INTEGRATED NANOSTRIP DIPOLE ANTENNAS FOR COHERENT 30 THZ INFRARED RADIATION

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 30THz (almost-equal-to 10 mum) CO2-laser radiation. The diodes are deposited on 385 mum silicon substrates which are covered with a layer of 1.6 mum SiO2 on both sides. We have found that in low-power applications 1.6 mum of SiO2 yields excellent quarter-wave matching layers for wavelengths centered at lambda0 = 10.8 mum. 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 length L of the dipole antenna. Thus, we have observed that the laser-induced response strongly increases for shorter antennas and exhibits a distinct maximum at L = 2.8 +/- 0.3 mum. 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 length L of the dipole antenna is varied. This observation indicates that antenna currents propagate on the nanostrip dipole antenna.