PHOTODETECTORS FOR AUTO-FOCUS SYSTEMS.

Four types of photodetectors with dual photodetecting elements and two types of position sensitive photodetectors (PSDs) have been developed and put into practical use for auto-focus systems in cameras. The PSDs, PN311/321, which make use of lateral photoeffect of a pn junction have the ability to detect a light spot position continuously without scanning. The response time and the noise characteristics of a reverse biased silicon pin photodiode were investigated, and the calculation results have been applied to the design of a structure. Additionally, a fabrication process for making a uniform resistive layer has been established. As a result, a high linearity of position sensing ( plus or minus 0. 3%), a low dark current (below 0. 3nA), and a high sensitivity have been achieved. These devices are suitable for auto-focus systems and extensive applications to position-sensing systems are expected.