Photodecomposition of Amorphous As2Se3 and As2S3

Electromagnetic radiation approximately equal to band‐gap energy has been established as responsible for the dissociation of amorphous As₂Se₃ and As₂S₃. The dissociation is accompanied by an optical densification observable as a ``photographic'' effect in thin films of these materials. The dissociation can be expressed by the following equations: $${\mathrm{As}}_2{\mathrm{Se}}_3\to {\displaystyle {lim}^{\mathrm{hv}}}x\mathrm{As}+{\mathrm{As}}_{\text{2−x}}{\mathrm{Se}}_3\text{,\hspace{0.17em}0<x<2\hspace{0.17em}}{\mathrm{As}}_2{\mathrm{S}}_3\to {\displaystyle {lim}^{\mathrm{hv}}}\mathrm{2As}+\mathrm{3S}.$$ The densification is reversible by thermal cycling to higher temperatures. A detailed analysis of the experimental results is given and a mechanism is proposed which explains the photodecomposition reactions and the thermally induced reversibility in As₂Se₃. The photographic cycling characteristics of As₂Se₃ are discussed in the light of its potential device application.