From Event: SPIE Optical Engineering + Applications, 2016
Although present imaging devices are mostly silicon-based devices such as CMOS and CCD, these devices are reaching their sensitivity limit due to the band gap of silicon. Amorphous selenium (a-Se) is a promising candidate for high- sensitivity photo imaging devices, because of its low thermal noise, high spatial resolution, as well as adaptability to wide-area deposition. In addition, internal signal amplification is reported on a-Se based photodetectors, which enables a photodetector having effective quantum efficiency over 100 % against visible light. Since a-Se has sensitivity to UV and soft X-rays, the reported internal signal amplification should be applicable to UV and X-ray detection. However, application of the internal signal amplification required high voltage, which caused unexpected breakdown at the contact or thin-film transistor-based signal read-out. For this reason, vacuum devices having electron-beam read-out is proposed. The advantages of vacuum-type devices are vacuum insulation and its extremely low dark current.
In this study, we present recent progresses in developing a-Se based photoconductive films and photodetector using nitrogen-doped diamond electron beam source as signal read-out. A novel electrochemical method is used to dope impurities into a-Se, turning the material from weak p-type to n-type. A p-n junction is formed within a-Se photoconductive film, which has increased the sensitivity of a-Se based photodetector. Our result suggests a possibility of high sensitivity photodetector that can potentially break the limit of silicon-based devices.
Tomoaki Masuzawa, Taishi Ebisudani, Jun Ochiai, Ichitaro Saito, Takatoshi Yamada, Daniel H. C. Chua, Hidenori Mimura, and Ken Okano, "Development of an amorphous selenium based photoconductor and its application in a high-sensitivity photodetector
(Conference Presentation)," Proc. SPIE 9957, Wide Bandgap Power Devices and Applications, 99570D (Presented at SPIE Optical Engineering + Applications: August 29, 2016; Published: 2 November 2016); https://doi.org/10.1117/12.2237545.5170791540001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon