GB1311404A - Photoelectric conductor devices - Google Patents

Abstract

1311404 Image pick-up tubes; phoioconductive devices TOKYO SHIBAURA ELECTRIC CO Ltd 17 Aug 1971 [17 Aug 1970] 38589/71 Headings H1D and H1K A photoconductive target comprises a first layer comprising photoconductive cadmium selenide, a second layer comprising a cadmium salt of an oxy-acid, and a high resistance third layer comprising a compound other than cadmium selenide. Typically the layers are deposited in the above order on a nesa glass signal electrode. The first layer may consist of CdSe which is substantially pure or doped with copper, silver, gold, indium, gallium, aluminium, halogens, tellurium antimony, bismuth, lead, tin, or alkali or alkaline earth metals. The second layer, which is preferably less than 2000 Š thick, may consist of the cadmium salt of selenious acid with or without an admixture of cadmium oxide, while suitable materials for the third layer, which may consist of a number of sublayers, are one or more of zinc sulphide, arsenic dier tri-sulphide, arsenic tri-selenide, germanium selenide, thallium sulphide or selenide, bismuth trisulphide or selenide, zinc selenide, cadmium telluride and antimony trisulphide or selenide. For solid state scanning the target may be additionally provided with strip electrodes on the third layer and for improved resolution the signal electrode may also be divided into strips. The targets exhibit lower dark currents varying less with ageing while retaining the sensitivity of known targets. A typical target is made by first vacuum depositing CdSe, then heating it for 15 minutes at 600‹ C, in nitrogen, for 30 minutes at 500‹ C. in Se vapour, and then heating in nitrogen containing oxygen and selenium vapour and cooling rapidly to form the selenious acid salt. Finally zinc sulphide is vacuum deposited to a thickness of 0À1 Á. Alternatively, after deposition the cadmium selenide is heated at 500‹ C. for 10- 50 minutes in nitrogen containing oxygen and selenium and the oxygen and selenium content reduced to zero while cooling rapidly. In this case the third layer is arsenic triselenide vacuum deposited to a thickness of 0À4 Á. Another way of forming the cadmium salt is by heating the selenide layer to 300‹ C. in the presence of selenium dioxide. A single crystal slice of the selenide may be stuck to the nesa glass in place of the deposited layer.