Calculation of the exciton binding energies in type-II GaAs/AlAs quantum-well structures: Application of the perturbation-variational expansion method

We report a calculation of the binding energies of both the heavy-hole and the light-hole excitons in type-II GaAs/AlAs quantum wells as a function of the size of the AlAs layer (or GaAs layer). We use a perturbation-variational expansion method to the first order in perturbation expansion. The exciton binding energies are calculated assuming infinite potential barriers and results thus obtained are compared with those of a published variational calculation. We find that the values of the exciton binding energies that we calculate are somewhat lower than those obtained using a variational calculation, even for small wells similar to the perturbation-variational method results in type-I quantum wells. An explanation of this behavior in terms of the average spatial separation of electrons and holes is given.