Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy

C. Sinito (Corresponding author), P. Corfdir, C. Pfüller, G. Gao, J. Bartolomé Vílchez, S. Kölling, A. Rodil Doblado, U. Jahn, J. Lähnemann, T. Auzelle, J. K. Zettler, T. Flissikowski, P. Koenraad, H.T. Grahn, L. Geelhaar, S. Fernández-Garrido, Oliver Brandt (Corresponding author)

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al deficient core and an Al rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies, but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.
LanguageEnglish
JournalNano Letters
DOIs
StateE-pub ahead of print - 6 Aug 2019

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Stark effect
Molecular beam epitaxy
Nanowires
nanowires
molecular beam epitaxy
Electron gas
Spontaneous emission
radiative lifetime
Quantum efficiency
ultraviolet radiation
spontaneous emission
Carrier concentration
Light emitting diodes
electron gas
Heterojunctions
quantum efficiency
Screening
Energy gap
light emitting diodes
screening

Keywords

    Cite this

    Sinito, C. ; Corfdir, P. ; Pfüller, C. ; Gao, G. ; Vílchez, J. Bartolomé ; Kölling, S. ; Doblado, A. Rodil ; Jahn, U. ; Lähnemann, J. ; Auzelle, T. ; Zettler, J. K. ; Flissikowski, T. ; Koenraad, P. ; Grahn, H.T. ; Geelhaar, L. ; Fernández-Garrido, S. ; Brandt, Oliver. / Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy. In: Nano Letters. 2019
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    title = "Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy",
    abstract = "Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al deficient core and an Al rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies, but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.",
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    author = "C. Sinito and P. Corfdir and C. Pf{\"u}ller and G. Gao and V{\'i}lchez, {J. Bartolom{\'e}} and S. K{\"o}lling and Doblado, {A. Rodil} and U. Jahn and J. L{\"a}hnemann and T. Auzelle and Zettler, {J. K.} and T. Flissikowski and P. Koenraad and H.T. Grahn and L. Geelhaar and S. Fern{\'a}ndez-Garrido and Oliver Brandt",
    note = "This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters (2019), copyright (C) American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.9b01521, the supporting information is available (free of charge) under the same link",
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    Sinito, C, Corfdir, P, Pfüller, C, Gao, G, Vílchez, JB, Kölling, S, Doblado, AR, Jahn, U, Lähnemann, J, Auzelle, T, Zettler, JK, Flissikowski, T, Koenraad, P, Grahn, HT, Geelhaar, L, Fernández-Garrido, S & Brandt, O 2019, 'Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy' Nano Letters. DOI: 10.1021/acs.nanolett.9b01521

    Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy. / Sinito, C. (Corresponding author); Corfdir, P.; Pfüller, C.; Gao, G.; Vílchez, J. Bartolomé; Kölling, S.; Doblado, A. Rodil; Jahn, U.; Lähnemann, J.; Auzelle, T.; Zettler, J. K.; Flissikowski, T.; Koenraad, P.; Grahn, H.T.; Geelhaar, L.; Fernández-Garrido, S.; Brandt, Oliver (Corresponding author).

    In: Nano Letters, 06.08.2019.

    Research output: Contribution to journalArticleAcademicpeer-review

    TY - JOUR

    T1 - Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy

    AU - Sinito,C.

    AU - Corfdir,P.

    AU - Pfüller,C.

    AU - Gao,G.

    AU - Vílchez,J. Bartolomé

    AU - Kölling,S.

    AU - Doblado,A. Rodil

    AU - Jahn,U.

    AU - Lähnemann,J.

    AU - Auzelle,T.

    AU - Zettler,J. K.

    AU - Flissikowski,T.

    AU - Koenraad,P.

    AU - Grahn,H.T.

    AU - Geelhaar,L.

    AU - Fernández-Garrido,S.

    AU - Brandt,Oliver

    N1 - This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters (2019), copyright (C) American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.9b01521, the supporting information is available (free of charge) under the same link

    PY - 2019/8/6

    Y1 - 2019/8/6

    N2 - Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al deficient core and an Al rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies, but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.

    AB - Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al deficient core and an Al rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies, but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.

    KW - cond-mat.mes-hall

    KW - cond-mat.mtrl-sci

    KW - physics.app-ph

    U2 - 10.1021/acs.nanolett.9b01521

    DO - 10.1021/acs.nanolett.9b01521

    M3 - Article

    JO - Nano Letters

    T2 - Nano Letters

    JF - Nano Letters

    SN - 1530-6984

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