Going back to history, the term terahertz gained popularity among spectroscopists during the mid-1970s, Terahertz science has become increasingly popular in the recent decade due largely to the advent of time-domain spectroscopy (TDS) with ultrashort-pulse laser sources, which makes it possible for researchers to carry out time-resolved “far-infrared” (FIR) studies and to explore spectroscopy and imaging applications in the submillimeter wavelength regime. Terahertz (THz) detectors play an increasing role in different areas of human activities e.g., security, biological, drugs and explosions detection, imaging, astronomy applications, etc.