Challenges in the NEGF Simulation of Quantum‐Well Photovoltaics Posed by Non‐Locality and Localization

Abstract

In this paper, the implications of non‐locality and localization for the implementation and performance of quantum‐opto‐electronic device simulators based on the non‐equilibrium Green's function formalism are considered. It is shown that in the case of electron–photon interaction enabling interband transitions, restriction of the non‐locality range (the spatial distance over which the coupling acts) not only leads to an underestimation of the coupling strength as for intraband electron‐phonon scattering, but also to an inaccurate spectral shape of the response functions and to the violation of selection rules applying to the scattering rates. On the other hand, localization of electronic states (the restriction of finite probability density to a small spatial region) induced by discontinuities and fluctuations in the band profile has a detrimental impact on the speed of convergence of the self‐consistent evaluation of Green's functions and scattering self‐energies, as illustrated by the example of photocarrier extraction from different quantum well configurations.