Fine structure of the exciton electroabsorption in semiconductor superlattices

TL;DR

This paper analytically investigates the fine structure of exciton electroabsorption in semiconductor superlattices under external electric fields, revealing how the field influences exciton energy levels, absorption spectra, and binding energies.

Contribution

It provides an explicit analytical description of the exciton fine structure and its dependence on electric field and superlattice parameters, advancing understanding of exciton behavior in layered semiconductors.

Findings

Electric fields compress the exciton energy levels.

Electric fields decrease optical peak intensities.

Electric fields increase exciton binding energy.

Abstract

Wannier-Mott excitons in a semiconductor layered superlattice (SL) of period much smaller than the 2D exciton Bohr radius in the presence of a longitudinal external dc electric field directed parallel to the SL axis are investigated analytically. The exciton states and the optical absorption coefficient are derived in the tight-binding and adiabatic approximations. Strong and weak electric fields providing spatially localized and extended electron and hole states, respectively, are studied. The dependencies of the exciton states and the exciton absorption spectrum on the SL parameters and the electric field strength are presented in an explicit form. We focus on the fine structure of the ground quasi-2D exciton level formed by the series of closely spaced energy levels adjacent for higher frequencies. These levels are related to the adiabatically slow relative exciton longitudinal motion governed by the potential formed by the in-plane exciton state. It is shown that the external electric fields compress the fine structure energy levels, decrease the intensities of the corresponding optical peaks and increase the exciton binding energy. A possible experimental study of the fine structure of the exciton electroabsorption is discussed.