Patent GB-781795-A (GB)
Title: Improvements relating to the manufacture of p-n junction devices
IPC: H01L29/00
Filed: 1955-03-03
Abstract: 781,795. Semi-conductor devices. GENERAL ELECTRIC CO. March 3, 1955 [March 12, 1954], No. 6338/55. Addition to 752,457. Class 37. The parent Specification describes and illustrates a method of forming P-N and N-P-N junctions wherein a monocrystalline body of semiconductor material containing activator elements characteristic of both conductivity types having substantially different segregation constants and with an initial conductivity type corresponding to that produced by the activator having the lower segregation constant, is subjected to heat treatment such that a portion of the body is melted to produce a liquid phase, to solid phase interface and the melted portion is permitted to re-crystallize so that the activator having the higher segregation constant is assimilated to greater extent than is the activator with lower segregation constant and accordingly the recrystallized portion includes at least a part having conductivity characteristics of the opposite type. In the present Specification, a P-N junction so formed has the weight ratio of each activator to germanium within the limits of 0.1 to 5,000 parts per million, and the weight ratio of the donor to the acceptor is less than the ratio of their mol. weights times the inverted ratio of their segregation constants but more than the ratio of their mol. weights times the square of the inverted ratio of their segregation constants. In one example, a high-back voltage P-N type diode having a strongly P-type zone and a weakly N-type zone is made by preparing a  melt consisting of 63 gr. of high purity (above 20 ohms cm.) germanium, 7.0 milligrams indium and 14 micrograms arsenic. A monocrystalline ingot is then grown and sliced into wires. The tip of a wire is then heated for about 5 seconds using an oxyhydrogen torch to barely melt the tip. The heat is removed and the tip allowed to recrystallize to form a P-N junction. Nickel leads are then soldered on with ordinary tin alloy solder. Diodes of this type pass a reverse current of 0.2 milliamps at - 100 volts and a forward current of about 14 milliamps at + 1 volt. In another example a high forward current diode having a strongly N-type zone and a weakly P-type zone is made by preparing a melt consisting of 20 grams of high purity (above 20 ohms cm.) germanium, 150 milligrams antimony and 0.5 milligrams gallium and then following the above-described method. The resulting diode passes about 1 milliampere reverse current at - 50 volts and about 50 milliamps forward current at + 1 volt. In the present Specification a method of forming an N-P-N junction comprises preparing a melt consisting of semi-conductor material, an acceptor activator, and a donor activator of substantially lower segregation constant than the acceptor activator, and in which the weight ratio of the donor to acceptor is from 0.5 to 1 times the ratio of their mol. weights times the square of the inverted ratio of their segregation constants, growing a crystalline ingot from the melt, extracting a small crystal from the ingot, locally remelting a surface adjacent zone of the extracted crystal, and cooling and recrystallizing the remelted region to convert the recrystallized zone into semi-conductor material of opposite conductivity from the remainder of the crystal. A P-type layer 0.001 inches thick is made by preparing a melt of 20 grams of germanium, 150 milligrams of antimony and 0.16 milligrams of gallium, and then following the same forming procedure. An additional lead 13 is connected to the P layer by an indium solder contact 14 overlapping the P-N junctions, the indium converting the surface adjacent region to which it is fused into P-type material. This type of transistor has a current gain factor of 100 to 500. For antimony and gallium, weight ratios of from 500 to 950 have been found to form an N-P-N transistor, while ratios from 850 to 950 have been found in addition to form P-type layers from 0.001 to 0.003 inches thick. Weight ratios from 100 to 500 of antimony to gallium form only one P-N junction and are useful in diodes. Specification 779,146 is referred to.