Theory of coherent generation in resonant-tunneling diodes

A rigorous quantum-mechanical description is given of coherent generation i n a resonant-tunneling diode for the simple model of a double-barrier struc ture. Exact analytical solutions of the Schrodinger equation are found for electrons in the presence of a weak electromagnetic field. The active and r eactive polarization currents are calculated over a wide frequency interval and are reduced to a simple and easy-to-visualize form. These expressions satisfy the Kramers-Kronig relations and general criteria of the theory of radiation and other formal requirements. An analysis of the threshold condi tions of generation is given. In particular, it is shown that generation is possible at microwave frequencies exceeding the inverse lifetime of an ele ctron in the quantum well. Thus, the "quasiclassical" idea of the existence of a limiting frequency, associated with the finite lifetime, turns out to be inapplicable for a resonant-tunneling diode, which occupies an intermed iate position between lasers and Gunn diodes. (C) 1999 American Institute o f Physics. [S1063-7761(99)02508-1].