Formation of gold nanoparticles by laser annealing and enhanced terahertz beam by plasmonics

The plasmonic effect increases photocurrents substantially. There are considerable efforts to exploit this phenomenon for various applications, such as a high-efficiency photovoltaic cell, photodetector, etc. In this presentation, we will report gold nanoparticles on a photoconductive antenna and substantial terahertz power enhancement by the plasmonics. A laser annealing process creates the gold nanoparticles, and the plasmonic effect occurs when the gold nanoparticles interact with the femtosecond laser beam. The photoconductive antenna contains a pair of Schottky electrodes, which are fabricated by depositing shallow titanium-gold layers on a semi-insulating GaAs substrate. After the fabrication, the photoconductive antenna is exposed to a rather intense femtosecond laser beam exceeding 130 mW while applying a 70 V AC bias voltage to the electrodes. This laser annealing process generates about 1 mW of terahertz beam, which is nearly stable until the annealing time past 60 minutes when terahertz power abruptly jumps more than 20 -30%. This sudden power enhancement is coincident with the formation of gold nanoparticles and dendrites in a tiny area around the electrodes. We found that the plasmonic effect enhances the photocurrents of more than one order of magnitude.