Patent GB-721671-A (GB)
Title: Signal translating devices utilizing semiconductive bodies and methods of making them
IPC: H01L29/00
Filed: 1950-11-29
Abstract: 721,671. Semi-conductor devices. WESTERN ELECTRIC CO., Inc., Nov. 29, 1950 [Nov. 30, 1949; Dec. 30, 1949], No. 29223/50. Class 37. [Also in Groups II and XXII] In a semi-conductor body of one conductivity type, a layer or zone of different conductivity is formed by applying material characteristic of the opposite conductivity type to a face of the body and then heating to effect diffusion of the material into the body. The zone may consist of a region of low conductivity of one type in a body of high conductivity of the same type, or of a region of opposite conductivity type to that of the body. Figs. 1 and 2a show a transistor device having a region 21 of " n " or lowconductivity N-type in a body of " N " or highconductivity N-type, the emitter 23 and collector 24 electrodes both being in contact with the " n " region. The body 20 consists of highconductivity N-type germanium, and region 21 is produced by depositing gold on this region through a mask, and heating for about five hours at 500‹ C. in hydrogen to diffuse the gold into the germanium. Excess gold is then removed by polishing or grinding. The gold acts as an acceptor impurity to produce the low-conductivity " n " zone. Other acceptor materials may be used and may be made sufficiently effective to convert the zone to P- type material. Alternatively, an N-type zone in a P-type block may be provided by using donor materials. Successive layers of donor and acceptor materials may be used providing N and P layers. In a further arrangement (Figs. 13, 15) a block comprising a thin P-portion between two N-portions 110A, 110B is produced by treating and bonding two N-type blocks. The faces 120A, 120B of N-type blocks 110A, 110B of germanium are lapped, etched and washed and covered with a layer of copper by electroplating or evaporation. The blocks are then pressed together and heated for about 18 hours at 700‹ to 900‹ C. in hydrogen, which has been passed over palladinized Alundum (Registered Trade Mark) to remove oxygen. Since the heat treatment may have converted some N-type to P-type, the unit is again heated for 24 hours at 500‹ C. to convert the bulk back to N-type. In place of copper, gold or aluminium may be used which act both as acceptors and bonding agents. Alternatively other bonding agents such as tin, silver or platinum may be used with one or more acceptors such as gallium, indium, thallium, gold, aluminium or boron. Agents which form low-melting eutectic mixtures with germanium are particularly suitable such as gold, aluminium, tin and platinum, which may be deposited by evaporation or electrodeposition in discreet layers, or simultaneously to form an alloy. Further control of the extent of the P-zone could be achieved by diffusion heat treatment before the sintering process. N-type zones can be formed in P-type blocks, using donor materials such as phosphorus, arsenic, antimony or bismuth. Assemblies having several zones may also be formed, such as an NPNP configuration. Donors and acceptors can be deposited simultaneously for control purposes. Silicon may be used in place of germanium. Fig. 13 shows a transistor comprising emitter, 111, base 113 and collector 112 electrodes on an N-type semi-conductor body with a portion of P-type conductivity between the emitter and collector electrodes. The arrangement provides a low base resistance with consequent low feedback, and high current gain. An intermediate P-type region may also be provided in transistors in which the emitter and collector electrodes are on opposite sides of a thin disc (Fig. 21). The emitter and collector connections may comprise rectifying contacts consisting of portions of opposite type conductivity in place of point contacts. The intermediate layer may alternatively consist of a low-conductivity region of the same conductivity type, instead of being the opposite type. Other transistor constructions which form the subject of Specification 721,740 are also described. Specifications 592,260, 592,303, 632,942, 632,980, [Group II], 694,021, 694,041, [Group XL (b)], 700,232, 700,236 and 700,241 also are referred to.