Optical characterization of highly n-type doped Ge0.95Sn0.05 rod antennas on Si(001) substrates

Plasmonic excitations in metal nanostructures can be used to control and manipulate optical energy in the visible and infrared spectrum and have been used to enable biosensing, to enhance absorption and quantum yields for photovoltaics and to enhance the energy efficiency of light-emitting devices. For light at mid-infrared (MIR) wavelengths, metals become less suitable for plasmonic applications as a result of the high Drude losses. At those wavelengths, highly doped semiconductors are potential alternatives. The doped group IV alloy GexSny has been shown to be particularly interesting. We present results on the fabrication and optical characterization of rod antennas fabricated from highly n-type doped Ge0.95Sn0.05 (n-GexSny) on Si(001) substrates. Extinction spectra were obtained via Fourier Transform Infrared (FTIR) Spectroscopy. To verify the measurement results the behavior of the n-Ge0.95Sn0.05 rod antennas was simulated. The results show that the n-Ge0.95Sn0.05 rod antennas absorb MIR radiation through plasmonic excitation. Two different peaks could be observed in the extinction spectra of the n-Ge0.95Sn0.05 rod antennas and attributed to two locally separated plasmonic modes. One mode forms on the n-Ge0.95Sn0.05/Si interface of the n-Ge0.95Sn0.05 rod antennas, the other one forms at the n-Ge0.95Sn0.05/air interface. We discuss possible applications of this type of n-Ge0.95Sn0.05 rod antennas for MIR sensing.