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An electrically pumped surface-emitting semiconductor green laser

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Science Advances  03 Jan 2020:
Vol. 6, no. 1, eaav7523
DOI: 10.1126/sciadv.aav7523
  • Fig. 1 Design of InGaN NCSEL diodes operating in the green wavelength.

    (A) Schematic of the InGaN nanocrystal arrays for the surface-emitting laser diode. (B) The diameter and lattice constant of the nanocrystals denoted as d and a, respectively. (C) Schematic of the InGaN/AlGaN nanowire heterostructure, which consists of an n-GaN cladding layer, a core-shell InGaN/AlGaN multiple quantum disk active region, and a p-GaN cladding layer. (D) The reciprocal lattice of a photonic crystal structure has six equivalent Γ′ points, which are coupled together by the Bragg grating vectors K1 and K2. (E) Calculated photonic band structure for transverse magnetic (TM) polarization from 2D finite-element method (2D-FEM) simulation. (F) The electric field profile of the band edge mode (λ = 523 nm) calculated by the 3D finite-difference time-domain method. (G) PL spectrum of an InGaN/AlGaN calibration sample showing spontaneous green emission. a.u., arbitrary units. (H and I) The top-view and titled-view scanning electron microscopy (SEM) images of an InGaN nanocrystal array.

  • Fig. 2 Structural characterization of InGaN/AlGaN core-shell quantum disk heterostructures.

    (A) STEM-HAADF image of a representative core-shell InGaN/AlGaN multiple quantum disk (MQD) heterostructure nanocrystal. (B) High-magnification image taken from the region marked in (A) and (C) schematic illustration for the quasi-3D structure of the semipolar active region and selected-area electron diffraction pattern of the InGaN/AlGaN core-shell heterostructure. (D) High-magnification HAADF image of the InGaN/AlGaN quantum disk region. (E) Energy-dispersive x-ray spectroscopy (EDXS) line profile of the InGaN/AlGaN quantum disks along the line labeled with “1” in (D). (F) EDXS point analysis of the AlGaN shell region marked as “A” and “B” in (B).

  • Fig. 3 Fabrication and characterization of InGaN NCSEL diodes.

    (A) Schematic illustration of the fabricated NCSEL device. Inset: Optical microscopy image of the device after metallic contact grids and electroluminescence (EL) image of the green lasing. (B) Current-voltage (I-V) characteristics of the NCSEL device. Inset: The I-V curve on a semi-log scale. (C) Electroluminescence spectra measured from different injection currents under CW biasing conditions at room temperature (R.T.). (D) Variations of the output power versus injection current. It shows a clear threshold of ~400 A/cm2. SP, spontaneous emission. (E) Variations of spectral linewidth (FWHM, full width at half maximum). (F) Peak wavelength position measured under different injection current densities.

  • Fig. 4 Far-field and polarization emission properties of InGaN NCSEL diodes.

    (A) Far-field radiation pattern of the nanocrystal laser structure simulated using the 3D FDTD method. Electroluminescence image of the far-field pattern observed below the threshold current density (200 A/cm2) (B) and slightly above the threshold current density (C) of the InGaN NCSEL recorded using a high-resolution charge-coupled device (CCD) camera above the device top surface. (D) Polarized electroluminescence spectra of the InGaN NCSEL measured under a current density of 1 kA/cm2. The polarization ratio is ~0.86. (E) The measured electroluminescence intensity as a function of the emission polarization angle (0° to 360°).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/1/eaav7523/DC1

    Text S1. Simulation for photon confinement in the vertical direction

    Text S2. Nanohole patterned Ti mask substrate for selective area epitaxy

    Text S3. Epitaxial growth of InGaN/AlGaN core-shell heterostructures

    Text S4. TEM specimen preparation using a focused ion beam system

    Text S5. Ga-polar n-GaN nanocrystal structure

    Text S6. Projection effect image and quasi-3D structure of InGaN/AlGaN quantum disk layers

    Text S7. Properties of semipolar InGaN/AlGaN core-shell heterostructures

    Text S8. NCSEL device fabrication

    Text S9. Electroluminescence measurement

    Text S10. Calculation of far-field radiation pattern

    Text S11. Measurement of far-field radiation pattern

    Text S12. Polarization measurement of the light emission of InGaN NCSELs

    Fig. S1. Variation of the effective refractive index along the growth direction and the TM polarized mode intensity profile.

    Fig. S2. Schematic illustration and field-emission SEM image of the patterned Ti thin-film nanohole mask fabricated on n-type GaN template substrate.

    Fig. S3. TEM lamella preparation of the nanocrystal.

    Fig. S4. Ga-polar n-GaN nanocrystal structure.

    Fig. S5. Projection effect in quasi-3D structure.

    Fig. S6. PL emission spectra of InGaN/AlGaN core-shell multiquantum disk nanocrystals (green curve) and InGaN/GaN multiquantum disk nanocrystals without AlGaN shell (blue curve) measured at 300 K.

    Fig. S7. Schematic illustration of the full device fabrication, including passivation, planarization, photolithography, and contact metallization techniques.

    Fig. S8. Schematic illustration of the measurement setup for electroluminescence spectra.

    Fig. S9. Schematic illustration of the far-field measurement setup with a CCD camera at a distance above the NCSEL device.

    Fig. S10. Schematic illustration of the polarization angle measurement.

    References (6983)

  • Supplementary Materials

    This PDF file includes:

    • Text S1. Simulation for photon confinement in the vertical direction
    • Text S2. Nanohole patterned Ti mask substrate for selective area epitaxy
    • Text S3. Epitaxial growth of InGaN/AlGaN core-shell heterostructures
    • Text S4. TEM specimen preparation using a focused ion beam system
    • Text S5. Ga-polar n-GaN nanocrystal structure
    • Text S6. Projection effect image and quasi-3D structure of InGaN/AlGaN quantum disk layers
    • Text S7. Properties of semipolar InGaN/AlGaN core-shell heterostructures
    • Text S8. NCSEL device fabrication
    • Text S9. Electroluminescence measurement
    • Text S10. Calculation of far-field radiation pattern
    • Text S11. Measurement of far-field radiation pattern
    • Text S12. Polarization measurement of the light emission of InGaN NCSELs
    • Fig. S1. Variation of the effective refractive index along the growth direction and the TM polarized mode intensity profile.
    • Fig. S2. Schematic illustration and field-emission SEM image of the patterned Ti thin-film nanohole mask fabricated on n-type GaN template substrate.
    • Fig. S3. TEM lamella preparation of the nanocrystal.
    • Fig. S4. Ga-polar n-GaN nanocrystal structure.
    • Fig. S5. Projection effect in quasi-3D structure.
    • Fig. S6. PL emission spectra of InGaN/AlGaN core-shell multiquantum disk nanocrystals (green curve) and InGaN/GaN multiquantum disk nanocrystals without AlGaN shell (blue curve) measured at 300 K.
    • Fig. S7. Schematic illustration of the full device fabrication, including passivation, planarization, photolithography, and contact metallization techniques.
    • Fig. S8. Schematic illustration of the measurement setup for electroluminescence spectra.
    • Fig. S9. Schematic illustration of the far-field measurement setup with a CCD camera at a distance above the NCSEL device.
    • Fig. S10. Schematic illustration of the polarization angle measurement.
    • References (6983)

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