Photoconductive selenium film target for image pick=up tube - has layered construction with addn. of tellurium and arsenic in non-homogeneous distribution to give improved long term performance

摘要

Photoconductive film comprises (a) a first layer contg. selenium together with tellurium and elements which can form deep levels in selenium, in an average concn. of =10 atom %; (b) a second layer contg. Se to which Te is added with a continuous distribution of concn. with a peak value of =15 atom% %. Film further comprises (c) a third layer contg. Se to which elements which can form deep levels in Se are added with a continuous distribution of concn. with a peak value of =15 atom %; and (d) a fourth layer contg. Se to which Te and elements which can form deep levels in selenium are added, in an average concn. of =10 atom %. Pref. the thickness of the layers (a), (b) and (c) are 100 angstroms, 200-5000 angstroms, and 500-300 angstroms respectively. The elements which can form deep levels in Se are e.g. As, Sb, Bi, Si and Ge. The concn. of elements added to the third layer is pref. greatest at the interface with the second layer, and falls gradually towards the interface with the fourth layer. The films are built up e.g. by successive deposition of layers is not 100 angstroms thick to give the required concn. distribution of the elements. These layers can be formed e.g. by stagewise vaporisation of the respective materials. The films are esp., useful as photoconductive targets in image pick-up tubes with rectifying contact layer. Variations in signal strength and the retained image effect normally obtd. when the same object is exposed continuously are eliminated.