GROWTH OF CDS NANOCRYSTALS IN SILICATE-GLASSES AND IN THIN SIO2-FILMSIN THE INITIAL-STAGES OF THE PHASE-SEPARATION OF A SOLID-SOLUTION

A study has been made of the growth of CdS semiconductor nanocrystals (quantum dots) in amorphous media, specifically, silicate glasses and thin films of SiO2. The glasses and films were initially doped with co mponents of the semiconductor compound. The CdS crystals were then gro wn by annealing the samples in air or hydrogen at various temperatures . The average dimensions of the crystals which formed were found from the width of x-ray diffraction lines and also from the spectral shift of the fundamental optical absorption edge. These dimensions were 1-20 nm. The experimental behavior of the average size as a function of th e annealing time shows that, in agreement with the theory of phase sep aration, the growth of the crystals occurs through a stage of the form ation of nucleating regions followed by a diffusive growth. Results on the average size of the nucleating regions as a function of the annea ling temperature yield the solubility temperature of CdS in the matrix material. The results also show that the composition of the atmospher e during the annealing strongly influences the growth processes and th e optical properties of CdS nanocrystals in thin SiO2 films.