Field effect enhancement in buffered quantum nanowire networks

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Field effect enhancement in buffered quantum nanowire networks

Filip Krizek, Joachim E. Sestoft, Pavel Aseev, Sara Marti-Sanchez, Saulius Vaitiekėnas, Lucas Casparis, Sabbir A. Khan, Yu Liu, Tomaš Stankevič, Alexander M. Whiticar, Alexandra Fursina, Frenk Boekhout, Rene Koops, Emanuele Uccelli, Leo P. Kouwenhoven, Charles M. Marcus, Jordi Arbiol, and Peter Krogstrup

Phys. Rev. Materials 2, 093401 – Published 7 September 2018

Abstract

III–V semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable high-quality nanowire-based platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer layers, where Sb is used as a surfactant. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of field effect mobility. We show that the networks possess strong spin-orbit interaction and long phase-coherence lengths with a temperature dependence indicating ballistic transport. With these findings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulfills the requirements for a wide range of quantum experiments and applications.

Received 18 April 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.2.093401

Physics Subject Headings (PhySH)

Aharonov-Bohm effect Crystal growth Nanocrystals Network formation & growth Quantum networks Rashba coupling Topological materials Topological quantum computing Topological superconductors

Condensed Matter, Materials & Applied PhysicsNetworksGeneral PhysicsQuantum Information, Science & Technology

Authors & Affiliations

Filip Krizek^1,*, Joachim E. Sestoft^1,*, Pavel Aseev^2,*, Sara Marti-Sanchez³, Saulius Vaitiekėnas¹, Lucas Casparis¹, Sabbir A. Khan¹, Yu Liu¹, Tomaš Stankevič¹, Alexander M. Whiticar¹, Alexandra Fursina⁴, Frenk Boekhout⁵, Rene Koops⁵, Emanuele Uccelli⁵, Leo P. Kouwenhoven^2,4, Charles M. Marcus¹, Jordi Arbiol^3,6, and Peter Krogstrup^1,†

¹Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
²QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
³Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, Catalonia, Spain
⁴Microsoft Station Q, Delft University of Technology, 2600 GA Delft, The Netherlands
⁵QuTech and Netherlands Organization for Applied Scientific Research (TNO), Stieltjesweg 1, 2628 CK Delft, The Netherlands
⁶ICREA, Passeig de Lluís Companys 23, 08010 Barcelona, Catalonia, Spain

^*These authors contributed equally to this work.
^†krogstrup@nbi.dk

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Vol. 2, Iss. 9 — September 2018

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Images

Figure 1
(a) SEM micrograph of 10- $μ m$ -long [100] InAs NWs grown on InP (001) with a ${SiO}_{x}$ mask. Inset shows a HAADF-STEM cross-section image of a NW, where the orientation and faceting is color correlated to the stereographic projection in (b). (b) Stereographic projection including the high-symmetry orientations of a [100] substrate, where the perimeter corresponds to in-plane NW directions (box fill color), with the facets normal to the NW given by the perpendicular orientations (corresponding border color). The graphics overlay an SEM micrograph of NWs selectively grown at increments of $3^{\circ}$ . Zoom-in shows a [100] NW grown next to off-axis NWs with roughened and vicinal faceting. (c) SEM micrographs of three NW networks aligned along the [110], $[1 \bar{1} 0]$ , and [100] directions. (d) SEM micrograph of [100]/[010] NW network junctions. Zoom-in shows how the crystal symmetry results in twofold-symmetric junctions indicated by the polar (111)A and (111)B facets.
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Figure 2
(a) SEM micrograph of a selectively grown GaAs(Sb) NW network. (b) AFM scans showing flat (001) top facets of GaAs(Sb) networks aligned along the [100]/[010] directions. Zoom-ins on highlighted areas show the extracted roughness of the top facet of a junction and a straight NW. (c) SEM micrograph of InAs NWs selectively grown on the top facet of the buffer. Inset shows the InAs NW morphology evolution with growth time, $t_{1 - 3}$ . (d) SEM micrographs of InAs NWs grown on the buffer in the three highest in-plane symmetry directions. The cross-section shapes of NWs from the same growth are presented in Figs. 3.
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Figure 3
Cross-section TEM micrographs of top-gated devices with InAs NWs grown on top of GaAs(Sb) buffer layers along the (a) [100], (b) $[1 \bar{1} 0]$ , and (c) [110] orientations. Top right insets are cross-sectional HAADF-STEM images of the InAs NW segments with pure crystalline structures, where the illustrated high-symmetry plane highlights the related facet polarity (As atoms, white; In atoms, blue). Bottom right insets show geometric phase analysis (GPA) rotational maps around the (111) planes. Scale bars are 50 nm. (d) GPA rotational map simulation for a [100]-oriented buffered NW showing elastic strain relaxation profiles. Scale bar is 50 nm. (e) Atomic-resolution aberration-corrected HAADF-STEM micrograph of the interface indicated in (b) showing misfit dislocations and strain. The bottom panel is the same image after fast Fourier transform (FFT) filtering, with a highlighted aperiodic misfit dislocation array. The blue line indicates the interface. (f) Atomic-resolution aberration-corrected HAADF-STEM micrograph of the interface indicated in (c) showing no misfit dislocations and pronounced strain as indicated by the white dashed lines (no strain) and red line (the actual plane displacement). The bottom panel is the same image after FFT filtering, with no visible misfit dislocations.
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Figure 4
(a) False-colored SEM micrograph of a typical top-gated four-probe NW device. Yellow, Ti/Au contacts; blue, gates; grey, InAs NW; $V_{SD}$ , bias voltage; $I$ , measured current; $V_{g}$ , gate voltage controlling the chemical potential; $W$ , gate width. (b) Conductance, $G$ , as a function of $V_{g}$ , for InAs grown on a GaAs substrate. Sketches illustrate the carrier density distribution as a function of $V_{g}$ . The two regimes correspond to transport residing in the whole InAs transport channel (lower negative $V_{g}$ ) and at the InAs/substrate interface (more negative $V_{g}$ ). (c) Conductance as a function of $V_{g}$ for InAs NWs grown on the GaAs(Sb) buffer along the [110], $[1 \bar{1} 0]$ , and [100] directions. (d) Resistance, $R$ , as a function of $V_{g}$ for multiple NW samples grown directly on InP, GaAs, and the buffer layer.
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Figure 5
(a, b) False-colored SEM micrographs of the four-probe NW loop devices. (c, d) Change in resistance, $Δ R$ , as a function of perpendicular magnetic field, $B_{⊥}$ , over a 100-mT range showing electron phase interference oscillations for the larger and smaller loop, respectively. (e) Overview SEM and cross-section HAADF-STEM micrographs of the Aharonov-Bohm loop structure showing the asymmetric cross-section. The dashed white line indicates where the cross-section was made. Scale bar corresponds to 500 nm. (f) Integrated FFT of the oscillations plotted as a function of temperature. The fitted line corresponds to the linear fit of the $h / e$ oscillation amplitudes and yields $l_{ϕ} \sim$ 13 $μ m$ . (g) Offset magnetoconductance traces showing WAL effects around $B = 0$ , for the diffusive and ballistic regime WAL expression fit.
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