Ab initio theory of free-carrier absorption in semiconductors

The absorption of light by free carriers in semiconductors results in optical loss for all photon wavelengths. Since free-carrier absorption competes with optical transitions across the band gap, it also reduces the efficiency of optoelectronic devices such as solar cells because it does not generate electron-hole pairs. In this work, we develop a first-principles theory of free-carrier absorption taking into account both single-particle excitations and the collective Drude term, and we demonstrate its application to the case of doped Si. We determine the free-carrier absorption coefficient as a function of carrier concentration and we obtain excellent agreement with experimental data. We identify the dominant processes that contribute to free-carrier absorption at various photon wavelengths, and analyze the results to evaluate the impact of this loss mechanism on the efficiency of Si-based optoelectronic devices.

Automated summary

This paper introduces the issue of light absorption by free carriers in semiconductors resulting in optical loss. It develops a theoretical model taking into account both single-particle excitations and the collective Drude term, and applies it to the case of doped Si. The model demonstrates excellent agreement with experimental data and analyzes the dominant processes contributing to free-carrier absorption at different photon wavelengths.