Optical Properties of Solvent-Dispersed and Polymer-Embedded Germanium Nanowires

The room temperature optical absorbance spectra of polymer-embedded and solvent-dispersed germanium (Ge) nanowires are reported. Homogeneous blends of Ge nanowires in a polymer (Kraton) were enabled by hydrophobic organic monolayer passivation of the nanowires, and stable dispersions of nanowires in a solvent were achieved by grafting poly(ethylene glycol) onto Ge nanowires. The nanowires exhibit enhanced light absorption compared to bulk Ge near the band edge, with a linear dependence on photon energy. An absorbance peak was also observed at about 600 nm, resulting from enhanced light trapping due to the high index of refraction of Ge at this wavelength. Discrete dipole approximation calculations revealed that the light trapping within the nanowires depends also on the nanowire size and incident light polarization. These optical effects are useful for applications requiring low reflectivity and strong light absorption, such as photovoltaics and antireflective coatings.