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Fabrication of photodiode by screen printing technique

The photodiode is one of the most commonly used devices for photodetectors. Light absorption in the semiconductor produces electron-hole pairs in the depletion region which are separated by the electric field, leading to the flow of current in the external circuit. This paper describes preparation and characterization of photodiodes by the screen printing technique. Screen-printing is a cost effective thick film deposition method, where a paste containing the desired materials is printed on the substrate. The substrate is then fired under a controlled environment to yield devices bonded to the substrate. In this experiment, a layer of phosphorous thick films were deposited on the Si-substrate. Then, the p-n junction was formed by the usual doping via the diffusion method. The samples were characterized for the rectifier effect, quantum efficiency, response time and rise time. In the optimization process, samples were doped at temperatures from 800-1000/spl deg/C. It was found that samples doped at 900/spl deg/C had the highest speed and response time of 0.32 s and rise time of 0.48 s. This sample also has the highest responsivity and quantum efficiency. Problems in the thermal diffusion process and electrode design are described in detail.