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Spontaneous emission control of single quantum dots in bottom-up nanowire waveguides
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Image of FIG. 1.
FIG. 1.

(Color) (a) Scanning electron micrographs of nanowires grown on the same chip using 25 nm gold catalysts and varying pitch. All images were acquired at the same magnification with the sample tilted by 30° with respect to the electron beam. Vertical and horizontal scale bars represent 2 μm. (b) Dependence of the nanowire diameter on the wire-to-wire distance for 25 nm (red circles) and 50 nm (black squares) gold catalysts. Inset shows the pitch of the growth array, L. We observe an increase of the nanowire diameter as L is enlarged from 0.8 to 2 μm with a saturation at larger nanowire spacing. The dashed line indicates the transition from competitive to independent growth at L ∼ 3 μm.

Image of FIG. 2.
FIG. 2.

(Color) (a) Power dependent PL spectroscopy of a single InAsP quantum dot in an InP nanowire. The intensity of PL emission is displayed as color. (b) Integrated PL intensity for exciton (X, black squares) and biexciton (XX, blue circles) emission peaks, fitted with Poisson statistics using linear and quadratic coefficients, respectively. (c) PL spectrum at low excitation power (0.8 μW). The exciton emission exhibits a linewidth (FWHM) of 120 μeV.

Image of FIG. 3.
FIG. 3.

(Color) Exciton lifetime measured via time-resolved photoluminescence on five different quantum dots embedded in nanowires with different diameters. The photoluminescence intensity (circles) is shown in a logarithmic scale and each curve is fitted with a mono-exponential decay (blue lines). As the nanowire diameter is increased, and accordingly the D/λ ratio, the quantum dot emission mode is confined in the nanowire and couples to the fundamental waveguide mode with an increased rate. The result is a significant shortening of the exciton lifetime.

Image of FIG. 4.
FIG. 4.

(Color) Exciton lifetime for D/λ ratios ranging from 0.14 to 0.30. Each experimental point represents the exciton lifetime measured for a single quantum dot. The exciton lifetime is long for small nanowire diameters (black circle) and decreases as the fundamental waveguide mode becomes available for the emitter at larger diameters. We observe optimum photonic confinement conditions at D/λ ∼ 0.245, where quantum dots exhibit a lifetime of 2 ns (dotted circle) which approaches the lifetime predicted for the same material system in bulk (red dashed dotted line). The suppression of the quantum dot coupling to waveguide modes that we observe for thin nanowires compared to nanowires having optimum waveguide conditions results in an inhibition factor of 12 for the spontaneous emission rate. Error bars are provided for D/λ ratio due to the variation of nanowire diameter measured within the same growth pattern.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spontaneous emission control of single quantum dots in bottom-up nanowire waveguides