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Utilizing short-carrier-lifetime semiconductors as the photo-absorbing substrate of photoconductive terahertz detectors has been considered a necessity to enable ultrafast operation and to recombine the slow photo-generated carriers that increase the detector noise and reduce the detector responsivity. However, most of the techniques used for growing short-carrier-lifetime semiconductors introduce a high density of defects in the semiconductor lattice, degrading the carrier mobility and drift velocity and, thus, the detector responsivity. To eliminate the need for a short-carrier-lifetime semiconductor, we present a novel photoconductive terahertz detector based on a nanocavity-coupled plasmonic nanoantenna array. The presented photoconductive terahertz detector uses an undoped GaAs layer embedded inside a nanocavity as the photoconductive active region. The nanocavity is specifically designed to confine the optical pump photons very tightly inside the undoped GaAs layer so that all the photo-generated carriers concentrate around an array of plasmonic nanoantennas, which are also designed to operate as broadband terahertz antennas. Therefore, the presented nanocavity-coupled plasmonic nanoantenna array maximizes the photo-generated carrier concentration and the induced terahertz electric field in response to an incident terahertz radiation near the plasmonic nanoantenna contact electrodes. This significantly increases the detector responsivity and offers photo-generated carrier transport times comparable to photoconductive terahertz detectors based on short-carrier-lifetime semiconductors. By using the presented detector in a time-domain terahertz spectroscopy system, we demonstrate resolving terahertz spectra with a large dynamic range over the 0.1-5 THz frequency range.
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