Small-Signal Modeling of Dissipative Carrier Transport in Nanodevices with Nonequilibrium Green’s Functions

Emerging applications in the field of finite-frequency mesoscopic physics require accurate modeling tools for the evaluation of carrier-transport dynamics, modulation bandwidth, and frequency conversion effects in nanodevices. With foundations in advanced concepts of many-body and quantum field theories, the nonequilibrium Green’s function technique is widely adopted in the calculation of steady-state carrier-transport properties of nanostrucures, while the evaluation of the frequency response is so far largely unexplored by genuine quantum models. Guided by the connection with drift-diffusion solvers within a local description of carrier-phonon scattering, we propose an accurate, yet computationally efficient nonequilibrium Green’s function model of dissipative carrier transport to study the small-signal properties of semiconductor nanostructures. From the numerical evaluation of steady-state Green’s functions and their functional derivatives, we compute spectrally resolved observables expressed in terms of familiar microscopic quantities germane to the drift-diffusion framework, the most prevalent tool in semiclassical device simulation. Besides drastically improving the convergence properties, the exact Jacobian, complemented with the contribution of the displacement current, gives access to the small-signal admittance. Current-conserving boundary conditions suitable for small-signal analysis provide the correct physical behavior near the contacts. Numerical examples show the accuracy and flexibility of the proposed model.