Terahertz radiation due to random grating coupled surface plasmon polaritons

We report on terahertz (THz) radiation under electrical pumping from a degenerate semiconductor possessing an electron accumulation layer. In InN, the random grating formed by topographical defects provides high-efficiency coupling of surface plasmon polaritons supported by the accumulation layer to the THz emission. The principal emission band occupies the 2-6 THz spectral range. We establish a link between the shape of emission spectra and the structural factor of the random grating and show that the change of slope of power dependencies is characteristic for temperature-dependent plasmonic mechanisms. The super-linear rise of a THz emission intensity on applied electric power provides advantage of such materials in emission yield.