Patent GB-1340671-A (GB)
Title: Process for epitaxially growing semiconductor crystals of predetermined conductivity type
IPC: H01L21/208
Filed: 1970-12-15
Abstract: 1340671 Growing semi-conductor crystals THOMSON-CSF 15 Dec 1970 [17 Dec 1969] 59571/70 Heading C1A [Also in Division B1] An epitaxially grown semi-conductor crystal of predetermined conductivity type is produced by (a) selecting three elements A, B, and C, A and B being from one of the two groups IV and VI of the Periodic Table and C being an element from the other of the two groups, the elements being capable of forming a solid solution A 1-x B x C (where x is the atomic fraction (B)/((A)+(B)), (b) preparing a bath consisting of a liquid mixture of the constituents, the mixture giving rise to a temperature/composition diagram with, as shown in Fig. 3, a stoichiometric line 1 and with a solidus curve 2 intersectingsaid line at a first point 10, the diagram having a liquidus curve 3 defining a second point 20 on the temperature level of said first point, the proportions of the elements being chosen to correspond to a third point 21 on said liquidus curve spaced from said second point 20 in a direction consistent with said predetermined conductivity type, (c) lowering the temperature of the bath from an elevated level to a level of incipient solidification corresponding to said third point, (d) immersing into the bath a substrate of the same crystal structure and that of a solid solution of said constituents, (e) progressively cooling the bath at a controlled rate with growth of a layer of said predetermined conductivity type on said substrate, (f) and terminating the controlled cooling of said bath at a final temperature below the level of incipient solidification with subsequent removal of substrate therefrom. Following termination of controlled cooling and prior to removal of the substrate, the proportion of said constituents may be modified in the bath to reverse the conductivity type with subsequent continuation of controlled cooling and formation of another layer of opposite conductivity type on said substrate. This modification may involve (1) a diminution of proportion of the element C with reference to the combined proportion of the other two elements, with substantially no change in the relative proportion of the other two elements or (2) the maintenance of the original proportion of the element C with reference to the combined proportion of the other two elements, with a change in the relative proportion of said other two elements. Preferably either selenium or tellurium is used as one of the elements and the other two elements of the composition are chosen from lead and tin and/or cadmium, zinc or mercury. As shown in Fig. 5, a substrate 30 of P-type conductivity is covered by an epitaxially grown N-type layer 31 forming therewith a junction 32, the two major faces of the body carrying electrodes represented by metal floatings 33 and 34. In another embodiment (Fig. 6, not shown) layer 31 is overlaid by a further epitaxially grown layer 35 of P-type and (Fig. 7, not shown) the layer 31 is subdivided into a multiplicity of cubic segments by etching through a mask of silicon oxide and the cubes provided on all lateral faces with semireflecting coatings. The semi-conductors may be used as photo-electric sensors, emitters of luminous radiation.