High responsivity random metal grating couplers for terahertz quantum well photodetectors

Terahertz quantum-well photodetectors (THz QWPs) have advantages in constructing THz high-speed communication and fast imaging systems. In this paper, GaAs/(Al,Ga)As THz QWPs with metal random-grating couples are designed, fabricated, and characterized. Both one-dimensional metal random grating devices and a contrast device with 45°-incident facet are fabricated, and their peak responsivities and photocurrent spectra are characterized with the samples soaked in the liquid helium. Compared with 45°-incident coupling, it is found that normal incidence with the random metal grating is an efficient method to improve the responsivity. The random metal grating THz QWP is ~400% improved in the peak responsivity.