Coherent phenomena in semiconductors

TL;DR

This paper reviews coherent phenomena in photoexcited semiconductors, emphasizing the role of phase coherence and Coulomb effects, analyzed through a density-matrix formalism to understand carrier dynamics and optical responses.

Contribution

It provides a comprehensive theoretical framework for analyzing coherent and incoherent processes in semiconductors, linking phase coherence to optical phenomena and carrier behavior.

Findings

Optically induced phase coherence significantly influences carrier photogeneration.

Coulomb interactions dominate the optical spectra of quantum-wire structures.

Field-induced phenomena like Bloch oscillations are key in superlattices.

Abstract

A review of coherent phenomena in photoexcited semiconductors is presented. In particular, two classes of phenomena are considered: On the one hand the role played by optically-induced phase coherence in the ultrafast spectroscopy of semiconductors; On the other hand the Coulomb-induced effects on the coherent optical response of low-dimensional structures. All the phenomena discussed in the paper are analyzed in terms of a theoretical framework based on the density-matrix formalism. Due to its generality, this quantum-kinetic approach allows a realistic description of coherent as well as incoherent, i.e. phase-breaking, processes, thus providing quantitative information on the coupled ---coherent vs. incoherent--- carrier dynamics in photoexcited semiconductors. The primary goal of the paper is to discuss the concept of quantum-mechanical phase coherence as well as its relevance and implications on semiconductor physics and technology. In particular, we will discuss the dominant role played by optically induced phase coherence on the process of carrier photogeneration and relaxation in bulk systems. We will then review typical field-induced coherent phenomena in semiconductor superlattices such as Bloch oscillations and Wannier-Stark localization. Finally, we will discuss the dominant role played by Coulomb correlation on the linear and non-linear optical spectra of realistic quantum-wire structures.