Supporting information for: A highly directional room-temperature single. photon device

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1 Supporting information for: A highly directional room-temperature single photon device Nitzan Livneh,, Moshe G. Harats,, Daniel Istrati, Hagai S. Eisenberg, and Ronen Rapaport,, Applied Physics Department, The Hebrew University of Jerusalem, Jerusalem Racah Institute for Physics, The Hebrew University of Jerusalem, Jerusalem These authors contributed equally to the paper ronenr@phys.huji.ac.il Sample Fabrication In the following we give an outline of the fabrication process: a thick layer of Ag was e- beam evaporated on a Si substrate. Ag bulls-eye gratings and fine re-alignment marks were fabricated on top of the Ag layer using standard e-beam lithography followed by a liftoff process. Each bulls-eye grating had 25 periods, which according to our simulations, should result in a nearly full extraction of the emitted photons S1 to the desired direction. On top of the grating a 250nm layer of SiO 2 was deposited using PECVD, to set the vertical position of the NQD layer. Next, a layer of 100nm of NQDs embedded in PMMA with a concentration of 2 NQDs/µm 2 was spin-coated over the sample (The PMMA and NQD solution was made by diluting the NQD solution with Toluene and mixing with PMMA A11). Next, a second e-beam lithography and resist development was performed using the re-alignment S1

2 marks, removing the PMMA/NQD layer from the surface, but leaving a PMMA/NQDs disk at the center of each bulls-eye grating with a diameter of less than 1µm. S2 Then, by using a buffer solution of hydrofluoric acid (BHF) a partial removal the SiO 2 layer was performed, removing NQDs that were adsorbed to the surface during the development stage of the PMMA/NQD layer. To finalize the structure, another layer of PMMA (without NQDs) was spin-coated on the device, to achieve the desired thickness for the waveguide layer and a smooth upper surface with a roughness of less than λ/10. There still is some uncertainty in the exact position of the NQD in both the axial and vertical directions, because of the finite width and thickness of the PMMA/NQD disk which was left after the second e-beam step. The positioning has a strong influence on the efficiency and on the emission pattern. S1 A finer process calibration with a thinner PMMA layer and a smaller unexposed area a higher accuracy can be achieved, thus improving the efficiency and performance of future devices. This calibration should be done carefully as the BHF can harm the NQDs in the thinner PMMA/NQDs layer and the e-beam process can reduce the quantum yield of the NQDs due to the re-scattering of electrons during the writing process. In this method there is a Poissonian distribution for the number of NQDs in every nanoantenna. When the fabrication is perfectly calibrated to leave 1 NQD in average, the probability for having exactly 1 emitter is as high as 36.8%. The above fabrication process is scalable, and many devices can be made in parallel on the same chip, so a very large number of SPS devices can be fabricated in one procedure. Measurements The measurements were done using a home built scanning microscope with single photon detection and photon correlation measurement capabilities. The NQD was excited by a 1MHz pulsed laser, at 405nm. The pulse duration was 55ps, with an average intensity of 1µW. The excitation and PL collection were done using an NA=0.65 objective. The PL S2

3 was spectrally filtered from the laser using a dichroic beam splitter and spectral filters. The Fourier plane measurements were done by placing a lens that forms an image of the back focal plane of the objective onto a Hamamatsu ORCA CMOS camera. A movie of the blinking in Fourier plane was taken and analyzed. The movie can be viewed in the supplementary information section. The 2 nd order correlation measurements of photons were done in a free-space Hanbury- Brown Twiss (HBT) setup, with two Excelitas single photon detectors connected to a SensL timing module, working in time tagging mode. The lifetime measurements were done in a start-stop configuration, with the excitation laser trigger as the stop input. The collection efficiency as a function of NA, presented in blue and red in Fig. 4 of the main text, was calculated by integrating the signal over all azimuthal angles ϕ and all angles θ from θ = 0 up to θ = θ(na) in the measured Fourier plane image, and normalized to the measured collection efficiency at the maximal θ(n A = 0.65). The theoretical calculated efficiencies presented in Fig. 4a follows the detailed calculations explained in detail in Ref. S1 The different terms in the g (2) (τ) measurement The signal detected at each detector has two main sources: the photons from the NQD and photons emitted from the metallic nanostructure. The g (2) function can be decomposed to four separate correlation terms: g (2) (τ) = g (2) NQD;NQD (τ) + g(2) N;N (τ) + g(2) NQD;N (τ) + g(2) N;NQD (τ) (1) The subscript N stands for noise photons and NQD stand for photons emitted from the NQD. The first term is the pure correlation of the NQD photons, the second is a pure correlation of the noise photons, and the last two terms are mixed terms of the NQD and noise signals. We neglected the influence of random noise, that only raises the 0 level and is easily discarded in a pulsed g (2) (τ) measurement. In pulsed excitation, the pure NQD S3

4 term will result in peaks with the same decay coefficient as of the NQDs lifetime - τ NQD. The lifetime of the noise is much shorter than the resolution of the experimental setup, so the decay coefficient of the pure noise term will be limited by the timing resolution of the measurement setup, and of the binning done in the data analysis. For the purpose of this discussion we can assume it as instantaneous, i.e delta function decay. Since the correlation of a delta function and of a declining exponent keeps the same decay coefficient as of the original exponent, the decay coefficient of the mixed terms will also have a decay coefficient of τ NQD. When the NQD is in OFF state, the only measured term is g (2) N;N (τ). When the NQD is in ON state, all 4 terms are taken into account. Since the signal to noise ratio is of SNR > 3, the pure noise term is the least significant. Calculating the efficiency of the single photon device The efficiency of the optical setup was calculated according to the optical element properties in table S1. Multiplication of all the efficiencies yields a total efficiency of 17.6 ± 2.8%. Table S1: experimental setup efficiency and error range Element Efficiency Error collection objective lens 82% 2% 6 protected silver mirrors 77.3% 2% 700nm shortpass dichroic beam splitter 98% 1% 550nm longpass filter 95.5% 1% 750nm longpass filter 97% 1% 850nm shortpass filter 65% 5% beam splitter cube 92% 2% coupling efficiency into the detector fibers 80% 10% single photon detectors 64% 2% Total experimental setup efficiency 17.6% 2.8% With a 1MHz excitation and NQD lifetime of 170ns the maximum photon rate approaches 1M Hz. During ON periods we measured over 1000 photons per 50ms. About 750 of the photons are emitted from the NQD and about 250 photons are emitted from the S4

5 metal. This gives an effective ON-time collected photon rate of 15kHz. Assuming an internal NQD quantum efficiency of 0.8, an experimental excitation power at 30% of the saturation value, and a 17% optics and detector efficiency, the measured total collection efficiency of photons from our device, for photons emitted into NA = 0.65 (the whole collection cone of our measurement system) exceeds 35%. The collection efficiency from the reference single NQD was less than 12%. Without a nanoantenna the photons from the NQD are emitted mostly into the waveguide layer. As can be seen in Fig. 3f of the main text, the photons escaping the waveguide layer are emitted in all directions, but mostly into θ > 30. This results in a very low fraction of the photons emitted into a low numerical aperture cone. Table S2: The collection efficiency ε = 1/( ) = and error range Efficiency Error Experimental setup efficiency 17.6% 2.8% NQD quantum efficiency 80% 10% excitation intensity - % from saturation 30% 5% Estimated collection efficiency to NA= % 9.3% Simulating the NQD and noise g (2) (τ) The probability for two photon emission from the system was extracted by simulating data of a system composed of an ideal NQD and a noise source. The simulated NQD does not blink and has a probability of 1 to emit 1 photon for each excitation pulse (which is the case for ON states). The metal has a Poissonian emission statistics for each excitation pulse. The mean number of photons per pulse is the fitting parameter extracted form the simulation. The emitted photons are randomly split with a 50% probability to two detectors. The g (2) (τ) is then calculated with the same code used for calculating the g (2) (τ) of the measured data. The emission time of the photons was randomly picked with a lifetime of 100ns for single photons emitter, and with a lifetime of 1ns for the noise source. A ratio of 1 : 0.35 NQD photons:noise photons fits best to the experimental results, as seen in Fig. 4c in the main S5

6 text. For a Poissonian statistics it means that in more than 70% of the pulses, only an NQD photon is collected. These results are in agreement with previous works. S3 Fourier plane blinking movie The attached movie is a part the measurement used to create Fig. 3e. Each movie frame is of 50ms. The movie is displayed in half of the real-time frame rate, for more clarity. The white circles mark the PL angle. During ON periods are marked by a red ON on the upper left corner of the movie frame. References (S1) Livneh, N.; Harats, M. G.; Yochelis, S.; Paltiel, Y.; Rapaport, R. ACS Photonics 2015, (S2) Martiradonna, L.; Stomeo, T.; Giorgi, M. D.; Cingolani, R.; Vittorio, M. D. Microelectron. Eng. 2006, 83, (S3) Nair, G.; Zhao, J.; Bawendi, M. G. Nano Lett. 2011, 11, S6

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