Tuning Spontaneous Emission through Waveguide Cavity Effects in Semiconductor Nanowires

Abstract

The ability to tailor waveguide cavities and couple them with quantum emitters has developed a realm of nanophotonics encompassing, for example, highly efficient single photon generation or the control of giant photon nonlinearities. Opening new grounds by pushing the interaction of the waveguide cavity and integrated emitters further into the deep subwavelength regime, however, has been complicated by nonradiative losses due to the increasing importance of surface defects when decreasing cavity dimensions. Here, we show efficient suppression of nonradiative recombination for thin waveguide cavities using core−shell semiconductor nanowires. We experimentally reveal the advantages of such nanowires, which host mobile emitters, that is, free excitons, in a one-dimensional (1D) waveguide, highlighting the resulting potential for tunable, active, nanophotonic devices. In our experiment, controlling the nanowire waveguide diameter tunes the luminescence lifetime of excitons in the nanowires across 2 orders of magnitude up to 80 ns. At the smallest wire diameters, we show that this luminescence lifetime can be manipulated by engineering the dielectric environment of the nanowires. Exploiting this unique handle on the spontaneous emission of mobile emitters, we demonstrate an all-dielectric spatial control of the mobile emitters along the axis of the 1D nanowire waveguide.

Quasi-1D exciton channels in strain-engineered 2D materials

“…First, standard SiO 2 /Si substrates (oxide thickness, 285 nm) were cleaned using a high-intensity ultrasonic bath in acetone and propan-2-ol for 2 min each and a subsequent blow dry using N 2 . To remove remaining adsorbates, the samples underwent an O 2 plasma cleaning for 5 min at 200 W. Epitaxially grown GaAs/Al 0.36 Ga 0.64 As core/shell nanowires, with 80 ± 9 nm diameter and a length of 8 ± 1 m, were then deposited by bringing the as-grown nanowire wafer into mechanical contact with a clean SiO 2 /Si substrate (36). Several hBN-encapsulated WSe 2 heterostructures were fabricated as follows: hBN crystals supplied by colleagues from National Institute for Materials Science (NIMS, Tsukuba) were cleaved and thinned down using two sheets of "Scotch Magic Tape."…”

Wurtzite quantum wires with strong spatial confinement: polarization anisotropies in single wire spectroscopy

“…The nanowire growth procedure was separated into two steps: In the first step, we synthesized the ultrathin GaAs cores at a substrate temperature of 540 °C for 95 min, a Ga rate of 0.7 Å/s and an As 4 /Ga ratio of 2. This step yields vertically grown wires with high wurtzite crystal phase purity, 7,11,12 an uniform length of 2 µm average and an average diameter of 30 nm (± 10 nm), thin enough to observe 1D spatial quantum confinement effects. 7 In the second step, the growth temperature was lowered to 460 °C while the As 4 /Ga ratio was increased to ∼ 4, enabling a lateral overgrowth of the ultrathin GaAs core with an Al 0.38 Ga 0.62 As shell.…”

“…These wires were optically preselected to display a defect-free emission, which is correlated with a high crystal phase purity. 11,12,25 A characteristic excitation power series of the PL emission of a single wire is shown in Figure 2a. While at low excitation power the emission (light brown curve) only displays the single narrow PL peak representative of the ground state emission (labeled "1" in 2a), up to four peaks arise in the spectrum as we gradually increase the excitation power, labeled "1" to "4".…”