Selective excitation of localised excitons in ZnSe1-xTexsolid solutions

Abstract

Employing selective monochromatic laser excitation, the photoluminescence in ZnSe1-xTe/sub /x alloys with Te concentrations 1%<or=x<or=2.3% is investigated. The structured emission band is interpreted as being due to recombination of excitons localised at different types of small Te clusters. The energy spectrum of these excitons is inhomogeneously broadened. The details of exciton-lattice interaction revealed under resonant excitation of these exciton states strongly favour the model of large-radii excitons tightly bound through the hole. For excitation above the exciton gap, resonant Raman scattering by longitudinal optical (LO) phonons is observed. The measured degree of polarisation is used to discriminate between this process and the narrow-line LO resonance luminescence found under selective excitation of the localised states. The smooth transformation from Raman scattering to resonance fluorescence indicates that, owing to strong interaction between the cluster and band states, no energy gap exists between the free and localised exciton states.