In this work a powerful terahertz antenna array with interdigital electrodes is fabricated, and the performance of one antenna unit is compared with a conventional resonant dipole antenna. The antenna unit has a better capacity of generating THz wave compared with a conventional resonant dipole antenna at the same bias electrical field and the same laser energy. However only 23 % of THz wave transmitted through the ceramic substrate of antenna array, if there is a hole drilled through ceramic substrate to release the THz wave, the THz amplitude of entire interdigital antenna array with 8 antenna units can be more than 10 times larger than that of resonant dipole antenna. To get this result, the pump beam is focused into a linear beam by a cylindrical lens to trigger the antenna array, and the linear THz wave is focused by a polyethylene lens before it reaches ZnTe crystal. Keywords: Terahertz antenna, antenna array, interdigital electrodes, resonant dipole antenna, GaAs
Terahertz spectroscopy is of great scientific and technological interest in many fields, such as explosives and chemical detection , biology threat detection , quality control and non-destructive testing , material analysis and testing  etc. In THz TDS system, photoconductive antenna is often used as THz source. So it is very important to design and prepare stable and robust photoconductive antenna . Although the structure and usage of the conventional largeaperture antennas are simple, the requirement of a bias voltage as high as 10 kV or more has limited their usage . In this paper, we fabricated a photoconductive antenna array with interdigital electrodes on commercial SI-GaAs substrate and compared the performance of one antenna unit of the array with a conventional resonant dipole antenna. And the absorption of ceramic substrate of antenna mount of interdigital antenna array is measured. The results indicate that the antenna unit can generate a higher THz wave and the interdigital antenna array is expected to emit THz wave with amplitude more than 10 times higher than that of the resonant dipole antenna at same electrical field.
The photoconductive antenna array with interdigital electrodes is composed of eight photoconductive antenna units. The substrate of antenna is commercial high-resistivity (> 107 cm) liquid-encapsulated-Czochralsky-(LEC) grown, (100)oriented, semi-insulating (SI) GaAs wafer. The schematic of the entire antenna array structure is shown in Fig. 1(a). Each unit has separate electrodes and could be operated independently. The spacing between electrodes and the width of the electrodes are 150 μm and 10 μm, respectively. The electrode pattern is made using a conventional photolithography technique. Ohmic contacts are obtained by using a standard mixture of Ni/Au-Ge/Au for the metallization and the thickness is 700 nm. The antenna array is mounted in an integrated circuit shell with ceramic substrate, and the electrodes are connected with pins by golden wire, which is shown in Fig. 1(b).
(b) Fig. 1 (a) Schematic of interdigital antenna array structure. (b) Interdigital antenna array mounted in an integrated circuit shell.
The performance of the emitter is compared with a conventional resonant dipole antenna, which has a 100 μm gap between electrodes, the substrate is...