Diffusion of oxygen in CdSe-photosensor arrays

Aiming to optimize the thin-film retina of the ‘Electronic Eye’, a novel camera, we investigated the microstructure and the spatial distribution of atomic species in a multilayer structure of CdSe-sensor arrays with both, transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). AES sputter depth-profiling revealed diffusion of oxygen from the SiO2-layer through the CdSe-layer into the Cr and Al metallization layers. In order to map the spatial distribution of oxygen in the CdSe-layer we employed a Zeiss EM 912 Ω transmission electron microscope, which is equipped with an imaging energy filter for acquiring electron spectroscopic images (ESI). Extraction of electron energy-loss spectra from ESI images revealed the formation of chromium oxide at the interface between Cr and Al. This oxide formation in the contact material and the oxide diffusion are held responsible for spatial inhomogeneities in the photoconductivity of CdSe-sensor arrays.