BOND ARRANGEMENT AND OPTICAL BAND-GAP IN GEXAS40-XS(SE)(60) GLASSES AND THIN-FILMS

The possible bond distribution in ternary glass systems of the GexAs40 -xS(Se)(60) family is given. A modified (by us) Ordered Bond Network M odel (OBNM) taking into account the difference in the magnitude of the heteropolar bonds as well as the presence of homopolar Ge-Ge and As-A s bonds is used. Manca's relation between mean bond energy and gap ene rgy (E(g)) is applied for the estimation of the optical band gap (E(g) (o)) of the investigated glasses. The values of E(g) are compared with experimentally determined E(g)(o) of fresh and annealed GexAs40-xS(Se )(60) films. The differences between calculated and experimentally obt ained E(g)(Z) dependences are discussed from the point of view of bond arrangement and topological considerations.