Electric measurement and nuclear microanalysis of the degradation induced in thin film semiconductors by electrode diffusion

So far electrical characteristics degradation of electronic devices made of amorphous semiconductor thin films has not been related to the evolution of the electrode-glass interface. For chalcogenide systems, binary (As50Te50) or quaternary (As38Ge14Te43S5) and gold electrodes, 3.5MeV alpha particle backscattering has evidenced a complex thermal diffusion process below the glass transition temperature of these materials. Compared with elementary media As and Te where the Fick's law applies such materials are subject to an 'easy path' diffusion process, interpreted by the Fisher's formalism initially proposed for the grain-boundary diffusion in polycristalline materials. In the other hand, the electrical performance degradations, mainly expressed by the change in the activation energy of the systems, is closely correlated with the gold content in the middle of the film. Various hypothesis are proposed to interpret such a mechanism, the most consistent being a gold migration at preferential diffusion sites, well localized, the material remaining basically amorphous. Some reordering due to the presence of the metal appears feasible in this temperature range where the atomic mobility is very low