  Developing low-power, high-sensitivity photodetectors for the terahertz (THz)
band that operate at room temperature is an important challenge in
optoelectronics. In this study, we introduce a photo-thermal-electric (PTE)
effect detector based on quasi-free standing bilayer graphene (BLG) on a
silicon carbide (SiC) substrate, designed for the THz frequency range. Our
detector's performance hinges on a quasi-optical coupling scheme, which
integrates an aspherical silicon lens, to optimize impedance matching between
the THz antenna and the graphene p-n junction. At room temperature, we achieved
a noise equivalent power (NEP) of less than 300 $pW/\sqrt{Hz}$. Through an
impedance matching analysis, we coupled a planar antenna with a graphene p-n
junction, inserted in parallel to the nano-gap of the antenna, via two coupling
capacitors. By adjusting the capacitors and the antenna arm length, we tailored
the antenna's maximum infrared power absorption to specific frequencies. The
sensitivity, spectral properties, and scalability of our material make it an
ideal candidate for future development of far-infrared detectors operating at
room temperature.
