Patent GB-1141098-A (GB)
Title: Semiconductor voltage transformer
IPC: H01L31/173
Filed: 1968-01-04
Abstract: 1,141,098. Semi-conductor devices. INTERNATIONAL BUSINESS MACHINES CORP. 4 Jan., 1968 [13 Jan., 1967], No. 628/68. Heading H1K. A semi-conductor voltage transformer comprises a plurality of series-connected PN junctions coupled, in operation, by recombination radiation to at least one other PN junction. As shown, Fig. 5, the transformer comprises a body of gallium arsenide having a plurality of PN junctions 26, effectively connected in series by electrodes 66A to 66C, electrically isolated from PN junction 12 by a region 22 of intrinsic or semi-insulating material. Junction 12 is forward biased and emits recombination radiation 34 which passes through region 22 to the junctions 26 where it generates both a photocurrent and a photovoltage. The output voltage and current of the arrangement are functions of the load impedance, the opencircuit voltage being four times, and the shortcircuit current being equal to, that of a single one of the junctions 26. The characteristic includes both a constant voltage portion and a constant current portion, Fig. 2 (not shown). The junctions can be produced by diffusion of zinc to form the P-type regions and tellurium to form the N-type regions, and the surface of the body may be metallized to prevent loss of radiation. The device may be connected so that the input voltage is also in series with the seriesconnected junctions and the load, Fig. 7 (not shown), to increase the output voltage. One of the series-connected junctions may have a smaller area, Fig. 3 (not shown), or may be arranged to receive a smaller proportion of the radiation or may have different doping levels than the other junctions to provide a lower saturation photo-current so that the transformer provides a constant-current output for a large range of load impedances. The body may have a semi-cylindrical shape with the emitting junction (12) extending along the axis of the cylinder, and the seriesconnected junctions extending parallel to the axis along the curved surface, Fig. 6 (not shown), to ensure that each of the series-connected junctions receives an equal amount of radiation. In a further embodiment the emitting junction and series-connected junctions are formed in the same surface of an intrinsic body with all the junctions co-planar, Fig. 10 (not shown). The emitting junction lases and the device may be arranged to form a resonant cavity for the radiation. The device may be used as a step-down transformer by connecting the input to the seriesconnected junctions and the load to the single large area junction which acts as a plurality of parallel-connected junctions, Fig. 8 (not shown). The output voltage is smaller than the input voltage but the current is larger. The device may be used as an A.C. transformer by biasing the input junction to a linear portion of its characteristic and superimposing the A.C. input on the bias. The output also comprises an A.C. signal superimposed on a direct voltage due to the D.C. input bias. The insulating material may also be gallium phosphide which may be epitaxially combined with gallium arsenide and has a larger band gap. Alternatively the insulating material may be an epoxy resin. The junctions may also be formed in gallium arsenide amphoterically doped with silicon, and may be produced by solution regrowth or vapour growth as well as by diffusion. The device may also be of indium phosphide epitaxially combined with semi-insulating gallium arsenide as the insulating material.