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Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission.

Sapienza L, Davanço M, Badolato A, Srinivasan K - Nat Commun (2015)

Bottom Line: Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications.However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes.Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices.

View Article: PubMed Central - PubMed

Affiliation: 1] Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA [2] Maryland NanoCenter, University of Maryland, College Park, Maryland 20742, USA [3] School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK.

ABSTRACT
Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (≈3).

No MeSH data available.


Related in: MedlinePlus

Optically locating single QDs.(a) Schematic of the photoluminescence imaging set-up. An infrared LED (emission centred at 940 nm) is used for illumination of the sample while either a 630-nm red LED or a 780-nm laser is used for excitation of the QDs, depending on whether excitation over a broad area (LED) or of individual QDs (laser) is required. Samples are placed within a cryostat on an x–y–z positioner. Imaging is done by directing the emitted and reflected light into an EMCCD camera, while spectroscopy is performed by collecting emission into a single-mode fibre and sending it to a grating spectrometer. (b) Example photoluminescence image from single QDs measured under red LED illumination only. A 900-nm LPF is inserted into the collection path when measuring the QD emission. (c) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the photoluminescence image, showing the profiles of the QD emission (symbols) and their Gaussian fits (lines). (d) Example image of the reflected light from the metallic alignment marks under red LED illumination only. (e) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the image in (d), showing the profiles of the reflected light from the metallic alignment marks (symbols) and their Gaussian fits (lines). (f) Peak position uncertainties measured from the Gaussian fits of line cuts of the EMCCD images, plotted as a function of magnification and field of view for the QD and metallic alignment marks. The uncertainties represent 1 standard deviation values determined by a nonlinear least squares fit of the data.
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f1: Optically locating single QDs.(a) Schematic of the photoluminescence imaging set-up. An infrared LED (emission centred at 940 nm) is used for illumination of the sample while either a 630-nm red LED or a 780-nm laser is used for excitation of the QDs, depending on whether excitation over a broad area (LED) or of individual QDs (laser) is required. Samples are placed within a cryostat on an x–y–z positioner. Imaging is done by directing the emitted and reflected light into an EMCCD camera, while spectroscopy is performed by collecting emission into a single-mode fibre and sending it to a grating spectrometer. (b) Example photoluminescence image from single QDs measured under red LED illumination only. A 900-nm LPF is inserted into the collection path when measuring the QD emission. (c) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the photoluminescence image, showing the profiles of the QD emission (symbols) and their Gaussian fits (lines). (d) Example image of the reflected light from the metallic alignment marks under red LED illumination only. (e) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the image in (d), showing the profiles of the reflected light from the metallic alignment marks (symbols) and their Gaussian fits (lines). (f) Peak position uncertainties measured from the Gaussian fits of line cuts of the EMCCD images, plotted as a function of magnification and field of view for the QD and metallic alignment marks. The uncertainties represent 1 standard deviation values determined by a nonlinear least squares fit of the data.

Mentions: An array of metal alignment marks is fabricated on quantum-dot-containing material through a standard lift-off process before sample interrogation (see Methods section). The samples are then placed on a stack of piezo-electric stages to allow motion along three orthogonal axes (x,y,z) within a closed-cycle cryostat that reaches temperatures as low as 6 K. The simplest photoluminescence imaging configuration we use is a subset of Fig. 1a, and starts with excitation by a 630-nm light emitting diode (LED), which is sent through a 90/10 (reflection/transmission percentage) beamsplitter and through a 20 × infinity-corrected objective (0.4 numerical aperture) to produce an ≈200 μm diameter spot on the sample. Reflected light and fluorescence from the sample goes back through the 90/10 beamsplitter and is imaged onto an Electron Multiplied Charged Couple Device (EMCCD) using a variable zoom system. When imaging the fluorescence from the QDs, the 630-nm LED power is set to its maximum power (≈40 mW, corresponding to an intensity of ≈130 W cm−2), and a 900-nm long-pass filter (LPF) is inserted in front of the EMCCD camera to remove reflected 630 nm light. Imaging of the alignment marks is done by reducing the LED power to 0.8 mW, turning off the EMCCD gain and removing the 900-nm LPF.


Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission.

Sapienza L, Davanço M, Badolato A, Srinivasan K - Nat Commun (2015)

Optically locating single QDs.(a) Schematic of the photoluminescence imaging set-up. An infrared LED (emission centred at 940 nm) is used for illumination of the sample while either a 630-nm red LED or a 780-nm laser is used for excitation of the QDs, depending on whether excitation over a broad area (LED) or of individual QDs (laser) is required. Samples are placed within a cryostat on an x–y–z positioner. Imaging is done by directing the emitted and reflected light into an EMCCD camera, while spectroscopy is performed by collecting emission into a single-mode fibre and sending it to a grating spectrometer. (b) Example photoluminescence image from single QDs measured under red LED illumination only. A 900-nm LPF is inserted into the collection path when measuring the QD emission. (c) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the photoluminescence image, showing the profiles of the QD emission (symbols) and their Gaussian fits (lines). (d) Example image of the reflected light from the metallic alignment marks under red LED illumination only. (e) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the image in (d), showing the profiles of the reflected light from the metallic alignment marks (symbols) and their Gaussian fits (lines). (f) Peak position uncertainties measured from the Gaussian fits of line cuts of the EMCCD images, plotted as a function of magnification and field of view for the QD and metallic alignment marks. The uncertainties represent 1 standard deviation values determined by a nonlinear least squares fit of the data.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525159&req=5

f1: Optically locating single QDs.(a) Schematic of the photoluminescence imaging set-up. An infrared LED (emission centred at 940 nm) is used for illumination of the sample while either a 630-nm red LED or a 780-nm laser is used for excitation of the QDs, depending on whether excitation over a broad area (LED) or of individual QDs (laser) is required. Samples are placed within a cryostat on an x–y–z positioner. Imaging is done by directing the emitted and reflected light into an EMCCD camera, while spectroscopy is performed by collecting emission into a single-mode fibre and sending it to a grating spectrometer. (b) Example photoluminescence image from single QDs measured under red LED illumination only. A 900-nm LPF is inserted into the collection path when measuring the QD emission. (c) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the photoluminescence image, showing the profiles of the QD emission (symbols) and their Gaussian fits (lines). (d) Example image of the reflected light from the metallic alignment marks under red LED illumination only. (e) Two orthogonal line cuts (horizontal=x axis, vertical=y axis) of the image in (d), showing the profiles of the reflected light from the metallic alignment marks (symbols) and their Gaussian fits (lines). (f) Peak position uncertainties measured from the Gaussian fits of line cuts of the EMCCD images, plotted as a function of magnification and field of view for the QD and metallic alignment marks. The uncertainties represent 1 standard deviation values determined by a nonlinear least squares fit of the data.
Mentions: An array of metal alignment marks is fabricated on quantum-dot-containing material through a standard lift-off process before sample interrogation (see Methods section). The samples are then placed on a stack of piezo-electric stages to allow motion along three orthogonal axes (x,y,z) within a closed-cycle cryostat that reaches temperatures as low as 6 K. The simplest photoluminescence imaging configuration we use is a subset of Fig. 1a, and starts with excitation by a 630-nm light emitting diode (LED), which is sent through a 90/10 (reflection/transmission percentage) beamsplitter and through a 20 × infinity-corrected objective (0.4 numerical aperture) to produce an ≈200 μm diameter spot on the sample. Reflected light and fluorescence from the sample goes back through the 90/10 beamsplitter and is imaged onto an Electron Multiplied Charged Couple Device (EMCCD) using a variable zoom system. When imaging the fluorescence from the QDs, the 630-nm LED power is set to its maximum power (≈40 mW, corresponding to an intensity of ≈130 W cm−2), and a 900-nm long-pass filter (LPF) is inserted in front of the EMCCD camera to remove reflected 630 nm light. Imaging of the alignment marks is done by reducing the LED power to 0.8 mW, turning off the EMCCD gain and removing the 900-nm LPF.

Bottom Line: Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications.However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes.Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices.

View Article: PubMed Central - PubMed

Affiliation: 1] Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA [2] Maryland NanoCenter, University of Maryland, College Park, Maryland 20742, USA [3] School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK.

ABSTRACT
Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (≈3).

No MeSH data available.


Related in: MedlinePlus