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Dynamic thermal emission control with InAs-based plasmonic metasurfaces

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Science Advances  07 Dec 2018:
Vol. 4, no. 12, eaat3163
DOI: 10.1126/sciadv.aat3163
  • Fig. 1 Configuration of an electrically tunable III-V–based metasurface for dynamic thermal emission control.

    (A) Device schematic of active metasurface. A high-doped (n++) InAs layer is epitaxially grown on top of a GaAs substrate and is used as a metallic mirror with a negative real dielectric constant at the operating wavelength. A low-doped (n+) InAs layer functions as an active layer whose carrier density and concomitant optical properties can be controlled with an external electrical bias. A thin Al2O3 layer serves as both a gate oxide and an optical spacer to a metasurface/grating made from Al strips. These strips form a series of nanocavities for gap plasmons that can be excited between the strips and a high-doped (n++) InAs mirror. The insets show enlarged schematics for no bias, accumulation, and depletion cases. (B) Cross-sectional SEM taken from one of the strip cavities. The thicknesses of the Al strips, the Al2O3 gate oxide, the n+ InAs active layer, and the n++ InAs bottom mirror are 50, 30, 50, and 500 nm, respectively. The strip width and period of the metasurface are 700 nm and 1.2 μm, respectively.

  • Fig. 2 Reciprocal relationship between the absorptivity and the emissivity.

    (A) FT-IR microscope with reflectivity and emissivity measurement modes. (B) Measured reflectivity (black curve) and emissivity at 200°C (red curve) spectra taken for a metasurface with 750-nm-wide strips spaced at a period of 1150 nm. The simulated reflectivity (blue curve) spectrum at normal incidence is shown. There are two reflection dips: a short wavelength dip around the wavelength of 5.4 μm and a long wavelength dip composed of two separate features centered around 7.2 and 8.0 μm. The reflectivity (black curve) dips and emissivity peaks coincide well with each other. (C) Real part of the dielectric constant (relative electric permittivity) of the low-doped (n+; blue curve) InAs and high-doped (n++; green curve) InAs layers and the infinite-frequency dielectric constant (εinf; red curve). (D and E) Electric field intensity distribution for normally incident illumination at wavelengths (λ) of 5.38 μm in (D) and 8.0 μm in (E).

  • Fig. 3 Dynamic control of thermal emission and reflection from the InAs-based metasurface.

    (A) Emissivity spectrum for no bias (red curve), depletion (green curve), and accumulation (blue curve). For the depletion, a positive bias of +10 V was applied, and for the accumulation, a negative bias of −7 V was applied, for the sake of avoiding dielectric breakdown. The inset shows the SEM of the sample. Scale bar, 1 μm. The grating width and period are 590 nm and 1.4 μm, respectively. The sample area is 600 μm × 600 μm. The hot plate temperature is set to 200°C. (B and C) Reflectivity spectrum from experiment (B) and simulation (C) for no bias, depletion, and accumulation. The color notations are the same as in (A). The grating width and period are 545 and 1285 nm, respectively. A positive bias of +15 V and a negative bias of −15 V were used, respectively.

  • Fig. 4 Polarization property of emitted field from the metasurface comprising one-dimensional metallic gratings.

    A polarizer is inserted in front of the detector. Thermal emission spectra were measured for orientation polarizer angles of 0° (black curve), 30° (blue curve), 60° (green curve), and 90° (red curve), respectively. The inset in (A) shows a schematic diagram of the Al gratings along with x and y axes. The arrows denote the electric field orientations that can pass the polarizer. The grating width and period are 775 and 1150 nm, respectively, and the hot plate is set to 200°C. Simulation results in (B) show good agreement with the measured data.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/12/eaat3163/DC1

    Section S1. Comparison of the spectral absorptivity and emissivity

    Section S2. Real and imaginary parts of the dielectric constants of the n+ and n++ InAs layers and the mode index

    Section S3. Photographs and SEM images of the samples for the tunable thermal emission measurements

    Section S4. Various scales for emissivity changes (absolute and relative plots)

    Section S5. Reflectivity tuning as a function of incremental electrical bias and the mode index

    Section S6. Electrical characterization of the gate oxide Al2O3 (IV and CV)

    Section S7. Refractive index of Al2O3 in mid-IR regime measured using ellipsometry

    Section S8. Reflectivity tuning from samples with various widths and periods

    Fig. S1. Comparison of the spectral absorptivity and emissivity.

    Fig. S2. Optical properties of the switching materials and gap plasmon resonator.

    Fig. S3. Optical microscopy and SEM images of the sample used for the tunable thermal emission measurement.

    Fig. S4. Dynamic control of thermal emission in various scales.

    Fig. S5. Tuning reflectivity with higher bias.

    Fig. S6. Capacitance-voltage measurement of Al2O3.

    Fig. S7. Dielectric strength measurements.

    Fig. S8. Refractive index of Al2O3.

    Fig. S9. Optical and SEM images of the sample for the reflectivity measurement.

    Fig. S10. Reflectivity from samples with various grating widths.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Comparison of the spectral absorptivity and emissivity
    • Section S2. Real and imaginary parts of the dielectric constants of the n+ and n++ InAs layers and the mode index
    • Section S3. Photographs and SEM images of the samples for the tunable thermal emission measurements
    • Section S4. Various scales for emissivity changes (absolute and relative plots)
    • Section S5. Reflectivity tuning as a function of incremental electrical bias and the mode index
    • Section S6. Electrical characterization of the gate oxide Al2O3 (IV and CV)
    • Section S7. Refractive index of Al2O3 in mid-IR regime measured using ellipsometry
    • Section S8. Reflectivity tuning from samples with various widths and periods
    • Fig. S1. Comparison of the spectral absorptivity and emissivity.
    • Fig. S2. Optical properties of the switching materials and gap plasmon resonator.
    • Fig. S3. Optical microscopy and SEM images of the sample used for the tunable thermal emission measurement.
    • Fig. S4. Dynamic control of thermal emission in various scales.
    • Fig. S5. Tuning reflectivity with higher bias.
    • Fig. S6. Capacitance-voltage measurement of Al2O3.
    • Fig. S7. Dielectric strength measurements.
    • Fig. S8. Refractive index of Al2O3.
    • Fig. S9. Optical and SEM images of the sample for the reflectivity measurement.
    • Fig. S10. Reflectivity from samples with various grating widths.

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