Absorption-enhanced broadband terahertz quantum well photodetector based on a ring-shaped plasmonic cavity

Terahertz quantum well photodetectors have the advantages of high speed, high sensitivity, and mature technology. However, as a bound-to-bound intersubband transition detector, its linewidth is inherently narrow. Conventional broadband detectors use a multi-color series connection method, which may have crosstalk problems between their active regions. Therefore, designing high-performance broadband terahertz detectors has always been a challenge. In this work, a simple spectral broadening scheme based on the ring grating plasmonic microcavity is proposed. Due to the combination of two microcavity resonance modes, the localized surface plasmons and the surface plasmon polaritons, broadband detection is achieved, and the full width at half maximum of the device coupling factor spectrum reaches 972 GHz. Compared with the conventional circular grating device, the amplitudes of | E Z | 2 /| E 0 | 2 at the peak positions corresponding to the two modes are increased by 29% and 6%, respectively. To enhance the absorption of the quantum well, the optical coupling characteristics of the device were investigated. By adjusting the absorption competition between the quantum well and the metal while maintaining the system in a critical coupling state, the absorptance of the quantum well exceeds 60.6%, which is significantly enhanced by 27 times compared to the standard 45° device.