Short-range structure in amorphous Ge-3(Se1-xSx)(4) and Ge-3(Se1-xTex)(4) alloys

The short-range structure in amorphous Ge-3(Se1-xSx)(4) alloys with x = 0 t o 1, and Ge-3(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 d irect Ge-Ge bond, such as X3/2Ge-(GeX2/2)(n)-GeX3/2, or Ge(Ge(4-m/4)X-m/2), are formed in the alloy, in addition to the remaining GeX4/2 tetrahedral u nits (X = Se, S and Te). The structural analysis by the X-ray diffraction m ethod 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 comp osition-independent and very close to the corresponding covalent values, an d 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 i n the present measurements, which suggests that every X atom in the alloy p referentially coordinates to Ge atoms. The local order corresponding to cry stalline GeX has not been found out in both amorphous alloys.