OPTICAL-PROPERTIES AND STRUCTURE OF UNHYDROGENATED, HYDROGENATED, ANDZINC-ALLOYED A-GEXSE1-X FILMS PREPARED BY RADIOFREQUENCY SPUTTERING

The optical absorption edges of films in the a-GexSe1-x system, prepar ed by radio-frequency sputtering, have been determined over the compos ition range 0.2 < x < 1. The largest optical gap occurs at a compositi on corresponding to GeSe2, as for glasses and evaporated films. Hydrog enation and alloying with up to 27% zinc both lead to only small chang es in the absorption edges. The electrical conductivity activation ene rgies are lower in films alloyed with zinc. Extended X-ray absorption fine structure (EXAFS) measurements confirm a chemically ordered rando m network model with Ge and Zn both being four-fold coordinated and Se two-fold coordinated. The optical data are interpreted in terms of ch anges in the local structure with composition.