Tunable enhancement of light absorption and scattering in Si1-xGex nanowires

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 Si1-xGex 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.