Research ArticleAPPLIED PHYSICS

Room temperature polariton lasing in quantum heterostructure nanocavities

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Science Advances  19 Apr 2019:
Vol. 5, no. 4, eaau9338
DOI: 10.1126/sciadv.aau9338
  • Fig. 1 Quantum heterostructure nanocavities.

    (A) Schematic illustration of a single nanorod polariton laser on an SiO2 substrate. The inset shows the shell structure, consisting of five pairs of Zn0.9Mg0.1O/ZnO QW layers. (B) SEM image of an as-grown QW nanorod array with an average rod diameter of ~600 nm and a rod length of ~2.7 μm. Scale bar, 1 μm. (C) STEM image showing a radial cross section of a QW nanorod. Scale bar, 100 nm. (D) Magnified STEM image of the QW region. The arrows indicate the ZnO wells. Scale bar, 20 nm. Note that the QW nanorod depicted in (C) and (D) was encapsulated with an additional ZnO layer to obtain high-contrast images of the QW region. (E) Elemental mapping images of an axial cross section of a QW nanorod, showing the conformal growth of QW layers on the core ZnO nanorod. Scale bar, 300 nm. (F) Exciton luminescence spectrum of a single QW nanorod at room temperature compared with the spectrum of a bare nanorod.

  • Fig. 2 Polariton dispersion at room temperature.

    (A) Excitonic (blue line) and waveguided (red line) PL spectra from the body center and end of a QW nanorod (diameter, 640 nm; length, 2.75 μm), respectively. The end emission exhibits multiple resonance peaks, which correspond to the eigenmodes of the exciton polaritons in the quantum heterostructure nanocavity. The dashed green lines represent the fitted Lorentzian line shapes used to determine the resonance energies in the lower polariton branch. The overall fitting line is displayed by the green line. The measurements were conducted using the 325-nm continuous-wave laser excitation at the power density of 670 W/cm2 for the acquisition time of 60 s. (B) Dispersion relation of the exciton polaritons along the long axis of the QW nanorod. The data points represent measured resonance energies with equidistant momenta at integer values of π/Lz, where Lz is the length of the nanorod. The orange solid line represents the fit to the theoretical model for the exciton polariton HE22-guided mode, indicating an estimated Rabi splitting energy of ~370 meV. The horizontal red dashed line represents the QW exciton energy. The inset shows the calculated electric field intensity (|Ey|2) profile in the radial cross-sectional plane for the HE22-guided mode at an energy of 3.20 eV, where white lines indicate the QW region. a.u., arbitrary units.

  • Fig. 3 Room temperature polariton lasing spectra.

    (A) SEM image of a single QW nanorod transferred onto an SiO2/Si substrate. Scale bar, 1 μm. (B to E) Optical images showing a transition from spontaneous to coherent emission with increasing pump fluence. The interference patterns associated with longitudinal Fabry-Pérot cavity modes are observed. (F) Spectral evolution of a single QW nanorod laser (diameter of 580 nm and length of 2.70 μm) near the lasing threshold. All lasing spectra were collected using a 355-nm pulsed wave laser excitation at the power density of 180 to 360 mW/cm2 for the acquisition time of 10 s. (G) Spectral map of the lasing behavior of the QW nanorod laser as a function of pump fluence. (H) Normalized emission spectra of the QW nanorod laser at low (360 μJ/cm2) and high (2272 μJ/cm2) pump fluences.

  • Fig. 4 Density and temperature dependence of polariton lasing.

    (A and B) Double-logarithmic plots of integrated intensity (A) and linewidth (B) as a function of pump fluence at room temperature for a QW nanorod and a bare nanorod, showing the clear threshold behavior of the lasing. (C) EHP density at the threshold pump fluence in the temperature range from 77 to 297 K for both the QW and bare nanorods. The horizontal dotted line indicates the Mott density of ZnO at room temperature. (D) Spectral map of the QW nanorod laser measured in the temperature range from 77 to 297 K, showing the temperature-dependent evolution of the lasing mode. The yellow dashed line represents the temperature-dependent exciton energy of the QW nanorod. The white dotted lines indicate the pure photon modes of Fabry-Pérot cavity resonances for the QW nanorod.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/4/eaau9338/DC1

    Section S1. Oscillator strength in bare and QW nanorods

    Section S2. Numerical simulation of the Fabry-Pérot cavity modes

    Section S3. Polariton dispersion curves with guided modes in the QW nanorod cavity

    Section S4. Rabi splitting energy in the QW nanorod cavity

    Section S5. Angle-resolved emission spectra from the QW nanorod and spatial coherence

    Section S6. Polariton dispersion above lasing threshold density

    Section S7. Statistical data for lasing thresholds

    Section S8. Room temperature lasing spectra of the bare ZnO nanorod cavity

    Section S9. Estimation of EHP density in bare and QW nanorods

    Section S10. Temperature-dependent lasing characteristics of the bare ZnO nanorod

    Fig. S1. Reflectance spectra of bare and QW nanorods at 5 K.

    Fig. S2. Electric field distribution for HE22 and HE13 waveguide modes in the nanorod cavity geometry.

    Fig. S3. Polariton dispersion curves.

    Fig. S4. Angle-resolved emission spectra from the QW nanocavity.

    Fig. S5. Photoluminescence spectra and polariton dispersion at the exciton density above the lasing threshold.

    Fig. S6. Statistical data of the lasing threshold for QW and bare nanorods.

    Fig. S7. Emission spectra of the bare ZnO nanorod cavity depending on the pump fluence.

    Fig. S8. Absorption spectra for ZnO and Zn0.9Mg0.1O layers.

    Fig. S9. Temperature-dependent lasing spectra of the bare ZnO nanorod.

    References (4550)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Oscillator strength in bare and QW nanorods
    • Section S2. Numerical simulation of the Fabry-Pérot cavity modes
    • Section S3. Polariton dispersion curves with guided modes in the QW nanorod cavity
    • Section S4. Rabi splitting energy in the QW nanorod cavity
    • Section S5. Angle-resolved emission spectra from the QW nanorod and spatial coherence
    • Section S6. Polariton dispersion above lasing threshold density
    • Section S7. Statistical data for lasing thresholds
    • Section S8. Room temperature lasing spectra of the bare ZnO nanorod cavity
    • Section S9. Estimation of EHP density in bare and QW nanorods
    • Section S10. Temperature-dependent lasing characteristics of the bare ZnO nanorod
    • Fig. S1. Reflectance spectra of bare and QW nanorods at 5 K.
    • Fig. S2. Electric field distribution for HE22 and HE13 waveguide modes in the nanorod cavity geometry.
    • Fig. S3. Polariton dispersion curves.
    • Fig. S4. Angle-resolved emission spectra from the QW nanocavity.
    • Fig. S5. Photoluminescence spectra and polariton dispersion at the exciton density above the lasing threshold.
    • Fig. S6. Statistical data of the lasing threshold for QW and bare nanorods.
    • Fig. S7. Emission spectra of the bare ZnO nanorod cavity depending on the pump fluence.
    • Fig. S8. Absorption spectra for ZnO and Zn0.9Mg0.1O layers.
    • Fig. S9. Temperature-dependent lasing spectra of the bare ZnO nanorod.
    • References (4550)

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