Intermediately bound exciton in a quantum well doped with transition metal impurities

Abstract

The possibility of an intermediately bound exciton in a quantum well, doped with transition metal impurities, is considered. Such bound excitons, in which both carriers are captured in an intermediate-radius orbital, can appear in a quantum well due to strong hybridization of the two-dimensional band states and the impurity $d$ states that are strongly suppressed in the bulk case due to symmetry considerations. The difference between the bound exciton in ${T}_{d}$ (zinc-blende) bulk semiconductors and in the quantum well is due to the lower symmetry of the latter, namely, a tetragonal ${D}_{2d}$ symmetry. In bulk systems, the outer carrier is bound by the Coulomb field of the first exciton carrier and may be considered to be within the framework of the hydrogenlike model. On the other hand in the quantum well, the central-cell pseudopotential appears to be the leading attracting potential for the outer carrier and can be described using Koster and Slater's model. These differences in binding mechanisms may lead to striking differences in the structure of the exciton spectra and in other magneto-optical properties.