Integrated nanostrip dipole antennas for coherent 30 THz infrared radiation

Abstract

We report on the experimental study of infrared nanostrip dipole antennas which are connected to thin-film nanometer Ni-NiO-Ni diodes. The integrated Ni-NiO-Ni diodes are used to detect 30 THz (≈10 µm) CO₂-laser radiation.

The diodes are deposited on 385 µm silicon substrates which are covered with a layer of 1.6 µm SiO₂ on both sides. We have found that in low-power applications 1.6 µm of SiO₂ yields excellent quarter-wave matching layers for wavelengths centered at ⋋₀ = 10.8 µm. By this method 79% of the incident CO₂-laser radiation is transmitted into the Si substrate compared to 48% without SiO₂ layer. The use of SiO₂ quarter-wave matching layers considerably improves the efficiency of infrared nanostrip dipole antennas. This has been confirmed by the study of the laser-induced response of the Ni-NiO-Ni diode detectors as a function of the lengthL of the dipole antenna. Thus, we have observed that the laser-induced response strongly increases for shorter antennas and exhibits a distinct maximum atL=2.8 ± 0.3 µm. For the first time, we have investigated the 30 THz radiation patterns of nanostrip dipole antennas of different lengths. On this occasion, we have observed that the radiation pattern changes when the lengthL of the dipole antenna is varied. This observation indicates that antenna currents propagate on the nanostrip dipole antenna.