Excitonic theory of stark ladder spectra in superlattices

Abstract
Predicting exciton behaviour in the Stark ladder regime is an interesting theoretical problem, requiring the treatment of strong coupling between a number of in-plane exciton states with different values of the electron-hole separation. In this paper a new method is described which allows an essentially exact calculation of Stark ladder spectra, with negligible broadening, over a wide range of fields. The oscillator strength at each energy is evaluated from an exciton Green's function which is constructed using numerical solutions of the set of coupled differential equations corresponding to the two dimensional in-plane motion on isolated layers. When suitably broadened, the spectra realistically reproduce those obtained experimentally. At higher resolution more details can be seen, including the Fano-resonance lineshapes of the exciton peaks caused by coupling to continuum states.