Amplification of terahertz radiation in a plasmon n–i–p–i graphene structure with charge-carrier injection

The absorption/amplification spectrum of terahertz radiation in inhomogeneous graphene ( n–i–p–i structure) with a periodic dual metal grating is theoretically investigated. It is shown that the amplification of terahertz radiation sharply increases at the plasmon-resonance frequency, when losses due to electron scattering and emission are balanced by the plasmon gain (related to the stimulated radiative interband recombination of electron–hole pairs in the inverted region of graphene).