Tunable enhancement of light absorption and scattering in Si1−xGexnanowires

Abstract

Semiconducting nanowires (NWs) are good candidates for new optoelectronic or photovoltaic devices due to their excellent ability to guide, scatter, or absorb light, from near ultraviolet to near infrared. The existence of morphology-dependent optical resonances opens a promising route to overcome the intrinsic limitations of the constituent material and optimize their interaction with light. We propose a thorough investigation of the optical properties of Si 1−x Ge x alloy nanowires addressing the influence of NW diameter, composition, light polarization, and angle of incidence on their scattering and absorption. Our results clearly show that the Ge composition provides an additional degree of freedom to tailor the optical response of these one-dimensional nano-objects and that resonant enhancement of both absorption and scattering can be obtained in the infrared range at relatively small diameters compared to pure Si nanowires. These results are confirmed by complementary light scattering and Raman spectroscopy experiments using confocal dark field optical microscopy on individual nanowires fabricated by Au-catalyzed vapor-liquid-solid synthesis.

Self-assembled antireflection coatings for light trapping based on SiGe random metasurfaces

“…2). However, theoretical simulations 65,66 and practical implementations 45,67,68 have unambiguously demonstrated the relevance of Ge for dielectric Mie resonators, at least for wavelengths larger than ∼500 nm.…”

Local electric field enhancement at the heterojunction of Si/SiGe axially heterostructured nanowires under laser illumination

“…This has been typically carried out by means of the Lorenz-Mie theory, in which the NW is described as an infinitely long cylinder immersed in a homogeneous and isotropic non-absorbing medium [28]. In the framework of this formalism, the calculation of the absorptionand scattering efficiencies, Q abs and Q sc respectively, has revealed a strong dependence of these coefficients onthe NW diameter, presenting resonances for certain diameters [6,17]. Alternatively, we have analysed the NW/laser beam interaction by solving the equivalent 2D Maxwell equations using the radio-frequency module of the COMSOL Multiphysics simulation software, contrasting our results with the solution of the Lorentz-Mie equations and obtaining an excellent agreement [29].…”

“…The broad range of unique optical properties of semiconductor NWs has been reported, e.g. waveguiding [5], optical resonances [6], and antenna effects, among others [7]. All these effects emerge because light interacts with the NWs in different ways depending on the NW diameter, wavelength, and the dielectric properties of the NW and the surrounding media.…”

“…This makesRaman spectroscopy an excellent probe for sensing the local electric field induced inside the NW under incident light. In addition, it is possible to take advantage of its capabilities as a powerful non-destructive technique for the characterization of the structure, composition, stress, thermal, electronic, and optical properties of semiconductor NWs [6,[14][15][16][17][18]. It is worth noting that up to nowresearch interest inlight/NWinterac-tion has been focused mainly on homogeneous single NWs and/or core-shell heterostructured NWs [19].However, the response of axially heterostructured NWs toEM waves is still unexplored.…”

Size and shape effects in the Raman scattering by single GaN nanowires

“…The fact that a single nanowire produces such a strong Raman scattering suggests a possible optical cavity resonance effect as GaN is a transparent material at the excitation wavelength. Such a cavity effect, also named antenna effect, has already been reported for both absorption, 16 Rayleigh 16,17 and Raman scattering in GaP nanowires 18 and in Si nanocones. 19,20 Raman resonance quality factors as high as 15 000 have been achieved in the case of GaP nanowires.…”