices, can also serve as the active channel for the high electron mobility transistors (HEMTs) for application in MMICs. Several examples of active and passive photonic devices grown by MBE are presented including an optical ridge waveguide, and a photodetector for detection of light in the 1.3 {micro}m range. The material structure includes a 3-layer AlGaAs/GaAs/AlGaAs optical waveguide and a thin InGaAs absorbing layer situated directly above the optical waveguide. Metal-semiconductor-metal (MSM) photodetectors are formed on the top surface of the InGaAs layer for collection of the photo-induced carriers. The optical ridge waveguide is designed for lateral incidence of the light to enhance the MSM photodetector responsivity. Initial measurements on the optical waveguide and photodetector are presented.

  1. Water-solubilizing Hydrophobic ZnAgInSe/ZnS QDs with Tumor-targeted cRGD-Sulfobetaine-PIMA-Histamine Ligands via a Self-assembly Strategy for Bio-Imaging.

    PubMed

    Deng, Tao; Peng, Yanan; Zhang, Rong; Wang, Jie; Zhang, Jie; Gu, Yue-Qing; Huang, Dechun; Deng, Dawei

    2017-03-15

    Exploring the organic-to-aqueous phase transfer of quantum dots (QDs) is significant for achieving their versatile applications in biomedαical fields. In this thematic issue, surface modification, size control and biocompatibility of QDs and QDs-based nanocomposites are core problems. Herein, the new highly fluorescent tumor-targeted QDs-clusters consisting of ZnAgInSe/ZnS (ZAISe/ZnS) QDs and sulfobetaine-PIMA-histamine (SPH) polymer with the ανβ3 integrin receptor cyclic RGD (c-RGD) were developed via ligand exchange and an accompanying self-assemble process. It was found that the structure of RGD-SPH QDs-clusters was propitious to reduce the capture of reticulo-endothelial system (RES) in virtue of external stealth ligands, and benefit to selectively accumulate at the tumor site after intravenous injection via active tumor targeting cooperated with the enhanced permeability and retention (EPR) effect. In the meantime, those clusters also recognized and enriched to cell surface when co-cultured with the ανβ3 integrin receptor overexpressed malignant cells (U87MG tumors). Based on the results, fabricating mutil-functional nanocomposites integrated with the long-term circulation and dual-targeting effects should be an interesting strategy for imaging cancer in vitro and in vivo.

  2. Visualization of hormone binding proteins in vivo based on Mn-doped CdTe QDs

    NASA Astrophysics Data System (ADS)

    Liu, Fang fei; Yu, Ying; Lin, Bi xia; Hu, Xiao gang; Cao, Yu juan; Wu, Jian zhong

    2014-10-01

    Daminozide (B9) is a growth inhibitor with important regulatory roles in plant growth and development. Locating and quantifying B9-binding proteins in plant tissues will assist in investigating the mechanism behind the signal transduction of B9. In this study, red fluorescent Mn-doped CdTe quantum dots (CdTeMn QDs) were synthesized by a high-temperature hydrothermal process. Since CdTeMn QDs possess a maximum fluorescence emission peak at 610 nm, their fluorescence properties are more stable than those of CdTe QDs. A B9-CdTeMn probe was synthesized by coupling B9 with CdTeMn QDs. The fluorescence intensity of the probe is double that of CdTeMn QDs; its fluorescence stability is also superior under different ambient conditions. The probe retains the biological activity of B9 and is unaffected by interference from the green fluorescent protein present in plants. Therefore, we used this probe to label B9-binding proteins selectively in root tissue sections of mung bean seedlings. These proteins were observed predominantly on the surfaces of the cell membranes of the cortex and epidermal parenchyma.

  3. Enhancement of QDs photoluminescence by localized surface plasmon effect of Au-NPs

    NASA Astrophysics Data System (ADS)

    Heydari, Esmaeil; Greco, Tonino; Stumpe, Joachim

    2012-04-01

    Photoluminescence enhancement of CdSe/CdS/ZnS QDs by localized surface plasmon resonance of large Au-NPs has been investigated. The photoluminescence of the QDs with an emission wavelength at 620 nm in a PMMA matrix is enhanced by immobilized Au-NPs. By considering the lifetime and excitation dependent photoluminescence we realized that the emission and excitation rate enhancements both contributed to the total photoluminescence enhancement. PL measurements were carried out for different sizes of Au-NPs to find out their influences on the emission of QDs. The largest enhancement is achieved by applying 80 nm Au-NPs. Silanization method gives us the opportunity easily to prepare samples with different concentrations of Au-NPs. It is revealed that increasing the concentration of the Au-NPs layer provides higher scattering cross section which contributes in PL enhancement.

  4. CdSe/ZnS core-shell QDs: Synthesis and investigating optical properties

    NASA Astrophysics Data System (ADS)

    Molaei, M.; Sarhani, F.; Bardsiri, F. Salari; Karmipour, M.

    2016-03-01

    In this work, CdSe quantum dots (QDs) were synthesized using a microwave activated reaction between NaHSe and CdSO4 in the presence of thioglycolic acid (TGA) as capping molecule and then using a one-pot method, ZnS shell was grown subsequently around CdSe cores by a room temperature reaction based on the photo-sensitivity of Na2S2O3 dissociation. Synthesized QDs were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-visible (UV-Vis) and photoluminescence (PL) spectroscopy. All these analyses confirmed the formation of CdSe QDs and successful growth of ZnS shell around CdSe cores.

  5. Fluorescent QDs-polystyrene composite nanospheres for highly efficient and rapid protein antigen detection

    NASA Astrophysics Data System (ADS)

    Zhou, Changhua; Mao, Mao; Yuan, Hang; Shen, Huaibin; Wu, Feng; Ma, Lan; Li, Lin Song

    2013-09-01

    In this paper, high-quality carboxyl-functionalized fluorescent (red, green, and blue emitting) nanospheres (46-103 nm) consisting of hydrophobic quantum dots (QDs) and polystyrene were prepared by a miniemulsion polymerization approach. This miniemulsion polymerization approach induced a homogeneous distribution and high aqueous-phase transport efficiency of fluorescent QDs in composite nanospheres, which proved the success of our encoding QDs strategy. The obtained fluorescent nanospheres exhibited high stability in aqueous solution under a wide range of pH, different salt concentrations, PBS buffer, and thermal treatment at 80 °C. Based on the red emitting composite nanosphere, we performed fluorescent lateral flow immunoassay (LFIA) strips for high-sensitivity and rapid alpha-fetal protein detection. The detection limit reached 0.1 ng/mL, which was 200 times higher than commercial colloidal gold-labeled LFIA strips, and it reached similar detection level in enzyme-linked immunosorbent assay kit.

  6. Comparison of Ge, InGaAs p-n junction solar cell

    NASA Astrophysics Data System (ADS)

    Korun, M.; Navruz, T. S.

    2016-04-01

    In this paper, the effect of material parameters on the efficiency of Ge and InGaAs p-n junction solar cells which are most commonly used as the sub-cell of multi-junction solar cells are investigated and the results due to these two cells are compared. The efficiency of Ge (EG =0.67 eV) solar cell which is easy to manufacture and inexpensive in cost, is compared with the efficiency of InGaAs (EG =0.74 eV) solar cell which is coming with drawback of high production difficulties and cost. The theoretical efficiency limit of Ge and InGaAs solar cells with optimum thickness were determined by using detailed balance model under one sun AM1.5 illumination. Since the band gap values of two cells are close to each other, approximate detailed balance efficiency limits of 16% for InGaAs and 14% for Ge are obtained. When drift-diffusion model is used and the thicknesses and doping concentrations are optimized, the maximum efficiency values are calculated as 13% for InGaAs and 9% for Ge solar cell. For each solar cell external quantum efficiency curves due to wavelength are also sketched and compared.

  7. Nonradiative resonant energy transfer between PbS QDs in porous matrix

    NASA Astrophysics Data System (ADS)

    Ushakova, Elena V.; Litvin, Aleksandr P.; Parfenov, Peter S.; Fedorov, Anatoly V.; Cherevkov, Sergei A.; Baranov, Alexander V.

    2013-09-01

    Nonradiative fluorescence resonance energy transfer (FRET) between lead sulfide quantum dots (QDs) of two different sizes embedded in porous matrix is observed by a fluorescence spectroscopy. Analysis of decays of photoluminescence from QD mixture shows that energy transfer in studied systems is determined by static quenching, specific for direct contact between QD-donor and QD-acceptor in the QDs close-packed ensembles. From steady-state spectral analysis it was found that efficiency of energy transfer depends on the molar ratio QD-donor/QD-acceptor and energy transfer from the donor to the acceptor passes by several channels.

  8. High performance multi-channel MOSFET on InGaAs for RF amplifiers

    NASA Astrophysics Data System (ADS)

    Adhikari, Manoj Singh; Singh, Yashvir

    2017-02-01

    In this paper, we propose a multi-channel MOSFET (MC-MOSFET) on In0.53Ga0.47As for the first time by utilising trenches in the conventional planar MOSFET (CP-MOSFET) for RF amplifier applications. The proposed multi-channel MOSFET (MC-MOSFET) has two vertical-gates placed in trenches creating multiple channels in p-body for parallel conduction of drain current. High-k Al2O3 having thickness of 2 nm is used as gate dielectric in the proposed device. The TaN gate electrodes are placed in two different trenches in the p-type InGaAs layer where multiple n-channels are formed. Simultaneous conduction from multiple channels enhances the drain current (ID) and gives higher transconductance (gm) leading to improvement in overall frequency response. Two-dimensional (2D) numerical simulations of both MC-MOSFET and CP-MOSFET are performed by using ATLAS device simulator and their different performance parameters are compared. The proposed multi-channel structure provides 6.79 times higher ID, 5.57 times improvement in gm, 2.5 times increase in unity current gain (ft), 15.85% higher unilateral power gain (fmax) and suppress the short-channel effects (SCEs) as compared with the CP-MOSFET.

  9. Characterization of photochemical filtration membranes in organic solvents by using sub-10nm fluorescent Cd-based QDs

    NASA Astrophysics Data System (ADS)

    Liu, Suwen; Zhang, Haizheng

    2013-04-01

    Semiconductor nanocrystals, also called quantum dots (QDs), have been proven as powerful fluorescent probes. This paper presents a new method to evaluate the retention efficiency of nanofiltration membranes using sub-10 nm fluorescent QDs in organic solvents. Two different Cd-based QDs with uniformed sizes (nominal 8 nm and 4 nm) were used as challenge particles in this study. Fluorescence spectrophotometer was used as a detector to measure the QDs concentration before and after filtration. High resolution transmission electron microscope (HRTEM) and dynamic light scattering (DLS) were employed for measuring particle size and size distribution, which revealed the QDs used in this study were with a narrow size distribution. Three different types of Entegris UPE membranes were tested by using this method. The filters were rated at 3 nm, 5 nm and 10 nm using bubble-point extrapolative methods were further confirmed by the QDs retention tests in solvents.

  10. Photoemission of reflection-mode InGaAs photocathodes after Cs,O activation and recaesiations

    NASA Astrophysics Data System (ADS)

    Yang, Mingzhu; Jin, Muchun

    2016-12-01

    In order to study the photoemission performance of InGaAs photocathodes, experiments of Cs,O activation, multiple recaesiation, and degradation are performed on a reflection-mode InGaAs photocathode. The photocurrent curves during Cs,O activation, recaesiation, and degradation are measured and analyzed. Based on the quantum efficiency formula of InGaAs photocathodes, the critical performance parameters were obtained by fitting the experimental curves. Results show that Cs-only activation results in a positive electron affinity surface and Cs,O activation leads the surface to a negative electron affinity. Recaesiations can make the degraded InGaAs photocathode recover to a good level. Meanwhile, the spectral response and life time of InGaAs photocathode become smaller and smaller as the recaesiation times increase.

  11. Multigenerational effects and DNA alterations of QDs-Indolicidin on Daphnia magna.

    PubMed

    Maselli, Valeria; Siciliano, Antonietta; Giorgio, Antonella; Falanga, Annarita; Galdiero, Stefania; Guida, Marco; Fulgione, Domenico; Galdiero, Emilia

    2017-02-24

    The complex QDs-Indolicidin (QDs-Ind) has been previously shown to be a good antimicrobial system with a low acute toxicity on Daphnia magna (D. magna). However, multigenerational effects caused by exposure to QDs-Ind and after subsequent recovery are still unknown. In this study, we performed multigenerational exposure tests and we evaluated individual fitness, population growth, DNA alteration, expression of Dhb (haemoglobin), Vtg (vitellogenin), CYP4 (cytochrome P450s CYP4 family), and CYP314 (cytochrome P450s mitochondrial family 314) genes on three generation of D. magna. Results showed that the total amount of eggs produced per female and total number of brood per female and body lengths were significantly decreased, Dhb, CYP4 were upregulated while Vtg was down-regulated except at reproduction days when it was slightly up-regulated under QDs-Ind exposure. Random Amplification of Polymorphic DNA (RAPD) method has proven to be useful to qualitative assess of DNA damage during generation and to underline modification in somatic or germinal cells. The results of the study suggest that effects of chronic exposure cannot be ignored.

  12. Indium and gallium diffusion through zirconia in the TiN/ZrO{sub 2}/InGaAs stack

    SciTech Connect

    Ceballos-Sanchez, O.; Martinez, E.; Guedj, C.; Veillerot, M.; Herrera-Gomez, A.

    2015-06-01

    Angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) was applied to the TiN/ZrO{sub 2}/InGaAs stack to assess its thermal stability. Through a robust ARXPS analysis, it was possible to observe subtle effects such as the thermally induced diffusion of substrate atomic species (In and Ga) through the dielectric layer. The detailed characterization of the film structure allowed for assessing the depth profiles of the diffused atomic species by means of the scenarios-method. Since the quantification for the amount of diffused material was done at different temperatures, it was possible to obtain an approximate value of the activation energy for the diffusion of indium through zirconia. The result is very similar to the previously reported values for indium diffusion through alumina and through hafnia.

  13. Fin width dependence on gate controllability of InGaAs channel FinFETs with regrown source/drain

    NASA Astrophysics Data System (ADS)

    Kise, Nobukazu; Kinoshita, Haruki; Yukimachi, Atsushi; Kanazawa, Toru; Miyamoto, Yasuyuki

    2016-12-01

    In this paper, we report on the structure and characteristics of an indium gallium arsenide (InGaAs) channel fin field effect transistor (FinFET) with a regrown source/drain. The fabrication process we propose is suitable for forming a channel with a high aspect ratio. In simulations, the subthreshold characteristics and drain current (Id) were improved by reducing the fin width. Following the simulations, fabricated devices showed improved gate controllability after the fin width was reduced. A short-channel device (Lch = 50 nm, Hfin = 50 nm, and Wfin = 20 nm) showed an Id of 367 μA/μm and a minimum subthreshold swing (SSmin) of 211 mV/dec at Vd = 0.5 V. The maximum-to-minimum Id ratio was 105.

  14. Surface-plasmon-polariton whispering-gallery mode analysis of the graphene monolayer coated InGaAs nanowire cavity.

    PubMed

    Zhao, Jing; Liu, Xianhe; Qiu, Weibin; Ma, Yuhui; Huang, Yixin; Wang, Jia-Xian; Qiang, Kan; Pan, Jiao-Qing

    2014-03-10

    In this article, we proposed and numerically studied the surface plasmon polariton whispering gallery mode properties of the graphene coated InGaAs nanowire cavity. The quality factor and the mode area were investigated as a function of the chemical potential, the cavity radius and the wavelength. A high cavity quality factor of 235 is predicted for a 5 nm radius cavity, accompanied by a mode area as small as3.75×10(-5)(λ(0))(2), when the chemical potential is 1.2 eV. The proposed structure offers a potential solution to high density integration of the nanophotonic devices with an ultra-compact footprint.

  15. Enhancement of spin lifetime in gate-fitted InGaAs narrow wires.

    PubMed

    Kunihashi, Yoji; Kohda, Makoto; Nitta, Junsaku

    2009-06-05

    We investigated the spin lifetime in gate-fitted InGaAs narrow wires from magnetotransport measurement. Applying positive gate bias voltage, the spin lifetimes in narrow wires became more than one order longer than those obtained from a Hall bar sample with two-dimensional electron gas. This enhancement of spin lifetime in gated wires is the first experimental evidence of dimensional confinement and resonant spin-orbit interaction effect controlled by gate bias voltage. Spin relaxation due to the cubic Dresselhaus term is negligible in the present InGaAs wires.

  16. Comparison of MOVPE grown GaAs, InGaAs and GaAsSb covering layers for different InAs/GaAs quantum dot applications

    NASA Astrophysics Data System (ADS)

    Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Hulicius, Eduard

    2017-04-01

    InAs/GaAs quantum dot (QD) heterostructures with different covering layers (CLs) prepared by MOVPE are compared in this work. The recombination energy of a structure covered only by GaAs depends nonlinearly on CL thickness. Experimental data of photoluminescence (PL) were supported by theoretical simulations. These simulations prove that the strain plays a major role in the structures. InGaAs strain reducing layer (SRL) was studied as well. Due to the strain reduction, the recombination energy is decreased, so the structure has longer PL wavelength. By theoretical simulations it was shown that for high content of In in InGaAs covering layer (approximately 45% and more), the heterostructure is type II, which would normally be unreachable for flat layers. For the structure with GaAsSb SRL, the band alignment is highly dependent on the SRL composition. The type I/type II transition occurs for approximately 15% of Sb; this value also slightly depends on the QD size. All structures were also studied by HRTEM to show different behavior of the CLs on the interface with InAs which highly influences the structure quality.

  17. Liver Toxicity of Cadmium Telluride Quantum Dots (CdTe QDs) Due to Oxidative Stress in Vitro and in Vivo

    PubMed Central

    Zhang, Ting; Hu, Yuanyuan; Tang, Meng; Kong, Lu; Ying, Jiali; Wu, Tianshu; Xue, Yuying; Pu, Yuepu

    2015-01-01

    With the applications of quantum dots (QDs) expanding, many studies have described the potential adverse effects of QDs, yet little attention has been paid to potential toxicity of QDs in the liver. The aim of this study was to investigate the effects of cadmium telluride (CdTe) QDs in mice and murine hepatoma cells alpha mouse liver 12 (AML 12). CdTe QDs administration significantly increased the level of lipid peroxides marker malondialdehyde (MDA) in the livers of treated mice. Furthermore, CdTe QDs caused cytotoxicity in AML 12 cells in a dose- and time-dependent manner, which was likely mediated through the generation of reactive oxygen species (ROS) and the induction of apoptosis. An increase in ROS generation with a concomitant increase in the gene expression of the tumor suppressor gene p53, the pro-apoptotic gene Bcl-2 and a decrease in the anti-apoptosis gene Bax, suggested that a mitochondria mediated pathway was involved in CdTe QDs’ induced apoptosis. Finally, we showed that NF-E2-related factor 2 (Nrf2) deficiency blocked induced oxidative stress to protect cells from injury induced by CdTe QDs. These findings provide insights into the regulatory mechanisms involved in the activation of Nrf2 signaling that confers protection against CdTe QDs-induced apoptosis in hepatocytes. PMID:26404244

  18. Characteristics of Monolithically Integrated InGaAs Active Pixel Imager Array

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Cunningham, T. J.; Pain, B.; Lange, M. J.; Olsen, G. H.

    2000-01-01

    Switching and amplifying characteristics of a newly developed monolithic InGaAs Active Pixel Imager Array are presented. The sensor array is fabricated from InGaAs material epitaxially deposited on an InP substrate. It consists of an InGaAs photodiode connected to InP depletion-mode junction field effect transistors (JFETs) for low leakage, low power, and fast control of circuit signal amplifying, buffering, selection, and reset. This monolithically integrated active pixel sensor configuration eliminates the need for hybridization with silicon multiplexer. In addition, the configuration allows the sensor to be front illuminated, making it sensitive to visible as well as near infrared signal radiation. Adapting the existing 1.55 micrometer fiber optical communication technology, this integration will be an ideal system of optoelectronic integration for dual band (Visible/IR) applications near room temperature, for use in atmospheric gas sensing in space, and for target identification on earth. In this paper, two different types of small 4 x 1 test arrays will be described. The effectiveness of switching and amplifying circuits will be discussed in terms of circuit effectiveness (leakage, operating frequency, and temperature) in preparation for the second phase demonstration of integrated, two-dimensional monolithic InGaAs active pixel sensor arrays for applications in transportable shipboard surveillance, night vision, and emission spectroscopy.

  19. Improved charge transportation at PbS QDs/TiO2 interface for efficient PEC hydrogen generation.

    PubMed

    Ikram, Ashi; Sahai, Sonal; Rai, Snigdha; Dass, Sahab; Shrivastav, Rohit; Satsangi, Vibha R

    2016-06-21

    The effect of lead sulfide (PbS) quantum dots (QDs) on the photoelectrochemical properties of TiO2 with a varied number of SILAR cycles has been investigated. The study has also highlighted physical processes including band alignment, charge recombination and transportation for a PbS QDs/TiO2 interface. The inclusion of PbS QDs underneath TiO2 thin film has significantly enhanced the PEC response due to a higher number of photogenerated charge carriers along with the efficient separation and facilitation of these carriers towards their respective electrodes. The uniqueness of the work lies in the high stability of the system as PbS QDs lie beneath the TiO2 thin film, compared to the commonly used QDs sensitization over metal oxide, along with a good photoresponse.

  20. Imaging surface plasmon polaritons using proximal self-assembled InGaAs quantum dots

    SciTech Connect

    Bracher, Gregor; Schraml, Konrad; Blauth, Mäx; Wierzbowski, Jakob; López, Nicolás Coca; Bichler, Max; Müller, Kai; Finley, Jonathan J.; Kaniber, Michael

    2014-07-21

    We present optical investigations of hybrid plasmonic nanosystems consisting of lithographically defined plasmonic Au-waveguides or beamsplitters on GaAs substrates coupled to proximal self-assembled InGaAs quantum dots. We designed a sample structure that enabled us to precisely tune the distance between quantum dots and the sample surface during nano-fabrication and demonstrated that non-radiative processes do not play a major role for separations down to ∼10 nm. A polarized laser beam focused on one end of the plasmonic nanostructure generates propagating surface plasmon polaritons that, in turn, create electron-hole pairs in the GaAs substrate during propagation. These free carriers are subsequently captured by the quantum dots ∼25 nm below the surface, giving rise to luminescence. The intensity of the spectrally integrated quantum dot luminescence is used to image the propagating plasmon modes. As the waveguide width reduces from 5 μm to 1 μm, we clearly observe different plasmonic modes at the remote waveguide end, enabling their direct imaging in real space. This imaging technique is applied to a plasmonic beamsplitter facilitating the determination of the splitting ratio between the two beamsplitter output ports as the interaction length L{sub i} is varied. A splitting ratio of 50:50 is observed for L{sub i}∼9±1 μm and 1 μm wide waveguides for excitation energies close to the GaAs band edge. Our experimental findings are in good agreement with mode profile and finite difference time domain simulations for both waveguides and beamsplitters.

  1. Measurement of 3-dimensional dopant distribution in InGaAs microdiscs grown selectively on Si (111)

    NASA Astrophysics Data System (ADS)

    Watanabe, Tohma; Takeuchi, Miyuki; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    The control of the dopant profile in 3-dimentional InGaAs microdiscs on Si (111) is essential for their device applications. However, such profiles can never be controlled by simply changing the supply of dopant precursors during the growth of microdiscs. This is because a variety of crystal planes, such as (111), {-110}, and irregular planes near the corners, surround a hexagonal pillar of InGaAs and the incorporation efficiency of dopant elements depends significantly on the kind of planes involved. We here observed the distributions of sulfur and zinc in p-i-n InGaAs microdiscs by both cross-sectional scanning capacitance microscopy (SCM) and secondary-ion mass spectrometry using focused ion beam (NanoSIMS). Even though the InGaAs shell was grown on the microdiscs using dimethylzinc (DMZn), no p-type region was found on the top of the microdiscs and the p-type region existed on the sidewall of the discs alone. This result suggested that the zinc incorporation efficiency on InGaAs (111) plane is much lower than that on {-110} planes. Complete encapsulation of the microdiscs with p-type region was possible by the post-diffusion of zinc during exposure to a mixture of tertiarybutylarsine (TBAs) and DMZn after the growth of InGaAs microdiscs.

  2. Growth and properties of the MOVPE GaAs/InAs/GaAsSb quantum dot structures

    NASA Astrophysics Data System (ADS)

    Hospodková, A.; Oswald, J.; Pangrác, J.; Kuldová, K.; Zíková, M.; Vyskočil, J.; Hulicius, E.

    2016-01-01

    This review paper summarizes some of results achieved during last years of our quantum dot (QD) research. We show that the QD shape (aspect ratio and elongation) significantly influences the QD photoluminescence (PL) spectrum. Magnetophotoluminescence can be used for determination of the anisotropy of QDs. While the calculated shifts in magnetic field of the energies of higher radiative transitions are found to be sensitive to the lateral elongation, the shift of the lowest transition is determined mainly by the exciton effective mass. This behavior can be used for determining both the effective mass and the elongation fairly reliably from the magnetophotoluminescence spectra displaying at least two resolved bands. Lateral shape of InAs/GaAs QDs in vertically correlated structures was also studied. We found the ways to control the QD elongation and consequently the energy difference between PL transitions by adjusting properly the spacer layer thickness. The main goal was to redshift QD PL emission towards telecommunication wavelengths of Metal Organic Vapor Phase Epitaxy prepared InAs/GaAs QDs using InGaAs or GaAsSb covering strain reducing layer (SRL). Our results proved that GaAsSb SRL improves the QD PL properties and the type I or type II band alignment can be controlled by both, GaAsSb composition and QD size. Maintaining the type I heterostructure is important for high luminescence efficiency and emission wavelength stability of QD structure. The simulation of electron structure in InAs QDs covered with GaAsSb SRL and experimental results reveal the importance of increasing QD size for obtaining a longer wavelength PL from the type I heterostructure. The type II structure of InAs/GaAs QDs covered by GaAsSb SRL with Sb content near 30% enabled us to achieve extremely long emission wavelength at 1.8 μm. The high amount of antimony in the SRL causes the preservation of QD size, and increased QD size prolongs the PL wavelength. The type II heterostructures with

  3. X ray photoelectron analysis of oxide-semiconductor interface after breakdown in Al{sub 2}O{sub 3}/InGaAs stacks

    SciTech Connect

    Shekhter, P.; Palumbo, F.; Cohen Weinfeld, K.; Eizenberg, M.

    2014-09-08

    In this work, the post-breakdown characteristics of metal gate/Al{sub 2}O{sub 3}/InGaAs structures were studied using surface analysis by x ray photoelectron spectroscopy. The results show that for dielectric breakdown under positive bias, localized filaments consisting of oxidized substrate atoms (In, Ga and As) were formed, while following breakdown under negative bias, a decrease of oxidized substrate atoms was observed. Such differences in the microstructure at the oxide-semiconductor interface after breakdown for positive and negative voltages are explained by atomic diffusion of the contact atoms into the gate dielectric in the region of the breakdown spot by the current induced electro-migration effect. These findings show a major difference between Al{sub 2}O{sub 3}/InGaAs and SiO{sub 2}/Si interfaces, opening the way to a better understanding of the breakdown characteristics of III-V complementary-metal-oxide-semiconductor technology.

  4. New InGaAs SWIR imaging solutions from III-VLab

    NASA Astrophysics Data System (ADS)

    Reverchon, J. L.; Decobert, J.; Huet, O.; Lagay, N.; Rouvie, A.; Robo, J. A.; Ni, Y.; Arion, B.; Noguier, V.; Zhu, Y. M.

    2011-11-01

    SWIR image sensors based on p-i-n photodiodes arrays present a tremendous interest in applications often requiring a high intra-scene dynamics. This paper describes a single-chip InGaAs SWIR camera with more than 120 dB intrinsic operational dynamic range with an innovative CMOS ROIC technology initially developed by New Imaging Technologies for visible CMOS camera chip. A simplified camera with on chip fixed pattern noise correction is presented. We also present the next generation of focal plane arrays (FPA) based on a VGA format of 640 x 512 pixels with a pitch of 15 μm. These FPAs are associated to a logarithmic wide dynamic range ROIC. We give the electro-optics performances and particularly the visible extension capabilities. This InGaAs VGA logarithmic single-chip camera allows a high resolution SWIR camera with minimized system complexity and low power consumption.

  5. Ultrahigh-resolution full-field optical coherence microscopy using InGaAs camera

    NASA Astrophysics Data System (ADS)

    Oh, W. Y.; Bouma, B. E.; Iftimia, N.; Yun, S. H.; Yelin, R.; Tearney, G. J.

    2006-01-01

    Full-field optical coherence microscopy (FFOCM) is an interferometric technique for obtaining wide-field microscopic images deep within scattering biological samples. FFOCM has primarily been implemented in the 0.8 μm wavelength range with silicon-based cameras, which may limit penetration when imaging human tissue. In this paper, we demonstrate FFOCM at the wavelength range of 0.9 - 1.4 μm, where optical penetration into tissue is presumably greater owing to decreased scattering. Our FFOCM system, comprising a broadband spatially incoherent light source, a Linnik interferometer, and an InGaAs area scan camera, provided a detection sensitivity of 86 dB for a 2 sec imaging time and an axial resolution of 1.9 μm in water. Images of phantoms, tissue samples, and Xenopus Laevis embryos were obtained using InGaAs and silicon camera FFOCM systems, demonstrating enhanced imaging penetration at longer wavelengths.

  6. Formation of ZnSe/Bi{sub 2}Se{sub 3} QDs by surface cation exchange and high photothermal conversion

    SciTech Connect

    Jia, Guozhi; Wang, Peng; Zhang, Yanbang; Wu, Zengna; Li, Qiang; Yao, Jianghong; Chang, Kai

    2015-08-15

    Water-dispersed core/shell structure ZnSe/Bi{sub 2}Se{sub 3} quantum dots were synthesized by ultrasonicwave-assisted cation exchange reaction. Only surface Zn ion can be replaced by Bi ion in ZnSe quantum dots, which lead to the ultrathin Bi{sub 2}Se{sub 3} shell layer formed. It is significance to find to change the crystal of QDs due to the acting of ultrasonicwave. Cation exchange mechanism and excellent photothermal conversion properties are discussed in detail.

  7. InGaAs focal plane array developments at III-V Lab

    NASA Astrophysics Data System (ADS)

    Rouvié, Anne; Reverchon, Jean-Luc; Huet, Odile; Djedidi, Anis; Robo, Jean-Alexandre; Truffer, Jean-Patrick; Bria, Toufiq; Pires, Mauricio; Decobert, Jean; Costard, Eric

    2012-06-01

    SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. For few years, III-VLab has been studying InGaAs imagery, gathering expertise in InGaAs material growth and imaging technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has lead to put quickly on the market a 320x256 InGaAs module, exhibiting high performances in terms of dark current, uniformity and quantum efficiency. In this paper, we present the last developments achieved in our laboratory, mainly focused on increasing the pixels number to VGA format associated to pixel pitch decrease (15μm) and broadening detection spectrum toward visible wavelengths. Depending on targeted applications, different Read Out Integrated Circuits (ROIC) have been used. Low noise ROIC have been developed by CEA LETI to fit the requirements of low light level imaging whereas logarithmic ROIC designed by NIT allows high dynamic imaging adapted for automotive safety.

  8. Conceptual design of wide-field focal plane with InGaAs image sensors

    NASA Astrophysics Data System (ADS)

    Komiyama, Y.; Nakaya, H.; Kashikawa, N.; Uchida, T.

    2016-08-01

    We present a conceptual design to implement wide-field focal plane assembly with InGaAs image sensors which are being tested intensively and reveled to be promising for astronomical use. InGaAs image sensors are sensitive up to 1.7 microns and would open a new window for the wide-field near-infrared (NIR) imaging survey once large format sensors are developed. The sensors are not necessarily cooled down to below 100 K, which is the case for prevailing NIR image sensors such as HgCdTe, enabling us to develop the NIR camera based on the technique developed for the CCD camera in optical wavelength. The major technical challenges to employ InGaAS image sensors for wide-field NIR camera are implementation of focal plane assembly and thermal design. In this article, we discuss these difficulties and show how we can conquer based on our experience to build Hyper Suprime-Cam, which is a wide-field imager with 116 2k4k CCDs attached to Subaru Telescope.

  9. InGaAs concentrator cells for laser power converters and tandem cells

    NASA Technical Reports Server (NTRS)

    Wojtczuk, S.; Vernon, S.; Gagnon, E.

    1993-01-01

    In(0.53)Ga(0.47)As N-on-P concentrator cells were made as part of an effort to develop 1.315 micron laser power converters. The 1.315 micron laser power conversion efficiency was estimated as 29.4 percent (at 5.57 W/cm(sup 2)) based on an 86 percent measured external quantum efficiency at 1.315 microns, and a measured open circuit voltage (484 mV), and fill-factor (67 percent) at the equivalent AM0 short-circuit photocurrent (5.07 A/cm(sup 2)). A 13.5 percent percent AMO efficiency was achieved at 89 suns and 25 C. Measured one-sun and 100-sun AMO efficiency, log I-V analysis, and quantum efficiency are presented for InGaAs cells with and without InP windows to passivate the front surface. Windowed cells performed better at concentration than windowless cells. Lattice mismatch between InGaAs epilayers and InP substrate was less than 800 ppm. Theoretical efficiency is estimated for 1.315 microns laser power converters versus the bandgap energy. Adding aluminum to InGaAs to form In(x)Al(y)Ga(1-x-y)As is presented as a way to achieve an optimal bandgap for 1.315 microns laser power conversion.

  10. The development of InGaAs short wavelength infrared focal plane arrays with high performance

    NASA Astrophysics Data System (ADS)

    Li, Xue; Gong, Haimei; Fang, Jiaxiong; shao, Xiumei; Tang, Hengjing; Huang, Songlei; Li, Tao; Huang, Zhangcheng

    2017-01-01

    High performance, various specifications InGaAs focal plane arrays(FPAs) were studied in Shanghai Institute of Technical Physics (SITP). On the one hand, the typical linear 256 × 1, 512 × 1 and 1024 × 1 FPAs were obtained for response wavelengths from 0.9 μm to 1.7 μm. The typical 320 × 256 FPAs and special sizes 512 × 128, 512 × 256 FPAs for the near infrared multi-spectral imaging were studied. The performance of InGaAs FPAs from 0.9 μm to 1.7 μm has improved enormously. The average peak detectivity, the response non-uniformity and non-operable pixel of the FPAs are superior to 3 × 1012 cm Hz1/2/W, 5% and 1% at the room temperature. On the other hand, the development of the extended InGaAs FPAs was also focused in SITP. The dark current of InGaAs detectors with the response wavelength from 1.0 μm to 2.5 μm decreases to about 10 nA/cm2 at 200 K. The dark current mechanisms for extended InGaAs detectors were studied by P/A photodiodes. The special sizes 512 × 256 FPAs has been fabricated since 2011. The average peak detectivity, the response non-uniformity and non-operable pixel of the FPAs are superior to 5 × 1011 cm Hz1/2/W, 8% and 2% at 200 K. In order to verify the performance of FPAs, the short wavelength infrared lens was used to form optical imaging system. The buildings, water, trees are sharply imaged by 320 × 256 FPAs with 0.9-1.7 μm wavelength and 512 × 1 FPAs with 0.9-2.5 μm wavelength at about hundreds of meters distance as target at daylight.

  11. Development of high-speed InGaAs linear array and camera for OCT and machine vision

    NASA Astrophysics Data System (ADS)

    Malchow, Douglas S.; Brubaker, Robert M.; Nguyen, Hai; Flynn, Kevin

    2008-02-01

    Spectral Domain Optical Coherence Tomography (SD-OCT) is a rapidly growing imaging technique for high-resolution visualization of structures within strongly scattering media. It is being used to create 2-D and 3-D images in biological tissues to measure structures in the eye, image abnormal growths in organ tissue, and to assess the health of arterial walls. The ability to image to depths of several millimeters with resolutions better than 5 microns has driven the need to maximize the image depth, while also increasing the imaging speed. Researchers are using short-wave-infrared light wavelengths from 1 to 1.6 microns to penetrate deeper in denser tissue than visible or NIR wavelengths. This, in turn, has created the need to increase the line rates of InGaAs linear array cameras by a factor of ten, while also increasing gain and reducing dead time. This paper will describe the development and characterization of a 1024 pixel linear array with 25 micron pitch and readout rate of over 45,000 lines per second and the resulting camera. This camera will also have application for machine vision inspection of hot glass globs, for sorting of fast moving agricultural materials and for quality control of pharmaceutical products.

  12. Crystal growth of compound semiconductors in a low-gravity environment (InGaAs crystals) (M-22)

    NASA Technical Reports Server (NTRS)

    Tatsumi, Masami

    1993-01-01

    Compound semiconductor crystals, such as gallium arsenide and indium phosphide crystals, have many interesting properties that silicon crystals lack, and they are expected to be used as materials for optic and/or electro-optic integrated devices. Generally speaking, alloy semiconductors, which consist of more than three elements, demonstrate new functions. For example, values of important parameters, such as lattice constant and emission wavelength, can be chosen independently. However, as it is easy for macroscopic and/or microscopic fluctuations of composition to occur in alloy semiconductor crystals, it is difficult to obtain crystals having homogeneous properties. Macroscopic change of composition in a crystal is caused by the segregation phenomenon. This phenomenon is due to a continuous change in the concentration of constituent elements at the solid-liquid interfacing during solidification. On Earth, attempts were made to obtain a crystal with homogeneous composition by maintaining a constant melt composition near the solid-liquid interface, through suppression of the convection flow of the melt by applying a magnetic field. However, the attempt was not completely successful. Convective flow does not occur in microgravity because the gravity in space is from four to six orders of magnitude less than that on Earth. In such a case, mass transfer in the melt is dominated by the diffusion phenomenon. So, if crystal growth is carried out at a rate that is higher than the rate of mass transfer due to this phenomenon, it is expected that crystals having a homogeneous composition will be obtained. In addition, it is also possible that microscopic composition fluctuations (striation) may disappear because microscopic fluctuations diminish in the absence of convection. We are going to grow a bulk-indium gallium arsenide (InGaAs) crystal using the gradient heating furnace (GHF) in the first material processing test (FMPT). The structure of the sample is shown where InGaAs

  13. Current-injection two-color lasing in a wafer-bonded coupled multilayer cavity with InGaAs multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Minami, Yasuo; Ota, Hiroto; Lu, Xiangmeng; Kumagai, Naoto; Kitada, Takahiro; Isu, Toshiro

    2017-04-01

    Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

  14. High efficiency silicon nanodisk laser based on colloidal CdSe/ZnS QDs

    PubMed Central

    Wang, Yao-Chen; Yuan, Chi-Tsu; Yang, Yi-Chun; Wu, Meng-Chyi; Tang, Jau; Shih, Min-Hsiung

    2011-01-01

    Introduction Using colloidal CdSe/ZnS quantum dots in the submicron-sized silicon disk cavity, we have developed a visible wavelength nanodisk laser that operates under extremely low threshold power at room temperature. Methods Time-resolved photoluminescence (PL) of QDs; nanodisk by e-beam lithography. Results Observation of lasing action at 594 nm wavelength for quantum dots on a nanodisk (750 nm in diameter) cavity and an ultra-low threshold of 2.8 µW. Conclusion From QD concentration dependence studies we achieved nearly sevenfold increase in spontaneous emission (SE) rate. We have achieved high efficient and high SE coupling rate in such a QD nanodisk laser. PMID:22110875

  15. Quantum dots (QDs) immobilization on metal nanowire end-facets for single photon source application

    NASA Astrophysics Data System (ADS)

    Kim, J.; Lee, B. C.; Kang, C.; Lee, S. Y.; Park, J. H.; Shin, H. J.

    2010-02-01

    We introduce a fabrication process to immobilize cadmium selenide (CdSe) Quantum Dots (QDs) on end-facets of metal nanowires, which can be possibly used as a cavity-free unidirectional single photon source with high coupling efficiency due to high Purcell factor. Nanowires were fabricated using E-beam lithography, E-beam evaporation, and lift-off process and finally covered with chemically deposited silicon dioxide (SiO2) layer. End-facets of metal nanowires were defined using wet etching process. QD immobilization was accomplished through surface modifications on both metal and QD surfaces. We immobilized thiol (-SH) functionalized 15 base pair (bp) ssDNA on Au nanowire surface to hybridize with its complimentary amine (- NH3) functionalized 15bp ssDNA and conjugated the amine functionalized 15bp ssDNA with QD. Presenting QD immobilization method showed high selectivity between metal nanowire and SiO2 surfaces.

  16. The influence of cell penetrating peptide branching on cellular uptake of QDs

    NASA Astrophysics Data System (ADS)

    Breger, Joyce; Delehanty, James; Susumu, Kimihiro; Anderson, George; Muttenhaler, Markus; Dawson, Philip; Medintz, Igor

    2016-03-01

    Semiconductor quantum dots (QDs) serve as a valuable platform for understating the intricacies of nanoparticle cellular uptake and fate for the development of theranostics. Developing novel internalization peptides that maximize cellular uptake while minimizing the amount of peptide is important to allow space on the nanoparticle for other cargo (e.g. drugs). We have designed a range of branched, dendritic internalization peptides composed of polyarginine (Arg9) branches (1 to 16 repeats) attached a dendritic wedge based on the sequence WP9G2H6. By attaching these branched dendritic peptides to QD's, we can study the influence of branching on cellular uptake as a function of time, ratio, and degree of branching.

  17. Quantum dots (QDs) based fluorescence probe for the sensitive determination of kaempferol

    NASA Astrophysics Data System (ADS)

    Tan, Xuanping; Liu, Shaopu; Shen, Yizhong; He, Youqiu; Yang, Jidong

    2014-12-01

    In this work, using the quenching of fluorescence of thioglycollic acid (TGA)-capped CdTe quantum dots (QDs), a novel method for the determination of kaempferol (KAE) has been developed. Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 552 nm against the concentration of KAE was observed in the range of 4-44 μg mL-1 with a detection limit (3σ/K) of 0.79 μg mL-1. In addition, the detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption and fluorescence (FL) spectroscopy. The method has been applied for the determination of KAE in pharmaceutical preparations with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

  18. ZnS quantum dot induced phase transitional changes and enhanced ferroelectric mesophase in QDs/FLC composites

    NASA Astrophysics Data System (ADS)

    Vimal, T.; Pandey, S.; Singh, D. P.; Gupta, S. K.; Agrahari, K.; Kumbhakar, P.; Kole, A. K.; Manohar, R.

    2017-01-01

    In the present study, we report the dielectric and electro - optical (E - O) study of ZnS quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC) material. Change in the SmC*- SmA phase transition temperature has been investigated by the thermal study. Width of SmC* phase is found to be slightly increased due to the dispersion of ZnS QDs, which has also been observed in the dielectric and E - O study of composites. Fitting of spontaneous polarization curves on the temperature scale has been done theoretically to obtain the change in SmC*- SmA phase transition temperature. A significant modification in the FLC material parameters (like spontaneous polarization, optical response time, tilt angle and rotational viscosity) has been observed after the dispersion of QDs. These modifications are the consequences of the strong dipolar interaction between the FLC molecule and QDs. Significant fastening of the optical response time for low conc. of QDs dispersed FLC composite shows its utilization in advanced display devices.

  19. Screened-exchange density functional approach to Auger recombination and impact ionization rates in InGaAs

    NASA Astrophysics Data System (ADS)

    Picozzi, Silvia; Asahi, Ryoji; Geller, Clint; Freeman, Arthur

    2004-03-01

    We present an ab-initio modeling approach for Auger recombination and impact ionization in semiconductors directed at i) quantitative rate determinations and 2) elucidating trends with respect to alloy composition, carrier concentration and temperature. We present a fully first-principles formalism (S.Picozzi, R.Asahi, C.B. Geller and A.J.Freeman, Phys.Rev.Lett. 89, 197601 (2002); Phys.Rev.B 65, 113206 (2002).), based on accurate energy bands and wave functions within the screened exchange local density approximation and the full-potential linearized augmented plane wave (FLAPW) method (E.Wimmer, H.Krakauer, M.Weinert, A.J.Freeman, Phys.Rev.B 24, 864 (1981)). Results are presented for electron- and hole-initiated impact ionization processes and Auger recombinations for p-type and n-type InGaAs. Anisotropy and composition effects in the related rates are discussed in terms of the underlying band-structures. Calculated Auger lifetimes, in general agreement with experiments, are studied for different recombination mechanisms (i.e. CCCH, CHHL, CHHS, involving conduction electrons (C), heavy- (H) and light-hole (L), spin split-off (S) band) in order to understand the dominant mechanism.

  20. Influence of nanowire density on the shape and optical properties of ternary InGaAs nanowires.

    PubMed

    Kim, Yong; Joyce, Hannah J; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Paladugu, Mohanchand; Zou, Jin; Suvorova, Alexandra A

    2006-04-01

    We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.

  1. Iron doped InGaAs: Competitive THz emitters and detectors fabricated from the same photoconductor

    NASA Astrophysics Data System (ADS)

    Globisch, B.; Dietz, R. J. B.; Kohlhaas, R. B.; Göbel, T.; Schell, M.; Alcer, D.; Semtsiv, M.; Masselink, W. T.

    2017-02-01

    Today, the optimum material systems for photoconductive emitters and receivers are different. In THz reflection measurements, this leads to complicated optics or performance compromises. We present photoconductive emitters and detectors fabricated from molecular beam epitaxy (MBE) grown iron (Fe) doped InGaAs, which are well suited for a THz time-domain spectroscopy as both emitters and detectors. As a photoconductive emitter, 75 μW ± 5 μW of radiated THz power was measured. As a detector, THz pulses with a bandwidth of up to 6 THz and a peak dynamic range of 95 dB could be detected. These results are comparable to state-of-the-art THz photoconductors, which allows for simple reflection measurements without a performance decrease. The incorporation of Fe in InGaAs during MBE growth is investigated by secondary ion mass spectroscopy, Hall, and transient differential transmission measurements. Growth temperatures close to 400 °C allow for homogeneous Fe doping concentrations up to 5 × 1020 cm-3 and result in a photoconductor with an electron lifetime of 0.3 ps, a resistivity of 2 kΩ cm, and an electron mobility higher than 900 cm2 V-1 s-1. We show that iron dopants are incorporated up to a maximum concentration of 1 × 1017 cm-3 into substitutional lattice sites. The remaining dopants are electrically inactive and form defects that are anneal-stable up to a temperature of 600 °C. The fast recombination center in Fe-doped InGaAs is an unidentified defect, representing ≈0.5% of the nominal iron concentration. The electron and hole capture cross section of this defect is determined as σ e = 3.8 × 10-14 cm2 and σ h = 5.5 × 10-15 cm2, respectively.

  2. Data on HepG2 cells changes following exposure to cadmium sulphide quantum dots (CdS QDs).

    PubMed

    Paesano, Laura; Perotti, Alessio; Buschini, Annamaria; Carubbi, Cecilia; Marmiroli, Marta; Maestri, Elena; Iannotta, Salvatore; Marmiroli, Nelson

    2017-04-01

    The data included in this paper are associated with the research article entitled "Markers for toxicity to HepG2 exposed to cadmium sulphide quantum dots; damage to mitochondria" (Paesano et al.) [1]. The article concerns the cytotoxic and genotoxic effects of CdS QDs in HepG2 cells and the mechanisms involved. In this dataset, changes in expression levels of candidate genes are reported, together with details concerning synthesis and properties of CdS QDs, additional information obtained through literature survey, measures of the mitochondrial membrane potential and the glutathione redox state.

  3. Development of a large area InGaAs APD receiver based on an impact ionization engineered detector for free-space lasercomm applications

    NASA Astrophysics Data System (ADS)

    Burris, H. R.; Ferraro, M. S.; Freeman, W. T.; Moore, C. I.; Murphy, J. L.; Rabinovich, W. S.; Smith, W. R.; Summers, L. L.; Thomas, L. M.; Vilcheck, M. J.; Clark, W. R.; Waters, W. D.

    2012-06-01

    The U.S. Naval Research Laboratory (NRL) is developing a small size, weight and power (SWaP) free space lasercomm terminal for small unmanned airborne platforms. The terminal is based on a small gimbal developed by CloudCap Technology. A receiver with a large field of view and with sensitivity sufficient to meet the program range goals is required for this terminal. An InGaAs Avalanche Photodiode (APD) with internal structures engineered to reduce excess noise and keff in high gain applications was selected as the detector. The detector is a 350 micron diameter impact ionization engineered (I2E) APD developed by Optogration, Inc. Results of development and characterization of the receiver will be presented.

  4. Room-temperature low-threshold current-injection InGaAs quantum-dot microdisk lasers with single-mode emission.

    PubMed

    Mao, Ming-Hua; Chien, Hao-Che; Hong, Jay-Zway; Cheng, Chih-Yi

    2011-07-18

    We fabricated current-injection InGaAs quantum-dot microdisk lasers with benzocyclobutene cladding in this work. The microdisk pedestal diameter is carefully designed to facilitate carrier injection and modal control. With this structure, low threshold current of 0.45 mA is achieved at room temperature from a device of 6.5 μm in diameter with single-mode emission from quantum-dot ground states. The negative characteristic temperature T0 of threshold current is observed between 80 K and 150 K. The transition temperature from negative T0 to positive T0 is 150 K which is higher than that of the edge-emitting lasers fabricated from the same wafer. This phenomenon indicates the lower loss level of our microdisk cavities. These microdisk lasers also show positive T0 significantly higher than that of the edge-emitting lasers from the same wafer.

  5. Low temperature performance of a commercially available InGaAs image sensor

    NASA Astrophysics Data System (ADS)

    Nakaya, Hidehiko; Komiyama, Yutaka; Kashikawa, Nobunari; Uchida, Tomohisa; Nagayama, Takahiro; Yoshida, Michitoshi

    2016-08-01

    We report the evaluation results of a commercially available InGaAs image sensor manufactured by Hamamatsu Photonics K. K., which has sensitivity between 0.95μm and 1.7μm at a room temperature. The sensor format was 128×128 pixels with 20 μm pitch. It was tested with our original readout electronics and cooled down to 80 K by a mechanical cooler to minimize the dark current. Although the readout noise and dark current were 200 e- and 20 e- /sec/pixel, respectively, we found no serious problems for the linearity, wavelength response, and intra-pixel response.

  6. Hydrodynamic study of terahertz three-dimensional plasma resonances in InGaAs diodes

    NASA Astrophysics Data System (ADS)

    Ziadé, Pierre; Kallassy, Ziad; Marinchio, Hugues; Sabatini, Giulio; Palermo, Christophe; Varani, Luca

    2009-11-01

    We investigate the presence of plasma resonances in InGaAs diodes under different optical excitation conditions. In particular, we study the case of diodes submitted to an optical photoexcitation presenting a beating in the terahertz frequency domain. The responses of the diodes are calculated using a hydrodynamic approach coupled to a one-dimensional Poisson solver. The results show clearly the presence of three-dimensional plasma resonances in the terahertz frequency domain. We also show that the resonances frequency and amplitude can be tuned by modifying the diode geometry and doping profile.

  7. Upconversion Nanoparticles for Security Printing and CdSe QDs for Drug Delivery Applications

    NASA Astrophysics Data System (ADS)

    Baride, Aravind

    demonstrated NIR light induced release of a target molecule, coumarin, from functionalized quantum dots. Coumarin, a model drug molecule, is released upon NIR two-photon excitation of cinnamate capped CdSe QDs. Electron transfer from the excited QD to the cinnamate ligand induces the release of coumarin. The electron transfer across the QD to the cinnamate ligand is confirmed by evaluation of uncaging activity in the cinnamate capped CdSe/ZnS core-shell QDs.

  8. Control of asymmetric strain relaxation in InGaAs grown by molecular-beam epitaxy

    SciTech Connect

    France, R.; Ptak, A. J.; Jiang, C.-S.; Ahrenkiel, S. P.

    2010-05-15

    InGaAs strain relaxation is studied by an in situ multibeam optical stress sensor (MOSS). Strain relaxation during growth of InGaAs on GaAs occurs at different thicknesses and rates along the directions perpendicular to its misfit dislocations, [110] and [110]. We show the asymmetry of relaxation between these directions in real time by aligning the MOSS laser array along [110] and [110]. This asymmetric relaxation data from the MOSS correlates with both x-ray diffraction relaxation analysis and an estimation of the misfit dislocation density from transmission electron microscopy images. Lowering the V/III ratio or raising the growth temperature lowers the thickness of the onset of dislocation formation, changes the relaxation rate, lowers the final relaxation during 2 {mu}m of growth, and shifts the initial direction of relaxation from [110] to [110]. We identify two phases of relaxation that occur at different growth thicknesses. Lowering the V/III ratio changes the relative contribution of each of these phases to the total relaxation of the epilayer.

  9. Gated Hall Effect Measurements on Selectively grown InGaAs Nanowires.

    PubMed

    Lindelöw, Fredrik Gustav; Zota, Cezar; Lind, Erik

    2017-02-23

    InGaAs nanowires is one of the promising material systems of replacing silicon in future CMOS transistors, due to its high electron mobility, in combination with the excellent electrostatic control from the tri-gate geometry. In this article, we report on gated Hall measurements on single and multiple In0.85Ga0.15As nanowires, selectively grown in a Hall bridge geometry with nanowire widths down to 50 nm and thicknesses of 10 nm. The gated nanowires can be used as junctionless transistors, which allows for a simplified device processing as no regrowth of contact layer or ion implantation is needed, which is especially beneficial as transistor dimensions are scaled down. The analysis shows that the InGaAs layer has a carrier concentration above 10^19 cm^-3, with a Hall carrier mobility of around 1000 cm^2V^-1s^-1. The gated Hall measurements reveal an increased carrier concentration as a function of applied gate voltage, with an increasing mobility for narrow nanowires but no significant effect on larger nanowires.

  10. Control of asymmetric strain relaxation in InGaAs grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    France, R.; Ptak, A. J.; Jiang, C.-S.; Ahrenkiel, S. P.

    2010-05-01

    InGaAs strain relaxation is studied by an in situ multibeam optical stress sensor (MOSS). Strain relaxation during growth of InGaAs on GaAs occurs at different thicknesses and rates along the directions perpendicular to its misfit dislocations, [110] and [11¯0]. We show the asymmetry of relaxation between these directions in real time by aligning the MOSS laser array along [110] and [11¯0]. This asymmetric relaxation data from the MOSS correlates with both x-ray diffraction relaxation analysis and an estimation of the misfit dislocation density from transmission electron microscopy images. Lowering the V/III ratio or raising the growth temperature lowers the thickness of the onset of dislocation formation, changes the relaxation rate, lowers the final relaxation during 2 μm of growth, and shifts the initial direction of relaxation from [110] to [11¯0]. We identify two phases of relaxation that occur at different growth thicknesses. Lowering the V/III ratio changes the relative contribution of each of these phases to the total relaxation of the epilayer.

  11. Imaging of the GI tract by QDs loaded heparin-deoxycholic acid (DOCA) nanoparticles.

    PubMed

    Khatun, Zehedina; Nurunnabi, Md; Cho, Kwang Jae; Lee, Yong-kyu

    2012-11-06

    This study presents an approach to deliver non invasive, near-IR imaging agent using oral delivery system. Low molecular weight heparin (LMWH)-deoxycholic acid (DOCA)/(LHD) nanoparticles formed by a self-assembly method was prepared to evaluate their physicochemical properties and oral absorption in vitro and in vivo. Near-IR QDs were prepared and loaded into LHD nanoparticles for imaging of the gastro-intestinal (GI) tract absorption. Q-LHD nanoparticles were almost spherical in shape with diameters of 194-217 nm. The size and fluorescent intensity of the Q-LHD nanoparticles were stable in 10% FBS solution and retained their fluorescent even after 5 days of incubation. Cell viability of Q-LHD nanoparticles maintained in the range of 80-95% for 24h incubation. No damage was found in tissues or organs during animal experiments. The in vivo oral absorption of Q-LHD was observed in SKH1 mice for 3h under different doses. From the results, we confirmed that Q-LHD was absorbed mostly into the ileum of small intestine containing intestinal bile acid transporter as observed in TEM and molecular imaging system. Our designed nanoparticles could be administered orally for bio-imaging and studying the bio-distribution of drug.

  12. Thermal activation of excitons in asymmetric InAs dots-in-a-well InxGa1-xAs/GaAs structures

    NASA Astrophysics Data System (ADS)

    Torchynska, T. V.; Casas Espinola, J. L.; Borkovska, L. V.; Ostapenko, S.; Dybiec, M.; Polupan, O.; Korsunska, N. O.; Stintz, A.; Eliseev, P. G.; Malloy, K. J.

    2007-01-01

    Photoluminescence, its temperature dependence, and photoluminescence excitation spectra of InAs quantum dots embedded in asymmetric InxGa1-xAs/GaAs quantum wells [dots in a well (DWELL)] have been investigated as a function of the indium content x (x=0.10-0.25) in the capping InxGa1-xAs layer. The asymmetric DWELL structures were created with the aim to investigate the influence of different barrier values at the quantum dot (QD)/quantum well interface on the photoluminescence thermal quenching process. The set of rate equations for the two stage model for the capture and thermal escape of excitons in QDs are solved to analyze the nature of thermal activation energies for the QD photoluminescence quenching process. The two stage model for exciton thermal activation was confirmed experimentally in the investigated QD structures as well. The localization of nonradiative defects in InAs /InGaAs DWELL structures is discussed on the base of comparison of theoretical and numerically calculated (fitting) results.

  13. Temperature Dependent Border Trap Response Produced by a Defective Interfacial Oxide Layer in Al2O3/InGaAs Gate Stacks.

    PubMed

    Tang, Kechao; Meng, Andrew C; Droopad, Ravi; McIntyre, Paul C

    2016-11-09

    Intentional oxidation of an As2-decapped (100) In0.57Ga0.43As substrate by additional H2O dosing during initial Al2O3 gate dielectric atomic layer deposition (ALD) increases the interface trap density (Dit), lowers the band edge photoluminescence (PL) intensity, and generates Ga-oxide detected by X-ray photoelectron spectroscopy (XPS). Aberration-corrected high resolution transmission electron microscopy (TEM) reveals formation of an amorphous interfacial layer which is distinct from the Al2O3 dielectric and which is not present without the additional H2O dosing. Observation of a temperature dependent border trap response, associated with the frequency dispersion of the accumulation capacitance and conductance of metal-oxide-semiconductor (MOS) structures, is found to be correlated with the presence of this defective interfacial layer. MOS capacitors prepared with additional H2O dosing show a notable decrease (∼20%) of accumulation dispersion over 5 kHz to 500 kHz when the measurement temperature decreases from room temperature to 77 K, while capacitors prepared with an abrupt Al2O3/InGaAs interface display little change (<2%) with temperature. Similar temperature-dependent border trap response is also observed when the (100) InGaAs surface is treated with a previously reported HCl(aq) wet cleaning procedure prior to Al2O3 ALD. These results point out the sensitivity of the temperature dependence of the border trap response in metal oxide/III-V MOS gate stacks to the presence of processing-induced interface oxide layers, which alter the dynamics of carrier trapping at defects that are not located at the semiconductor interface.

  14. Albumin-Mediated Biomineralization of Paramagnetic NIR Ag2S QDs for Tiny Tumor Bimodal Targeted Imaging in Vivo.

    PubMed

    Zhang, Jing; Hao, Guangyu; Yao, Chenfei; Yu, Jiani; Wang, Jun; Yang, Weitao; Hu, Chunhong; Zhang, Bingbo

    2016-07-06

    Bimodal imaging has captured increasing interests due to its complementary characteristics of two kinds of imaging modalities. Among the various dual-modal imaging techniques, MR/fluorescence imaging has been widely studied owing to its high 3D resolution and sensitivity. There is, however, still a strong demand to construct biocompatible MR/fluorescence contrast agents with near-infrared (NIR) fluorescent emissions and high relaxivities. In this study, BSA-DTPA(Gd) derived from bovine serum albumin (BSA) as a novel kind of biotemplate is employed for biomineralization of paramagnetic NIR Ag2S quantum dots (denoted as Ag2S@BSA-DTPA(Gd) pQDs). This synthetic strategy is found to be bioinspired, environmentally benign, and straightforward. The obtained Ag2S@BSA-DTPA(Gd) pQDs have fine sizes (ca. 6 nm) and good colloidal stability. They exhibit unabated NIR fluorescent emission (ca. 790 nm) as well as high longitudinal relaxivity (r1 = 12.6 mM(-1) s(-1)) compared to that of commercial Magnevist (r1 = 3.13 mM(-1) s(-1)). In vivo tumor-bearing MR and fluorescence imaging both demonstrate that Ag2S@BSA-DTPA(Gd) pQDs have pronounced tiny tumor targeting capability. In vitro and in vivo toxicity study show Ag2S@BSA-DTPA(Gd) pQDs are biocompatible. Also, biodistribution analysis indicates they can be cleared from body mainly via liver metabolism. This protein-mediated biomineralized Ag2S@BSA-DTPA(Gd) pQDs presents great potential as a novel bimodal imaging contrast agent for tiny tumor diagnosis.

  15. Electron-beam-induced current and cathodoluminescence characterization of InGaAs strain-balanced multiquantum well photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Tundo, Stefania; Mazzer, Massimo; Nasi, Lucia; Lazzarini, Laura; Salviati, Giancarlo; Rohr, Carsten; Abbott, Paul; Bushnell, David B.; Barnham, Keith W. J.; Clarke, Graham; Peng, Ruwen

    2003-11-01

    InxGa1-xAs/InyGa1-yAs strain-balanced quantum well cells (QWCs) have been shown to be beneficial for photovoltaic applications in particular to extend the light absorption edge of a single-junction cell toward the near infrared with a lower reduction of the open-circuit voltage compared to a single band-gap cell. The strain-balancing condition ensures that the multi-quantum well as a whole does not relax. However, if the mismatch between wells and barriers exceeds a critical limit, the structure becomes vulnerable to morphological or compositional fluctuations, which can lead to a local structural breakdown with the generation of extended defects of a completely different nature from misfit dislocations. In this work, we investigated a series of strain-balanced InGaAs QWCs grown on InP for thermophotovoltaic applications by means of electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements. Despite being electrically active, these defects appear to have a minor impact on the dark current of the cells but cause a drop of the photocurrent at relatively low forward bias voltage. The higher carrier collection efficiency revealed both by EBIC and CL at the boundaries of the defects suggests that a notch in the valence band edge limits the collection of holes generated in the MQW and the energy states, induced by the defects inside the energy gap, assist the tunneling of holes through the notch. At zero bias, the overall reduction of the collection efficiency is of the order of a few percent but the rate of recombination of photogenerated carriers increases dramatically with increasing forward-bias voltage as the junction built-in field drops more rapidly where the density of in-gap states is higher.

  16. Effect of size and composition fluctuations on the luminescent properties of ensemble of InGaAs nano-objects

    NASA Astrophysics Data System (ADS)

    Yakovliev, Artem; Holubenko, Roman

    2015-09-01

    The luminescent properties of InGaAs/GaAs heterostructures with InGaAs nanoscale objects were investigated. Multilayer heterostructures were grown using molecular beam epitaxy technique. The shapes of the photoluminescence spectra were studied in the temperature range from 10 K to 290 K. The electronic spectrum of heterosystems as well as the energy of interband transitions for InGaAs nano-objects were calculated for different sizes and InGaAs component composition. It is shown that the shape of the photoluminescence spectra is determined by the Gaussian distribution of the energy of band-to-band optical transitions between the ground states of the conduction band and valence band of nanoscale objects. The physical reason for the observed energy dispertion is the variation of sizes, heterogeneity of component composition and strain relief in the ensemble of InGaAs nano-objects. Non-monotonous temperature dependence of the width of the photoluminescence spectra indicates the existence of temperature-dependent redistribution of photoexcited charge carriers between neighbouring nanoislands having different energy of the ground states.

  17. Short wave infrared InGaAs focal plane arrays detector: the performance optimization of photosensitive element

    NASA Astrophysics Data System (ADS)

    Gao, Xin-jiang; Tang, Zun-lie; Zhang, Xiu-chuan; Chen, Yang; Jiang, Li-qun; Cheng, Hong-bing

    2009-07-01

    Significant progress has been achieved in technology of the InGaAs focal plane arrays (FPA) detector operating in short wave infrared (SWIR) last two decades. The no cryogenic cooling, low manufacturing cost, low power, high sensitivity and maneuverability features inherent of InGaAs FPA make it as a mainstream SWIR FPA in a variety of critical military, national security, aerospace, telecommunications and industrial applications. These various types of passive image sensing or active illumination image detecting systems included range-gated imaging, 3-Dimensional Ladar, covert surveillance, pulsed laser beam profiling, machine vision, semiconductor inspection, free space optical communications beam tracker, hyperspectroscopy imaging and many others. In this paper the status and perspectives of hybrid InGaAs FPA which is composed of detector array (PDA) and CMOS readout integrate circuit (ROIC) are reviewed briefly. For various low light levels applications such as starlight or night sky illumination, we have made use of the interface circuit of capacitive feedback transimpedance amplifier (CTIA) in which the integration capacitor was adjustable, therefore implements of the physical and electrical characteristics matches between detector arrays and readout intergrate circuit was achieved excellently. Taking into account the influences of InGaAs detector arrays' optoelectronic characteristics on performance of the FPA, we discussed the key parameters of the photodiode in detailed, and the tradeoff between the responsivity, dark current, impedance at zero bias and junction capacitance of photosensitive element has been made to root out the impact factors. As a result of the educed approach of the photodiode's characteristics optimizing which involve with InGaAs PDA design and process, a high performance InGaAs FPA of 30um pixel pitch and 320×256 format has been developed of which the response spectrum range over 0.9um to 1.7um, the mean peak detectivity (λ=1.55

  18. Structural and emission properties of InGaAs/GaAs quantum dots emitting at 1.3 μm

    SciTech Connect

    Goldmann, Elias Jahnke, Frank; Paul, Matthias; Kettler, Jan; Jetter, Michael; Michler, Peter; Krause, Florian F.; Müller, Knut; Mehrtens, Thorsten; Rosenauer, Andreas

    2014-10-13

    A combined experimental and theoretical study of InGaAs/GaAs quantum dots (QDs) emitting at 1.3 μm under the influence of a strain-reducing InGaAs quantum well is presented. We demonstrate a red shift of 20–40 nm observed in photoluminescence spectra due to the quantum well. The InGaAs/GaAs QDs grown by metal organic vapor phase epitaxy show a bimodal height distribution (1 nm and 5 nm) and indium concentrations up to 90%. The emission properties are explained with combined tight-binding and configuration-interaction calculations of the emission wavelengths in conjunction with high-resolution scanning transmission electron microscopy investigations of QD geometry and indium concentrations in the QDs, which directly enter the calculations. QD geometries and concentration gradients representative for the ensemble are identified.

  19. Development of a Quantum Dot, 0.6 eV InGaAs Thermophotovoltaic (TPV) Converter

    NASA Technical Reports Server (NTRS)

    Forbes, David; Sinharoy, Samar; Raffalle, Ryne; Weizer, Victor; Homann, Natalie; Valko, Thomas; Bartos,Nichole; Scheiman, David; Bailey, Sheila

    2007-01-01

    Thermophotovoltaic (TPV) power conversion has to date demonstrated conversion efficiencies exceeding 20% when coupled to a heat source. Current III-V semiconductor TPV technology makes use of planar devices with bandgaps tailored to the heat source. The efficiency can be improved further by increasing the collection efficiency through the incorporation of InAs quantum dots. The use of these dots can provide sub-gap absorption and thus improve the cell short circuit current without the normal increase in dark current associated with lowering the bandgap. We have developed self-assembled InAs quantum dots using the Stranski-Krastanov growth mode on 0.74 eV In0.53GaAs lattice-matched to InP and also on lattice-mismatched 0.6 eV In0.69GaAs grown on InP through the use of a compositionally graded InPAsx buffer structure, by metalorganic vapor phase epitaxy (MOVPE). Atomic force microscopy (AFM) measurements showed that the most reproducible dot pattern was obtained with 5 monolayers of InAs grown at 450 C. The lattice mismatch between InAs and In0.69GaAs is only 2.1%, compared to 3.2% between InAs and In0.53GaAs. The smaller mismatch results in lower strain, making dot formation somewhat more complicated, resulting in quantum dashes, rather than well defined quantum dots in the lattice-mismatched case. We have fabricated 0.6 eV InGaAs planer TPV cells with and without the quantum dashes

  20. Threshold Dose of Three Types of Quantum Dots (QDs) Induces Oxidative Stress Triggers DNA Damage and Apoptosis in Mouse Fibroblast L929 Cells.

    PubMed

    Zhang, Ting; Wang, Yiqing; Kong, Lu; Xue, Yuying; Tang, Meng

    2015-10-26

    Although it has been reported that fluorescent quantum dots (QDs) have obvious acute toxic effects in vitro, their toxic effects at low doses or threshold doses are still unknown. Therefore, we evaluated the biological histocompatibility and in vitro toxicity of three types of QDs at threshold doses. Also, we compared the toxic effects of QDs with different raw chemical compositions and sizes. The results showed that low concentrations of QDs (≤7 μg/mL) had no obvious effect on cell viability and cell membrane damage, oxidative damage, cell apoptosis or DNA damage. However, QD exposure led to a significant cytotoxicity at higher doses (≥14 μg/mL) and induced abnormal cellular morphology. In addition, when comparing the three types of QDs, 2.2 nm CdTe QDs exposure showed a significantly increased proportion of apoptotic cells and significant DNA damage, suggesting that size and composition contribute to the toxic effects of QDs. Based on these discussions, it was concluded that the concentration (7 μg/mL) may serve as a threshold level for these three types of QDs only in L929 fibroblasts, whereas high concentrations (above 14 μg/mL) may be toxic, resulting in inhibition of proliferation, induction of apoptosis and DNA damage in L929 fibroblasts.

  1. Threshold Dose of Three Types of Quantum Dots (QDs) Induces Oxidative Stress Triggers DNA Damage and Apoptosis in Mouse Fibroblast L929 Cells

    PubMed Central

    Zhang, Ting; Wang, Yiqing; Kong, Lu; Xue, Yuying; Tang, Meng

    2015-01-01

    Although it has been reported that fluorescent quantum dots (QDs) have obvious acute toxic effects in vitro, their toxic effects at low doses or threshold doses are still unknown. Therefore, we evaluated the biological histocompatibility and in vitro toxicity of three types of QDs at threshold doses. Also, we compared the toxic effects of QDs with different raw chemical compositions and sizes. The results showed that low concentrations of QDs (≤7 μg/mL) had no obvious effect on cell viability and cell membrane damage, oxidative damage, cell apoptosis or DNA damage. However, QD exposure led to a significant cytotoxicity at higher doses (≥14 μg/mL) and induced abnormal cellular morphology. In addition, when comparing the three types of QDs, 2.2 nm CdTe QDs exposure showed a significantly increased proportion of apoptotic cells and significant DNA damage, suggesting that size and composition contribute to the toxic effects of QDs. Based on these discussions, it was concluded that the concentration (7 μg/mL) may serve as a threshold level for these three types of QDs only in L929 fibroblasts, whereas high concentrations (above 14 μg/mL) may be toxic, resulting in inhibition of proliferation, induction of apoptosis and DNA damage in L929 fibroblasts. PMID:26516873

  2. S-nitrosocysteine-decorated PbS QDs/TiO2 nanotubes for enhanced production of singlet oxygen.

    PubMed

    Ratanatawanate, Chalita; Chyao, Amy; Balkus, Kenneth J

    2011-03-16

    Nitric oxide (NO) is an endogenous diatomic molecule important in regulation of numerous physiological functions. The photorelease of NO in a controlled manner can potentially be used in photodynamic therapy (PDT). We present here a method to combine S-nitrosocysteine with TiO(2) nanotube-doped PbS quantum dots (PbS QDs) as a nitric oxide-releasing vehicle to promote production of singlet oxygen. The PbS QDs with a diameter ∼3.6 nm (PbS/TNTs) were attached to the TiO(2) nanotube by using a thiolactic acid linker. S-nitrosocysteine-decorated PbS/TiO(2) nanotubes were prepared by dipping PbS/TNTs in a cysteine solution followed by nitrosylation. The results suggest that this hybrid nanomaterial is capable of photoreleasing nitric oxide and producing singlet oxygen using near-IR light.

  3. Ultrasensitive fluorescence immunoassay for detection of ochratoxin A using catalase-mediated fluorescence quenching of CdTe QDs

    NASA Astrophysics Data System (ADS)

    Huang, Xiaolin; Zhan, Shengnan; Xu, Hengyi; Meng, Xianwei; Xiong, Yonghua; Chen, Xiaoyuan

    2016-04-01

    Herein, for the first time we report an improved competitive fluorescent enzyme linked immunosorbent assay (ELISA) for the ultrasensitive detection of ochratoxin A (OTA) by using hydrogen peroxide (H2O2)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (QDs). In this immunoassay, catalase (CAT) was labeled with OTA as a competitive antigen to connect the fluorescence signals of the QDs with the concentration of the target. Through the combinatorial use of H2O2-induced fluorescence quenching of CdTe QDs as a fluorescence signal output and the ultrahigh catalytic activity of CAT to H2O2, our proposed method could be used to perform a dynamic linear detection of OTA ranging from 0.05 pg mL-1 to 10 pg mL-1. The half maximal inhibitory concentration was 0.53 pg mL-1 and the limit of detection was 0.05 pg mL-1. These values were approximately 283- and 300-folds lower than those of horseradish peroxidase (HRP)-based conventional ELISA, respectively. The reported method is accurate, highly reproducible, and specific against other mycotoxins in agricultural products as well. In summary, the developed fluorescence immunoassay based on H2O2-induced fluorescence quenching of CdTe QDs can be used for the rapid and highly sensitive detection of mycotoxins or haptens in food safety monitoring.Herein, for the first time we report an improved competitive fluorescent enzyme linked immunosorbent assay (ELISA) for the ultrasensitive detection of ochratoxin A (OTA) by using hydrogen peroxide (H2O2)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (QDs). In this immunoassay, catalase (CAT) was labeled with OTA as a competitive antigen to connect the fluorescence signals of the QDs with the concentration of the target. Through the combinatorial use of H2O2-induced fluorescence quenching of CdTe QDs as a fluorescence signal output and the ultrahigh catalytic activity of CAT to H2O2, our proposed method could be used to

  4. InGaAs PV device development for TPV power systems

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Hoffman, Richard W., Jr.; Jenkins, Phillip P.; Brinker, David J.; Scheiman, David; Lowe, Roland A.; Chubb, Donald

    1994-01-01

    Indium gallium arsenide (InGaAs) photovoltaic devices have been fabricated with bandgaps ranging from 0.75 eV to 0.60 on Indium phosphide (InP) substrates. Reported efficiencies have been as high as 11.2 percent (AMO) for the lattice matched 0.75 eV devices. The 0.75 eV cell demonstrated 14.8 percent efficiency under a 1500 K blackbody with a projected efficiency of 29.3 percent. The lattice mismatched devices (0.66 and 0.60 eV) demonstrated measured efficiencies of 8 percent and 6 percent respectively under similar conditions. Low long wavelength response and high rack currents are responsible for the poor performance of the mismatched devices. Temperature coefficients have been measured and are presented for all of the bandgaps tested.

  5. InGaAs PV Device Development for TPV Power Systems

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Hoffman, Richard W., Jr.; Jenkins, Phillip P.; Brinker, David J.; Scheiman, David; Lowe, Roland; Chubb, Donald

    1994-01-01

    lndium Gallium Arsenide (InGaAs) photovoltaic devices have been fabricated with bandgaps ranging from 0.75 eV to 0.60 eV on Indium Phosphide (InP) substrates. Reported efficiencies have been as high as 11.2% (AMO) for the lattice matched 0.75 eV devices. The 0.75 eV cell demonstrated 14.8% efficiency under a 1500 K blackbody with a projected efficiency of 29.3%. The lattice mismatched devices (0.66 and 0.60 eV) demonstrated measured efficiencies of 8% and 6% respectively under similar conditions. Low long wavelength response and high dark currents are responsible for the poor performance of the mismatched devices. Temperature coefficients have been measured and are presented for all of the bandgaps tested.

  6. TDDA technology for high spatial resolution SWIR InGaAs imaging

    NASA Astrophysics Data System (ADS)

    Jia, Jianxin; Wang, Yueming; Zhuang, Xiaoqiong; Yao, Yi; Wang, Shengwei; Zhao, Ding; Shu, Rong; Wang, Jianyu

    2016-11-01

    With the development of remote sensing technology, shortwave infrared (SWIR) imaging technology has got more and more attention because of its ability through the fog and high spatial resolution. High spatial resolution SWIR imaging often requires high frame frequency. If the frame frequency is too high, it could cause the shortage of the image's signal to noise ratio (SNR), seriously affecting image quality. In order to solve the contradiction between high spatial resolution and sensitivity, time delay and digital accumulation (TDDA) technology is proposed in this paper to improve system's SNR and image quality. A prototype of SWIR imaging system based on a large format area InGaAs detector is designed, which demonstrates TDDA technology. The experiment results indicate that TDDA technology can increase system's SNR of the square root of accumulative stage and improve image's uniformity. The results in this paper are helpful for the improvement and application of high spatial resolution SWIR imaging technology.

  7. InGaAs single photon avalanche detector with ultralow excess noise

    SciTech Connect

    Zhao Kai; Zhang, Arthur; Lo, Yu-hwa; Farr, William

    2007-08-20

    An InGaAs single photon avalanche detector capable of sub-Geiger mode (Photomultiplier-tube-like) operation is reported. The device achieves a stable gain at around 10{sup 6}. The gain fluctuation is greatly suppressed through a self-quenching effect, thus an equivalent excess noise factor as low as 1.001 is achieved. In the photon counting experiment, the device is operated in the nongated mode under a dc bias. Because of its unique characteristics of self-quenching and self-recovery, no external quenching circuit is needed. The device shows a single photon response of around 30 ns and a self-recovery time of about 300 ns.

  8. InGaAs PV Device Development for TPV Power Systems

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Hoffman, Richard W., Jr.; Jenkins, Phillip P.; Scheiman, David; Lowe, Roland; Landis, Geoffrey A.

    1994-01-01

    Indium gallium arsenide (InGaAs) photovoltaic devices have been fabricated with bandgaps ranging from 0.75 eV to 0.60 eV on Indium Phosphide (InP) substrates. Reported efficiencies have been as high as 11.2 percent (AMO) for the lattice matched 0.75 eV devices. The 0.75 eV cell demonstrated 14.8 percent efficiency under a 1500 K blackbody with a projected efficiency of 29.3 percent. The lattice mismatched devices (0.66 and 0.60 eV) demonstrated measured efficiencies of 8 percent and 6 percent respectively under similar conditions. Low long wavelength response and high dark currents are responsible for the poor performance of the mismatched devices. Temperature coefficients have been measured and are presented for all of the bandgaps tested.

  9. Hydrodynamic study of terahertz three-dimensional plasma resonances in InGaAs diodes

    NASA Astrophysics Data System (ADS)

    Ziadé, P.; Marinchio, H.; Laurent, T.; Sabatini, G.; Kallassy, Z.; Palermo, C.; Varani, L.

    2010-07-01

    Using a hydrodynamic model self-consistently coupled to a Poisson solver, we investigate the time and frequency response of InGaAs diodes excited at room temperature by an optical photoexcitation presenting a beating in the terahertz frequency domain. The analysis of the main physical quantities, such as the local electric field and the conduction current density, evidences the presence of strong resonances that are interpreted as three-dimensional plasma oscillations excited by the optical beating. By studying the influence of the geometry and doping of the diode, it is shown that, in most cases, the highly doped contacts mainly control the frequency of the plasma mode while the diode length is a crucial parameter to evidence a second resonance related to the diode active region. Moreover, the amplitude of the plasma resonances can be enhanced at high doping levels and by increasing the level of the optical photoexcitation.

  10. Carrier dynamics in InGaAs with embedded ErAs nanoislands

    SciTech Connect

    Azad, Abul K.; Prasankumar, Rohit P.; Talbayev, Diyar; Taylor, Antoinette J.; O'Hara, John F.; Averitt, Richard D.; Zide, Joshua M. O.; Lu Hong; Gossard, Arthur C.

    2008-09-22

    Using time-resolved optical-pump terahertz-probe spectroscopy, we study the ultrafast carrier dynamics in In{sub 0.53}Ga{sub 0.47}As:ErAs, a potential candidate for 1550 nm based terahertz photoconductive detectors. Material growth is performed by codepositing ErAs nanoislands with Be-compensated InGaAs on an InP:Fe substrate using molecular beam epitaxy. The material shows a rapid photoconductivity response following optical excitation. Photoexcitation with {approx}0.5 {mu}J/cm{sup 2} 800 nm femtosecond laser pulses yields a 3.2 ps carrier lifetime in optical-pump terahertz-probe experiments. We also measure the carrier lifetime using a 1550 nm femtosecond optical pump-probe system, and it is found to agree well with the terahertz measurements. These short lifetimes demonstrate significant potential for implementing terahertz systems using telecommunication based technologies.

  11. Chirped InGaAs quantum dot molecules for broadband applications

    PubMed Central

    2012-01-01

    Lateral InGaAs quantum dot molecules (QDMs) formed by partial-cap and regrowth technique exhibit two ground-state (GS) peaks controllable via the thicknesses of InAs seed quantum dots (x), GaAs cap (y), and InAs regrowth (z). By adjusting x/y/z in a stacked QDM bilayer, the GS peaks from the two layers can be offset to straddle, stagger, or join up with each other, resulting in multi-GS or broadband spectra. A non-optimized QDM bilayer with a 170-meV full-width at half-maximum is demonstrated. The temperature dependencies of the emission peak energies and intensities from the chirped QDM bilayers are well explained by Varshni's equation and thermal activation of carriers out of constituent quantum dots. PMID:22480323

  12. Vacuum packaging of InGaAs focal plane array with four-stage thermoelectric cooler

    NASA Astrophysics Data System (ADS)

    Mo, De-feng; Liu, Da-fu; Yang, Li-yi; Xu, Qin-fei; Li, Xue

    2013-09-01

    The InGaAs focal plane array (FPA) detectors, covering the near-infrared 1~2.4 μm wavelength range, have been developed for application in space-based spectroscopy of the Earth atmosphere. This paper shows an all-metal vacuum package design for area array InGaAs detector of 1024×64 pixels, and its architecture will be given. Four-stage thermoelectric cooler (TEC) is used to cool down the FPA chip. To acquire high heat dissipation for TEC's Joule-heat, tungsten copper (CuW80) and kovar (4J29) is used as motherboard and cavity material respectively which joined by brazing. The heat loss including conduction, convection and radiation is analyzed. Finite element model is established to analyze the temperature uniformity of the chip substrate which is made of aluminum nitride (AlN). The performance of The TEC with and without heat load in vacuum condition is tested. The results show that the heat load has little influence to current-voltage relationship of TEC. The temperature difference (ΔT) increases as the input current increases. A linear relationship exists between heat load and ΔT of the TEC. Theoretical analysis and calculation show that the heat loss of radiation and conduction is about 187 mW and 82 mW respectively. Considering the Joule-heat of readout circuit and the heat loss of radiation and conduction, the FPA for a 220 K operation at room temperature can be achieved. As the thickness of AlN chip substrate is thicker than 1 millimeter, the temperature difference can be less than 0.3 K.

  13. Development of high performance SWIR InGaAs focal plane array

    NASA Astrophysics Data System (ADS)

    Nagi, Richie; Bregman, Jeremy; Mizuno, Genki; Oduor, Patrick; Olah, Robert; Dutta, Achyut K.; Dhar, Nibir K.

    2015-05-01

    Banpil Photonics has developed a novel InGaAs based photodetector array for Short-Wave Infrared (SWIR) imaging, for the most demanding security, defense, and machine vision applications. These applications require low noise from both the detector and the readout integrated circuit arrays. In order to achieve high sensitivity, it is crucial to minimize the dark current generated by the photodiode array. This enables the sensor to function in extremely low light situations, which enables it to successfully exploit the benefits of the SWIR band. In addition to minimal dark current generation, it is essential to develop photodiode arrays with higher operating temperatures. This is critical for reducing the power consumption of the device, as less energy is spent in cooling down the focal plane array (in order to reduce the dark current). We at Banpil Photonics are designing, simulating, fabricating and testing SWIR InGaAs arrays, and have achieved low dark current density at room temperature. This paper describes Banpil's development of the photodetector array. We also highlight the fabrication technique used to reduce the amount of dark current generated by the photodiode array, in particular the surface leakage current. This technique involves the deposition of strongly negatively doped semiconductor material in the area between the pixels. This process reduces the number of dangling bonds present on the edges of each pixel, which prevents electrons from being swept across the surface of the pixels. This in turn drastically reduces the amount of surface leakage current at each pixel, which is a major contributor towards the total dark current. We present the optical and electrical characterization data, as well as the analysis that illustrates the dark current mechanisms. Also highlighted are the challenges and potential opportunities for further reduction of dark current, while maintaining other parameters of the photodiode array, such as size, weight, temperature

  14. Growth of InGaAs nanowires on Ge(111) by selective-area metal-organic vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshida, Akinobu; Tomioka, Katsuhiro; Ishizaka, Fumiya; Motohisa, Junichi

    2017-04-01

    We report the growth of InGaAs nanowires (NWs) on Ge(111) substrates using selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) for novel InGaAs/Ge hybrid complementary metal-oxide-semiconductor (CMOS) applications. Ge(111) substrates with periodic arrays of mask opening were prepared, and InGaAs was selectively grown on the opening region of Ge(111). A uniform array of InGaAs NWs with a diameter around 100 nm was successfully grown using appropriate preparation of the initial surfaces with an AsH3 thermal treatment and flow-rate modulation epitaxy (FME). We found that optimizing partial pressure of AsH3 and the number of FME cycles improved the yield of vertical InGaAs NWs. Line-scan profile analysis of energy dispersive X-ray (EDX) spectrometry showed that the In composition in the InGaAs NW was almost constant from the bottom to the top. Transmission electron microscope (TEM) analysis revealed that the interface between InGaAs NW and Ge had misfit dislocations, but their distance was longer than that expected from the difference in their lattice constants.

  15. Characterization of Si volume- and delta-doped InGaAs grown by molecular beam epitaxy

    SciTech Connect

    Fedoryshyn, Y.; Kaspar, P.; Jaeckel, H.; Beck, M.

    2010-05-15

    Bulk InGaAs layers were grown at 400 deg. C lattice-matched to InP semi-insulating substrates by molecular beam epitaxy. Si doping of the layers was performed by applying volume- and delta-doping techniques. The samples were characterized by capacitance-voltage, van der Pauw-Hall, secondary ion mass spectroscopy and photoluminescence measurements. Good agreement in terms of dependence of mobility and Burstein-Moss shift shift on doping concentration in samples doped by the two different techniques was obtained. Amphoteric behavior of Si was observed at doping concentrations higher than {approx}2.9x10{sup 19} cm{sup -3} in both delta- and volume-doped samples. Degradation of InGaAs crystalline quality occurred in samples with Si concentrations higher than {approx}4x10{sup 19} cm{sup -3}.

  16. Interface Defect Hydrogen Depassivation and Capacitance-Voltage Hysteresis of Al2O3/InGaAs Gate Stacks.

    PubMed

    Tang, Kechao; Palumbo, Felix Roberto; Zhang, Liangliang; Droopad, Ravi; McIntyre, Paul C

    2017-03-01

    We investigate the effects of pre- and postatomic layer deposition (ALD) defect passivation with hydrogen on the trap density and reliability of Al2O3/InGaAs gate stacks. Reliability is characterized by capacitance-voltage hysteresis measurements on samples prepared using different fabrication procedures and having different initial trap densities. Despite its beneficial capability to passivate both interface and border traps, a final forming gas (H2/N2) anneal (FGA) step is correlated with a significant hysteresis. This appears to be caused by hydrogen depassivation of defects in the gate stack under bias stress, supported by the observed bias stress-induced increase of interface trap density, and strong hydrogen isotope effects on the measured hysteresis. On the other hand, intentional air exposure of the InGaAs surface prior to Al2O3 ALD increases the initial interface trap density (Dit) but considerably lowers the hysteresis.

  17. Arsenic-Dominated Chemistry in the Acid Cleaning of InGaAs and InAlAs Surfaces

    SciTech Connect

    Sun, Y.; Pianetta, P.; Chen, P.-T.; Kobayashi, M.; Nishi, Y.; Goel, N.; Garner, M.; Tsai, W.

    2008-10-31

    The surface cleaning of InGaAs and InAlAs is studied using Synchrotron Radiation Photoelectron Spectroscopy. Thermal annealing at 400 C can not completely remove the native oxides from those surfaces. Elemental arsenic build-up is observed on both surfaces after acid treatment using HCl, HF or H{sub 2}SO{sub 4} solutions, which is similar to acid-cleaned GaAs surface. Cleaned InGaAs surface is oxide free but small amount of aluminum oxide remains on cleaned InAlAs surface. The common chemical reactions between III-As semiconductors and acid solutions are identified and are found to be dominated by arsenic chemistry.

  18. A simple device for measuring the spectral transmittance of lens used in InGaAs image intensifier apparatus

    NASA Astrophysics Data System (ADS)

    Bai, Xiaofeng; Guo, Hui; Yin, Lei; He, Yingping; Hou, Zhipeng; Miao, Zhuang; Yan, Lei

    2014-09-01

    In this article, in order to accurately measure the spectral transmittance of imaging lens used in InGaAs imaging apparatus, a simple device, which spectrum ranges from 400 nanometers to 2000 nanometers, based on double grating monochromator and self-collimating has been founded by using stable shortwave infrared radiant source, accurate double grating monochromator and telescope, stable silicon detector and cooled HgCdTe infrared detector. An imaging lens whose spectral transmittance has been known is measured on it. Comparing the test results to known data provided by manufacture, it is shown that the testing device founded in this article is competent to measure spectral transmittance of shortwave infrared imaging lens and which max relative deviation is no more than +/-2.5%. It is worthwhile for selecting InGaAs image intensifier assembly and evaluating the quality of shortwave infrared imaging lens.

  19. 15 μm pixel-pitch VGA InGaAs module for very low background applications

    NASA Astrophysics Data System (ADS)

    Rouvié, A.; Huet, O.; Reverchon, J. L.; Robo, J. A.; Truffer, J. P.; Decobert, J.; Costard, E.; Bois, P.

    2011-11-01

    Thanks to the high transmission coefficient of short infrared wavelengths in the atmosphere and specific contrasts, SWIR imaging is an attractive technology for space applications such as astronomical or earth observation. Detection module must demonstrate high uniformity, sensitivity and resolution combined with compactness to meet the needs of this application field. Image sensors based on InGaAs photodiodes arrays present very low dark currents even at ambient temperature as high quality materials can be grown on InP substrates. Besides, the suppression of InP substrate after hybridization is a way to extend the detection range towards visible wavelengths. These properties result in a new generation of sensitive, compact and multifunctional InGaAs detection modules. In this paper, we describe the performances of an uncooled VGA InGaAs module recently developed. The 640x512 array with a pitch of 15μm allows high resolution images. The excellent crystalline quality induces very low dark current densities at ambient temperature. The readout circuit is based on a capacitive trans-impedance amplifier with correlated double sampling resulting in low readout noise figure. This compact module appears as a serious alternative to the existing technologies for low light level imaging in the [0.4μm-1.7μm] spectral range.

  20. Determination of the technological growth parameters in the InAs-GaAs system for the MOCVD synthesis of “Multimodal” InAs QDs

    SciTech Connect

    Salii, R. A.; Mintairov, S. A.; Brunkov, P. N.; Nadtochiy, A. M.; Payusov, A. S.; Kalyuzhnyy, N. A.

    2015-08-15

    The specific features of growth in the InAs-GaAs system by the metal-organic chemical vapor deposition method are studied. The dependences of the In content of the InxGa{sub 1−x}As solid solution and of the InAs growth rate on the molar flow of In in a wide temperature range (480–700°C) are determined. The growth processes of InAs quantum dots (QDs) on GaAs with different surface misorientations are examined. The conditions are found in which InAs QDs are formed with a small number of defects and at a high density on a GaAs “sublayer” grown at a high rate. An epitaxial technique is developed for the synthesis of InAs QDs with multimodal size distribution and an extended photoluminescence spectrum, which can be effectively used in designing solar cells with QDs in the active region.

  1. Dually enriched Cu:CdS@ZnS QDs with both polyvinylpyrrolidone twisting and SiO2 loading for improved cell imaging.

    PubMed

    Li, Mei; Xu, Chaoying; Wu, Lan; Wu, Peng; Hou, Xiandeng

    2015-02-28

    Through harvesting of the increased Stokes shift of CdS QDs via Cu-doping, the concentration-quenching or aggregation-quenching of CdS QDs was largely alleviated. A dually-enriched strategy with both polyvinylpyrrolidone (PVP) twisting and SiO2 loading was developed for generating a highly luminescent doped-dots (d-dots) assembly for improved cell imaging.

  2. Development of hybrid organic-inorganic surface imprinted Mn-doped ZnS QDs and their application as a sensing material for target proteins.

    PubMed

    Tan, Lei; Huang, Cong; Peng, Rongfei; Tang, Youwen; Li, Weiming

    2014-11-15

    Applying molecular imprinting techniques to the surface of functionalized quantum dots (QDs) allows the preparation of molecularly imprinted polymers (MIPs) with accessible, surface exposed binding sites and excellent optical properties. This paper demonstrates a new strategy for producing such hybrid organic-inorganic imprinted Mn-doped ZnS QDs for specific recognition of bovine hemoglobin. The technique provides surface grafting imprinting in aqueous solutions using amino modified Mn-doped ZnS QDs as supports, acrylamide and methacrylic acid as functional monomers, γ-methacryloxypropyl trimethoxy silane as the grafting agent, and bovine hemoglobin as a template. The amino propyl functional monomer layer directs the selective occurrence of imprinting polymerization at the QDs surface through copolymerization of grafting agents with functional monomers, but also acts as an assistive monomer to drive the template into the formed polymer shells to create effective recognition sites. Using MIP-QDs composites as a fluorescence sensing material, trace amounts of bovine hemoglobin are signaled with high selectivity by emission intensity changes of Mn-doped ZnS QDs, which is embedded into the imprinted polymers.

  3. Electrical and Optical Gain Lever Effects in InGaAs Double Quantum Well Diode Lasers

    SciTech Connect

    Pocha, M D; Goddard, L L; Bond, T C; Nikolic, R J; Vernon, S P; Kallman, J S; Behymer, E M

    2007-01-03

    In multisection laser diodes, the amplitude or frequency modulation (AM or FM) efficiency can be improved using the gain lever effect. To study gain lever, InGaAs double quantum well (DQW) edge emitting lasers have been fabricated with integrated passive waveguides and dual sections providing a range of split ratios from 1:1 to 9:1. Both the electrical and the optical gain lever have been examined. An electrical gain lever with greater than 7 dB enhancement of AM efficiency was achieved within the range of appropriate DC biasing currents, but this gain dropped rapidly outside this range. We observed a 4 dB gain in the optical AM efficiency under non-ideal biasing conditions. This value agreed with the measured gain for the electrical AM efficiency under similar conditions. We also examined the gain lever effect under large signal modulation for digital logic switching applications. To get a useful gain lever for optical gain quenched logic, a long control section is needed to preserve the gain lever strength and a long interaction length between the input optical signal and the lasing field of the diode must be provided. The gain lever parameter space has been fully characterized and validated against numerical simulations of a semi-3D hybrid beam propagation method (BPM) model for the coupled electron-photon rate equation. We find that the optical gain lever can be treated using the electrical injection model, once the absorption in the sample is known.

  4. Extremely low nonalloyed and alloyed contact resistance using an InAs cap layer on InGaAs by molecular-beam epitaxy

    NASA Technical Reports Server (NTRS)

    Peng, C. K.; Chen, J.; Chyi, J.; Morkoc, H.

    1988-01-01

    Extremely low alloyed and nonalloyed ohmic contact resistances have been formed on n-type InAs/In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As structures grown on InP(Fe) by molecular-beam epitaxy. To insure the accuracy of the small contact resistances measured, an extended transmission line model was used to extrapolate contact resistances from test patterns with multiple gap spacings varying from 1 to 20 microns. For a 150-A-thick InAs layer doped to 2 x 10 to the 18th/cu cm and a 0.1-micron-thick InGaAs layer doped to 1 x 10 to the 18th/cu cm, a specific contact resistance of 2.6 x 10 to the -8th ohm-asterisk sq cm was measured for the nonalloyed contact, while a resistance less than 1.7 x 10 to the -8th ohm-asterisk sq cm is reported for the alloyed contact. Conventional Au-Ge/Ni/Au was used for the ohmic metal contact and alloying was performed at 500 C for 50 s in flowing H2. Using a thermionic field emission model, the barrier height at the InAs/InGaAs interface was calculated to be 20 meV.

  5. Performance of AlGaAs, GaAs and InGaAs cells after 1 MeV electron irradiation

    NASA Technical Reports Server (NTRS)

    Curtis, Henry B.; Hart, Russell E., Jr.

    1987-01-01

    Electron irradiations were made on three different types of III-V cells. AlGaAs, GaAs, and InGaAs cells with bandgaps of approximately 1.72, 1.43, and 1.1 eV, respectively, were tested. All of the cells were concentrator cells and performance data from one sun to beyond 100x AMO were taken. The total 1 MeV electron fluence was 3 times 10 to the 15th power e/square cm with data taken at several intermediate fluences. Cell performance is presented as a function of electron fluence for various concentration ratios and two different temperatures (25 and 80 C). Since these three cell types are potential candidates for the individual cells in a cascade structure, it is possible to calculate the loss in performance of cascade cells under 1 MeV irradiation. Data are presented which show the calculated performance of both series-connected and separately connected cascade cells.

  6. A novel fluorescent turn-on biosensor based on QDs@GSH-GO fluorescence resonance energy transfer for sensitive glutathione S-transferase sensing and cellular imaging.

    PubMed

    Chang, Lifang; He, Xiwen; Chen, Langxing; Zhang, Yukui

    2017-03-17

    A novel fluorescent turn-on biosensor based on fluorescence resonance energy transfer (FRET) from GSH functionalized Mn-doped ZnS QDs to graphene oxide (GO) was constructed to determine glutathione S-transferases (GSTs) in live cells and human urine. The QDs@GSH is adsorbed on the GO surface via hydrogen bonding interaction between the GSH on the surface of QDs@GSH and GO, and as a result, fluorescence quenching of the QDs@GSH takes place because of FRET. The FRET efficiency from QDs@GSH to GO was calculated to be 86.3%. However, in the presence of GSTs, the FRET process could be inhibited by the specific interaction between the GSH on the surface of QDs@GSH and GSTs, which would keep the QDs@GSH far away from the GO surface, leading to the recovery of the fluorescence. The proposed sensor exhibited high sensitivity, selectivity, and excellent specificity in the buffer, live cells and human urine for the detection of GSTs. Under the physiological conditions (pH 7.4), dissociation constants and the detection limit of GST and ATP6 V1F (a GST-tagged protein) were estimated to be 8.0 × 10(-9) M, 2.1 × 10(-10) M and 3.5 × 10(-9) M, 7.2 × 10(-11) M, respectively. The presented method has been successfully utilized for the determination of the GSTs in live cells and human urine without any complicated pretreatment and the recovery was in the range of 80%-90%.

  7. Size- and site-dependent reconstruction in CdSe QDs evidenced by 77Se{1H} CP-MAS NMR spectroscopy.

    PubMed

    Lovingood, Derek D; Achey, Randall; Paravastu, Anant K; Strouse, Geoffrey F

    2010-03-17

    Evidence of size-dependent reconstruction in quantum dots leading to changes in bonding is observed through analysis of the (77)Se{(1)H} cross-polarization magic angle spinning and (77)Se spin-echo solid-state NMR for Cd(77)Se quantum dots. The CP-MAS and spin-echo data indicate discrete surface and core (77)Se sites exist with the QD, in which the surface is comprised of numerous reconstructed lattice planes. Due to the nearly 100% enrichment level for (77)Se, efficient spin coupling is observed between the surface (77)Se and sublayer (77)Se sites due to spin diffusion in the Cd(77)Se quantum dots. The observed chemical shift for the discrete (77)Se sites can be correlated to the effective mass approximation via the Ramsey expression, indicating a 1/r(2) size dependence for the change in chemical shift with size, while a plot of chemical shift versus the inverse band gap is linear. The correlation of NMR shift for the discrete sites allows a valence bond theory interpretation of the size-dependent changes in bonding character within the reconstructed QD. The NMR results provide a structural model for the QDs in which global reconstruction occurs below 4 nm in diameter, while an apparent self-limiting reconstruction process occurs above 4 nm.

  8. Efficient double-quenching of electrochemiluminescence from CdS:Eu QDs by hemin-graphene-Au nanorods ternary composite for ultrasensitive immunoassay

    PubMed Central

    Liu, Jing; Cui, Meirong; Zhou, Hong; Zhang, Shusheng

    2016-01-01

    A novel ternary composite of hemin-graphene-Au nanorods (H-RGO-Au NRs) with high electrocatalytic activity was synthesized by a simple method. And this ternary composite was firstly used in construction of electrochemiluminescence (ECL) immunosensor due to its double-quenching effect of quantum dots (QDs). Based on the high electrocatalytic activity of ternary complexes for the reduction of H2O2 which acted as the coreactant of QDs-based ECL, as a result, the ECL intensity of QDs decreased. Besides, due to the ECL resonance energy transfer (ECL-RET) strategy between the large amount of Au nanorods (Au NRs) on the ternary composite surface and the CdS:Eu QDs, the ECL intensity of QDs was further quenched. Based on the double-quenching effect, a novel ultrasensitive ECL immunoassay method for detection of carcinoembryonic antigen (CEA) which is used as a model biomarker analyte was proposed. The designed immunoassay method showed a linear range from 0.01 pg mL−1 to 1.0 ng mL−1 with a detection limit of 0.01 pg mL−1. The method showing low detection limit, good stability and acceptable fabrication reproducibility, provided a new approach for ECL immunoassay sensing and significant prospect for practical application. PMID:27460868

  9. COUGAR: a liquid nitrogen cooled InGaAs camera for astronomy and electro-luminescence

    NASA Astrophysics Data System (ADS)

    Van Bogget, Urbain; Vervenne, Vincent; Vinella, Rosa Maria; van der Zanden, Koen; Merken, Patrick; Vermeiren, Jan

    2014-06-01

    A SWIR FPA was designed and manufactured with 640*512 pixels, 20 μm pitch and InGaAs detectors for electroluminescence characterization and astronomical applications in the [0.9 - 1.55 μm] range. The FPA is mounted in a liquid nitrogen dewar and is operated by a low noise frontend electronics. One of the biggest problem in designing sensors and cameras for electro-luminescence measurements is the autoillumination of the detectors by the readout circuit. Besides of proper shielding of the detectors, the ROIC shall be optimized for minimal electrical activity during the integration time of the very-weak signals coming from the circuit under test. For this reason a SFD (or Source Follower per Detector) architecture (like in the Hawaii sensor) was selected, resulting in a background limited performance of the detector. The pixel has a (somewhat arbitrary) full well capacity of 400 000 e- and a sensitivity of 2.17 μV/e-. The dark signal is app. 1 e-/pixel/sec and with the appropriate Fowler sampling the dark noise lowers below 5 e-rms. The power consumption of the circuit is limited 2 mW, allowing more than 24 hours of operation on less than 1 l of liquid nitrogen. The FPA is equipped with 4 outputs (optional readout on one single channel) and is capable of achieving 3 frames per second. Due to the non-destructive readout it is possible to determine in a dynamic way the optimal integration time for each observation. The Cougar camera is equipped with ultra-low noise power supply and bias lines; the electronics contain also a 24 bit AD converter to fully exploit the sensitivity of the FPA and the camera.

  10. Imaging early demineralization on tooth occlusional surfaces with a high definition InGaAs camera

    NASA Astrophysics Data System (ADS)

    Fried, William A.; Fried, Daniel; Chan, Kenneth H.; Darling, Cynthia L.

    In vivo and in vitro studies have shown that high contrast images of tooth demineralization can be acquired in the near-IR due to the high transparency of dental enamel. The purpose of this study is to compare the lesion contrast in reflectance at near-IR wavelengths coincident with high water absorption with those in the visible, the near-IR at 1300-nm and with fluorescence measurements for early lesions in occlusal surfaces. Twenty-four human molars were used in this in vitro study. Teeth were painted with an acidresistant varnish, leaving a 4×4 mm window in the occlusal surface of each tooth exposed for demineralization. Artificial lesions were produced in the exposed windows after 1 and 2-day exposure to a demineralizing solution at pH 4.5. Lesions were imaged using NIR reflectance at 3 wavelengths, 1310, 1460 and 1600-nm using a high definition InGaAs camera. Visible light reflectance, and fluorescence with 405-nm excitation and detection at wavelengths greater than 500-nm were also used to acquire images for comparison. Crossed polarizers were used for reflectance measurements to reduce interference from specular reflectance. The contrast of both the 24 hr and 48 hr lesions were significantly higher (P<0.05) for NIR reflectance imaging at 1460-nm and 1600-nm than it was for NIR reflectance imaging at 1300-nm, visible reflectance imaging, and fluorescence. The results of this study suggest that NIR reflectance measurements at longer near-IR wavelengths coincident with higher water absorption are better suited for imaging early caries lesions.

  11. Development of an Indium Gallium Arsenide (InGaAs) Short Wave Infrared (SWIR) Line Scan Imaging System

    DTIC Science & Technology

    2011-09-01

    for and used in the visible region, and thus is not optimized to operate at the SWIR range . The BK7 lens cannot be used here due to its limited FOV...area) and a wall at the lower portion (dark area). Light coming from the window is mostly in the visible range , with most of SWIR energy filtered...256 pixel InGaAs linear array sensor operating at the short wave IR ( SWIR ) (0.8–1.7 µm) range and a PC controller. Specifically, the following are

  12. Spin Polarization of Carriers in InGaAs Self-Assembled Quantum Rings Inserted in GaAs-AlGaAs Resonant Tunneling Devices

    NASA Astrophysics Data System (ADS)

    Orsi Gordo, V.; Gobato, Y. Galvão; Galeti, H. V. A.; Brasil, M. J. S. P.; Taylor, D.; Henini, M.

    2017-03-01

    In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs.

  13. Effect of spacer layer thickness on multi-stacked InGaAs quantum dots grown on GaAs (311)B substrate for application to intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Shoji, Yasushi; Narahara, Kohei; Tanaka, Hideharu; Kita, Takashi; Akimoto, Katsuhiro; Okada, Yoshitaka

    2012-04-01

    We have investigated the properties of multi-stacked layers of self-organized In0.4Ga0.6As quantum dots (QDs) on GaAs (311)B grown by molecular beam epitaxy. We found that a high degree of in-plane ordering of QDs structure with a six-fold symmetry was maintained though the growth has been performed at a higher growth rate than the conventional conditions. The dependence of photoluminescence characteristics on spacer layer thickness showed an increasing degree of electronic coupling between the stacked QDs for thinner spacer layers. The external quantum efficiency for an InGaAs/GaAs quantum dot solar cell (QDSC) with a thin spacer layer thickness increased in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. Furthermore, a photocurrent production by 2-step photon absorption has been observed at room temperature for the InGaAs/GaAs QDSC with a spacer layer thickness of 15 nm.

  14. InP-based lattice-matched InGaAsP and strain-compensated InGaAs /InGaAs quantum well cells for thermophotovoltaic applications

    NASA Astrophysics Data System (ADS)

    Rohr, Carsten; Abbott, Paul; Ballard, Ian; Connolly, James P.; Barnham, Keith W. J.; Mazzer, Massimo; Button, Chris; Nasi, Lucia; Hill, Geoff; Roberts, John S.; Clarke, Graham; Ginige, Ravin

    2006-12-01

    Quantum well cells (QWCs) for thermophotovoltaic (TPV) applications are demonstrated in the InGaAsP material system lattice matched to the InP substrate and strain-compensated InGaAs /InGaAs QWCs also on InP substrates. We show that lattice-matched InGaAsP QWCs are very well suited for TPV applications such as with erbia selective emitters. QWCs with the same effective band gap as a bulk control cell show a better voltage performance in both wide and erbialike emission. We demonstrate a QWC with enhanced efficiency in a narrow-band spectrum compared to a bulk heterostructure control cell with the same absorption edge. A major advantage of QWCs is that the band gap can be engineered by changing the well thickness and varying the composition to the illuminating spectrum. This is relatively straightforward in the lattice-matched InGaAsP system. This approach can be extended to longer wavelengths by using strain-compensation techniques, achieving band gaps as low as 0.62eV that cannot be achieved with lattice-matched bulk material. We show that strain-compensated QWCs have voltage performances that are at least as good as, if not better than, expected from bulk control cells.

  15. A comparative study on the performance of hybrid solar cells containing ZnSTe QDs in hole transporting layer and photoactive layer

    NASA Astrophysics Data System (ADS)

    Najeeb, Mansoor Ani; Abdullah, Shahino Mah; Aziz, Fakhra; Ahmad, Zubair; Shakoor, R. A.; Mohamed, A. M. A.; Khalil, Uzma; Swelm, Wageh; Al-Ghamdi, Ahmed A.; Sulaiman, Khaulah

    2016-12-01

    In this paper, ZnSTe quantum dots-based hybrid solar cells (HSC) with two different device architectures have been investigated. The improved performance of the poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C71 butyric acid methyl ester (PC71BM)-based bulk heterojunction (BHJ) solar cells by the incorporation of ZnSTe quantum dots (QDs) with an average size of 2.96 nm in PEDOT:PSS layer and active layer that have been demonstrated. Although the efficiency of both types of devices is almost the same, a close comparison reveals different reasons behind their improved performance. The device prepared with QDs in the HTL has shown reduced series resistance, increased shunt resistance, and improved mobility. On the other hand, QDs in the photoactive layer demonstrates increased photo-generation leading to improved efficiency.

  16. Components-dependent optical nonlinearity in a series of CdSexS1-x and CdSexS1-x/ZnS QDs

    NASA Astrophysics Data System (ADS)

    Zhao, Shunlong; Wu, Feng; Zhang, Siwen; Wang, Qian; Li, Songtao; Cheng, Xiaoman

    2016-08-01

    The different compositions of the ternary alloyed CdSexS1-x and CdSexS1-x/ZnS core/shell quantum dots(CSQDs) have been synthesized by the chemical routes. The nonlinear optical properties of these QDs were investigated using Z-scan technique under the excitation of the 1064 nm picosecond laser pulse. The Z-scan results reveal that the nonlinear refractive indices of these QDs can be tuned by changing the ratio of Se and S components. Nonlinear optical (NLO) properties have been shown to be enhanced in CSQDs as compared to their core semiconductor counterparts. These QDs exhibit the components-tuned nonlinear refraction indices, which lead to a wide application in the photonic field.

  17. A facile lyophilization synthesis of MoS2 QDs@graphene as a highly active electrocatalyst for hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Li, Wenzhu; Li, Feng; Wang, Xiang; Tang, Yu; Yang, Yuanyuan; Gao, Wenbin; Li, Rong

    2017-04-01

    The development of robust, active and nonprecious electrocatalysts for hydrogen evolution reaction is quite urgent but still challenging. Here MoS2 QDs@Graphene is prepared via a facile lyophilization method, which leads to a better dispersion of MoS2 QDs on the graphene and optimizes the electronic mobility between the MoS2 layers. Impressively, the electrocatalyst MoS2 QDs@Graphene demonstrates the remarkable activity for HER in 0.5 M H2SO4 solution, with a current density of 10 mA cm-2 at a low overpotential of 140 mV and strong stability in acid condition. The achieved excellent performance is attributed to its morphology with large amount of active sites fabricated by the lyophilization method. This new method opens new pathway for the fabrication of non-precious metal electrocatalysts achieving high activity.

  18. Enhanced DSSCs efficiency via Cooperate co-absorbance (CdS QDs) and plasmonic core-shell nanoparticle (Ag@PVP)

    NASA Astrophysics Data System (ADS)

    Amiri, Omid; Salavati-Niasari, Masoud; Bagheri, Samira; Yousefi, Amin Termeh

    2016-05-01

    This paper describes cooperate the co-absorbance (CdS QDs) and the plasmonic core-shell nanoparticles (Ag@PVP) of dye synthesized solar cells in which CdS QDs and Ag@PVP are incorporated into the TiO2 layer. Cooperative nanoparticles show superior behavior on enhancing light absorption in comparison with reference cells. Cooperated DSSC exhibits the best performance with the power conversion efficiency of 7.64% which is superior to that of the free–modified DSSC with the PCE of 5%. Detailed studies offer an effective approach to enhance the efficiency of dye synthesized solar cells.

  19. Enhanced DSSCs efficiency via Cooperate co-absorbance (CdS QDs) and plasmonic core-shell nanoparticle (Ag@PVP)

    PubMed Central

    Amiri, Omid; Salavati-Niasari, Masoud; Bagheri, Samira; Yousefi, Amin Termeh

    2016-01-01

    This paper describes cooperate the co-absorbance (CdS QDs) and the plasmonic core-shell nanoparticles (Ag@PVP) of dye synthesized solar cells in which CdS QDs and Ag@PVP are incorporated into the TiO2 layer. Cooperative nanoparticles show superior behavior on enhancing light absorption in comparison with reference cells. Cooperated DSSC exhibits the best performance with the power conversion efficiency of 7.64% which is superior to that of the free–modified DSSC with the PCE of 5%. Detailed studies offer an effective approach to enhance the efficiency of dye synthesized solar cells. PMID:27143126

  20. Develop multipurpose InGaAs focal plane array visible/SWIR camera for staring and range-gated applications

    NASA Astrophysics Data System (ADS)

    Nichter, James E.; Martin, Tara J.; Onat, Bora M.

    2007-04-01

    Military imaging is the largest application sector for shortwave infrared (SWIR) detectors, followed by spectroscopy (for the sorting of products and materials), and thermal sensing. Each application places different demands on the detectors, and fulfilling these requirements has driven the production of higher-quality, lower-cost imagers. The Visible SWIR Camera images digital pictures under day and starlight-only conditions, enabling the transmission of those images between soldiers on the battlefield. Additional functions are a windowing capability for comm link reception, and range-gating ability (viewing a specific depth of field at a specified range.) The combination of gated and video imaging is achieved through a high bandwidth pixel with a capacitive transimpedance amplifier (CTIA) design. Two different sensitivities in the CTIA pixel are achieved by switching between two feedback capacitor sizes, allowing for different illumination conditions. Anti-blooming is provided in the all solidstate gated camera, to prevent charge spreading from oversaturated pixels. All pixels are gated simultaneously for "snapshot" exposure. The low dark current and high bandwidth of the InGaAs photodetectors enables both high sensitivity imaging at long exposure times and high bandwidth at short exposure times. The spectral response of InGaAs extends from 0.9 μm to 1.7 μm, The Visible SWIR Camera is very reliable, in addition to being small and lightweight.

  1. High efficient photovoltaic power converter suitable for 920nm to 970nm InGaAs laser diodes

    NASA Astrophysics Data System (ADS)

    Liu, James; Wu, Ta-Chung; Cohen, Mort; Werthen, Jan G.

    2005-09-01

    In this work, we report a highly efficient Photovoltaic Power Converter (PPC) suitable for 920 nm to 970 nm InGaAs MQW lasers for the first time. The epitaxial layers were grown by low pressure MOCVD on the semi-insulting GaAs substrate. The epi layers consist of a p-n junction of In0.12Ga0.88As and the window layer of p+ AlInGaAs. The device is made of seven or eight pie-segments of equal area series-connected by means of air-bridges. Under 500mW of 940nm laser illumination, the open-circuit voltage of the eight-segment InGaAs chip is 6.7V. The short-circuit current is 29.7mA. Its maximum delivered electrical power is 171.2mW, equal to a 34.2% overall power conversion efficiency. We also demonstrate the high temperature characteristic and stability of the device.

  2. Surface analysis of InP and InGaAs after low temperature diffusion of Zinc

    NASA Astrophysics Data System (ADS)

    Le Goff, Florian; Mathiot, Daniel; Decobert, Jean; Le Goec, Jean-Pierre; Parillaud, Olivier; Reverchon, Jean-Luc

    2016-09-01

    In order to develop III-V based devices integrated directly above post-processed silicon wafers, low temperature diffusion of zinc in n-type InP and InGaAs is studied at compatible temperatures, below 425 oC. We particularly focus on the resulting surface degradation. Efficient Zn diffusion is obtained for InGaAs samples, where the surface remains mirror-like after thermal treatment. Conversely, no significant diffusion occurs in InP where the surface is deeply deteriorated. The stability study for InP under thermal annealing in various ambients allows us to rule out thermal dephosphorization as the main cause of the surface degradation. On the basis of experimental observations and thermodynamic considerations, it is suggested that InP degradation is linked to the direct interaction of Zn and P, inducing the formation of parasitic Zn x P2 alloys, which also hinders the efficient diffusion of Zn into the InP substrate.

  3. InGaAs Nanomembrane/Si van der Waals Heterojunction Photodiodes with Broadband and High Photoresponsivity.

    PubMed

    Um, Doo-Seung; Lee, Youngsu; Lim, Seongdong; Park, Jonghwa; Yen, Wen-Chun; Chueh, Yu-Lun; Kim, Hyung-Jun; Ko, Hyunhyub

    2016-10-05

    Development of broadband photodetectors is of great importance for applications in high-capacity optical communication, night vision, and biomedical imaging systems. While heterostructured photodetectors can expand light detection range, fabrication of heterostructures via epitaxial growth or wafer bonding still faces significant challenges because of problems such as lattice and thermal mismatches. Here, a transfer printing technique is used for the heterogeneous integration of InGaAs nanomembranes on silicon semiconductors and thus the formation of van der Waals heterojunction photodiodes, which can enhance the spectral response and photoresponsivity of Si photodiodes. Transfer-printed InGaAs nanomembrane/Si heterojunction photodiode exhibits a high rectification ratio (7.73 × 10(4) at ±3 V) and low leakage current (7.44 × 10(-5) A/cm(2) at -3 V) in a dark state. In particular, the photodiode shows high photoresponsivities (7.52 and 2.2 A W(-1) at a reverse bias of -3 V and zero bias, respectively) in the broadband spectral range (400-1250 nm) and fast rise-fall response times (13-16 ms), demonstrating broadband and fast photodetection capabilities. The suggested III-V/Si van der Waals heterostructures can be a robust platform for the fabrication of high-performance on-chip photodetectors compatible with Si integrated optical chips.

  4. Electron and proton damage on InGaAs solar cells having an InP window layer

    NASA Technical Reports Server (NTRS)

    Messenger, Scott R.; Cotal, Hector L.; Walters, Robert J.; Summers, Geoffrey P.

    1995-01-01

    As part of a continuing program to determine the space radiation resistance of InP/ln(0.53)Ga(0.47)As tandem solar cells, n/p In(0.53)Ga(0. 47)As solar cells fabricated by RTI were irradiated with 1 MeV electrons and with 3 MeV protons. The cells were grown with a 3 micron n-lnP window layer to mimic the top cell in the tandem cell configuration for both AMO solar absorption and radiation effects. The results have been plotted against 'displacement damage dose' which is the product of the nonionizing energy loss (NIEL) and the particle fluence. A characteristic radiation damage curve can then be obtained for predicting the effect of all particles and energies. AMO, 1 sun solar illumination IV measurements were performed on the irradiated InGaAs solar cells and a characteristic radiation degradation curve was obtained using the solar cell conversion efficiency as the model parameter. Also presented are data comparing the radiation response of both n/p and p/n (fabricated by NREL) InGaAs solar cells as a function of base doping concentration. For the solar cell efficiency, the radiation degradation was found to be independent of the sample polarity for the same base doping concentration.

  5. Border trap reduction in Al{sub 2}O{sub 3}/InGaAs gate stacks

    SciTech Connect

    Tang, Kechao; McIntyre, Paul C.; Winter, Roy; Eizenberg, Moshe; Zhang, Liangliang; Droopad, Ravi

    2015-11-16

    The effect of Al{sub 2}O{sub 3} atomic layer deposition (ALD) temperature on the border trap density (N{sub bt}) of Al{sub 2}O{sub 3}/InGaAs gate stacks is investigated quantitatively, and we demonstrate that lowering the trimethylaluminum (TMA)/water vapor ALD temperature from 270 °C to 120 °C significantly reduces N{sub bt}. The reduction of N{sub bt} coincides with increased hydrogen incorporation in low temperature ALD-grown Al{sub 2}O{sub 3} films during post-gate metal forming gas annealing. It is also found that large-dose (∼6000 L) exposure of the In{sub 0.53}Ga{sub 0.47}As (100) surface to TMA immediately after thermal desorption of a protective As{sub 2} capping layer is an important step to guarantee the uniformity and reproducibility of high quality Al{sub 2}O{sub 3}/InGaAs samples made at low ALD temperatures.

  6. GaAsSb/InAs/(In)GaAs type II quantum dots for solar cell applications

    NASA Astrophysics Data System (ADS)

    Vyskočil, Jan; Hospodková, Alice; Petříček, Otto; Pangrác, Jiří; Zíková, Markéta; Oswald, Jiří; Vetushka, Aliaksei

    2017-04-01

    We focused on design of suitable underlying and covering layers of InAs/GaAs quantum dots (QDs) with the aim to increase the carrier extraction rate in the QD solar cell structures. Covering QDs by a GaAsSb strain reducing layer (SRL) with type II band alignment significantly improves photogenerated carrier extraction from InAs QDs. An additional thin InGaAs SRL below InAs QDs further enhances the extraction of photogenerated carriers. Properties of QD structures without any SRL, with GaAsSb covering SRL, and with combination of thin below-QDs InGaAs and GaAsSb covering SRLs are compared and the mechanism of carrier extraction is discussed. We showed that thin below-QDs InGaAs SRL together with increasing profile of antimony concentration in covering GaAsSb SRL can significantly improve the resulting properties of solar cell structures with InAs QDs.

  7. Highly luminescent InP/GaP/ZnS QDs emitting in the entire color range via a heating up process

    NASA Astrophysics Data System (ADS)

    Park, Joong Pill; Lee, Jae-Joon; Kim, Sang-Wook

    2016-07-01

    InP-based quantum dots (QDs) have attracted much attention for use in optical applications, and several types of QDs such as InP/ZnS, InP/ZnSeS, and InP/GaP/ZnS have been developed. However, early synthetic methods that involved rapid injection at high temperatures have not been able to reproducibly produce the required optical properties. They were also not able to support commercialization efforts successfully. Herein, we introduce a simple synthetic method for InP/GaP/ZnS core/shell/shell QDs via a heating process. The reaction was completed within 0.5 h and a full color range from blue to red was achieved. For emitting blue color, t-DDT was applied to prevent particle growth. From green to orange, color variation was achieved by adjusting the quantity of myristic acid. Utilizing large quantities of gallium chloride led to red color. With this method, we produced high-quality InP/GaP/ZnS QDs (blue QY: ~40%, FWHM: 50 nm green QY: ~85%, FWHM: 41 nm red QY: ~60%, FWHM: 65 nm). We utilized t-DDT as a new sulfur source. Compared with n-DDT, t-DDT was more reactive, which allowed for the formation of a thicker shell.

  8. Direct detection of sulfide ions [S2-] in aqueous media based on fluorescence quenching of functionalized CdS QDs at trace levels: analytical applications to environmental analysis.

    PubMed

    Gore, Anil H; Vatre, Sandip B; Anbhule, Prashant V; Han, Sung-Hwan; Patil, Shivajirao R; Kolekar, Govind B

    2013-03-07

    A novel, simple but highly selective fluorescent probe is developed for the direct detection of sulfide ions [S(2-)] based on the fluorescence quenching of the functionalized CdS QDs in aqueous solution at trace levels and successfully applied for quantitation of S(2-) from water samples in a complex matrix exclusive of pretreatment by standard addition method.

  9. Photoluminescence quantum yields of PbSe and PbS QDs in the range of 1000 nm to 2000 nm (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Beard, Matthew C.; Semonin, Octavi E.; Johnson, Justin C.; Marshall, Ashley; Zhang, Jianbing; Chernomordik, Boris D.

    2016-03-01

    PbS and PbSe quantum dots (QDs) are promising strong infrared emitters. We have developed several synthetic routes to producing PbS and PbSe QDs with a variety of sizes such that the bandgap can be continuously tuned from 2000 to 1000 nm. We provide a simple and accurate synthetic route to reproducibly produce PbS QDs with a narrow size-distribution and high chemical yield. The different synthetic routes lead to differences in their surface chemistry and to differences in their air stability and photoluminescence quantum yields (PLQY). To characterize the PLQY we directly measured the PLQY IR-26 (a standard IR emitting organic dye) at a range of concentrations as well as the PLQY of PbS and PbSe QDs for a range of sizes. We find that the PLQY of IR-26 has a weak concentration dependence due to reabsorption, with a PLQY of 0:048_0:002% for low concentrations, lower than previous reports by a full order of magnitude. We also find a dramatic size dependence for both PbS and PbSe QDs, with the smallest dots exhibiting a PLQY in excess of 60% while larger dots fall below 3%. A model, including nonradiative transition between electronic states and energy transfer to ligand vibrations, appears to explain this size dependence. These findings provide both a better characterization of photoluminescence for near infrared emitters. Halogen surface passivation provides both a larger PLQY (~ 30% improvement) as well as increased air stability.

  10. Light-trapping for room temperature Bose-Einstein condensation in InGaAs quantum wells.

    PubMed

    Vasudev, Pranai; Jiang, Jian-Hua; John, Sajeev

    2016-06-27

    We demonstrate the possibility of room-temperature, thermal equilibrium Bose-Einstein condensation (BEC) of exciton-polaritons in a multiple quantum well (QW) system composed of InGaAs quantum wells surrounded by InP barriers, allowing for the emission of light near telecommunication wavelengths. The QWs are embedded in a cavity consisting of double slanted pore (SP2) photonic crystals composed of InP. We consider exciton-polaritons that result from the strong coupling between the multiple quantum well excitons and photons in the lowest planar guided mode within the photonic band gap (PBG) of the photonic crystal cavity. The collective coupling of three QWs results in a vacuum Rabi splitting of 3% of the bare exciton recombination energy. Due to the full three-dimensional PBG exhibited by the SP2 photonic crystal (16% gap to mid-gap frequency ratio), the radiative decay of polaritons is eliminated in all directions. Due to the short exciton-phonon scattering time in InGaAs quantum wells of 0.5 ps and the exciton non-radiative decay time of 200 ps at room temperature, polaritons can achieve thermal equilibrium with the host lattice to form an equilibrium BEC. Using a SP2 photonic crystal with a lattice constant of a = 516 nm, a unit cell height of 2a=730nm and a pore radius of 0.305a = 157 nm, light in the lowest planar guided mode is strongly localized in the central slab layer. The central slab layer consists of 3 nm InGaAs quantum wells with 7 nm InP barriers, in which excitons have a recombination energy of 0.944 eV, a binding energy of 7 meV and a Bohr radius of aB = 10 nm. We take the exciton recombination energy to be detuned 35 meV above the lowest guided photonic mode so that an exciton-polariton has a photonic fraction of approximately 97% per QW. This increases the energy range of small-effective-mass photonlike states and increases the critical temperature for the onset of a Bose-Einstein condensate. With three quantum wells in the central slab layer

  11. Growth-temperature dependence of optical spin-injection dynamics in self-assembled InGaAs quantum dots

    SciTech Connect

    Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

    2014-09-07

    The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In{sub 0.5}Ga{sub 0.5}As was studied by increasing the sheet density of the dots from 2 × 10{sup 10} to 7 × 10{sup 10} cm{sup −2} and reducing their size through a decrease in growth temperature from 500 to 470 °C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

  12. Room-temperature InGaAs detector arrays for 1.0 - 1.7 microns spectroscopy

    NASA Technical Reports Server (NTRS)

    Olsen, G. H.; Joshi, A. M.; Mykietyn, E.; Colosi, J.; Woodruff, K. M.

    1989-01-01

    Linear arrays of 256 element InGaAs detectors with 100 x 30 micron pixels were mounted in multiplexer packages and tested in an optical multichannel analyzer (OMA). Typical performance characteristics include dark current (-5V) of 400 picoamps and responsivities of 0.75 A/W (1.3 microns) and 0.14 A/W (0.85 microns). The 256 element exhibited a mean room-temperature dark current of under 400 picoamps when mounted in the OMA and a dynamic range over 11 bits (2000:1). Future applications, including room-temperature detector arrays for 2.5 microns and avalanche photodiode arrays for 1.0-1.7 microns, are discussed.

  13. Experimental demonstration of hot-carrier photo-current in an InGaAs quantum well solar cell

    SciTech Connect

    Hirst, L. C.; Walters, R. J.; Führer, M. F.; Ekins-Daukes, N. J.

    2014-06-09

    An unambiguous observation of hot-carrier photocurrent from an InGaAs single quantum well solar cell is reported. Simultaneous photo-current and photoluminescence measurements were performed for incident power density 0.04–3 kW cm{sup −2}, lattice temperature 10 K, and forward bias 1.2 V. An order of magnitude photocurrent increase was observed for non-equilibrium hot-carrier temperatures >35 K. This photocurrent activation temperature is consistent with that of equilibrium carriers in a lattice at elevated temperature. The observed hot-carrier photo-current is extracted from the well over an energy selective GaAs barrier, thus integrating two essential components of a hot-carrier solar cell: a hot-carrier absorber and an energy selective contact.

  14. InP and InGaAs Submicron Gate Microwave Power Transistors for 20 GHz Applications

    DTIC Science & Technology

    1991-06-01

    R . Nguyen, R . A . Stall, and M. A . McKee, "Indium Gallium Arsenide Microwave Power Transistors", IEEE Trans. Microwave Theory Tech., to appear in 1991...4 AD-A238 595 REPORT DOCUMENTATIOII 111IIIIIIII’___ 11 11 IN’ 11111 111 U 1 111 nI, i-- jt ncode’ a -U monP) nnq1n ! mrr~jo Ccad a ’ tn4 op, 1f Mad...Maximum 200 WOUEsl .InGaAs MISFETs witl, 0.7 gm gate lengths and 0.2 mm gate widths have demnonstratedl a1 I)1lut~IlTI i1-t 0.92 X/mm at 18 G1I1z with a

  15. Gain-switched pulses from InGaAs ridge-quantum-well lasers limited by intrinsic dynamical gain suppression.

    PubMed

    Chen, Shaoqiang; Yoshita, Masahiro; Ito, Takashi; Mochizuki, Toshimitsu; Akiyama, Hidefumi; Yokoyama, Hiroyuki

    2013-03-25

    Gain-switched pulses of InGaAs double-quantum-well lasers fabricated from identical epitaxial laser wafers were measured under both current injection and optical pumping conditions. The shortest output pulse widths were nearly identical (about 40 ps) both for current injection and optical pumping; this result attributed the dominant pulse-width limitation factor to the intrinsic gain properties of the lasers. We quantitatively compared the experimental results with theoretical calculations based on rate equations incorporating gain nonlinearities. Close consistency between the experimental data and the calculations was obtained only when we assumed a dynamically suppressed gain value deviated from the steady-state gain value supported by standard microscopic theories.

  16. New design of InGaAs guided-mode resonance photodiode for SWIR low dark current imaging

    NASA Astrophysics Data System (ADS)

    Verdun, Michaël.; Portier, Benjamin; Jaworowicz, Katarzyna; Jaeck, Julien; Dupuis, Christophe; Haidar, Riad; Pardo, Fabrice; Pelouard, Jean-Luc

    2016-04-01

    We investigate a full-dielectric guided mode resonant photodiode. It has been designed to enhance the absorption by excitation of several resonances in the SWIR domain. The device consists of an InP/InGaAs/InP P-i-N heterojunction containing an active layer as thin as 90 nm on top of a subwavelength lamellar grating and a gold mirror. We successfully compared the electro-optical characterizations of individual pixels with electro-magnetic simulations. In particular, we observe near perfect collection of the photo-carriers and external quantum efficiency (EQE) of up to 71% around 1.55 μm. Moreover, compared with InGaAs resonator state-of-the-art detector, we show a broader spectral response in the 1.2-1.7 μm range, thus paving the way for SWIR low dark current imaging.

  17. Sensitivity and noise of micro-Hall magnetic sensors based on InGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Chenaud, B.; Segovia-Mera, A.; Delgard, A.; Feltin, N.; Hoffmann, A.; Pascal, F.; Zawadzki, W.; Mailly, D.; Chaubet, C.

    2016-01-01

    We study the room-temperature performance of micro-Hall magnetic sensors based on pseudomorphic InGaAs quantum wells. Active areas of our sensors range from 1 to 80 μm. We focus on the smallest detectable magnetic fields in small sensors and perform a systematic study of noise at room temperature in the frequency range between 1 Hz and 100 kHz. Our data are interpreted by the mobility fluctuation model. The Hooge parameter is determined for the applied technology. We show that, independently of the experimental frequency, the ratio of sensitivity to noise is proportional to characteristic length of the sensor. The resolution of 1 mG/√{Hz } is achievable in a 3 μm sensor at room temperature.

  18. Magnetically tunable singlet-triplet spin qubit in a four-electron InGaAs coupled quantum dot

    NASA Astrophysics Data System (ADS)

    Weiss, K. M.; Miguel-Sanchez, J.; Elzerman, J. M.

    2013-11-01

    A pair of self-assembled InGaAs quantum dots filled with two electrons can act as a singlet-triplet spin qubit that is robust against nuclear spin fluctuations as well as charge noise. This results in a T2* coherence time two orders of magnitude longer than that of a single electron, provided the qubit is operated at a particular ``sweet spot'' in gate voltage. However, at this fixed operating point the ground-state splitting can no longer be tuned into resonance with e.g. another qubit, limiting the options for coupling multiple qubits. Here, we propose using a four-electron coupled quantum dot to implement a singlet-triplet qubit that features a magnetically tunable level splitting. As a first step towards full experimental realization of this qubit design, we use optical spectroscopy to demonstrate the tunability of the four-electron singlet-triplet splitting in a moderate magnetic field.

  19. Optical Spin Noise of a Single Hole Spin Localized in an (InGa)As Quantum Dot

    NASA Astrophysics Data System (ADS)

    Dahbashi, Ramin; Hübner, Jens; Berski, Fabian; Pierz, Klaus; Oestreich, Michael

    2014-04-01

    We advance spin noise spectroscopy to the ultimate limit of single spin detection. This technique enables the measurement of the spin dynamic of a single heavy hole localized in a flat (InGa)As quantum dot. Magnetic field and light intensity dependent studies reveal even at low magnetic fields a strong magnetic field dependence of the longitudinal heavy hole spin relaxation time with an extremely long T1 of ≥180 μs at 31 mT and 5 K. The wavelength dependence of the spin noise power discloses for finite light intensities an inhomogeneous single quantum dot spin noise spectrum which is explained by charge fluctuations in the direct neighborhood of the quantum dot. The charge fluctuations are corroborated by the distinct intensity dependence of the effective spin relaxation rate.

  20. An InGaAs detector based radiation thermometer and fixed-point blackbodies for temperature scale realization at NIM

    SciTech Connect

    Hao, X.; Yuan, Z.; Wang, J.; Lu, X.

    2013-09-11

    In this paper, we describe an InGaAs detector based radiation thermometer (IRT) and new design of fixed-point blackbodies, including Sn, Zn, Al and Cu, for the establishment of a temperature scale from 200 °C to 1085 °C at the National Institute of Metrology of China. The construction and calibration of the IRT with the four fixed-point blackbodies are described. Characteristics of the IRT, such as the size-of-source effect, the amplifier performance and its stability are determined. The design of the four fixed-points, with 10 mm diameter of aperture and 0.9999 emissivity, is described. The uncertainty of the scale realization is elaborated.

  1. An InGaAs detector based radiation thermometer and fixed-point blackbodies for temperature scale realization at NIM

    NASA Astrophysics Data System (ADS)

    Hao, X.; Yuan, Z.; Wang, J.; Lu, X.

    2013-09-01

    In this paper, we describe an InGaAs detector based radiation thermometer (IRT) and new design of fixed-point blackbodies, including Sn, Zn, Al and Cu, for the establishment of a temperature scale from 200 °C to 1085 °C at the National Institute of Metrology of China. The construction and calibration of the IRT with the four fixed-point blackbodies are described. Characteristics of the IRT, such as the size-of-source effect, the amplifier performance and its stability are determined. The design of the four fixed-points, with 10 mm diameter of aperture and 0.9999 emissivity, is described. The uncertainty of the scale realization is elaborated.

  2. Time-resolved spectroscopy of low-dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Murphy, Joseph R.

    This dissertation is a survey of ultrafast time-resolved optical measurements conducted on a variety of low-dimensional semiconductor systems to further the understanding of the dynamic behavior in the following systems: ZnMnTe/ZnSe quantum dots, ZnTe/ZnMnSe quantum dots, InGaAs quantum wells, CdMnSe colloidal quantum dots, multi-shell CdSe/CdMnS/CdS colloidal nanoplatelets, and graphene and graphene-related solutions and films. Using time-resolved photoluminescence to study epitaxially-grown ZnTe and ZnMnTe quantum dots in corresponding ZnMnSe and ZnSe matrices, the location dependence of manganese ions in respect to magnetic polaron formation is shown. The structure with manganese ions located in the matrix exhibited magnetic polaron behavior consistent with previous literature, whereas the structure with the magnetic ions located within the quantum dots exhibited unconventional magnetic polaron properties. These properties, including temperature and magnetic field insensitivity, were explained through the use of a model that predicted an increased internal magnetic field due to a decreased effective volume of the magnetic polaron and a higher effective temperature due to laser heating. Magneto-time-resolved photoluminescence measurements on a system of colloidal CdMnSe quantum dots show that the magnetic polaron properties differ significantly from the epitaxially grown quantum dots. First the timescales at which the magnetic polaron forms and the polarization saturates are different by more than an order of magnitude, and second, the magnetic polaron energy exhibited step-like behavior as the strength of the externally applied magnetic field is increased. The field dependent MP formation energy that is observed experimentally is explained as due to the breaking of the antiferromagnetic coupling of Mn dimers within the QDs. This model is further verified by the observation of quantized behavior in the Zeeman energy splitting. Through the use of magneto

  3. Catastrophic facet and bulk degradation in high power multi-mode InGaAs strained quantum well single emitters

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Presser, Nathan; Foran, Brendan; Ives, Neil; Moss, Steven C.

    2009-02-01

    Extensive investigations by a number of groups have identified catastrophic sudden degradation as the main failure mode in both single-mode and multi-mode InGaAs-AlGaAs strained quantum well (QW) lasers. Significant progress made in performance characteristics of broad-area InGaAs strained QW single emitters in recent years has led to an optical output power of over 20W and a power conversion efficiency of over 70% under CW operation. However, unlike 980nm single-mode lasers that have shown high reliability operation under a high optical power density of ~50MW/cm2, broad-area lasers have not achieved the same level of reliability even under a much lower optical power density of ~5MW/cm2. This paper investigates possible mechanisms that prevent broad-area lasers from achieving high reliability operation by performing accelerated lifetests of these devices and in-depth failure mode analyses of degraded devices with various destructive and non-destructive techniques including EBIC, FIB, and HR-TEM techniques. The diode lasers that we have investigated are commercial MOCVD-grown broad-area strained InGaAs single QW lasers at ~975nm. Both passivated and unpassivated broad-area lasers were studied that yielded catastrophic failures at the front facet and also in the bulk. To investigate the role that generation and propagation of defects plays in degradation processes via recombination enhanced defect reaction (REDR), EBIC was employed to study dark line defects in degraded lasers, failed under different stress conditions, and the correlation between DLDs and stress levels is reported. FIB was then employed to prepare TEM samples from the DLD areas for cross-sectional HR-TEM analysis.

  4. Spectral imaging of chemical compounds using multivariate optically enhanced filters integrated with InGaAs VGA cameras

    NASA Astrophysics Data System (ADS)

    Priore, Ryan J.; Jacksen, Niels

    2016-05-01

    Infrared hyperspectral imagers (HSI) have been fielded for the detection of hazardous chemical and biological compounds, tag detection (friend versus foe detection) and other defense critical sensing missions over the last two decades. Low Size/Weight/Power/Cost (SWaPc) methods of identification of chemical compounds spectroscopy has been a long term goal for hand held applications. We describe a new HSI concept for low cost / high performance InGaAs SWIR camera chemical identification for military, security, industrial and commercial end user applications. Multivariate Optical Elements (MOEs) are thin-film devices that encode a broadband, spectroscopic pattern allowing a simple broadband detector to generate a highly sensitive and specific detection for a target analyte. MOEs can be matched 1:1 to a discrete analyte or class prediction. Additionally, MOE filter sets are capable of sensing an orthogonal projection of the original sparse spectroscopic space enabling a small set of MOEs to discriminate a multitude of target analytes. This paper identifies algorithms and broadband optical filter designs that have been demonstrated to identify chemical compounds using high performance InGaAs VGA detectors. It shows how some of the initial models have been reduced to simple spectral designs and tested to produce positive identification of such chemicals. We also are developing pixilated MOE compressed detection sensors for the detection of a multitude of chemical targets in challenging backgrounds/environments for both commercial and defense/security applications. This MOE based, real-time HSI sensor will exhibit superior sensitivity and specificity as compared to currently fielded HSI systems.

  5. Dependence of electron mobility on gate voltage sweeping width and deposition temperature in MOSFETs with HfO2/Al2O3/InGaAs gate stacks

    NASA Astrophysics Data System (ADS)

    Ohsawa, Kazuto; Netsu, Seiko; Kise, Nobukazu; Noguchi, Shinji; Miyamoto, Yasuyuki

    2017-04-01

    In this study, we fabricated MOSFETs with Al2O3/InGaAs or HfO2/Al2O3/InGaAs gate stacks. The surface was subjected to nitrogen plasma and trimethylaluminum cleaning prior to low-temperature atomic layer deposition. Electron mobility was extracted using the capacitance–gate voltage (C–V G) and drain current–gate voltage (I D–V G) characteristics. We determined that the mobility decreased when the gate voltage sweeping width increased during C–V G and I D–V G measurements. In addition, we determined that the lowering of the deposition temperature to 120 °C improved the mobility of MOSFETs with HfO2/Al2O3/InGaAs gate stacks as compared with that corresponding to deposition at 300 °C. Furthermore, HfO2/Al2O3/InGaAs gate stacks with various Al2O3 thicknesses were fabricated. When the number of Al2O3 deposition cycles was more than 4, the mobility of MOSFETs with HfO2/Al2O3/InGaAs gate stacks improved, reaching the value of the Al2O3/InGaAs gate stack.

  6. Efficient eco-friendly inverted quantum dot sensitized solar cells† †Electronic supplementary information (ESI) available: TEM images of QDs, XPS spectra, UV-vis and PL spectra of the sensitized electrodes, details about photophysical characterization and IPCE spectra interpretation. See DOI: 10.1039/c5ta06769c Click here for additional data file.

    PubMed Central

    Park, Jinhyung; Sajjad, Muhammad T.; Jouneau, Pierre-Henri; Ruseckas, Arvydas; Faure-Vincent, Jérôme; Reiss, Peter

    2016-01-01

    Recent progress in quantum dot (QD) sensitized solar cells has demonstrated the possibility of low-cost and efficient photovoltaics. However, the standard device structure based on n-type materials often suffers from slow hole injection rate, which may lead to unbalanced charge transport. We have fabricated efficient p-type (inverted) QD sensitized cells, which combine the advantages of conventional QD cells with p-type dye sensitized configurations. Moreover, p-type QD sensitized cells can be used in highly promising tandem configurations with n-type ones. QDs without toxic Cd and Pb elements and with improved absorption and stability were successfully deposited onto mesoporous NiO electrode showing good coverage and penetration according to morphological analysis. Detailed photophysical charge transfer studies showed that high hole injection rates (108 s–1) observed in such systems are comparable with electron injection in conventional n-type QD assemblies. Inverted solar cells fabricated with various QDs demonstrate excellent power conversion efficiencies of up to 1.25%, which is 4 times higher than the best values for previous inverted QD sensitized cells. Attempts to passivate the surface of the QDs show that traditional methods of reduction of recombination in the QD sensitized cells are not applicable to the inverted architectures. PMID:27478616

  7. Enhanced electrochemiluminescence quenching of CdS:Mn nanocrystals by CdTe QDs-doped silica nanoparticles for ultrasensitive detection of thrombin

    NASA Astrophysics Data System (ADS)

    Shan, Yun; Xu, Jing-Juan; Chen, Hong-Yuan

    2011-07-01

    This work reports an aptasensor for ultrasensitive detection of thrombin based on remarkably efficient energy-transfer induced electrochemiluminescence (ECL) quenching from CdS:Mn nanocrystals (NCs) film to CdTe QDs-doped silica nanoparticles (CdTe/SiO2 NPs). CdTe/SiO2 NPs were synthesized via the Stöber method and showed black bodies' strong absorption in a wide spectral range without excitonic emission, which made them excellent ECL quenchers. Within the effective distance of energy scavenging, the ECL quenching efficiency was dependent on the number of CdTe QDs doped into the silica NPs. Using ca. 200 CdTe QDs doped silica NPs on average of 40 nm in diameter as ECL quenching labels, attomolar detection of thrombin was successfully realized. The protein detection involves a competition binding event, based on thrombin replacing CdTe/SiO2 NPs labeled probing DNA which is hybridized with capturing aptamer immobilized on a CdS:Mn NCs film modified glassy carbon electrode surface by specific aptamer-protein affinity interactions. It results in the displacement of ECL quenching labels from CdS:Mn NCs film and concomitant ECL signal recovery. Owing to the high-content CdTe QDs in silica NP, the increment of ECL intensity (ΔIECL) and the concentration of thrombin showed a double logarithmic linear correlation in the range of 5.0 aM~5.0 fM with a detection limit of 1aM. And, the aptasensor hardly responded to antibody, bovine serum albumin (BSA), haemoglobin (Hb) and lysozyme, showing good detection selectivity for thrombin. This long-distance energy scavenging could have a promising application perspective in the detection of biological recognition events on a molecular level.This work reports an aptasensor for ultrasensitive detection of thrombin based on remarkably efficient energy-transfer induced electrochemiluminescence (ECL) quenching from CdS:Mn nanocrystals (NCs) film to CdTe QDs-doped silica nanoparticles (CdTe/SiO2 NPs). CdTe/SiO2 NPs were synthesized via

  8. Secondary coordination sphere accelerates hole transfer for enhanced hydrogen photogeneration from [FeFe]-hydrogenase mimic and CdSe QDs in water.

    PubMed

    Wen, Min; Li, Xu-Bing; Jian, Jing-Xin; Wang, Xu-Zhe; Wu, Hao-Lin; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

    2016-07-15

    Achieving highly efficient hydrogen (H2) evolution via artificial photosynthesis is a great ambition pursued by scientists in recent decades because H2 has high specific enthalpy of combustion and benign combustion product. [FeFe]-Hydrogenase ([FeFe]-H2ase) mimics have been demonstrated to be promising catalysts for H2 photoproduction. However, the efficient photocatalytic H2 generation system, consisting of PAA-g-Fe2S2, CdSe QDs and H2A, suffered from low stability, probably due to the hole accumulation induced photooxidation of CdSe QDs and the subsequent crash of [FeFe]-H2ase mimics. In this work, we take advantage of supramolecular interaction for the first time to construct the secondary coordination sphere of electron donors (HA(-)) to CdSe QDs. The generated secondary coordination sphere helps realize much faster hole removal with a ~30-fold increase, thus leading to higher stability and activity for H2 evolution. The unique photocatalytic H2 evolution system features a great increase of turnover number to 83600, which is the highest one obtained so far for photocatalytic H2 production by using [FeFe]-H2ase mimics as catalysts.

  9. Sensitive fluorescence detection of ATP based on host-guest recognition between near-infrared β-Cyclodextrin-CuInS2 QDs and aptamer.

    PubMed

    Hu, Tianyu; Na, Weidan; Yan, Xu; Su, Xingguang

    2017-04-01

    We have developed a near-infrared (NIR) fluorescent aptamer-based sensor for sensitive detection of adenosine-5'-triphosphate (ATP) by using a ATP-binding aptamer and β-Cyclodextrin-CuInS2 quantum dots (β-CD-CuInS2 QDs). The fluorescence of β-CD-CuInS2 QDs has a slight enhancement with the addition of ATP-binding aptamer due to the host-guest recognition between aptamer and β-CD. When ATP is added, it will bind to aptamer to form G-quadruplexes. Aptamer-ATP complexes can enter into the hydrophobic cavities of β-CD and result in great enhancement of the fluorescence intensity. Under the optimum conditions, the fluorescence intensity of β-CD-CuInS2 QDs is proportional to the concentration of ATP, which shows a good linear response toward ATP concentration range of 6-1200μmolL(-1), the detection limit for ATP is 3μmolL(-1). The present assay shows a good selectivity for ATP over other biologically important proteins, and it is applied to the determination of ATP in human serum sample with satisfactory results.

  10. Secondary coordination sphere accelerates hole transfer for enhanced hydrogen photogeneration from [FeFe]-hydrogenase mimic and CdSe QDs in water

    PubMed Central

    Wen, Min; Li, Xu-Bing; Jian, Jing-Xin; Wang, Xu-Zhe; Wu, Hao-Lin; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

    2016-01-01

    Achieving highly efficient hydrogen (H2) evolution via artificial photosynthesis is a great ambition pursued by scientists in recent decades because H2 has high specific enthalpy of combustion and benign combustion product. [FeFe]-Hydrogenase ([FeFe]-H2ase) mimics have been demonstrated to be promising catalysts for H2 photoproduction. However, the efficient photocatalytic H2 generation system, consisting of PAA-g-Fe2S2, CdSe QDs and H2A, suffered from low stability, probably due to the hole accumulation induced photooxidation of CdSe QDs and the subsequent crash of [FeFe]-H2ase mimics. In this work, we take advantage of supramolecular interaction for the first time to construct the secondary coordination sphere of electron donors (HA−) to CdSe QDs. The generated secondary coordination sphere helps realize much faster hole removal with a ~30-fold increase, thus leading to higher stability and activity for H2 evolution. The unique photocatalytic H2 evolution system features a great increase of turnover number to 83600, which is the highest one obtained so far for photocatalytic H2 production by using [FeFe]-H2ase mimics as catalysts. PMID:27417065

  11. Constructing a MoS₂ QDs/CdS Core/Shell Flowerlike Nanosphere Hierarchical Heterostructure for the Enhanced Stability and Photocatalytic Activity.

    PubMed

    Liang, Shijing; Zhou, Zhouming; Wu, Xiuqin; Zhu, Shuying; Bi, Jinhong; Zhou, Limin; Liu, Minghua; Wu, Ling

    2016-02-15

    MoS₂ quantum dots (QDs)/CdS core/shell nanospheres with a hierarchical heterostructure have been prepared by a simple microwave hydrothermal method. The as-prepared samples are characterized by XRD, TEM, SEM, UV-VIS diffuse reflectance spectra (DRS) and N₂-sorption in detail. The photocatalytic activities of the samples are evaluated by water splitting into hydrogen. Results show that the as-prepared MoS₂ QDs/CdS core/shell nanospheres with a diameter of about 300 nm are composed of the shell of CdS nanorods and the core of MoS₂ QDs. For the photocatalytic reaction, the samples exhibit a high stability of the photocatalytic activity and a much higher hydrogen evolution rate than the pure CdS, the composite prepared by a physical mixture, and the Pt-loaded CdS sample. In addition, the stability of CdS has also been greatly enhanced. The effect of the reaction time on the formations of nanospheres, the photoelectric properties and the photocatalytic activities of the samples has been investigated. Finally, a possible photocatalytic reaction process has also been proposed.

  12. Secondary coordination sphere accelerates hole transfer for enhanced hydrogen photogeneration from [FeFe]-hydrogenase mimic and CdSe QDs in water

    NASA Astrophysics Data System (ADS)

    Wen, Min; Li, Xu-Bing; Jian, Jing-Xin; Wang, Xu-Zhe; Wu, Hao-Lin; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

    2016-07-01

    Achieving highly efficient hydrogen (H2) evolution via artificial photosynthesis is a great ambition pursued by scientists in recent decades because H2 has high specific enthalpy of combustion and benign combustion product. [FeFe]-Hydrogenase ([FeFe]-H2ase) mimics have been demonstrated to be promising catalysts for H2 photoproduction. However, the efficient photocatalytic H2 generation system, consisting of PAA-g-Fe2S2, CdSe QDs and H2A, suffered from low stability, probably due to the hole accumulation induced photooxidation of CdSe QDs and the subsequent crash of [FeFe]-H2ase mimics. In this work, we take advantage of supramolecular interaction for the first time to construct the secondary coordination sphere of electron donors (HA‑) to CdSe QDs. The generated secondary coordination sphere helps realize much faster hole removal with a ~30-fold increase, thus leading to higher stability and activity for H2 evolution. The unique photocatalytic H2 evolution system features a great increase of turnover number to 83600, which is the highest one obtained so far for photocatalytic H2 production by using [FeFe]-H2ase mimics as catalysts.

  13. Low interface defect density of atomic layer deposition BeO with self-cleaning reaction for InGaAs metal oxide semiconductor field effect transistors

    SciTech Connect

    Shin, H. S.; Yum, J. H.; Johnson, D. W.; Harris, H. R.; Hudnall, Todd W.; Oh, J.; Kirsch, P.; Wang, W.-E.; Bielawski, C. W.; Banerjee, S. K.; Lee, J. C.; Lee, H. D.

    2013-11-25

    In this paper, we discuss atomic configuration of atomic layer deposition (ALD) beryllium oxide (BeO) using the quantum chemistry to understand the theoretical origin. BeO has shorter bond length, higher reaction enthalpy, and larger bandgap energy compared with those of ALD aluminum oxide. It is shown that the excellent material properties of ALD BeO can reduce interface defect density due to the self-cleaning reaction and this contributes to the improvement of device performance of InGaAs MOSFETs. The low interface defect density and low leakage current of InGaAs MOSFET were demonstrated using X-ray photoelectron spectroscopy and the corresponding electrical results.

  14. Influence of interface traps inside the conduction band on the capacitance-voltage characteristics of InGaAs metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Taoka, Noriyuki; Yokoyama, Masafumi; Kim, Sang Hyeon; Suzuki, Rena; Iida, Ryo; Takenaka, Mitsuru; Takagi, Shinichi

    2016-11-01

    We investigated the influences of the AC response with interface/bulk-oxide traps near the conduction band (CB) and a low effective density of states (DOS) on the accumulation capacitance C acc of an n-type InGaAs metal-oxide-semiconductor (MOS) capacitor. We found that the capacitance associated with the interface traps inside the CB significantly increases C acc compared to the C acc value constrained by a low DOS. These results indicate that accurate characterization inside the CB and considering the capacitance due to the interface traps inside the CB in the MOS capacitance-voltage curves are indispensable for accurate characterization of InGaAs MOS interface properties.

  15. Toward a single-chip TECless/NUCless InGaAs SWIR camera with 120-dB intrinsic operation dynamic range

    NASA Astrophysics Data System (ADS)

    Ni, Y.; Arion, B.; Zhu, Y. M.; Potet, P.; Huet, Odile; Reverchon, Jean Luc; Truffer, Jean Patrick; Robo, Jean Alexandre; Costard, Eric

    2011-06-01

    This paper describes a single-chip InGaAs SWIR camera with more than 120dB instant operational dynamic range with an innovative CMOS ROIC technology, so called MAGIC, invented and patented by New Imaging Technologies. A 320x256- pixel InGaAs 25μm pitch photodiode array, designed and fabricated by III-Vlab/Thales Research & Technology(TRT), has been hybridized on this new generation CMOS ROIC. With NIT's MAGIC technology, the sensor's output follows a precise logarithmic law in function of incoming photon flux and gives instant operational dynamic range (DR) better than 120 dB. The ROIC incorporates the entire video signal processing function including a CCIR TV encoder, so a complete SWIR InGaAs camera with standard video output has been realized on a single 30x30 mm2 PCB board with ¼ W power consumption. Neither TEC nor NUC is needed from room temperature operation. The camera can be switched on and off instantly, ideal for all the portable battery operated SWIR band observation applications. The measured RMS noise and FPN noise on the prototype sensor in dark conditions are 0.4 mV and 0.27 mV respectively. The signal excursion from pixel is about 300mV over the 120 dB dynamic range. The FPN remains almost constant over the whole operation dynamic range. The NEI has been measured to be 3,71E+09 ph/s/cm2 with 92 equivalent noise photons at 25Hz frame rate, better than the same architecture of InGaAs photodiode array hybridized on an Indigo ROIC ISC9809 with a pitch of 30 μm for which a readout noise of 120 electrons is observed.

  16. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    PubMed

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  17. Low defect InGaAs quantum well selectively grown by metal organic chemical vapor deposition on Si(100) 300 mm wafers for next generation non planar devices

    NASA Astrophysics Data System (ADS)

    Cipro, R.; Baron, T.; Martin, M.; Moeyaert, J.; David, S.; Gorbenko, V.; Bassani, F.; Bogumilowicz, Y.; Barnes, J. P.; Rochat, N.; Loup, V.; Vizioz, C.; Allouti, N.; Chauvin, N.; Bao, X. Y.; Ye, Z.; Pin, J. B.; Sanchez, E.

    2014-06-01

    Metal organic chemical vapor deposition of GaAs, InGaAs, and AlGaAs on nominal 300 mm Si(100) at temperatures below 550 °C was studied using the selective aspect ratio trapping method. We clearly show that growing directly GaAs on a flat Si surface in a SiO2 cavity with an aspect ratio as low as 1.3 is efficient to completely annihilate the anti-phase boundary domains. InGaAs quantum wells were grown on a GaAs buffer and exhibit room temperature micro-photoluminescence. Cathodoluminescence reveals the presence of dark spots which could be associated with the presence of emerging dislocation in a direction parallel to the cavity. The InGaAs layers obtained with no antiphase boundaries are perfect candidates for being integrated as channels in n-type metal oxide semiconductor field effect transistor (MOSFET), while the low temperatures used allow the co-integration of p-type MOSFET.

  18. A multiple antibiotic and serum resistant oligotrophic strain, Klebsiella pneumoniae MB45 having novel dfrA30, is sensitive to ZnO QDs

    PubMed Central

    2011-01-01

    Background The aim of this study was to describe a novel trimethoprim resistance gene cassette, designated dfrA30, within a class 1 integron in a facultatively oligotrophic, multiple antibiotic and human serum resistant test strain, MB45, in a population of oligotrophic bacteria isolated from the river Mahananda; and to test the efficiency of surface bound acetate on zinc oxide quantum dots (ZnO QDs) as bactericidal agent on MB45. Methods Diluted Luria broth/Agar (10-3) media was used to cultivate the oligotrophic bacteria from water sample. Multiple antibiotic resistant bacteria were selected by employing replica plate method. A rapid assay was performed to determine the sensitivity/resistance of the test strain to human serum. Variable region of class 1 integron was cloned, sequenced and the expression of gene coding for antibiotic resistance was done in Escherichia coli JM 109. Identity of culture was determined by biochemical phenotyping and 16S rRNA gene sequence analyses. A phylogenetic tree was constructed based on representative trimethoprim resistance-mediating DfrA proteins retrieved from GenBank. Growth kinetic studies for the strain MB45 were performed in presence of varied concentrations of ZnO QDs. Results and conclusions The facultatively oligotrophic strain, MB45, resistant to human serum and ten antibiotics trimethoprim, cotrimoxazole, ampicillin, gentamycin, netilmicin, tobramycin, chloramphenicol, cefotaxime, kanamycin and streptomycin, has been identified as a new strain of Klebsiella pneumoniae. A novel dfr gene, designated as dfrA30, found integrated in class 1 integron was responsible for resistance to trimethoprim in Klebsiella pneumoniae strain MB45. The growth of wild strain MB45 was 100% arrested at 500 mg/L concentration of ZnO QDs. To our knowledge this is the first report on application of ZnO quantum dots to kill multiple antibiotics and serum resistant K. pneumoniae strain. PMID:21595893

  19. Waveguide saturable absorbers at 1.55 μm based on intraband transitions in GaN/AlN QDs.

    PubMed

    Monteagudo-Lerma, L; Valdueza-Felip, S; Naranjo, F B; Corredera, P; Rapenne, L; Sarigiannidou, E; Strasser, G; Monroy, E; González-Herráez, M

    2013-11-18

    We report on the design, fabrication and optical characterization of GaN/AlN quantum-dot-based waveguides for all-optical switching via intraband absorption saturation at 1.55 µm. The transmittance of the TM-polarized light increases with the incident optical power due to the saturation of the s-p(z) intraband absorption in the QDs. Single-mode waveguides with a ridge width of 2 µm and a length of 1.5 mm display 10 dB absorption saturation of the TM-polarized light for an input pulse energy of 8 pJ and 150 fs.

  20. Impact of stoichiometry on the electronic structure of PbS quantum dots.

    PubMed

    Kim, Donghun; Kim, Dong-Ho; Lee, Joo-Hyoung; Grossman, Jeffrey C

    2013-05-10

    Although the stoichiometry of bulk lead sulfide (PbS) is exactly 1:1, that of quantum dots (QDs) can be considerably different from this crystalline limit. Employing first-principles calculations, we show that the impact of PbS QD stoichiometry on the electronic structure can be enormous, suggesting that control over the overall stoichiometry in the QD will play a critical role for improving the efficiency of optoelectronic devices made with PbS QDs. In particular, for bare PbS QDs, we find that: (i) stoichiometric PbS QDs are free from midgap states even without ligand passivation and independent of shape, (ii) off stoichiometry in PbS QDs introduces new states in the gap that are highly localized on certain surface atoms, and (iii) further deviations in stoichiometry lead to QDs with "metallic" behavior, with a dense number of energy states near the Fermi level. We further demonstrate that this framework holds for the case of passivated QDs by considering the attachment of ligand molecules as stoichiometry variations. Our calculations show that an optimal number of ligands makes the QD stoichiometric and heals unfavorable electronic structure, whereas too few or too many ligands cause effective off stoichiometry, resulting in QDs with defect states in the gap.

  1. Kelvin probe force and surface photovoltage microscopy observation of minority holes leaked from active region of working InGaAs /AlGaAs/GaAs laser diode

    NASA Astrophysics Data System (ADS)

    Ankudinov, A. V.; Evtikhiev, V. P.; Ladutenko, K. S.; Rastegaeva, M. G.; Titkov, A. N.; Laiho, R.

    2007-01-01

    A method for direct observation of carrier leakage from active regions of working semiconductor light-emitting diodes and lasers is suggested. In this method, Kelvin probe force and surface photovoltage microscopies are used to measure local changes in the surface potential of the device mirror on which a high concentration of the leaked carriers is expected. The applicability of the method is demonstrated by studying in detail the leakage current on the mirrors of high-power InGaAs /AlGaAs/GaAs laser diodes in action. It is shown that minority holes arrive at the mirror surface from the active zone of the laser and spread over to regions of the n emitter and n substrate. This observation is confirmed by exposing the mirror to external light with photon energy exceeding the band gap of the laser structure and measuring the generated surface photovoltage. Owing to surface channels formed by the surface band bending, the holes can move tens of micrometers from the place of their generation. The leakage currents are evaluated on the basis of the surface potential distributions observed. It is found that as the injection current of the laser increases, the leakage current grows until onset of lasing.

  2. Selenium quantum dots: Preparation, structure, and properties

    NASA Astrophysics Data System (ADS)

    Qian, Fuli; Li, Xueming; Tang, Libin; Lai, Sin Ki; Lu, Chaoyu; Lau, Shu Ping

    2017-01-01

    An interesting class of low-dimensional nanomaterials, namely, selenium quantum dots (SeQDs), which are composed of nano-sized selenium particles, is reported in this study. The SeQDs possess a hexagonal crystal structure. They can be synthesized in large quantity by ultrasound liquid-phase exfoliation using NbSe2 powders as the source material and N-Methyl-2-pyrrolidone (NMP) as the dispersant. During sonication, the Nb-Se bonds dissociate; the SeQDs are formed, while niobium is separated by centrifugation. The SeQDs have a narrow diameter distribution from 1.9 to 4.6 nm and can be dispersed with high stability in NMP without the need for passivating agents. They exhibit photoluminescence properties that are expected to find useful applications in bioimaging, optoelectronics, as well as nanocomposites.

  3. Fabrication and cyto-compatibility of Fe3O4/SiO2/graphene-CdTe QDs/CS nanocomposites for drug delivery.

    PubMed

    Ou, Jun; Wang, Fang; Huang, Yuanjie; Li, Duosheng; Jiang, Yuming; Qin, Qing-Hua; Stachurski, Z H; Tricoli, Antonio; Zhang, Tina

    2014-05-01

    Synthesis of magnetic Fe3O4/SiO2/graphene-CdTe QDs/chitosan nanocomposites (FGQCs) is investigated with respect to their potential of improving the drug loading content above that of magnetic/fluorescent bifunctional nanocomposites. To evaluate the performance of the FGQCs, their surface morphology was thoroughly assessed. The in vitro interaction between the FGQCs and heptoma cell line smmc-7721 cells was observed for the first time by TEM ultrathin section imaging. At an excitation wavelength of 365 nm, the graphene-QDs exhibit a strong luminescence in aqueous environments. The loading content and entrapment efficiency of the FGQCs were 70% and 50%, respectively. The cytotoxicity of this novel drug delivery system was evaluated in vitro using heptoma cell line smmc-7721 and quantified by the 3-(4,5-dimethylthiazol-z-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results show that FGQCs are a promising new multifunctional material for drug delivery in biological and medical applications.

  4. Various types of semiconductor photocatalysts modified by CdTe QDs and Pt NPs for toluene photooxidation in the gas phase under visible light

    NASA Astrophysics Data System (ADS)

    Marchelek, M.; Grabowska, E.; Klimczuk, T.; Lisowski, W.; Zaleska-Medynska, A.

    2017-01-01

    A novel synthesis process was used to prepare TiO2 microspheres, TiO2 P-25, SrTiO3 and KTaO3 decorated by CdTe QDs and/or Pt NPs. The effect of semiconductor matrix, presence of CdTe QDs and/or Pt NPs on the semiconductor surface as well as deposition technique of Pt NPs (photodeposition or radiolysis) on the photocatalytic activity were investigated. The as-prepared samples were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), photoluminescence spectrometry (PL), Fourier transform infrared (FT-IR) and Raman spectra, diffuse reflectance spectroscopy (DRS) and BET surface area analysis. The photocatalytic decomposition of toluene in gas phase, activated by light-emitting diodes (LEDs), with the CdTe/Pt nanoparticles-modified TiO2 microspheres, P25, SrTiO3 and KTaO3 semiconductors was investigated under UV-vis and visible irradiation.The results showed that the photoactivity depends on semiconductor matrix. The highest photoactivity under Vis light was observed for KTaO3/CdTe-Pt(R) sample (56% of toluene was decompose after 30 min of irradiation). The efficiency of the most active sample was 3 times higher than result for P25 and two times higher than for unmodified KTaO3.

  5. Structural and optical characterization of pure and starch-capped ZnO quantum dots and their photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Vidhya, K.; Saravanan, M.; Bhoopathi, G.; Devarajan, V. P.; Subanya, S.

    2015-02-01

    Among the different types of metal oxides, zinc oxide (ZnO) is a most commonly used metal oxide in a broad variety of applications. In the present investigation, a modified green synthesis route was used to synthesize pure and starch-capped ZnO (ZnO/starch) quantum dots (QDs) and studied their structural and optical characteristics. In this study, hexagonal crystal structure was observed in both pure and ZnO/starch QDs using X-ray diffraction technique. A spherical-shaped surface morphology was found with the size of 5-10 nm using transmission electron microscope technique. The interaction between ZnO QDs and starch molecules was proved via Fourier infra-red spectrometer technique. On the other hand, their fluorescence behaviors were investigated using photoluminescence technique, in that the ZnO/starch QDs showed an enhanced emission behavior when compared to the pure ZnO QDs. Further, the solar photocatalytic activity of both the ZnO QDs was examined with the dye Rhodamine B (RhB) at the end of 30, 60, 90, and 120 min. In this, ZnO/starch QDs show a good and more decomposition of RhB than pure ZnO QDs. Collectively, in the present study, green synthesis route produced an efficient QDs (pure and ZnO/starch) and it will be very useful for many other QDs. The ZnO/starch QDs are suitable for decomposing the RhB and other toxic organic dyes.

  6. Impact of doping and MOCVD conditions on minority carrier lifetime of zinc- and carbon-doped InGaAs and its applications to zinc- and carbon-doped InP/InGaAs heterostructure bipolar transistors

    NASA Astrophysics Data System (ADS)

    Cui, Delong; Hubbard, Seth M.; Pavlidis, Dimitris; Eisenbach, Andreas; Chelli, Cyril

    2002-06-01

    The impact of doping and metalorganic chemical vapour deposition growth conditions on the minority carrier lifetime of zinc- and carbon-doped InGaAs is reported. Room temperature photoluminescence measurements have been employed to obtain direct information on the non-radiative lifetime of the materials. Low growth temperature and low V/III ratio lead to the lower carrier lifetime of the carbon-doped InGaAs samples. InP/InGaAs heterostructure bipolar transistors were grown and fabricated using both zinc- and carbon-doped InGaAs layers as the base regions. The current gain values measured for these devices agree well with the values calculated from the carrier lifetime and mobility/diffusion coefficient measurements.

  7. High-Performance Wrap-Gated InGaAs Nanowire Field-Effect Transistors with Sputtered Dielectrics

    PubMed Central

    Shen, Li-Fan; Yip, SenPo; Yang, Zai-xing; Fang, Ming; Hung, TakFu; Pun, Edwin Y.B.; Ho, Johnny C.

    2015-01-01

    Although wrap-gated nanowire field-effect-transistors (NWFETs) have been explored as an ideal electronic device geometry for low-power and high-frequency applications, further performance enhancement and practical implementation are still suffering from electron scattering on nanowire surface/interface traps between the nanowire channel and gate dielectric as well as the complicated device fabrication scheme. Here, we report the development of high-performance wrap-gated InGaAs NWFETs using conventional sputtered Al2O3 layers as gate dielectrics, instead of the typically employed atomic layer deposited counterparts. Importantly, the surface chemical passivation of NW channels performed right before the dielectric deposition is found to significantly alleviate plasma induced defect traps on the NW channel. Utilizing this passivation, the wrap-gated device exhibits superior electrical performances: a high ION/IOFF ratio of ~2 × 106, an extremely low sub-threshold slope of 80 mV/decade and a peak field-effect electron mobility of ~1600 cm2/(Vs) at VDS = 0.1 V at room temperature, in which these values are even better than the ones of state-of-the-art NWFETs reported so far. By combining sputtering and pre-deposition chemical passivation to achieve high-quality gate dielectrics for wrap-gated NWFETs, the superior gate coupling and electrical performances have been achieved, confirming the effectiveness of our hybrid approach for future advanced electronic devices. PMID:26607169

  8. Evaluation of InGaAs 640×512 detector array manufactured by Chunghwa Leading Photonics Tech

    NASA Astrophysics Data System (ADS)

    Nagayama, Takahiro; Takeuchi, Nami; Kokusho, Takuma; Yamanaka, Asa; Nishiyama, Miho; Kaneda, Hidehiro

    2014-07-01

    Focal Plane Arrays (FPA) are key items for modern astronomical observations in the near infrared wavelength, but it is very expensive and not easy to get them. Less expensive NIR FPAs with reasonable performance are very important to spread NIR observation extensively. FPA640×512 manufactured by Chunghwa Leading Photonics Tech is a 640×512 InGaAs detector covering the 0.9-1.7 μm wavelength. Since this array is significantly cheaper than the commonly used NIR FPAs in the astronomical observation, it is possible to be a good choice for particular projects which do not need many pixels, if FPA640×512 has acceptable performance for the purpose. We have evaluated one test grade array of FPA640×512 both in the room and low temperature environment. In order to evaluate the characteristics of this FPA in the low temperature environment, we cooled it down by the mechanical refrigerator and confirmed that it works at 100 K. We have found that the dark current reduces exponentially as the FPA temperature decreases, but it hits the bottom at~1000 e-/sec bellow 200 K with the default setting. We are trying to reduce the dark current by optimizing the bias voltage and the current to the MUX circuit. The latest experiments have shown the possibility that the dark current decreases to~200 e-/sec. This value is still higher than that of NIR FPAs used in the scientific observation, but it may be applicable for the particular purpose, for example, FPAs for slit viewer in spectrometers, wave front sensor, and so on.

  9. Compact multichannel receiver using InGaAs APDs for single-pulse eye-safe laser radar imagery

    NASA Astrophysics Data System (ADS)

    Burns, Hoyt N.; Yun, Steven T.; Dinndorf, Kenneth M.; Hayden, David R.

    1997-08-01

    Active imaging laser radars form 3D images which can be processed to provide target identification and precision aimpoint definition in real time. Earlier raster-scanned and pushbroom-scanned 3D imaging laser radar receivers required multiple laser pulses to assemble a complete 3D image frame. Platform/target motion and atmospheric effects caused tearing and jitter in the assembled 3D images, which complicated the subsequent image processing and necessitated the use of stabilized scanning systems. This paper describes the current status of the parallel/multichannel imaging laser radar receiver (PMR) which is being developed under an SBIR Phaser II program by the USAF Wright Laboratories Armament Directorate. The PMR uses an array of multichannel laser radar receivers to form single-pulse, 3D laser radar images, thus eliminating the complex and costly scanning system, and enabling much higher frame rates than were ever before possible. The heart of the PMR is the multichannel optical receiver photonic hybrid (MORPH), a high performance 16-channel laser radar receiver module which uses an array of InGaAs avalanche photodiodes for eyesafe operation. The MORPH provides high downrange resolution, multihit range data for each detector on a compact circuit card. Optical flux is transferred from the receiver focal plane to each MORPH via a fiber optic ribbon cable. An array of MORPHs are plugged into a compact passive backplane, along with a single digital control card (DCC). The DCC, which is the same form factor as the MORPH, synchronizes the MORPHs and transfers the digital range information to the host processor over a standard parallel data interface cable. The system described here illustrates one approach to integrating and packaging high-density photonic arrays and their associated signal processing electronics to yield a compact, low power, scannerless, high performance imaging laser radar receiver, using existing technology.

  10. Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

    SciTech Connect

    Wen, Lei; Gao, Fangliang; Li, Jingling; Guan, Yunfang; Wang, Wenliang; Zhou, Shizhong; Lin, Zhiting; Zhang, Xiaona; Zhang, Shuguang E-mail: mssgzhang@scut.edu.cn; Li, Guoqiang E-mail: mssgzhang@scut.edu.cn

    2014-11-21

    High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an In{sub x}Ga{sub 1−x}As interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of In{sub x}Ga{sub 1−x}As (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in In{sub x}Ga{sub 1−x}As interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when the In composition does not reach the proper value (∼10%), the In{sub x}Ga{sub 1−x}As adopts a lower strain relaxation and undergoes a lattice constant smaller than unstrained GaAs, and therefore introduces compressive stress to GaAs grown on top. When In composition exceeds the proper value, the In{sub x}Ga{sub 1−x}As will adopt a higher strain relaxation and undergoes a lattice constant larger than unstrained GaAs, and therefore introduces tensile stress to GaAs grown on top. As a result, In{sub x}Ga{sub 1−x}As interlayers with improper In composition introduces enlarged misfit stress to GaAs epilayers grown on top, and deteriorates the quality of GaAs epilayers. This work demonstrates a simple but effective method to grow high-quality GaAs epilayers and brings up a broad prospect for the application of GaAs-based optoelectronic devices on Si substrates.

  11. Analysing radiative and non-radiative recombination in InAs QDs on Si for integrated laser applications

    NASA Astrophysics Data System (ADS)

    Orchard, Jonathan R.; Woodhead, Chris; Shutts, Samuel; Wu, Jiang; Sobiesierski, Angela; Young, Rob J.; Beanland, Richard; Liu, Huiyun; Smowton, Peter M.; Mowbray, David J.

    2016-03-01

    Three InAs quantum dot (QD) samples with dislocation filter layers (DFLs) are grown on Si substrates with and without in-situ annealing. Comparison is made to a similar structure grown on a GaAs substrate. The three Si grown samples have different dislocation densities in their active region as revealed by structural studies. By determining the integrated emission as a function of laser power it is possible to determine the power dependence of the radiative efficiency and compare this across the four samples. The radiative efficiency increases with decreasing dislocation density; this also results in a decrease in the temperature quenching of the PL. A laser structures grown on Si and implementing the same optimum DFL and annealing procedure exhibits a greater than 3 fold reduction in threshold current as well as a two fold increase in slope efficiency in comparison to a device in which no annealing is applied.

  12. High-optical-power handling InGaAs photodiodes and balanced receivers for high-spurious free dynamic range (SFDR) analog photonic links

    NASA Astrophysics Data System (ADS)

    Joshi, Abhay M.; Wang, Xinde; Mohr, Dan; Becker, Donald; Patil, Ravikiran

    2004-08-01

    We have developed 20 mA or higher photocurrent handling InGaAs photodiodes with 20 GHz bandwidth, and 10 mA or higher photocurrent handling InGaAs photodiodes with >40 GHz bandwidth. These photodiodes have been thoroughly tested for reliability including Bellcore GR 468 standard and are built to ISO 9001:2000 Quality Management System. These Dual-depletion InGaAs/InP photodiodes are surface illuminated and yet handle such large photocurrent due to advanced band-gap engineering. They have broad wavelength coverage from 800 nm to 1700 nm, and thus can be used at several wavelengths such as 850 nm, 1064 nm, 1310 nm, 1550 nm, and 1620 nm. Furthermore, they exhibit very low Polarization Dependence Loss of 0.05dB typical to 0.1dB maximum. Using above high current handling photodiodes, we have developed classical Push-Pull pair balanced photoreceivers for the 2 to 18 GHz EW system. These balanced photoreceivers boost the Spurious Free Dynamic Range (SFDR) by almost 3 dB by eliminating the laser RIN noise. Future research calls for designing an Avalanche Photodiode Balanced Pair to boost the SFDR even further by additional 3 dB. These devices are a key enabling technology in meeting the SFDR requirements for several DoD systems.

  13. Investigation of electrically active defects in InGaAs quantum wire intermediate-band solar cells using deep-level transient spectroscopy technique

    NASA Astrophysics Data System (ADS)

    Saqri, Noor alhuda Al; Felix, Jorlandio F.; Aziz, Mohsin; Kunets, Vasyl P.; Jameel, Dler; Taylor, David; Henini, Mohamed; Abd El-sadek, Mahmmoud S.; Furrow, Colin; Ware, Morgan E.; Benamara, Mourad; Mortazavi, Mansour; Salamo, Gregory

    2017-01-01

    InGaAs quantum wire (QWr) intermediate-band solar cell-based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current-voltage (I-V) and capacitance-voltage (C-V) techniques, were found to change with temperature over a wide range of 20-340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr-doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr-doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D, and E3QWR_D with activation energies of 0.0037, 0.0053, and 0.041 eV, respectively.

  14. Investigation of electrically active defects in InGaAs quantum wire intermediate-band solar cells using deep-level transient spectroscopy technique.

    PubMed

    Al Saqri, Noor Alhuda; Felix, Jorlandio F; Aziz, Mohsin; Kunets, Vasyl P; Jameel, Dler; Taylor, David; Henini, Mohamed; Abd El-Sadek, Mahmmoud S; Furrow, Colin; Ware, Morgan E; Benamara, Mourad; Mortazavi, Mansour; Salamo, Gregory

    2017-01-27

    InGaAs quantum wire (QWr) intermediate-band solar cell-based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current-voltage (I-V) and capacitance-voltage (C-V) techniques, were found to change with temperature over a wide range of 20-340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr-doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr-doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D, and E3QWR_D with activation energies of 0.0037, 0.0053, and 0.041 eV, respectively.

  15. Comparison of the degradation characteristics of AlON/InGaAs and Al2O3/InGaAs stacks

    NASA Astrophysics Data System (ADS)

    Palumbo, F.; Krylov, I.; Eizenberg, M.

    2015-03-01

    In this paper, the degradation characteristics of MOS (Metal-Oxide-Semiconductor) stacks with Al2O3/AlON or Al2O3 only as dielectric layers on InGaAs were studied. The dielectric nitrides are proposed as possible passivation layers to prevent InGaAs oxidation. At negative bias, it has been found out that the main contribution to the overall degradation of the gate oxide is dominated by the generation of positive charge in the gate oxide. This effect is pronounced in MOS stacks with Al2O3/AlON as dielectric, where we think the positive charge is mainly generated in the AlON interlayer. At positive bias, the degradation is dominated by buildup of negative charge due to electron trapping in pre-existing or stress-induced traps. For stress biases where the leakage currents are low, the changes in the electrical characteristics are dominated by electron-trapping into traps located in energy levels in the upper part of the semiconductor gap. For stress biases with higher leakage current levels, the electron trapping occurs in stress-induced traps increasing the shift of VFB towards positive bias. The overall results clearly show that the improvement of the high-k dielectric/InGaAs interface by introducing N into the Al-oxide does not necessarily mean an increase in the reliability of the MOS stack.

  16. Quantum dots (QDs) restrain human cervical carcinoma HeLa cell proliferation through inhibition of the ROCK-c-Myc signaling.

    PubMed

    Chen, Liqun; Qu, Guangbo; Zhang, Changwen; Zhang, Shuping; He, Jiuyang; Sang, Nan; Liu, Sijin

    2013-03-01

    Cancers often cause significant morbidity and even death to patients. To date, conventional therapies, such as chemotherapy, radiation and surgery, are often limited; meanwhile, novel anticancer therapeutics are urgently needed to improve clinical treatments. Rapid application of nanotechnology and nanomaterials represents a promising vista for the development of anti-cancer therapeutics. However, how to integrate the novel properties of nanotechnology and nanomaterials into cancer treatment warrants close investigation. In the current study, we report a novel finding about the inhibitory effect of CdSe quantum dots (QDs) on Rho-associated kinase (ROCK) activity in cervical carcinoma HeLa cells associated with the attenuation of the ROCK-c-Myc signaling. We mechanistically demonstrated that QD-conducted ROCK inhibition greatly diminished c-Myc protein stability due to reduced phosphorylation, and also suppressed its activity in transcribing target genes (e.g. HSPC111). Thus, the treatment of QDs greatly restrained HeLa cell growth by inducing cell cycle arrest at G1 phase due to the reduced ability of c-Myc in driving cell proliferation. Additionally, since HSPC111, one of the c-Myc targets, is involved in regulating cell growth through ribosomal biogenesis and assembly, the downregulation of HSPC111 could also contribute to diminished proliferation in HeLa cells upon QD treatment. These results together suggested that inhibition of ROCK activity or ROCK-mediated c-Myc signaling in tumor cells upon QD treatment might represent a promising strategy to restrain tumor progression for human cervical carcinoma.

  17. Billiard simulation and FFT analysis of AAS oscillations in nanofabricated InGaAs

    NASA Astrophysics Data System (ADS)

    Koga, Takaaki; Faniel, Sebastien; Mineshige, Shunsuke; Matsuura, Toru; Sekine, Yoshiaki

    2010-03-01

    Gate-voltage-dependent amplitude of magneto-conductance oscillation was analyzed using FFT method. The obtained FFT spectrum was compared with the areal dependence of the occurrence and spin interferece amplitude, calculated for Altshuler-Aronov-Spivak (AAS) type time-reversal pairs of the interference paths on all possible classical trajectroies that were obtained by extensive billiard simulations within the given structures. We have calcuated generic spin interference (SI) curves as a function of the Rashba parameter α, for various values of the Dresselhaus parameter b41^6c6c [eVå^3]. The comparison between theory and experiment suggested that the value of b41^6c6c should be considerably reduced from 27 eVå^3, the generally known value from the k.p theory.

  18. Ex post manipulation of barriers in InGaAs tunnel injection devices

    SciTech Connect

    Talalaev, Vadim G.; Cirlin, George E.; Novikov, Boris V.; Fuhrmann, Bodo; Werner, Peter; Tomm, Jens W.

    2015-01-05

    Ex post manipulation of ∼1.1 μm emitting InGaAs/GaAs-based quantum dot–quantum well tunnel injection light emitting devices is demonstrated experimentally. The devices were operated at elevated forward currents until irreversible alterations were observed. As a result, changes in the steady-state optical spectra (electroluminescence, photoluminescence, and photocurrent), in carrier kinetics, in transport properties, and real structure are found. Except for degradation effects, e.g., of larger quantum dots, also restoration/annealing effects such as increased tunnel barriers are observed. The results furnish evidence for a generic degradation mode of nanostructures. We qualitatively interpret the mechanisms involved on both the nanoscopic and the device scales.

  19. Electron microscopy of GaAs Structures with InAs and as quantum dots

    SciTech Connect

    Nevedomskii, V. N.; Bert, N. A. Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2011-12-15

    An electron-microscopy study of GaAs structures, grown by molecular-beam epitaxy, containing two coupled layers of InAs semiconductor quantum dots (QDs) overgrown with a thin buffer GaAs layer and a layer of low-temperature-grown gallium arsenide has been performed. In subsequent annealing, an array of As nanoinclusions (metallic QDs) was formed in the low-temperature-grown GaAs layer. The variation in the microstructure of the samples during temperature and annealing conditions was examined. It was found that, at comparatively low annealing temperatures (400-500 Degree-Sign C), the formation of the As metallic QDs array weakly depends on whether InAs semiconductor QDs are present in the preceding layers or not. In this case, the As metallic QDs have a characteristic size of about 2-3 nm upon annealing at 400 Degree-Sign C and 4-5 nm upon annealing at 500 Degree-Sign C for 15 min. Annealing at 600 Degree-Sign C for 15 min in the growth setup leads to a coarsening of the As metallic QDs to 8-9 nm and to the formation of groups of such QDs in the area of the low-temperature-grown GaAs which is directly adjacent to the buffer layer separating the InAs semiconductor QDs. A more prolonged annealing at an elevated temperature (760 Degree-Sign C) in an atmosphere of hydrogen causes a further increase in the As metallic QDs' size to 20-25 nm and their spatial displacement into the region between the coupled InAs semiconductor QDs.

  20. Optimising the defect filter layer design for III/V QDs on Si for integrated laser applications

    NASA Astrophysics Data System (ADS)

    Orchard, Jonathan R.; Wu, Jiang; Chen, Siming; Jiang, Qi; Ward, Thomas; Beanland, Richard; Lui, Huiyun; Mowbray, David

    2015-02-01

    We introduce the concept of using strained superlattice structures as defect filters, with their purpose to reduce the upwards propagation of dislocations that result from the lattice mismatch which occurs when III-V materials are grown on silicon substrates. Three samples with defect filter layers are grown on Si with and without in situ annealing and are compared to a similar structure grown on a GaAs substrate. Transmission electron microscopy is used to verify the effectiveness of the different designs grown on Si, with the twice-annealed sample reducing the number of defects present in the active region by 99.9%. Optical studies carried out exhibit brighter room temperature emission and reduced photoluminescence quenching with temperature in samples where annealing is performed. Photoluminescence excitation measurements reveal a ~20 meV redshift in the position of the GaAs exciton for the samples grown on Si compared to that of GaAs, indicating a residual inplane tensile strain ~0.35% in the GaAs of the active region for the samples grown on Si.

  1. MT6415CA: a 640×512-15µm CTIA ROIC for SWIR InGaAs detector arrays

    NASA Astrophysics Data System (ADS)

    Eminoglu, Selim; Isikhan, Murat; Bayhan, Nusret; Gulden, M. Ali; Incedere, O. Samet; Soyer, S. Tuncer; Kocak, Serhat; Yilmaz, Gokhan S.; Akin, Tayfun

    2013-06-01

    This paper reports the development of a new low-noise CTIA ROIC (MT6415CA) suitable for SWIR InGaAs detector arrays for low-light imaging applications. MT6415CA is the second product in the MT6400 series ROICs from Mikro-Tasarim Ltd., which is a fabless IC design house specialized in the development of monolithic imaging sensors and ROICs for hybrid imaging sensors. MT6415CA is a low-noise snapshot CTIA ROIC, has a format of 640 × 512 and pixel pitch of 15 µm, and has been developed with the system-on-chip architecture in mind, where all the timing and biasing for this ROIC are generated on-chip without requiring any external inputs. MT6415CA is a highly configurable ROIC, where many of its features can be programmed through a 3-wire serial interface allowing on-the-fly configuration of many ROIC features. It performs snapshot operation both using Integrate-Then-Read (ITR) and Integrate-While-Read (IWR) modes. The CTIA type pixel input circuitry has three gain modes with programmable full-well-capacity (FWC) values of 10.000 e-, 20.000 e-, and 350.000 e- in the very high gain (VHG), high-gain (HG), and low-gain (LG) modes, respectively. MT6415CA has an input referred noise level of less than 5 e- in the very high gain (VHG) mode, suitable for very low-noise SWIR imaging applications. MT6415CA has 8 analog video outputs that can be programmed in 8, 4, or 2-output modes with a selectable analog reference for pseudo-differential operation. The ROIC runs at 10 MHz and supports frame rate values up to 200 fps in the 8-output mode. The integration time can be programmed up to 1s in steps of 0.1 µs. The ROIC uses 3.3 V and 1.8V supply voltages and dissipates less than 150 mW in the 4-output mode. MT6415CA is fabricated using a modern mixed-signal CMOS process on 200 mm CMOS wafers, and tested parts are available at wafer or die levels with test reports and wafer maps. A compact USB 3.0 camera and imaging software have been developed to demonstrate the imaging

  2. InGaAs axial-junction nanowire-array solar cells

    NASA Astrophysics Data System (ADS)

    Nakai, Eiji; Chen, Muyi; Yoshimura, Masatoshi; Tomioka, Katsuhiro; Fukui, Takashi

    2015-01-01

    Axial p-i-n junction nanowire (NW) solar cells (SCs) with a position-controlled GaAs-based NW array were fabricated by selective-area metal organic vapor phase epitaxy (SA-MOVPE). The measured electron-beam-induced current (EBIC) signals showed the formation of an axial p-i-n junction, which confirms power generation under sunlight illumination. The series resistance of the NW SCs is much higher than that of conventional planar SCs based on Si or other III-V compound semiconductors. The main difficulty concerning the fabrication of these NW SCs is the degradation of series resistance between the GaAs-based NWs and the indium-tin oxide (ITO) deposited as a transparent electrode. The series resistance of the fabricated GaAs-based NW SCs was reduced by introducing a tin doping contact layer between the ITO and the NW array, which is formed by pulse doping. As a result of this improved structure, the fabricated SCs exhibited an open-circuit voltage of 0.544 V, a short-circuit current of 18.2 mA/cm2, and a fill factor of 0.721 for an overall conversion efficiency of 7.14% under AM1.5G illumination. The series resistance of the SCs could be decreased to 0.132 Ω·cm2, which is one order of magnitude lower than that of the SC without a highly doped contact layer. This reduced series resistance indicates that nanostructure SCs with transparent electrodes and multijunction NW SCs with high efficiencies can be fabricated on a commercial basis in the near future.

  3. A low-noise 15-μm pixel-pitch 640×512 hybrid InGaAs image sensor for night vision

    NASA Astrophysics Data System (ADS)

    Guellec, Fabrice; Dubois, Sébastien; de Borniol, Eric; Castelein, Pierre; Martin, Sébastien; Guiguet, Romain; Tchagaspanian, Micha"l.; Rouvié, Anne; Bois, Philippe

    2012-03-01

    Hybrid InGaAs focal plane arrays are very interesting for night vision because they can benefit from the nightglow emission in the Short Wave Infrared band. Through a collaboration between III-V Lab and CEA-Léti, a 640x512 InGaAs image sensor with 15μm pixel pitch has been developed. The good crystalline quality of the InGaAs detectors opens the door to low dark current (around 20nA/cm2 at room temperature and -0.1V bias) as required for low light level imaging. In addition, the InP substrate can be removed to extend the detection range towards the visible spectrum. A custom readout IC (ROIC) has been designed in a standard CMOS 0.18μm technology. The pixel circuit is based on a capacitive transimpedance amplifier (CTIA) with two selectable charge-to-voltage conversion gains. Relying on a thorough noise analysis, this input stage has been optimized to deliver low-noise performance in high-gain mode with a reasonable concession on dynamic range. The exposure time can be maximized up to the frame period thanks to a rolling shutter approach. The frame rate can be up to 120fps or 60fps if the Correlated Double Sampling (CDS) capability of the circuit is enabled. The first results show that the CDS is effective at removing the very low frequency noise present on the reference voltage in our test setup. In this way, the measured total dark noise is around 90 electrons in high-gain mode for 8.3ms exposure time. It is mainly dominated by the dark shot noise for a detector temperature settling around 30°C when not cooled. The readout noise measured with shorter exposure time is around 30 electrons for a dynamic range of 71dB in high-gain mode and 108 electrons for 79dB in low-gain mode.

  4. Solar cells based on InP/GaP/Si structure

    NASA Astrophysics Data System (ADS)

    Kvitsiani, O.; Laperashvil, D.; Laperashvili, T.; Mikelashvili, V.

    2016-10-01

    Solar cells (SCs) based on III-V semiconductors are reviewed. Presented work emphases on the Solar Cells containing Quantum Dots (QDs) for next-generation photovoltaics. In this work the method of fabrication of InP QDs on III-V semiconductors is investigated. The original method of electrochemical deposition of metals: indium (In), gallium (Ga) and of alloys (InGa) on the surface of gallium phosphide (GaP), and mechanism of formation of InP QDs on GaP surface is presented. The possibilities of application of InP/GaP/Si structure as SC are discussed, and the challenges arising is also considered.

  5. Impact of the non-planar morphology of pre-patterned substrates on the structural and electronic properties of embedded site-controlled InAs quantum dots

    SciTech Connect

    Hakkarainen, T. V.; Tommila, J.; Schramm, A.; Guina, M.; Luna, E.

    2013-11-07

    We present an experimental and theoretical analysis of the influence of a surface nanopattern on the properties of embedded InAs/GaAs quantum dots (QD). In particular, we analyze QDs grown on nanoimprint lithography (NIL) patterned grooves and investigate the influence of the non-planar surface morphology on the size, shape, strain distribution, and electronic structure of the embedded QDs. We show that the height reduction of InAs QDs during GaAs capping is significantly less pronounced for the QDs grown on the pattern than for the self-assembled QDs. Furthermore, the pattern has a strong impact on the strain and composition profile within the QD. The experimentally observed strain distribution was successfully reproduced with a three-dimensional model assuming an inverse-cone type composition gradient. Moreover, we show that the specific morphology of the QDs grown in the grooves gives rise to an increase of the vertically polarized photoluminescence emission which was explained by employing 8-band k.p calculations. Our findings emphasize that the surface curvature of the pattern not only determines the nucleation sites of the QDs but also has a strong impact on their morphological properties including shape, size, composition profile, and strain distribution. These properties are strongly cross-correlated and determine the electronic and optical characteristics of the QDs.

  6. A bio-chemical application of N-GQDs and g-C3N4 QDs sensitized TiO2 nanopillars for the quantitative detection of pcDNA3-HBV.

    PubMed

    Pang, Xuehui; Bian, Hongjun; Wang, Weijie; Liu, Cheng; Khan, Malik Saddam; Wang, Qiao; Qi, Jianni; Wei, Qin; Du, Bin

    2017-05-15

    Herein, TiO2 nanopillars (NPs)/N-doped graphene quantum dots (N-GQDs)/g-C3N4 QDs heterojunction efficiently suppressed the photogenerated charges recombination and improved photo-to-current conversion efficiency. The introduced N-GQDs and g-C3N4 QDs could result in more effective separation of the photogenerated charges, and thus produce a further increase of the photocurrent. TiO2 NPs/N-GQDs/g-C3N4 QDs were firstly applied as the photoactive materials for the fabrication of the biosensors, and the primers of pcDNA3-HBV were then adsorbed on the TiO2 NPs/N-GQDs/g-C3N4 QDs modified electrode under the activation of EDC/NHS. With increase of the pcDNA3-HBV concentration, the photocurrent reduced once the double helix between the primers and pcDNA3-HBV formed. The developed photoelectrochemical (PEC) biosensor showed a sensitive response to pcDNA3-HBV in a linear range of 0.01 fmol/L to 20nmol/L with a detection limit of 0.005 fmol/L under the optimal conditions. The biosensor exhibited high sensitivity, good selectivity, good stability and reproducibility.

  7. Fe-implanted InGaAs photoconductive terahertz detectors triggered by 1.56 μm femtosecond optical pulses

    NASA Astrophysics Data System (ADS)

    Suzuki, Masato; Tonouchi, Masayoshi

    2005-04-01

    Performance of InGaAs photoconductive antennas at an excitation wavelength of 1.56μm has been studied as a terahertz (THz) detector. THz waves in time domain are successfully detected, triggered with 1.56μm femtosecond optical pulses, owing to Fe implantation and annealing at 400 and 580 °C. The peak amplitudes of the THz detected waves by the as-implanted and the low-temperature-annealed detectors saturate with increasing the excitation power. The thermal annealing affects both the frequency component and the amplitude of the THz detected waveforms. In particular, annealing at 580 °C induces twice the increase in the amplitude of the signals.

  8. Interface trap density and mobility extraction in InGaAs buried quantum well metal-oxide-semiconductor field-effect-transistors by gated Hall method

    SciTech Connect

    Chidambaram, Thenappan; Madisetti, Shailesh; Greene, Andrew; Yakimov, Michael; Tokranov, Vadim; Oktyabrsky, Serge; Veksler, Dmitry; Hill, Richard

    2014-03-31

    In this work, we are using a gated Hall method for measurement of free carrier density and electron mobility in buried InGaAs quantum well metal-oxide-semiconductor field-effect-transistor channels. At room temperature, mobility over 8000 cm{sup 2}/Vs is observed at ∼1.4 × 10{sup 12} cm{sup −2}. Temperature dependence of the electron mobility gives the evidence that remote Coulomb scattering dominates at electron density <2 × 10{sup 11} cm{sup −2}. Spectrum of the interface/border traps is quantified from comparison of Hall data with capacitance-voltage measurements or electrostatic modeling. Above the threshold voltage, gate control is strongly limited by fast traps that cannot be distinguished from free channel carriers just by capacitance-based methods and can be the reason for significant overestimation of channel density and underestimation of carrier mobility from transistor measurements.

  9. Near-infrared electroluminescence and photo detection in InGaAs p-i-n microdisks grown by selective area growth on silicon

    SciTech Connect

    Kjellman, Jon Øyvind; Sugiyama, Masakazu; Nakano, Yoshiaki

    2014-06-16

    Microselective-area growth of p-i-n InGaAs disks on (111) silicon by metalorganic chemical vapor deposition is a promising technology for III/V-on-Si integration. As a proof-of-concept, room-temperature electroluminescence is reported from ensembles of p-i-n InGaAs-on-Si micro-disks. The observed spectrum shows peak luminescence at 1.78 μm with a local maxima at 1.65 μm. The disks are also shown to generate a measurable photo current when illuminated by infrared light with less energy than the silicon bandgap energy. This makes these InGaAs-on-Si disks a promising technology for monolithic integration of light sources and detectors with silicon photonics and complementary metal-oxide-semiconductor electronics for optical communication, sensing, and imaging.

  10. Fermi level pinning in metal/Al{sub 2}O{sub 3}/InGaAs gate stack after post metallization annealing

    SciTech Connect

    Winter, R.; Krylov, I.; Cytermann, C.; Eizenberg, M.; Tang, K.; Ahn, J.; McIntyre, P. C.

    2015-08-07

    The effect of post metal deposition annealing on the effective work function in metal/Al{sub 2}O{sub 3}/InGaAs gate stacks was investigated. The effective work functions of different metal gates (Al, Au, and Pt) were measured. Flat band voltage shifts for these and other metals studied suggest that their Fermi levels become pinned after the post-metallization vacuum annealing. Moreover, there is a difference between the measured effective work functions of Al and Pt, and the reported vacuum work function of these metals after annealing. We propose that this phenomenon is caused by charging of indium and gallium induced traps at the annealed metal/Al{sub 2}O{sub 3} interface.

  11. Characteristics of the dynamics of breakdown filaments in Al{sub 2}O{sub 3}/InGaAs stacks

    SciTech Connect

    Palumbo, F.; Shekhter, P.; Eizenberg, M.; Cohen Weinfeld, K.

    2015-09-21

    In this paper, the Al{sub 2}O{sub 3}/InGaAs interface was studied by X-ray photoelectron spectroscopy (XPS) after a breakdown (BD) event at positive bias applied to the gate contact. The dynamics of the BD event were studied by comparable XPS measurements with different current compliance levels during the BD event. The overall results show that indium atoms from the substrate move towards the oxide by an electro-migration process and oxidize upon arrival following a power law dependence on the current compliance of the BD event. Such a result reveals the physical feature of the breakdown characteristics of III-V based metal-oxide-semiconductor devices.

  12. InGaAs tunnel FET with sub-nanometer EOT and sub-60 mV/dec sub-threshold swing at room temperature

    NASA Astrophysics Data System (ADS)

    Alian, A.; Mols, Y.; Bordallo, C. C. M.; Verreck, D.; Verhulst, A.; Vandooren, A.; Rooyackers, R.; Agopian, P. G. D.; Martino, J. A.; Thean, A.; Lin, D.; Mocuta, D.; Collaert, N.

    2016-12-01

    InGaAs homojunction Tunnel FET devices are demonstrated with sub-60 mV/dec Sub-threshold Swing (SS) measured in DC. A 54 mV/dec SS is achieved at 100 pA/μm over a drain voltage range of 0.2-0.5 V. The SS remains sub-60 mV/dec over 1.5 orders of magnitude of current at room temperature. Trap-Assisted Tunneling (TAT) is found to be negligible in the device evidenced by low temperature dependence of the transfer characteristics. Equivalent Oxide Thickness (EOT) is found to play the major role in achieving sub-60 mV/dec performance. The EOT of the demonstrated devices is 0.8 nm.

  13. Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots.

    PubMed

    Li, Yan; Sinitsyn, N; Smith, D L; Reuter, D; Wieck, A D; Yakovlev, D R; Bayer, M; Crooker, S A

    2012-05-04

    The problem of how single central spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying time scales and dynamical responses (exponential, power-law, gaussian, etc.). Here we detect the small random fluctuations of central spins in thermal equilibrium [holes in singly charged (In,Ga)As quantum dots] to reveal the time scales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at a zero magnetic field that increase to ∼5  μs as dominant hole-nuclear relaxation channels are suppressed with small (100 G) applied fields. Concomitantly, the noise line shape evolves from Lorentzian to power law, indicating a crossover from exponential to slow [∼1/log(t)] dynamics.

  14. Enhanced electrogenerated chemiluminescence behavior of C3N4 QDs@ C3N4 nanosheet and its signal-on aptasensing for platelet derived growth factor.

    PubMed

    Xu, Huifeng; Liang, Shijing; Zhu, Xi; Wu, Xiuqin; Dong, Yongqiang; Wu, Haishan; Zhang, Wenxia; Chi, Yuwu

    2017-06-15

    A novel g-C3N4 nanosheets embedded with C3N4 QDs nanocomposites (QD@CNNS) was prepared by simple oxidation using hydrogen peroxide and UV light irradiation. This nanocomposite exhibits more stable and stronger electrochemiluminescent (ECL) behavior compared with CNNS. Coupling this nanocomposite with Fc-labeled aptamer, a signal-on aptasensor for platelet derived growth factor BB (PDGF-BB) is fabricated. Initially, the Fc-labeled aptamer binds onto QD@CNNS via π-π conjugation and electrostatic interaction, quenching ECL emission from QD@CNNS. The introduction of target efficiently recovers the ECL signal by the formation of PDGF-BB/aptamer complex. The ECL intensity is proportion to the concentration of PDGF-BB in the range of 0.02-80nM with a detection limit of 0.013nM. This work demonstrates a simple synthesis method to obtain QD@CNNS with excellent ECL behavior, and opens up the application of g-C3N4 nanocomposite in signal-on aptasensing.

  15. Characteristics and reliability of high power multi-mode InGaAs strained quantum well single emitters with CW output powers of over 5W

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Presser, Nathan; Mason, Maribeth; Moss, Steven C.

    2006-02-01

    High-power multi-mode broad area InGaAs strained quantum well (QW) single emitters (λ ~ 920-980nm) have been mainly used for industrial applications. Recently, these broad area lasers with CW output powers >5W have also found applications in communications as pump lasers for Er-Yb co-doped fiber amplifiers. This application requires very demanding characteristics including higher reliability than industrial applications. In contrast to 980nm single mode InGaAs strained QW lasers that are widely employed in both terrestrial and submarine applications, the fact that multimode lasers have never been used in optical communications necessitates careful study of these lasers. We report investigations of performance characteristics, reliability, and failure modes of high-power multi-mode single emitters. The lasers studied were broad area strained InGaAs-GaAs single QW lasers grown either by MOCVD or MBE. Typical apertures were around 100μm wide and cavity lengths were <=4.2mm. AR-HR coated laser diode chips were mounted on carriers with junction down configuration to reduce thermal impedance. Laser thresholds were <=453mA at RT. At 6A injection current typical CW output powers were over 5W at 25°C with wall-plug efficiency of ~60%. Characteristics measured included thermal impedance and optical beam profiles that are critical in understanding performance and reliability. Automatic current control burn-in tests with different stress conditions were performed and log (I)-V characteristics were measured at RT to correlate degradation in optical output power and an increase in trap density estimated from the 2κ•T term in bulk recombination current. We also report initial analysis of lifetest results and failure modes from these lasers.

  16. Quantum Dots Encapsulated within Phospholipid Membranes: Phase-Dependent Structure, Photostability, and Site-Selective Functionalization

    PubMed Central

    2015-01-01

    Lipid vesicle encapsulation is an efficient approach to transfer quantum dots (QDs) into aqueous solutions, which is important for renewable energy applications and biological imaging. However, little is known about the molecular organization at the interface between a QD and lipid membrane. To address this issue, we investigated the properties of 3.0 nm CdSe QDs encapsulated within phospholipid membranes displaying a range of phase transition temperatures (Tm). Theoretical and experimental results indicate that the QD locally alters membrane structure, and in turn, the physical state (phase) of the membrane controls the optical and chemical properties of the QDs. Using photoluminescence, ICP-MS, optical microscopy, and ligand exchange studies, we found that the Tm of the membrane controls optical and chemical properties of lipid vesicle-embedded QDs. Importantly, QDs encapsulated within gel-phase membranes were ultrastable, providing the most photostable non-core/shell QDs in aqueous solution reported to date. Atomistic molecular dynamics simulations support these observations and indicate that membranes are locally disordered displaying greater disordered organization near the particle–solution interface. Using this asymmetry in membrane organization near the particle, we identify a new approach for site-selective modification of QDs by specifically functionalizing the QD surface facing the outer lipid leaflet to generate gold nanoparticle–QD assemblies programmed by Watson–Crick base-pairing. PMID:24417287

  17. A comparison between HfO2/Al2O3 nano-laminates and ternary HfxAlyO compound as the dielectric material in InGaAs based metal-oxide-semiconductor (MOS) capacitors

    NASA Astrophysics Data System (ADS)

    Krylov, Igor; Pokroy, Boaz; Eizenberg, Moshe; Ritter, Dan

    2016-09-01

    We compare the electrical properties of HfO2/Al2O3 nano-laminates with those of the ternary HfxAlyO compound in metal oxide semiconductor (MOS) capacitors. The dielectrics were deposited by atomic layer deposition on InGaAs. Water, ozone, and oxygen plasma were tested as oxygen precursors, and best results were obtained using water. The total dielectric thickness was kept constant in our experiments. It was found that the effective dielectric constant increased and the leakage current decreased with the number of periods. Best results were obtained for the ternary compound. The effect of the sublayer thicknesses on the electrical properties of the interface was carefully investigated, as well as the role of post-metallization annealing. Possible explanations for the observed trends are provided. We conclude that the ternary HfxAlyO compound is more favorable than the nano-laminates approach for InGaAs based MOS transistor applications.

  18. Low defect InGaAs quantum well selectively grown by metal organic chemical vapor deposition on Si(100) 300 mm wafers for next generation non planar devices

    SciTech Connect

    Cipro, R.; Gorbenko, V.; Baron, T. Martin, M.; Moeyaert, J.; David, S.; Bassani, F.; Bogumilowicz, Y.; Barnes, J. P.; Rochat, N.; Loup, V.; Vizioz, C.; Allouti, N.; Chauvin, N.; Bao, X. Y.; Ye, Z.; Pin, J. B.; Sanchez, E.

    2014-06-30

    Metal organic chemical vapor deposition of GaAs, InGaAs, and AlGaAs on nominal 300 mm Si(100) at temperatures below 550 °C was studied using the selective aspect ratio trapping method. We clearly show that growing directly GaAs on a flat Si surface in a SiO{sub 2} cavity with an aspect ratio as low as 1.3 is efficient to completely annihilate the anti-phase boundary domains. InGaAs quantum wells were grown on a GaAs buffer and exhibit room temperature micro-photoluminescence. Cathodoluminescence reveals the presence of dark spots which could be associated with the presence of emerging dislocation in a direction parallel to the cavity. The InGaAs layers obtained with no antiphase boundaries are perfect candidates for being integrated as channels in n-type metal oxide semiconductor field effect transistor (MOSFET), while the low temperatures used allow the co-integration of p-type MOSFET.

  19. Effects of gate-last and gate-first process on deep submicron inversion-mode InGaAs n-channel metal-oxide-semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Gu, J. J.; Wu, Y. Q.; Ye, P. D.

    2011-03-01

    Recently, encouraging progress has been made on surface-channel inversion-mode In-rich InGaAs NMOSFETs with superior drive current, high transconductance and minuscule gate leakage, using atomic layer deposited (ALD) high-k dielectrics. Although gate-last process is favorable for high-k/III-V integration, high-speed logic devices require a self-aligned gate-first process for reducing the parasitic resistance and overlap capacitance. On the other hand, a gate-first process usually requires higher thermal budget and may degrade the III-V device performance. In this paper, we systematically investigate the thermal budget of gate-last and gate-first process for deep-submicron InGaAs MOSFETs. We conclude that the thermal instability of (NH4)2S as the pretreatment before ALD gate dielectric formation leads to the potential failure of enhancement-mode operation and deteriorates interface quality in the gate-first process. We thus report on the detailed study of scaling metrics of deep-submicron self-aligned InGaAs MOSFET without sulfur passivation, featuring optimized threshold voltage and negligible off-state degradation.

  20. Electronic structure of cobalt doped CdSe quantum dots using soft X-ray spectroscopy

    SciTech Connect

    Joshua T. Wright; Su, Dong; van Buuren, Tony; Meulenberg, Robert W.

    2014-08-21

    The electronic structure and magnetic properties of cobalt doped CdSe quantum dots (QDs) are studied using electron microscopy, soft X-ray spectroscopy, and magnetometry. Magnetometry measurements suggest these QDs are superparamagnetic, contrary to a spin-glass state observed in the bulk analogue. Moreover, the electron microscopy shows well formed QDs, but with cobalt existing as doped into the QD and as unreacted species not contained in the QD. X-ray absorption measurements at the Co L3-edge suggest that changes in spectra features as a function of particle size can be described considering combination of a cobalt ion in a tetrahedral crystal field and an octahedrally coordinated (impurity) phase. With decreasing particle sizes, the impurity phase increases, suggesting that small QDs can be difficult to dope.

  1. Structure and properties of InAs/AlAs quantum dots for broadband emission

    NASA Astrophysics Data System (ADS)

    Meng, X. Q.; Jin, P.; Liang, Z. M.; Liu, F. Q.; Wang, Z. G.; Zhang, Z. Y.

    2010-11-01

    The InAs quantum dots (QDs) on an AlAs layer are grown on GaAs substrates by molecular beam epitaxy technique. The properties of materials and optics of such QD structures have been investigated by cross sectional transmission electron microscopy and photoluminescence (PL) techniques. It is discovered that the inhomogeneous strain filed mainly exists below InAs QDs layers in the case of no wetting layer. The full width at half maximums (FWHMs) and intensities of PL emission peaks of InAs QDs are found to be closely related to the thickness of the thin AlAs layers. The InAs QDs on an eight monolayer AlAs layer, with wide FWHMs and large integral intensity of PL emission peaks, are favorable for producing broadband QD superluminescent diodes, external-cavity QD laser with large tuning range.

  2. Control of electrochemical signals from quantum dots conjugated to organic materials by using DNA structure in an analog logic gate.

    PubMed

    Chen, Qi; Yoo, Si-Youl; Chung, Yong-Ho; Lee, Ji-Young; Min, Junhong; Choi, Jeong-Woo

    2016-10-01

    Various bio-logic gates have been studied intensively to overcome the rigidity of single-function silicon-based logic devices arising from combinations of various gates. Here, a simple control tool using electrochemical signals from quantum dots (QDs) was constructed using DNA and organic materials for multiple logic functions. The electrochemical redox current generated from QDs was controlled by the DNA structure. DNA structure, in turn, was dependent on the components (organic materials) and the input signal (pH). Independent electrochemical signals from two different logic units containing QDs were merged into a single analog-type logic gate, which was controlled by two inputs. We applied this electrochemical biodevice to a simple logic system and achieved various logic functions from the controlled pH input sets. This could be further improved by choosing QDs, ionic conditions, or DNA sequences. This research provides a feasible method for fabricating an artificial intelligence system.

  3. Three-dimensional imaging for precise structural control of Si quantum dot networks for all-Si solar cells

    NASA Astrophysics Data System (ADS)

    Kourkoutis, Lena F.; Hao, Xiaojing; Huang, Shujuan; Puthen-Veettil, Binesh; Conibeer, Gavin; Green, Martin A.; Perez-Wurfl, Ivan

    2013-07-01

    All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to reduced inter-QD coupling in the layer. Efficient carrier transport via mini-bands is in this case more likely across the multilayers provided the SiO2 spacer layer is thin enough to allow coupling in the vertical direction.All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to

  4. Hybrid structures based on quantum dots and graphene nanobelts

    NASA Astrophysics Data System (ADS)

    Reznik, I. A.; Gromova, Yu. A.; Zlatov, A. S.; Baranov, M. A.; Orlova, A. O.; Moshkalev, S. A.; Maslov, V. G.; Baranov, A. V.; Fedorov, A. V.

    2017-01-01

    Luminescence and photoelectric properties of hybrid structures based on CdSe/ZnS quantum dots (QDs) and multilayer graphene have been investigated. A correlation between the luminescence quantum yield of QDs and their photoelectric properties in hybrid structures is established. It is shown that a decrease in the QD luminescence quantum yield due to adsorption of 1-(2-pyridylazo)-2-naphtol azo dye molecules onto the QD surface and a photoinduced increase in the QD luminescence quantum yield are accompanied by a symbate change in the hybrid structure photoconductivity.

  5. A sensitive and selective sensing platform based on CdTe QDs in the presence of l-cysteine for detection of silver, mercury and copper ions in water and various drinks.

    PubMed

    Gong, Tingting; Liu, Junfeng; Liu, Xinxin; Liu, Jie; Xiang, Jinkun; Wu, Yiwei

    2016-12-15

    Water soluble CdTe quantum dots (QDs) have been prepared simply by one-pot method using potassium tellurite as stable tellurium source and thioglycolic acid (TGA) as stabilizer. The fluorescence of CdTe QDs can be improved 1.3-fold in the presence of l-cysteine (Cys), however, highly efficiently quenched in the presence of silver or mercury or copper ions. A sensitive and selective sensing platform for analysis of silver, mercury and copper ions has been simply established based on CdTe QDs in the presence of l-cysteine. Under the optimum conditions, excellent linear relationships exist between the quenching degree of the sensing platform and the concentrations of Ag(+), Hg(2+) and Cu(2+) ranging from 0.5 to 40ngmL(-1). By using masking agents of sodium diethyldithiocarbamate (DDTC) for Ag(+) and Cu(2+), NH4OH for Ag(+) and Hg(2+) and 1-(2-Pyridylazo)-2-naphthol (PAN) for Hg(2+) and Cu(2+), Hg(2+), Cu(2+) and Ag(+) can be exclusively detected in coexistence with other two ions, and the detection limits (3σ) were 0.65, 0.063 and 0.088ngmL(-1) for Ag(+), Hg(2+) and Cu(2+), respectively. This effective sensing platform has been used to detection of Ag(+), Hg(2+) and Cu(2+) in water and various drinks with satisfactory results.

  6. Photoreflectance and photoluminescence study of InAs dots-in-a-well nanostructures

    SciTech Connect

    Nedzinskas, Ramūnas; Čechavičius, Bronislovas; Kavaliauskas, Julius; Karpus, Vytautas; Valušis, Gintaras; Li, Lianhe; Khanna, Suraj P.; Linfield, Edmund H.

    2013-12-04

    InAs quantum dots (QDs), embedded within InGaAs/GaAs/AlAs and GaAs/AlAs quantum wells (QWs), are examined by photoreflectance and photoluminescence techniques. Optical properties and electronic structure of two differently designed dots-in-a-well nanostructures is revealed focusing on the effect of strain-reducing InGaAs layer, which is discussed in detail. It is found that the use of InGaAs capping layer red-shifts the QD ground-state interband transition energy by about 100 meV maintaining strong quantization of the electronic states. The changes in InAs QD electronic properties are ascribed mainly to QD size/shape variation due to decomposition of InGaAs layer during growth process.

  7. Effect of the bimodality of a QD array on the optical properties and threshold characteristics of QD lasers

    SciTech Connect

    Nadtochiy, A. M.; Mintairov, S. A.; Kalyuzhnyy, N. A.; Rouvimov, S. S.; Shernyakov, Yu. M.; Payusov, A. S.; Maximov, M. V.; Zhukov, A. E.

    2015-08-15

    Heterostructures with InGaAs quantum dots (QDs) are synthesized on vicinal GaAs (001) substrates. The photoluminescence (PL) spectra and threshold characteristics of edge-emitting QD lasers are studied in the temperature range 10-400 K. The structural properties of QDs are examined by transmission electron microscopy. Analysis of the PL spectra demonstrates the bimodality of the QD array, which leads to an unusual temperature behavior of the PL spectra and threshold current density. A model of the population of a bimodal QD array by carriers, describing the observed phenomena, is considered.

  8. Synthesis and characterizations of ternary InGaAs nanowires by a two-step growth method for high-performance electronic devices.

    PubMed

    Hou, Jared J; Han, Ning; Wang, Fengyun; Xiu, Fei; Yip, Senpo; Hui, Alvin T; Hung, TakFu; Ho, Johnny C

    2012-04-24

    InAs nanowires have been extensively studied for high-speed and high-frequency electronics due to the low effective electron mass and corresponding high carrier mobility. However, further applications still suffer from the significant leakage current in InAs nanowire devices arising from the small electronic band gap. Here, we demonstrate the successful synthesis of ternary InGaAs nanowires in order to tackle this leakage issue utilizing the larger band gap material but at the same time not sacrificing the high electron mobility. In this work, we adapt a two-step growth method on amorphous SiO(2)/Si substrates which significantly reduces the kinked morphology and surface coating along the nanowires. The grown nanowires exhibit excellent crystallinity and uniform stoichiometric composition along the entire length of the nanowires. More importantly, the electrical properties of those nanowires are found to be remarkably impressive with I(ON)/I(OFF) ratio >10(5), field-effect mobility of ∼2700 cm(2)/(V·s), and ON current density of ∼0.9 mA/μm. These nanowires are then employed in the contact printing and achieve large-scale assembly of nanowire parallel arrays which further illustrate the potential for utilizing these high-performance nanowires on substrates for the fabrication of future integrated circuits.

  9. A 50 MHz-1 GHz high linearity CATV amplifier with a 0.15 μm InGaAs PHEMT process

    NASA Astrophysics Data System (ADS)

    Jian, Xu; Zhigong, Wang; Ying, Zhang; Jing, Huang

    2011-07-01

    A 50 MHz-1 GHz low noise and high linearity amplifier monolithic-microwave integrated-circuit (MMIC) for cable TV is presented. A shunt AC voltage negative feedback combined with source current negative feedback is adopted to extend the bandwidth and linearity. A novel DC bias feedback is introduced to stabilize the operation point, which improved the linearity further. The circuit was fabricated with a 0.15 μm InGaAs PHEMT (pseudomorphic high electron mobility transistor) process. The test was carried out in 75 Ω systems from 50 MHz to 1 GHz. The measurement results showed that it gave a small signal gain of 16.5 dB with little gain ripples of less than ± 1 dB. An excellent noise figure of 1.7-2.9 dB is obtained in the designed band. The IIP3 is 16 dBm, which shows very good linearity. The CSO and CTB are high up to 68 dBc and 77 dBc, respectively. The chip area is 0.56 mm2 and the power dissipation is 110 mA with a 5 V supply. It is ideally suited to cable TV systems.

  10. Determination of limiting factors of photovoltaic efficiency in quantum dot sensitized solar cells: Correlation between cell performance and structural properties

    NASA Astrophysics Data System (ADS)

    Giménez, Sixto; Lana-Villarreal, Teresa; Gómez, Roberto; Agouram, Said; Muñoz-Sanjosé, V.; Mora-Seró, Iván

    2010-09-01

    Semiconductor quantum dots (QDs) are important candidates as light absorbing materials in low cost and high efficiency sensitized solar cells (SCs). We present a combination of structural, chemical, electrical, and optical characterization that provides insight to the photovoltaic efficiencies of devices formed by TiO2 electron conducting oxide network sensitized with CdSe. In devices using colloidal QDs the collection efficiency under short circuit conditions (CESCs) for photoinjected electrons is rather high (˜90%) but the photovoltaic performance is limited by the low loading of QDs into the mesoporous TiO2 structure. On the other hand, chemical bath deposited (CBD) QDSCs exhibit a remarkably high optical density, but only slightly higher short circuit current and efficiency. It is observed that CESC is ˜50% due to the high recombination rates of the closed packed QDs structure. Our results indicate routes for improvement of QDSCs performance by the increase in colloidal QDs loading and the reduction in recombination in QDs grown in situ.

  11. Quantum dots based mesoporous structured imprinting microspheres for the sensitive fluorescent detection of phycocyanin.

    PubMed

    Zhang, Zhong; Li, Jinhua; Wang, Xiaoyan; Shen, Dazhong; Chen, Lingxin

    2015-05-06

    Phycocyanin with important physiological/environmental significance has attracted increasing attention; versatile molecularly imprinted polymers (MIPs) have been applied to diverse species, but protein imprinting is still quite difficult. Herein, using phycocyanin as template via a sol-gel process, we developed a novel fluorescent probe for specific recognition and sensitive detection of phycocyanin by quantum dots (QDs) based mesoporous structured imprinting microspheres (SiO2@QDs@ms-MIPs), obeying electron-transfer-induced fluorescence quenching mechanism. When phycocyanin was present, a Meisenheimer complex would be produced between phycocyanin and primary amino groups of QDs surface, and then the photoluminescent energy of QDs would be transferred to the complex, leading to the fluorescence quenching of QDs. As a result, the fluorescent intensity of the SiO2@QDs@ms-MIPs was significantly decreased within 8 min, and accordingly a favorable linearity within 0.02-0.8 μM and a high detectability of 5.9 nM were presented. Excellent recognition specificity for phycocyanin over its analogues was displayed, with a high imprinting factor of 4.72. Furthermore, the validated probe strategy was successfully applied to seawater and lake water sample analysis, and high recoveries in the range of 94.0-105.0% were attained at three spiking levels of phycocyanin, with precisions below 5.3%. The study provided promising perspectives to develop fluorescent probes for convenient, rapid recognition and sensitive detection of trace proteins from complex matrices, and further pushed forward protein imprinting research.

  12. The influence of surface preparation on low temperature HfO{sub 2} ALD on InGaAs (001) and (110) surfaces

    SciTech Connect

    Kent, Tyler; Edmonds, Mary; Kummel, Andrew C.; Tang, Kechao; Negara, Muhammad Adi; McIntyre, Paul; Chobpattana, Varistha; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi

    2015-10-28

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher C{sub max} hypothesized to be a result of poor nucleation of HfO{sub 2} on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low D{sub it} high C{sub ox} MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

  13. The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces

    NASA Astrophysics Data System (ADS)

    Kent, Tyler; Tang, Kechao; Chobpattana, Varistha; Negara, Muhammad Adi; Edmonds, Mary; Mitchell, William; Sahu, Bhagawan; Galatage, Rohit; Droopad, Ravi; McIntyre, Paul; Kummel, Andrew C.

    2015-10-01

    Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher Cmax hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low Dit high Cox MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

  14. High resolution synchrotron radiation based photoemission study of the in situ deposition of molecular sulphur on the atomically clean InGaAs surface

    NASA Astrophysics Data System (ADS)

    Chauhan, Lalit; Hughes, Greg

    2012-06-01

    High resolution synchrotron radiation core level photoemission studies were performed on atomically clean 0.5 μm thick In0.53Ga0.47As (100) epilayers lattice matched to InP substrates following the removal of a 100 nm protective arsenic cap at 410 °C. Both n-type (Si doped 5 × 1017 cm-3) and p-type (Be doped 5 × 1017 cm-3) InGaAs samples were subsequently exposed in situ to molecular sulphur at room temperature, and the resulting changes in the surface chemical composition were recorded. The photoemission spectra indicate evidence of As-S, Ga-S, and In-S bond formation and the substitution of As in the near surface region by sulphur. Annealing to 400 °C results in the complete removal of the As-S bonding component with both Ga-S and In-S bonding configurations remaining. After the anneal, the Fermi level position for both n-type and p-type samples resides at the top of the bandgap indicating a near flat band condition for n-type and significant band bending on the p-type sample. The results of angle resolved photoemission measurements suggest that the sulphur has substituted arsenic in the near surface region resulting in both samples displaying n-type surface behaviour. Annealing to higher temperatures results in the loss of In from the surface without any significant change in the Ga, As, or S signals. Work function measurements on both doping types after sulphur deposition and anneal show similar behaviour displaying a value close to 6 eV which is indicative of the formation of a surface dipole layer related to the presence of sulphur on the surface.

  15. Study of InGaAs-based modulation doped field effect transistor structures using variable-angle spectroscopic ellipsometry

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Sieg, R. M.; Yao, H. D.; Snyder, P. G.; Woollam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.

    1991-01-01

    Variable-angle spectroscopic ellipsometry was used to estimate the thicknesses of all layers within the optical penetration depth of InGaAs-based modulation doped field effect transistor structures. Strained and unstrained InGaAs channels were made by molecular beam epitaxy (MBE) on InP substrates and by metal-organic chemical vapor deposition on GaAs substrates. In most cases, ellipsometrically determined thicknesses were within 10% of the growth-calibration results. The MBE-made InGaAs strained layers showed large strain effects, indicating a probable shift in the critical points of their dielectric function toward the InP lattice-matched concentration.

  16. Investigation on multi-frequency oscillations in InGaAs planar Gunn diode with multiple anode-cathode spacings

    NASA Astrophysics Data System (ADS)

    Li, B.; Alimi, Y.; Ma, G. L.

    2016-12-01

    Current oscillations in an AlGaAs/InGaAs/AlGaAs-based two-dimensional electron gas (2DEG)-based hetero-structure have been investigated by means of semiconductor device simulation software SILVACO, with an interest on the charge domain formation at large biases. Single-frequency oscillations are generated in planar Gunn diodes with uniform anode and cathode contacts. The oscillation frequency reduces as the applied bias voltage increases. We show that it is possible to create multiple, independent charge domains in a novel Gunn diode structure with designed multiple anode-cathode spacings. This enables simultaneous generation of multiple frequency oscillations in a single planar device, in contrast to traditional vertical Gunn diodes where only single-frequency oscillations can be achieved. More interestingly, frequency mixing in multiple-channel configured Gunn diodes appeared. This proof-of-concept opens up the possibility for realizing compact self-oscillating mixer at millimeter-wave applications.

  17. Simultaneous coupling of surface plasmon resonance and photonic bandgap to InGaAs quantum well emission

    SciTech Connect

    Gao, Hongwei; Teng, Jinghua; Chua, Soo Jin

    2016-01-07

    A photonic bandgap structure was created on the 100 nm thick GaAs barrier layer with Au nanodisks deposited inside the holes. To mitigate the nonradiative surface recombination of GaAs, the Au nanodisks were formed on top of a 15 nm SiO{sub 2} deposited in the holes. A maximum 7.6-fold increase in photoluminescence intensity was obtained at the etch depth of 80 nm. In this configuration, the Au nanodisk is separated from the quantum well by 20 nm of GaAs and 15 nm of SiO{sub 2}. The experimental result was verified by the simulation based on this structure. There was a good agreement between experiments with simulation results.

  18. Correlation of atomic structure and photoluminescence of the same quantum dot: pinpointing surface and internal defects that inhibit photoluminescence.

    PubMed

    Orfield, Noah J; McBride, James R; Keene, Joseph D; Davis, Lloyd M; Rosenthal, Sandra J

    2015-01-27

    In a size regime where every atom counts, rational design and synthesis of optimal nanostructures demands direct interrogation of the effects of structural divergence of individuals on the ensemble-averaged property. To this end, we have explored the structure-function relationship of single quantum dots (QDs) via precise observation of the impact of atomic arrangement on QD fluorescence. Utilizing wide-field fluorescence microscopy and atomic number contrast scanning transmission electron microscopy (Z-STEM), we have achieved correlation of photoluminescence (PL) data and atomic-level structural information from individual colloidal QDs. This investigation of CdSe/CdS core/shell QDs has enabled exploration of the fine structural factors necessary to control QD PL. Additionally, we have identified specific morphological and structural anomalies, in the form of internal and surface defects, that consistently vitiate QD PL.

  19. DC and RF characterization of InGaAs replacement metal gate (RMG) nFETs on SiGe-OI FinFETs fabricated by 3D monolithic integration

    NASA Astrophysics Data System (ADS)

    Deshpande, V.; Djara, V.; O'Connor, E.; Hashemi, P.; Balakrishnan, K.; Caimi, D.; Sousa, M.; Czornomaz, L.; Fompeyrine, J.

    2017-02-01

    We report the first RF characterization of short-channel replacement metal gate (RMG) InGaAs-OI nFETs built in a 3D monolithic (3DM) CMOS process. This process features RMG InGaAs-OI nFET top layer and SiGe-OI fin pFET bottom layer. We demonstrate state-of-the-art device integration on both levels. The bottom layer SiGe-OI pFETs are fabricated with a Gate-First (GF) process with fins and featuring epitaxial raised source drain (RSD) as well as silicide contact layer. The top layer InGaAs nFETs are fabricated with a RMG process featuring a self-aligned epitaxial raised source drain (RSD). We show that the 3D monolithic integration scheme does not degrade the performance of the bottom SiGe-OI pFETs owing to an optimized thermal budget for the top InGaAs nFETs. From the RF characterizations performed (post-3D monolithic process) on multifinger-gate InGaAs-OI nFETs, we extract a cut-off frequency (Ft) of 16.4 GHz at a gate-length (Lg) of 120 nm. Measurements on various gate lengths shows increasing cut-off frequency with decreasing gate-length.

  20. Spin Seebeck effect in an (In,Ga)As quantum well with equal Rashba and Dresselhaus spin-orbit couplings

    NASA Astrophysics Data System (ADS)

    Capps, Jeremy; Marinescu, D. C.; Manolescu, Andrei

    2016-02-01

    We demonstrate that a spin-dependent Seebeck effect can be detected in quantum wells with zinc-blend structure with equal Rashba-Dresselhaus spin-orbit couplings. This theory is based on the establishment of an itinerant antiferromagnetic state, a low total-energy configuration realized in the presence of the Coulomb interaction enabled by the k =0 degeneracy of the opposite-spin single-particle energy spectra. Transport in this state is modeled by using the solutions of a Boltzmann equation obtained within the relaxation time approximation. Numerical estimates performed for realistic GaAs samples indicate that at low temperatures, the amplitude of the spin Seebeck coefficient can be increased by scattering on magnetic impurities.

  1. MT6425CA: a 640 X 512-25μm CTIA ROIC for SWIR InGaAs detector arrays

    NASA Astrophysics Data System (ADS)

    Eminoglu, Selim; Mahsereci, Yigit Uygar; Altiner, Caglar; Akin, Tayfun

    2012-06-01

    This paper reports the development of a new CTIA ROIC (MT6425CA) suitable for SWIR InGaAs detector arrays. MT6425CA has a format of 640 × 512 with a pixel pitch of 25 μm and has a system-on-chip architecture, where all the critical timing and biasing for this ROIC are generated by programmable blocks on-chip. MT6425CA is a highly configurable and flexible ROIC, where many of its features can be programmed through a 3-wire serial interface allowing on-the-fly configuration of many ROIC features. The ROIC runs on 3.3V supply voltage at nominal clock speed of 10 MHz clock. It performs snapshot operation both using Integrate-Then-Read (ITR) and Integrate-While- Read (IWR) modes. The CTIA type pixel input circuitry has a full-well-capacity (FWC) of about 320,000e-, with an input referred read noise of less than 110e- at 300K. MT6425CA has programmable number of outputs, where 4, 2, or 1 output can be selected along with an analog reference for pseudo-differential operation. The integration time can be programmed up to 1s in steps of 0.1μs. The gain and offset in the ROIC can be programmed to adjust the output offset and voltage swing. ROIC dissipates less than 130mW from a 3.3V supply at full speed and full frame size with 4 outputs, providing both low-power and low-noise operation. MT6425CA is fabricated using a modern mixed-signal CMOS process on 200mm CMOS wafers with a high yield above 75%, yielding more than 50 working parts per wafer. It has been silicon verified, and tested parts are available either in wafer and die levels with a complete documentation including test reports and wafer maps. A USB based camera electronics and camera development platform with software are available to help customers to evaluate the imaging performance of MT6425CA in a fast and efficient way.

  2. Boron doped Si rich oxide/SiO{sub 2} and silicon rich nitride/SiN{sub x} bilayers on molybdenum-fused silica substrates for vertically structured Si quantum dot solar cells

    SciTech Connect

    Lin, Ziyun Wu, Lingfeng; Jia, Xuguang; Zhang, Tian; Puthen-Veettil, Binesh; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-07-28

    Vertically structured Si quantum dots (QDs) solar cells with molybdenum (Mo) interlayer on quartz substrates would overcome current crowding effects found in mesa-structured cells. This study investigates the compatibility between boron (B) doped Si QDs bilayers and Mo-fused silica substrate. Both Si/SiO{sub 2} and Si/SiN{sub x} based QDs bilayers were studied. The material compatibility under high temperature treatment was assessed by examining Si crystallinity, microstress, thin film adhesion, and Mo oxidation. It was observed that the presence of Mo interlayer enhanced the Si QDs size confinement, crystalline fraction, and QDs size uniformity. The use of B doping was preferred compared to phosphine (PH{sub 3}) doping studied previously in terms of better surface and interface properties by reducing oxidized spots on the film. Though crack formation due to thermal mismatch after annealing remained, methods to overcome this problem were proposed in this paper. Schematic diagram to fabricate full vertical structured Si QDs solar cells was also suggested.

  3. Hybrid InGaAs quantum well-dots nanostructures for light-emitting and photo-voltaic applications.

    PubMed

    Mintairov, S A; Kalyuzhnyy, N A; Lantratov, V M; Maximov, M V; Nadtochiy, A M; Rouvimov, Sergei; Zhukov, A E

    2015-09-25

    Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm(-2) for the terrestrial spectrum and by 4.1 mA cm(-2) for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm(-1) and 37 A cm(-2) per layer, respectively.

  4. Atomic Scale Dynamics of Contact Formation in the Cross-Section of InGaAs Nanowire Channels.

    PubMed

    Chen, Renjie; Jungjohann, Katherine L; Mook, William M; Nogan, John; Dayeh, Shadi A

    2017-04-12

    Alloyed and compound contacts between metal and semiconductor transistor channels enable self-aligned gate processes which play a significant role in transistor scaling. At nanoscale dimensions and for nanowire channels, prior experiments focused on reactions along the channel length, but the early stage of reaction in their cross sections remains unknown. Here, we report on the dynamics of the solid-state reaction between metal (Ni) and semiconductor (In0.53Ga0.47As), along the cross-section of nanowires that are 15 nm in width. Unlike planar structures where crystalline nickelide readily forms at conventional, low alloying temperatures, nanowires exhibit a solid-state amorphization step that can undergo a crystal regrowth step at elevated temperatures. In this study, we capture the layer-by-layer reaction mechanism and growth rate anisotropy using in situ transmission electron microscopy (TEM). Our kinetic model depicts this new, in-plane contact formation which could pave the way for engineered nanoscale transistors.

  5. Investigation of the energy spectra and the electron-hole alignment of the InAs/GaAs quantum dots with an ultrathin cap layer

    NASA Astrophysics Data System (ADS)

    Gorshkov, Alexey P.; Volkova, Natalia S.; Istomin, Leonid A.; Zdoroveishev, Anton V.; Levichev, Sergey

    2016-08-01

    The effects of indium composition and the thickness of the combined InGaAs/GaAs thin cap layer on the energy spectra and relative electron-hole alignment of InAs quantum dots (QDs) grown by metal organic vapor phase epitaxy (MOVPE) are investigated by photoelectrical spectroscopy in a semiconductor/electrolyte system. In structures with InAs QDs and an InGaAs strain reducing layer, the shift of the hole's wave function to the QDs' top was revealed, which indicates In enrichment of the area near the top of QD'. In structures with an ultrathin GaAs cap layer a change of the sign of the built-in dipole moment was observed. This is explained by coupling effects of quantum-confined electrons with surface states.

  6. High kappa Dielectrics on InGaAs and GaN - Growth, Interfacial Structural Studies, and Surface Fermi Level Unpinning

    DTIC Science & Technology

    2011-04-20

    devices, e.g. hetero-junction field-effect transistors (HFETs) and bipolar junction transistors (BJTs). Compared to conventional high power RF...AlGaN/GaN HFETs, GaN metal-oxide-semiconductor field-effect- transistors (MOSFETs) feature lower gate leakage currents, a larger gate voltage sweep range...reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching

  7. TEM study of dislocations structure in In0.82Ga0.18As/InP heterostructure with InGaAs as buffer layer

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Guo, Zuo-xing; Yuan, De-zeng; Wei, Qiu-lin; Zhao, Lei

    2016-05-01

    In order to improve the quality of detector, In x Ga1- x As ( x=0.82) buffer layer has been introduced in In0.82Ga0.18As/InP heterostructure. Dislocation behavior of the multilayer is analyzed through plane and cross section [110] by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The dislocations are effectively suppressed in In x Ga1- x As ( x=0.82) buffer layer, and the density of dislocations in epilayer is reduced obviously. No lattice mismatch between buffer layer and epilayer results in no misfit dislocation (MD). The threading dislocations (TDs) are directly related to the multiplication of the MDs in buffer layer.

  8. Optical properties of amorphous silicon quantum dots (a-Si QDs) with various dot size using extended Hückel theory

    NASA Astrophysics Data System (ADS)

    Setianto, Men, Liu Kin; Faizal, Ferry; Wibawa, Bambang Mukti; Hardjo, Doy Hardoyo; Panatarani, Camellia; Joni, I. Made

    2013-09-01

    A high quality amorphous silicon (a-Si) nanostructures has grown experimentally to study the origin of light emission and the quantum confinement effect in a-Si. The quantum confinement effect increases the band gap of material as the size of quantum structure decreases, which results in a blue shift in optical luminescence and energy absorption. Here we demonstrate this effect using extended Hückel method to calculate fundamental band gap and optical absorption energy of a-Si samples with various dot sizes. As result, when the dot size was decreased from 2.2 to 1.0 nm, the absorption spectra peak shifted toward higher energy from 2.278 eV to 3.856 eV.

  9. Structure and transport properties of Ge quantum dots in a SiO2 matrix

    NASA Astrophysics Data System (ADS)

    Slunjski, R.; Dubček, P.; Radić, N.; Bernstorff, S.; Pivac, B.

    2015-06-01

    Germanium (Ge) nanoparticles or quantum dots (QDs) embedded in a transparent dielectric matrix have properties radically different from the bulk semiconductor and present a great potential for application in electronic and optoelectronic devices. Due to quantum confinement properties, the optical bandgap of QD-based materials can be tuned by varying the nanoparticle size. These properties may be exploited for the fabrication of nanoscale electronic devices or advanced solar cells. In this work we explored structural and transport properties of QD based superstructures for advanced solar cells. Magnetron cosputtering was used for deposition and upon suitable thermal treatment a superstructure of QDs was formed. Transport properties were explored by I-V measurement in the dark together with a C-V characterization. The obtained results were modeled with the known transport mechanisms for QDs containing materials. A special emphasis is given to trap controlled space charge limited current and hopping conductivity mechanism. We have shown that in our samples a significant charge is stored in the SiO2 layers with embedded Ge QDs. That charge is predominantly stored into traps at or close to the Ge(QDs)/SiO2 interface.

  10. Anisotropic Transport of Electrons in a Novel FET Channel with Chains of InGaAs Nano-Islands Embedded along Quasi-Periodic Multi-Atomic Steps on Vicinal (111)B GaAs

    SciTech Connect

    Akiyama, Y.; Kawazu, T.; Noda, T.; Sakaki, H.

    2010-01-04

    We have studied electron transport in n-AlGaAs/GaAs heterojunction FET channels, in which chains of InGaAs nano-islands are embedded along quasi-periodic steps. By using two samples, conductance G{sub para}(V{sub g}) parallel to the steps and G{sub perp}(V{sub g}) perpendicular to them were measured at 80 K as functions of gate voltage V{sub g}. At sufficiently high V{sub g}, G{sub para} at 80 K is several times as high as G{sub perp}, which manifests the anisotropic two-dimensional transport of electrons. When V{sub g} is reduced to -0.7 V, G{sub perp} almost vanishes, while {sub Gpara} stays sizable unless V{sub g} is set below -0.8 V. These results indicate that 'inter-chain' barriers play stronger roles than 'intra-chain' barriers.

  11. Probing structure-induced optical behavior in a new class of self-activated luminescent 0D/1D CaWO₄ metal oxide – CdSe nanocrystal composite heterostructures

    SciTech Connect

    Han, Jinkyu; McBean, Coray; Wang, Lei; Hoy, Jessica; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Sfeir, Matthew Y.; Fischer, Daniel A.; Taylor, Gordon T.; Misewich, James A.; Wong, Stanislaus S.

    2015-01-30

    In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dot (QDs) coupled with (ii) both one and zero-dimensional (1D and 0D) motifs of self-activated luminescence CaWO₄ metal oxides. Specifically, ~4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ~230 nm in diameter and ~3 μm in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ~ 80 nm) of CaWO₄ through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementary electron microscopy and spectroscopy (i.e. IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO₄ as compared with unbound CaWO₄. We propose that a photo-induced electron transfer process occurs from CaWO₄ to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO₄ nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO₄ within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO₄ itself.

  12. Design of bull’s eye structures on gate-defined lateral quantum dots

    NASA Astrophysics Data System (ADS)

    Fukai, Rio; Nakagawa, Tomohiro; Kiyama, Haruki; Oiwa, Akira

    2017-04-01

    Quantum repeaters are required for realizing long-distance quantum communication. The quantum repeater consists of a quantum memory to store quantum information and an interface between photonic flying qubits and the memory qubits. Electron spins in gate-defined quantum dots (QDs), which have a relatively long coherence time and high electrical tunability, are promising candidates for such memory qubits because the fundamental technologies of detecting and manipulating single photoelectron spins have been established. The remaining challenge for the realization of quantum repeaters is an efficient coupling between photons and electron spins in the QDs. In this study, we discuss the enhancement of the transmission and the maintenance of the incident light polarization through bull’s eye structures on gate-defined QDs on the basis of electromagnetic field simulations.

  13. Photosensitive functionalized surface-modified quantum dots for polymeric structures via two-photon-initiated polymerization technique.

    PubMed

    Krini, Redouane; Ha, Cheol Woo; Prabhakaran, Prem; Mard, Hicham El; Yang, Dong-Yol; Zentel, Rudolf; Lee, Kwang-Sup

    2015-06-01

    In this paper, the surface modification of CdSe- and CdZnS-based quantum dots (QDs) with a functional silica shell is reported. Functionalized silica shells are prepared by two routes: either by ligand exchange and a modified Stöber process or by a miniemulsion process with amphiphilic poly(oxyethylene) nonylphenylether also know as Igepal CO-520 (IG) as oligomeric amphiphile and modified silica precursors. The polymerizable groups on the functionalized silica shell allow covalent bonding to a polymer matrix and prevent demixing during polymerization and crosslinking. This allows the homogeneous incorporation of QDs in a crosslinked polymer matrix. This paper furthermore demonstrates that the resulting QDs, which are i) shielded with a proper silica shell and ii) functionalized with crosslinkable groups, can be used in two-photon-initiated polymerization processes in combination with different photoresists to obtain highly luminescent 3D structures. The resulting luminescent structures are attractive candidates for photonics and metamaterials research.

  14. Contactless electroreflectance spectroscopy of optical transitions in low dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Misiewicz, J.; Kudrawiec, R.

    2012-06-01

    The authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes), QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies of these transitions have been compared with theoretical calculations and in this way the band structure has been determined for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented and discussed for selected QW and QD structures.

  15. Hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot structure with enhanced photoluminescence

    SciTech Connect

    Ji, Hai-Ming; Liang, Baolai Simmonds, Paul J.; Juang, Bor-Chau; Yang, Tao; Young, Robert J.; Huffaker, Diana L.

    2015-03-09

    We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL. These hybrid QD structures show potential for high efficiency QD solar cell applications.

  16. Hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot structure with enhanced photoluminescence

    NASA Astrophysics Data System (ADS)

    Ji, Hai-Ming; Liang, Baolai; Simmonds, Paul J.; Juang, Bor-Chau; Yang, Tao; Young, Robert J.; Huffaker, Diana L.

    2015-03-01

    We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL. These hybrid QD structures show potential for high efficiency QD solar cell applications.

  17. Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition.

    PubMed

    Zhang, Z; Wang, R F; Zhang, J; Li, H S; Zhang, J; Qiu, F; Yang, J; Wang, C; Yang, Y

    2016-07-29

    The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

  18. Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Wang, R. F.; Zhang, J.; Li, H. S.; Zhang, J.; Qiu, F.; Yang, J.; Wang, C.; Yang, Y.

    2016-07-01

    The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

  19. Quantum Yield Heterogeneity among Single Nonblinking Quantum Dots Revealed by Atomic Structure-Quantum Optics Correlation.

    PubMed

    Orfield, Noah J; McBride, James R; Wang, Feng; Buck, Matthew R; Keene, Joseph D; Reid, Kemar R; Htoon, Han; Hollingsworth, Jennifer A; Rosenthal, Sandra J

    2016-02-23

    Physical variations in colloidal nanostructures give rise to heterogeneity in expressed optical behavior. This correlation between nanoscale structure and function demands interrogation of both atomic structure and photophysics at the level of single nanostructures to be fully understood. Herein, by conducting detailed analyses of fine atomic structure, chemical composition, and time-resolved single-photon photoluminescence data for the same individual nanocrystals, we reveal inhomogeneity in the quantum yields of single nonblinking "giant" CdSe/CdS core/shell quantum dots (g-QDs). We find that each g-QD possesses distinctive single exciton and biexciton quantum yields that result mainly from variations in the degree of charging, rather than from volume or structure inhomogeneity. We further establish that there is a very limited nonemissive "dark" fraction (<2%) among the studied g-QDs and present direct evidence that the g-QD core must lack inorganic passivation for the g-QD to be "dark". Therefore, in contrast to conventional QDs, ensemble photoluminescence quantum yield is principally defined by charging processes rather than the existence of dark g-QDs.

  20. Aggregation of quantum dots in hybrid structures based on TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kolesova, Ekaterina P.; Orlova, Anna O.; Maslov, Vladimir G.; Gun'ko, Yurii K.; Cleary, Olan; Baranov, Aleksander V.; Fedorov, Anatoly V.

    2016-04-01

    A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based on TiO2 nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir- Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of structure formation. A photodegradation of luminescence properties of the structures is associated with the formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the structure formation and the concentration of TiO2 nanoparticles. A decay of luminescence of QD aggregates in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform QD surface concentration by visible light resulted in a photopassivation of their surface, which is accompanied by significant increase of luminescence quantum yield of QDs.

  1. Influence of electromechanical effects and wetting layers on band structures of AlN/GaN quantum dots and spin control

    NASA Astrophysics Data System (ADS)

    Prabhakar, Sanjay; Melnik, Roderick

    2010-09-01

    In a series of recent papers we demonstrated that coupled electromechanical effects can lead to pronounced contributions in band structure calculations of low dimensional semiconductor nanostructures (LDSNs) such as quantum dots (QDs), wires, and even wells. Some such effects are essentially nonlinear. Both strain and piezoelectric effects have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering, and other applications. However, the influence of spin orbit effects in presence of external magnetic field on single and vertically coupled QD has been largely neglected in the literature. The electron spin splitting terms which are coupled to the magnetic field through the Pauli spin matrix in these QDs become important in the design of optoelectronic devices as well as in tailoring properties of QDs in other applications areas. At the same time, single and vertically stacked QDs are coupled with electromagnetic and mechanical fields which become increasingly important in many applications of LDSN-based systems, in particular, where spin splitting energy is important. These externally applied electric and magnetic fields as well as the separation between the vertically coupled QDs can be used as tuning parameters. Indeed, as electromagnetic and elastic effects are often significant in LDSNs, it is reasonable to expect that the externally applied magnetic fields oriented along a direction perpendicular to the plane of two-dimensional electron gas in the QDs may also be used as a tuning parameter in the application of light emitting diodes, logic devices, for example, OR gates, AND gates and others. In this paper, by using the fully coupled model of electroelasticity, we analyze the influence of these effects on optoelectronic properties of QDs. Results are reported for III-V type semiconductors with a major focus given to AlN/GaN based QD systems.

  2. Band structures of laterally coupled quantum dots, accounting for electromechanical effects

    NASA Astrophysics Data System (ADS)

    Prabhakar, Sanjay; Melnik, Roderick; Patil, Sunil

    2010-09-01

    In a series of recent papers we demonstrated that coupled electro-mechanical effects can lead to pronounced contributions in band structure calculations of low dimensional semiconductor nanostructures (LDSNs) such as quantum dots, wires, and even wells. Some such effects are essentially nonlinear. Both strain and piezoelectric effects have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering and other applications. However, these effects have been largely neglected in literature while laterally coupled quantum dots (QDs) have been studied. The superposition of electron wave functions in these QDs become important in the design of optoelectronic devices as well in tayloring properties of QDs in other applications areas. At the same time, laterally grown QDs coupled with electric and mechanical fields are becoming increasingly important in many applications of LDSN-based systems, in particular where the tunneling of electron wave function through wetting layer (WL) becomes important and the distance between the dots is treated as a tuning parameter. Indeed, as electric and elastic effects are often significant in LDSNs, it is reasonable to expect that the separation between the QDs may also be used as a tuning parameter in the application of logic devices, for example, OR gates, AND gates and others. In this contribution, by using the fully coupled model of electroelasticity, we build on our previous results while analyzing the influence of these effects on optoelectronic properties of QDs. Results are reported for III-V type semiconductors with a major focus given to GaN/AlN based QD systems.

  3. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect

    Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M.; Lin, Y. H.; Goldman, R. S.

    2013-08-19

    We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

  4. Size-confined fixed-composition and composition-dependent engineered band gap alloying induces different internal structures in L-cysteine-capped alloyed quaternary CdZnTeS quantum dots

    NASA Astrophysics Data System (ADS)

    Adegoke, Oluwasesan; Park, Enoch Y.

    2016-06-01

    The development of alloyed quantum dot (QD) nanocrystals with attractive optical properties for a wide array of chemical and biological applications is a growing research field. In this work, size-tunable engineered band gap composition-dependent alloying and fixed-composition alloying were employed to fabricate new L-cysteine-capped alloyed quaternary CdZnTeS QDs exhibiting different internal structures. Lattice parameters simulated based on powder X-ray diffraction (PXRD) revealed the internal structure of the composition-dependent alloyed CdxZnyTeS QDs to have a gradient nature, whereas the fixed-composition alloyed QDs exhibited a homogenous internal structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis confirmed the size-confined nature and monodispersity of the alloyed nanocrystals. The zeta potential values were within the accepted range of colloidal stability. Circular dichroism (CD) analysis showed that the surface-capped L-cysteine ligand induced electronic and conformational chiroptical changes in the alloyed nanocrystals. The photoluminescence (PL) quantum yield (QY) values of the gradient alloyed QDs were 27–61%, whereas for the homogenous alloyed QDs, the PL QY values were spectacularly high (72–93%). Our work demonstrates that engineered fixed alloying produces homogenous QD nanocrystals with higher PL QY than composition-dependent alloying.

  5. Growth technique and effect of post growth annealing on the optical properties of In(Ga)As/GaAs quantum dot heterostructures

    NASA Astrophysics Data System (ADS)

    Panda, Debiprasad; Ahmad, Aijaz; Adhikary, Sourav; Ghadi, Hemant; Chakrabarti, Subhananda

    2016-09-01

    In this paper, we have proposed a technique to maintain the constant overgrowth percentage of quantum dots (QDs) in all layers of a multistacked heterostructure and hence the dot size uniformity is achieved. Two samples have been grown and compared in terms of their optical properties. Post growth annealing was carried out to observe the variation in their properties. The active layer of sample A is composed of 2.7 monolayer (ML) InAs QDs and the QD deposition amount is same for all the stacks. For the proposed sample B, 8ML In(Ga)As QDs were grown as seed layer, and the subsequent QD deposition is kept constant at 5ML. The overgrowth percentage in all QD layers were constant ( 40%) for this sample. Monomodal photoluminescence (PL) emission spectra was observed for the proposed sample B, whereas sample A has multimodal spectra. The samples were subjected to post growth annealing in argon atmosphere for 650, 700, 750, 800, 850, and 900°C. A negligible shift in the PL peak was observed for sample B up to 750°C, which confirms better thermal stability. The PL activation energy variation with respect to the annealed temperature was negligible for the proposed sample B ( 165 meV up to 750 °C). Hence the proposed growth mode of In(Ga)As multistacked QD heterostructure has better optical characteristics than the conventional structure in terms of PL spectra, FWHM, and also activation energy.

  6. Investigation of Pd-InGaAs for the formation of self-aligned source/drain contacts in InGaAs metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Kong, Eugene Y.-J.; Ivana; Zhang, Xingui; Zhou, Qian; Pan, Jisheng; Zhang, Zheng; Yeo, Yee-Chia

    2013-07-01

    The formation of salicide-like source/drain contacts on III-V MOSFETs necessitates a search for suitable metals that can react with III-V materials to form ohmic contacts with low sheet resistance and contact resistivity. To advance this search, the reaction between Pd and In0.53Ga0.47As is explored in this work. Reaction temperatures ranging from 200 to 400 °C were investigated, and extensive physical and electrical characterization was performed. Pd completely reacts with In0.53Ga0.47As after annealing at temperatures as low as 200 °C for 60 s to form a very smooth and uniform Pd-InGaAs film with good interfacial quality. Pd-InGaAs formed at 250 °C was found to have a work function of ˜4.6 ± 0.1 eV, sheet resistance of ˜77.3 Ω/square for a thickness of 20 nm, and contact resistivity of ˜8.35 × 10-5 Ω cm2 on In0.53Ga0.47As with n-type active doping concentration of ˜2 × 1018 cm-3. With further development, Pd-InGaAs could potentially be useful as self-aligned contacts for InGaAs transistors.

  7. Barrier reduction via implementation of InGaN interlayer in wafer-bonded current aperture vertical electron transistors consisting of InGaAs channel and N-polar GaN drain

    SciTech Connect

    Kim, Jeonghee Laurent, Matthew A.; Li, Haoran; Lal, Shalini; Mishra, Umesh K.

    2015-01-12

    This letter reports the influence of the added InGaN interlayer on reducing the inherent interfacial barrier and hence improving the electrical characteristics of wafer-bonded current aperture vertical electron transistors consisting of an InGaAs channel and N-polar GaN drain. The current-voltage characteristics of the transistors show that the implementation of N-polar InGaN interlayer effectively reduces the barrier to electron transport across the wafer-bonded interface most likely due to its polarization induced downward band bending, which increases the electron tunneling probability. Fully functional wafer-bonded transistors with nearly 600 mA/mm of drain current at V{sub GS} = 0 V and L{sub go} = 2 μm have been achieved, and thus demonstrate the feasibility of using wafer-bonded heterostructures for applications that require active carrier transport through both materials.

  8. Synthesis, Structural and Optical Characterization of CdTeSe/ZnSe and CdTeSe/ZnTe Core/Shell Ternary Quantum Dots for Potential Application in Solar Cells

    NASA Astrophysics Data System (ADS)

    Hung, Le Xuan; Thang, Pham Nam; Van Nong, Hoang; Yen, Nguyen Hai; Chinh, Vu Đuc; Van Vu, Le; Hien, Nguyen Thi Thuc; de Marcillac, Willy Daney; Hong, Phan Ngoc; Loan, Nguyen Thu; Schwob, Catherine; Maître, Agnès; Liem, Nguyen Quang; Bénalloul, Paul; Coolen, Laurent; Nga, Pham Thu

    2016-08-01

    This work presents the results on the fabrication, structural and optical properties of CdTeSe/ZnTe and CdTeSe/ZnSe n monolayers (ML) (with n = 0,1,2,4 and 6 being the nominal shell monolayer thickness) ternary alloyed core/shell quantum dots (QDs). Transmission electron microscopy has been used to observe the shape and size of the QDs. These QDs crystallize at the zinc-blende phase. Raman scattering has been used to characterize the CdTeSe QDs' alloy composition in the fabrication and coating processes. The Raman spectrum of CdTeSe QDs, in the frequency range from 100 cm-1 to 300 cm-1, is a composite band with two peaks at 160 cm-1 and 192 cm-1. When the thickness of the ZnTe shell is 4 ML, the peak of the Raman spectrum only appears at 160 cm-1. For the ZnSe 4 ML shell, the peak only appears at ˜200 cm-1. This shows that the nature of the CdTeSe QDs is either CdTe-rich or CdSe-rich depending on the shell of each sample. The shell thickness of 2 ML does not change the ternary core QDs' crystalline phase. The absorption and photoluminescence spectra show that the absorption and emission bands can be shifted to 900 nm, depending on each ternary alloyed QD core/shell sample. This near-infrared spectrum region is suitable for applications in solar cells.

  9. Optical and magnetotransport properties of InGaAs/GaAsSb/GaAs structures doped with a magnetic impurity

    SciTech Connect

    Kalentyeva, I. L. Zvonkov, B. N.; Vikhrova, O. V.; Danilov, Yu. A.; Demina, P. B.; Dorokhin, M. V.; Zdoroveyshchev, A. V.

    2015-11-15

    InGaAs/GaAsSb/GaAs bilayer quantum-well structures containing a magnetic-impurity δ-layer (Mn) at the GaAs/InGaAs interface are experimentally studied for the first time. The structures are fabricated by metal organic chemical-vapor deposition (MOCVD) and laser deposition on substrates of conducting (n{sup +}) and semi-insulating GaAs in a single growth cycle. The InGaAs-layer thickness is varied from 1.5 to 5 nm. The significant effect of a decrease in the InGaAs quantum-well thickness on the optical and magnetotransport properties of the structures under study is detected. Nonlinear magnetic-field dependence of the Hall resistance and negative magnetoresistance at temperatures of ≤30–40 K, circular polarization of the electroluminescence in a magnetic field, opposite behaviors of the photoluminescence and electroluminescence emission intensities in the structures, and an increase in the contribution of indirect transitions with decreasing InGaAs thickness are observed. Simulation shows that these effects can be caused by the influence of the δ-layer of acceptor impurity (Mn) on the band structure and the hole concentration distribution in the bilayer quantum well.

  10. Structuralism.

    ERIC Educational Resources Information Center

    Piaget, Jean

    Provided is an overview of the analytical method known as structuralism. The first chapter discusses the three key components of the concept of a structure: the view of a system as a whole instead of so many parts; the study of the transformations in the system; and the fact that these transformations never lead beyond the system but always…

  11. Stability Test of White LED with Bilayer Structure of Red InP Quantum Dots and Yellow YAG:Ce3+ Phosphor.

    PubMed

    Park, Kwangwon; Deressa, Gemechu; Kim, Daehan; Kim, Jongsu; Kim, Jihoon; Kim, Taehoon

    2016-02-01

    The white-light-emitting diode (white LED), based on the bilayer structure of red InP quantum dots (QDs) with 610 nm peak, and yellow YAG:Ce3+ phosphor with 550 nm peak, were fabricated through a conventional 5050 type LED fabrication process. The white LED exhibited high luminous efficiency of >130 Im/W and high color rendering index of >80 under operating current of 60 mA and color temperature of 5800 K. As an increase of QDs concentrations, the white LED showed higher color rendering index along with lower luminous efficiency, and the energy loss in the reabsorption process between yellow YAG:Ce3+ emission and red QD absorption was observed. As the temperature increases, the x-color coordinates were significantly changed, indicating that the InP QDs still have lower thermal stability. Also our white LED showed about 50% lumen maintenance after 45,000 hours of normal operation.

  12. Influence of the growth conditions on the optical and structural properties of self-assembled InAs/GaAs quantum dots for low As/In ratio

    NASA Astrophysics Data System (ADS)

    Ozdemir, Samet; Suyolcu, Y. Eren; Turan, Servet; Aslan, Bulent

    2017-01-01

    We report on the growth and characterization of self-assembled InAs/GaAs quantum dots (QDs). The influence of the systematically changed growth conditions on the opto-electronic and structural properties of the QDs were investigated. Combination of the amount of the deposited InAs, growth temperature and growth rate were optimized for low As/In flux ratio to obtain well-resolved ground and excited states in the low temperature photoluminescence (PL) spectra. SEM and TEM techniques were also used for the characterization of QDs. The results were evaluated simply through the conservation of mass approximation and the x-ray diffraction measurements with fitted curves. The extracted InAs and wetting layer thicknesses were brought out that the XRD analysis reflects the overall tendency of the QD density change and WL behaviors in response to the changes in growth conditions.

  13. Spectral Barcoding of Quantum Dots: Deciphering Structural Motifs from the Excitonic Spectra

    SciTech Connect

    Mlinar, V.; Zunger, A.

    2009-01-01

    Self-assembled semiconductor quantum dots (QDs) show in high-resolution single-dot spectra a multitude of sharp lines, resembling a barcode, due to various neutral and charged exciton complexes. Here we propose the 'spectral barcoding' method that deciphers structural motifs of dots by using such barcode as input to an artificial-intelligence learning system. Thus, we invert the common practice of deducing spectra from structure by deducing structure from spectra. This approach (i) lays the foundation for building a much needed structure-spectra understanding for large nanostructures and (ii) can guide future design of desired optical features of QDs by controlling during growth only those structural motifs that decide given optical features.

  14. Observation of charge transport through CdSe/ZnS quantum dots in a single-electron transistor structure

    NASA Astrophysics Data System (ADS)

    Kobo, Masanori; Yamamoto, Makoto; Ishii, Hisao; Noguchi, Yutaka

    2016-10-01

    We fabricated single-electron transistors (SETs) having CdSe/ZnS core-shell-type quantum dots (CdSe/ZnS-QDs) as a Coulomb island using a wet chemistry technique. The CdSe/ZnS-QDs were deposited onto Au electrodes with or without the assistance of a self-assembled monolayer of octane(di)thiols. The CdSe/ZnS-QDs were adsorbed onto the Au electrodes even without the interlayer of thiol molecules depending on the concentration of the CdSe/ZnS-QD solution. The electron-transport characteristics through the CdSe/ZnS-QDs were examined in an SET structure at 13 K. Coulomb blockade behavior with typical gate voltage dependence was clearly observed. The estimated charge addition energies of a CdSe/ZnS-QD ranged from 70 to 280 meV. Moreover, additional structures, including negative differential conductance, appeared in the stability diagram in the source-drain bias region beyond 100 mV; these structures are specific to single-charge transport through the discrete energy levels in the Coulomb island.

  15. Study on spin and optical polarization in a coupled InGaN/GaN quantum well and quantum dots structure

    PubMed Central

    Yu, Jiadong; Wang, Lai; Di Yang; Zheng, Jiyuan; Xing, Yuchen; Hao, Zhibiao; Luo, Yi; Sun, Changzheng; Han, Yanjun; Xiong, Bing; Wang, Jian; Li, Hongtao

    2016-01-01

    The spin and optical polarization based on a coupled InGaN/GaN quantum well (QW) and quantum dots (QDs) structure is investigated. In this structure, spin-electrons can be temporarily stored in QW, and spin injection from the QW into QDs via spin-conserved tunneling is enabled. Spin relaxation can be suppressed owing to the small energy difference between the initial state in the QW and the final states in the QDs. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements are carried out on optical spin-injection and -detection. Owing to the coupled structure, spin-conserved tunneling mechanism plays a significant role in preventing spin relaxation process. As a result, a higher circular polarization degree (CPD) (~49.1%) is achieved compared with conventional single layer of QDs structure. Moreover, spin relaxation time is also extended to about 2.43 ns due to the weaker state-filling effect. This coupled structure is believed an appropriate candidate for realization of spin-polarized light source. PMID:27759099

  16. Study on spin and optical polarization in a coupled InGaN/GaN quantum well and quantum dots structure.

    PubMed

    Yu, Jiadong; Wang, Lai; Di Yang; Zheng, Jiyuan; Xing, Yuchen; Hao, Zhibiao; Luo, Yi; Sun, Changzheng; Han, Yanjun; Xiong, Bing; Wang, Jian; Li, Hongtao

    2016-10-19

    The spin and optical polarization based on a coupled InGaN/GaN quantum well (QW) and quantum dots (QDs) structure is investigated. In this structure, spin-electrons can be temporarily stored in QW, and spin injection from the QW into QDs via spin-conserved tunneling is enabled. Spin relaxation can be suppressed owing to the small energy difference between the initial state in the QW and the final states in the QDs. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements are carried out on optical spin-injection and -detection. Owing to the coupled structure, spin-conserved tunneling mechanism plays a significant role in preventing spin relaxation process. As a result, a higher circular polarization degree (CPD) (~49.1%) is achieved compared with conventional single layer of QDs structure. Moreover, spin relaxation time is also extended to about 2.43 ns due to the weaker state-filling effect. This coupled structure is believed an appropriate candidate for realization of spin-polarized light source.

  17. Study on spin and optical polarization in a coupled InGaN/GaN quantum well and quantum dots structure

    NASA Astrophysics Data System (ADS)

    Yu, Jiadong; Wang, Lai; di Yang; Zheng, Jiyuan; Xing, Yuchen; Hao, Zhibiao; Luo, Yi; Sun, Changzheng; Han, Yanjun; Xiong, Bing; Wang, Jian; Li, Hongtao

    2016-10-01

    The spin and optical polarization based on a coupled InGaN/GaN quantum well (QW) and quantum dots (QDs) structure is investigated. In this structure, spin-electrons can be temporarily stored in QW, and spin injection from the QW into QDs via spin-conserved tunneling is enabled. Spin relaxation can be suppressed owing to the small energy difference between the initial state in the QW and the final states in the QDs. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements are carried out on optical spin-injection and -detection. Owing to the coupled structure, spin-conserved tunneling mechanism plays a significant role in preventing spin relaxation process. As a result, a higher circular polarization degree (CPD) (~49.1%) is achieved compared with conventional single layer of QDs structure. Moreover, spin relaxation time is also extended to about 2.43 ns due to the weaker state-filling effect. This coupled structure is believed an appropriate candidate for realization of spin-polarized light source.

  18. Multi-Quantum Well Structures to Improve the Performance of Multijunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Samberg, Joshua Paul

    Current, lattice matched triple junction solar cell efficiency is approximately 44% at a solar concentration of 942x. Higher efficiency for such cells can be realized with the development of a 1eV bandgap material lattice matched to Ge. One of the more promising materials for this application is that of the InGaAs/GaAsP multi-quantum well (MQW) structure. By inserting a stress/strain-balanced InGaAs/GaAsP MQW structure into the iregion of a GaAs p-i-n diode, the absorption edge of the p-i-n diode can be red shifted with respect to that of a standard GaAs p-n diode. Compressive stress in the InGaAs wells are balanced via GaAsP barriers subjected to tensile stress. Individually, the InGaAs and GaAsP layers are grown below their critical layer thickness to prevent the formation of misfit and threading dislocations. Until recently InGaAs/GaAsP MQWs have been somewhat hindered by their usage of low phosphorus-GaAsP barriers. Presented within is the development of a high-P composition GaAsP and the merits for using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high composition GaAsP the carriers are collected via tunneling (for barriers .30A) as opposed to thermionic emission. Thus, by utilizing thin, high content GaAsP barriers one can increase the percentage of the intrinsic region in a p-i-n structure that is comprised of the InGaAs well in addition to increasing the number of periods that can be grown for a given depletion width. However, standard MQWs of this type inherently possess undesirable compressive strain and quantum size effects (QSE) that cause the optical absorption of the InGaAs wells to blue shift. To circumvent these deleterious QSEs stress balanced, pseudomorphic InGaAs/GaAsP staggered MQWs were developed. Tunneling is still a viable mode for carrier transport in the staggered MQW structures. GaAs interfacial layers within the multi

  19. Hybrid quantum well/quantum dot structures for broad spectral bandwidth devices

    NASA Astrophysics Data System (ADS)

    Chen, Siming; Zhou, Kejia; Zhang, Ziyang; Childs, David T. D.; Orchard, Jonathan R.; Hogg, Richard A.; Kennedy, Kenneth; Hughes, Max.

    2012-02-01

    In this paper we report a hybrid quantum well (QW) and quantum dot (QD) structure to achieve a broad spontaneous emission and gain spectra. A single quantum well is introduced into a multi-layer stack of quantum dots, spectrally positioned to cancel the losses due to the second excited state of the dots. Attributed to the combined effect of QW and QDs, we show room temperature spontaneous emission with a 3dB bandwidth of ~250 nm and modal gain spanning over ~300 nm. We describe how this is achieved by careful design of the structure, balancing thermal emission from the QW and transport/capture processes in the QDs. We will also compare results from a QD-only epitaxial structure to describe how broadband gain/emission can be achieved in this new type of structure.

  20. Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

    PubMed Central

    2014-01-01

    Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%. PACS 81.07.Ta; 78.67.Pt; 88.40.jj PMID:25489285

  1. Effect of rapid thermal annealing on the noise properties of InAs/GaAs quantum dot structures

    SciTech Connect

    Arpatzanis, N.; Tsormpatzoglou, A.; Dimitriadis, C. A.; Song, J. D.; Choi, W. J.; Lee, J. I.; Charitidis, C.

    2007-09-01

    Self-assembled InAs quantum dots (QDs) were grown by molecular beam epitaxy (MBE) on n{sup +}-GaAs substrates, capped between 0.4 {mu}m thick n-type GaAs layers with electron concentration of 1x10{sup 16} cm{sup -3}. The effect of rapid thermal annealing at 700 deg. C for 60 s on the noise properties of the structure has been investigated using Au/n-GaAs Schottky diodes as test devices. In the reference sample without containing QDs, the noise spectra show a generation-recombination (g-r) noise behavior due to a discrete energy level located about 0.51 eV below the conduction band edge. This trap is ascribed to the M4 (or EL3) trap in GaAs MBE layers, related to a chemical impurity-native defect complex. In the structure with embedded QDs, the observed g-r noise spectra are due to a midgap trap level ascribed to the EL2 trap in GaAs, which is related to the InAs QDs dissolution due to the thermal treatment.

  2. Effect of rapid thermal annealing on the noise properties of InAs /GaAs quantum dot structures

    NASA Astrophysics Data System (ADS)

    Arpatzanis, N.; Tsormpatzoglou, A.; Dimitriadis, C. A.; Song, J. D.; Choi, W. J.; Lee, J. I.; Charitidis, C.

    2007-09-01

    Self-assembled InAs quantum dots (QDs) were grown by molecular beam epitaxy (MBE) on n+-GaAs substrates, capped between 0.4μm thick n-type GaAs layers with electron concentration of 1×1016cm-3. The effect of rapid thermal annealing at 700°C for 60s on the noise properties of the structure has been investigated using Au /n-GaAs Schottky diodes as test devices. In the reference sample without containing QDs, the noise spectra show a generation-recombination (g-r) noise behavior due to a discrete energy level located about 0.51eV below the conduction band edge. This trap is ascribed to the M4 (or EL3) trap in GaAs MBE layers, related to a chemical impurity-native defect complex. In the structure with embedded QDs, the observed g-r noise spectra are due to a midgap trap level ascribed to the EL2 trap in GaAs, which is related to the InAs QDs dissolution due to the thermal treatment.

  3. Low dimensional III-V compound semiconductor structures

    NASA Astrophysics Data System (ADS)

    Kobayashi, Nobuhiko P.

    2009-08-01

    Material incompatibilities among dissimilar group III-V compound semiconductors (III-V CSs) often place limits on combining epitaxial thin films, however low-dimensional epitaxial structures (e.g., quantum dots and nanowires) demonstrate coherent growth even on incompatible surfaces. First, InAs QDs grown by molecular beam epitaxy on GaAs are described. Two-dimensional to three-dimensional morphological transition, lateral size evolution and vertical alignment of InAs QDs in a single and multiple stacks will be illustrated. Second, InP nanowires grown on non-single crystalline surfaces by metal organic chemical vapor deposition are described with the view toward applications where III-V CSs are functionally integrated onto various material platforms.

  4. Impact of heterogeneous passivation of trimethylphosphine oxide and di-methylphosphine oxide surface ligands on the electronic structure of CdnSen (n=6, 15) quantum dots: A DFT study

    NASA Astrophysics Data System (ADS)

    Ganesan, Paramasivam; Lakshmipathi, Senthilkumar

    2016-09-01

    We report the significant influence of multiple capping ligands such as tri-methylphosphine oxide (TMPO) and di-methylphosphine oxide (DMPO) on the surface morphology and electronic structure of CdnSen (n=6, 15) quantum dots (QDs) using density functional theory (DFT). From the structural parameters the TMPO passivated structures shows strong structural distortion along non-polar 11 2 bar 0 surface. Besides, the binding energy values indicate that the TMPO ligands are weakly bound to 11 2 bar 0 surface. On introducing DMPO at 11 2 bar 0 non-polar surface from binding energy values, we observe significant surface reconstruction and stabilization of the structure due to the Se-H dative bond in addition to strong Cd-O bond. The NBO analysis indicates that charge transfer is maximum between metal and ligand in 11 2 bar 0 surface. The results of PDOS and molecular orbital (MO) analyses show that DMPO ligands significantly contribute to the occupied molecular orbitals near HOMO, which is not case in QDs with pure TMPO ligand. Further, the absorption spectra of CdSe QDs indicate that optical gaps are blue shifted by DMPOs. Hence, the multiple ligands can be employed in tuning the desired structural and optoelectronic properties of colloidal QDs (CQDs).

  5. Electronic structure of (In,Mn)As quantum dots buried in GaAs investigated by soft-x-ray ARPES

    NASA Astrophysics Data System (ADS)

    Bouravleuv, A. D.; Lev, L. L.; Piamonteze, C.; Wang, X.; Schmitt, T.; Khrebtov, A. I.; Samsonenko, Yu B.; Kanski, J.; Cirlin, G. E.; Strocov, V. N.

    2016-10-01

    Electronic structure of a molecular beam epitaxy-grown system of (In,Mn)As quantum dots (QDs) buried in GaAs is explored with soft-x-ray angle-resolved photoelectron spectroscopy (ARPES) using photon energies around 1 keV. This technique, ideally suited for buried systems, extends the momentum-resolving capabilities of conventional ARPES with enhanced probing depth as well as elemental and chemical state specificity achieved with resonant photoexcitation. The experimental results resolve the dispersive energy bands of the GaAs substrate buried in ∼2 nm below the surface, and the impurity states (ISs) derived from the substitutional Mn atoms in the (In,Mn)As QDs and oxidized Mn atoms distributed near the surface. An energy shift of the Mn ISs in the QDs compared to (In,Mn)As DMS is attributed to the band offset and proximity effect at the interface with the surrounding GaAs. The absence of any ISs in the vicinity of the VBM relates the electron transport in (In,Mn)As QDs to the prototype (In,Mn)As diluted magnetic semiconductor. The SX-ARPES results are supported by measurements of the shallow core levels under variation of probing depth through photon energy. X-ray absorption measurements identify significant diffusion of interstitial Mn atoms out of the QDs towards the surface, and the role of magnetic circular dichroism is to block the ferromagnetic response of the (In,Mn)As QDs. Possible routes are drawn to tune the growth procedure aiming at practical applications of the (In,Mn)As based systems.

  6. Electronic structure of (In,Mn)As quantum dots buried in GaAs investigated by soft-x-ray ARPES.

    PubMed

    Bouravleuv, A D; Lev, L L; Piamonteze, C; Wang, X; Schmitt, T; Khrebtov, A I; Samsonenko, Yu B; Kanski, J; Cirlin, G E; Strocov, V N

    2016-10-21

    Electronic structure of a molecular beam epitaxy-grown system of (In,Mn)As quantum dots (QDs) buried in GaAs is explored with soft-x-ray angle-resolved photoelectron spectroscopy (ARPES) using photon energies around 1 keV. This technique, ideally suited for buried systems, extends the momentum-resolving capabilities of conventional ARPES with enhanced probing depth as well as elemental and chemical state specificity achieved with resonant photoexcitation. The experimental results resolve the dispersive energy bands of the GaAs substrate buried in ∼2 nm below the surface, and the impurity states (ISs) derived from the substitutional Mn atoms in the (In,Mn)As QDs and oxidized Mn atoms distributed near the surface. An energy shift of the Mn ISs in the QDs compared to (In,Mn)As DMS is attributed to the band offset and proximity effect at the interface with the surrounding GaAs. The absence of any ISs in the vicinity of the VBM relates the electron transport in (In,Mn)As QDs to the prototype (In,Mn)As diluted magnetic semiconductor. The SX-ARPES results are supported by measurements of the shallow core levels under variation of probing depth through photon energy. X-ray absorption measurements identify significant diffusion of interstitial Mn atoms out of the QDs towards the surface, and the role of magnetic circular dichroism is to block the ferromagnetic response of the (In,Mn)As QDs. Possible routes are drawn to tune the growth procedure aiming at practical applications of the (In,Mn)As based systems.

  7. Regulated self-assembly of epitaxial silicon-germanium quantum structures and their properties

    NASA Astrophysics Data System (ADS)

    Vandervelde, Thomas Edwin

    Most proposed next generation architectures use quantum dots (QDs) in their design. Current lithography techniques either do not have the resolution required or are too time intensive for practical creation of these architectures. This has led many to suggest that the answer lies in self-assembly of QDs. Many unresolved issues, however, remain before we can implement this concept. The four areas of research discussed in this dissertation improve the fundamental understanding of processes involved in self-assembly. Once we had established that our system was producing the highest quality samples, we were able to say with confidence that the structures we observed were due to intrinsic phenomena, and not the result of contamination. In addition, because the existing standard curves lacked the sensitivity associated with modern analytical equipment, we employed more exploratory techniques (i.e. combinatorial epitaxy) to establish base growth conditions and define the evolution of structures. The examination of various growth conditions yielded the discovery of quantum fortresses (QFs), a novel, self-assembled, Quantum Cellular Automata (QCA)-like structure. We mapped the possible conditions under which these QFs form to gain a further understanding of their evolution. Additionally, we electrically tested their ability to act as SETs and quantum mechanically calculated growth conditions that result in those QFs that would best function as a QCA unit cell. To form a QCA circuit, QFs need to align in specific configurations. We investigated the fundamentals of a new technique to direct QF alignment. We demonstrated that FIB-mediated disruption of 1/10th ML or less is sufficient to guide island formation through the creation of preferential binding sites and denuded zones. In addition, we investigated the effect of altering growth conditions on the ability of large-scale features to align QDs. We also examined the ability of QDs to self-order into superlattice structures

  8. Structural and electrophysical properties of In{sub 0.52}Al{sub 0.48}As/In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As/InP HEMT nanoheterostructures with different combinations of InAs and GaAs inserts in quantum well

    SciTech Connect

    Galiev, G. B.; Vasiliev, A. L.; Vasil’evskii, I. S.; Imamov, R. M.; Klimov, E. A.; Klochkov, A. N.; Lavruhin, D. V.; Maltsev, P. P.; Pushkarev, S. S.; Trunkin, I. N.

    2015-05-15

    A complex investigation of structural and electrical properties of In{sub 0.52}Al{sub 0.48}As/In{sub y}Ga{sub 1−y}As/In{sub 0.52}Al{sub 0.48}As nanoheterostructures on InP substrates containing thin InAs and GaAs inserts in a quantum well (QW) has been performed. The GaAs nanolayers are grown at the QW boundaries between InGaAs and InAlAs layers, while the double InAs inserts are grown in InGaAs layers symmetrically with respect to the QW center. The layer and interface structures have been studied by transmission electron microscopy. It is shown that, when using the proposed epitaxial growth conditions, the introduction of ∼1.2-nm-thick InAs nanoinserts into the InGaAs QW and a ∼1-nm-thick GaAs nanobarrier at the QW boundaries does not induce structural defects. The diffusion of the InAlAs/InGaAs interface (2–3 monolayers) and InAs/InGaAs nanoinsert interface (1–2 monolayers) has been estimated. Measured Hall mobilities and electron concentrations in structures with different combinations of InAs and GaAs inserts have been analyzed using calculated energy band diagrams and electron density distributions. It is found that the photoluminescence spectra of the structures under study have differences caused by specific structural features of coupled QWs (specifically, the change in the In molar fraction due to InAs inserts and the change in the QW thickness due to GaAs transition barriers.

  9. Structural and optical characterization of CuInS2 quantum dots synthesized by microwave-assisted continuous flow methods

    NASA Astrophysics Data System (ADS)

    Fitzmorris, Robert C.; Oleksak, Richard P.; Zhou, Zheng; Mangum, Benjamin D.; Kurtin, Juanita N.; Herman, Gregory S.

    2015-07-01

    Semiconductor quantum dots (QDs) have recently been incorporated into consumer displays and lighting technologies. Now that these materials are being produced on industrial scales, it is important to investigate scalable synthetic methods and less toxic materials and chemistries. To achieve these goals, we have synthesized cadmium-free, visible light-emitting QDs using a microwave-assisted continuous flow reactor. After synthesis, the CuInS2 QD cores underwent a near-complete Zn cation exchange reaction in a batch reactor, followed by the growth of a ZnS shell. Analysis of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy data indicate that the crystal structure changes from CuInS2 (chalcopyrite) to ZnS (zincblende) during the cation exchange reaction. Compositional analysis indicated that the core/shell QDs were 98 % ZnS, with Cu and In present at much lower concentrations. The photoluminescence (PL) peak position was blue shifted for longer cation exchange reactions, and it was found that the ZnS shell was necessary for improved PL stability. The synthesized QDs have a PL down conversion efficiency of 65 % when using a blue LED source.

  10. Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties

    SciTech Connect

    Dialynas, G. E.; Kalliakos, S.; Xenogianni, C.; Androulidaki, M.; Kehagias, T.; Komninou, P.; Savvidis, P. G.; Pelekanos, N. T.; Hatzopoulos, Z.

    2010-11-15

    The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 10{sup 8} cm{sup -2} all the way up to a few times 10{sup 10} cm{sup -2}. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.

  11. Photoelectric properties of the metamorphic InAs/InGaAs quantum dot structure at room temperature

    SciTech Connect

    Golovynskyi, S. L.; Seravalli, L.; Trevisi, G.; Frigeri, P.; Gombia, E.; Dacenko, O. I.; Kondratenko, S. V.

    2015-06-07

    We present the study of optical and photoelectric properties of InAs quantum dots (QDs) grown on a metamorphic In{sub 0.15}Ga{sub 0.85}As buffer layer: such nanostructures show efficient light emission in the telecom window at 1.3 μm (0.95 eV) at room temperature. We prepared a sample with vertical geometry of contacts isolated from the GaAs substrate. The structure is found to be photosensitive in the spectral range above 0.9 eV at room temperature, showing distinctive features in the photovoltage and photocurrent spectra attributed to QDs, InAs wetting layer, and In{sub 0.15}Ga{sub 0.85}As metamorphic buffer, while a drop in the photoelectric signal above 1.36 eV is related to the GaAs layer. No effect of defect centers on the photoelectrical properties is found, although they are observed in the absorption spectrum. We conclude that metamorphic QDs have a low amount of interface-related defects close to the optically active region and charge carriers can be effectively collected into InAs QDs.

  12. Exciton fine structure and spin relaxation in semiconductor colloidal quantum dots.

    PubMed

    Kim, Jeongho; Wong, Cathy Y; Scholes, Gregory D

    2009-08-18

    Quantum dots (QDs) have discrete quantum states isolated from the environment, making QDs well suited for quantum information processing. In semiconductor QDs, the electron spins can be coherently oriented by photoexcitation using circularly polarized light, creating optical orientation. The optically induced spin orientation could serve as a unit for data storage and processing. Carrier spin orientation is also envisioned to be a key component in a related, though parallel, field of semiconductor spintronics. However, the oriented spin population rapidly loses its coherence by interaction with the environment, thereby erasing the prepared information. Since long-lasting spin orientation is desirable in both areas of investigation, spin relaxation is the central focus of investigation for optimization of device performance. In this Account, we discuss a topic peripherally related to these emerging areas of investigation: exciton fine structure relaxation (EFSR). The radiationless transition occurring in the exciton fine structure not only highlights a novel aspect of QD exciton relaxation but also has implications for carrier spin relaxation in QDs. We focus on examining the EFSR in connection with optical spin orientation and subsequent ultrafast relaxation of electron and hole spin densities in the framework of the exciton fine structure basis. Despite its significance, the study of exciton fine structure in colloidal QDs has been hampered by the experimental challenge arising from inhomogeneous line broadening that obscures the details of closely spaced fine structure states in the frequency domain. In this Account, we show that spin relaxation occurring in the fine structure of CdSe QDs can be probed by a time-domain nonlinear polarization spectroscopy, circumventing the obstacles confronted in the frequency-domain spectroscopy. In particular, by combining polarization sequences of multiple optical pulses with the unique optical selection rules of

  13. 2.5-μm InGaAs photodiodes grown on GaAs substrates by interfacial misfit array technique

    NASA Astrophysics Data System (ADS)

    Jurczak, Pamela; Sablon, Kimberly A.; Gutiérrez, Marina; Liu, Huiyun; Wu, Jiang

    2017-03-01

    In0.85Ga0.15As photodetectors grown on GaAs substrates using an interfacial misfit array-based simple buffer are studied. The material quality is assessed with a range of characterization tools showing low surface roughness and low density of threading dislocations. These results indicate a significant improvement on crystal quality compared to structures grown on InP substrates by using metamorphic buffers. Quantum efficiency and responsivity measurements show good performance of the fabricated devices between 1.5 and 2.5 μm, making them highly suitable for short-wavelength infrared applications.

  14. Optical coupling from InGaAs subcell to InGaP subcell in InGaP/InGaAs/Ge multi-junction solar cells.

    PubMed

    Shu, G W; Lin, J Y; Jian, H T; Shen, J L; Wang, S C; Chou, C L; Chou, W C; Wu, C H; Chiu, C H; Kuo, H C

    2013-01-14

    Spatially-resolved electroluminescence (EL) images in the triple-junction InGaP/InGaAs/Ge solar cell have been investigated to demonstrate the subcell coupling effect. Upon irradiating the infrared light with an energy below bandgap of the active layer in the top subcell, but above that in the middle subcell, the EL of the top subcell quenches. By analysis of EL intensity as a function of irradiation level, it is found that the coupled p-n junction structure and the photovoltaic effect are responsible for the observed EL quenching. With optical coupling and photoswitching effects in the multi-junction diode, a concept of infrared image sensors is proposed.

  15. InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shapiro, J. N.; Lin, A.; Wong, P. S.; Scofield, A. C.; Tu, C.; Senanayake, P. N.; Mariani, G.; Liang, B. L.; Huffaker, D. L.

    2010-12-01

    We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAs nanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy (EDS) indicates formation of axial InxGa1-xAs (x˜0.20) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth. Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillar heterostructures is crucial for optimized device integration.

  16. Symmetry Breaking and Fine Structure Splitting in Zincblende Quantum Dots: Atomistic Simulations of Long-Range Strain and Piezoelectric Field

    NASA Astrophysics Data System (ADS)

    Ahmed, Shaikh; Usman, Muhammad; Heitzinger, Clemens; Rahman, Rajib; Schliwa, Andrei; Klimeck, Gerhard

    2007-04-01

    Electrons and holes captured in self-assembled quantum dots (QDs) are subject to symmetry breaking that cannot be represented in with continuum material representations. Atomistic calculations reveal symmetry lowering due to effects of strain and piezo-electric fields. These effects are fundamentally based on the crystal topology in the quantum dots. This work studies these two competing effects and demonstrates the fine structure splitting that has been demonstrated experimentally can be attributed to the underlying atomistic structure of the quantum dots.

  17. Direct and phonon-assisted indirect Auger and radiative recombination lifetime in HgCdTe, InAsSb, and InGaAs computed using Green's function formalism

    NASA Astrophysics Data System (ADS)

    Wen, Hanqing; Pinkie, Benjamin; Bellotti, Enrico

    2015-07-01

    Direct and phonon-assisted (PA) indirect Auger and radiative recombination lifetime in HgCdTe, InAsSb, and InGaAs is calculated and compared under different lattice temperatures and doping concentrations. Using the Green's function theory, the electron self energy computed from the electron-phonon interaction is incorporated into the quantum-mechanical expressions of Auger and radiative recombination, which renders the corresponding minority carrier lifetime in the materials due to both direct and PA indirect processes. Specifically, the results of two pairs of materials, namely, InAs0.91Sb0.09, Hg0.67Cd0.33Te and In0.53Ga0.47As, Hg0.38Cd0.62Te with cutoff wavelengths of 4 μm and 1.7 μm at 200 K and 300 K, respectively, are presented. It is shown that for InAs0.91Sb0.09 and Hg0.67Cd0.33Te, when the lattice temperature falls below 250 K the radiative process becomes the limiting factor of carrier lifetime in both materials at an n-type doping of 1015 cm-3, while at a constant temperature of 200 K, a high n-type doping (ND > 5 × 1015 cm-3 for InAs0.91Sb0.09 and 3 × 1015 cm-3 for Hg0.67Cd0.33Te) makes the Auger process dominate. For the Auger lifetime in In0.53Ga0.47As and Hg0.38Cd0.62Te, the calculation suggested that under all the temperatures and n-doping concentrations investigated in this paper, radiative process is always the limiting factor of the materials' minority carrier lifetime. The calculation of the PA indirect Auger process in the four materials further demonstrated its indispensable contribution to the materials' total Auger rate especially at low temperature, which is necessary to reproduce some experimental data. By fitting the Beattie-Landsberg-Blakemore (BLB) formula to the numerical Auger results, the corresponding overlap integral factors | F 1 F 2 | in BLB theory are evaluated and presented to facilitate fast and accurate Auger calculations in the IR detector simulations.

  18. Probing structure-induced optical behavior in a new class of self-activated luminescent 0D/1D CaWO₄ metal oxide – CdSe nanocrystal composite heterostructures

    DOE PAGES

    Han, Jinkyu; McBean, Coray; Wang, Lei; ...

    2015-01-30

    In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dot (QDs) coupled with (ii) both one and zero-dimensional (1D and 0D) motifs of self-activated luminescence CaWO₄ metal oxides. Specifically, ~4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ~230 nm in diameter and ~3 μm in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ~ 80 nm) of CaWO₄ through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementarymore » electron microscopy and spectroscopy (i.e. IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO₄ as compared with unbound CaWO₄. We propose that a photo-induced electron transfer process occurs from CaWO₄ to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO₄ nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO₄ within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO₄ itself.« less

  19. The Synthesis and Structural Properties of Crystalline Silicon Quantum Dots upon Thermal Annealing of Hydrogenated Amorphous Si-Rich Silicon Carbide Films

    NASA Astrophysics Data System (ADS)

    Wen, Guozhi; Zeng, Xiangbin; Li, Xianghu

    2016-08-01

    Silicon quantum dots (QDs) embedded in non-stoichiometric hydrogenated silicon carbide (SiC:H) thin films have been successfully synthesized by plasma-enhanced chemical vapor deposition and post-annealing. The chemical composition analyses have been carried out by x-ray photoelectron spectroscopy (XPS). The bonding configurations have been deduced from Fourier transform infrared absorption measurements (FTIR). The evolution of microstructure with temperature has been characterized by glancing incident x-ray diffraction (XRD) and Raman diffraction spectroscopy. XPS and FTIR show that it is in Si-rich feature and there are a few hydrogenated silicon clusters in the as-grown sample. XRD and Raman diffraction spectroscopy show that it is in amorphous for the as-grown sample, while crystalline silicon QDs have been synthesized in the 900°C annealed sample. Silicon atoms precipitation from the SiC matrix or silicon phase transition from amorphous SiC is enhanced with annealing temperature increase. The average sizes of silicon QDs are about 5.1 nm and 5.6 nm, the number densities are as high as 1.7 × 1012 cm-2 and 3.2 × 1012 cm-2, and the crystalline volume fractions are about 58.3% and 61.3% for the 900°C and 1050°C annealed samples, respectively. These structural properties analyses provide an understanding about the synthesis of silicon QDs upon thermal annealing for applications in next generation optoelectronic and photovoltaic devices.

  20. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    SciTech Connect

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru; Suzuki, Hidetoshi; Sasaki, Takuo; Takahasi, Masamitu

    2015-11-14

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

  1. Surface photovoltage spectroscopy of an InGaAs/GaAs/AlGaAs single quantum well laser structure

    NASA Astrophysics Data System (ADS)

    Ashkenasy, N.; Leibovitch, M.; Shapira, Yoram; Pollak, Fred H.; Burnham, G. T.; Wang, X.

    1998-01-01

    An InGaAs/GaAs/AlGaAs single quantum well graded-index-of-refraction separate-confinement hetero-structure laser has been analyzed using surface photovoltage spectroscopy (SPS) in a contactless, nondestructive way at room temperature. Numerical simulation of the resulting spectrum made it possible to extract growth parameters, such as the InGaAs well width, the well and cladding compositions, as well as important electro-optic structure data of this device, including the lasing wavelength and built-in electric field. The results highlight the power of SPS in obtaining performance parameters of actual laser devices, containing two-dimensional structures, in a contactless, nondestructive way.

  2. Capability of coupled CdSe/TiO2 heterogeneous structure for photocatalytic degradation and photoconductivity

    NASA Astrophysics Data System (ADS)

    Zhang, Miao; Xu, Yanyan; Lv, Jianguo; Yang, Lei; Jiang, Xishun; He, Gang; Song, Xueping; Sun, Zhaoqi

    2014-11-01

    Highly ordered TiO2 nanotube arrays (TiO2-NTAs), with a uniform tube size on titanium substrate, were obtained by means of reoxidation and annealing. A composite structure, CdSe quantum dots@TiO2 nanotube arrays (CdSe QDs@TiO2-NTAs), was fabricated by assembling CdSe quantum dots into TiO2-NTAs via cyclic voltammetry electrochemical deposition. The X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), and transmission electron microscope (TEM) were carried out for the determination of the composition and structure of the tubular layers. Optical properties were investigated by ultraviolet-visible spectrophotometer (UV-Vis). Photocurrent response under visible light illumination and photocatalytic activity of samples by degradation of methyl orange were measured. The results demonstrated that the photo absorption of the composite film shifted to the visible region, and the photocurrent intensity was greatly enhanced due to the assembly of CdSe QDs. Especially, photocurrent achieved a maximum of 1.853 μA/cm2 after five voltammetry cycles of all samples. After irradiation under ultra violet-visible light for 2 h, the degradation rate of composition to methyl orange (MO) reached 88.20%, demonstrating that the CdSe QDs@TiO2-NTAs exhibited higher photocatalytic activity.

  3. Capability of coupled CdSe/TiO2 heterogeneous structure for photocatalytic degradation and photoconductivity.

    PubMed

    Zhang, Miao; Xu, Yanyan; Lv, Jianguo; Yang, Lei; Jiang, Xishun; He, Gang; Song, Xueping; Sun, Zhaoqi

    2014-01-01

    Highly ordered TiO2 nanotube arrays (TiO2-NTAs), with a uniform tube size on titanium substrate, were obtained by means of reoxidation and annealing. A composite structure, CdSe quantum dots@TiO2 nanotube arrays (CdSe QDs@TiO2-NTAs), was fabricated by assembling CdSe quantum dots into TiO2-NTAs via cyclic voltammetry electrochemical deposition. The X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), and transmission electron microscope (TEM) were carried out for the determination of the composition and structure of the tubular layers. Optical properties were investigated by ultraviolet-visible spectrophotometer (UV-Vis). Photocurrent response under visible light illumination and photocatalytic activity of samples by degradation of methyl orange were measured. The results demonstrated that the photo absorption of the composite film shifted to the visible region, and the photocurrent intensity was greatly enhanced due to the assembly of CdSe QDs. Especially, photocurrent achieved a maximum of 1.853 μA/cm(2) after five voltammetry cycles of all samples. After irradiation under ultra violet-visible light for 2 h, the degradation rate of composition to methyl orange (MO) reached 88.20%, demonstrating that the CdSe QDs@TiO2-NTAs exhibited higher photocatalytic activity.

  4. Capability of coupled CdSe/TiO2 heterogeneous structure for photocatalytic degradation and photoconductivity

    PubMed Central

    2014-01-01

    Highly ordered TiO2 nanotube arrays (TiO2-NTAs), with a uniform tube size on titanium substrate, were obtained by means of reoxidation and annealing. A composite structure, CdSe quantum dots@TiO2 nanotube arrays (CdSe QDs@TiO2-NTAs), was fabricated by assembling CdSe quantum dots into TiO2-NTAs via cyclic voltammetry electrochemical deposition. The X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), and transmission electron microscope (TEM) were carried out for the determination of the composition and structure of the tubular layers. Optical properties were investigated by ultraviolet-visible spectrophotometer (UV-Vis). Photocurrent response under visible light illumination and photocatalytic activity of samples by degradation of methyl orange were measured. The results demonstrated that the photo absorption of the composite film shifted to the visible region, and the photocurrent intensity was greatly enhanced due to the assembly of CdSe QDs. Especially, photocurrent achieved a maximum of 1.853 μA/cm2 after five voltammetry cycles of all samples. After irradiation under ultra violet-visible light for 2 h, the degradation rate of composition to methyl orange (MO) reached 88.20%, demonstrating that the CdSe QDs@TiO2-NTAs exhibited higher photocatalytic activity. PMID:25489287

  5. Low temperature Zn diffusion for GaSb solar cell structures fabrication

    NASA Technical Reports Server (NTRS)

    Sulima, Oleg V.; Faleev, Nikolai N.; Kazantsev, Andrej B.; Mintairov, Alexander M.; Namazov, Ali

    1995-01-01

    Low temperature Zn diffusion in GaSb, where the minimum temperature was 450 C, was studied. The pseudo-closed box (PCB) method was used for Zn diffusion into GaAs, AlGaAs, InP, InGaAs and InGaAsP. The PCB method avoids the inconvenience of sealed ampoules and proved to be simple and reproducible. The special design of the boat for Zn diffusion ensured the uniformality of Zn vapor pressure across the wafer surface, and thus the uniformity of the p-GaSb layer depth. The p-GaSb layers were studied using Raman scattering spectroscopy and the x-ray rocking curve method. As for the postdiffusion processing, an anodic oxidation was used for a precise thinning of the diffused GaSb layers. The results show the applicability of the PCB method for the large-scale production of the GaSb structures for solar cells.

  6. Engineering band structure in nanoscale quantum-dot supercrystals.

    PubMed

    Baimuratov, Anvar S; Rukhlenko, Ivan D; Fedorov, Anatoly V

    2013-07-01

    Supercrystals made of periodically arranged semiconductor quantum dots (QDs) are promising structures for nanophotonics applications due to almost unlimited degrees of freedom enabling fine tuning of their optical responses. Here we demonstrate broad engineering opportunities associated with the possibility of tailoring the energy bands of excitons in two-dimensional quantum-dot supercrystals through the alteration in the QD arrangement. These opportunities offer an unprecedented control over the optical properties of the supercrystals, which may be used as a versatile material base for advanced photonics devices on the nanoscale.

  7. Enhancement of carrier lifetimes in type-II quantum dot/quantum well hybrid structures

    NASA Astrophysics Data System (ADS)

    Couto, O. D. D.; de Almeida, P. T.; dos Santos, G. E.; Balanta, M. A. G.; Andriolo, H. F.; Brum, J. A.; Brasil, M. J. S. P.; Iikawa, F.; Liang, B. L.; Huffaker, D. L.

    2016-08-01

    We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL) measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness.

  8. Structural and optical properties of germanium nanostructures on Si(100) and embedded in high-k oxides

    PubMed Central

    2011-01-01

    The structural and optical properties of Ge quantum dots (QDs) grown on Si(001) for mid-infrared photodetector and Ge nanocrystals embedded in oxide matrices for floating gate memory devices are presented. The infrared photoluminescence (PL) signal from Ge islands has been studied at a low temperature. The temperature- and bias-dependent photocurrent spectra of a capped Si/SiGe/Si(001) QDs infrared photodetector device are presented. The properties of Ge nanocrystals of different size and density embedded in high-k matrices grown using radio frequency magnetron sputtering have been studied. Transmission electron micrographs have revealed the formation of isolated spherical Ge nanocrystals in high-k oxide matrix of sizes ranging from 4 to 18 nm. Embedded nanocrystals in high band gap oxides have been found to act as discrete trapping sites for exchanging charge carriers with the conduction channel by direct tunneling that is desired for applications in floating gate memory devices. PMID:21711749

  9. Structural, photoconductivity and photoluminescence characterization of cadmium sulfide quantum dots prepared by a co-precipitation method

    NASA Astrophysics Data System (ADS)

    Mishra, Sheo K.; Srivastava, Rajneesh K.; Prakash, S. G.; Yadav, Raghvendra S.; Panday, A. C.

    2011-03-01

    In this paper, cadmium sulfide (CdS) quantum dots (QDs) are synthesized by a simple co-precipitation method. X-ray diffraction (XRD) confirmed the formation of a cubical zinc blend structure of CdS nanoparticles. Transmission Electron Microscopy (TEM) images revealed that the CdS QDs are of 2-5 nm in size. The UV-vis absorption spectra showed an absorption peak at 427 nm (˜2.90 eV) indicating a blue shift of 0.48 eV as compared to bulk CdS. We estimated the particle sizes with the help of X-ray diffraction (XRD) patterns (3.665 nm) and the shift of the band gap absorption in the UV-vis spectrum (4.276 nm), which is very close to the TEM micrograph result. The photoluminescence spectrum shows three major emission peaks centered at 453 nm (˜2.73 eV), 526 nm (˜2.35 eV) and 551 nm (˜2.24 eV) at room temperature, which may be attributed to excitonic transitions, donor-acceptor (D-A) pairs recombination and the sulphur interstitial defects (Is) present in the band gap. To study the photoconductivity, the field dependence of the photocurrent and the dark-current was assessed, as was the time-resolved rise and decay photocurrent spectrum and wavelength-dependence photocurrent spectrum assessment of the CdS QDs. The time-resolved rise and decay photocurrent spectra exhibited negative photoconductivity (NPC) behavior when the CdS QDs were illuminated with 490 nm light. Such anomalous NPC may be attributed to the light-induced desorption of water molecules. The wavelength-dependence of the photocurrent was found to be close to the absorption and PL spectrum. The photoconductivity properties of the CdS QDs were measured using a thick film of powder without any binder. These CdS QDs can find potential application in optoelectronic devices and photodetectors.

  10. Influence of Mn2+ concentration on Mn2+-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties

    NASA Astrophysics Data System (ADS)

    Sotelo-Gonzalez, Emma; Roces, Laura; Garcia-Granda, Santiago; Fernandez-Arguelles, Maria T.; Costa-Fernandez, Jose M.; Sanz-Medel, Alfredo

    2013-09-01

    The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn2+ (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn2+-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn2+ and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions.The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn2+ (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be

  11. Quantum structures for multiband photon detection

    NASA Astrophysics Data System (ADS)

    Perera, A. G. U.

    2006-06-01

    The work describes multiband photon detectors based on semiconductor micro-and nano-structures. The devices considered include quantum dot, homojunction, and heterojunction structures. In the quantum dot structures, transitions are from one state to another, while free carrier absorption and internal photoemission play the dominant role in homo or heterojunction detectors. Quantum dots-in-a-well (DWELL) detectors can tailor the response wavelength by varying the size of the well. A tunnelling quantum dot infrared photodetector (T-QDIP) could operate at room temperature by blocking the dark current except in the case of resonance. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunnelling, while the dark current is blocked by AlGaAs/InGaAs tunnelling barriers placed in the structure. A two-colour infrared detector with photoresponse peaks at ˜6 and ˜17 μm at room temperature will be discussed. A homojunction or heterojunction interfacial workfunction internal photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect near infrared (NIR) photons due to interband transitions and mid/far infrared (MIR/FIR) radiation due to intraband transitions. The threshold wavelength of the interband response depends on the band gap of the barrier material, and the MIR/FIR response due to intraband transitions can be tailored by adjusting the band offset between the emitter and the barrier. GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and with GaN/AlGaN structures the detection capability can be extended into the ultraviolet region. These detectors are useful in numerous applications such as environmental monitoring, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.

  12. Quantum structures for multiband photon detection

    NASA Astrophysics Data System (ADS)

    Perera, A. G. U.

    2005-09-01

    The work describes multiband photon detectors based on semiconductor micro- and nano-structures. The devices considered include quantum dot, homojunction, and heterojunction structures. In the quantum dot structures, transitions are from one state to another, while free carrier absorption and internal photoemission play the dominant role in homo or heterojunction detectors. Quantum Dots-in-a-Well (DWELL) detectors can tailor the response wavelength by varying the size of the well. A tunneling Quantum Dot Infrared Photodetector (T-QDIP) could operate at room temperature by blocking the dark current except in the case of resonance. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers placed in the structure. A two-color infrared detector with photoresponse peaks at ~6 and ~17 μm at room temperature will be discussed. A Homojunction or HEterojunction Interfacial Workfunction Internal Photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect near infrared (NIR) photons due to interband transitions and mid/far infrared (MIR/FIR) radiation due to intraband transitions. The threshold wavelength of the interband response depends on the band gap of the barrier material, and the MIR/FIR response due to intraband transitions can be tailored by adjusting the band offset between the emitter and the barrier. GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and with GaN/AlGaN structures the detection capability can be extended into the ultraviolet region. These detectors are useful in numerous applications such as environmental monitoring, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.

  13. InGaAsP-based uni-travelling carrier photodiode structure grown by solid source molecular beam epitaxy.

    PubMed

    Natrella, Michele; Rouvalis, Efthymios; Liu, Chin-Pang; Liu, Huiyun; Renaud, Cyril C; Seeds, Alwyn J

    2012-08-13

    We report the first InGaAsP-based uni-travelling carrier photodiode structure grown by Solid Source Molecular Beam Epitaxy; the material contains layers of InGaAsP as thick as 300 nm and a 120 nm thick InGaAs absorber. Large area vertically illuminated test devices have been fabricated and characterised; the devices exhibited 0.1 A/W responsivity at 1550 nm, 12.5 GHz -3 dB bandwidth and -5.8 dBm output power at 10 GHz for a photocurrent of 4.8 mA. The use of Solid Source Molecular Beam Epitaxy enables the major issue associated with the unintentional diffusion of zinc in Metal Organic Vapour Phase Epitaxy to be overcome and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of Gas Source Molecular Beam Epitaxy.

  14. Optical Spectroscopy of Nano Materials and Structures

    NASA Astrophysics Data System (ADS)

    Guo, Wenhao

    broadening which is caused by the bandgap change. The experimental results confirm our speculation. When we make the nanowire straight again, the redshift disappears. It is believed that this piezoelectric effect is very important to the application of nanowires, and it would benefit the actual design and fabrication for the electronic devices for the next generation. Lastly, as for the OD case, the charge transfer mechanism occurring at the interface between graphene and ZnO QDs is investigated. We fabricate a hybrid structure by placing ZnO QDs on top of graphene. With UV light illumination on this device, it will generate electron-hole pairs inside QDs. Before they recombine, the holes will be separated and trapped into the surface states, and discharge the oxygen ions adsorbed on the surface of QDs. The unpaired electrons are then transferred to the graphene layer with a relative long lifetime. After the UV light is switched off, the oxygen molecules will re-adsorb to the QDs surface, capture electrons and recover the graphene's transport properties. Therefore, this hybrid device shows an ultrasensitive response to on-off of the UV laser, with a photoconductive gain as high as 10 7, which can be utilized for practical graphene-based UV sensors and detectors with very high responsivity. This gain can be further enhanced by another 2-3 orders by increasing source-drain voltage, shortening the sample's length, etc. It is believed that optical spectroscopy provides a convenient, efficient and useful method to study the nanomaterials and nanostructures. It is easy to set up, has no harm or degradation to the sample, and could go beyond the diffraction limit. With appropriate design and creative ideas, optical spectroscopy can be further explored, and will boost the development of nanoscience and technology. (Abstract shortened by UMI.).

  15. Effect of surface passivating ligand on structural and optoelectronic properties of polymer : CdSe quantum dot composites

    NASA Astrophysics Data System (ADS)

    Kumari, Kusum; Kumar, Umesh; Sharma, Shailesh N.; Chand, Suresh; Kakkar, Rita; Vankar, V. D.; Kumar, Vikram

    2008-12-01

    We demonstrate the effect of surface passivation of cadmium selenide quantum dots (CdSe QDs) (~5-7 nm) by tri-n-octylphosphene-oxide (TOPO) and oleic acid (OA) on the structural and optoelectronic properties of their respective polymer : CdSe composites by dispersing them in poly(2-methoxy-5(2-ethylhexyloxy)-1,4-phenylinevinylene) and poly(3-hexylthiophene) polymers. It has been found that OA passivated-QDs (~7 nm), as compared with TOPO passivated CdSe QDs (~5 nm), are of (i) high quality that provide better steric stability against coagulation, homogeneity and photostability to their respective polymer : CdSe composites, (ii) show low value of Stern-Volmer quenching constant (KSV) calculated from photoluminescence quenching measurements. These effects have been attributed to (i) CdSe(OA) (~7 nm) particles having relatively smaller surface energies compared with CdSe(TOPO) (~5 nm) particles thus showing lesser quenching capabilities (ii) dominance of respective processes of photoinduced Förster energy transfer between host polymer (donors) and guest CdSe nanocrystals (acceptors) in polymer : CdSe(OA) composites and charge transfer in polymer : CdSe(TOPO) composites.

  16. Structure of interfaces in GaN/AlN and Ge/Si multilayered heterosystems by XAFS spectroscopy

    NASA Astrophysics Data System (ADS)

    Erenburg, S. B.; Trubina, S. V.; Zhuravlev, K. S.; Malin, T. V.; Zinovyev, V. A.; Dvurechenskii, A. V.; Kuchinskaya, P. A.; Kvashnina, K. O.

    2016-11-01

    III-nitride heterostructures in the form of multilayered quantum wells (MQWs) or quantum dots (QDs) and interacting Ge QDs (“quantum molecules”) are promising candidates for high-speed intersubband (ISB) optical devices relying on the quantum confinement of electrons. Microstructural parameters (interatomic distances, coordination numbers, and Debye-Waller factors) were determined by means of EXAFS spectroscopy based on the Synchrotron Radiation, and the relationship between the variations in these parameters and the morphology of superlattices and symmetric assembles of QDs were established. The EXAFS technique has been used to study the local structure of thin hexagonal GaN/AlN MQWs grown by ammonia MBE at different temperatures. It is shown that the heterointerface intermixing leads to a decrease in the Ga-Al interatomic distance and the Ga-Ga coordination number in MQWs. The degree of intermixing in the boundary layers rises from 30% to 40% with increase of the growth temperature from 795 to 895 °C. It was found that in the first phase of quantum molecules growth Ge atoms concentration is 25%. With further growth (deposition of the base layers) Ge concentration increases up to 35-45%, depending on the temperature (from 610 to 550 °C) of deposition.

  17. Effect of carrier capture by deep levels on lateral photoconductivity of InGaAs/GaAs quantum dot structures

    NASA Astrophysics Data System (ADS)

    Vakulenko, O. V.; Golovynskyi, S. L.; Kondratenko, S. V.

    2011-08-01

    Having used thermally stimulated conductivity (TSC) technique, we identified deep electron traps that produce strong effects on charge carrier transport and photoconductivity in InGaAs/GaAs quantum dot (QD) structures. The values of deep levels below the conduction band of GaAs at 0.16, 0.22, and 0.35 eV are obtained from the analysis of the shapes of TSC curves after the excitation with the quanta energy hv = 0.9, 1.2, and 1.6 eV. The level 0.16 eV in depth is an effective electron trap that provides crossing of lateral conductivity with a high-resistance mode and, therefore, causes a high photocurrent sensitivity of about 3 A/W at 77 K with excitation by interband transitions in QDs. We determined the charge density of electrons captured by the (Ec - 0.16 eV) level to be 2 × 10-6 C/cm2 at 77 K that induces electric field ˜ 105 V/cm in a vicinity of QDs. The state at Ec - 0.22 eV is shown to be related to the recombination center that can hold non-equilibrium holes over a long time under the condition that the non-equilibrium holes are localized by the quantum states of QDs. In the course of long-term electron storage in a vicinity of QDs, an electron trapped at the (Ec - 0.16) eV level can be recaptured by a deeper spatially remote (Ec - 0.22 eV) level that allows the TSC peak observation at 106 K.

  18. Room-Temperature Multi-Peak NDR in nc-Si Quantum-Dot Stacking MOS Structures for Multiple Value Memory and Logic

    NASA Astrophysics Data System (ADS)

    Qian, Xin-Ye; Chen, Kun-Ji; Huang, Jian; Wang, Yue-Fei; Fang, Zhong-Hui; Xu, Jun; Huang, Xin-Fan

    2013-07-01

    Room-temperature negative differential resistance (NDR) characteristics are observed in a nanocrystalline Si quantum dot (nc-Si QD) floating-gate MOS structure, which is fabricated by plasma-enhanced chemical vapor deposition. Clear multi-NDR peaks for the electrons and holes, shown in the I—V curves, which are significant for the application of multiple value memory and logic, are proved to be induced by electron and hole resonant tunneling into the nc-Si QDs from the substrate. The calculation results indicate that these NDR characteristics should be associated with the Coulomb blockade effect and the quantum confinement effect of the nc-Si QDs. Furthermore, low-temperature I—V characteristics are also investigated to confirm the room-temperature results.

  19. Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy

    SciTech Connect

    Maryński, A.; Sĕk, G.; Musiał, A.; Andrzejewski, J.; Misiewicz, J.; Gilfert, C.; Reithmaier, J. P.; Capua, A.; Karni, O.; Gready, D.; Eisenstein, G.; Atiya, G.; Kaplan, W. D.; Kölling, S.

    2013-09-07

    The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As{sub 2} source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data.

  20. Electronic band structure and optical gain of GaNxBiyAs1-x-y/GaAs pyramidal quantum dots

    NASA Astrophysics Data System (ADS)

    Song, Zhi-Gang; Bose, Sumanta; Fan, Wei-Jun; Li, Shu-Shen

    2016-04-01

    The electronic band structure and optical gain of GaNxBiyAs1-x-y/GaAs pyramidal quantum dots (QDs) are investigated using the 16-band k ṡ p model with constant strain. The optical gain is calculated taking both homogeneous and inhomogeneous broadenings into consideration. The effective band gap falls as we increase the composition of nitrogen (N) and bismuth (Bi) and with an appropriate choice of composition we can tune the emission wavelength to span within 1.3 μm-1.55 μm, for device application in fiber technology. The extent of this red shift is more profound in QDs compared with bulk material due to quantum confinement. Other factors affecting the emission characteristics include virtual crystal, strain profile, band anticrossing (BAC), and valence band anticrossing (VBAC). The strain profile has a profound impact on the electronic structure, specially the valence band of QDs, which can be determined using the composition distribution of wave functions. All these factors eventually affect the optical gain spectrum. With an increase in QD size, we observe a red shift in the emission energy and emergence of secondary peaks owing to transitions or greater energy compared with the fundamental transition.

  1. Materials, structures, and devices for high-speed electronics

    NASA Technical Reports Server (NTRS)

    Woollam, John A.; Snyder, Paul G.

    1992-01-01

    Advances in materials, devices, and instrumentation made under this grant began with ex-situ null ellipsometric measurements of simple dielectric films on bulk substrates. Today highly automated and rapid spectroscopic ellipsometers are used for ex-situ characterization of very complex multilayer epitaxial structures. Even more impressive is the in-situ capability, not only for characterization but also for the actual control of the growth and etching of epitaxial layers. Spectroscopic ellipsometry has expanded from the research lab to become an integral part of the production of materials and structures for state of the art high speed devices. Along the way, it has contributed much to our understanding of the growth characteristics and material properties. The following areas of research are summarized: Si3N4 on GaAs, null ellipsometry; diamondlike carbon films; variable angle spectroscopic ellipsometry (VASE) development; GaAs-AlGaAs heterostructures; Ta-Cu diffusion barrier films on GaAs; GaAs-AlGaAs superlattices and multiple quantum wells; superconductivity; in situ elevated temperature measurements of III-V's; optical constants of thermodynamically stable InGaAs; doping dependence of optical constants of GaAs; in situ ellipsometric studies of III-V epitaxial growth; photothermal spectroscopy; microellipsometry; and Si passivation and Si/SiGe strained-layer superlattices.

  2. High-resolution X-ray diffraction in crystalline structures with quantum dots

    NASA Astrophysics Data System (ADS)

    Punegov, V. I.

    2015-05-01

    We review the current status of nondestructive high-resolution X-ray diffractometry research on semiconductor structures with quantum dots (QDs). The formalism of the statistical theory of diffraction is used to consider the coherent and diffuse X-ray scattering in crystalline systems with nanoinclusions. Effects of the shape, elastic strain, and lateral and vertical QD correlation on the diffuse scattering angular distribution near the reciprocal lattice nodes are considered. Using short-period and multicomponent superlattices as an example, we demonstrate the efficiency of data-assisted simulations in the quantitative analysis of nanostructured materials.

  3. Influence of As{sub 4} flux on the growth kinetics, structure, and optical properties of InAs/GaAs quantum dots

    SciTech Connect

    Garcia, A.; Mateo, C. M.; Defensor, M.; Salvador, A.; Hui, H. K.; Boothroyd, C. B.; Philpott, E.

    2007-10-01

    We report the effects of variations in As{sub 4} growth flux on the evolution of molecular beam epitaxy grown InAs quantum dots (QDs) and their structures and optical properties. For InAs QDs grown under As-stable conditions, evaluated through photoluminescence and atomic force microscopy (AFM) measurements, it is evident that QD size increases with As{sub 4} pressure along with improvement in size uniformity. Furthermore, transmission electron microscopy measurements for InAs layers of critical thicknesses ({approx}1.7 ML) showed decreasing QD density with increasing As{sub 4} pressure accompanied by a strong reduction in photoluminescence (PL) integral intensity. These show that high As{sub 4} fluxes suppress InAs QD formation while the decreasing PL intensity seems to indicate cluster formation that features nonradiative recombination. AFM measurements show larger and denser QDs for samples grown at higher As{sub 4} pressures. These are explained on the basis of adatom condensation during surface cooling and the influence of As{sub 4} pressure on indium incorporation.

  4. Growth and Strain Evaluation of InGaP/InGaAs/Ge Triple-Junction Solar Cell Structures

    NASA Astrophysics Data System (ADS)

    Alhomoudi, Ibrahim A.

    2016-10-01

    Metalorganic chemical vapor deposition (MOCVD) has been used for development of photovoltaic (PV) structures that enable enhanced efficiency for triple-junction solar cell (TJSC) devices. The in-plane strain, lattice match, surface defects, surface morphology, compositional uniformity, threading dislocations (TDs), and depth profile of each layer of the TJSC structure have been examined. The heteroepitaxial layers were found to be near lattice matched to the substrate with excellent coherence between the layers. The analysis explained that the indium gallium phosphide (InGaP) and indium gallium arsenide (InGaAs) layers on germanium (Ge) substrate are a strained structure with purely tetragonal crystalline phase, which indicates that the TJSC structural layers could maintain high crystalline quality. The biaxial in-plane strain in each layer of the TJSC structure is compressive and varies in magnitude for each layer in the structure, being strongly influenced by the Ge substrate and the multiple epilayers of the PV structure. Transmission electron microscopy (TEM) results show no TDs observed over a region with area of 500 nm2, with surface defect density less than 1 × 108 cm-2. No evidence of stacking faults and no visible defects of antiphase domains (APDs) at interfaces were observed, indicating adequate nucleation of epitaxial layers on the substrate and on subsequent growth layers. Furthermore, secondary-ion mass spectrometry (SIMS) analysis showed no significant Ge diffusion from the substrate into the TJSC structure.

  5. Capping effect of GaAsSb and InGaAsSb on the structural and optical properties of type II GaSb/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    He, Jun; Bao, Feng; Zhang, Jinping

    2012-04-01

    We systematically study the influence of group V intermixing on the structural and optical properties of type II GaSb/GaAs quantum dots (QDs) capped by selected capping layers. Compared to GaSb QDs capped directly by a GaAs layer, we observe a strong enhancement of photoluminescence (PL) intensity and a significant red-shift of the photoluminescence peak energy to 1.35 μm at 300 K by the introduction of a GaAsSb capping layer. In addition, Z-contrast cross sectional transmission electron microscopy shows Sb segregation and group V mixing is greatly suppressed by GaAsSb or InGaAsSb capping layers. The new capping layers offers the possibility of controlling optical properties of type II GaSb/GaAs quantum dots and this opens up new means for achieving high efficient GaSb/GaAs quantum dot solar cell.

  6. Exciton fine structure and spin/valley dynamics in nanosystems (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Glazov, Mikhail M.

    2015-09-01

    In my invited talk the fine structure of neutral and charged excitons for GaAs/AlGaAs quantum dots (QDs) grown on (111) plane as well for transition metal dichalcogenides (TMDCs) monolayers will be discussed. These, at first glance, different systems posses similar trigonal symmetry, which makes exciton fine structure and spin dynamics unusual compared with standard low-dimensional semiconductors. The effects of long-range exchange interaction induced mixing of excitons in two valleys of TMDCs and of magneto-induced mixing of bright and dark excitonic states in trigonal QDs are predicted and confirmed experimentally. Manifestations of excitonic spin/valley dynamics in photoluminescence, pump-probe Kerr rotation and spin noise are discussed. The presentation will be based on the following references: [1] G. Sallen, B. Urbaszek, M. M. Glazov, et al., Dark-Bright Mixing of Interband Transitions in Symmetric Semiconductor Quantum Dots, Phys. Rev. Lett. 107, 166604 (2011). [2] L. Bouet, M. Vidal, T. Mano, N. Ha, T. Kuroda, M. V. Durnev, M. M. Glazov, et al., Charge tuning in [111] grown GaAs droplet quantum dots, Appl. Phys. Lett. 105, 082111 (2014). [3] M. M. Glazov, et al., Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides Phys. Rev. B 89, 201302(R) (2014). [4] C. R. Zhu, K. Zhang, M. Glazov, et al., Exciton valley dynamics probed by Kerr rotation in WSe2 monolayers, Phys. Rev. B 90, 161302(R) (2014).

  7. Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, Z. B.; Lei, W.; Chen, B.; Wang, Y. B.; Liao, X. Z.; Tan, H. H.; Zou, J.; Ringer, S. P.; Jagadish, C.

    2014-01-01

    Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.

  8. Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition

    SciTech Connect

    Chen, Z. B.; Chen, B.; Wang, Y. B.; Liao, X. Z.; Lei, W.; Tan, H. H.; Jagadish, C.; Zou, J.; Ringer, S. P.

    2014-01-13

    Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.

  9. Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

    SciTech Connect

    Xu, Ming Jaffré, Alexandre Alvarez, José Kleider, Jean-Paul Boutchich, Mohamed; Jittrong, Apichat; Chokamnuai, Thitipong; Panyakeow, Somsak; Kanjanachuchai, Songphol

    2015-02-27

    We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

  10. Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures

    NASA Astrophysics Data System (ADS)

    Küster, Achim; Heyn, Christian; Ungeheuer, Arne; Juska, Gediminas; Tommaso Moroni, Stefano; Pelucchi, Emanuele; Hansen, Wolfgang

    2016-06-01

    Strain-free epitaxial quantum dots (QDs) are fabricated by a combination of Al local droplet etching (LDE) of nanoholes in AlGaAs surfaces and subsequent hole filling with GaAs. The whole process is performed in a conventional molecular beam epitaxy (MBE) chamber. Autocorrelation measurements establish single-photon emission from LDE QDs with a very small correlation function g (2)(0)≃ 0.01 of the exciton emission. Here, we focus on the influence of the initial hole depth on the QD optical properties with the goal to create deep holes suited for filling with more complex nanostructures like quantum dot molecules (QDM). The depth of droplet etched nanoholes is controlled by the droplet material coverage and the process temperature, where a higher coverage or temperature yields deeper holes. The requirements of high quantum dot uniformity and narrow luminescence linewidth, which are often found in applications, set limits to the process temperature. At high temperatures, the hole depths become inhomogeneous and the linewidth rapidly increases beyond 640 °C. With the present process technique, we identify an upper limit of 40-nm hole depth if the linewidth has to remain below 100 μeV. Furthermore, we study the exciton fine-structure splitting which is increased from 4.6 μeV in 15-nm-deep to 7.9 μeV in 35-nm-deep holes. As an example for the functionalization of deep nanoholes, self-aligned vertically stacked GaAs QD pairs are fabricated by filling of holes with 35 nm depth. Exciton peaks from stacked dots show linewidths below 100 μeV which is close to that from single QDs.

  11. Quantum-dot blue light emitting diodes utilizing organic/inorganic hybrid structures

    NASA Astrophysics Data System (ADS)

    Wu, Feifei; Hu, Lian; Zhang, Bingpo; Li, Ruifeng; Wu, Huizhen

    2015-02-01

    We report blue color quantum-dot light-emitting diodes (QDLEDs) using an organic-inorganic hybrid structure and CdZnS-ZnS core-shell quantum-dot emitters. In the device organic ploy(3,4-ethylenedioxythiophene):ploy(styrene sulfonate) (PEDOT:PSS) and NN‧-bis(3-methylphenyl)-NN‧-bis(phenyl)-99-spiro-bifluorene (TPD) thin films are respectively used as the hole-injection layer (HIL) and the hole-transporting layer (HTL), and an inorganic ZnSnO thin film is used as the electron-transporting layer (ETL). In the blue QDLEDs, the function of the TPD-HTL is explored and it is found that the device employing a TPD-HTL exhibits much better optical characteristics compared with that having an identical device layout but without the TPD-HTL. The TPD HTL acts as a transition layer and offers a ladder for the injected holes from PEDOT:PSS to the QDs, leading to an more efficient hole injection. It is further found that the intensity ratio between surface-state emission (SSE) and band-edge emission (BEE) (RS/B) of the two devices shows significant difference at high bias voltages. The SSE becomes more prominent at higher bias voltage in the QDLEDs due to the imbalance injection of holes and electrons. The injected holes firstly encounter the excessive electrons accumulated at the surface of the charged QDs, thus the probability of hole-electron recombination at the QDs surface is greatly enhanced at high bias voltages.

  12. Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures.

    PubMed

    Küster, Achim; Heyn, Christian; Ungeheuer, Arne; Juska, Gediminas; Tommaso Moroni, Stefano; Pelucchi, Emanuele; Hansen, Wolfgang

    2016-12-01

    Strain-free epitaxial quantum dots (QDs) are fabricated by a combination of Al local droplet etching (LDE) of nanoholes in AlGaAs surfaces and subsequent hole filling with GaAs. The whole process is performed in a conventional molecular beam epitaxy (MBE) chamber. Autocorrelation measurements establish single-photon emission from LDE QDs with a very small correlation function g ((2))(0)≃ 0.01 of the exciton emission. Here, we focus on the influence of the initial hole depth on the QD optical properties with the goal to create deep holes suited for filling with more complex nanostructures like quantum dot molecules (QDM). The depth of droplet etched nanoholes is controlled by the droplet material coverage and the process temperature, where a higher coverage or temperature yields deeper holes. The requirements of high quantum dot uniformity and narrow luminescence linewidth, which are often found in applications, set limits to the process temperature. At high temperatures, the hole depths become inhomogeneous and the linewidth rapidly increases beyond 640 °C. With the present process technique, we identify an upper limit of 40-nm hole depth if the linewidth has to remain below 100 μeV. Furthermore, we study the exciton fine-structure splitting which is increased from 4.6 μeV in 15-nm-deep to 7.9 μeV in 35-nm-deep holes. As an example for the functionalization of deep nanoholes, self-aligned vertically stacked GaAs QD pairs are fabricated by filling of holes with 35 nm depth. Exciton peaks from stacked dots show linewidths below 100 μeV which is close to that from single QDs.

  13. Probing the band structure and local electronic properties of low-dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Walrath, Jenna Cherie

    Low-dimensional semiconductor structures are important for a wide variety of applications, and recent advances in nanoscale fabrication are paving the way for increasingly precise nano-engineering of a wide range of materials. It is therefore essential that the physics of materials at the nanoscale are thoroughly understood to unleash the full potential of nanotechnology, requiring the development of increasingly sophisticated instrumentation and modeling. Of particular interest is the relationship between the local density of states (LDOS) of low-dimensional structures and the band structure and local electronic properties. This dissertation presents the investigation of the band structure, LDOS, and local electronic properties of nanostructures ranging from zero-dimensional (0D) quantum dots (QDs) to two-dimensional (2D) thin films, synthesizing computational and experimental approaches including Poisson-Schrodinger band structure calculations, scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and scanning thermoelectric microscopy (SThEM). A method is presented for quantifying the local Seebeck coefficient (S) with SThEM, using a quasi-3D conversion matrix approach to directly convert temperature gradient-induced voltages S. For a GaAs p-n junction, the resulting S-profile is consistent with that computed using the free carrier concentration profile. This combined computational-experimental approach is expected to enable nanoscale measurements of S across a wide variety of heterostructure interfaces. The local carrier concentration, n, is profiled across epitaxial InAs/GaAs QDs, where SThEM is used to profile the temperature gradient-induced voltage, which is converted to a profile of the local S and finally to an n profile. The S profile is converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. The combined computational-experimental approach suggests a reduced n in the QD center in

  14. Structural and orientation effects on electronic energy transfer between silicon quantum dots with dopants and with silver adsorbates.

    PubMed

    Vinson, N; Freitag, H; Micha, D A

    2014-06-28

    Starting from the atomic structure of silicon quantum dots (QDs), and utilizing ab initio electronic structure calculations within the Förster resonance energy transfer (FRET) treatment, a model has been developed to characterize electronic excitation energy transfer between QDs. Electronic energy transfer rates, KEET, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag3, have been calculated and analyzed to extend previous work on light absorption by QDs. The effects of their size and relative orientation on energy transfer rates for each system have also been considered. Using time-dependent density functional theory and the hybrid functional HSE06, the FRET treatment was employed to model electronic energy transfer rates within the dipole-dipole interaction approximation. Calculations with adsorbed Ag show that: (a) addition of Ag increases rates up to 100 times, (b) addition of Ag3 increases rates up to 1000 times, (c) collinear alignment of permanent dipoles increases transfer rates by an order of magnitude compared to parallel orientation, and (d) smaller QD-size increases transfer due to greater electronic orbitals overlap. Calculations with dopants show that: (a) p-type and n-type dopants enhance energy transfer up to two orders of magnitude, (b) surface-doping with P and center-doping with Al show the greatest rates, and (c) KEET is largest for collinear permanent dipoles when the dopant is on the outer surface and for parallel permanent dipoles when the dopant is inside the QD.

  15. High-resolution 3D structural and optical analyses of hybrid or composite materials by means of scanning probe microscopy combined with the ultramicrotome technique: an example of application to engineering of liquid crystals doped with fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Mochalov, Konstantin E.; Efimov, Anton E.; Bobrovsky, Alexey Yu.; Agapov, Igor I.; Chistyakov, Anton A.; Oleinikov, Vladimir A.; Nabiev, Igor

    2013-05-01

    Combination of nanometer-scale 3D structural analysis with optical characterization of the same material is a challenging task. Its results may be important for nanophotonics, materials science, and quality control. We have developed a new technique for complementary high-resolution structural and optical characterization followed by optical spectroscopic and microscopic measurements accompanied by reconstruction of the 3D structure in the same area of the sample. The 3D structure is reconstructed by combination of ultramicrotomic and SPM techniques allowing the study of the 3D distribution of implanted nanoparticles and their effect on the matrix structure. The combination of scanning probe nanotomography (SPN) and optical microspectroscopy makes it possible to direct estimate how the 3D structural characteristics of materials affect their macroscopic optical properties. The technique developed has been applied to the engineering of materials made from cholesteric liquid crystals and fluorescent quantum dots (QDs). These materials permit photochemical patterning and image recording through the changes in the dissymmetry factor of circular polarization of QD emission. The differences in the polarisation images and morphological characteristics of the liquid crystal matrix have proved to be correlated with the arrangement of the areas of homogeneous distribution and nonhomogeneous clustering of QDs. The reconstruction of the 3D structure of the liquid crystal matrix in the areas of homogeneous QD distribution has shown that QDs embedded into cholesteric liquid crystal matrices do not perturb their periodic planar texture. The combined optical/SPM/ultramicrotome technique will be indispensable for evaluating the effects of inorganic nanoparticles on the organisation of organic and liquid crystal matrices, biomedical materials, cells, and tissues.

  16. Single-photon and photon pair emission from MOVPE-grown In(Ga)As quantum dots: shifting the emission wavelength from 1.0 to 1.3 μm

    NASA Astrophysics Data System (ADS)

    Kettler, Jan; Paul, Matthias; Olbrich, Fabian; Zeuner, Katharina; Jetter, Michael; Michler, Peter

    2016-03-01

    InAs quantum dots grown on a GaAs substrate have been one of the most successful semiconductor material systems to demonstrate single-photon-based quantum optical phenomena. In this context, we present the feasibility to extend the low-temperature photoluminescence emission range of In(Ga)As/GaAs quantum dots grown by metal-organic vapor-phase epitaxy from the typical window between 880 and 960 nm to wavelengths above 1.3 μm. A low quantum dot density can be obtained throughout this range, enabling the demonstration of single- and cascaded photon emission. We further analyze polarization-resolved micro-photoluminescence from a large number of individual quantum dots with respect to anisotropy and size of the underlying fine-structure splittings in the emission spectra. For samples with elevated emission wavelengths, we observe an increasing tendency of the emitted photons to be polarized along the main crystal axes.

  17. Noise spectroscopy of nanowire structures: fundamental limits and application aspects

    NASA Astrophysics Data System (ADS)

    Vitusevich, Svetlana; Zadorozhnyi, Ihor

    2017-04-01

    Nanowires (NWs) have recently emerged as a new class of materials demonstrating unique properties which may completely differ from their bulk counterparts. The main aim of this work is to give an overview of results on noise and fluctuation phenomena in NW-based structures. We emphasize that noise is one of the main parameters, which determines the characteristics of the device structures and sets the fundamental limits of the working principles and operation regimes of NWs as key electronic elements, including field-effect transistors (FETs). We review the studies focusing on the understanding of noise sources and the main application aspects of noise spectroscopy. Noise application aspects will provide information about the performance of core–shell NW structures, the gate-coupling effect and its advantages for detection of the useful signal with prospects to extract it from the noise level, random telegraph signal as a useful tool for enhanced sensitivity, novel components of noise reflecting dielectric polarization fluctuation processes and fluctuation phenomena as a sensitive tool for molecular charge dynamics in NW FETs. Moreover, noise spectroscopy assists understanding of electronic transport regimes and effects, transport peculiarities in topological materials and aspects reflecting Majorana bound states. Thus noise in NWs on the basis of Si, Ge, Si/Ge, GaAs, InAs, InGaAs, Au, GaAs/AlGaAs, GaAsSb, SnO2, GaN, ZnO, CuO, In2O3 and AlGaN/GaN materials reflects a great variety of phenomena and processes, information about their stability and reliability. It can be utilized for numerous different applications in nanoelectronics and bioelectronics.

  18. Viability of imaging structures inside human dentin using dental transillumination

    NASA Astrophysics Data System (ADS)

    Grandisoli, C. L.; Alves-de-Souza, F. D.; Costa, M. M.; Castro, L.; Ana, P. A.; Zezell, D. M.; Lins, E. C.

    2014-02-01

    Dental Transillumination (DT) is a technique for imaging internal structures of teeth by detecting infrared radiation transmitted throughout the specimens. It was successfully used to detect caries even considering dental enamel and dentin scatter infrared radiation strongly. Literature reports enamel's scattering coefficient is 10 to 30 times lower than dentin; this explain why DT is useful for imaging pathologies in dental enamel, but does not disable its using for imaging dental structures or pathologies inside the dentin. There was no conclusive data in the literature about the limitations of using DT to access biomedical information of dentin. The goal in this study was to present an application of DT to imaging internal structures of dentin. Slices of tooth were confectioned varying the thickness of groups from 0.5 mm up to 2,5 mm. For imaging a FPA InGaAs camera Xeva 1.7- 320 (900-1700 nm; Xenics, Inc., Belgium) and a 3W lamp-based broadband light source (Ocean Optics, Inc., USA) was used; bandpass optical filters at 1000+/-10 nm, 1100+/-10 nm, 1200+/-10 nm and 1300+/-50 nm spectral region were also applied to spectral selection. Images were captured for different camera exposure times and finally a computational processing was applied. The best results revealed the viability to imaging dent in tissue with thickness up to 2,5 mm without a filter (900-1700nm spectral range). After these results a pilot experiment of using DT to detect the pulp chamber of an incisive human tooth was made. New data showed the viability to imaging the pulp chamber of specimen.

  19. Super-high density Si quantum dot thin film utilizing a gradient Si-rich oxide multilayer structure.

    PubMed

    Kuo, Kuang-Yang; Huang, Pin-Ruei; Lee, Po-Tsung

    2013-05-17

    A gradient Si-rich oxide multilayer (GSRO-ML) deposition structure is proposed to achieve super-high density Si quantum dot (QD) thin film formation while preserving QD size controllability for better photovoltaic properties. Our results indicate that the Si QD thin film using a GSRO-ML structure can efficiently increase the QD density and control the QD size. Its optical properties clearly promise the capability of effective bandgap engineering even though these QDs are closely formed. The Si QD thin film using a GSRO-ML structure obviously reveals better electro-optical properties than those using a [silicon dioxide/silicon-rich oxide] multilayer ([SiO2/SRO]-ML) structure owing to the better optical absorption and carrier transport properties. Therefore, we successfully demonstrate that our proposed GSRO-ML structure has great potential for application in solar cells integrating Si QD thin films.

  20. Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures.

    PubMed

    Fillipov, Stanislav; Puttisong, Yuttapoom; Huang, Yuqing; Buyanova, Irina A; Suraprapapich, Suwaree; Tu, Charles W; Chen, Weimin M

    2015-06-23

    Fine-structure splitting (FSS) of excitons in semiconductor nanostructures is a key parameter that has significant implications in photon entanglement and polarization conversion between electron spins and photons, relevant to quantum information technology and spintronics. Here, we investigate exciton FSS in self-organized lateral InAs/GaAs quantum-dot molecular structures (QMSs) including laterally aligned double quantum dots (DQDs), quantum-dot clusters (QCs), and quantum rings (QRs), by employing polarization-resolved microphotoluminescence (μPL) spectroscopy. We find a clear trend in FSS between the studied QMSs depending on their geometric arrangements, from a large FSS in the DQDs to a smaller FSS in the QCs and QRs. This trend is accompanied by a corresponding difference in the optical polarization directions of the excitons between these QMSs, namely, the bright-exciton lines are linearly polarized preferably along or perpendicular to the [11̅0] crystallographic axis in the DQDs that also defines the alignment direction of the two constituting QDs, whereas in the QCs and QRs, the polarization directions are randomly oriented. We attribute the observed trend in the FSS to a significant reduction of the asymmetry in the lateral confinement potential of the excitons in the QRs and QCs as compared with the DQDs, as a result of a compensation between the effects of lateral shape anisotropy and piezoelectric field. Our work demonstrates that FSS strongly depends on the geometric arrangements of the QMSs, which effectively tune the degree of the compensation effects and are capable of reducing FSS even in a strained QD system to a limit similar to strain-free QDs. This approach provides a pathway in obtaining high-symmetry quantum emitters desirable for realizing photon entanglement and spintronic devices based on such nanostructures, utilizing an uninterrupted epitaxial growth procedure without special requirements for lattice-matched materials combinations

  1. Multi-color tunneling quantum dot infrared photodetectors operating at room temperature

    NASA Astrophysics Data System (ADS)

    Ariyawansa, G.; Perera, A. G. U.; Su, X. H.; Chakrabarti, S.; Bhattacharya, P.

    2007-04-01

    Quantum dot structures designed for multi-color infrared detection and high temperature (or room temperature) operation are demonstrated. A novel approach, tunneling quantum dot (T-QD), was successfully demonstrated with a detector that can be operated at room temperature due to the reduction of the dark current by blocking barriers incorporated into the structure. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers placed in the structure. A two-color tunneling-quantum dot infrared photodetector (T-QDIP) with photoresponse peaks at 6 μm and 17 μm operating at room temperature will be discussed. Furthermore, the idea can be used to develop terahertz T-QD detectors operating at high temperatures. Successful results obtained for a T-QDIP designed for THz operations are presented. Another approach, bi-layer quantum dot, uses two layers of InAs quantum dots (QDs) with different sizes separated by a thin GaAs layer. The detector response was observed at three distinct wavelengths in short-, mid-, and far-infrared regions (5.6, 8.0, and 23.0 μm). Based on theoretical calculations, photoluminescence and infrared spectral measurements, the 5.6 and 23.0 μm peaks are connected to the states in smaller QDs in the structure. The narrow peaks emphasize the uniform size distribution of QDs grown by molecular beam epitaxy. These detectors can be employed in numerous applications such as environmental monitoring, spectroscopy, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.

  2. Tuning InP self-assembled quantum structures to telecom wavelength: A versatile original InP(As) nanostructure "workshop"

    NASA Astrophysics Data System (ADS)

    Mura, E. E.; Gocalinska, A.; Juska, G.; Moroni, S. T.; Pescaglini, A.; Pelucchi, E.

    2017-03-01

    The influence of hydride exposure on previously unreported self-assembled InP(As) nanostructures is investigated, showing an unexpected morphological variability with growth parameters, and producing a large family of InP(As) nanostructures by metalorganic vapour phase epitaxy, from dome and ring-like structures to double dot in a ring ensembles. Moreover, preliminary microphotoluminescence data are indicating the capped rings system as an interesting candidate for single quantum emitters at telecom wavelengths, potentially becoming a possible alternative to InAs QDs for quantum technology and telecom applications.

  3. Photon-number discrimination using a semiconductor quantum dot, optically gated, field-effect transistor

    NASA Astrophysics Data System (ADS)

    Gansen, Eric J.; Rowe, Mary A.; Greene, Marion B.; Rosenberg, Danna; Harvey, Todd E.; Su, Mark Y.; Nam, Sae Woo; Mirin, Richard P.

    2007-09-01

    We demonstrate photon-number discrimination using a novel semiconductor detector that utilizes a layer of self-assembled InGaAs quantum dots (QDs) as an optically addressable floating gate in a GaAs/AlGaAs δ-doped field-effect transistor. When the QDOGFET (quantum dot, optically gated, field-effect transistor) is illuminated, the internal gate field directs the holes generated in the dedicated absorption layer of the structure to the QDs, where they are trapped. The positively charged holes are confined to the dots and screen the internal gate field, causing a persistent change in the channel current that is proportional to the total number of holes trapped in the QD ensemble. We use highly attenuated laser pulses to characterize the response of the QDOGFET cooled to 4 K. We demonstrate that different photon-number states produce well resolved changes in the channel current, where the responses of the detector reflect the Poisson statistics of the laser light. For a mean photon number of 1.1, we show that decision regions can be defined such that the QDOGFET determines the number (0, 1, 2, or >=3) of detected photons with a probability of accuracy >=83 % in a single-shot measurement.

  4. Dual-wavelength mode-locking of novel chirped multilayer quantum-dot lasers

    NASA Astrophysics Data System (ADS)

    Chiang, Chun-Ping; Lin, Gray; Chen, Yu-Chen; Cheng, Hsu-Chieh

    2016-09-01

    Monolithic passively mode-locked lasers are investigated based on chirped multilayer InAs/InGaAs QDs. Three chirped wavelengths, with stacking numbers of 2, 3 and 5 layers, are designed with capped InGaAs thickness of 4, 3 and 1 nm, respectively. The ridge-waveguide devices of 5-μm width and 3-mm length are fabricated to have absorber-to-gain length ratio of 1:9. A curve tracer is used to analyze the hysteresis on the light-current curve. Two kinks in the L-I curve are observed at threshold current near 50 mA and at higher current of about 150 mA. The lasing wavelength just above threshold is centered at 1268 nm and the RF spectrum of mode-locking is peaked at 13.32 GHz. At well above threshold of 200 mA, another RF peak at 13.21 GHz occurs that corresponds to shorter lasing wavelength around 1233 nm. The two lasing wavelengths are originated from ground-state transitions of two groups of InAs/InGaAs QDs. Simultaneous dual-wavelength mode-locking is therefore achieved at rather low forward current and low reverse bias by incorporating this novel design of QD structure.

  5. Novel hybrid structure silica/CdTe/molecularly imprinted polymer: synthesis, specific recognition, and quantitative fluorescence detection of bovine hemoglobin.

    PubMed

    Li, Dong-Yan; He, Xi-Wen; Chen, Yang; Li, Wen-You; Zhang, Yu-Kui

    2013-12-11

    This work presented a novel strategy for the synthesis of the hybrid structure silica/CdTe/molecularly imprinted polymer (Si-NP/CdTe/MIP) to recognize and detect the template bovine hemoglobin (BHb). First, amino-functionalized silica nanoparticles (Si-NP) and carboxyl-terminated CdTe quantum dots (QDs) were assembled into composite nanoparticles (Si-NP/CdTe) using the EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) chemistry. Next, Si-NP/CdTe/MIP was synthesized by anchoring molecularly imprinted polymer (MIP) layer on the surface of Si-NP/CdTe through the sol-gel technique and surface imprinting technique. The hybrid structure possessed the selectivity of molecular imprinting technique and the sensitivity of CdTe QDs as well as well-defined morphology. The binding experiment and fluorescence method demonstrated its special recognition performance toward the template BHb. Under the optimized conditions, the fluorescence intensity of the Si-NP/CdTe/MIP decreased linearly with the increase of BHb in the concentration range 0.02-2.1 μM, and the detection limit was 9.4 nM. Moreover, the reusability and reproducibility and the successful applications in practical samples indicated the synthesis of Si-NP/CdTe/MIP provided an alternative solution for special recognition and determination of protein from real samples.

  6. Core-shell structured photovoltaic devices based on PbS quantum dots and silicon nanopillar arrays.

    PubMed

    Song, Tao; Zhang, Fute; Lei, Xiaofei; Xu, Yonglan; Lee, Shuittong; Sun, Baoquan

    2012-02-21

    We fabricated three-dimensional silicon nanopillar array (SiNP)-based photovoltaic (PV) devices using PbS quantum dots (QDs) as the hole-transporting layers. The core-shell structured device, which is based on high aspect ratio SiNPs standing on roughed silicon substrates, displays a higher PV performance with a power conversion efficiency (PCE) of 6.53% compared with that of the planar device (2.11%). The enhanced PCE is ascribed to the increased light absorption and the improved charge carrier collections in SiNP-modified silicon surfaces. We also show that, for the core-shell structured device, the thickness of the shell layer plays a critical role in enhancing the PV performance and around five monolayers of QDs are preferred for efficient hole-transporting. Wafer-scale PV devices with a radial PbS/SiNP heterojunction can be fabricated by solution phase techniques at low temperatures, suggesting a facile route to fabricate unique three-dimensional nanostructured devices.

  7. Capping layer growth rate and the optical and structural properties of GaAsSbN-capped InAs/GaAs quantum dots

    SciTech Connect

    Ulloa, J. M. Utrilla, A. D.; Guzman, A.; Hierro, A.

    2014-10-07

    Changing the growth rate during the heteroepitaxial capping of InAs/GaAs quantum dots (QDs) with a 5 nm-thick GaAsSbN capping layer (CL) strongly modifies the QD structural and optical properties. A size and shape transition from taller pyramids to flatter lens-shaped QDs is observed when the CL growth rate is decreased from 1.5 to 0.5 ML/s. This indicates that the QD dissolution processes taking place during capping can be controlled to some extent by the GaAsSbN CL growth rate, with high growth rates allowing a complete preservation of the QDs. However, the dissolution processes are shown to have a leveling effect on the QD height, giving rise to a narrower size distribution for lower growth rates. Contrary to what could be expected, these effects are opposite to the strong blue-shift and improvement of the photoluminescence (PL) observed for higher growth rates. Nevertheless, the PL results can be understood in terms of the strong impact of the growth rate on the Sb and N incorporation into the CL, which results in lower Sb and N contents at higher growth rates. Besides the QD-CL band offsets and QD strain, the different CL composition alters the band alignment of the system, which can be transformed to type-II at low growth rates. These results show the key role of the alloyed CL growth parameters on the resulting QD properties and demonstrate an intricate correlation between the PL spectra and the sample morphology in complex QD-CL structures.

  8. Band structures of cylindrical AlN/GaN quantum dots with fully coupled piezoelectric models

    NASA Astrophysics Data System (ADS)

    Prabhakar, Sanjay; Melnik, Roderick

    2010-08-01

    We study the coupled electro-mechanical effects in the band structure calculations of low dimensional semiconductor nanostructures (LDSNs) such as AlN/GaN quantum dots. Some effects in these systems are essentially nonlinear. Strain, piezoelectric effects, eigenvalues and wave functions of a quantum dot have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering and other applications. However, with a few noticeable exceptions, the influence of piezoelectric effects in the electron wave functions in Quantum Dots (QDs) studied with fully coupled models has been largely neglected in the literature. In this paper, by using the fully coupled model of electroelasticity, we analyze the piezoelectric effects into the band structure of cylindrical quantum dots. Results are reported for III-V type semiconductors with a major focus given to AlN/GaN based QD systems.

  9. Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure

    NASA Astrophysics Data System (ADS)

    Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke

    2016-10-01

    It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.

  10. Stability and controllability of InGaAs/GaAsP wire-on-well (WoW) structure for multi-junction solar cells

    NASA Astrophysics Data System (ADS)

    Cho, Hirofumi; Toprasertpong, Kasidit; Sodabanlu, Hassanet; Watanabe, Kentaroh; Sugiyama, Masakazu; Nakano, Yoshiaki

    2017-04-01

    Wire on Well (WoW) structure embedded in a matrix is naturally formed by growing InxGa1-xAs/GaAs1-yPy strained multiple quantum wells (MQW) on vicinal substrates and employing triethylgallium (TEGa) as a precursor in low-temperature MOVPE. The structure is useful for the subcell in current-matched mult-junction solar cells with lattice-matched materials because of its ability of band-gap tuning. In this research, high density and uniform In0.30Ga0.70As/GaAs0.6P0.4 WoW was obtained up to 200 stacks and its structure was analyzed by X-ray diffraction reciprocal space mapping, atomic force microscopy and scanning transmission electron microscopy. The structure of the wire can be controlled by changing the equivalent layer thicknesses of In0.30Ga0.70As and GaAs0.6P0.4. The photoluminescence peak from the WoW shifted according to the size of InGaAs wires and the intensity was dependent on the accumulation of lattice-mismatch stress.

  11. All solution processed low turn-on voltage near infrared LEDs based on core-shell PbS-CdS quantum dots with inverted device structure

    NASA Astrophysics Data System (ADS)

    Sanchez, Rafael S.; Binetti, Enrico; Torre, Jose A.; Garcia-Belmonte, G.; Striccoli, Marinella; Mora-Sero, Ivan

    2014-07-01

    Colloidal semiconductor quantum dots (QDs) are extraordinarily appealing for the development of light emitting devices (LEDs) due to tunable and pure color emission, brightness and solution processability. This last advantage of the QD-LEDs is even more evident in the field of infrared emission where the devices currently used are prepared by high cost epitaxial techniques. Here we show the fabrication of low cost NIR QD-LEDs based on high quantum yield core-shell PbS-CdS QDs and a novel inverted device structure. Devices are produced using SnO2:F (FTO) as the conductive transparent contact, nanostructured TiO2 as the electron transport layer (ETL) and poly(3-hexylthiophene) P3HT as the hole transport layer (HTL). Despite the roughness of this ETL, the obtained external quantum efficiencies (EQEs) are similar to previously reported values, obtained with regular configuration and more expensive ITO substrates. A turn-on voltage as low as the QD band gap (1.47 eV) is achieved for a large area (1.54 cm2) and relatively stable QD-LEDs.Colloidal semiconductor quantum dots (QDs) are extraordinarily appealing for the development of light emitting devices (LEDs) due to tunable and pure color emission, brightness and solution processability. This last advantage of the QD-LEDs is even more evident in the field of infrared emission where the devices currently used are prepared by high cost epitaxial techniques. Here we show the fabrication of low cost NIR QD-LEDs based on high quantum yield core-shell PbS-CdS QDs and a novel inverted device structure. Devices are produced using SnO2:F (FTO) as the conductive transparent contact, nanostructured TiO2 as the electron transport layer (ETL) and poly(3-hexylthiophene) P3HT as the hole transport layer (HTL). Despite the roughness of this ETL, the obtained external quantum efficiencies (EQEs) are similar to previously reported values, obtained with regular configuration and more expensive ITO substrates. A turn-on voltage as low as

  12. Theoretical investigation of the effect of asymmetry on optical anisotropy and electronic structure of Stranski-Krastanov quantum dots

    NASA Astrophysics Data System (ADS)

    Kumar, Jitendra; Kapoor, Sheetal; Gupta, Saral K.; Sen, Pranay K.

    2006-09-01

    The effect of size and shape anisotropy on the optical properties of Stranski-Krastanov quantum dots (QDs) is theoretically investigated. The QD is modeled using anisotropic parabolic confinement potential. The complex structure of the valence band is described by Luttinger Hamiltonian. The energy spectra and eigenfunctions of hole states are calculated by numerical diagonalization of the Hamiltonian. The dipole matrix elements are obtained for the interband transitions and hence the degree of linear polarization is calculated. The formulation is applied to self-assembled CdSe quantum dots for numerical analysis. The variation of energy eigenvalues with the QD shape anisotropy parameter is studied and the effect of valence subband mixing is clearly identified. The crossings and anticrossings of the valence subbands have been explained in terms of the symmetries of the corresponding eigenstates. It is worthy to note that these symmetry properties of the energy states are responsible for the specific types of dipole selection rules for the anisotropic QDs. The degree of linear polarization is found to increase almost linearly with anisotropy parameter for the transitions from heavy-hole ground states. On the contrary, for the excited hole states, the change is nonmonotonic due to strong anisotropy-dependent mixing effects.

  13. Effect of spacer layer thickness on structural and optical properties of multi-stack InAs/GaAsSb quantum dots

    SciTech Connect

    Kim, Yeongho; Ban, Keun-Yong Honsberg, Christiana B.; Boley, Allison; Smith, David J.

    2015-10-26

    The structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) with different spacer layer thicknesses (d{sub s} = 2, 5, 10, and 15 nm) are reported. X-ray diffraction analysis reveals that the strain relaxation of the GaAsSb spacers increases linearly from 0% to 67% with larger d{sub s} due to higher elastic stress between the spacer and GaAs matrix. In addition, the dislocation density in the spacers with d{sub s} = 10 nm is lowest as a result of reduced residual strain. The photoluminescence peak energy from the QDs does not change monotonically with increasing d{sub s} due to the competing effects of decreased compressive strain and weak electronic coupling of stacked QD layers. The QD structure with d{sub s} = 10 nm is demonstrated to have improved luminescence properties and higher carrier thermal stability.

  14. One-pot synthesis of mesoporous structured ratiometric fluorescence molecularly imprinted sensor for highly sensitive detection of melamine from milk samples.

    PubMed

    Xu, Shoufang; Lu, Hongzhi

    2015-11-15

    A facile strategy was developed to prepare mesoporous structured ratiometric fluorescence molecularly imprinted sensor for highly sensitive and selective determination of melamine using CdTe QDs as target sensitive dye and hematoporphyrin as reference dyes. One-pot synthesis method was employed because it could simplify the imprinting process and shorten the experimental period. The as-prepared fluorescence MIPs sensor, which combined ratiometric fluorescence technique with mesoporous silica materials into one system, exhibited excellent selectivity and sensitivity. Under optimum conditions, these mesoporous structured ratiometric fluorescence MIP@QDs sensors showed detection limit as low as 38 nM, which was much lower than those non-mesoporous one. The recycling process was sustainable at least 10 times without obvious efficiency decrease. The feasibility of the developed method in real samples was successfully evaluated through the analysis of melamine in raw milk and milk powder samples with satisfactory recoveries of 92-101%. The developed method proposed in this work proved to be a convenient, rapid, reliable and practical way to prepared high sensitive and selective fluorescence sensors with potentially applicable for trace pollutants analysis in complicated samples.

  15. Deep level centers and their role in photoconductivity transients of InGaAs/GaAs quantum dot chains

    SciTech Connect

    Kondratenko, S. V. Vakulenko, O. V.; Mazur, Yu. I. Dorogan, V. G.; Marega, E.; Benamara, M.; Ware, M. E.; Salamo, G. J.

    2014-11-21

    The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80 K after excitation of electron-hole pairs due to interband transitions in both the InGaAs QDs and the GaAs matrix. Giant optically induced quenching of in-plane conductivity driven by recharging of EL2 centers is observed in the spectral range from 0.83 eV to 1.0 eV. Conductivity loss under photoexcitation is discussed in terms of carrier localization by analogy with carrier distribution in disordered media.

  16. Deep level centers and their role in photoconductivity transients of InGaAs/GaAs quantum dot chains

    NASA Astrophysics Data System (ADS)

    Kondratenko, S. V.; Vakulenko, O. V.; Mazur, Yu. I.; Dorogan, V. G.; Marega, E.; Benamara, M.; Ware, M. E.; Salamo, G. J.

    2014-11-01

    The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80 K after excitation of electron-hole pairs due to interband transitions in both the InGaAs QDs and the GaAs matrix. Giant optically induced quenching of in-plane conductivity driven by recharging of EL2 centers is observed in the spectral range from 0.83 eV to 1.0 eV. Conductivity loss under photoexcitation is discussed in terms of carrier localization by analogy with carrier distribution in disordered media.

  17. Density functional calculation of the structural and electronic properties of germanium quantum dots

    SciTech Connect

    Anas, M. M.; Gopir, G.

    2015-04-24

    We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.

  18. Density functional calculation of the structural and electronic properties of germanium quantum dots

    NASA Astrophysics Data System (ADS)

    Anas, M. M.; Gopir, G.

    2015-04-01

    We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.

  19. Carrier capture dynamics of single InGaAs/GaAs quantum-dot layers

    SciTech Connect

    Chauhan, K. N.; Riffe, D. M.; Everett, E. A.; Kim, D. J.; Yang, H.; Shen, F. K.

    2013-05-28

    Using 800 nm, 25-fs pulses from a mode locked Ti:Al{sub 2}O{sub 3} laser, we have measured the ultrafast optical reflectivity of MBE-grown, single-layer In{sub 0.4}Ga{sub 0.6}As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and annealing temperature. With increasing excited carrier density, the capture rate decreases; this slowing of the dynamics is attributed to Pauli state blocking within the InGaAs quantum layer.

  20. Structure, strain, and composition profiling of InAs/GaAs(211)B quantum dot superlattices

    SciTech Connect

    Florini, N.; Dimitrakopulos, G. P.; Kioseoglou, J.; Kehagias, Th.; Germanis, S.; Pelekanos, N. T.; Katsidis, C.; Hatzopoulos, Z.

    2016-01-21

    The morphology, nanostructure, and strain properties of InAs quantum dots (QDs) grown on GaAs(211)B, uncapped or buried, are explored by transmission electron microscopy and related quantitative techniques. Besides the built-in piezoelectric field, other differences of (211) growth compared to (100)-oriented growth are discussed in terms of the (211) surface non-singularity, leading to anisotropic shape of the QDs and local chemical inhomogeneity of the wetting layer. The shape of the uncapped QDs was precisely defined as truncated pyramidal, elongated along the 〈111〉 direction, and bounded by the (110), (100), and (213) facets. Local strain measurements showed that large surface QDs were almost unstrained due to plastic relaxation, exhibiting small residual elastic strain at the interface that gradually diminished toward their apex. Conversely, buried QDs were pseudomorphically grown on GaAs. By postulating a plane stress state, we have established a systematic increase of the local strain from the base toward the apex region of the QDs. Using Vegard's law, their chemical composition profiles were calculated, revealing an indium content gradient along the growth direction and compositional variants among different QDs. Photoluminescence measurements showed variations in emission energy between the QDs and consistency with a graded In-content, which complied with the quantitative strain analysis.

  1. Full-band structure modeling of the radiative and non-radiative properties of semiconductor materials and devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Bellotti, Enrico; Wen, Hanqing; Pinkie, Benjamin; Matsubara, Masahiko; Bertazzi, Francesco

    2015-08-01

    Understanding the radiative and non-radiative properties of semiconductor materials is a prerequisite for optimizing the performance of existing light emitters and detectors and for developing new device architectures based on novel materials. Due to the ever increasing complexity of novel semiconductor systems and their relative technological immaturity, it is essential to have design tools and simulation strategies that include the details of the microscopic physics and their dependence on the macroscopic (continuum) variables in the macroscopic device models. Towards this end, we have developed a robust full-band structure based approach that can be used to study the intrinsic material radiative and non-radiative properties and evaluate the same characteristics of low-dimensional device structures. A parallel effort is being carried out to model the effect of substrate driven stress/strain and material quality (dislocations and defects) on microscopic quantities such as non-radiative recombination rate. Using this modeling approach, we have extensively studied the radiative and non-radiative properties of both elemental (Si and Ge) and compound semiconductors (HgCdTe, InGaAs, InAsSb and InGaN). In this work we outline the details of the modelling approach, specifically the challenges and advantages related to the use of the full-band description of the material electronic structure. We will present a detailed comparison of the radiative and Auger recombination rates as a function of temperature and doping for HgCdTe and InAsSb that are two important materials for infrared detectors and emitters. Furthermore we will discuss the role of non-radiatiave Auger recombination processes in explaining the performance of light emitter diodes. Finally we will present the extension of the model to low dimensional structures employed in a number of light emitter and detector structures.

  2. All solution processed low turn-on voltage near infrared LEDs based on core-shell PbS-CdS quantum dots with inverted device structure.

    PubMed

    Sanchez, Rafael S; Binetti, Enrico; Torre, Jose A; Garcia-Belmonte, G; Striccoli, Marinella; Mora-Sero, Ivan

    2014-08-07

    Colloidal semiconductor quantum dots (QDs) are extraordinarily appealing for the development of light emitting devices (LEDs) due to tunable and pure color emission, brightness and solution processability. This last advantage of the QD-LEDs is even more evident in the field of infrared emission where the devices currently used are prepared by high cost epitaxial techniques. Here we show the fabrication of low cost NIR QD-LEDs based on high quantum yield core-shell PbS-CdS QDs and a novel inverted device structure. Devices are produced using SnO2:F (FTO) as the conductive transparent contact, nanostructured TiO2 as the electron transport layer (ETL) and poly(3-hexylthiophene) P3HT as the hole transport layer (HTL). Despite the roughness of this ETL, the obtained external quantum efficiencies (EQEs) are similar to previously reported values, obtained with regular configuration and more expensive ITO substrates. A turn-on voltage as low as the QD band gap (1.47 eV) is achieved for a large area (1.54 cm(2)) and relatively stable QD-LEDs.

  3. Photoluminescence enhancement in double Ge/Si quantum dot structures

    NASA Astrophysics Data System (ADS)

    Zinovieva, A. F.; Zinovyev, V. A.; Nikiforov, A. I.; Timofeev, V. A.; Mudryi, A. V.; Nenashev, A. V.; Dvurechenskii, A. V.

    2016-12-01

    The luminescence properties of double Ge/Si quantum dot structures are studied at liquid helium temperature depending on the Si spacer thickness d in QD molecules. A seven-fold increase in the integrated photoluminescence intensity is obtained for the structures with optimal thickness d = 2 nm. This enhancement is explained by increasing the overlap integral of electron and hole wavefunctions. Two main factors promote this increasing. The first one is that the electrons are localized at the QD base edges and their wavefunctions are the linear combinations of the states of in-plane Δ valleys, which are perpendicular in k-space to the growth direction [001]. This results in the increasing probability of electron penetration into Ge barriers. The second factor is the arrangement of Ge nanoclusters in closely spaced QD groups. The strong tunnel coupling of QDs within these groups increases the probability of hole finding at the QD base edge, that also promotes the increase in the radiative recombination probability.

  4. Photoluminescence enhancement in double Ge/Si quantum dot structures

    NASA Astrophysics Data System (ADS)

    Zinovieva, A. F.; Zinovyev, V. A.; Nikiforov, A. I.; Timofeev, V. A.; Mudryi, A. V.; Nenashev, A. V.; Dvurechenskii, A. V.

    2016-12-01

    Luminescence properties of double Ge/Si quantum dot structures were studied at liquid helium temperature depending on the Si spacer thickness d in QD molecules. A seven-fold increase of the integrated photoluminescence intensity was obtained for the structures with optimal thickness d = 2 nm. This enhancement is explained by increasing the overlap integral of electron and hole wave functions. Two main factors promote this increasing. The first one is that the electrons are localized at the QD base edges and their wave functions are the linear combinations of the states of in-plane Δ valleys, which are perpendicular in k-space to the growth direction [001]. This results in the increasing probability of electron penetration into Ge barriers. The second factor is the arrangement of Ge nanoclusters in closely spaced QD groups. The strong tunnel coupling of QDs within these groups increases the probability of hole finding at the QD base edge, that also promotes the increase of the radiative recombination probability.

  5. Transient carrier transfer in tunnel injection structures

    NASA Astrophysics Data System (ADS)

    Talalaev, V. G.; Tomm, J. W.; Zakharov, N. D.; Werner, P.; Gösele, U.; Novikov, B. V.; Sokolov, A. S.; Samsonenko, Y. B.; Egorov, V. A.; Cirlin, G. E.

    2008-07-01

    InGaAs tunnel injection nanostructures consisting of a single quantum well as injector and a quantum dot layer as emitter are studied by time-resolved photoluminescence spectroscopy. The quantum dot photoluminescence undergoes substantial changes when proceeding from direct quantum dot excitation to quantum well excitation, which causes an indirect population of the dot ground states. This results in a lowered effective carrier temperature within the dots. Results on the carrier transfer versus barrier thickness are discussed within the Wentzel-Kramers-Brillouin approximation. Deviations for barrier thicknesses <5nm are assigned to the formation of nanobridges that are actually detected by transmission electron microscopy.

  6. Stoichiometric effect on electrical, optical, and structural properties of composition-tunable In(x)Ga(1-x)As nanowires.

    PubMed

    Hou, Jared J; Wang, Fengyun; Han, Ning; Xiu, Fei; Yip, SenPo; Fang, Ming; Lin, Hao; Hung, Tak F; Ho, Johnny C

    2012-10-23

    Ternary InGaAs nanowires have recently attracted extensive attention due to their superior electron mobility as well as the ability to tune the band gap for technological applications ranging from high-performance electronics to high-efficiency photovoltaics. However, due to the difficulties in synthesis, there are still considerable challenges to assess the correlation among electrical, optical, and structural properties of this material system across the entire range of compositions. Here, utilizing a simple two-step growth method, we demonstrate the successful synthesis of composition and band gap tunable In(x)Ga(1-x)As alloy nanowires (average diameter = 25-30 nm) by manipulating the source powder mixture ratio and growth parameters. The lattice constants of each NW composition have been well correlated with the chemical stoichiometry and confirmed by high-resolution transmission electron microscopy and X-ray diffraction. Importantly, the as-grown NWs exhibit well-controlled surface morphology and low defect concentration without any phase segregation in all stoichiometric compositions. Moreover, it is found that the electrical nanowire device performances such as the turn-off and I(ON)/I(OFF) ratios are improved when the In concentration decreases at a cost of mobility degradation. More generally, this work suggests that a careful stoichiometric design is required for achieving optimal nanowire device performances.

  7. High-power 1.25 µm InAs QD VECSEL based on resonant periodic gain structure

    NASA Astrophysics Data System (ADS)

    Albrecht, Alexander R.; Rotter, Thomas J.; Hains, Christopher P.; Stintz, Andreas; Xin, Guofeng; Wang, Tsuei-Lian; Kaneda, Yushi; Moloney, Jerome V.; Malloy, Kevin J.; Balakrishnan, Ganesh

    2011-03-01

    We compare an InAs quantum dot (QD) vertical external-cavity surface-emitting laser (VECSEL) design consisting of 4 groups of 3 closely spaced QD layers with a resonant periodic gain (RPG) structure, where each of the 12 QD layers is placed at a separate field antinode. This increased the spacing between the QDs, reducing strain and greatly improving device performance. For thermal management, the GaAs substrate was thinned and indium bonded to CVD diamond. A fiber-coupled 808 nm diode laser was used as pump source, a 1% transmission output coupler completed the cavity. CW output powers over 4.5 W at 1250 nm were achieved.

  8. Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures

    SciTech Connect

    Estacio, Elmer; Pham, Minh Hong; Takatori, Satoru; Cadatal-Raduban, Marilou; Nakazato, Tomoharu; Shimizu, Toshihiko; Sarukura, Nobuhiko; Somintac, Armando; Defensor, Michael; Awitan, Fritz Christian B.; Jaculbia, Rafael B.; Salvador, Arnel; Garcia, Alipio

    2009-06-08

    We report on the intense terahertz emission from InAs/GaAs quantum dot (QD) structures grown by molecular beam epitaxy. Results reveal that the QD sample emission was as high as 70% of that of a p-type InAs wafer, the most intense semiconductor emitter to date. Excitation wavelength studies showed that the emission was due to absorption in strained undoped GaAs, and corresponds to a two order-of-magnitude enhancement. Moreover, it was found that multilayer QDs emit more strongly compared with a single layer QD sample. At present, we ascribe the intense radiation to huge strain fields at the InAs/GaAs interface.

  9. Time domain terahertz spectroscopy of semiconductor bulk and multiple quantum wells structures

    NASA Astrophysics Data System (ADS)

    Chen, Yue

    A time-domain terahertz spectroscopic system with high source power (average power > 10 nW) and high signal-to- noise ratio (>104) was developed and used to study ultrafast electronic processes in semiconductor structures. The physics of the spectroscopy, the theoretical basis of the interferometry, the model of the electron-electromagnetic field interaction, and the principle of experimental data processing are presented. The first direct measurement of the intervalley scattering time in In 0.53Ga0.47As was performed. The intervalley scattering time constants obtained were τLΓ = 35 fs and τLΓ = 450 fs. The spectroscopic data showed that at low carrier density the carrier- carrier scattering is unimportant. The intervalley deformation potential was obtained from the measured intervalley scattering time constant τ LΓ. The transient conductivity was obtained using time-domain terahertz spectroscopy. The frequency dependent terahertz spectroscopy enabled us to uniquely determine the transient mobility and density. The transient electron mobility is ~5200 cm2/Vs, which is less than the Hall mobility. For large photocarrier densities, this discrepancy is attributed to the additional momentum relaxation associated with electron-hole scattering. Using pump pulses with wavelength of 810 run, the electron trapping time in low-temperature-grown GaAs was accurately determined. The measured trapping time is slightly larger than that observed from a band-edge pump- probe measurements. We argue that the terahertz technique provides the most reliable measure of carrier lifetime due to the unique interaction. The carrier dynamics of low-temperature-grown InGaAs bulk and InGaAs/InAlAs multiple quantum wells were investigated. We were able to differentiate the two dominant mechanisms in the electron decay process, trapping and recombination. A trapping time as fast as 1.3-2.6 ps was observed for photo-excited electrons. The effects of Be-doping and growth temperature on the

  10. Growth and properties of AIIIBV QD structures for intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Vyskočil, J.; Gladkov, P.; Petříček, O.; Hospodková, A.; Pangrác, J.

    2015-03-01

    Intermediate band solar cells theoretically offer a promising way to significantly increase cell efficiency compared to a single-junction solar cell. We focused on the preparation of antimony containing materials as a covering of QD layers. In this article we discuss how the concentration gradient of GaAsSb strain reducing layers can influence the resulting optical properties of the solar cell structures. The main principle of the structure is that the absorption of light is achieved at QD excited states with a better overlap of electron and hole wave functions. With fast relaxation of carriers to the ground state, the electrons and holes are quickly spatially separated. Two different composition gradients of GaAsSb SRL were used for the solar cell structure. One or five quantum dot stacks were compared. The maximal PC increased approximately 17 times with increasing number of QD layers from 1 to 5. The highest PC was achieved for sample I5A with increasing concentration of Sb in the SRL, especially in the QD absorption region. The possible explanation is a better carrier separation in this type of structure suppressing the radiative recombination rate in QDs. These results suggest a high application potential of this structure for photovoltaics.

  11. Influence of Photoactive Layer Structure on Device Performance of Poly(2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylene vinylene)-CuInS2/ZnO Solar Cells.

    PubMed

    Yue, Wenjin; Sun, Wenshan; Wang, Songming; Zhang, Guoqiang; Lan, Mingyang; Nie, Guangjun

    2015-06-01

    This paper reported ternary MEH-PPV-CuInS2/ZnO solar cells, which were fabricated with the mixture of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and CuInS2 quantum dots (QDs) as photovoltaic layer and ZnO nanorod arrays (ZnO-NAs) as electron acceptor. The effects of photoactive layer structure (e.g., the change of spinning rate, thermal annealing temperature, annealing order and annealing method) on device performance are observed, and devices are measured by steady current-voltage (J-V) curve under the monochromic illumination at 470 nm. Results showed that the spinning rate of photoactive layer at 2000 rpm obtained the optimum thickness, moreover, solvent annealing firstly then the deposition of the positive electrode, finally thermal annealing at 140 degrees C contributing to the better reorganization for polymer and CuInS2 QDs to form the more stable phase-segregated state in the photovoltaic layer in the MEH-PPV-CuInS2/ZnO-NAs solar cells, obtaining the maximum power conversion efficiency of 2.54% under the monochromic illumination at 470 nm.

  12. Probing oxygen consumption in epileptic brain slices with QDs-based FRET sensors

    NASA Astrophysics Data System (ADS)

    Zhang, Chunfeng; Ingram, Justin; Schiff, Steven; Xu, Jian; Xiao, Min

    2011-02-01

    We developed ratiometric optical oxygen sensors to probe the oxygen consumption during epileptic events in rat brain slices. The oxygen sensors consist of the sensing part of phosphorescence dyes (Platinum (II) octaethylporphine ketone) and reference part of nanocystal quantum dots (NQDs) embedded in polymer blends, with pre-designed excitation through fluorescence resonance energy transfer (FRET) from NQDs to the oxygen sensitive dyes (OSDs). The ratiometric FRET sensors with fast temporal response and excellent bio-compatibility are suitable for real time quantitative dissolved oxygen (D.O.) probes in biological microenvironment. Coating the sensors onto the micro-pipettes, we performed simultaneous oxygen probes at pyramidal and oriens layers in rat hippocampal CA1. Different spatiotemporal patterns with maximum D.O. decreases of 9.9+/-1.1 mg/L and 4.9+/-0.7 mg/L during seizure events were observed in pyramidal and oriens layers, respectively.

  13. Suppressed blinking in single quantum dots (QDs) immobilized near silver island films (SIFs)

    NASA Astrophysics Data System (ADS)

    Fu, Yi; Zhang, Jian; Lakowicz, Joseph R.

    2007-10-01

    In this report, we use single-molecule spectroscopic method to study emission behaviors of streptavidin-conjugated quantum dots immobilized on a biotinylated BSA (bovine serum albumin) monolayer near non-continuous rough silver nanostructures. We observed greatly reduced blinking and enhanced emission fluorescence of quantum dots next to silver island films.

  14. Correlation of nanoscale structure with electronic and magnetic properties in semiconductor materials

    NASA Astrophysics Data System (ADS)

    He, Li

    , with ferromagnetism/paramagnetism transition temperature in the range of 20-200 K. The magnetic properties of 300-350°C implanted Ge:Mn (which produced crystalline Ge films) varied significantly with implantation dose and annealing condition due to precipitation and phase transformation of MnxGe1-x secondary phase particles, Mn5Ge3, Mn11Ge8 and Mn5Ge2 (zeta). The third part of this work aimed at design of a new experimental method to correlate the structure and energy levels of individual quantum dots (QD) by combining TEM and ballistic electron emission spectroscopy (BEES). A p-type delta doping layer to flatten the QD energy band (otherwise, the Schottky barrier at the BEES metal base/n-type semiconductor interface causes band bending), and an etch-stop layer to prevent etching holes in TEM samples was included in the QD sample structure. TEM analysis found QDs to be of cone shape with the base diameter ranging from about 10 to 50 nm. Preliminary BEES characterization on a sample without QD marks detected a QD energy level 0.12 eV below the In0.5Al0.3Ga0.2P matrix layer conduction band. Micron- and nanometer-scale marks were fabricated by FIB milling and TEM electron beam induced carbon deposition, respectively, to index individual QDs so that TEM and BEES characterization could be performed on the same QDs in the future. Overall, this work explored different semiconductor nanostructures with the broad goal of correlation of nanoscale structure with electronic and magnetic properties. The originality of this research lies in the design and performance of novel experimental methods, and the improved understanding of structure-property relationships at the nanoscale.

  15. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    stark shift, coherent coupling of electronic states in a quantum dot molecule etc.; (3) to assess the potential use of the quantum dots in real device implementation and to provide physical insight to the experimentalists. Full three dimensional strain and electronic structure simulations of quantum dot structures containing multi-million atoms are done using NEMO 3-D. Both single and vertically stacked quantum dot structures are analyzed in detail. The results show that the strain and the piezoelectricity significantly impact the electronic structure of these devices. This work shows that the InAs quantum dots when placed in the InGaAs quantum well red shifts the emission wavelength. Such InAs/GaAs-based optical devices can be used for optical-fiber based communication systems at longer wavelengths (1.3um -- 1.5um). Our atomistic simulations of InAs/InGaAs/GaAs quantum dots quantitatively match with the experiment and give the critical insight of the physics involved in these structures. A single quantum dot molecule is studied for coherent quantum coupling of electronic states under the influence of static electric field applied in the growth direction. Such nanostructures can be used in the implementation of quantum information technologies. A close quantitative match with the experimental optical measurements allowed us to get a physical insight into the complex physics of quantum tunnel couplings of electronic states as the device operation switches between atomic and molecular regimes. Another important aspect is to design the quantum dots for a desired isotropic polarization of the optical emissions. Both single and coupled quantum dots are studied for TE/TM ratio engineering. The atomistic study provides a detailed physical analysis of these computationally expensive large nanostructures and serves as a guide for the experimentalists for the design of the polarization independent devices for the optical communication systems.

  16. Direct Patterning of CdSe Quantum Dots into Sub-100 nm Structures

    SciTech Connect

    Hampton, Meredith J.; Templeton, Joseph L.; DeSimone, Joseph M.

    2010-03-02

    Ordered, two-dimensional cadmium selenide (CdSe) arrays have been fabricated on indium-doped tin oxide (ITO) electrodes using the pattern replication in nonwetting templates (PRINT) process. CdSe quantum dots (QDs) with an average diameter of 2.7 nm and a pyridine surface ligand were used for patterning. The PRINT technique utilizes a perfluoropolyether (PFPE) elastomeric mold that is tolerant of most organic solvents, thus allowing solutions of CdSe QDs in 4-picoline to be used for patterning without significant deformation of the mold. Nanometer-scale diffraction gratings have been successfully replicated with CdSe QDs.

  17. Origins of interlayer formation and misfit dislocation displacement in the vicinity of InAs/GaAs quantum dots

    SciTech Connect

    Huang, S.; Kim, S. J.; Pan, X. Q.; Goldman, R. S.

    2014-07-21

    We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

  18. Characterization of spin-orbit coupling in gated wire structures using Al2O3/In0.75Ga0.25As/In0.75Al0.25As inverted heterojunctions

    NASA Astrophysics Data System (ADS)

    Ohori, Takahiro; Akabori, Masashi; Hidaka, Shiro; Yamada, Syoji

    2016-10-01

    Gated parallel wire structures obtained from inverted-modulation-doped heterojunctions made of high-In-content metamorphic InGaAs/InAlAs were investigated. The narrowest wire width was found to be ˜190 nm made using electron beam lithography and reactive ion etching. Magneto-transport was measured at low temperatures. Weak anti-localization and suppression with applied negative gate voltages were observed in low-mobility wide wires (1360 nm), which were considered for a two-dimensional system. The dependence on the gate voltage of spin-orbit coupling parameters was also obtained by fitting. The parameters decreased as the negative gate voltages increased. The trend might originate not from the electron system at the InGaAs/InAlAs interface but from the other electron system accumulated at the Al2O3/InGaAs interface, which can also contribute to conductivity. In high-mobility narrow wires (190 nm), which are close to a one-dimensional system, weak anti-localization peaks were still observed, indicating strong spin-orbit coupling. In addition, the critical widths of wires corresponding to zero conductance were estimated to be <100 nm. Therefore, our metamorphic modulation doped heterojunctions seem suitable for smaller spin-FETs.

  19. Structural ceramics

    SciTech Connect

    Wachtman, J.B. Jr.

    1989-01-01

    The present work discusses opportunities for application of structural ceramics in heat engines, industrial-wear parts, prosthetics and bearings; conceptual and detailed design principles for structural ceramics; the processing, consolidation, and properties of members of the SiC family of structural ceramics; and the silicon nitride and sialon families of hot-pressed, sintered, and reaction-bonded, structural ceramics. Also discussed are partially-stabilized zirconia and zirconia-toughened ceramics for structural applications, the processing methods and mechanisms of fiber-reinforcement in ceramic-matrix fiber-reinforced composites, and the tribological properties of structural ceramics.

  20. Effects of anisotropy and Coulomb interactions on quantum transport in a quadruple quantum-dot structure

    NASA Astrophysics Data System (ADS)

    Kagan, M. Yu.; Val'kov, V. V.; Aksenov, S. V.

    2017-01-01

    We present an analytical and numerical investigation of the spectral and transport properties of a quadruple quantum-dot (QQD) structure which is one of the popular low-dimensional systems in the context of fundamental quantum physics study, future electronic applications, and quantum calculations. The density of states, occupation numbers, and conductance of the structure were analyzed using the nonequilibrium Green's functions in the tight-binding approach and the equation-of-motion method. In particular the anisotropy of hopping integrals and on-site electron energies as well as the effects of the finite intra- and interdot Coulomb interactions were investigated. It was found out that the anisotropy of the kinetic processes in the system leads to the Fano-Feshbach asymmetrical peak. We demonstrated that the conductance of the QQD device has a wide insulating band with steep edges separating triple-peak structures if the intradot Coulomb interactions are taken into account. The interdot Coulomb correlations between the central QDs result in the broadening of this band and the occurrence of an additional band with low conductance due to the Fano antiresonances. It was shown that in this case the conductance of the anisotropic QQD device can be dramatically changed by tuning the anisotropy of on-site electron energies.

  1. Website Structure

    ERIC Educational Resources Information Center

    Jackson, Larry S.

    2009-01-01

    This dissertation reports the results of an exploratory data analysis investigation of the relationship between the structures used for information organization and access and the associated storage structures within state government websites. Extending an earlier claim that hierarchical directory structures are both the preeminent information…

  2. Relative degradation of near infrared avalanche photodiodes from proton irradiation

    NASA Technical Reports Server (NTRS)

    Becker, Heidi; Johnston, Allan H.

    2004-01-01

    InGaAs and Ge avalanche photodiodes are compared for the effects of 63-MeV protons on dark current. Differences in displacement damage factors are discussed as they relate to structural differences between devices.

  3. 1.55 µm InAs/GaAs quantum dots and high repetition rate quantum dot SESAM mode-locked laser.

    PubMed

    Zhang, Z Y; Oehler, A E H; Resan, B; Kurmulis, S; Zhou, K J; Wang, Q; Mangold, M; Süedmeyer, T; Keller, U; Weingarten, K J; Hogg, R A

    2012-01-01

    High pulse repetition rate (≥ 10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

  4. A Structural Study of InGaAs/InGaAs Strain-Balanced MQW for TPV Applications

    NASA Astrophysics Data System (ADS)

    Tundo, S.; Mazzer, M.; Nasi, L.; Lazzarini, L.; Ferrari, C.; Salviati, G.; Passaseo, A.; Torsello, G.; Diso, D.; Licciulli, A.; Barnham, K.; Daukes, N. Ekins; Rohr, C.; Abbott, P.; Clarke, G.

    2003-01-01

    Multi-quantum well photovoltaic cells offer a number of advantages over conventional "single-gap"cells for thermophotovoltaic applications, first of all because they can reach a higher open circuit voltage under the same radiation source and with the same absorption edge. Material quality issues and the constraints imposed by the commercial available substrates indicate that InxGa1-xAs/InyGa1-yAs/InP strain-balanced heterostructures are suitable to obtain good quality multi-quantum wells with an absorption edge just below 2.0 μm. Structural stability in the presence of a high density of elastic energy such as in the case of a strain-balanced multi-layer is a very important issue to be addressed by optimising key parameters like composition, thickness of wells and barriers and number of periods. In this paper we present and discuss the mechanisms of plastic relaxation of these structures with a particular attention to the impact of the extended defects generated by the local breakdown of the crystal lattice to the electrical properties of the devices. Then, after the presentation of the optimum structure with an absorption edge at 1.96 μm, we discuss the issue of a further extension of the absorption edge through the use of a so-called virtual substrate, that is a buffer structure between the substrate and the device designed to relax to a given extent with a minimum number of dislocations propagating towards the active region. On the basis of a recipe based on the experimental results on InGaAs single and multi-layers grown on GaAs, we have designed a series of step-graded buffer structures providing good virtual substrates with a lattice parameter larger than GaAs. Strain-balanced multi-quantum wells have been grown on InxGa1-xAs virtual substrates with 0.14 < × < 0.35 with a residual density of threading dislocations of about 105 cm-2. Work is in progress to remove the residual morphological undulation (cross hatch) induced by the misfit dislocations confined

  5. Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology

    PubMed Central

    Nandwana, Vikas; Subramani, Chandramouleeswaran; Eymur, Serkan; Yeh, Yi-Cheun; Tonga, Gulen Yesilbag; Tonga, Murat; Jeong, Youngdo; Yang, Boqian; Barnes, Michael D.; Cooke, Graeme; Rotello, Vincent M.

    2011-01-01

    We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly. PMID:22016664

  6. Molecular interaction investigation between three CdTe:Zn(2+) quantum dots and human serum albumin: A comparative study.

    PubMed

    Huang, Shan; Qiu, Hangna; Liu, Yi; Huang, Chusheng; Sheng, Jiarong; Su, Wei; Xiao, Qi

    2015-12-01

    Water-soluble Zn-doped CdTe quantum dots (CdTe:Zn(2+) QDs) have attracted great attention in biological and biomedical applications. In particular, for any potential in vivo application, the interaction of CdTe:Zn(2+) QDs with human serum albumin (HSA) is of greatest importance. As a step toward the elucidation of the fate of CdTe:Zn(2+) QDs introduced to organism, the molecular interactions between CdTe:Zn(2+) QDs with three different sizes and HSA were systematically investigated by spectroscopic techniques. Three CdTe:Zn(2+) QDs with maximum emission of 514 nm (green QDs, GQDs), 578 nm (yellow QDs, YQDs), and 640 nm (red QDs, RQDs) were tested. The binding of CdTe:Zn(2+) QDs with HSA was a result of the formation of HSA-QDs complex and electrostatic interactions played major roles in stabilizing the complex. The Stern-Volmer quenching constant, associative binding constant, and corresponding thermodynamic parameters were calculated. The site-specific probe competitive experiments revealed that the binding location of CdTe:Zn(2+) QDs with HSA was around site I. The microenvironmental and conformational changes of HSA induced by CdTe:Zn(2+) QDs were analyzed. These results suggested that the conformational change of HSA was dramatically at secondary structure level and the biological activity of HSA was weakened in the present of CdTe:Zn(2+) QDs with bigger size.

  7. Emission wavelength tuning of fluorescence by fine structural control of optical metamaterials with Fano resonance

    PubMed Central

    Moritake, Y.; Kanamori, Y.; Hane, K.

    2016-01-01

    We demonstrated fine emission wavelength tuning of quantum dot (QD) fluorescence by fine structural control of optical metamaterials with Fano resonance. An asymmetric-double-bar (ADB), which was composed of only two bars with slightly different bar lengths, was used to obtain Fano resonance in the optical region. By changing the short bar length of ADB structures with high dimensional accuracy in the order of 10 nm, resonant wavelengths of Fano resonance were controlled from 1296 to 1416 nm. Fluorescence of QDs embedded in a polymer layer on ADB metamaterials were modified due to coupling to Fano resonance and fine tuning from 1350 to 1376 nm was observed. Wavelength tuning of modified fluorescence was reproduced by analysis using absorption peaks of Fano resonance. Tuning range of modified fluorescence became narrow, which was interpreted by a simple Gaussian model and resulted from comparable FWHM in QD fluorescence and Fano resonant peaks. The results will help the design and fabrication of metamaterial devices with fluorophores such as light sources and biomarkers. PMID:27622503

  8. Effective Medium Approach for Planar QD Structures

    DTIC Science & Technology

    2001-06-01

    condition (EBC) method is extended to nano- scale planar meso- scopic systems. The EBCs appear as a result of the 2D-homogenization procedure and have...intrinsic spatial inhomogeneity. Since the inho- mogeneity scale is much less than the optical wavelength, QDs can be treated as electrically small objects...Real parts of these poles determine resonant frequencies while imaginary parts • ve the homogeneous linewidths. It can easily be shown that EBCs

  9. Reconfigurable structure

    NASA Technical Reports Server (NTRS)

    Curtis, Steven A. (Inventor)

    2010-01-01

    A reconfigurable structure includes a plurality of selectively extensible and retractable limbs, at least one node pivotably receiving respective ends of at least two limbs, and an actuator associated with each limb for extending and retracting the limb. The structure may further include an addressable module associated with each actuator to control the actuator.

  10. Structural Ceramics

    NASA Technical Reports Server (NTRS)

    1986-01-01

    This publication is a compilation of abstracts and slides of papers presented at the NASA Lewis Structural Ceramics Workshop. Collectively, these papers depict the scope of NASA Lewis' structural ceramics program. The technical areas include monolithic SiC and Si3N4 development, ceramic matrix composites, tribology, design methodology, nondestructive evaluation (NDE), fracture mechanics, and corrosion.

  11. Tau Structures

    PubMed Central

    Avila, Jesus; Jiménez, Juan S.; Sayas, Carmen L.; Bolós, Marta; Zabala, Juan C.; Rivas, Germán; Hernández, Felix

    2016-01-01

    Tau is a microtubule-associated protein that plays an important role in axonal stabilization, neuronal development, and neuronal polarity. In this review, we focus on the primary, secondary, tertiary, and quaternary tau structures. We describe the structure of tau from its specific residues until its conformation in dimers, oligomers, and larger polymers in physiological and pathological situations. PMID:27877124

  12. Protein Structure

    ERIC Educational Resources Information Center

    Asmus, Elaine Garbarino

    2007-01-01

    Individual students model specific amino acids and then, through dehydration synthesis, a class of students models a protein. The students clearly learn amino acid structure, primary, secondary, tertiary, and quaternary structure in proteins and the nature of the bonds maintaining a protein's shape. This activity is fun, concrete, inexpensive and…

  13. On Structure.

    ERIC Educational Resources Information Center

    Acland, Henry

    Structure as an aspect of educational setting is discussed and illustrated in the course of an argument indicating that efforts to change schools, including Project Follow Through, should aim to change structures rather than people. It is asserted that educational reform in America usually attempts to change people, especially children, and that…

  14. Organisational Structure

    ERIC Educational Resources Information Center

    National Centre for Vocational Education Research (NCVER), 2006

    2006-01-01

    An understanding of organisational structure can provide guidance for organisations that want to change and innovate. Many writers agree that this understanding allows organisations to shape how their work is done to ultimately achieve their business goals--and that too often structure is given little consideration in business strategy and…

  15. (Indium,gallium)arsenide quantum dot materials for solar cell applications: Effect of strain-reducing and strain-compensated barriers on quantum dot structural and optical properties

    NASA Astrophysics Data System (ADS)

    Pancholi, Anup

    The last few years have seen rapid advances in nanoscience and nanotechnology, allowing unprecedented manipulation of nanostructures controlling solar energy capture, conversion, and storage. Quantum confined nanostructures, such as quantum wells (QWs) and quantum dots (QDs) have been projected as potential candidates for the implementation of some high efficiency photovoltaic device concepts, including the intermediate band solar cell (IBSC). In this dissertation research, we investigated multiple inter-related themes, with the main objective of providing a deeper understanding of the physical and optical properties of QD structures relevant to the IBSC concept. These themes are: (i) Quantum engineering and control of energy levels in QDs, via a detailed study of the electronic coupling in multilayer QD structures; (ii) Controlled synthesis of well-organized, good quality, high volume density, and uniform-size QD arrays, in order to maximize the absorption efficiency and to ensure the coupling between the dots and the formation of the minibands; and (iii) Characterization of carrier dynamics and development of techniques to enhance the charge transport and efficient light harvesting. A major issue in a QD-based IBSC is the occurrence of charge trapping, followed by recombination in the dots, which results in fewer carriers being collected and hence low quantum efficiency. In order to collect most of the light-generated carriers, long radiative lifetimes, higher mobilities, and a lower probability of non-radiative recombination events in the solar cell would be desirable. QD size-dependent radiative lifetime and electronic coupling in multilayer QD structures were studied using photoluminescence (PL) and time-resolved photoluminescence (TRPL). For the uncoupled QD structures with thick barriers between the adjacent QD layers, the radiative lifetime was found to increase with the QD size, which was attributed to increased oscillator strength in smaller size dots. On

  16. Physics and Technology of III-V Pseudomorphic Structures

    DTIC Science & Technology

    1990-11-15

    GaAs and InAs 2. Experimental procedures 11 AS BEPC(oir) MOMBE InAs The experiments were performed in a modified 0 o0.9 0 .50.6 prototype Perkin-Elmer...compared. The MEE technique results in better luminescent and device properties for hi2h indium concentration in the active layer. 2. EXPERIMENTAL ...surface: (3) a 150A InGaAs channel. the thickness of which is kept constant throughout the experiment : (4) a top delta-doped region in an Al 0 .28Gao

  17. 3-4 Heterojunction Structures and High Speed Devices

    DTIC Science & Technology

    1989-02-17

    Continue on rmen if ,wanuary and k by k Aum~mr) FIELD GROUP SU, GROUP "t-A4SItRACT (Continue on revwi if nucenary =n idmti by soc numhAt 1his effort...on InP, quantum wells, optical properties of bulk AJGaAs and InGaAs were among many projects that were explored. • i 1 II. PROGRESS MADE Field -effect...Transistors A. NIODFET Heterojunction Quantum Well The modulation-doped field -effect transistor (MODFET) offers great promise for low-noise microwave

  18. Suppression of thermal carrier escape and efficient photo-carrier generation by two-step photon absorption in InAs quantum dot intermediate-band solar cells using a dot-in-well structure

    NASA Astrophysics Data System (ADS)

    Asahi, S.; Teranishi, H.; Kasamatsu, N.; Kada, T.; Kaizu, T.; Kita, T.

    2014-08-01

    We investigated the effects of an increase in the barrier height on the enhancement of the efficiency of two-step photo-excitation in InAs quantum dot (QD) solar cells with a dot-in-well structure. Thermal carrier escape of electrons pumped in QD states was drastically reduced by sandwiching InAs/GaAs QDs with a high potential barrier of Al0.3Ga0.7As. The thermal activation energy increased with the introduction of the barrier. The high potential barrier caused suppression of thermal carrier escape and helped realize a high electron density in the QD states. We observed efficient two-step photon absorption as a result of the high occupancy of the QD states at room temperature.

  19. Spacecraft Structures

    NASA Video Gallery

    This activity challenges students to solve a real-world problem that is part of the space program using creativity, cleverness and scientific knowledge while learning about forces, structures and e...

  20. Multicolored silica coated CdSe core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Goftman, Valentina V.; Markin, Alexey V.; De Saeger, Sarah; Goryacheva, Irina Y.

    2016-04-01

    Silanization is a convenient route to provide water-solubility to the quantum dots (QDs) with different structure. Green, orange and red emitting CdSe-based QDs were synthesized by varying of number and material of wider-band gap shells and fluorescent properties of QDs were characterized before and after silanization. It was shown that structure of the QD influences on the quantum yield of the silanized QDs: the better CdSe core is protected with wider-band gap semiconductor shells, the more fluorescence properties remain after silica coated QD possess. Hence silica coated QDs have a great perspectives for the multiplex analysis.

  1. CdSe quantum dots synthesized by laser ablation in water and their photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Horoz, Sabit; Lu, Liyou; Dai, Qilin; Chen, Jiajun; Yakami, Baichhabi; Pikal, J. M.; Wang, Wenyong; Tang, Jinke

    2012-11-01

    CdSe quantum dots (QDs) have been prepared by a facile and clean synthesis method--laser ablation in water. The structural and luminescent properties of the CdSe QDs have been investigated. The CdSe QDs of wurtzite crystal structure have an average particle size of about 5 nm. The QDs can be attached to ZnO nanowires making them ideal for applications in QD-sensitized nanowire solar cells. A uniqueness of the QDs attached to the ZnO nanowires by this laser ablation method is that they do not contain ligands, and the preparation avoids the complicated process of ligand exchange.

  2. Structural Analysis

    NASA Technical Reports Server (NTRS)

    1991-01-01

    After an 800-foot-tall offshore oil recovery platform collapsed, the engineers at Engineering Dynamics, Inc., Kenner, LA, needed to learn the cause of the collapse, and analyze the proposed repairs. They used STAGSC-1, a NASA structural analysis program with geometric and nonlinear buckling analysis. The program allowed engineers to determine the deflected and buckling shapes of the structural elements. They could then view the proposed repairs under the pressure that caused the original collapse.

  3. Structures research

    NASA Technical Reports Server (NTRS)

    Abu-Saba, Elias; Mcginley, Williams; Shen, Ji-Yao

    1992-01-01

    The main objective of the structures group is to provide quality aerospace research with the Center for Aerospace Research - A NASA Center for Excellence at North Carolina Agricultural and Technical State University. The group includes dedicated faculty and students who have a proven record in the area of structures, in particular space structures. The participating faculty developed accurate mathematical models and effective computational algorithms to characterize the flexibility parameters of joint dominated beam-truss structures. Both experimental and theoretical modelling has been applied to the dynamic mode shapes and mode frequencies for a large truss system. During the past few months, the above procedures has been applied to the hypersonic transport plane model. The plane structure has been modeled as a lumped mass system by Doctor Abu-Saba while Doctor Shen applied the transfer matrix method with a piecewise continuous Timoshenko tapered beam model. Results from both procedures compare favorably with those obtained using the finite element method. These two methods are more compact and require less computer time than the finite element method. The group intends to perform experiments on structural systems including the hypersonic plane model to verify the results from the theoretical models.

  4. Structures Division

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The NASA Lewis Research Center Structures Division is an international leader and pioneer in developing new structural analysis, life prediction, and failure analysis related to rotating machinery and more specifically to hot section components in air-breathing aircraft engines and spacecraft propulsion systems. The research consists of both deterministic and probabilistic methodology. Studies include, but are not limited to, high-cycle and low-cycle fatigue as well as material creep. Studies of structural failure are at both the micro- and macrolevels. Nondestructive evaluation methods related to structural reliability are developed, applied, and evaluated. Materials from which structural components are made, studied, and tested are monolithics and metal-matrix, polymer-matrix, and ceramic-matrix composites. Aeroelastic models are developed and used to determine the cyclic loading and life of fan and turbine blades. Life models are developed and tested for bearings, seals, and other mechanical components, such as magnetic suspensions. Results of these studies are published in NASA technical papers and reference publication as well as in technical society journal articles. The results of the work of the Structures Division and the bibliography of its publications for calendar year 1995 are presented.

  5. Centriole structure

    PubMed Central

    Winey, Mark; O'Toole, Eileen

    2014-01-01

    Centrioles are among the largest protein-based structures found in most cell types, measuring approximately 250 nm in diameter and approximately 500 nm long in vertebrate cells. Here, we briefly review ultrastructural observations about centrioles and associated structures. At the core of most centrioles is a microtubule scaffold formed from a radial array of nine triplet microtubules. Beyond the microtubule triplets of the centriole, we discuss the critically important cartwheel structure and the more enigmatic luminal density, both found on the inside of the centriole. Finally, we discuss the connectors between centrioles, and the distal and subdistal appendages outside of the microtubule scaffold that reflect centriole age and impart special functions to the centriole. Most of the work we review has been done with electron microscopy or electron tomography of resin-embedded samples, but we also highlight recent work performed with cryoelectron microscopy, cryotomography and subvolume averaging. Significant opportunities remain in the description of centriolar structure, both in mapping of component proteins within the structure and in determining the effect of mutations on components that contribute to the structure and function of the centriole. PMID:25047611

  6. Composite structural materials. [aircraft structures

    NASA Technical Reports Server (NTRS)

    Ansell, G. S.; Loewy, R. G.; Wiberley, S. E.

    1980-01-01

    The use of filamentary composite materials in the design and construction of primary aircraft structures is considered with emphasis on efforts to develop advanced technology in the areas of physical properties, structural concepts and analysis, manufacturing, and reliability and life prediction. The redesign of a main spar/rib region on the Boeing 727 elevator near its actuator attachment point is discussed. A composite fabrication and test facility is described as well as the use of minicomputers for computer aided design. Other topics covered include (1) advanced structural analysis methids for composites; (2) ultrasonic nondestructive testing of composite structures; (3) optimum combination of hardeners in the cure of epoxy; (4) fatigue in composite materials; (5) resin matrix characterization and properties; (6) postbuckling analysis of curved laminate composite panels; and (7) acoustic emission testing of composite tensile specimens.

  7. Adenovirus structure.

    PubMed

    Rux, John J; Burnett, Roger M

    2004-12-01

    Structural studies continue to play an essential role as the focus of adenovirus research shifts in emphasis from basic biology to adenovirus-based vector technologies. A crucial step in developing novel therapeutics for gene replacement, cancer, and vaccines is often to modify the virion. Such engineered changes are designed to retarget the virus, or to reduce the immunological responses to infection. These efforts are far more effective when they are based on detailed structural knowledge. This minireview provides a brief summary of the wealth of information that has been obtained from the combined application of X-ray crystallography and electron microscopy. This knowledge now includes a good working model for the architectural organization of the virion, and atomic resolution molecular structures for all the major capsid proteins, hexon, penton, and fiber. We highlight new developments, which include the structure of the penton base and the discovery that adenovirus has several relatives. We sketch how the structural information can be used to engineer novel virions and conclude with the prospects for future progress.

  8. Tension Structure

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The fabric structure pictured is the Campus Center of La Verne College, La Verne, California. Unlike the facilities shown on the preceding pages, it is not air-supported. It is a "tension structure," its multi-coned fabric membrane supported by a network of cables attached to steel columns which function like circus tent poles. The spider-web in the accompanying photo is a computer graph of the tension pattern. The designers, Geiger-Berger Associates PC, of New York City, conducted lengthy computer analysis to determine the the best placement of columns and cables. The firm also served as structural engineering consultant on the Pontiac Silverdome and a number of other large fabric structures. Built by Birdair Structures, Inc., Buffalo, New York, the La Verne Campus Center was the first permanent facility in the United States enclosed by the space-spinoff fabric made of Owens-Corning Beta fiber glass coated with Du Pont Teflon TFE. The flexible design permits rearrangement of the interior to accommodate athletic events, student activities, theatrical productions and other recreational programs. Use of fabric covering reduced building cost 30 percent below conventional construction.

  9. Panchromatic quantum-dot-sensitized solar cells based on a parallel tandem structure.

    PubMed

    Zhou, Na; Yang, Yueyong; Huang, Xiaoming; Wu, Huijue; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

    2013-04-01

    A tandem-structure sensitized solar cell, comprising different inorganic semiconductor quantum dots (QDs) as sensitizers in two different compartments, has been designed for the first time with the aim of extending the light-absorption range of current technologies. In this system, the CdS/CdSe co-sensitized quantum-dot solar cell (QDSC) is in the upper part, whereas the PbS/CdS co-sensitized QDSC is in the lower part; these are connected in parallel with each other. In the middle of the tandem solar cell, a Cu2 S mesh counter electrode is employed. By optimizing the electrode thickness and QD-deposition time, short-circuit photocurrent density values of as high as 25.12 mA cm(-2) have been achieved; this value is nearly equal to the sum of the two constituent QD-sensitized devices and gives rise to a solar power-conversion efficiency of 5.06 %.

  10. Single active-layer structured dual-function devices using hybrid polymer-quantum dots.

    PubMed

    Son, Dong-Ick; Park, Dong-Hee; Ie, Sang-Yub; Choi, Won-Kook; Choi, Ji-Won; Li, Fushan; Kim, Tae-Whan

    2008-10-01

    We demonstrate hybrid polymer-quantum dot dual-function devices with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum dots dispersed with poly N-vinylcarbazole (PVK) and 1,3,5-tirs-(N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on an indium-tin-oxide (ITO)/glass substrate by using a simple spin-coating technique. The dual-function devices are composed of light-emitting diodes (LED) on the top side and nonvolatile organic bistable memory devices (OBD) on the bottom side and can show electroluminescence (EL) along with electrical bistability concurrently. Both the functionality of LEDs and OBDs can be successfully achieved by adding an electron transport layer (ETL) TPBi to the OBD to attain an LED in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and the LiF/Al electrode. Through transmission electron microscopy (TEM) study, it is revealed that CdSe/ZnS QDs distributed on the interface of the hole transport layer (HTL) and ETL significantly take part in the electroluminescence process rather than those existing at the outer surface of the ETL.

  11. Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

    SciTech Connect

    Albert, VV; Ivanov, SA; Tretiak, S; Kilina, SV

    2011-07-07

    Simulations of ligated semiconductor quantum dots (QDs) and their physical properties, such as morphologies, QD-ligand interactions, electronic structures, and optical transitions, are expected to be very sensitive to computational methodology. We utilize Density Functional Theory (DFT) and systematically study how the choice of density functional, atom-localized basis set, and a solvent affects the physical properties of the Cd{sub 33}Se{sub 33} cluster ligated with a trimethyl phosphine oxide ligand. We have found that qualitative performance of all exchange-correlation (XC) functionals is relatively similar in predicting strong QD-ligand binding energy ({approx}1 eV). Additionally, all functionals predict shorter Cd-Se bond lengths on the QD surface than in its core, revealing the nature and degree of QD surface reconstruction. For proper modeling of geometries and QD-ligand interactions, however, augmentation of even a moderately sized basis set with polarization functions (e.g., LANL2DZ* and 6-31G*) is very important. A polar solvent has very significant implications for the ligand binding energy, decreasing it to 0.2-0.5 eV. However, the solvent model has a minor effect on the optoelectronic properties, resulting in persistent blue shifts up to {approx}0.3 eV of the low-energy optical transitions. For obtaining reasonable energy gaps and optical transition energies, hybrid XC functionals augmented by a long-range Hartree-Fock orbital exchange have to be applied.

  12. Structures protection

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Materials of which an aircraft is made and the methods used to hold these materials together forming the aircraft structure were studied as factors important in protecting a modern aircraft from hazardous natural environments. Since all-metal aircraft are being replaced by aircraft constructed partly of fiber reinforced plastics with desirable light weight and high strength properties but with poor electrical conductivity, the danger of lightning strikes has become more serious. Lightning effects on metal structures were reviewed and design protection was discussed. The expected lightning effects on nonmetallic materials such as fiberglass and advanced composites were also reviewed.

  13. BEEM studies of heterojunction offsets and dislocations in buried semiconductor structures

    NASA Astrophysics Data System (ADS)

    Bhargava, Sidharth

    1998-12-01

    Ballistic Electron Emission Microscopy (BEEM) has been established as a powerful new low-energy electron microscopy for the nondestructive local electronic characterization of semiconductor heterostructures. The development of BEEM spectroscopy and BEEM imaging has been described through studies on various III--V and II--VI semiconductor systems. BEEM spectroscopy (BEES) studies of Schottky barriers on Au/GaAs and Au/CdTe were performed in order to produce baselines for future measurements. Temperature-dependent measurements yielded insight into the mechanisms that govern Schottky barrier formation. Au/HgCdTe and Au/InAs/AlAsSb were studied to understand the affects of strain on BEES spectroscopy. HgCdTe, though not severely lattice mismatched from CdTe, has many regions of micron-size variations, thus causing a great number of local variations. The amount of strain between InAs and AlAsSb can be controlled through addition of As. BEES results were obtained on both of these systems. Placing planar structures underneath the surface (GaAs/AlGaAs and InAs/AlAsSb) allows us to modulate the BEES threshold and to test the experimental sensitivity towards sub-surface features. Both systems allowed for the determination of band offsets at the semiconductor heterointerfaces. To establish BEEM as a technique to image semiconductor interfacial features, cross-hatch misfit dislocations in InGaAs/GaAs were examined. This cross-hatch pattern, arising from misfit dislocation cores located >500A beneath the surface, were correlated with the backscattering of injected electrons. The scattering was proven to be coming from beneath the surface, not at the surface, through analysis of the simultaneous STM and BEEM images, specifically through a lateral shift in the dislocation position between the STM and BEEM image, and through the study of samples with thinner InGaAs layers. Monte Carlo simulations were performed to test the hypothesis that the backscattering was caused by fine

  14. Structural evolution

    SciTech Connect

    Burr, M.T.

    1993-03-01

    In this special report, financial executives discuss key trends in power project finance, new funding sources and evolving project structures. Industry wide, financial firms and developers are striving to improve the cost-effectiveness and efficiency of project financing, for projects in both greenfield development and the growing secondary market.

  15. Nanocrystal structures

    DOEpatents

    Eisler, Hans J.; Sundar, Vikram C.; Walsh, Michael E.; Klimov, Victor I.; Bawendi, Moungi G.; Smith, Henry I.

    2006-12-19

    A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II–VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

  16. Structural Adaptation

    ERIC Educational Resources Information Center

    Crowley, Julianne; Titmus, Morgan

    2016-01-01

    This article explores an alternative conception held by high school and first-year university biology students regarding the structure of the left and right ventricles of the heart and the significance of the left ventricular wall being thicker than the right. The left ventricular wall of the heart is thicker than the right ventricular wall due to…

  17. Lightweight Structures.

    ERIC Educational Resources Information Center

    Shaver and Co., Michigan City, IN.

    One of the newest and most promising developments in architecture has been the use of lightweight structures for encapsulating space. Using this new technology, builders can enclose large and small areas at a fraction of the cost of conventional construction and at the same time provide interior space that is totally flexible. This brochure shows…

  18. Band-structure tailoring and surface passivation for highly efficient near-infrared responsive PbS quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Zhou, Ru; Niu, Haihong; Ji, Fengwei; Wan, Lei; Mao, Xiaoli; Guo, Huier; Xu, Jinzhang; Cao, Guozhong

    2016-11-01

    PbS is a promising light harvester for near-infrared (NIR) responsive quantum dot (QD) photovoltaics due to its narrow bulk band gap (0.41 eV) and large exciton Bohr radius (18 nm). However, the relatively low conduction band (CB) and high-density surface defects of PbS as two major drawbacks for its use in solar cells severely hamper the photovoltaic performance enhancement. In this work, a modified solution-based successive ionic layer adsorption and reaction (SILAR) utilizing mixed cationic precursors of Pb2+ and Cd2+ is explored, and such a scheme offers two benefits, band-structure tailoring and surface passivation. In-situ deposited CdS suppresses the excessive growth of PbS in the mesopores, thereby facilitating the favorable electron injection from PbS to TiO2 in view of the up-shifted CB level of QDs; the intimate interpenetration of two sulfides with each other leads to superior passivation of trap state defects on PbS, which suppresses the interfacial charge recombination. With the construction of photovoltaics based on such a hybrid (Pb,Cd)S/CdS configuration, impressive power conversion efficiency up to 4.08% has been reached, outperforming that of the conventional PbS/CdS pattern (2.95%). This work highlights the great importance of band-structure tailoring and surface passivation for constructing highly efficient PbS QD photovoltaics.

  19. Fluorescence property of ZnO nanoparticles and the interaction with bromothymol blue.

    PubMed

    Yue, Qiaoli; Cheng, Jinmei; Li, Guang; Zhang, Ke; Zhai, Yanling; Wang, Lei; Liu, Jifeng

    2011-05-01

    We synthesized ZnO quantum dots (QDs) simply in alcoholic solution, and investigated the interaction between ZnO QDs and bromothymol blue. The structural, morphological, size and spectral properties of ZnO QDs were studied. It was found that ZnO QDs were spherical nanoparticles in the crystal structure, and the average diameter of ZnO QDs was about 4.8 nm. The excitation and emission peaks were located at 346 nm and 520 nm, respectively, which were obtained on a common fluorophotometer. The quantum yield of ZnO QDs was obtained by using quinine sulfate as a reference reagent. In addition, the fluorescence of ZnO QDs can be quenched by bromothymol blue, and the quenching mechanism was proposed in a dynamic quenching mode.

  20. Lightweight Structures

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2001-01-01

    Present structural concepts for hot static structures are conventional "sheet & stringer" or truss core construction. More weight-efficient concepts such as honeycomb and lattice block are being investigated, in combination with both conventional superalloys and TiAl. Development efforts for components made from TiAl sheet are centered on lower cost methods for sheet and foil production, plus alloy development for higher temperature capability. A low-cost casting technology recently developed for aluminum and steel lattice blocks has demonstrated the required higher strength and stiffness, with weight efficiency approach- ing honeycombs. The current effort is based on extending the temperature capability by developing lattice block materials made from IN-718 and Mar-M247.

  1. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  2. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  3. Structural Geology

    NASA Astrophysics Data System (ADS)

    Weber, John; Frankel, Kurt L.

    2011-05-01

    Structural geology and continental tectonics were ushered in to the modern quantitative age of geosciences with the arrival of the global plate tectonics paradigm (circa 1968), derived using new data from the oceans' depths, and John Ramsay's 1967 seminal work, Folding and Fracturing of Rocks. Fossen is to be applauded for crafting a unique, high-caliber, and accessible undergraduate textbook on structural geology that faithfully reflects this advance and the subsequent evolution of the discipline. This well-written text draws on Fossen's wealth of professional experience, including his broad and diverse academic research and experience in the petroleum industry. This book is beautifully illustrated, with excellent original color diagrams and with impressive color field photographs that are all keyed to locations and placed into geologic context.

  4. Terminal structure

    DOEpatents

    Schmidt, Frank; Allais, Arnaud; Mirebeau, Pierre; Ganhungu, Francois; Lallouet, Nicolas

    2009-10-20

    A terminal structure (2) for a superconducting cable (1) is described. It consists of a conductor (2a) and an insulator (2b) that surrounds the conductor (2a), wherein the superconducting cable (1) has a core with a superconducting conductor (5) and a layer of insulation that surrounds the conductor (5), and wherein the core is arranged in such a way that it can move longitudinally in a cryostat. The conductor (2a) of the terminal structure (2) is electrically connected with the superconducting conductor (5) or with a normal conductor (6) that is connected with the superconducting conductor (5) by means of a tubular part (7) made of an electrically conductive material, wherein the superconducting conductor (5) or the normal conductor (6) can slide in the part (7) in the direction of the superconductor.

  5. Microplastic Structures

    NASA Astrophysics Data System (ADS)

    Feely, Wayne E.

    1986-07-01

    Thick coatings (5-15μm) of a new dual image, aqueous developable photoresist can be exposed using a light attenuating photomask consisting of clear, opaque and grey areas and then processed to yield thermally stable 3-dimensional structures which are potentially useful as mechanical and optical components of devices. In the positive mode, relief and intaglio images are produced by processing similar to positive novolak based resists with 1- 2μm resolution and with the added feature that the images can be made thermally stable to temperatures >300° C. Negative mode processing of coated wafers imaged with the special mask produces thermally stable structures with tunnels or hollow chambers as well as cantilever beams. Because these structures are crosslinked at the time of development, processing in the negative mode shows much wider latitude than is the case in the positive mode. Images by negative mode processing are capable of submicron resolution, higher aspect ratio (>3 vs <1.6), and inward sloping wall profiles adjustable by exposure. The acid hardening resin compositions cover a broad range of compositions so that resins can be tailored to meet specific property requirements.

  6. Structural representation of data structures

    NASA Astrophysics Data System (ADS)

    Cantoni, Virginio; Gaggia, Alessandro; Gatti, Riccardo; Lombardi, Luca

    2014-06-01

    Study of the morphology of proteins, and their 3D structure, supports investigations of their functions and represents an initial step towards protein-based drug design. The goal of this paper is to define techniques, based on the geometrical and topological structure of protein surfaces, for the detection and analysis of sites of potential protein-protein and protein-ligand interactions. Two protein representation modalities based on the Concavity Tree (CT) and the Enriched Complex Extended Gaussian Image (EC-EGI) are considered. In particular, the concavity tree, in which the interface is usually extended and roughly planar, is considered to be better suited to protein-protein interaction studies. Instead, the EGI is more suited to protein-ligand interactions, in which the small ligand molecule usually has to fit into the protein cavity. In fact, the histogram of the orientations is better suited to representing a mainly convex object and its dual matching region (the cavity). Both these data structures are open, and can be easily integrated with biochemical features.

  7. Airfoil structure

    DOEpatents

    Frey, G.A.; Twardochleb, C.Z.

    1998-01-13

    Past airfoil configurations have been used to improve aerodynamic performance and engine efficiencies. The present airfoil configuration further increases component life and reduces maintenance by reducing internal stress within the airfoil itself. The airfoil includes a chord and a span. Each of the chord and the span has a bow being summed to form a generally ``C`` configuration of the airfoil. The generally ``C`` configuration includes a compound bow in which internal stresses resulting from a thermal temperature gradient are reduced. The structural configuration reduces internal stresses resulting from thermal expansion. 6 figs.

  8. Airfoil structure

    DOEpatents

    Frey, Gary A.; Twardochleb, Christopher Z.

    1998-01-01

    Past airfoil configurations have been used to improve aerodynamic performance and engine efficiencies. The present airfoil configuration further increases component life and reduces maintenance by reducing internal stress within the airfoil itself. The airfoil includes a chord and a span. Each of the chord and the span has a bow being summed to form a generally "C" configuration of the airfoil. The generally "C" configuration includes a compound bow in which internal stresses resulting from a thermal temperature gradient are reduced. The structural configuration reduces internal stresses resulting from thermal expansion.

  9. Liposome-coated quantum dots targeting the sentinel lymph node

    NASA Astrophysics Data System (ADS)

    Chu, Maoquan; Zhuo, Shu; Xu, Jiang; Sheng, Qiunan; Hou, Shengke; Wang, Ruifei

    2010-01-01

    Sentinel lymph node (SLN) mapping with near-infrared (NIR) quantum dot (QDs) have many advantages over traditional methods. However, as an inorganic nanomaterial, QDs have low biocompatibility and low affinity to the lymphatic system. Here, we encapsulated QDs into nanoscale liposomes and then used these liposome-coated QDs for SLN mapping. The results showed that the liposome-coated QDs exhibited core-shell characterization, and their fluorescence emission did not decrease but slightly increased after being continuously excited by a xenon lamp source (150 W) at 488 nm at 37 °C for 1 h. After storing at 4 °C for more than one and half years, the liposome-coated QDs were found to have retained their spherical structure containing a large amount of QDs. When liposome-coated QDs with average size of 55.43 nm were injected intradermally into the paw of a mouse, the SLN was strongly fluorescent within only a few seconds and visualized easily in real time. Moreover, the fluorescence of the QDs trapped in the SLN could be observed for at least 24 h. Compared with the SLN mapping of QDs absent of liposomes and liposome-coated QDs with a larger average size (100.3 and 153.6 nm), more QDs migrated into the SLN when the liposome-coated QDs with smaller average size (55.43 nm) were injected. This technique may make a great contribution to the improvement of the biocompatibility of QDs and the targeting delivery capacity of QDs into the SLN.

  10. The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

    SciTech Connect

    Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani; Osman, Rozana Aina Maulat; Taking, Sanna

    2015-05-15

    The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% of efficiency. For multilayer which includes both GaAs and InGaAs, the output power, P{sub max} was 8.91nW/cm² with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.

  11. The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

    NASA Astrophysics Data System (ADS)

    Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani; Osman, Rozana Aina Maulat; Taking, Sanna

    2015-05-01

    The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% of efficiency. For multilayer which includes both GaAs and InGaAs, the output power, Pmax was 8.91nW/cm² with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.

  12. Structures of

    PubMed

    Kirik; Solovyov; Blokhin; Yakimov

    2000-06-01

    Crystal structures of [Pd(NH3)2X2] complexes, where X = Br or I, diamminediiodo-/-dibromopalladium(II), have been studied by X-ray powder diffraction. The series consists of five complexes: cis-[Pd(NH3)2Br2] (I) [a = 13.3202 (7), b = 12.7223 (6), c = 7.05854 (3) A, Z = 8, space group Pbca], trans-[Pd(NH3)2Br2] (II) [a = 6.7854 (3), b = 7.1057 (3), c = 6.6241 (2) A, alpha = 103.221 (3), beta = 102.514 (2), gamma = 100.386 (3) degrees, Z = 2, space group P1], beta-trans-[Pd(NH3)2Br2] (III) [a = 8.4315 (3), b = 8.4206 (3), c = 8.0916 (2) A, Z = 4, space group Pbca], cis-[Pd(NH3)2I2] (IV) [a = 13.9060 (8), b = 13.5035 (8), c = 7.5050 (4) A, Z = 8, space group Pbca], and beta-trans-[Pd(NH3)2I2] (V) [a = 8.8347 (5), b = 8.8410 (5), c = 8.6081 (2) A, Z = 4, space group Pbca]. Patterson synthesis and Rietveld refinement have been used for structural determination. Molecular structures with column- or parquet-type packing of flat complexes are characteristic of these substances. Corresponding cis- and beta-trans compounds are isostructural. The thermal transformations cis-->trans-->beta-trans (cis-->beta-trans in the case of iodine) are considered. Cl derivatives are also discussed. The transformations proceed irreversibly and are accompanied by decreasing specific volume. Owing to these features, they can be classified as chemical reactions. High-temperature X-ray powder diffraction was used to study the transformations in air. The set of data is consistent with a solid state transformation from cis to trans. According to this model, the columns of molecules remain intact during the process, and the transformation proceeds via the breaking of Pd...X and Pd...N intermolecular bonds. The powder diffraction data have been deposited in ICDD-JCPDS (45-0596, 46-0876, 46-0879, 47-1690, 48-1185).

  13. Positively charged and pH self-buffering quantum dots for efficient cellular uptake by charge mediation and monitoring cell membrane permeability.

    PubMed

    Wang, Suhua; Song, Haipeng; Ong, Wei Yi; Han, Ming Yong; Huang, Dejian

    2009-10-21

    Positively charged and pH self-buffering quantum dots (Tren-QDs) were achieved by surface functionalization with tris(2-aminoethyl)amine (Tren) derivatives, which are attached to the inorganic cores of QDs through bidentate chelating of dithiocarbamates. The Tren-QDs exhibit pH buffering capability by absorbing or releasing protons due to the surface polyamine groups as the surrounding pH fluctuates. Such self-buffering capability stabilizes the photoluminescence of the Tren-QDs against acid. The Tren-QDs bear positive charges through protonation of the surface polyamine groups under physiological conditions and the surface positive charges improve their cellular uptake efficiency by charge mediation, which has been demonstrated by BV-2 microglia cells. The photoluminescence of Tren-QDs shows a selective Stern-Volmer response to copper ions and this property has been preliminarily evaluated for investigating the BV-2 cell membrane structure by monitoring the photoluminescence of intracellular Tren-QDs.

  14. Positively charged and pH self-buffering quantum dots for efficient cellular uptake by charge mediation and monitoring cell membrane permeability

    NASA Astrophysics Data System (ADS)

    Wang, Suhua; Song, Haipeng; Ong, Wei Yi; Han, Ming Yong; Huang, Dejian

    2009-10-01

    Positively charged and pH self-buffering quantum dots (Tren-QDs) were achieved by surface functionalization with tris(2-aminoethyl)amine (Tren) derivatives, which are attached to the inorganic cores of QDs through bidentate chelating of dithiocarbamates. The Tren-QDs exhibit pH buffering capability by absorbing or releasing protons due to the surface polyamine groups as the surrounding pH fluctuates. Such self-buffering capability stabilizes the photoluminescence of the Tren-QDs against acid. The Tren-QDs bear positive charges through protonation of the surface polyamine groups under physiological conditions and the surface positive charges improve their cellular uptake efficiency by charge mediation, which has been demonstrated by BV-2 microglia cells. The photoluminescence of Tren-QDs shows a selective Stern-Volmer response to copper ions and this property has been preliminarily evaluated for investigating the BV-2 cell membrane structure by monitoring the photoluminescence of intracellular Tren-QDs.

  15. Mn-doped near-infrared quantum dots as multimodal targeted probes for pancreatic cancer imaging

    NASA Astrophysics Data System (ADS)

    Yong, Ken-Tye

    2009-01-01

    This work presents a novel approach to producing manganese (Mn)-doped quantum dots (Mnd-QDs) emitting in the near-infrared (NIR). Surface functionalization of Mnd-QDs with lysine makes them stably disperse in aqueous media and able to conjugate with targeting molecules. The nanoparticles were structurally and compositionally characterized and maintained a high photoluminescence quantum yield and displayed paramagnetism in water. The receptor-mediated delivery of bioconjugated Mnd-QDs into pancreatic cancer cells was demonstrated using the confocal microscopy technique. Cytotoxicity of Mnd-QDs on live cells has been evaluated. The NIR-emitting characteristic of the QDs has been exploited to acquire whole animal body imaging with high contrast signals. In addition, histological and blood analysis of mice have revealed that no long-term toxic effects arise from MnD-QDs. These studies suggest multimodal Mnd-QDs have the potentials as probes for early pancreatic cancer imaging and detection.

  16. Digital structural

    USGS Publications Warehouse

    Dohm, J.M.; Anderson, R.C.; Tanaka, K.L.

    1998-01-01

    Magmatic and tectonic activity have both contributed significantly to the surface geology of Mars. Digital structural mapping techniques have now been used to classify and date centers of tectonic activity in the western equatorial region. For example, our results show a center of tectonic activity at Valles Marineris, which may be associated with uplift caused by intrusion. Such evidence may help explain, in part, the development of the large troughs and associated outflow channels and chaotic terrain. We also find a local centre of tectonic activity near the source region of Warrego Valles. Here, we suggest that the valley system may have resulted largely from intrusive-related hydrothermal activity. We hope that this work, together with the current Mars Global Surveyor mission, will lead to a better understanding of the geological processes that shaped the Martian surface.

  17. Armor structures

    DOEpatents

    Chu, Henry Shiu-Hung [Idaho Falls, ID; Lacy, Jeffrey M [Idaho Falls, ID

    2008-04-01

    An armor structure includes first and second layers individually containing a plurality of i-beams. Individual i-beams have a pair of longitudinal flanges interconnected by a longitudinal crosspiece and defining opposing longitudinal channels between the pair of flanges. The i-beams within individual of the first and second layers run parallel. The laterally outermost faces of the flanges of adjacent i-beams face one another. One of the longitudinal channels in each of the first and second layers faces one of the longitudinal channels in the other of the first and second layers. The channels of the first layer run parallel with the channels of the second layer. The flanges of the first and second layers overlap with the crosspieces of the other of the first and second layers, and portions of said flanges are received within the facing channels of the i-beams of the other of the first and second layers.

  18. Performance of four-stage thermoelectric cooler for extended wavelength InGaAs detectors

    NASA Astrophysics Data System (ADS)

    Mo, De-feng; Yang, Li-yi; Liu, Da-fu; Xu, Qin-fei; Li, Tao; Li, Xue

    2015-04-01

    Experimental setup for evaluating four-stage thermoelectric cooler's performance was designed. Effects of input power, heat dissipation condition and heat load on the temperature difference (ΔT) of four-stage thermoelectric coolers' hot and cold faces were obtained experimentally. The result shows that, the ΔT increases as the input power increases. A linear relationship exists between input current and feedback voltage. In different cooling conditions, the ΔT of thermoelectric cooler (TEC) increases with the temperature of hot face. As the temperature increasing on hot face is 1K, the ΔT increasing of TEC can be about 0.5K. Meanwhile, the power consumption of TEC also increases slightly. Water condensation can be prevented in either dry nitrogen environment or vacuum environment, but the vacuum level has great influence to the ΔT, especially in low operation temperature. The better the vacuum level is, the smaller the convection heat loss has. When the operation temperature of focal plane array (FPA) is lower than 220K, it is prior to use vacuum packaging. Considering the Joule-heat of readout circuit and the heat loss of wire conduction, the minimum working temperature of FPA can reach below 200 K when the temperature of the hot face is 285K. And the coefficient of performance (COP) of TEC can increase sharply from 0.8% to 4% when the controlled operation temperature is 220K rather than 200K.

  19. Resonant intersubband plasmon induced current in InGaAs quantum wells on GaAs

    SciTech Connect

    Holzbauer, Martin Klang, Pavel; Detz, Hermann; Maxwell Andrews, Aaron; Strasser, Gottfried; Gornik, Erich; Bakshi, Pradip

    2014-03-24

    We present measurements of the current enhancement due to the coupling of two intersubband plasmons in In{sub 0.05}Ga{sub 0.95}As quantum wells. With changing bias, an emissive and an absorptive intersubband plasmon mode cross attractively and trapped electrons in the ground state gain enough energy from the plasma wave to be lifted up to the second subband, where they can contribute to the current. This effect can be directly observed as an increase of 33% in the current. A magnetic field applied parallel to the growth direction allows a control of the strength of the intersubband plasmon coupling up to a quenching.

  20. Large Diameter, High Speed InGaAs Receivers for Free-Space Lasercom

    DTIC Science & Technology

    2007-01-01

    space optical communication ( FSO ) systems, it is usually desirable to have the sensitivity of the detector as high as possible to reduce the required...generator of an Agilent 86130A 3.6Gbps Error Performance Analyzer provided a pseudo-random bit sequence (PRBS) input to a commercial OC-48 transmitter...the receiver was applied to the error detector of the Agilent 86130A, while the negative output was applied to a Tektronix model TDS5054 digital

  1. Nanoscale imaging of the photoresponse in PN junctions of InGaAs infrared detector

    NASA Astrophysics Data System (ADS)

    Xia, Hui; Li, Tian-Xin; Tang, Heng-Jing; Zhu, Liang; Li, Xue; Gong, Hai-Mei; Lu, Wei

    2016-02-01

    Electronic layout, such as distributions of charge carriers and electric field, in PN junction is determinant for the photovoltaic devices to realize their functionality. Considerable efforts have been dedicated to the carrier profiling of this specific region with Scanning Probe Microscope, yet reliable analysis was impeded by the difficulty in resolving carriers with high mobility and the unclear surface effect, particularly on compound semiconductors. Here we realize nanometer Scanning Capacitance Microscopic study on the cross-section of InGaAs/InP photodetctors with the featured dC/dV layout of PN junction unveiled for the first time. It enables us to probe the photo-excited minority carriers in junction region and diagnose the performance deficiency of the diode devices. This work provides an illuminating insight into the PN junction for assessing its basic capability of harvesting photo-carriers as well as blocking leakage current in nanoscopic scale.

  2. Shot noise at the quantum point contact in InGaAs heterostructure

    SciTech Connect

    Nishihara, Yoshitaka; Nakamura, Shuji; Ono, Teruo; Kobayashi, Kensuke; Kohda, Makoto; Nitta, Junsaku

    2013-12-04

    We study the shot noise at a quantum point contact (QPC) fabricated in an InGaAs/InGaAsP heterostructure, whose conductance can be electrically tuned by the gate voltages. Shot noise suppression is observed at the conductance plateau of N(2e{sup 2}/h) (N = 4,5,and 6), which indicates the coherent quantized channel formation in the QPC. The electron heating effect generated at the QPC explains the deviation of the observed Fano factor from the theory.

  3. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes.

    PubMed

    Farrell, Alan C; Senanayake, Pradeep; Hung, Chung-Hong; El-Howayek, Georges; Rajagopal, Abhejit; Currie, Marc; Hayat, Majeed M; Huffaker, Diana L

    2015-12-02

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III-V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure.

  4. Nanoscale imaging of the photoresponse in PN junctions of InGaAs infrared detector

    PubMed Central

    Xia, Hui; Li, Tian-Xin; Tang, Heng-Jing; Zhu, Liang; Li, Xue; Gong, Hai-Mei; Lu, Wei

    2016-01-01

    Electronic layout, such as distributions of charge carriers and electric field, in PN junction is determinant for the photovoltaic devices to realize their functionality. Considerable efforts have been dedicated to the carrier profiling of this specific region with Scanning Probe Microscope, yet reliable analysis was impeded by the difficulty in resolving carriers with high mobility and the unclear surface effect, particularly on compound semiconductors. Here we realize nanometer Scanning Capacitance Microscopic study on the cross-section of InGaAs/InP photodetctors with the featured dC/dV layout of PN junction unveiled for the first time. It enables us to probe the photo-excited minority carriers in junction region and diagnose the performance deficiency of the diode devices. This work provides an illuminating insight into the PN junction for assessing its basic capability of harvesting photo-carriers as well as blocking leakage current in nanoscopic scale. PMID:26892069

  5. Wavy growth onset in strain-balanced InGaAs multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Nasi, L.; Ferrari, C.; Lanzi, A.; Lazzarini, L.; Balboni, R.; Clarke, G.; Mazzer, M.; Rohr, C.; Abbott, P.; Barnham, K. W. J.

    2005-01-01

    Different strain-balanced InGaAs/InGaAs multi-quantum wells (MQWs) were grown on (0 0 1) InP to be used as active layers of thermophotovoltaic devices. Transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD) were performed to correlate the evolution of the layer interfaces from planar to wavy and the consequent nucleation of extended defects with the well and barrier compositions and thicknesses and the growth temperature. The existence of a critical elastic energy density for the wavy growth onset has been experimentally confirmed by changing both the well and barrier misfit and the multi-quantum well layer thickness. A decrease of the growth temperature shifts the critical energy to higher values. An empirical model to predict the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period and the growth temperature is presented and successfully applied for the growth of high quality 40 repetitions MQWs with a well misfit of about 1.5%.

  6. Intervalley separation in the conduction band of InGaAs measured by terahertz excitation spectroscopy

    SciTech Connect

    Molis, G.; Krotkus, A.; Vaicaitis, V.

    2009-03-02

    Spectral dependencies of terahertz radiation from the femtosecond laser-illuminated surfaces of Ga{sub x}In{sub 1-x}As (x=1, 0.8, and 0.47) have been investigated experimentally at high optical fluencies and laser wavelengths ranging from 600 to 800 nm. The terahertz pulse amplitude increased with the increasing laser photon energy due to larger excess energies of photoexcited electrons and more efficient spatial separation of electrons and holes at the illuminated surface. This increase was stopped with the onset of electron transitions to subsidiary conduction band valleys. Analysis of these experiments was used for evaluating the energy positions of the X and L conduction band valleys in Ga{sub x}In{sub 1-x}As alloys as a function of their composition.

  7. 1-Picosecond InGaAs Photodetector for Operation at 1300-1600 nm

    DTIC Science & Technology

    1993-11-15

    states and thermally-ionized carriers which reduces the sheet resistance by more than one order of magnitude. Material defects also lower the...effect indium has on resistivity we have grown a set of three Wvllability C( lattice-matched samples for measuring sheet resistance . Figure 1 shows n...curve of sheet resistance -d ..... Special Picotronix, Inc., Ann Arbor, MI. 2 Per telecon ONR 2/28/94 C1iC vs. indium concentration for the three

  8. All-optical tomography of electron spins in (In,Ga)As quantum dots

    NASA Astrophysics Data System (ADS)

    Varwig, S.; René, A.; Economou, Sophia E.; Greilich, A.; Yakovlev, D. R.; Reuter, D.; Wieck, A. D.; Reinecke, T. L.; Bayer, M.

    2014-02-01

    We demonstrate the basic features of an all-optical spin tomography on picosecond time scale. The magnetization vector associated with a mode-locked electron spin ensemble in singly charged quantum dots is traced by ellipticity measurements using picosecond laser pulses. After optical orientation the spins precess about a perpendicular magnetic field. By comparing the dynamics of two interacting ensembles with the dynamics of a single ensemble we find buildup of a spin component along the magnetic field in the two-ensemble case. This component arises from a Heisenberg-like spin-spin interaction.

  9. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes

    PubMed Central

    Farrell, Alan C.; Senanayake, Pradeep; Hung, Chung-Hong; El-Howayek, Georges; Rajagopal, Abhejit; Currie, Marc; Hayat, Majeed M.; Huffaker, Diana L.

    2015-01-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III–V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure. PMID:26627932

  10. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Farrell, Alan C.; Senanayake, Pradeep; Hung, Chung-Hong; El-Howayek, Georges; Rajagopal, Abhejit; Currie, Marc; Hayat, Majeed M.; Huffaker, Diana L.

    2015-12-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III-V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure.

  11. Spectroscopic investigations on the effect of N-Acetyl-L-cysteine-Capped CdTe Quantum Dots on catalase

    NASA Astrophysics Data System (ADS)

    Sun, Haoyu; Yang, Bingjun; Cui, Erqian; Liu, Rutao

    2014-11-01

    Quantum dots (QDs) are recognized as some of the most promising semiconductor nanocrystals in biomedical applications. However, the potential toxicity of QDs has aroused wide public concern. Catalase (CAT) is a common enzyme in animal and plant tissues. For the potential application of QDs in vivo, it is important to investigate the interaction of QDs with CAT. In this work, the effect of N-Acetyl-L-cysteine-Capped CdTe Quantum Dots with fluorescence emission peak at 612 nm (QDs-612) on CAT was investigated by fluorescence, synchronous fluorescence, fluorescence lifetime, ultraviolet-visible (UV-vis) absorption and circular dichroism (CD) techniques. Binding of QDs-612 to CAT caused static quenching of the fluorescence, the change of the secondary structure of CAT and the alteration of the microenvironment of tryptophan residues. The association constants K were determined to be K288K = 7.98 × 105 L mol-1 and K298K = 7.21 × 105 L mol-1. The interaction between QDs-612 and CAT was spontaneous with 1:1 stoichiometry approximately. The CAT activity was also inhibited for the bound QDs-612. This work provides direct evidence about enzyme toxicity of QDs-612 to CAT in vitro and establishes a new strategy to investigate the interaction between enzyme and QDs at a molecular level, which is helpful for clarifying the bioactivities of QDs in vivo.

  12. Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications

    NASA Astrophysics Data System (ADS)

    Stanca, Loredana; Petrache, Sorina Nicoleta; Serban, Andreea Iren; Staicu, Andrea Cristina; Sima, Cornelia; Munteanu, Maria Cristina; Zărnescu, Otilia; Dinu, Diana; Dinischiotu, Anca

    2013-05-01

    Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO2 QDs after 1, 3, and 7 days from their administration. QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection. Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO2 QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered. Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the

  13. Hybrid structures of polycationic aluminum phthalocyanines and quantum dots.

    PubMed

    Maksimov, E G; Gvozdev, D A; Strakhovskaya, M G; Paschenko, V Z

    2015-03-01

    Semiconductor nanocrystals (CdSe/ZnS quantum dots, QDs) were used as inorganic focusing antenna, allowing for the enhancement of fluorescence and photosensitizing activity of polycationic aluminum phthalocyanines (PCs). It was found that QDs form stable complexes with PCs in aqueous solutions due to electrostatic interactions. In such hybrid complexes, we observed highly efficient nonradiative energy transfer from QD to PC, leading to a sharp increase in the effective absorption cross section of PC in the absorption bands of the CdSe/ZnS quantum dots. When hybrid complexes are excited within these bands, the intensity of PC fluorescence and the rate of photosensitized singlet oxygen generation increases significantly (up to 500 and 350%, correspondingly) compared to free PC at the same concentration. The observed effect is of interest for modeling primary stages of photosynthesis and increasing photosensitizing activity of dyes used in photodynamic therapy.

  14. Asteroid structure

    NASA Astrophysics Data System (ADS)

    Asphaug, E.

    2014-07-01

    Even before the first space missions to asteroids, in the mid-1990s, it was known that asteroids have weird structures. Photometry indicated complicated shapes, and the pioneering radar investigations by Ostro and colleagues followed by adaptive optics campaigns and flybys showed odd binary forms, and confirmed the common presence of satellites, and indications of highly varying surface roughness. Some asteroids turned out to be dominated by a single major cratering event, while others showed no evidence of a major crater, or perhaps for global crater erasure. The first space mission to orbit an asteroid, NEAR, found a mixture of heavily cratered terrains and geomorphically active 'ponds', and indicated evidence for global seismicity from impact. The next mission to orbit an asteroid, Hayabusa, found what most agree is a rubble pile, with no major craters and an absence of fines. There is to date no direct evidence of asteroid interior geology, other than measurements of bulk density, and inferences made for mass distribution asymmetry based on dynamics, and inferences based on surface lineaments. Interpolating from the surface to the interior is always risky and usually wrong, but of course the answer is important since we are someday destined to require this knowledge in order to divert a hazardous asteroid from impact with the Earth. Even considering the near-subsurface, here we remain as ignorant as we were about the Moon in the early 1960s, whether the surface will swallow us up in dust, or will provide secure landing and anchoring points. Laboratory experimentation in close to zero-G is still in its early stages. Adventures such as mining and colonization will surely have to wait until we better know these things. How do we get from here to there? I will focus on 3 areas of progress: (1) asteroid cratering seismology, where we use the surface craters to understand what is going on inside; (2) numerical modeling of collisions, which predicts the internal

  15. Synthesis and characterization of InP and InN colloidal quantum dots.

    SciTech Connect

    Boyle, Timothy J.; Osinski, Marek; Greenberg, Melisa; Bunge, Scott D.; Chen, Weiliang; Smolyakov, G. A.; Pulford, B. N.; Jiang, Ying-Bing

    2005-04-01

    InP quantum dots (QDs) with zinc blende structure and InN QDs with hexagonal structure were synthesized from appropriate organometallic precursors in a noncoordinating solvent using myristic acid as a ligand. The QDs were characterized by TEM, the associated energy dispersive spectroscopy (EDS), electron diffraction, and steady state UV-VIS optical absorption and photoluminescence spectroscopy. To our best knowledge, this paper reports synthesis of InN colloidal quantum dots for the first time.

  16. Structural Biology Fact Sheet

    MedlinePlus

    ... Home > Science Education > Structural Biology Fact Sheet Structural Biology Fact Sheet Tagline (Optional) Middle/Main Content Area What is structural biology? Structural biology is a field of science focused ...

  17. Design optimization for two-step photon absorption in quantum dot solar cells by using infrared photocurrent spectroscopy

    NASA Astrophysics Data System (ADS)

    Tamaki, R.; Shoji, Y.; Okada, Y.

    2016-03-01

    Multi-stacked quantum dot solar cell (QDSC) is a promising candidate for intermediate band solar cell, which can exceed thermodynamic efficiency limit of single-junction solar cells. In recent years, lots of effort has been made to evaluate and understand the photo-carrier response of two-step photon absorption in QDSCs. One crucial issue is to suppress thermal excitation of photo-carriers out of QDs, which obscures the QD filling under quasi-equilibrium at operation conditions. We have investigated infrared photocurrent spectra of the QD states to conduction band (CB) transition by using Fourier transform infrared (FTIR) spectroscopy. Multi-stacked In(Ga)As QDSCs with different barrier materials, such as GaAs, GaNAs, GaAsSb, and AlGaAs, were investigated. The IR absorption edge of the QD to CB transition was evaluated at low temperature by analyzing the low energy tail of the FTIR spectra. The threshold temperature of the two-step photon absorption in In(Ga)As QDSCs was determined by observing temperature dependence of the IR photo-response. A universal linear relationship between the threshold temperature and the IR absorption edge was obtained in In(Ga)As QDSCs with varied barrier materials. The threshold temperature of 295 K was predicted for the absorption edge at 0.459 eV by extrapolating the linear relationship. It reveals strategy for cell optimization to achieve efficient two-step photon absorption at ambient conditions.

  18. Magnetic multilayer structure

    DOEpatents

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2017-03-21

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  19. Magnetic multilayer structure

    SciTech Connect

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2016-07-05

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  20. Probing Spin and Spin-Orbit Coupling effects in Narrow-gap Semiconductor Nano-structures by THz Magneto-photoresponse Spectroscopy and Magneto-transport Measurements

    NASA Astrophysics Data System (ADS)

    Pakmehr, Mehdi

    Using the spin degree of freedom in a emergent field Known as Spintronics has motivated scientist in different disciplines including physicist within last 10 years. Due to different interaction mechanisms which affects the physical behavior of spin (eg its state and transport properties) within solid medium (Semiconductors in our case), one needs to distinguish these mechanisms and their importance for making any practical spin based devices. For example the idea of making spin based transistors with electrons being transported within InGaAs and their spin state is being controlled by Rashba type field has been around for around 25 years but injection of spin polarized currents from a source into the channel has not been solved yet. Spin orbit coupling (SOC) is one of the mechanisms which changes the spin state of electrons and avoid the existence of pure spin state as a favorable one from device point of view. SOC could have a different origin depending on material type or structure of device. One method of measuring and quantifying this mechanisms within semiconductor nanostructures is through measuring the parameters known as Lande g-factor. This parameters turns out to be a promising one to probe different effects on electronic band structure including quantum confinement, strain, electric filed, etc. We probe a combination of these effects (SOC, Strain, band mixing, etc) by measuring different g-factor tensor components of narrow gap Zinc blend semiconductor nanostructures which we hope finally serve to the purpose of making reliable spin based devices* (Spintronics). To reach this goal we have developed and implemented THz magneto-Photoresponse spectroscopy in conjunction with magneto-transport measurements at cryogenic temperatures. The samples include InAs and HgTe based Quantum wells as well as InAs based quantum point contact. Our findings clarify the situation where the combination of SOC, Strain, quantum confinements as well as many body electron effect