Gap-engineered high-performance broad spectral-band plasmonic terahertz detectors for wireless communication

Photodetectors based on semiconductor surface plasmon polariton (SPP) offer a promising route for high-performance broad spectral-band terahertz (THz) detection by overcoming bandgap limits of conventional semiconductor detectors. However, the active region's dimension of SPP-based photodetectors must be optimized to balance field enhancement with macroscopic channel resistance and ensure efficient photoresponse. In this work, we systematically investigate the dimensional scaling effect in spiral-antenna-coupled InSb THz detectors. By varying the central gap (5-20 µm) under a constant-DC-field bias, we decouple the competing physical mechanisms governing device performance. While the narrowest gap (5 µm) maximizes intrinsic SPP excitation and current responsivity (3500 A W^-1 at 75.4 GHz), an optimal intermediate gap (10 µm) achieves the best balance. This optimized device delivers a peak voltage responsivity of 1.81 × 10⁵V W^-1 and a noise equivalent power of 1.93 × 10^-14 W Hz^-1/2, exhibiting a broad spectral response (0.0265-0.5 THz) and a fast response speed (∼5 µs). Leveraging these metrics, we demonstrate a proof-of-concept THz wireless communication link. Assisted by a robust dual-envelope tracking algorithm to mitigate free-space baseline drift, the system achieves a peak error-free data rate of 210 kbps. This empirical study provides practical geometric design guidelines for next-generation subwavelength SPP detectors.