Transistor structures and methods of manufacturing same

844,685. Transistors. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 27, 1956 [Aug. 29, 1955], No. 26079/56. Class 37. A transistor comprises a PNI or NPI body with an ohmic connection to each of its three zones. Such a device may be made by pulling a seed crystal from a germanium melt to which a donor or acceptor impurity is added at some stage in the growth. A PI or NI junction body with the dimensions shown in Fig. 1 is cut from the resulting ingot and an N or P type zone 5 (Fig. 4) formed in the surface of the P or N zone by an alloying process. Ohmic connections 7, 8, 9 are then made to the P, N and I zones. The resistivity of the middle zone (3), which should be not much thicker than the minority carrier diffusion length, is less than 10 ohm. cm. whereas the intrinsic region 2 has a resistivity as high as possible, i.e. about 50 ohm cm. An alternative method of making such a transistor is to heat a metal such as Pb or Au, doped with donor and acceptor impurities having different rates of diffusion e.g. As and In in contact with a surface of a body of intrinsic Ge. The resulting diffusion gives rise to a PNI structure on account of the more rapid diffusion of the arsenic. Ohmic connections are made to the zones as before. A third method of making the device is to heat a body of intrinsic Ge at 700‹C. in the vapour of As to form a region 18 (Fig. 7) of N type conductivity completely surrounding an intrinsic core 17. A P type layer 20 is then formed by alloying or deposited by electrolysis on part of the upper surface of the body and an ohmic contact 19 made on another part of the same surface by electro-plating or soldering. The surface of the body is then covered with an acid resistant coating 21 and the body etched to expose the intrinsic material as shown in Fig. 9. After removal of the resistant coating ohmic connections are made to the N and I regions and to the contact 19.