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Ayuso-Pérez I, Luna E, da Silva A, Ruhstorfer D, Matzeck M, Koblmüller G, Engel-Herbert R. Microscopic insights into metal diffusion and ohmic contact formation in delta-doped GaAs/(Al,Ga)As core/shell nanowires. NANOTECHNOLOGY 2024; 35:325206. [PMID: 38684144 DOI: 10.1088/1361-6528/ad449b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2024] [Accepted: 04/29/2024] [Indexed: 05/02/2024]
Abstract
Semiconductor nanowires (NWs) are promising candidates for use in electronic and optoelectronic applications, offering numerous advantages over their thin film counterparts. Their performance relies heavily on the quality of the contacts to the NW, which should exhibit ohmic behavior with low resistance and should be formed in a reproducible manner. In the case of heterostructure NWs for high-mobility applications that host a two-dimensional electron gas, ohmic contacts are particularly challenging to implement since the NW core constituting the conduction channel is away from the NW surface. We investigated contact formation to modulation-doped GaAs/(Al,Ga)As core/shell NWs using scanning transmission electron microscopy, energy dispersive x-ray spectroscopy and electron tomography to correlate microstructure, diffusion profile and chemical composition of the NW contact region with the current-voltage (I-V) characteristics of the contacted NWs. Our results illustrate how diffusion, alloying and phase formation processes essential to the effective formation of ohmic contacts are more intricate than in planar layers, leading to reproducibility challenges even when the processing conditions are the same. We demonstrate that the NW geometry plays a crucial role in the creation of good contacts. Both ohmic and rectifying contacts were obtained under nominally identical processing conditions. Furthermore, the presence of Ge in the NW core, in the absence of Au and Ni, was found as the key factor leading to ohmic contacts. The analysis contributes to the current understanding of ohmic contact formation to heterostructure core/shell NWs offering pathways to enhance the reproducibility and further optimization of such NW contacts.
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Affiliation(s)
- Irene Ayuso-Pérez
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
| | - Esperanza Luna
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
| | - Alessandra da Silva
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
| | - Daniel Ruhstorfer
- Walter-Schottky-Institut, School of Natural Sciences, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany
| | - Margarita Matzeck
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
| | - Gregor Koblmüller
- Walter-Schottky-Institut, School of Natural Sciences, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany
| | - Roman Engel-Herbert
- Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
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2
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Esmaielpour H, Isaev N, Makhfudz I, Döblinger M, Finley JJ, Koblmüller G. Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells. ACS APPLIED NANO MATERIALS 2024; 7:2817-2824. [PMID: 38357220 PMCID: PMC10863615 DOI: 10.1021/acsanm.3c05041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 12/08/2023] [Accepted: 12/11/2023] [Indexed: 02/16/2024]
Abstract
III-V nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core-shell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.
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Affiliation(s)
- Hamidreza Esmaielpour
- Walter
Schottky Institut, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
| | - Nabi Isaev
- Walter
Schottky Institut, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
| | - Imam Makhfudz
- IM2NP,
UMR CNRS 7334, Aix-Marseille Université, Marseille 13013, France
| | - Markus Döblinger
- Department
of Chemistry, Ludwig-Maximilians-University
Munich, Munich 81377, Germany
| | - Jonathan J. Finley
- Walter
Schottky Institut, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
| | - Gregor Koblmüller
- Walter
Schottky Institut, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
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3
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Huang C, Dede D, Morgan N, Piazza V, Hu X, Fontcuberta I Morral A, Lauhon LJ. Trapping Layers Prevent Dopant Segregation and Enable Remote Doping of Templated Self-Assembled InGaAs Nanowires. NANO LETTERS 2023. [PMID: 37402180 PMCID: PMC10375592 DOI: 10.1021/acs.nanolett.3c00281] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/06/2023]
Abstract
Selective area epitaxy is a promising approach to define nanowire networks for topological quantum computing. However, it is challenging to concurrently engineer nanowire morphology, for carrier confinement, and precision doping, to tune carrier density. We report a strategy to promote Si dopant incorporation and suppress dopant diffusion in remote doped InGaAs nanowires templated by GaAs nanomembrane networks. Growth of a dilute AlGaAs layer following doping of the GaAs nanomembrane induces incorporation of Si that otherwise segregates to the growth surface, enabling precise control of the spacing between the Si donors and the undoped InGaAs channel; a simple model captures the influence of Al on the Si incorporation rate. Finite element modeling confirms that a high electron density is produced in the channel.
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Affiliation(s)
- Chunyi Huang
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - Didem Dede
- Laboratory of Semiconductor Materials, Institute of Materials, EPFL, Route Cantonale, Lausanne, Vaud 1015, Switzerland
| | - Nicholas Morgan
- Laboratory of Semiconductor Materials, Institute of Materials, EPFL, Route Cantonale, Lausanne, Vaud 1015, Switzerland
| | - Valerio Piazza
- Laboratory of Semiconductor Materials, Institute of Materials, EPFL, Route Cantonale, Lausanne, Vaud 1015, Switzerland
| | - Xiaobing Hu
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
- The NUANCE Center, Northwestern University, Evanston, Illinois 60208, United States
| | - Anna Fontcuberta I Morral
- Laboratory of Semiconductor Materials, Institute of Materials, EPFL, Route Cantonale, Lausanne, Vaud 1015, Switzerland
| | - Lincoln J Lauhon
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
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4
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Schmiedeke P, Panciera F, Harmand JC, Travers L, Koblmüller G. Real-time thermal decomposition kinetics of GaAs nanowires and their crystal polytypes on the atomic scale. NANOSCALE ADVANCES 2023; 5:2994-3004. [PMID: 37260482 PMCID: PMC10228496 DOI: 10.1039/d3na00135k] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 05/02/2023] [Indexed: 06/02/2023]
Abstract
Nanowires (NWs) offer unique opportunities for tuning the properties of III-V semiconductors by simultaneously controlling their nanoscale dimensions and switching their crystal phase between zinc-blende (ZB) and wurtzite (WZ). While much of this control has been enabled by direct, forward growth, the reverse reaction, i.e., crystal decomposition, provides very powerful means to further tailor properties towards the ultra-scaled dimensional level. Here, we use in situ transmission electron microscopy (TEM) to investigate the thermal decomposition kinetics of clean, ultrathin GaAs NWs and the role of distinctly different crystal polytypes in real-time and on the atomic scale. The whole process, from the NW growth to the decomposition, is conducted in situ without breaking vacuum to maintain pristine crystal surfaces. Radial decomposition occurs much faster for ZB- compared to WZ-phase NWs, due to the development of nano-faceted sidewall morphology and sublimation along the entire NW length. In contrast, WZ NWs form single-faceted, vertical sidewalls with decomposition proceeding only via step-flow mechanism from the NW tip. Concurrent axial decomposition is generally faster than the radial process, but is significantly faster (∼4-fold) in WZ phase, due to the absence of well-defined facets at the tip of WZ NWs. The results further show quantitatively the influence of the NW diameter on the sublimation and step-flow decomposition velocities elucidating several effects that can be exploited to fine-tune the NW dimensions.
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Affiliation(s)
- Paul Schmiedeke
- Technical University of Munich, Walter Schottky Institute, TUM School of Natural Sciences, Physics Department Garching 85747 Germany
| | - Federico Panciera
- Centre for Nanoscience and Nanotechnology, CNRS, Université Paris-Saclay 10 Boulevard Thomas Gobert 91120 Palaiseau France
| | - Jean-Christophe Harmand
- Centre for Nanoscience and Nanotechnology, CNRS, Université Paris-Saclay 10 Boulevard Thomas Gobert 91120 Palaiseau France
| | - Laurent Travers
- Centre for Nanoscience and Nanotechnology, CNRS, Université Paris-Saclay 10 Boulevard Thomas Gobert 91120 Palaiseau France
| | - Gregor Koblmüller
- Technical University of Munich, Walter Schottky Institute, TUM School of Natural Sciences, Physics Department Garching 85747 Germany
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Aydin A, Fransson J, Sisman A. Quantum shape oscillations in the thermodynamic properties of confined electrons in core-shell nanostructures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:025301. [PMID: 34654006 DOI: 10.1088/1361-648x/ac303a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 10/15/2021] [Indexed: 06/13/2023]
Abstract
Quantum shape effect appears under the size-invariant shape transformations of strongly confined structures. Such a transformation distinctively influences the thermodynamic properties of confined particles. Due to their characteristic geometry, core-shell nanostructures are good candidates for quantum shape effects to be observed. Here we investigate the thermodynamic properties of non-interacting degenerate electrons confined in core-shell nanowires consisting of an insulating core and a GaAs semiconducting shell. We derive the expressions of shape-dependent thermodynamic quantities and show the existence of a new type of quantum oscillations due to shape dependence, in chemical potential, internal energy, entropy and specific heat of confined electrons. We provide physical understanding of our results by invoking the quantum boundary layer concept and evaluating the distributions of quantized energy levels on Fermi function and in state space. Besides the density, temperature and size, the shape per se also becomes a control parameter on the Fermi energy of confined electrons, which provides a new mechanism for fine tuning the Fermi level and changing the polarity of semiconductors.
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Affiliation(s)
- Alhun Aydin
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States of America
| | - Jonas Fransson
- Department of Physics and Astronomy, Uppsala University, 75120, Uppsala, Sweden
| | - Altug Sisman
- Department of Physics and Astronomy, Uppsala University, 75120, Uppsala, Sweden
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Del Giudice F, Becker J, de Rose C, Döblinger M, Ruhstorfer D, Suomenniemi L, Treu J, Riedl H, Finley JJ, Koblmüller G. Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties. NANOSCALE 2020; 12:21857-21868. [PMID: 33107547 DOI: 10.1039/d0nr05666a] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor-solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
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Affiliation(s)
- F Del Giudice
- Walter Schottky Institute and Physics Department, Technical University of Munich, Garching, Germany.
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Rezaie Heris H, Kateb M, Erlingsson SI, Manolescu A. Thermoelectric properties of tubular nanowires in the presence of a transverse magnetic field. NANOTECHNOLOGY 2020; 31:424006. [PMID: 32585640 DOI: 10.1088/1361-6528/aba02a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We calculate the charge and heat current associate with electrons, generated by a temperature gradient and chemical potential difference between two ends of a tubular nanowire of 30 nm radius in the presence of an external magnetic field perpendicular to its axis. We consider a nanowire based on a semiconductor material, and use the Landauer-Büttiker approach to calculate the transport quantities. We obtain the variation of the Seebeck coefficient (S), thermal conductivity (κ), and the figure of merit (ZT), with respect to the temperature up to 20 K, and with the magnetic field up to 3 T. In particular we show that the Seebeck coefficient can change sign in this domain of parameters. In addition κ and ZT have oscillations when the magnetic field increases. These oscillations are determined by the energy spectrum of the electrons.
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Affiliation(s)
- Hadi Rezaie Heris
- School of Science and Engineering, Reykjavik University, Menntavegur 1, IS-102 Reykjavik, Iceland
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