Electroabsorption in narrow coupled double quantum wells: Coulombic coupling effects

The effects of Coulombic coupling between different subband pairs on the electroabsorption spectra of narrow coupled double quantum wells (QWs) have been studied. It is shown via detailed comparison between electroabsorption spectra calculated using a full excitonic Green's function method, a decoupled excitonic Green's function method, a variational method, and experimental data that inclusion of the Coulombic coupling between different subband pairs is required for correct prediction of electroabsorption in the narrow well system. It is also shown that, due to Coulombic coupling, it is necessary to include unbound QW states, above the QW edge, in the simulation of electroabsorption and electrorefraction. These results are of particular significance for the accurate calculation of electrorefraction, by Kramers-Kronig transformation of QW electroabsorption spectra, in coupled QW structures containing narrow QWs.