Photoconductive device having a target including a selenium blocking layer

1,137,107. Photo-conductive device. RADIO CORPORATION OF AMERICA. 17 Feb., 1966 [4 March, 1965], No. 7105/66. Heading H1K. A photo-conductive device comprises a conductive layer, a photo-conductive layer of selenium or selenium alloy over the conductive layer and a thin layer of pure vitreous selenium between the conductive layer and the photo-conductive layer, said thin layer being 100 to 1800 A thick. A glass envelope 14 is closed at one end by a glass plate 16, indium ring 18 and clamping ring 20. A mesh screen 22 is mounted across one end of a tubular focusing electrode 24. The photo-conductive target comprises a SnO layer 26, a stabilizing layer 32 of Au, Ag, Cu, Rh, Pd, Ge, GeO 2 , Sb 2 S 3 or Sb 2 O 3 to prevent crystallization of a blocking layer 30 of vitreous Se, an evaporated layer 28 of Se/Te/As/Sb alloy and a further stabilizing layer 34 of Ge, GeO 2 , Sb 2 S 3 , or Sb 2 O 3 . One or both of the stabilizing layers 32 and 34 may be omitted. The blocking layer 30 is said to eliminate ohmic contact between the conductive layer 26 and the selenium alloy 28 during operation of the device thus reducing dark current.