1
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Dey AB, Sanyal MK, Schropp A, Achilles S, Keller TF, Farrer I, Ritchie DA, Bertram F, Schroer CG, Seeck OH. Culling a Self-Assembled Quantum Dot as a Single-Photon Source Using X-ray Microscopy. ACS NANO 2023; 17:16080-16088. [PMID: 37523736 PMCID: PMC10763734 DOI: 10.1021/acsnano.3c04835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 07/27/2023] [Indexed: 08/02/2023]
Abstract
Epitaxially grown self-assembled semiconductor quantum dots (QDs) with atom-like optical properties have emerged as the best choice for single-photon sources required for the development of quantum technology and quantum networks. Nondestructive selection of a single QD having desired structural, compositional, and optical characteristics is essential to obtain noise-free, fully indistinguishable single or entangled photons from single-photon emitters. Here, we show that the structural orientations and local compositional inhomogeneities within a single QD and the surrounding wet layer can be probed in a screening fashion by scanning X-ray diffraction microscopy and X-ray fluorescence with a few tens of nanometers-sized synchrotron radiation beam. The presented measurement protocol can be used to cull the best single QD from the enormous number of self-assembled dots grown simultaneously. The obtained results show that the elemental composition and resultant strain profiles of a QD are sensitive to in-plane crystallographic directions. We also observe that lattice expansion after a certain composition-limit introduces shear strain within a QD, enabling the possibility of controlled chiral-QD formation. Nanoscale chirality and compositional anisotropy, contradictory to common assumptions, need to be incorporated into existing theoretical models to predict the optical properties of single-photon sources and to further tune the epitaxial growth process of self-assembled quantum structures.
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Affiliation(s)
- Arka Bikash Dey
- Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany
| | - Milan K. Sanyal
- Surface
Physics and Material Science Division, Saha
Institute of Nuclear Physics, Kolkata, West Bengal 700064, India
| | - Andreas Schropp
- Center
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg 22607, Germany
| | - Silvio Achilles
- Center
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg 22607, Germany
| | - Thomas F. Keller
- Center
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg 22607, Germany
- Physics
Department, University of Hamburg, Hamburg 20355, Germany
| | - Ian Farrer
- Department
of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom
| | - David A. Ritchie
- Cavendish
Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Florian Bertram
- Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany
| | - Christian G. Schroer
- Center
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg 22607, Germany
| | - Oliver H. Seeck
- Deutsches
Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany
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2
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Kraus S, Bonn M, Cánovas E. Room-temperature solution-phase epitaxial nucleation of PbS quantum dots on rutile TiO 2 (100). NANOSCALE ADVANCES 2020; 2:377-383. [PMID: 36134011 PMCID: PMC9417650 DOI: 10.1039/c9na00601j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 12/02/2019] [Indexed: 05/02/2023]
Abstract
Owing to its simplicity and versatility, the successive ionic layer adsorption and reaction (SILAR) method is increasingly being employed to develop low-cost hetero-nanostructured sensitized oxide systems for solar energy conversion, such as solar cells and solar fuels schemes. Understanding the nature of the SILAR quantum dot (QD) nucleation and growth on an insulating oxide is then critical as it will determine the QD density and spatial distribution, as well as the optoelectronic properties of the QD/oxide interfaces (e.g. QD bandgap onset). Here, we demonstrate epitaxial nucleation of lead sulfide (PbS) QDs onto a planar rutile titanium dioxide (100) surface employing the SILAR method. The QDs nucleated by SILAR are crystalline structures characterized by a truncated pyramidal shape, with nucleation occurring preferentially along the rutile (010) and (001) crystal orientations. The PbS QD size distribution is constrained by lattice mismatch causing strain in the lead sulfide. These results highlight the potential of SILAR for the facile growth of high-quality epitaxial nanostructures in liquid phase, under ambient conditions and at room temperature.
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Affiliation(s)
- Stefan Kraus
- Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz Germany
| | - Mischa Bonn
- Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz Germany
| | - Enrique Cánovas
- Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz Germany
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) Faraday 9 28049 Madrid Spain
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3
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Quantitative strain analysis of InAs/GaAs quantum dot materials. Sci Rep 2017; 7:45376. [PMID: 28349927 PMCID: PMC5368971 DOI: 10.1038/srep45376] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Accepted: 02/22/2017] [Indexed: 11/12/2022] Open
Abstract
Geometric phase analysis has been applied to high resolution aberration corrected (scanning) transmission electron microscopy images of InAs/GaAs quantum dot (QD) materials. We show quantitatively how the lattice mismatch induced strain varies on the atomic scale and tetragonally distorts the lattice in a wide region that extends several nm into the GaAs spacer layer below and above the QDs. Finally, we show how V-shaped dislocations originating at the QD/GaAs interface efficiently remove most of the lattice mismatch induced tetragonal distortions in and around the QD.
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4
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Grigoriev D, Lazarev S, Schroth P, Minkevich A, Köhl M, Slobodskyy T, Helfrich M, Schaadt D, Aschenbrenner T, Hommel D, Baumbach T. Asymmetric skew X-ray diffraction at fixed incidence angle: application to semiconductor nano-objects. J Appl Crystallogr 2016. [DOI: 10.1107/s1600576716006385] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
A procedure for obtaining three-dimensionally resolved reciprocal-space maps in a skew X-ray diffraction geometry is described. The geometry allows tuning of the information depth in the range from tens of micrometres for symmetric skew diffraction down to tens of nanometres for strongly asymmetric skew geometries, where the angle of incidence is below the critical angle of total external reflection. The diffraction data are processed using a rotation matrix formalism. The whole three-dimensional reciprocal-space map can be measured by performing a single azimuthal rotation of the sample and using a two-dimensional detector, while keeping the angle of incidence and the X-ray information depth fixed (FIXD method). Having a high surface sensitivity under grazing-incidence conditions, the FIXD method can be applied to a large variety of Bragg reflections, particularly polar ones, which provide information on strain and chemical composition separately. In contrast with conventional grazing-incidence diffraction, the FIXD approach reveals, in addition to the lateral (in-plane) components, the vertical (out-of-plane) component of the strain field, and therefore allows the separation of the scattering contributions of strained epitaxial nanostructures by their vertical misfit. The potential of FIXD is demonstrated by resolving the diffraction signal from a single layer of InGaN quantum dots grown on a GaN buffer layer. The FIXD approach is suited to the study of free-standing and covered near-surface nano-objects, as well as vertically extended multilayer structures.
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5
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Density dependent composition of InAs quantum dots extracted from grazing incidence x-ray diffraction measurements. Sci Rep 2015; 5:15732. [PMID: 26506865 PMCID: PMC4623704 DOI: 10.1038/srep15732] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 09/28/2015] [Indexed: 11/08/2022] Open
Abstract
Epitaxial InAs quantum dots grown on GaAs substrate are being used in several applications ranging from quantum communications to solar cells. The growth mechanism of these dots also helps us to explore fundamental aspects of self-organized processes. Here we show that composition and strain profile of the quantum dots can be tuned by controlling in-plane density of the dots over the substrate with the help of substrate-temperature profile. The compositional profile extracted from grazing incidence x-ray measurements show substantial amount of inter-diffusion of Ga and In within the QD as a function of height in the low-density region giving rise to higher variation of lattice parameters. The QDs grown with high in-plane density show much less spread in lattice parameter giving almost flat density of In over the entire height of an average QD and much narrower photoluminescence (PL) line. The results have been verified with three different amounts of In deposition giving systematic variation of the In composition as a function of average quantum dot height and average energy of PL emission.
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6
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Cantelli V, Geaymond O, Ulrich O, Zhou T, Blanc N, Renaud G. The In situ growth of Nanostructures on Surfaces (INS) endstation of the ESRF BM32 beamline: a combined UHV-CVD and MBE reactor for in situ X-ray scattering investigations of growing nanoparticles and semiconductor nanowires. JOURNAL OF SYNCHROTRON RADIATION 2015; 22:688-700. [PMID: 25931085 DOI: 10.1107/s1600577515001605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 01/24/2015] [Indexed: 06/04/2023]
Abstract
This paper presents the upgraded `In situ growth of Nanoscructures on Surfaces' (INS) endstation of the InterFace beamline IF-BM32 at the European Synchrotron Radiation Facility (ESRF). This instrument, originally designed to investigate the structure of clean surfaces/interfaces/thin-films by surface X-ray diffraction, has been further developed to investigate the formation and evolution of nanostructures by combining small- and wide-angle X-ray scattering methodologies, i.e. grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXD). It consists of a UHV chamber mounted on a z-axis type goniometer, equipped with residual gas analysis, reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) to complete the X-ray scattering investigations. The chamber has been developed so as up to eight sources of molecular beam epitaxy (MBE) can be simultaneously mounted to elaborate the nanostructures. A chemical vapor deposition (CVD) set-up has been added to expand the range of growing possibilities, in particular to investigate in situ the growth of semiconductor nanowires. This setup is presented in some detail, as well as the first in situ X-ray scattering measurements during the growth of silicon nanowires.
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Affiliation(s)
- V Cantelli
- Université Grenoble Alpes, F-38000 Grenoble, France
| | - O Geaymond
- Université Grenoble Alpes, F-38000 Grenoble, France
| | - O Ulrich
- Université Grenoble Alpes, F-38000 Grenoble, France
| | - T Zhou
- Université Grenoble Alpes, F-38000 Grenoble, France
| | - N Blanc
- Université Grenoble Alpes, F-38000 Grenoble, France
| | - G Renaud
- Université Grenoble Alpes, F-38000 Grenoble, France
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7
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Large modulation of zero-dimensional electronic states in quantum dots by electric-double-layer gating. Nat Commun 2014; 4:2664. [PMID: 24154536 DOI: 10.1038/ncomms3664] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 09/24/2013] [Indexed: 11/08/2022] Open
Abstract
Electrical manipulation and read-out of quantum states in zero-dimensional nanostructures by nano-gap metal electrodes is expected to bring about innovation in quantum information processing. However, electrical tunability of the quantum states in zero-dimensional nanostructures is limited by the screening of gate electric fields. Here we demonstrate a new way to realize wide-range electrical modulation of quantum states of single self-assembled InAs quantum dots (QDs) with a liquid-gated electric-double-layer (EDL) transistor geometry. The efficiency of EDL gating is 6-90 times higher than that of the conventional solid gating. The quantized energy level spacing is modulated from ~15 to ~25 meV, and the electron g-factor is electrically tuned over a wide range. Such a field effect tuning can be explained by the modulation in the confinement potential of electrons in the QDs. The EDL gating on the QDs also provides potential compatibility with optical manipulation of single-electron charge/spin states.
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8
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Usman M, Tasco V, Todaro MT, De Giorgi M, O'Reilly EP, Klimeck G, Passaseo A. The polarization response in InAs quantum dots: theoretical correlation between composition and electronic properties. NANOTECHNOLOGY 2012; 23:165202. [PMID: 22469563 DOI: 10.1088/0957-4484/23/16/165202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.
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Affiliation(s)
- Muhammad Usman
- Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, Ireland.
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9
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Favre-Nicolin V, Coraux J, Richard MI, Renevier H. Fast computation of scattering maps of nanostructures using graphical processing units. J Appl Crystallogr 2011. [DOI: 10.1107/s0021889811009009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
Abstract
Scattering maps from strained or disordered nanostructures around a Bragg reflection can be either computed quickly using approximations and a (fast) Fourier transform or obtained using individual atomic positions. In this article, it is shown that it is possible to compute up to 4 × 1010 reflections atoms s−1using a single graphics card, and the manner in which this speed depends on the number of atoms and points in reciprocal space is evaluated. An open-source software library (PyNX) allowing easy scattering computations (including grazing-incidence conditions) in the Python language is described, with examples of scattering from non-ideal nanostructures.
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10
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García-Santamaría F, Chen Y, Vela J, Schaller RD, Hollingsworth JA, Klimov VI. Suppressed auger recombination in "giant" nanocrystals boosts optical gain performance. NANO LETTERS 2009; 9:3482-8. [PMID: 19505082 PMCID: PMC2897714 DOI: 10.1021/nl901681d] [Citation(s) in RCA: 251] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron-hole (exciton) recombination energy is transferred to a third charge carrier. This process severely limits the lifetime and bandwidth of optical gain, leads to large nonradiative losses in light-emitting diodes and photovoltaic cells, and is believed to be responsible for intermittency ("blinking") of emission from single nanocrystals. The development of nanostructures in which Auger recombination is suppressed has recently been the subject of much research in the colloidal nanocrystal field. Here, we provide direct experimental evidence that so-called "giant" nanocrystals consisting of a small CdSe core and a thick CdS shell exhibit a significant (orders of magnitude) suppression of Auger decay rates. As a consequence, even multiexcitons of a very high order exhibit significant emission efficiencies, which allows us to demonstrate optical amplification with an extraordinarily large bandwidth (>500 meV) and record low excitation thresholds. This demonstration represents an important milestone toward practical lasing technologies utilizing solution-processable colloidal nanoparticles.
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11
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Schülli TU, Vastola G, Richard MI, Malachias A, Renaud G, Uhlík F, Montalenti F, Chen G, Miglio L, Schäffler F, Bauer G. Enhanced relaxation and intermixing in Ge islands grown on pit-patterned Si(001) substrates. PHYSICAL REVIEW LETTERS 2009; 102:025502. [PMID: 19257289 DOI: 10.1103/physrevlett.102.025502] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2008] [Indexed: 05/25/2023]
Abstract
We compare elastic relaxation and Si-Ge distribution in epitaxial islands grown on both pit-patterned and flat Si(001) substrates. Anomalous x-ray diffraction yields that nucleation in the pits provides a higher relaxation. Using an innovative, model-free fitting procedure based on self-consistent solutions of the elastic problem, we provide compositional and elastic-energy maps. Islands grown on flat substrates exhibit stronger composition gradients and do not show a monotonic decrease of elastic energy with height. Both phenomena are explained using both thermodynamic and kinetic arguments.
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Affiliation(s)
- T U Schülli
- CEA Grenoble, INAC/SP2M, 17 rue des martyrs, F-38054 Grenoble, France
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12
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Ngo CY, Yoon SF, Loke WK, Cao Q, Lim DR, Wong V, Sim YK, Chua SJ. Investigation of Semiconductor Quantum Dots for Waveguide Electroabsorption Modulator. NANOSCALE RESEARCH LETTERS 2008; 3:486-490. [PMID: 20596370 PMCID: PMC2894240 DOI: 10.1007/s11671-008-9184-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2008] [Accepted: 10/02/2008] [Indexed: 05/29/2023]
Abstract
In this work, we investigated the use of 10-layer InAs quantum dot (QD) as active region of an electroabsorption modulator (EAM). The QD-EAM is a p-i-n ridge waveguide structure with intrinsic layer thickness of 0.4 mum, width of 10 mum, and length of 1.0 mm. Photocurrent measurement reveals a Stark shift of ~5 meV (~7 nm) at reverse bias of 3 V (75 kV/cm) and broadening of the resonance peak due to field ionization of electrons and holes was observed for E-field larger than 25 kV/cm. Investigation at wavelength range of 1,300-1320 nm reveals that the largest absorption change occurs at 1317 nm. Optical transmission measurement at this wavelength shows insertion loss of ~8 dB, and extinction ratio of ~5 dB at reverse bias of 5 V. Consequently, methods to improve the performance of the QD-EAM are proposed. We believe that QDs are promising for EAM and the performance of QD-EAM will improve with increasing research efforts.
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Affiliation(s)
- CY Ngo
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - SF Yoon
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - WK Loke
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Q Cao
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - DR Lim
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Vincent Wong
- Temasek Laboratories @ NTU, Nanyang Technological University, 50 Nanyang Drive, Singapore, 639798, Singapore
| | - YK Sim
- Temasek Laboratories @ NTU, Nanyang Technological University, 50 Nanyang Drive, Singapore, 639798, Singapore
| | - SJ Chua
- Institute of Materials Research and Engineering, 3 Research Link, Singapore, 117602, Singapore
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13
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Fälth JF, Yoon SF, Fitzgerald EA. The influence of substrate temperature on InAsN quantum dots grown by molecular beam epitaxy. NANOTECHNOLOGY 2008; 19:455606. [PMID: 21832783 DOI: 10.1088/0957-4484/19/45/455606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The effect of substrate temperature, 390-480 °C, during molecular beam epitaxy growth of InAsN quantum dots has been studied. The quantum dot formation was studied in situ, and it is shown that the quantum dots are close to fully relaxed within 4 monolayers (ML) of InAsN deposition. Further, the indium concentration was estimated to be 84%, 67%, 55% and 31% for 4 ML thick quantum dots grown at 390, 420, 450 and 480 °C, respectively. Thus, Ga incorporation was demonstrated at all substrate temperatures. The dot diameter and height increased from 23 to 38 nm, and 2.5 to 8.9 nm, respectively, when the growth temperature was increased from 390 to 480 °C. The 5 K photoluminescence intensity and wavelength both increased with substrate temperature.
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Affiliation(s)
- J F Fälth
- School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore. Singapore-MIT Alliance, Nanyang Avenue, 639798, Singapore
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14
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Rastelli A, Stufler S, Schliwa A, Songmuang R, Manzano C, Costantini G, Kern K, Zrenner A, Bimberg D, Schmidt OG. Hierarchical self-assembly of GaAs/AlGaAs quantum dots. PHYSICAL REVIEW LETTERS 2004; 92:166104. [PMID: 15169246 DOI: 10.1103/physrevlett.92.166104] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2003] [Indexed: 05/24/2023]
Abstract
A novel structure containing self-assembled, unstrained GaAs quantum dots is obtained by combining solid-source molecular beam epitaxy and atomic-layer precise in situ etching. Photo-luminescence (PL) spectroscopy reveals light emission with very narrow inhomogeneous broadening and clearly resolved excited states at high excitation intensity. The dot morphology is determined by scanning probe microscopy and, combined with single band and eight-band k.p theory calculations, is used to interpret PL and single-dot spectra with no adjustable structural parameter.
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Affiliation(s)
- A Rastelli
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
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15
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Pryor CE, Flatté ME. Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits. PHYSICAL REVIEW LETTERS 2003; 91:257901. [PMID: 14754157 DOI: 10.1103/physrevlett.91.257901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Indexed: 05/24/2023]
Abstract
A quantum dot spin light emitting diode provides a test of carrier spin injection into a qubit and a means for analyzing carrier spin injection and local spin polarization. Even with 100% spin-polarized carriers the emitted light may be only partially circularly polarized due to the geometry of the dot. We have calculated carrier polarization-dependent optical matrix elements for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. Calculations for typical SAQD geometries with emission along [110] show light that is only 5% circularly polarized for spin states that are 100% polarized along [110]. Measuring along the growth direction gives near unity conversion of spin to photon polarization and is the least sensitive to uncertainties in SAQD geometry.
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Affiliation(s)
- C E Pryor
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA.
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16
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Maltezopoulos T, Bolz A, Meyer C, Heyn C, Hansen W, Morgenstern M, Wiesendanger R. Wave-function mapping of InAs quantum dots by scanning tunneling spectroscopy. PHYSICAL REVIEW LETTERS 2003; 91:196804. [PMID: 14611601 DOI: 10.1103/physrevlett.91.196804] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2003] [Indexed: 05/24/2023]
Abstract
Scanning tunneling spectroscopy is used to investigate the single-electron states and the corresponding squared wave functions of single and freestanding strain-induced InAs quantum dots grown on GaAs(001). Several peaks are found in dI/dV curves, which belong to different single-electron states. Spatially resolved dI/dV images reveal (000), (100), (010), (200), and (300) states, where the numbers describe the number of nodes in [11;0], [110], and [001] directions, respectively. The total number and energetic sequence of states is different for different dots. Interestingly, the (010) state is often missing, even when (200) and (300) states are present. We interpret this anisotropy in electronic structure as a consequence of the shape asymmetry of the dots.
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Affiliation(s)
- Theophilos Maltezopoulos
- Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
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17
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Malachias A, Kycia S, Medeiros-Ribeiro G, Magalhães-Paniago R, Kamins TI, Williams RS. 3D composition of epitaxial nanocrystals by anomalous X-ray diffraction: observation of a Si-rich core in Ge domes on Si(100). PHYSICAL REVIEW LETTERS 2003; 91:176101. [PMID: 14611360 DOI: 10.1103/physrevlett.91.176101] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2003] [Indexed: 05/24/2023]
Abstract
Three-dimensional composition maps of nominally pure Ge domes grown on Si(001) at 600 degrees C were obtained from grazing incidence anomalous x-ray scattering data at the Ge K edge. The data were analyzed in terms of a stack of layers with laterally varying concentration. The results demonstrated that the domes contained a Si-rich core covered by a Ge-rich shell and were independently supported by selective etch experiments. The composition profile resulted from substrate Si alloying into the Ge during growth to partially relax the stress in and under the domes.
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Affiliation(s)
- A Malachias
- Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
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18
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Schülli TU, Stangl J, Zhong Z, Lechner RT, Sztucki M, Metzger TH, Bauer G. Direct determination of strain and composition profiles in SiGe islands by anomalous x-Ray diffraction at high momentum transfer. PHYSICAL REVIEW LETTERS 2003; 90:066105. [PMID: 12633307 DOI: 10.1103/physrevlett.90.066105] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2002] [Indexed: 05/24/2023]
Abstract
Anomalous x-ray scattering is employed for quantitative measurements of the Ge composition profile in islands on Si(001). The anomalous effect in SiGe is enhanced exploiting the dependence of the complex atomic form factors on the momentum transfer. Comparing the intensity ratios for x-ray energies below and close to the K edge of Ge at various Bragg reflections in the grazing incidence diffraction setup, the sensitivity for the Ge profile is considerably enhanced. The method is demonstrated for SiGe dome-shaped islands grown on Si(001). It is found that the composition inside the island changes rather abruptly, whereas the lattice parameter relaxes continuously.
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Affiliation(s)
- T U Schülli
- Institute for Semiconductor Physics, Johannes Kepler Universität Linz, A-4040 Linz, Austria
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Aspect ratio dependent strains in InAs/InP quantum dots measured by synchrotron radiation x-ray diffraction. ACTA ACUST UNITED AC 2003. [DOI: 10.1116/1.1537713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Sheng W, Leburton JP. Anomalous quantum-confined Stark effects in stacked InAs/GaAs self-assembled quantum dots. PHYSICAL REVIEW LETTERS 2002; 88:167401. [PMID: 11955264 DOI: 10.1103/physrevlett.88.167401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2001] [Indexed: 05/23/2023]
Abstract
Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs) are predicted to exhibit strong hole localization even with vanishing separation between the dots, and a nonparabolic dependence of the interband transition energy on the electric field, which is not encountered in single SAD structures. Our study based on an eight-band strain-dependent k x p Hamiltonian indicates that this anomalous quantum confined Stark effect is caused by the three-dimensional strain field distribution which influences drastically the hole states in the stacked SAD structures.
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Affiliation(s)
- Weidong Sheng
- Beckman Institute for Advanced Science and Technology and Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Schmidbauer M, Hanke M, Köhler R. X-Ray Diffuse Scattering on Self-Organized Mesoscopic Structures. CRYSTAL RESEARCH AND TECHNOLOGY 2002. [DOI: 10.1002/1521-4079(200202)37:1<3::aid-crat3>3.0.co;2-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Self-organized semiconductor nanostructures: shape, strain and composition. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2002. [DOI: 10.1016/s0928-4931(01)00415-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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