Hybrid Semiconductor Nanowire–Metallic Yagi-Uda Antennas

Abstract

We demonstrate the directional emission of individual GaAs nanowires by coupling this emission to YagiUda optical antennas. In particular, we have replaced the resonant metallic feed element of the nanoantenna by an individual nanowire and measured with the microscope the photoluminescence of the hybrid structure as a function of the emission angle by imaging the back focal plane of the objective. The precise tuning of the dimensions of the metallic elements of the nanoantenna leads to a strong variation of the directionality of the emission, being able to change this emission from backward to forward. We explain the mechanism leading to this directional emission by finite difference time domain simulations of the scattering efficiency of the antenna elements. These results cast the first step toward the realization of electrically driven optical Yagi-Uda antenna emitters based on semiconductors nanowires. KEYWORDS: Semiconductor nanowire, Yagi-Uda optical antenna, directional emission, Fourier microscopy B ecause of the unique optical properties of semiconductor nanowires they are an excellent platform for optoelectronic and photonic applications. 1−3 The possibility of controlling their composition, geometry, and crystallographic morphology opens up a great freedom in designing different devices with desired properties. 4 In recent years, several studies have been realized on optically 5 and electrically 6 driven nanolasers, solar cells, 7−9 optical switches, 10 and single photon sources coupled to optical waveguides. 11,12 The photoluminescence properties of nanowires and the coupling of their emission to leaky and guided modes have been studied extensively. 13−17 In addition, the coupling of nanowires with plasmonic nanostructures modifies their optical properties. 18−20 In parallel, in the past decade many efforts have been done to enhance the efficiency and modify the direction of the emission of quantum emitters including quantum dots and fluorescent molecules. 21−25 Yagi-Uda optical antennas are an example of a structure showing a pronounced directionality of the emission. 24,26−31 In this system, the emission of a single quantum emitter couples to the antenna feed element, which is a metallic nanorod acting as a half-wavelength dipole nanoantenna. The permittivity of noble metals, including Au, Ag, and Al, and the size of the nanorods leads to plasmonic resonances in the visible range of the electromagnetic spectrum. These resonances modify the spontaneous emission rate of nearby emitters due to the change of the local density of optical states. 32 Subsequently, the scattering of the feed element emission with the antenna elements and the interference of this scattered radiation in the far-field leads to a strong directional emission. This emission can be controlled by the resonant response of the elements forming the Yagi-Uda antenna and their spacing.In this Letter, we demonstrate a hybrid semiconductor− metal Yagi-Uda antenna. This hybrid system is realized by replacing the resonant met...

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