Patent GB-753133-A (GB)
Title: Improvements in or relating to electric semi-conducting devices
Inventor: DRAKE CYRIL FRANCIS
IPC: H01L21/24
Filed: 1953-07-22
Abstract: 753,133. Semi-conductor devices. STANDARD TELEPHONES & CABLES, Ltd. July 22, 1953, No. 20395/53. Class 37. A transistor, rectifier or other semi-conductor device comprises a single crystal slice having a recess in at least one face, below which are a plurality of layers of successively opposite conductivity types and electrodes are secured to two or more of the layers. Fig. 1g shows a PNP transistor comprising a single crystal N-type germanium body 1 having a base electrode 13, and emitter and collector electrodes 12 and 10 respectively, in recesses and engaging P-type layers on the N-type body 1. The base electrode may alternatively consist of a copper coating 15 on the outside of the body 1, especially for coaxial mounting arrangements. The emitter recess is made smaller than the collector recess to improve the carrier collection process, and different impurity concentrations of the P-type layers are provided to improve the collector and emitter resistances. The transistor is produced by cutting a recess 2 (Fig. 1e) in a disc 1 of N-type germanium, etching, evaporating gold (an acceptor material) on to one surface, and heating to 850‹ for four hours in hydrogen to diffuse the gold into the germanium over the whole surface of the body. After annealing, recess 6 is cut, the under surface etched while the remaining surface is protected by rubber paint, to remove the P- layer from that portion, which is then plated with an acceptor material such as aluminium. The body is then heated to 850‹ C. for five minutes to diffuse the aluminium into the lower surface of the germanium to provide a P-type layer 8. The upper and lower surfaces are then ground off, and the body annealed by heating to 550‹ and cooling slowly to remove lattice defects produced in the original N-type body by the previous heating treatments. The bottom of the recesses 2 and 6, and part of the lower surface of the body are copper plated and electrodes 10, 12 and 13 soldered to the copper plating. Indium may be used as solder for emitter electrode 12. The edges of the PN junction may be etched, and the whole covered with a, protective material. Fig. 2c shows an alternative NPN construction having collector electrode 30 engaging the original N-type body, base electrode 29 engaging P-type layer 19, and emitter electrode 28 engaging an N-type layer 20 on top of P layer 19. This construction is produced by a method similar to that for Fig. 1e, g and the additional N layer 20 is produced by heating to diffuse a layer of donor material such as antimony, deposited on the P layer on the upper surface of the body. Fig. 3 shows an NPNP arrangement, with the base electrode 40 in contact with N-type body 31, emitter electrode 38 in contact with P layer 36, a " control " electrode 41 in contact with P layer 34, and collector electrode 39 in contact with N-layer 35. The invention may be applied to two electrode devices, as by having only electrodes 10 and 12 in Fig. 1g, or electrodes 39 and 38 in Fig. 3b which are separated by NPN and NPNP layers respectively. Such devices may have voltage-current characteristics as described in Specification 686,958. The recesses in the semi-conductor may consist of holes in disc-shaped bodies, or channels cut in rectangular shaped bodies. A plurality of devices may be produced simultaneously by carrying out many of the processes on a large sheet of semi-conductor which is then cut to form the separate elements. Conversion of conductivity may be effected by heating'instead of impurity diffusion. Information for calculating the extent of diffusion is given. Silicon may be used in place of germanium. Specification 700,231 also is referred to.