Optical absorption from an indirect transition in bismuth nanowires

Abstract

Simulations of the optical absorption in bismuth nanowires resulting from an indirect interband $L\ensuremath{-}T$-point transition are presented. The absorption dependence at room temperature on the band overlap, effective masses, and wire diameter is explored. The polarization, wave number, and wire size dependence of the high intensity absorption peak observed in bismuth nanowires at $\ensuremath{\sim}1000{\mathrm{cm}}^{\ensuremath{-}1}$ can be explained by our model. The polarization dependence of the optical absorption arises from a surface component of the optical coupling term which enhances this indirect transition. Simulations of the absorption from a valence-band $L\ensuremath{-}T$-point transition correctly predict the magnitude of the increase in the peak energy (wave number) with decreasing wire diameter. The wave numbers of the simulated and measured absorption peaks differ by $\ensuremath{\sim}400{\mathrm{cm}}^{\ensuremath{-}1}.$ Several explanations for this discrepancy are proposed.