Influence of light on structure of amorphous selenium layers

Abstract

After exposure of amorphous selenium islands to luminous ux of 1¢10 6 lx, they do not become crystalline, but remain amorphous. However, light stimulates polymerization of molecules in those islands. For this reason, heating of a layer that is exposed to light does not cause a decrease of the mean thickness of the layer, but heating of the layer in the dark causes a decrease of its mean thickness. Therefore, the mean thickness of the illuminated layer is 3 to 4 times greater than the mean thickness of the layer in the dark. In addition, the fraction of the substrate covered by the islands is 1.5 to 2 times larger in the exposed layer than in the unexposed layer. However, illumination of a continuous layer speeds up its transformation into an island-type layer. Therefore, in order to obtain an extremely thin continuous layer of amorphous selenium, during growth of the layer it must be exposed to light only until it becomes continuous. Starting from that moment, the light must be switched off.