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 light 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.
| Language | English |
|---|---|
| Pages | 5938-5948 |
| Journal | Nano Letters |
| Volume | 19 |
| Issue number | 9 |
| Early online date | 6 Aug 2019 |
| DOIs | |
| State | Published - Sep 2019 |
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Keywords
- (Al,Ga)N
- luminescence spectroscopy
- nanowire heterostructures
- polarization doping
- quantum-confined Stark effect
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Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy. / Sinito, C.; Corfdir, P.; Pfüller, C.; Gao, G.; Bartolomé, J.; Kölling, S.; Rodil Doblado, A.; Jahn, U.; Lähnemann, J.; Auzelle, T.; Zettler, J.K.; Flissikowski, T.; Koenraad, P.; Grahn, H.T.; Geelhaar, L.; Fernández-Garrido, S.; Brandt, O.
In: Nano Letters, Vol. 19, No. 9, 09.2019, p. 5938-5948.Research output: Contribution to journal › Article › Academic › peer-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 - Bartolomé,J.
AU - Kölling,S.
AU - Rodil Doblado,A.
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,O.
PY - 2019/9
Y1 - 2019/9
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 light 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 light 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 - (Al,Ga)N
KW - luminescence spectroscopy
KW - nanowire heterostructures
KW - polarization doping
KW - quantum-confined Stark effect
UR - http://www.scopus.com/inward/record.url?scp=85072012146&partnerID=8YFLogxK
U2 - 10.1021/acs.nanolett.9b01521
DO - 10.1021/acs.nanolett.9b01521
M3 - Article
VL - 19
SP - 5938
EP - 5948
JO - Nano Letters
T2 - Nano Letters
JF - Nano Letters
SN - 1530-6984
IS - 9
ER -