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Density-Matrix Modeling of Terahertz Photon-Assisted Tunneling and Optical Gain in Resonant Tunneling Structures

Photon-assisted tunneling current under terahertz (THz) irradiation is analyzed for resonant tunneling structures using the density-matrix theory. Close agreement with measured results was obtained. The analysis is extended to the THz optical gain due to the inter-quantum well transition which is the most important factor in the discussion on developing intersubband THz lasers.