The effects of Coulombic coupling between different subband pairs on the electroabsorption spectra of narrow coupled double quantum wells (QW's) have been studied. It is shown,ia 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 vr ell 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 QW's.

This paper reports a study of electroabsorption in GaAs-AlGaAs coupled quantum wells comparing spectra obtained from a variational model with those obtained using the excitonic Green's function (EGF) approach of Chuang et al [see, Phys. Rev. B, vol. 43, p. 1500, 1991] validating the results, where possible, by further comparison with experiment. The single band electron and hole wave functions and energy levels used to calculate the excitonic wave functions in either the variational or EGF model are found numerically for any arbitrary CQW structure.

We review the basic ideas of holographic LEED, and the latest progress in the field. We compare several proposed computer reconstruction schemes. Using experimental diffuse LEED data from O/Ni(001) and K/Ni(001) surfaces, we show that the capability now exists for filtering out the effects on the diffraction patterns of possible long-range order amongst the adsorbates, thus making holographic LEED much more analogous to photoelectron holography. Inclusion of a scattered-wave kernel to compensate for the variation of the magnitude of the reference wave at the positions of potential object-wave sources enables the reconstruction of a fully three-dimensional image of substrate atoms in the immediate vicinity of atomic adsorbates from a set of just normal-incidence diffuse LEED patterns.