US2890976A

US2890976A - Monocrystalline tubular semiconductor

Info

Publication number: US2890976A
Application number: US478685A
Authority: US
Inventors: Lehovec Kurt
Original assignee: Sprague Electric Co
Current assignee: Sprague Electric Co
Priority date: 1954-12-30
Filing date: 1954-12-30
Publication date: 1959-06-16
Anticipated expiration: 1976-06-16

Description

MONOCRYSTALLINE TUBULAR SEMICONDUCTOR Filed Dec. 50, 1954 FIG. 2

INVENTOR. KU RT LEHOVEC BY cmm wg HIS ATTO NEYS MONDCRYSTALLINE TUBULAR SEMICONDUCTOR Kurt Lehovec,Williamstown, Mass., assignor to Sprague Electric Company, North Adams, Mass, a corporation of Massachusetts Application December 30, 1954, Serial No. 478,685

4 Claims. (Cl. 148-33) This invention relates to new and improved monoa: ed Stes Patent 9 crystalline semiconductive structures and more particularly to novel embodiments of monocrystalline germanium and silicon having electrical and chemical applications.

Some chemical reactions require containers that are quite inert at elevated temperatures and are able to withstand high pressures. Although the prior art bombs used for this purpose are readily constructed to withstand pressures, they are generally made of relatively active metal and are accordingly subject toattack by the reactants, particularly at elevated temperatures, so that the reactants frequently become contaminated.

Among the objects of this invention is the provision of improved containers in which the above difiiculty is minimized. It is a further object of this invention to provide monocrystalline tubular semiconductors that can be used to provide either containers or electrical translating elements for rectifiers, transistors or the like.

The above as well as additional objects and advantages of the present invention will be more apparent from the following description of several of its exemplifications taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a perspective view of a container illustrating the present invention;

Figure 2 is a sectional view of an open-ended tube representing another embodiment of this invention; and

Figure 3 is a perspective view of a translator element typical of the present invention.

According to the present invention a tube of semiconductor material such as silicon or germanium is provided in the form of a single crystal. These semiconductor materials are relatively inert in the chemical sense, more so than the metals generally used for reactor bombs. In addition, the fact that they are in the form of a single crystal makes them exceptionally strong and easily capable of resisting the high pressure that may be applied to chemical reactions. Either of these materials in a wall thickness of for example, will withstand quite a few atmospheres of pressure.

The tubular construction can be provided by either drilling out the center of a suitably dimensioned rod, or by directly growing the semiconductor crystal around an elongated core. Referring to Fig. 1, there is shown a container in the form of a tube having one end open and one end closed. When used under pressure, the open end can be covered as by a semiconductor slab or lid, and the contact points of the lid to the bomb can be fused together by local heating. Alternatively, the open mouth of the container can be provided with a securing element, such as external threads or lugs against which a correspondingly-shaped portion of the lid can be secured so as to form a cap. Any soft material inert to the reactants can be used as a gasket between the container and cap. For temperatures of about 300 C. or below, polytetrafluoroethylene or lead sheet make suitable gaskets.

The growing of a container in the form shown in Fig. 1 can be effected in the manner described in U. S. Letters Patent 2,631,356, granted March 17, 1953, except that a solid inert core is inserted through the seed crystal and pulled outwith it as the crystallization growth progresses. As pointed out in that patent, this is a conventionalway of growing semiconductor crystals, and the external diameter of the growing mass is readily controllable. By selecting a core of a material that has a thermal expansion coefficient greater than that of the semiconductor material, .the withdrawal of the core from the grown mass of semiconductor is simplified. A carbon rod makes suitable core for the growth of a cylindrical germanium crystal. Best results are obtained, however, if the grown mass containing the core is subjected to a relatively low temperature, -70 C. for example, to facilitate the withdrawal. Such a temperature is conveniently provided by Dry Ice. The strength of the container can also be improved by smoothing its external surfaces, as by a machining and polishing operation.

Instead of having the crystal grown in such a way as to close one end of the tube, the pulling of the mass can be controlled so that the growth is discontinued before the end of the core is reached. In other words, the growing mass can then be quickly removed from the liquid material to provide a tube which is open at both ends. When such a tube is used as a reactor bomb, lids or caps can be provided on both open ends.

A feature of the present invention is the fact that the tubular construction is also readily adapted for providing electrical translating elements such as are used in rectifiers or transistors. To this end, the tube can be provided with an electrical conductivity junction. When the tube is grown from a liquid in the manner indicated above, the junction is readily furnished by merely doping the surface of the core with the appropriate type of impurity. At the high temperature of the growing operation, this impurity tends to diffuse into the semiconductor material from the core.

After the semiconductor tube has been grown, impurities providing the desired type of conductivity upon incorporation into the semiconductor can be introduced as follows: The impurity is introduced into the space either inside or outside of the tube, and is diffused into the semiconductor by heat treatment. It is recommended to introduce the impurities in gaseous form; e.g. in an n-type germanium tube, boron hydride is passed at elevated temperatures, thereby rendering the inner side of the germanium p-type by diffusion of boron into the germanium.

Fig. 2 shows a single crystal semiconductor tube having an electrical conductivity junction provided in the above manner. The body of material has its external portion 10 of one type of electrical conductivity such as the N-type, provided by an extremely small. content of antimony, for example. The balance or inner portion 12 of the body can have a P-type electrical conductivity, as for example by reason of the diffusion of indium in small concentrations. At the limit of diffusion, there is a junction 14 where the different electrical conductivities meet.

The tube of Fig. 2 can be sliced transversely into thin rings which make suitable bodies to which contacts can be connected for making a rectifier or transistor. Lowresistance, or so-called ohmic contacts can be applied, as by soldering, to the

respective portions

10, 12 of the tube, before or after it is sliced. Point contact electrodes can also be connected to the semiconductor slices whether or not they have a junction.

More than one junction can be provided in the tube or the individual slices, as by diffusing an additional impurity into the body from its external or internal face. Where the second diffusion takes place from the same face as the first dilfusion, the second should not penetrate as far as the first. Fig'. 3{shows'a slice of the above typeinwhich two junctions are present. Here the successivezones of the semiconductor are identified as 20, 22 and'24'Withthe intervening

junctions

26 and 28. The zo'n es can have either the N-P-Nor P- NP sequence, with suitable connections being provided as indicated above to complete a'corresponding type of transistor.

The presence or absence of a junction in a semiconductqr body has no effect on its ability to satisfactorily res-ist-pressuresas well as chemical attack when used as a container or bomb for chemical reactions. 7 Byway of example, the drilling out of a rod, referred to above,'canbe efiected either by a mechanical drilling arrangement using a standard drilling tool, or it can be ac- Tc omplished electromechamically. The electromechanical dissolution of germanium, for example, is described in the December 195 3- issue of the Proceedings of the I.R.E., volume 41, pages 1706+1708, and all that is. necessary is that a germanium rod be connected asan anode with respect to a cathode of pointed 'form with the point advancing into the germanium as it is dissolved. Inasmuch as the electrolyit ic current will concentrate on the portions of the germanium close to the point of the cathode, the anodic dissolution will proceed in a penetrating fashion to create "an opening to 20 times the diameter of the pointed cathode, depending upon the distance that is maintained between the cathode and the anode. To make a container for chemical reactions, a'suitable internal diameter is /zf or even less. For translating elements, internal diameters as little as- A "or even 3 are preferred. Asmany-apparently widelydifierent embodiments of this invention maybe made without departing from the spil-itandscope hereof, it is to be understood thatthe invention is notlimited to the specific embodiments hereof. except as defined in the appended claims. What is claimed is:

LA bomb type chemical reactioncontainer in the 4 form of a tubular single crystal of semiconductor material of the class-consisting of silicon and germanium, the tube having a closed bottom.

2. A process for producing a monocrystalline tubular semi-conductor of a material of the class consisting of silicon and germanium which comprises inserting a core of an inert material havinga-thermal expansion co efiicient greater than the semi-conductor material into a seed crystal of the semi-conductor material, growing a crystal of the semi-conductor material on the core, and s'ubjectingthe grown crystal and core to a low tempera ture to facilitate removal of the core.

3. A tube of semiconductor material of the class coni sisting of silicon and germanium, said tube being inthe form of an elongated single crystal, at least one end of said tube being closed to provide a bomb type chemical reaction container.

4. An annular semiconductor body of a material of the .class consisting of silicon and germanium, said body being in the form ofan elongated annular single crystal, saidbody having atleast one concentrically disposed ringshaped-electrical'conductivity junction extending therethrough, said body having at least one closed end to provide a bomb type chemical reaction container capable of dilfusing conductioin impurities from saidring-shaped junction.

References'Citedin the file of this patent UNITED STATES PATENTS OTHER REFERENCES B1 1 Cr tal r w h, page 508, 1951-

Claims

2. A PROCESS FOR PRODUCING A MONOCRYSTALLINE TUBULAR SEMI-CONDUCTOR OF A MATERIAL OF THE CLASS CONSISTING OF SILICON AND GERMANIUM WHICH COMPRISES INSERTING A CORE OF AN INERT MATERIAL HAVING A THERMAL EXPANSION COEFFICIENT GREATER THAN THE SEMI-CONDUCTOR MATERIAL INTO A SEED CRYSTAL OF THE SEMI-CONDUCTOR MATERIAL, GROWING A CRYSTAL OF THE SEMI-CONDUCTOR MATERIAL ON THE CORE, AND SUBJECTING THE GROWN CRYSTAL AND CORE TO A LOW TEMPERATURE TO FACILITATE REMOVAL OF THE CORE.