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Heyn C, Gräfenstein A, Pirard G, Ranasinghe L, Deneke K, Alshaikh A, Bester G, Hansen W. Dot-Size Dependent Excitons in Droplet-Etched Cone-Shell GaAs Quantum Dots. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:nano12172981. [PMID: 36080018 PMCID: PMC9457581 DOI: 10.3390/nano12172981] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 08/25/2022] [Accepted: 08/26/2022] [Indexed: 06/01/2023]
Abstract
Strain-free GaAs quantum dots (QDs) are fabricated by filling droplet-etched nanoholes in AlGaAs. Using a template of nominally identical nanoholes, the QD size is precisely controlled by the thickness of the GaAs filling layer. Atomic force microscopy indicates that the QDs have a cone-shell shape. From single-dot photoluminescence measurements, values of the exciton emission energy (1.58...1.82 eV), the exciton-biexciton splitting (1.8...2.5 meV), the exciton radiative lifetime of bright (0.37...0.58 ns) and dark (3.2...6.7 ns) states, the quantum efficiency (0.89...0.92), and the oscillator strength (11.2...17.1) are determined as a function of the dot size. The experimental data are interpreted by comparison with an atomistic model.
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Affiliation(s)
- Christian Heyn
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Andreas Gräfenstein
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Geoffrey Pirard
- Physical Chemistry and Physics Departments, University of Hamburg, HARBOR Build., Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Leonardo Ranasinghe
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Kristian Deneke
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Ahmed Alshaikh
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Gabriel Bester
- Physical Chemistry and Physics Departments, University of Hamburg, HARBOR Build., Luruper Chaussee 149, 22761 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Wolfgang Hansen
- Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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Martin Lanzoni E, Covre da Silva SF, Knopper MF, Garcia AJ, Costa CAR, Deneke C. Imaging the electrostatic landscape of unstrained self-assemble GaAs quantum dots. NANOTECHNOLOGY 2022; 33:165701. [PMID: 34983039 DOI: 10.1088/1361-6528/ac47ce] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 01/03/2022] [Indexed: 06/14/2023]
Abstract
Unstrained GaAs quantum dots are promising candidates for quantum information devices due to their optical properties, but their electronic properties have remained relatively unexplored until now. In this work, we systematically investigate the electronic structure and natural charging of GaAs quantum dots at room temperature using Kelvin probe force microscopy (KPFM). We observe a clear electrical signal from these structures demonstrating a lower surface potential in the middle of the dot. We ascribe this to charge accumulation and confinement inside these structures. Our systematical investigation reveals that the change in surface potential is larger for a nominal dot filling of 2 nm and then starts to decrease for thicker GaAs layers. Usingk·pcalculation, we show that the confinement comes from the band bending due to the surface Fermi level pinning. We find a correlation between the calculated charge density and the KPFM signal indicating thatk·pcalculations could be used to estimate the KPFM signal for a given structure. Our results suggest that these self-assembled structures could be used to study physical phenomena connected to charged quantum dots like Coulomb blockade or Kondo effect.
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Affiliation(s)
- Evandro Martin Lanzoni
- São Paulo State University (UNESP), Institute of Science and Technology, 18087-180 Sorocaba, Brazil
- Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970 Campinas, Brazil
- University of Luxembourg, Physics and Materials Science Research Unit, 1511 Luxembourg, Luxembourg
| | - Saimon F Covre da Silva
- Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970 Campinas, Brazil
- Universidade Federal de Viçosa (UFV), Departamento de Física, 36570-000 Viçosa, Brasil
| | - Matthijn Floris Knopper
- Eindhoven University of Technology (TU/e), Department of Applied Physics, 5600 Eindhoven,The Netherland
| | - Ailton J Garcia
- Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970 Campinas, Brazil
- Universidade Estadual de Campinas, Instituto de Física 'Gleb Wataghin', 13083-859 Campinas, Brazil
| | - Carlos Alberto Rodrigues Costa
- Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970 Campinas, Brazil
| | - Christoph Deneke
- Universidade Estadual de Campinas, Instituto de Física 'Gleb Wataghin', 13083-859 Campinas, Brazil
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Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature. NANOMATERIALS 2021; 11:nano11030690. [PMID: 33802007 PMCID: PMC8001385 DOI: 10.3390/nano11030690] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/03/2021] [Accepted: 03/06/2021] [Indexed: 11/16/2022]
Abstract
Epitaxially grown quantum dots (QDs) are established as quantum emitters for quantum information technology, but their operation under ambient conditions remains a challenge. Therefore, we study photoluminescence (PL) emission at and close to room temperature from self-assembled strain-free GaAs quantum dots (QDs) in refilled AlGaAs nanoholes on (001)GaAs substrate. Two major obstacles for room temperature operation are observed. The first is a strong radiative background from the GaAs substrate and the second a significant loss of intensity by more than four orders of magnitude between liquid helium and room temperature. We discuss results obtained on three different sample designs and two excitation wavelengths. The PL measurements are performed at room temperature and at T = 200 K, which is obtained using an inexpensive thermoelectric cooler. An optimized sample with an AlGaAs barrier layer thicker than the penetration depth of the exciting green laser light (532 nm) demonstrates clear QD peaks already at room temperature. Samples with thin AlGaAs layers show room temperature emission from the QDs when a blue laser (405 nm) with a reduced optical penetration depth is used for excitation. A model and a fit to the experimental behavior identify dissociation of excitons in the barrier below T = 100 K and thermal escape of excitons from QDs above T = 160 K as the central processes causing PL-intensity loss.
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Schimpf C, Reindl M, Klenovský P, Fromherz T, Covre Da Silva SF, Hofer J, Schneider C, Höfling S, Trotta R, Rastelli A. Resolving the temporal evolution of line broadening in single quantum emitters. OPTICS EXPRESS 2019; 27:35290-35307. [PMID: 31878701 DOI: 10.1364/oe.27.035290] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 10/31/2019] [Indexed: 06/10/2023]
Abstract
Light emission from solid-state quantum emitters is inherently prone to environmental decoherence, which results in a line broadening and in the deterioration of photon indistinguishability. Here we employ photon correlation Fourier spectroscopy (PCFS) to study the temporal evolution of such a broadening in two prominent systems: GaAs and In(Ga)As quantum dots. Differently from previous experiments, the emitters are driven with short laser pulses as required for the generation of high-purity single photons, the time scales we probe range from a few nanoseconds to milliseconds and, simultaneously, the spectral resolution we achieve can be as small as ∼ 2µeV. We find pronounced differences in the temporal evolution of different optical transition lines, which we attribute to differences in their homogeneous linewidth and sensitivity to charge noise. We analyze the effect of irradiation with additional white light, which reduces blinking at the cost of enhanced charge noise. Due to its robustness against experimental imperfections and its high temporal resolution and bandwidth, PCFS outperforms established spectroscopy techniques, such as Michelson interferometry. We discuss its practical implementation and the possibility to use it to estimate the indistinguishability of consecutively emitted single photons for applications in quantum communication and photonic-based quantum information processing.
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da Silva SFC, Mardegan T, de Araújo SR, Ramirez CAO, Kiravittaya S, Couto ODD, Iikawa F, Deneke C. Fabrication and Optical Properties of Strain-free Self-assembled Mesoscopic GaAs Structures. NANOSCALE RESEARCH LETTERS 2017; 12:61. [PMID: 28110446 PMCID: PMC5253139 DOI: 10.1186/s11671-016-1782-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 12/09/2016] [Indexed: 06/06/2023]
Abstract
We use a combined process of Ga-assisted deoxidation and local droplet etching to fabricate unstrained mesoscopic GaAs/AlGaAs structures exhibiting a high shape anisotropy with a length up to 1.2 μm and a width of 150 nm. We demonstrate good controllability over size and morphology of the mesoscopic structures by tuning the growth parameters. Our growth method yields structures, which are coupled to a surrounding quantum well and present unique optical emission features. Microscopic and optical analysis of single structures allows us to demonstrate that single structure emission originates from two different confinement regions, which are spectrally separated and show sharp excitonic lines. Photoluminescence is detected up to room temperature making the structures the ideal candidates for strain-free light emitting/detecting devices.
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Affiliation(s)
- Saimon Filipe Covre da Silva
- Laboratório Nacional de Nanotecnologia (LNNano/CNPEM), 13083-100 Campinas, SP Brazil
- Departamento de Física, Universidade Federal de Viçosa, 36570-900 Viçosa, MG Brazil
| | - Thayná Mardegan
- Laboratório Nacional de Nanotecnologia (LNNano/CNPEM), 13083-100 Campinas, SP Brazil
- Universidade Federal de Itajubá, Campus Itabira, 35903-087 Itabira, MG Brazil
| | | | | | - Suwit Kiravittaya
- Department of Electrical and Computer Engineering, Faculty of Engineering, Naresuan University, Phitsanulok, 65000 Thailand
| | - Odilon D. D. Couto
- Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas, 13083-859 Campinas, SP Brazil
| | - Fernando Iikawa
- Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas, 13083-859 Campinas, SP Brazil
| | - Christoph Deneke
- Laboratório Nacional de Nanotecnologia (LNNano/CNPEM), 13083-100 Campinas, SP Brazil
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Küster A, Heyn C, Ungeheuer A, Juska G, Tommaso Moroni S, Pelucchi E, Hansen W. Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures. NANOSCALE RESEARCH LETTERS 2016; 11:282. [PMID: 27255902 PMCID: PMC4891312 DOI: 10.1186/s11671-016-1495-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 05/23/2016] [Indexed: 06/02/2023]
Abstract
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.
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Affiliation(s)
- Achim Küster
- Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany.
| | - Christian Heyn
- Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany
| | - Arne Ungeheuer
- Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany
| | - Gediminas Juska
- Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland
| | - Stefano Tommaso Moroni
- Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland
| | - Emanuele Pelucchi
- Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland
| | - Wolfgang Hansen
- Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany
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Sonnenberg D, Küster A, Graf A, Heyn C, Hansen W. Vertically stacked quantum dot pairs fabricated by nanohole filling. NANOTECHNOLOGY 2014; 25:215602. [PMID: 24784358 DOI: 10.1088/0957-4484/25/21/215602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Strain-free, vertically coupled GaAs quantum dots (QDs) with an ultra-low density below 1 × 10(7) cm(-2) are fabricated by filling of self-assembled nanoholes with a GaAs/AlGaAs/GaAs layer sequence. The sizes of the two QDs, forming a QD pair (QDP), as well as the AlGaAs tunnel-barrier between the dots are tuned independently. We present atomic force microscopy studies of the QDP formation steps. We have performed photoluminescence studies of single QDPs with varied dot size and tunnel-barrier thickness. The data indicate non-resonant tunnelling between the dots. Furthermore, we apply the quantum confined Stark effect to tune the photoluminescence energy by up to 25 meV.
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Affiliation(s)
- D Sonnenberg
- Institute of Applied Physics, University of Hamburg, D-20355 Hamburg, Germany
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Li X, Wu J, Wang ZM, Liang B, Lee J, Kim ES, Salamo GJ. Origin of nanohole formation by etching based on droplet epitaxy. NANOSCALE 2014; 6:2675-2681. [PMID: 24445506 DOI: 10.1039/c3nr06064k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Creating and manipulating materials at the nanoscale with controllable size, shape and nucleation site is an important task to meet the urgent demands for quantum structures with designed properties. In the last ten years, droplet epitaxy has been emerging as a versatile fabrication method for various complex nanostructures, such as quantum dots, quantum rings, double-rings, and so on. However, there is a lack of understanding of the deep nanohole formation based on droplet epitaxy at a high substrate temperature. Here we fabricate self-organized GaAs nanoholes by Ga droplet etching at high temperature based on droplet epitaxy, and they present good optoelectronic properties and have promising applications in fabrication of nanodevices due to their unique topology. A theoretical model is correspondingly proposed to explain the basic mechanism and simulate the time evolution of the nanohole structures. Our analysis shows that the morphology of the nanohole nanostructures can be well controlled through regulating experimental conditions.
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Affiliation(s)
- Xinlei Li
- MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, P. R. China.
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Polojärvi V, Schramm A, Guina M, Stemmann A, Heyn C. Stacked GaAs quantum dots fabricated by refilling of self-organized nanoholes: optical properties and post-growth annealing. NANOTECHNOLOGY 2011; 22:105603. [PMID: 21289401 DOI: 10.1088/0957-4484/22/10/105603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We study the photoluminescence and impact of post-growth annealing of stacked, strain-free GaAs quantum dots fabricated by refilling of self-organized nanoholes using molecular beam epitaxy. Temperature- and power-dependent photoluminescence studies reveal an excellent optical quality of the quantum-dot stack. After high-temperature post-growth annealing only slight blueshifts and an increase in full width at half-maximum of the photoluminescence peak are observed, indicating very high-temperature stability and crystalline quality of the stacked GaAs quantum-dot structure.
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Affiliation(s)
- Ville Polojärvi
- Optoelectronics Research Centre, Tampere University of Technology, FIN-33101 Tampere, Finland
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