Many-Body Effects in Multi-Valley Scenarios

Abstract

The generation of a dense electron—hole system in semiconductors, e.g., by optical pumping, brings about significant modifications in the excitonic spectrum and the electronic band structure. The reasons are screening — i.e., the collective response of the electron—hole system to interactions resulting from Coulomb and exchange effects — and the removal of oscillator strength by occupation of states in phase space. These many-particle effects are accompanied by large optical nonlinearities close to the energies of the band gaps with most interesting prospects for applications in communication technology. After a general review of screening effects in semiconductors, we illustrate the influence of multi-valley band structures on the properties of electron—hole plasmas and degenerate carrier gases. The narrowing of various band or subband gaps in bulk material, or quantum wells and quantum wires, respectively are dicussed in the framework of multi-valley models. A laser-induced crossover from adirect- to an indirect-gap semiconductor is found as a result of a differential renormalization of various conduction-band minima. The role of screening is analyzed not only in electron—hole plasmas of different dimensions but also in one-component plasmas, where the Fermi-edge singularity is its most important consequence. A further result of screening is the condensation of the electron—hole plasma into a liquid phase. The disorder-related dynamics of droplet formation in Al x Ga1−x As as well as the observation of quantum-confined droplets are presented. The chapter closes with a discussion of optical nonlinearities at the direct gap of indirect semiconductors as direct applications of screening in multi-valley semiconductors.KeywordsCarrier DensitySide ValleyPair DensityLineshape AnalysisCrossover CompositionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.