Effect of Size Confinement on the Electronic States of CdS Cluster in a Germanium Oxide Matrix

Abstract

Change in the electronic state due to size confinement was studied for the CdS cluster embedded in GeO2 glass by photoacoustic, optical absorption and photoluminescence spectroscopies. The cluster size increases with increasing annealing temperature and time. The activation energy of ion diffusion during cluster growth is 0.45 eV. When the cluster size becomes less than about twice the exciton size, the energy bands become discrete. The energies of 1st and 2nd excited states increase with decreasing cluster size. The size dependence of the ist excited state determined experimentally coincides with the calculation. The energy of the surface state also shifts in parallel with the shift of the 1st excited state. When the cluster size decreases, the intensity of the edge emission decreases faster than that of the surface emission.