Abstract

The history of photoconductive camera tubes using the internal photoelectric effect began in 1950 with the Vidicon camera tube [1]. A photoconductive camera tube performs both photoelectric conversion and signal storage on a photoconductive target, which is a vapor-deposited film of Sb₂S₃ in Vidicon tubes. Although the Vidicon tube boasts a simple, small, and lightweight structure compared with the Image Orthicon tube that used the external photoelectric effect, it also suffers from several weak points such as large lag and dark current. The Vidicon, as a result, has not found much use in broadcasting-type television cameras that require high levels of picture quality. These weak points stem from the fact that excited carriers are easily trapped in Sb₂S₃-deposited film and that charge is injected into the target from external electrodes (injection-type target). However, the Plumbicon camera tube announced in 1963 features a target formed by a PbO film with a p–i–n structure that blocks the injection of charge from external electrodes (blocking-type target) [2]. With this type of target, the Plumbicon became the first photoconductive camera tube to feature low lag and low dark current among other superior features. In the 1970s, the Plumbicon rode the wave of change to color television broadcast facilities and became the leading tube for broadcast-class color television cameras replacing the Image Orthicon tube that used the external photoelectric effect. The research and development of photoconductive camera tubes was quite active. The 1970s, for example, saw the back-to-back development and commercialization of various blocking-type photoconductive camera tubes, including the Chalnicon using CdSe, CdSeO₃, and As₂S₃ as targets [3] and the Saticon using Se–As–Te [4,5].