Structure of photodoped and thermally Zn-doped glassy arsenic sulfide films

The structure of photodoped and thermally Zn-doped arsenic sulfide amorphous films has been investigated. X-ray-diffraction and electron-diffraction studies indicate that, after Zn doping, the ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films remain amorphous, although the amount of dissolved zinc is about 55 at. %. An extended x-ray-absorption fine-structure (EXAFS) study has been made at both sulfur and zinc K edges. EXAFS analysis indicates that the structure of photodoped and thermally Zn-doped films is similar. Zinc was shown to be surrounded by S and As atoms, while sulfur is bonded to zinc and arsenic. The interatomic distances obtained correlate with those found in c-ZnS and c-${\mathrm{Zn}}_3$ ${\mathrm{As}}_2$. The x-ray-absorption edge (Zn K edge) for doped films is situated in between those for c-ZnS and metallic zinc. Infrared absorption measurements also show the formation of Zn-S bonds. Despite the similarity in structure, photodoped and thermally doped films give electron spin resonance signals with different g factors. Different models for zinc dissolution in chalcogenide glasses are proposed and discussed on the basis of the experimental data.