Photoluminescence Redistribution of InGaN Nanowires Induced by Plasmonic Silver Nanoparticles

Abstract

Hybrid nanostructures based on InGaN nanowires with decorated plasmonic silver nanoparticles are investigated in the present study. It is shown that plasmonic nanoparticles induce the redistribution of room temperature photoluminescence between short-wavelength and long-wavelength peaks of InGaN nanowires. It is defined that short-wavelength maxima decreased by 20%, whereas the long-wavelength maxima increased by 19%. We attribute this phenomenon to the energy transfer and enhancement between the coalesced part of the NWs with 10-13% In content and the tips above with an In content of about 20-23%. A proposed Fröhlich resonance model for silver NPs surrounded by a medium with refractive index of 2.45 and spread 0.1 explains the enhancement effect, whereas the decreasing of the short-wavelength peak is associated with the diffusion of charge carriers between the coalesced part of the NWs and the tips above.

Keywords: Fröhlich resonance; InGaN nanowires; hybrid nanostructures; molecular beam epitaxy; silver nanoparticles.

Figure 1

Typical SEM images of InGaN NWs in cross-section (a) and plan view (b).

Figure 2

(a) Typical HAADF-STEM image of the InGaN NW; (b) high-resolution elemental mapping of Ga intensity along the NW; (c) high-resolution elemental mapping of In intensity along the NW; (d) Typical EDX spectrum of the upper part of NW; (e) Typical EDX spectrum of the coalesced part of NW. Green and purple colors correspond to Ga and In, respectively.

Figure 3

RT PL spectrum of initial InGaN NW array. The short-wavelength PL and long-wavelength PL are attributed to the coalesced part of the NWs and the tips in the upper part of the NWs, respectively.

Figure 4

(a) The optical density of silver NPs solutions and silver NPs with a silicon oxide shell; typical SEM images of (b) Ag NPs and (c) Ag NPs with a silicon oxide shell.

Figure 5

Plan-view SEM images of (a) sample 1 and (b) sample 2; (c) schematical image of the InGaN NW array before and after NPs deposition.

Figure 6

RT PL spectra of sample 1 (a) and sample 2 (b).

Figure 7

Dependences of the PL enhancement by plasmon nanoparticles on the wavelength. Subfigures (a,b) correspond to the cases of Ag nanoparticles and core-shell Ag/SiO_x nanoparticles. Red lines show the ratios of experimentally measured PL spectra of InGaN nanowires with and without plasmonic nanoparticles. Green dotted lines show theoretically predicted enhancement of PL spectra by the plasmonic nanoparticle surrounded by uniform media with refractive index 2.45. Blue dashed lines demonstrate broadening of calculated PL enhancement spectra in the case of normal spread of effective refractive index of the surrounding media in the range (2.45 ± 0.1).

Figure 8

The distribution of the Poynting vector modulus in the process of light scattering on a nanoparticle at the interface between air and InGaN nanowire: (a) silver nanoparticle, λ = 485 nm. (b) core-shell nanoparticle, λ = 473 nm. Figure shows the cut plane of a nanoparticle located on the surface of a nanowire (the interface between air and InGaN). The x coordinate is parallel to the nanowire, and the y coordinate is perpendicular. Both are expressed in nm.