Terahertz wave generation using graphene and compound semiconductor nano-heterostructures

This paper reviews recent advances in terahertz wave generation using graphene and compound semiconductor nano-heterostructures. The excitation of two-dimensional (2D) plasmons in high-electron mobility transistors (HEMTs) and related semiconductor nano-heterostructures has been used for emission of THz electromagnetic radiation. Plasmons in graphene (which is one or several monolayers of a honeycomb carbon lattice) have a higher velocity and peculiar transport properties owing to the massless and gapless energy spectrum of graphene. Optical and/or injection pumping of graphene results in a negative-dynamic conductivity in the THz spectral range, which may enable new types of THz lasers. Fundamental physics behind the device operation mechanisms and experimental results are demonstrated including coherent monochromatic THz radiation from InP-based HEMT-type emitters and stimulated emission of THz radiation with a giant gain via excitation of surface plasmon polaritons in optically pumped monolayer intrinsic graphene.