Ultrafast terahertz detectors based on three-dimensional meta-atoms

TL;DR

This paper introduces ultrafast, sub-wavelength terahertz detectors using 3D meta-atoms, achieving GHz response speeds by reducing device size below the diffraction limit, enabling ultra-fast THz detection.

Contribution

The work presents a novel 3D split-ring meta-atom architecture for THz detectors that surpasses diffraction-limited designs, significantly increasing detection speed and reducing dark current.

Findings

Achieved optical response speeds up to ~3 GHz in detector arrays.

Demonstrated sub-wavelength (lambda/10) device size with ultra-low dark currents.

Projected device operation speeds up to tens of GHz based on S-parameter analysis.

Abstract

Terahertz (THz) and sub-THz frequency emitter and detector technologies are receiving increasing attention, underpinned by emerging applications in ultra-fast THz physics, frequency-combs technology and pulsed laser development in this relatively unexplored region of the electromagnetic spectrum. In particular, semiconductor-based ultrafast THz receivers are required for compact, ultrafast spectroscopy and communication systems, and to date, quantum well infrared photodetectors (QWIPs) have proved to be an excellent technology to address this given their intrinsic ps-range response However, with research focused on diffraction-limited QWIP structures (lambda/2), RC constants cannot be reduced indefinitely, and detection speeds are bound to eventually meet un upper limit. The key to an ultra-fast response with no intrinsic upper limit even at tens of GHz is an aggressive reduction in device size, below the diffraction limit. Here we demonstrate sub-wavelength (lambda/10) THz QWIP detectors based on a 3D split-ring geometry, yielding ultra-fast operation at a wavelength of around 100 {\mu}m. Each sensing meta-atom pixel features a suspended loop antenna that feeds THz radiation in the ~20 m3 active volume. Arrays of detectors as well as single-pixel detectors have been implemented with this new architecture, with the latter exhibiting ultra-low dark currents below the nA level. This extremely small resonator architecture leads to measured optical response speeds - on arrays of 300 devices - of up to ~3 GHz and an expected device operation of up to tens of GHz, based on the measured S-parameters on single devices and arrays.