Patent GB-1218451-A (GB)
Title: Improvements in or relating to light/electric translating arrangements
Inventor: HAKKI BASIL WAHID
IPC: G05B11/00
Filed: 1968-05-09
Abstract: 1218451 Semi-conductor devices WESTERN ELECTRIC CO Inc 9 May 1968 [15 May 1967] 21985/68 Headings H3U UC U22 U30 U28 and U31 [Also in Division C4] Photo-sensitive or light emissive units are mounted on the surface of a semi-conductor strip and are scanned by a high field domain which is caused to pass along the semi-conductor strip. Domains may be propagated in Gunn effect semiconductors such as gallium arsenide, gallium antimonide, indium phosphide, or cadmium telluride and in Piezo-electric semi-conductors such as cadmium sulphide. Fig. 2 shows one column of a rectangular array mounted on a common semiinsulator substrate 22, each column being energized in turn. The N-type strip 11 in which the domain is propagated in response to a D.C. bias applied across the end contacts 18, 19 bears a series of P-type islands 13 forming luminescent diodes 12 with the N-type material. The individual diodes are activated by the passage of a domain beneath them. The field associated with the domain provides reverse bias across part of the junction and forward bias across another part so that carriers are formed and recombine with the emission of light. A video signal is applied from source 16 via capacitors 15 to modulate the light output. (The P-type islands may be replaced by an electroluminescent layer but such an arrangement is less efficient). In a light-receptor modification the semi-conductor is chosen for maximum photoresponse and an image falling on the structure produces outputs at the diodes as each is scanned which are fed to a load 25 replacing the video signal source. Instead of taking the output in this way, each diode may be provided with a metallic electrode which is left floating, the output being taken across a load in series with the domain propagating bias supply. In a light-emitting structure generally similar to that of Fig. 2, the domain propagating strip is an N-type surface layer on a semi-insulating cadmium sulphide substrate. The individual diodes are carried by the surface layer and each have lower and upper layers respectively of N- and P-type gallium arsenophosphide. In a further lightemitting array Fig. 5 the strip is of gallium arsenide cut with the (100) axis along its length and operated in the Piezo-electric mode. To stabilize the site of domain initiation a separately energized section of the material 526/518 is operated in the Gunn mode and the domain thus formed continues into the acoustic/Piezo-electric section 518/519. In this embodiment the lightemitting diodes are MIS structures sharing a common layer 529 of activated zinc sulphide or zinc oxide, a common insulating layer 530, and having individual metallic contacts 531. The reversebias/forward-bias sequence caused by the passage of the domain causes such diodes to emit light. An embodiment similar in principle Fig. 6, (not shown) has a series of metallic electrodes 634 formed directly on the domain-propagating strip. Formed over these and the layer is a layer (635) of insulating material, a layer of semi-conductor (636) a further layer (637) of insulating material and a set of individual metallized areas (638) linking adjacent MIS devices. This arrangement produces four MIS junctions in series for each site - one diode of the pair responds to the leading edge of the domain while the ''upstream" diode is responding to the trailing edge - and reduces the risk of insulator breakdown.