Terahertz Generation through Bias-free Telecommunication Compatible Photoconductive Nanoantennas over a 5 THz Radiation Bandwidth

We demonstrate a broadband and highly reliable photoconductive terahertz emitter based on plasmonic nanoantennas that operates at telecommunication optical wavelengths (~1550 nm) at which low-cost and compact lasers are commercially available. The photoconductive substrate is specifically grown to induce a built-in electric field at the interface between the nanoantennas and photoconductive substrate. This built-in electric field drifts the photocarriers generated by the optical pump beam and produces the terahertz feed current to the nanoantennas while eliminating the need for an external bias voltage. The bias-free operation suppresses the dark current that is detrimental to the photoconductive emitters that operate at telecommunication optical wavelengths. Despite their great promise, the bandwidth of previously demonstrated bias-free photoconductive terahertz emitters has been limited by the limited extent of the built-in electric field in the photoconductive substrate. Here we present a telecommunication-compatible, bias-free photoconductive terahertz emitter that offers more than a 5 THz radiation bandwidth and a 100 dB dynamic range.