Giant Thickness Contraction and Related Effects in Amorphous Chalcogenides

Abstract

One of the most remarkable radiation induced structural transformations known in any inorganic material was first reported in 1979 from our Laboratory¹. Irradiation of thin films of amorphous Se_0.75Ge_0.25 vacuum deposited at an angle of incidence of 80°, with 30/mW/cm² light intensity from a 250 U H vapour lamp showed a thickness contraction or physical densification of ∼12 Significantly larger (up to ∼ 39) densification was later observed on irradiation of such films with energetic electrons and ions. This giant densification leads to optical densification changes in optical constants and a red shift in the optical absorption edge and hence photodarkening. Among other significant changes induced are in the chemical etching both dry and wet rates, diffusion rates of superimposed metallic layer, and electrochemical absorption effects. The various radiation induced effects and their applications in high resolution submicron lithography, reprography and image storage have been investigated extensively by our students and others and the results are reported in literature^1-22