Quantum-kinetic theory of steady-state photocurrent generation in thin films: Coherent versus incoherent coupling

TL;DR

This paper develops a quantum-kinetic framework using nonequilibrium Green's functions to compare coherent and incoherent light-matter coupling effects on photocurrent generation in thin semiconductor films, highlighting their similarities under certain conditions.

Contribution

It introduces a unified quantum-kinetic model for steady-state photocurrent in thin films, incorporating both classical and quantized electromagnetic field interactions within the nonequilibrium Green's function formalism.

Findings

Close spectral and integral photocurrent patterns for coherent and incoherent coupling.

Effective self-energy formulations for both classical and quantum field interactions.

Self-consistent numerical solutions of Dyson and Keldysh equations for photon Green's functions.

Abstract

The generation of photocurrents due to coupling of electrons to both classical and quantized electromagnetic fields in thin semiconductor films is described within the framework of the nonequilibrium Green's function formalism. For the coherent coupling to classical fields corresponding to single field operator averages, an effective two-time intraband self-energy is derived from a band decoupling procedure. The evaluation of coherent photogeneration is performed self-consistently with the propagation of the fields by using for the latter a transfer matrix formalism with an extinction coefficient derived from the electronic Green's functions. For the "incoherent" coupling to fluctuations of the quantized fields, which need to be considered for the inclusion of spontaneous emission, the first self-consistent Born self-energy is used, with full spatial resolution in the photon Green's functions. These are obtained from the numerical solution of Dyson and Keldysh equations including a nonlocal photon self-energy based on the same interband polarization function as used for the coherent case. A comparison of the spectral and integral photocurrent generation pattern reveals a close agreement between coherent and incoherent coupling for the case of an ultrathin, selectively contacted absorber layer at short circuit conditions.