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911,668. Semi-conductor devices. WESTERN ELECTRIC CO. Inc. March 23, 1961 [March 25, 1960], No. 10613/61. Class 37. A PN junction in an N-type silicon body is produced by alloy-diffusion of a layer of aluminium and boron oxide into the surface of the body. In one embodiment phosphorus is diffused into a slice 11 of P-type silicon having 5x1019 impurity centres per c.c. to produce an N-type layer 12. The layer is then masked and a series of coatings 13 consisting of gold with 1% or less antimony is deposited on the surface. The mask is moved 1 mil and a second series of coatings 14 is produced by co-operation of aluminium and boron oxide sequentially or simultaneously. The aluminium may be in the form of a wire surrounded by a tungsten filament; if desired a further film of aluminium may be deposited on to the boron oxide. The slice is then heated to 700‹ C. for about one minute, and then abruptly to 1000‹ C. and down again by sudden cooling, this heating "spike" lasting for about 10 seconds. This process results in ohmic electrodes due to the diffusion of the gold-antimony, and additional thin P-regions with acceptor concentration equal to or exceeding 1019 per c.c. The slice is then cut to provide a plurality of mesa diffused base transistors with the P-type regions forming high injection efficiency emitters. The invention may also be applied to the production of tunnel diodes. Specifications 809,642 and 911,667 are referred to.