Fabrication of mid-infrared plasmonic antennas based on heavily doped germanium thin films

In this work, the growth and the fabrication of heavily doped germanium plasmonic antennas for mid-infrared applications are reported. By tuning the phosphorus doping concentration and the antenna geometrical parameters, plasma frequencies for targeting the 8–15 μm spectral region are achieved. 1 μm thick, heavily doped (2.3 × 1019 cm− 3) germanium was used to fabricate dipole antennas of 800 nm width with a gap spacing of 300 nm which demonstrate resonance frequencies around 13 μm and 13.5 μm for 2 μm and 3 μm long structures, respectively. This technology has the potential to be used for mid-infrared sensing applications of hazardous gases and liquids