Enhanced absorption of solar light in Ge/Si core-sheath nanowires compared to Si/Ge core-sheath and Si1−xGex nanowires: A theoretical study

Abstract

Coaxial core-sheath semiconductor nanowires exhibit an improved light absorption efficiency, rendering them promising building blocks in photovoltaic devices. In the present theoretical work, we focus on the optical properties of Si/Ge and Ge/Si core-sheath nanowires, compared to Si1−xGex alloy variants (without coated shell) of the same composition in Si and Ge. Using the analytical Lorenz-Mie theory, we compute both the absorption and scattering efficiencies, with a particular attention devoted to the shell thickness influence. The leaky modes resonances, associated to the optical response enhancement, are investigated and compared for all core/sheath and alloy variants. The optical resonances are found to keep almost the same spectral positions regardless the nanowire structure. More interestingly, core-sheath nanowires absorb more efficiently visible to near-infrared light than Si1−xGex alloys. Finally, the integrated solar absorption Jsolar, which is a figure of merit proportional to the photocurrent generated in a nanowire, is more efficient in the case of Ge/Si core-sheath nanowires than in the two other structures.