Band-gap energies of sol-gel-derived SrTiO3 thin films

Band-gap energies of sol-gel-derived SrTiO3 thin films were studied in term s of annealing temperature and film thickness. The band-gap energies of hig hly crystallized films were comparable to those of single crystals reported , whereas for poor-crystallized films, their band-gap energy values were mu ch larger than those of single crystals. The larger band-gap energy shift w as believed to be mainly due to both quantum size effect and existence of a morphous phase in thin films. The band-gap energies also showed a strong de pendence on film thickness. There was a critical film thickness (similar to 200 nm), above which the films had band-gap energies close to those of cry stals or bulks, but below that, the values shifted largely, which can be at tributed to the influence of crystallinity of thin films. Such a thickness effect of band-gap energy should be of high interest in optical device appl ications. (C) 2001 American Institute of Physics.