Resonant Raman scattering at bound excitons in ZnSe/GaAs epilayers

The authors determine the electronic structure of the dominant donor-exciton complex (D0,X) in high-quality ZnSe/GaAs epilayers grown by molecular beam epitaxy. Besides the recombination line I2 from the ground state of this complex, a set of further lines, called I2i (i=a, . . ., e), was observed in luminescence and excitation spectroscopy. They represent transitions into (or from) excited states (D0,X)i* of the same exciton complex which are described by single-hole excitation with different hole quantum numbers n, l. Additionally, strong resonant electronic Raman scattering (RRS) occurs at these donor-bound exciton states. Several scattering lines S2i with non-constant Stokes shifts are identified as involving (D0,X) complexes with varying binding energies as resonant intermediate states. This phenomenon is explained by the strain influence in ZnSe/GaAs for different layer thicknesses, although the incorporation of different donor impurities may also contribute to the variations of the Stokes shifts.