THz power optimization and analysis of plasmonic unbiased photoconductive THz emitters coupled to a spiral-like dipole antenna

Abstract

We propose a new spiral-like dipole antenna-coupled and unbiased terahertz (THz) photomixer with plasmonic unsymmetrical interdigitated electrodes (UIEs). Each electrode pair is made of subwavelength metal–semiconductor–metal (MSM) structures constituting heterogeneous Schottky contacts. From the optical view and analysis of the electrical transport in the semiconductor, by applying a systematic procedure to achieve optimum design, it is possible to benefit from advantages of having high THz photocurrent derived from the plasmonic enhanced optical absorption and, hence, photogeneration as well as severe built-in Schottky field in the photoconductor. Furthermore, from the electromagnetic view, by introducing an output resonant THz antenna having great impedance matching with the photomixer device, the efficiency of free-space coupling has significantly been enhanced. By exploiting all aspects of design, it has been provided to achieve the THz power of 409 µW from the spiral-like dipole antenna coupled to the proposed plasmonic UIEs with 10 × 10 µ m 2 active area and pitch of Λ = 395 n m . This is more than 1 order of magnitude larger THz power than the highest THz power radiated from the same area of a conventional dipole antenna-coupled unbiased array of the near-field emitters. Also, this improvement is more than 3 orders of magnitude higher THz power as compared with the power radiated from a non-plasmonic far-field operating antenna-less THz chip of the same size.