Short-Range Structure in Amorphous Ge3(Se1—xSx)4 and Ge3(Se1—xTex)4 Alloys

Abstract

The short-range structure in amorphous Ge3(Se1—xSx)4 alloys with x = 0 to 1, and Ge3(Se1—xTex)4 alloys with x = 0 to 0.25 has been investigated through X-ray diffraction and Raman scattering measurements. Raman spectra in both amorphous alloys have revealed that structural units containing a direct Ge–Ge bond, such as X3/2Ge–(GeX2/2)n–GeX3/2, or Ge(Ge(4—m)/4Xm/2), are formed in the alloy, in addition to the remaining GeX4/2 tetrahedral units (X = Se, S and Te). The structural analysis by the X-ray diffraction method has indicated that the bonding distances of Ge–S, Ge–Se, Ge–Te and Ge–Ge pairs, which are involved in the first coordination shell, are all composition-independent and very close to the correponding covalent values, and the coordination numbers of the constituting atoms are nearly four for Ge and two for X. Any indication on a direct X–X bond has not been observed in the present measurements, which suggests that every X atom in the alloy preferentially coordinates to Ge atoms. The local order corresponding to crystalline GeX has not been found out in both amorphous alloys.