Limits...
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

Single-photon emission from an optimised device.(a) Image of the photoluminescence from a single QD within the cavity, collected under 630 nm LED illumination. Scale bar represents 5 μm. (b) Far-field image of the photoluminescence from a QD in a circular grating cavity, along with line cuts from the two-dimensional Gaussian fit to the data along the x and y axes, shown as solid white lines. The upper right inset shows a two-dimensional image plot of the interpolated data, while the bottom curves plot the (uninterpolated) experimental data (symbols) and their Gaussian fits (solid lines). (c) Photon flux into the 0.4 numerical aperture collection objective (left y axis) and at the detector (right y axis), plotted as a function of 780 nm excitation power (in saturation units), for a QD in a circular grating (QD in BE, red symbols) and in unpatterned GaAs (QD in bulk, black symbols). (d) Examples of photoluminescence spectra collected under different excitation power (colour coded in panel (c)). (e) Photon collection coincidence events measured under pulsed 857 nm excitation, using a Hanbury–Brown and Twiss set-up. The disappearance of the central peak (zoomed-in plot in the inset) is the signature of pure single-photon emission. The uncertainty value is given by the standard deviation in the area of the peaks away from time zero. See Supplementary Fig. 2 for additional relevant data. (f) Time-resolved photoluminescence measurements collected under pulsed 780 nm excitation, showing the excited state decays (symbols) fitted by single exponential curves (solid lines). The shaded grey areas correspond to the 95% confidence intervals in the fit.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4525159&req=5

f4: Single-photon emission from an optimised device.(a) Image of the photoluminescence from a single QD within the cavity, collected under 630 nm LED illumination. Scale bar represents 5 μm. (b) Far-field image of the photoluminescence from a QD in a circular grating cavity, along with line cuts from the two-dimensional Gaussian fit to the data along the x and y axes, shown as solid white lines. The upper right inset shows a two-dimensional image plot of the interpolated data, while the bottom curves plot the (uninterpolated) experimental data (symbols) and their Gaussian fits (solid lines). (c) Photon flux into the 0.4 numerical aperture collection objective (left y axis) and at the detector (right y axis), plotted as a function of 780 nm excitation power (in saturation units), for a QD in a circular grating (QD in BE, red symbols) and in unpatterned GaAs (QD in bulk, black symbols). (d) Examples of photoluminescence spectra collected under different excitation power (colour coded in panel (c)). (e) Photon collection coincidence events measured under pulsed 857 nm excitation, using a Hanbury–Brown and Twiss set-up. The disappearance of the central peak (zoomed-in plot in the inset) is the signature of pure single-photon emission. The uncertainty value is given by the standard deviation in the area of the peaks away from time zero. See Supplementary Fig. 2 for additional relevant data. (f) Time-resolved photoluminescence measurements collected under pulsed 780 nm excitation, showing the excited state decays (symbols) fitted by single exponential curves (solid lines). The shaded grey areas correspond to the 95% confidence intervals in the fit.

Mentions: Using the QD positions with respect to alignment marks as determined by photoluminescence imaging, emission wavelengths as determined by grating spectrometer measurements, and the aforementioned calibration of the circular grating geometry to match target wavelengths, we fabricate (see Methods section) a series of circular grating cavities containing single QDs. Photoluminescence imaging of the devices after fabrication, as shown in Fig. 4a for a representative device excited by the 630-nm LED, qualitatively indicates that the QD emission originates from the centre of the bullseye structure, as intended. A measurement of the far-field emission from the device on the EMCCD, as shown in Fig. 4b, shows that it is close to a circular Gaussian function, as confirmed by a nonlinear least squares fit. As the overlap with a perfect circular Gaussian is ≈70%, this far-field patten is expected to mode match well to a single-mode fibre, an important consideration for long-distance transmission of single photons for quantum information applications.


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)

Single-photon emission from an optimised device.(a) Image of the photoluminescence from a single QD within the cavity, collected under 630 nm LED illumination. Scale bar represents 5 μm. (b) Far-field image of the photoluminescence from a QD in a circular grating cavity, along with line cuts from the two-dimensional Gaussian fit to the data along the x and y axes, shown as solid white lines. The upper right inset shows a two-dimensional image plot of the interpolated data, while the bottom curves plot the (uninterpolated) experimental data (symbols) and their Gaussian fits (solid lines). (c) Photon flux into the 0.4 numerical aperture collection objective (left y axis) and at the detector (right y axis), plotted as a function of 780 nm excitation power (in saturation units), for a QD in a circular grating (QD in BE, red symbols) and in unpatterned GaAs (QD in bulk, black symbols). (d) Examples of photoluminescence spectra collected under different excitation power (colour coded in panel (c)). (e) Photon collection coincidence events measured under pulsed 857 nm excitation, using a Hanbury–Brown and Twiss set-up. The disappearance of the central peak (zoomed-in plot in the inset) is the signature of pure single-photon emission. The uncertainty value is given by the standard deviation in the area of the peaks away from time zero. See Supplementary Fig. 2 for additional relevant data. (f) Time-resolved photoluminescence measurements collected under pulsed 780 nm excitation, showing the excited state decays (symbols) fitted by single exponential curves (solid lines). The shaded grey areas correspond to the 95% confidence intervals in the fit.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Single-photon emission from an optimised device.(a) Image of the photoluminescence from a single QD within the cavity, collected under 630 nm LED illumination. Scale bar represents 5 μm. (b) Far-field image of the photoluminescence from a QD in a circular grating cavity, along with line cuts from the two-dimensional Gaussian fit to the data along the x and y axes, shown as solid white lines. The upper right inset shows a two-dimensional image plot of the interpolated data, while the bottom curves plot the (uninterpolated) experimental data (symbols) and their Gaussian fits (solid lines). (c) Photon flux into the 0.4 numerical aperture collection objective (left y axis) and at the detector (right y axis), plotted as a function of 780 nm excitation power (in saturation units), for a QD in a circular grating (QD in BE, red symbols) and in unpatterned GaAs (QD in bulk, black symbols). (d) Examples of photoluminescence spectra collected under different excitation power (colour coded in panel (c)). (e) Photon collection coincidence events measured under pulsed 857 nm excitation, using a Hanbury–Brown and Twiss set-up. The disappearance of the central peak (zoomed-in plot in the inset) is the signature of pure single-photon emission. The uncertainty value is given by the standard deviation in the area of the peaks away from time zero. See Supplementary Fig. 2 for additional relevant data. (f) Time-resolved photoluminescence measurements collected under pulsed 780 nm excitation, showing the excited state decays (symbols) fitted by single exponential curves (solid lines). The shaded grey areas correspond to the 95% confidence intervals in the fit.
Mentions: Using the QD positions with respect to alignment marks as determined by photoluminescence imaging, emission wavelengths as determined by grating spectrometer measurements, and the aforementioned calibration of the circular grating geometry to match target wavelengths, we fabricate (see Methods section) a series of circular grating cavities containing single QDs. Photoluminescence imaging of the devices after fabrication, as shown in Fig. 4a for a representative device excited by the 630-nm LED, qualitatively indicates that the QD emission originates from the centre of the bullseye structure, as intended. A measurement of the far-field emission from the device on the EMCCD, as shown in Fig. 4b, shows that it is close to a circular Gaussian function, as confirmed by a nonlinear least squares fit. As the overlap with a perfect circular Gaussian is ≈70%, this far-field patten is expected to mode match well to a single-mode fibre, an important consideration for long-distance transmission of single photons for quantum information applications.

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