Structure of amorphous GexSe1-x and GexSeyZnz thin films:: an EXAFS study

Extended X-ray absorption fine structure (EXAFS) measurements have been made on thin films of a-GexS1-x with 0.2 < x < 1. The results show that the Ge-Ge, Ge-Se and Se-Se bond lengths have values 2.45, 2.37 and 2.32 (all +/-0.03) A, respectively and are independent of film composition. The partial atomic coordination numbers of Ge and Se suggest that the films have a predominantly chemically ordered 4-2 coordinated covalent bond network structure throughout the whole composition range, as found by others for Ge-Se bulk glasses with x < 0.4. EXAFS data for a-GexSey Zn-z films show that the lengths of Ge-Zn and Se-Zn bonds are 2.57 +/- 0.05 and 2.44 +/- 0.03 Angstrom, independent of the composition. Results on the atomic coordinations reveal that Zn is fourfold coordinated and preferentially bonds to Se atoms. (C) 2002 Elsevier Science B.V. All rights reserved.