Raman investigation of photoinduced diffusion in amorphous Ge/Se multilayers

Abstract

Multilayered, evaporated films of a-Ge/Se were prepared and investigated structurally via Raman spectroscopy. Under the intense illumination the near uniform layers were observed to mix, manifested by a growth in the Raman feature associated with the GeSe4 tetrahedral unit. Intervening layers of predominately GeSe2 thus formed in a layer morphology and arose from the photoinduced diffusion of the Se atoms through the network. The growth of the mixed layers is then modelled. From a comparison of the photoinduced diffusion cross sections evaluated from the model with photostructural changes and other photoinduced effects such as photoluminescence (PL) and photoconductivity (PC) in, particularly, a-Se, it is shown that the diffusion mechanism appears to follow that of the photodarkening phenomena (where the optical absorption edge is shifted to lower energies on irradiation of around band gap light), several models of which are discussed.