Intense Terahertz Radiation from GaAs Photoconductive Antenna Array

In this paper, we fabricated an intense photoconductive antenna array with eight antenna units. Each unit has separate electrodes and could be operated independently. The spacing between electrodes and the width of the electrodes axe 150 mu m and 10 mu m, respectively. The substrate is commercial semi-insulating GaAs. The electrode pattern is made using a conventional photolithography technique. Ohmic contacts axe 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. Those antennas axe tested by TDS-Z2 system made in Zomega Terahertz Corporation. A fiber laser (IMRA F-100) has been used in the system as the excitation source for the generation of THz radiation. The pump beam has a power of 90 mW, wavelength of 800 nm. and the 1/e beam diameter on the emitter surface is about 20 mu m, and so only one antenna unit is illuminated in our experiment. The field waveform is measured using an electrooptic sampling method employing a 1-mm-thick ZnTe crystal. To understand the behavior of interdigital antenna array, THz transmission 'through the ceramic substrate is measured. Only 23% of THz wave transmitted through the substrate. If a hole is drilled through the ceramic substrate to make THz wave go through, the THz amplitude of antenna unit will increase more than 4 times, and the THz amplitude from the antenna unit is 4/3 times larger than the THz amplitude from the stripline antenna at the same electrical field.