Improvements relating to photo-conductive targets and especially television pick-up tubes and analogous image pick-up tubes

摘要

794,331. Semi-conductor devices. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 11, 1954 [Aug. 11, 1953], No. 22096/53. Class 37. [Also in Group XL (a)] Time-lag in a low-velocity photo-conductive iconoscope is reduced by increasing the thickness of the target layer above 8 microns and so reducing the capacity. This is done by combining the photo-conductive layer with a further thicker layer of semi-conductive material having a range, for the charge carrier involved in the photo-conduction, which is long compared with that of the photo-conductive layer, so as not to impede conduction. In one form the photo-conductive layer 5 of P-type material (such as Se or Se+Te) is deposited directly on the conductive signal plate 4, and the layer 6 of P-type semi-conductor covers the layer 5 and is exposed to the scanning beam. The layer 6 may be a single crystal, or of mosaic form to reduce transverse conduction; it may be cassitarite (SnO 2 ), Brookite (TiO 2 ), polybasite (9Ag 2 S, Sb 2 S 3 ) or spodumene (LiAl(SiO 4 ) 2 ). In another form, an N-type photo-conductive layer of antimony trisulphide is deposited on one side of an N- type semi-conductive layer of Rochelle salt or alkali halide, and a signal plate on the other side. To improve colour response the second layer may also be photo-conductive, for example, to blue light while passing on the red light to the red-sensitive first layer; in this case the second layer may be cadmium sulphide. The relative thicknesses may be 0.5 microns for the photo-conductor and 19.5 microns for the semi-conductor. Specification 794,332 is referred to. Reference has been directed by the Comptroller to Specification 705,533.