Influence of Bulk and Surface Properties on Image Sensing Silicon Diode Array

A television camera tube with a silicon diode array target has been reported recently by Crowell, Gordon and their co-workers. 1-3 A target of the general type used in this tube was first proposed in 1951 by Reynolds, 4 later discussed by Heijne, 5 and recently analyzed by Wendland. 8 It is similar, but not identical in operation, to the evaporatedfilm photoconductive target, typically antimony trisulfide, which is commonly used in vidicon TV camera tubes. 7 A vidicon-type tube is of interest for use in the Picturephone® visual telephone station set because it is the least expensive and smallest camera tube that has the required sensitivity and resolution. The silicon target has certain potential advantages over the evaporated-film photoconductive target. This paper describes the effect of bulk and surface properties on the performance of the silicon target. The properties that dominate the conversion of incident photons to electrons in the external circuit and the diode leakage current are analyzed in detail. These analyses, together with the relevant processing techniques and resulting behavior, have been combined into a description of silicon diode arrays for image sensing. The operation of the silicon target is illustrated in Fig. 1. A scanning electron beam charges the diocle-array side of the silicon target down to cathode (ground) potential while the n-region is held a few volts above ground. This puts reverse bias on the diodes. Light shining on the other side of the target and absorbed in the n-region generates holes, some of which diffuse to the diodes and reduce the negative charge on the p-regions.