Patent GB-1059395-A (GB)
Title: Improvements in and relating to solid state electron devices
IPC: H01L27/00
Filed: 1964-06-12
Abstract: <PICT:1059395/C6-C7/1> A semi-conductor device comprises two electrodes separated by a layer of a ternary II-VI compound the composition of which is graded between the electrodes to produce different energy band gaps at the electrodes.  The device is produced in the apparatus shown in Fig. 6 in which glass substrates 20, 54, 60 are supported over boats 34, 36 containing zinc sulphide and cadmium sulphide respectively.  Shutters 50, 52 cover these sources and a further shutter (not shown) may cover substrate 20.  Screen 64 is provided between the boats to prevent deposition from boat 34 on to wafer 60 and from boat 36 on to wafer 54.  Wafer 20 has a metal electrode 22, which may be gold, chromium, indium or platinum vapour deposited on it, and wafers 54 and 60 are provided with lamps 55 and 58 and photo-cells 56 and 62 to monitor the rate of deposition of the zinc sulphide and cadmium sulphide respectively. The apparatus is evacuated and the boats heated to just below the evaporating points of their contents.  The heating is stopped, the apparatus is filled with argon, and a high voltage is applied to electrode 68 to produce a glow discharge which cleans substrates 54 and 60 and electrode 22. The apparatus is again evacuated and a layer of zinc-cadmium sulphide is deposited on electrode 22 graded from 100% cadmium sulphide at electrode 22 to 70% to 95% cadmium sulphide at the exposed face on which a second electrode is vapour deposited.  The properties of the semi-conductor layer may be improved by vacuum baking before deposition of the electrode.  The size and shape of the semi-conductor layer and the deposited electrode may be controlled by masking during deposition or by etching using a photo-lithographic technique.  The device may be used as a voltage variable capacitance diode, or as a photo-diode, and may also be used for the cathode of a vacuum tube by using a thick electrode instead of the substrate and by using a thin film of gold coated with a low work function metal for the second electrode so that high energy electrons are emitted easily.  As shown, Fig. 8, a triode structure comprises a substrate 90 on which are successively deposited a metal collector electrode 92 a layer 96 of zinc-cadmium sulphide, which may be of uniform composition or graded from 100% cadmium sulphide at electrode 92 to 80% cadmium sulphide at the other surface, a thin metal base electrode 94, a layer 100% of zinc-cadmium sulphide graded from 85% cadmium sulphide to 100% cadmium sulphide, and an indium emitter electrode 98.  The base layer may be replaced by a mesh or grid of metal.  The semi-conductor materials may comprise the oxides, selenides and tellurides of zinc, cadmium, strontium and mercury, and the electrodes may be of chromium or platinum. Several circuit components can be formed on a single substrate and one or both electrodes of a diode device, as previously described, may be extended to make connections with electrodes of other circuit elements.  Alternatively a circuit element, such as a capacitor, may be formed on top of the diode structure using the deposited electrode as a common connection.