Diffusion of silver associated with photodoping into amorphous chalcogenides

The photo-enhanced reaction between metallic silver and amorphous chalcogenides is known as “photodoping”. Diffusion of silver in chalcogenides associated with photodoping has been investigated by an optical edge tracing technique using a microscopic spectrophotometer. It is suggested that the photodoping with silver involves two different steps; a photochemical reaction between metallic silver and chalcogenides by the aid of photo-excitation of chalcogenides and the diffusion of silver in the doped region. The amount of the silver diffusing through the doped region is about 20% of the maximum amount of the silver dissolved in the chalcogenide layer. Diffusion of silver in a chalcogenide containing sulfur or germanium is very slow compared with that in a chalcogenide containing selenium or tellerium, indicating that the diffusion rate of silver greatly depends upon the chemical composition of the chalcogenide. Further, the diffusion of silver in As₂Se₃ film proceeds at least 100 times faster with light of 4 mW/cm² and 380 nm in wavelength than it does in the dark. It is also confirmed that light excitation in the region doped with silver effectively causes photodoping.