US2829994A

US2829994A - Method for preparing silicon-germanium alloys

Info

Publication number: US2829994A
Application number: US538901A
Authority: US
Inventors: Phyllis E Stello
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1955-10-06
Filing date: 1955-10-06
Publication date: 1958-04-08
Anticipated expiration: 1975-04-08

Description

A ril 8, 1958 P. E. STELLO 2,829,994

METHOD FOR PREPARING SILICON-GERMANIUM ALLOYS Filed om. s, 1955 .sumar GAS SOURCE PH YLL/S E. 5mm 0,

IN VENTOR BY a ATT RNEY United States Patent Phyllis E. Stello, Inglewood, Califi, Aircraft Company, Culver City, Delaware Application October 6, 1955, Serial No. 538,901 8 Claims. (Cl. ii-1.6)

assignor to Hughes Calif., a corporation of This invention relates to semiconductor translating devices and, more particularly, to a method for preparing silicon-germanium alloy crystals for use in semiconductor translating devices. 7

It has long been known in the semiconductor art that monatomic semiconductors, such as germanium and silicon, may be employed as the semiconductor crystals in semiconductor translating devices. In addition, it has been recognized that, in many instances, especially in the production of semiconductor amplifiers or transistors, it is desirable to utilize single crystal semiconductor specimens in order to avoid undesirable grain boundaries in the specimens which may affect the production yield in the manufacture of the devices and which often adversely affect the electrical behavior of the completed devices.

The term, single crystal, as employed herein, signifies that the semiconductor material is free from grain boundaries, such as those which characterize polycrystalline semiconductor material in which a plurality of rela tively minute single crystals arebonded together in a nonoriented fashion. Accordingly, within the meaning of the term as herein utilized, single crystal semiconductor material may have certain types of lattice defects, such as isolated interstitial impurity atoms and lineage. The crystal lattice may also include displacement atoms of an intentionally added donor or acceptor impurity, for example, for determining the conductivity type of the semiconductor material.

It has been recognized in the semiconductor art that silicon has many physical advantages over germanium, in particular, its ability to withstand relatively high operating temperatures. Nevertheless, the use of germanium has advanced more rapidly in recent years due to the advent of production techniques which are readily adaptable to the refinement or purification and growing of single crystal germanium, but which have not been employed with equal success in processing silicon.

In the prior art, relatively large single crystals of germanium have been produced by two methods: namely,

the zone melting technique and the classical crystal growing technique of Czochralski. According to the latter method, a seed crystal of germanium is brought into contact with a melt of germanium and is thereafter withdrawn at a predetermined rate to incorporate a portion of the melt as a growing single crystal ingot.

According to the zone melting method, on the other hand, a seed crystal of germanium is placed in one end of a boat-like crucible,,the remainder of the crucible being filled with an ingot of high-purity germanium with no regard to crystal structure. The crucible is then passed through a heat zone provided by a heating element to produce a locally melted region in the germanium, this molten region progressively moving throughout the ingot as the crucible is moved past the heating element. As the germanium solidifies out of the molten region, it grows onto the single crystal seed, thereby producing a single crystal ingot. According to this prior art technique, the

2,829,994 Patented Apr. s, 1958 semiconductor material is also purified due to the tendency of most impurities in the melt to remain in the liquid phase, thereby producing a single crystal ingot of relatively high purity germanium.

Although each of the above methods has been successively utilized for producing single crystal germanium, the production of high purity silicon single crystal ingots by these methods has heretofore been diflicult to achieve for several reasons. First, silicon becomes extremely active when raised to its melting point of 1440 C. and will react with many known types of crucible material, thereby introducing relatively large amounts of undesired impurities into the silicon. Second, the physical nature of silicon is such that it increases in volume when it is frozen or solidified from the liquid phase. When attempts are made to grow silicon single crystal ingots in a crucible, such as that employed with a zone melting apparatus, difliculties are introduced due to the wetting action of the silicon upon the surface of the crucible. In addition, the difference in the coefficients of thermal expansion of silicon and the conventional crucible materials, such as quartz, frequently result in complete fracture of the crucible as the silicon ingot is being cooled.

Recent advances, such as that disclosed in copending application Serial No. 386,433, for Methods for Preparing Silicon for Semiconductor Translating Devices, by J. N. Carman, Jr., filed October 16, 1953, have made possible the production of silicon ingots by means of zone melting techniques by growing the ingots from a melt of low melting point solvent metal which includes silicon as one of itsconstituents, and at least one other element having a high rejection factor relative to silicon.

However, it has now been found that silicon-germanium alloys will have many of the physical and electrical advantages of silicon while maintaining the properties of germanium which make its production in single crystal form easier than the production of silicon. Crystals of silicon-germanium alloy are advantageous for use in diodes since alloys containing up to 10% silicon can be prepared in the same zone melting furnaces that are now being used togrow germanium crystals. Further, the band gap of germanium-silicon alloy crystals used in semiconductor devices in which the alloy has of the order of 10 atomic percent of germanium is 20% higher than the band gap of single crystal germanium and, in addition, it is felt that the recovery time for diodes made with silicon-germanium alloy crystals is less than for germanium diodes fabricated in' the same manner from single crystal germanium.

However, prior to the present invention, the advantages of growing crystals at low temperatures with relatively high band gaps has been partially cancelled by the difficulties encountered in growing two-component crystals. Since theproperties of the silicon-germanium alloys are dependent upon their composition, the crystals must be homogeneous. When a molten mixture of silicon and germanium is cooled slowly, the first alloy increment that solidifies has a higher silicon content than the next. The silicon concentration gradually decreases until almost pure germanium remains at the tail of the ingot. Not only will the ingot vary in composition lengthwise but the individual grains within the alloy will exhibit a cored structure. The most common method of the prior art for forming silicon-germanium alloys is to mix a quantity of silicon with a quantity of germanium which is melted to form an alloy and to quench the mixture in an attempt to obtain uniform distribution of the silicon within the germanium. This method has not proven satisfactory, however, since the center of the alloy crystal, having frozen first, will have a higher silicon content than the alloy near the grain boundary.

Cther difiiculties, which will become apparent during the description of the present invention given hereinafter, have been encountered and have not heretofore been overcome by methods known to the prior art.

Accordingly, it is an object of the present invention to provide a method and means for producing silicongermaniurn alloy single crystals.

It is another object of the present invention to provide a method for producing silicon-germanium alloy crystals which is adapted to mass production techniques and ease of manufacture.

It is still another object of the present invention to provide a method for converting polycrystalline silicon and germanium to single crystal silicon-germanium alloy which is accurately predetermined as to composition.

Still another object of the present invention is to provide a method for producing single crystal alloys of gcrmanium and silicon which are of the purity required for use in semiconductor devices and of the required predetermined uniform composition.

It is a still further object of the present invention to provide a method for producing single crystal silicon-germanium alloys in a zone melting apparatus of the type well-known to the art.

The method of the present invention comprises the steps of placing a single crystal seed of germanium in contact with a predetermined quantity of silicon of the requisite purity in solid form and a predetermined quantity of germanium of the requisite purity in solid form by forming a cavity throughout the length of a germanium ingot and after solidifying the germanium ingot filling the cavity with silicon in solid form. A temperature gradient is then produced at the junction of the seed crystal and the solid silicon and germanium, so that the silicon and germanium are progressively melted and precipitated in the direction away from the seed crystal to produce a single-crystal ingot of silicon-germanium alloy.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which the presently preferred embodiment of the method of the present invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

Fig. 1 is a schematic diagram, partly in section, of a zone melting apparatus for carrying out the method of the present invention;

.Fig. 2 is a sectional diagram of the crucible used in the zone melting apparatus of Fig. l with a quartz rod in position in accordance with the present invention;

Fig. 3 is a sectional diagram of the crucible used in the zone melting apparatus of Fig. l which is charged in accordance with the present invention;

Fig. 4 is a section taken along line 44 of Fig. 3; and

Fig. 5 is a binary phase diagram of silicon-germanium alloy.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views. there is shown in Fig. 1 one form of apparatus for carrying out the method of the present invention. The apparatus includes a boat-like crucible for receiving the silicon and germanium to be alloyed and a zone melting furnace which comprises a hollow cylindrical member such as quartz tube 12, for holding the crucible 10, and a heater unit generally designated 14. Heater unit 14 surrounds the quartz tube 12 at a region intermediate its length and is energizable from an electrical energy source 16 upon closure of a switch 18 to heat the region of the crucible adjacent the heater unit.

Heater unit 14 may comprise either a radiant heating element or a radio-frequency induction heating unit. As

4 shown in Fig. l, the heater unit includes a radiant heating coil 20 which is enclosed by insulative supporting block 22 and is electrically coupled to electrical energy source 16.

As shown in Fig. l the zone melting furnace also includes two end caps 24 and 26, respectively, for enclosing the ends of quartz tube 12, each end cap having a relatively large aperture for supplying crucible 10 with a non-reactive atmosphere from a source 32 of gas under pressure. Each end cap also includes a relatively small orifice for permitting two externally tensioned metallic guide wires 28 and 30, respectively, to be mechanically coupled to opposite ends of the crucible 10. The wire 28 is connected to a spool 34 which is driven by an electric motor 36 through a reduction gear unit 38 to move the crucible 10 through the tube 12 at a predetermined rate relative to the heater unit 14 when the zone melting furnace is placed in operation. The wire 30, on the other hand, is tensioned by a force such as that supplied by a weight 31 to provide uniform movement of the crucible through the tube 12 when the wire 28 is being wound upon the spool 34.

Since silicon reacts with carbon, the silicon-germanium alloy, with the exception of low silicon content alloys, cannot be grown in carbon coated quartz boats such as those which are commonly used in the production of germanium single crystals. In the presently preferred embodiment, a quartz crucible coated on the internal surface with zirconium oxide is used, although other rcfractory materials such as beryllium, alumina, silica, and magnesia may be used.

In accordance with the method of the present invention, a quartz rod is used to form a cavity in a germanium ingot by placing a quartz rod 40 along the bottom of the crucible 10 as shown in Fig. 2. The quartz rod 40 follows the inner surface of the crucible 10 roughly along the longitudinal centerline although the exact location is not critical. The quartz rod is bent to extend above the crucible at both ends thereof. The crucible is charged with polycrystalline germanium which is then melted in the crucible and allowed to solidify to form an ingot. The ends of the quartz rod extend above the surface of the germanium in order to prevent breaking of the rod due to contraction of the germanium upon cooling. After solidifying the germanium ingot is removed from the crucible and has a configuration similar to that of the crucible. The quartz rod is removed from the germanium ingot, leaving a cavity extending throughout the length of the ingot at the lower surface of the ingot having a cross-sectional area substantially equal to the cross sectional area of the quartz rod 40.

The cavity in the germanium ingot is then filled with polycrystalline silicon of the purity required in the final alloy. The silicon may be polycrystalline or single crystal, for example, a single crystal rod of silicon which is grown for example by the Czochralski method may also be used. In this embodiment the cavity is filled by forming a silicon rod 42 (see Fig. 3) having a cross sectional configuration and area substantially equal to the configuration and area of the quartz rod which was used to form the cavity in the germanium ingot.

Referring now to Figs. 3 and 4, the charged crucible to be used in growing the single crystal germanium-silicon alloy is shown in cross section. A germanium single crystal seed 44 is placed at one end of the crucible. A zone of polycrystalline germanium 46 substantially equal in length to the length of a molten zone as described hereinafter is placed adjacent the seed crystal. The germanium ingot 48 with the silicon rod 42 positioned within the cavity is placed in the crucible 10 by cutting an amount from the end of the ingot substantially equal to the volume of the germanium seed crystal 44 and the germanium zone 46 such that the ingot of source material 50 when placed in the crucible is in contact with the surface of the germanium zone 46 and the germanium zone is in contact with the seed crystal 44. Thus, the crucible charge comprises a germanium single crystal seed 44 in contact with the germanium zone 46 which is, in turn, in contact with the source material which is a predetermined amount of germanium and silicon in solid form wherein the silicon is uniformly distributed throughout the length of the germanum.

Although a zone of germanium is utilized in this embodiment, it will be seen hereinafter that a zone of germanium-silicon mixture of a specified percentage should be used. However, in the illustrative embodiment, since an alloy having a composition of only silicon is being formed, the percentage of silicon in the zone is so small that pure germanium may be used as will be discussed in greater detail in connection with Fig. 5.

It may be shown theoretically that the growth of single crystals is enhanced by growing crystals from single crystal seeds which are crystallographically oriented so that crystal growth takes place perpendicular to a predetermined crystal plane or facet of the seed. Accordingly, in producing single crystal germanium-silicon alloy according to the method of this invention, a single crystal seed of germanium is preferably oriented crystallographically when placed in the crucible. It has been found preferable to orient the single crystal seed of silicon so that crystal growth takes place perpendicular to the (111) plane. It is considered, however, that crystal growth may also be enhanced by orienting the seed crystal so that the seed crystal grows out from another crystallographic surface such as the (100) plane, for example. It should be expressly understood that although orientation of the seed crystal appears to be preferable, it is not thought to be essential from the present understanding of solid state physics and metallurgical phenomena involved in producing single crystal silicon germanium ingots according to the method of this invention.

The germanium-zone 46 sees a cross section of the source material 50 as shown in Fig. 4 which to the seed crystal is a virtual alloy rather than a true alloy, that is in cross section, a predetermined percentage of the surface of the source material 50 which is in contact with the germanium zone 46 is germanium 48 and a predetermined percentage of the source material in contact with the germanium is silicon 42. Since the cross-sectional area of the germanium and silicon in the ingot are constant throughout the length of the ingot, the composition of the virtualalloy taken along any cross section throughout the length of the ingot is also constant.

After the charge, as described above, has been placed in the crucible 10, guide wires 28 and 30 are attached to the crucible and the crucible is positioned within the quartz tube 12, substantially as shown, so that the germanium zone 46 and the adjacent surface of the germanium seed crystal 44 are within the heating zone of the unit heater 14. End caps 24, 26 are then employed to close off the ends of the quartz tube 12 after which the crucible is supplied by a non-reactive atmosphere from the gas source 32. It will be recognized, of course, that the methods of the present invention may also be carried out in a vacuum.

The switch 18 is closed to energize the heater unit 14 and raise the temperature of the material within the molten zone described by the radiant heater unit to a temperature value within a predetermined range above the melting point of the germanium seed crystal 44, zone 46, and the source material 50. Since the melting point of the combined germanium-silicon source material will be dependent upon the percentage of silicon present in the source material, the temperature to which the heating unit 14 is raised will be dependent upon the alloy being produced, as described in more detail hereinafter. For example, in the presently preferred embodiment, wherein an alloy containing 95 atomic percent germapium and 5 atomic percent silicon is to be produced, a

in the crucible is permitted to cool heater temperature of the order of 1100 C. is used to form a molten zone having a temperature of the order of 950 C. In operation, the crucible 10 is positioned as shown in Fig. 1 so that the interface between the germanium seed crystal 44 and the germanium zone 46 is within the heated zone and becomes molten. After the germanium zone 46 has become molten, the crucible 10 is moved past the heating coil 20 at a predetermined rate as described hereinafter. The crucible is moved by energizing the motor 36 to rotate the spool 34 and move the crucible from right to left as shown in Fig. 1.

Since the radiant heat is confined to a zone through which the crucible passes, the material within the crucible will become molten only in a zone, the length of which, along the length of the crucible, is determined by the length and temperature of the heating zone and the rate at which the crucible passes through the zone. Thus, after the portion of the seed crystal which is in contact with the germanium zone 46 becomes molten such that the seed crystal is wet by the germanium, the crucible is moved at a constant predetermined rate through the heating zone. The source material 50 passing into the zone becomes molten and the silicon and germanium mix into a homogeneous mixture. As the molten zone of source material passes through the heating zone, it begins to freeze and grow onto the single crystal germanium seed 44 in a homogeneous single crystal lattice structure of silicon-germanium alloy having a homogeneous composition equal to 5 atomic percent silicon and atomic percent germanium in this illustrative embodiment.

The molten zone of source material is moved progres sively from left to right in Fig. l as the crucible is moved through the heating zone from right to left. The molten source material which has become a homogeneous mixture of silicon and germanium freezes and solidifies as it emerges from the heating zone and continues to redeposit in a single crystal lattice upon the preceding portion of the silicon-germanium alloy crystal, thus causing a single crystal silicon-germanium alloy ingot to be progressively grown.

The fact that the silicon-germanium alloy comes out of the solution to grow onto the single crystal germanium so as to preserve the single crystal structure thereof may be substantiated theoretically by metallurgic analysis of the phenomena of single crystal growth. After the molten zone of silicon-germanium alloy has been moved progressively throughout the ingot of source material, the charge and the crucible is removed from the zone melting furnace. Thereafter, the only step remaining in the production of the single crystal ingot of silicon-germanium alloy is to cut off the germanium seed crystal and the end of the ingot opposed to the seed crystal for reasons given hereinafter.

Referring now to Fig. 5, a binary phase diagram for silicon-germanium alloys as a function of temperature is shown. Such phase diagrams may be found by referring to the Metals Reference Book, by Smithalls, published by New York Interscience Publishers, Inc. (1949 edition) By referring to the binary phase diagram, the temperature of the molten zone which is required for the production of a given alloy may be determined by one skilled in the art. When an alloy having a composition of C as shown in Fig. 5, is desired, a liquid composition within the molten Zone of composition C is necessary to precipitate out the required alloy. For example, if an alloy of germanium and silicon having approximately 52% germanium is required, the temperature of the molten zone must be maintained constant at approximately 1100 C. and the source material feeding silicon and germanium into the molten zone must be constant at the composition C or 52% germanium. As the source material enters the molten zone, therefore, it is raised to a temperature of 1100" C. and becomes fully liquid at the composition C As the liquid composition C comes into contact with,

the single crystal germanium seed or the surface ofthe Silicon-germanium alloy which has been grown onto the surface of the seed, it regrows upon the seed in a single crystal lattice having a'composition of C Thus, it may be seen that it is important to maintain the temperature vof the molten zone constant in order that the progress of the silicon-germanium alloy is made along the isothermal line of the phase diagram from composition C to C and back to C in'a single crystal structure.

Two compositions of germanium-silicon mixture are required therefore, a mixture of germanium and silicon in solid form having a composition C and a molten zone of germanium-silicon mixture having a composition of C In the illustrative embodiment described hereinbefore in which an alloy containing silicon was produced, the zone 46 adjacent the seed crystal was pure germanium. By referring to the binary phase diagrams, it may be seen that for a composition C of 95% germanium, the composition C on the isothermal line from C will contain such a small percentage of silicon that pure germanium may be used with negligible error. After the germanium zone 46 of Fig. 3 has become molten and source material 59 begins to melt, the molten zone is soon equalized at a composition C From the foregoing it may be seen that the source material 50 defined herein as a virtual alloy supplies continuously germanium and silicon at a composition C which passes into the molten zone which is maintained constant at composition C As the molten zone progresses, silicon-germanium alloy is frozen from the molten zone at composition C but as a homogeneous and uniform single crystal alloy.

Since the first molten zone to be formed in the operation is pure germanium in this embodiment, rather than an alloy of the required composition, the first alloy crystals grown will contain more germanium than is desired or is present in the source material. By considering concentration changes as the crystal grows, it is possible to determine the zone lengths required to establish equilibrium between the source material and the molten zone.

In forming silicon-germanium alloys by the method of the present invention, certain parameters must be observed and maintained constant for optimum results. The length of the molten zone along the longitudinal axis of the crucible, the temperature of the molten zone, and the rate at which the molten zone is moved through the source material must be maintained constant in order to promote uniform single crystal growth upon re-freezing of the alloy.

In order .to more fully describe the present invention,

an illustrative example of the formation of an alloy of a given specific composition will be described. In order to form an alloy containing substantially 5% silicon and 95% germanium, the source material is formed as described hereinbefore by placing a quartz rod having a square cross section 4.5 mm. on a side in the crucible which has been coated with zirconium oxide. The crosssectional area of the quartz rod is thus sq. millimeters. The crucible is then filled with sufiicient germanium to form an ingot having a cross-sectional area of approximately 400 sq. millimeters and the germanium is melted and refrozen. A germanium source ingot having a crosssectional area of 380 sq. millimeters with a cavity of 20 sq. millimeters running throughout the length of the ingot is formed.

The cavity is then filled with a silicon rod cut from a single crystal silicon ingot. The rod is cut to form a uniform cross section which is square in configuration and 4.5 millimeters on a side to fill the cavity. With the rod in place, the cross-sectional area of the ingot at any position along its length consists of 95% germanium and 5% silicon.

A quantity of single crystal germanium is placed in one end of the crucible to form a single crystal seed 44 and a zone of polycrystalline germanium 46 two inches in length is positioned adjacent the seed. The end of the source ingot is cut off and the ingot is replaced in the crucible such that a cross section of the ingot St) is in contact with the zone of germanium 46.

Although a square quartz rod and silicon rod have been shown and described for clarity, a quartz rod of circular cross section and a corresponding round rod of silicon is often used since round rods are most easily formed or machined.

After an inert atmosphere has. been created in the crucible. the electrical energy source is energized as described hercinhefore and the temperature of the heated zone is raised to a value of the order of 1100 C. to create a molten zone having a temperature of the order of 950 C. After the interface of the germanium zone and the seed has been melted and a molten zone has been formed, the motor 36 is energized to move the crucible through the heated zone at a predetermined rate. In this illustrative embodiment, the length of the when zone is maintained constant at approximately two inches and the rate of movement of the crucible is also maintained constant at approximately 0.1 inch per hour.

Thus, as the crucible is moved through the heated zone, a constant source of germanium and silicon in specific amounts is fed into the molten zone where homogeneity is obtained by the mixing action of the molten zone. As the material which is a uniform mixture containing germanium and 5% silicon emerges from the molten zone, it re-freezes and crystallizes in a single crystal lattice upon the single crystal germanium or the single crystal alloy which has preceded it from the molten zone. As the molten zone moves throughout the length of the ingot source material, an ingot of silicon-germanium alloy which is uniform in composition is formed. After the complete alloy ingot has been formed it is removed from the crucible and the ends are removed since each end will contain an excess percentage of germanium due to the zone of germanium used to form the initial molten zone. The amount of the ingot to be removed at each end may be determined by one skilled in the art. However, in this embodiment, the amount removed from each end is equal to approximately a zone length or two inches.

Thus, the present invention provides a method and means for producing a uniform silicon-germanium alloy by the zone melting method which allows lower temperatures to be used and accomplishes uniformity not heretofore possible by methods of the prior art.

What is claimed is:

1. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of: providing an ingot of germanium-silicon source material, said germanium-silicon source ingot having a predetermined quantity of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium; positioning a zone of germanium and silicon of a second predetermined composition longitudinally adjacent said germanium-silicon source ingot; positioning a germanium seed crystal adjacent said germanium-silicon zone; locally heating a portion of the ingot, zone, and crystal to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium-silicon zone; and moving the ingot, zone, and crystal relative to the local heating while maintaining said temperature substantially constant at said predetermined value to move the molten zone through the source material ingot away from the seed crystal to deposit germanium-silicon alloy of a composition substantially equal to the composition determined by the first predetermined quantity of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone to maintain the composition thereof substantially equal to said second composition.

2. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of: providing an ingot of germanium-silicon source material, said germanium-silicon source ingot having a predetermined percentage of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium, said silicon being in the form of a silicon rod extending longitudinally through said germanium ingot; positioning a zone of germanium and siliconhaving a second predetermined percentage of silicon longitudinally adjacent said germanium-silicon source ingot; positioning a germanium seed crystal adjacent said germanium-silicon zone; locally heating the ingot, zone, and crystal to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium-silicon zone; and moving the ingot, zone, and crystal relative to the local heating while maintaining said temperature sub stantially constant at said predetermined value to move the molten zone through the source material ingot away from the seed crystal to deposit homogeneous germaniumsilicon alloy of a composition substantially equal to the composition determined by the first predetermined percentage of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone to maintain the composition thereof substantially equal to the composition determined by said second percentage of silicon.

3. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of: positioning in a crucible an ingot of germaniumsilicon source material, said germanium-silicon source ingot having a predetermined percentage of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium, said silicon being in the form of a silicon rod extending longitudinally through said germanium ingot; positioning a zone of germanium adjacent said germanium-silicon source ingot; positioning a germanium seed crystal adjacent said germanium zone; locally heating the crucible and its contents to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium zone; and moving the crucible relative to the local heating to move the molten zone through the source material away from the seed crystal while maintaining said temperature substantially constant at said predetermined value to deposit homogeneous single crystal germanium-silicon alloy of a composition substantially equal to the composition determined by the first predetermined percentage of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone.

4. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of: providing an ingot or" germanium-silicon source material of a first predetermined composition, said germanium-silicon source ingot having a predetermined quantity of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium; positioning a zone of germanium and silicon of a second predetermined composition longitudinally adjacent said germanium-silicon source ingot, said second predetermined composition corresponding substantially to that of a germanium-silicon alloy in the liquid state at the temperature where a germanium-silicon alloy of said first predetermined composition solidifies; positioning a germanium seed crystal adjacent said germaniumsilicon zone; locally heating the ingot, zone, and crystal to said temperature to create a molten alloy zone between the single crystal and the source material ingot substantially equal in length to the length of said germaniumeilicon zone; and moving the ingot, zone, and

predetermined equal to said second composition.

5. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of: positioning in a crucible an ingot of germaniumsilicon source material of a first predetermined composition, said germanium-silicon source ingot having a predetermined percentage of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium, said silicon being in the form of a rod of uniform cross section having a first predetermined cross-sectional area extending longitudinally throughout said germanium ingot, said germanium ingot having a uniform cross section of a second predetermined cross-sectional area, the ratio of said first and second cross-sectional areas being substantially equal to the ratio of silicon and germanium desired. in said germanium-silicon alloy; positioning a zone of germanium and silicon of a second predetermined composition longitudinally adjacent said germanium-silicon source ingot; positioning a germanium seed crystal adjacent said germanium-silicon zone; longitudinally heating the crucible and its contents to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium-silicon zone;

' and moving the crystal relative to the longitudinal heating while maintaining said temperature substantially constant at said predetermined value to move the molten zone through the source material ingot away from the seed crystal to deposit silicon-germanium alloy of a composition substantially equal to the composition determined by the first predetermined quantity of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone to maintain the composition thereof substantially equal to said second composition.

6. The method of growing a single crystal ingot of germanium-silicon alloy, said method comprising the steps of positioning in a crucible an ingot of germaniumsilicon source material, said germanium-silicon source ingot having a predetermined percentage of solid silicon positioned immediately adjacent to and throughout the length of an ingot of solid germanium, said silicon being in the form of a rod of uniform cross section having a first predetermined cross-sectional area extending longitudinally throughout said germanium ingot, said germanium ingot having a uniform cross section of a second predetermined cross-sectional area, the ratio of said first and second cross-sectional areas being substantially equal to the ratio of silicon and germanium desired in said germanium-silicon alloy; positioning a zone of germanium adjacent said germanium-silicon source ingot; positioning a germanium seed crystal adjacent said germanium zone; locally heating the crucible and its contents to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium zone and moving the crucible relative to the local heating while maintaining said temperature substantially constant at said predetermined value to move the molten zone through the source material away from the seed crystal to deposit homogeneous single crystal germanium-silicon alloy of a composition substantially equal to the composition determined by the predetermined percentage of silicon in said source mate gitudinally adjacent said germaniumsilicon source ingot;

positioning a germanium seed crystal adjacent said germanium-silicon zone; locally heating the ingot, zone, and crystal to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium-silicon zone; and moving the crystal relative to the local heating while maintaining said temperature substantially constant at said predetermined value to move the molten zone through the source material ingot away from the seed crystal to deposit germanium-silicon alloy of a composition substantially equal to the composition determined by the quantity of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone to maintain the composition thereof substantially equal to said second composition.

8. The method of growing a single crystal ingot of silicon-germanium alloy, said method comprising the steps of: forming a cavity of uniform predetermined cross-sectional area throughout the length of an ingot of germanium, said ingot of germanium having a uniform predetermined cross-sectional area; filling said cavity with a rod of solid silicon; positioning said ingot of germanium and silicon in a crucible; positioning a zone of germanium adjacent said silicon-germanium source ingot; positioning a germanium seed crystal adjacent said germanium zone; locally heating the crucible and its contents to create a molten alloy zone having a predetermined temperature between the single crystal and the source material ingot substantially equal in length to the length of said germanium zone and moving the crucible relative to the local heating while maintaining said temperature substantially constant at said predetermined value to move the molten zone through the source material away from the seed crystal to deposit homogeieous single crystal silicon-germanium alloy of a composition substantially equal to the composition determined by the quantity of silicon in said source material from the molten alloy zone, and to deposit silicon and germanium from the source material ingot into the molten zone.

References Cited in the file of this patent UNITED STATES PATENTS Hopkins Feb. 27, 1940 Pfann Mar. 20, 1956 OTHER REFERENCES U. S DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,829,994 Phyllis En Stello April 8, 1958 Attesting Officer Column 5, line 7, for "germanum" read germanium column 11, line 10,, after "with" insert m a rod of column 12, line 2, before "filling," insert w substantially a Signed and sealed this 24th day of June 1958,

(SEAL) Attest:

H KARL AXLINE ROBERT c. WATSON Qanmissioner of Patents

Claims

1. THE METHOD OF GROWING A SINGLE CRYSTAL INGOT OF GERMANIUM-SILICON ALLOY, SAID METHOD COMPRISING THE STEPS OF: PROVIDING AN INGOT OF GERMANIUM-SILICON SOURCE MATERIAL, SAID GERMANIUM-SILICON SOURCE INGOT HAVING A PREDETERMINED QUANTITY OF SOLID SILICON POSITIONED IMMEDIATELY ADJACENT TO AND THROUGHOUT THE LENGHT OF AN INGOT OF SOLID GERMANIUM, POSITIONING A ZONE OF GERMANIUM AND SILICON OF A SECOND PREDETERMINED COMPOSITION LONGITUDINALLY ADJACENT SAID GERMANIUM-SILICON SOURCE INGOT, POSITIONING A GERMANIUM SEED CRYSTAL ADJACENT SAID GERMANIUM-SILICON ZONE, LOCALLY HEATING A PORTION OF THE INGOT, ZONE, AND CRYSTAL TO CREATE A MOLTEN ALLOY ZONE HAVING A PREDETERMINED TEMPERATURE BETWEEN THE SINGLE CRYSTAL AND THE SOURCE MATERIAL INGOT SUBSTANTIALLY EQUAL IN LENGTH TO THE LENGTH OF SAID GERMANIUM-SILICON ZONE, AND MOVING THE INGOT, ZONE, AND CRYSTAL RELATIVE TO THE LOCAL HEATING WHILE MAINTAINING SAID TEMPERATURE SUBSTANTIALLY CONSTANT AT SAID PREDETERMINED VALUE TO MOVE THE MOLTEN ZONE THROUGH THE SOURCE MATERIAL INGOT AWAY FROM THE SEED CRYSTAL TO DEPOSIT GERMANIUM-SILICON ALLOY OF A COMPOSITION SUBSTANTIALLY EQUAL TO THE COMPOSITION DETERMINED BY THE FIRST PREDETERMINED QUANTITY OF SILICON IN SAID SOURCE MATERIAL FROM THE MOLTEN ALLOY ZONE, AND TO DEPOSIT SILICON AND GERMANIUM FROM THE SOURCE MATERIAL INGOT INTO THE MOLTEN ZONE TO MAINTAIN THE COMPOSITION THEREOF SUBSTANTIALLY EQUAL TO SAID SECOND COMPOSITION.