Small-signal ac response: a self-consistent non-equilibrium Green's function approach

摘要

Starting from the fundamental equations for non-equilibrium Green's functions (NEGFs) and taking the internal induced ac potentials into account by self-consistent iteration, this paper obtains the gauge-invariant equations of ac charge and ac current in terms of NEGFs. We proved the gauge invariance of our formulation and performed the displacement current partition. As regards the computation, we found that a severe error would arise from numerical integration and destroy the gauge invariance of the theory. Fortunately, it can be corrected by adding a term and the huge computational burden that would otherwise emerge is avoided. Finally, we computed the admittance dispersion of a resonant tunnelling diode as a preliminary application. The results show that the peaks of total admittance have a direct relation to the peaks in the density of states and the displacement current always plays the role of a retarding ac current.