Optically Transparent Electrodes for Photoresponse Enhancement of MSM Photodetector

The paper presents the obtaining of transparent conducting ZnO thin layers and their application as interdigitated transparent Schottky electrodes in a silicon based metal-semiconductor-metal (MSM-PD) photodiode structure. Optically transparent electrodes from impurity-doped ZnO thin layers have been prepared by vacuum thermal deposition method from metallic powders of Zn, Al and Sn followed by oxidation at 623K. The optical properties, investigated by spectro-photometry, show a high transparency (T>85%) over a large spectral range 0.4-1mum and from electrical properties measurements a low resistivity of <10^-4 resulted. These TCO layers have been deposited on silicon epitaxial wafers and MSM-PD with interdigitated transparent ZnO electrodes was achieved. An enhanced responsivity, was obtained by eliminating the surface shadowing by opaque electrodes. The measured capacitance of 1.4pF assures a high speed response in the GHz range