Three-dimensional plasmonic light concentrators for efficient terahertz generation

Photoconductive antennas are extensively used in time-domain terahertz imaging and spectroscopy systems to generate terahertz radiation [1, 2]. These emitters consist of a terahertz antenna fabricated on a photoconductive semiconductor. When the semiconductor is pumped by a femtosecond laser and a bias voltage is applied to the antenna arms, an ultrafast photocurrent is generated. As this photocurrent drives the antenna, a pulsed terahertz radiation is generated. However, only the carriers that drift to the antenna arms in a sub-picosecond time scale can efficiently contribute to the generation of terahertz radiation. The rest of the photocarriers, namely the slow photocarriers, cause extra thermal dissipation and degrade device reliability. To improve device reliability, short carrier lifetime semiconductors are often used, which recombine the slow carriers and prevent early thermal breakdown. However, short carrier lifetime semiconductors cannot offer high carrier drift velocities. Therefore, the radiation efficiency of photoconductive emitters fabricated on short carrier lifetime substrates is limited. In this work, we present a highly reliable and efficient photoconductive terahertz emitter that circumvents the use of short carrier lifetime substrates by utilizing three-dimensional plasmonic light concentrators.