Plasmonic Interference in Superstructured Metal Photonic Crystals

Surface plasma waves (SPWs) excited by illumination of 2-dimensional superstructured metal photonic crystals (SMPCs) are investigated with extraordinary optical transmission (EOT). An <i>m</i> × <i>m</i> lattice of holes (<i>m</i> = 3 with the period <i>p</i> of 3 μm) fabricated in an Au film atop a GaAs substrate (refractive index <i>n</i>_<i>d</i>), referred to as a basis plasmonic antenna (BPA), forms an SMPC that consists of 24 × 24 BPAs with varying spacing between BPAs, <i>d</i>. Two categories of <i>d</i> are examined: κ = <i>d</i>/<i>p</i> = <i>i</i> (<i>i</i> an integer), where SPWs generated at each BPA interfere constructively and κ ≠ <i>i</i> (<1), where the interference leads to drastic changes in the EOT. In the first category, the EOT associated with the fundamental SPW wavelength, <i>T</i>₁, decreases with increasing κ, but has an almost invariant peak wavelength, λ₁, at ∼10.1 μm (≅<i>n</i>_<i>d</i><i>p</i>), as expected. In the second category, however, the λ₁ for the dominant EOT peak clearly shows a red-shift to ∼12 μm with <i>T</i>₁ reduced to ∼0 at κ = 0.5, and <i>T</i>₁ has a damped oscillatory dependence on κ. The shift implies strong plasmonic interference between BPAs that follows ∼<i>n</i>_<i>d</i><i>p</i>(<i>m</i> + κ)/<i>H</i> with the integral harmonic order of the Fourier transform of the SMPC, <i>H</i>. This rescaling of the geometric pattern, incommensurate to the BPA period, accompanies the EOT degraded with the dipole deviation from individual holes that provides important relations for the crosstalk among antennas in plasmonic circuits

Nanoscale Patterned Growth Assisted by Surface Out-Diffusion of Adatoms from Amorphous Mask Films in Molecular Beam Epitaxy

Nanoscale patterned growth (NPG) of GaAs requires the suppression of nucleation on the amorphous SiO₂ mask film, defined on a substrate by patterning. It is determined by the Ga adatom kinetics on SiO₂, leading to desorption and surface out-diffusion (SOD) to the area beyond the mask. Their relative contributions to NPG are examined both theoretically and experimentally. From the rate equation of thin-film growth, a relationship between incident Ga flux and growth temperature for NPG is analytically derived as a function of the lateral dimension of the SiO₂ mask film, <i>L</i>_M. In the NPG by molecular beam epitaxy, <i>L</i>_M is varied in the range of Ga adatom migration length. From comparison with the model, the activation energy of a Ga adatom for desorption, <i>E</i>_des, is found to be comparable to that for surface diffusion, <i>E</i>_diff, on the SiO₂ mask. They are both in the range of 2.7–2.9 eV, lower than the Ga desorption energy from the GaAs substrate, confirming the validity of SOD and, as a result, NPG. This also implies that they are not clearly distinguishable on the amorphous surface, in contrast to crystalline surfaces, where <i>E</i>_diff < <i>E</i>_des, which is attributed to the random fluctuations in the potential lacking long-range order. SOD can induce an actual growth rate significantly enhanced from the nominal rate calibrated on an unpatterned wide area by the additional adatom diffusion flux across the substrate–mask boundary. Its role in controlling the shape and size of the nanostructures selectively grown on the adjacent substrate surface is addressed

Media 1: Ultrafast optical wide field microscopy

Originally published in Optics Express on 08 April 2013 (oe-21-7-8763

Nonpolar InGaN/GaN Core–Shell Single Nanowire Lasers

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core–shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core–shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core–shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core–shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core–shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV–visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature