Patent GB-902423-A (GB)
Title: Improvements in semiconductor devices and methods of making the same
IPC: C30B15/10
Filed: 1959-05-13
Abstract: 902,423. Semi-conductor devices. GENERAL ELECTRIC CO. May 13, 1959 [May 15, 1958], No. 16424/59. Class 37. A semi-conductor body has a wide intrinsic region which is formed by heating and applying an electric field across a PN junction, so that mobile activator impurities on one side of the junction migrate across to form the intrinsic region. In one example a high peak inverse voltage PIN diode is produced by applying a thin lithium layer to a 20 ohm cm. P-type body of silicon containing boron and heating to 300 to 700 C. for 1 to 60 minutes to diffuse the lithium and form an N-type layer. A reverse bias of about 100 v. (i.e. 10<SP>5</SP> volts per cm.) is then applied while heating to 100 to 175 C. so that the mobile lithium atoms drift across the PN junction, thereby providing an intrinsic region. The lithium was applied as a droplet of lithium in mineral oil. Fig. 8 shows an anologue transistor comprising source electrode 24 connected to N-type region 18 in a conical cavity, drain electrode 25 connected to N-type region 17 in a disc shape cavity, and grid or gate electrode 26 to P-type body 12. An intrinsic region 21, 22 is formed by diffusing lithium into a P-type 1 ohm cm. silicon body containing boron as previously described, whereby a gate region 23 is formed between the source and drain electrodes. Fig. 10 shows a solid state thyratron device as described in Specification 902,424 which is produced by diffusing lithium into a 1 ohm cm. silicon P-type body containing boron as previously described to produce N-type and intrinsic regions. Depressions are etched into the body before the lithium is applied to form electrodes 34 and 35, and an additional electrode is used during the drift process to provide a potential round the periphery of the body so that region 41 remains P-type to provide a control electrode additional to that provided by the N-type region 34. In operation, control electrodes 34 and 41 are biased in the reverse direction so that a forward bias pulse to either results in the injection of majority carriers to provide a current flow between cathode electrode 35 and anode 40 and also a reduction in the reverse bias due to the action of resistors 46 and 47 connected in the bias circuits so that the main current continues after cessation of the pulse and the control electrodes lose control. Additional control electrodes may be provided. In a further example, an NPIN high-frequency transistor is produced by first diffusing boron into a weak P-type silicon body containing 10<SP>16</SP> atoms per c.c. of indium by heating the body in B 2 O 3  for 2 hours at 1200 C. to form a strong P-type region. The surface boron is then removed by etching and further diffusion effected by heating for 10 hours at 1200 C. to widen the P+ region. Phosphorus is then diffused into the same face to form an N-type outer layer, by heating for 5 hours at 1200 C. in P 2 O 5  vapour. The body is ground to remove any N-type region from all surfaces except one. Lithium is deposited on the opposite surface to form an N-type layer which is further diffused under the influence of an electric field as previously described, to provide an intrinsic region, thus forming a NPIN body. Germanium, silicon carbide boron and A 3 B 5  compounds such as indium antimonide, gallium arsenide or aluminium antimonide may be used instead of silicon.