The binding energy of excitons to ionized shallow donors in a quantum well, in the vicinity of the type-I to type-II transition, was estimated for impurities that were situated anywhere within the structure. The -X hybridization in the Brillouin zone was included. This became relevant when the energies of the conduction sub-band minima in the 2 materials became closer. The calculation was performed variationally by using a 3-parameter trial function like those which were used to describe a singly ionized molecule. This model also permitted the calculation of the binding energies of the neutral impurity and of the free exciton. It was found that the ratio of the binding energy of the exciton to that of an ionized donor and that of the neutral donor was equal to 0.95, for all of the well-widths which were considered. It was independent of the position of the impurity within the well.

I.C.Da Cunha Lima, A.Ghazali, P.D.Emmel: Physical Review B, 1996, 54[19], 13996-14002