EXCITON STARK LADDER IN SEMICONDUCTOR SUPERLATTICES

We present a method for calculating the 1s exciton states of type-I and type-II superlattices in an applied static electric field. Our approach is based upon choosing localized exciton wave functions as the basis in which to expand the exciton eigenstates. We calculate the excitonic optical-absorption spectra of a number of very different type-I GaAs/Ga(1-x)Al(x)As superlattices, as a function of electric field, and find our results for the 65-angstrom superlattice of Agullo-Rueda, Mendez, and Hong [Phys. Rev. B 40, 1357 (1989)] to be in good agreement with the experimental photocurrent spectra over the full range of field strengths. In addition, we explain many of the low-field effects generally seen, such as the ladder absorption asymmetry, oscillations in the absorption of individual levels, and the nonlinear dependence of the exciton-Stark-ladder energy levels on the field strength. Finally, we discuss the electric-field range for which a modified single-particle picture provides an adequate picture of the qualitative features of the exciton Stark ladder.