US3058915A

US3058915A - Crystal growing process

Info

Publication number: US3058915A
Application number: US2982A
Authority: US
Inventors: Allan I Bennett
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-01-18
Filing date: 1960-01-18
Publication date: 1962-10-16
Anticipated expiration: 1979-10-16
Also published as: GB913677A; CH412817A; DE1222022B

Description

Oct. 16, 1962 A. l. BENNETT CRYSTAL GROWING PROCESS Filed Jan. 18, 1960 Fig.3.

Fig. 5.

6 .m m M F A R m R P "H Ell .l H m 6 2 8 4 5 5 O 6 8 w 5 2 k 6 2 2 6 5 GIH IHH I I I llllll I fl 0 5 INVENTOR Allen I. Bennett BY MTG? EY WITNESSES R @zm/w W rates nit This invention relates to a process for producing dendritic crystals of solid materials, and in particular to a process for producing dendritic crystals of a semiconductor material.

In the dendritic growth of semiconductor crystals from a melt it is necessary, in initiating growth, to have the melted material wet the seed. If such wetting does not occur, the dendrites or other crystals which result will not be isomorphous crystalline continuations of the seed, and will in general grow at an angle to the pull direction. The latter dendrites will have irregular faces and will be highly variable in configuration and exhibit poorly controllable electrical and mechanical characteristics. In addition, since the point at which the laterally growing dendrite intersects the melt surface moves away from the center of the crucible and eventually reaches the edge of the crucible, such growth at an angle to the pull direction prohibits the production of long or continuous dendrites.

In practicing dendritic growth, as set forth in US. patent application Serial No. 844,288, filed October 5, 1959, the assignee being the same as that of the present invention, it is pointed out that it has been the practice to have the melt initially above the melting point, the seed then being inserted into the melt and thus wetted. With the seed in the melt, the melt is then supercooled. If this is properly done, the desired linear isomorphous dendritic growth can be initiated on the seed.

It is sometimes inconvenient or undesirable to have the melt initially above the melting point, and instead preferable to introduce the seed into an already supercooled melt. A cold seed introduced into a supercooled melt will, however, not be wetted by the melt, and it will result in the previously described undesired non-isomorphous angular growth.

The object of the present invention is to provide a process enabling a dendritic crystal of precisely controlled thickness and having two substantially parallel faces to be pulled from a supercooled melt of solid material as an isomorphous direct axial prolongation of a suitably oriented seed by melting the tip of the seed and contracting the melt therewith to provide wetting of the seed by the melt.

Another object of the present invention is to provide a process for producing a dendritic crystal of precisely controlled thickness and having two substantially flat parallel faces from a super-cooled melt of a solid material as an isomorphous direct axial prolongation of a suitably oriented seed comprising, disposing the seed adjacent to the surface of a supercooled melt of the material from which the crystal is to be prepared and passing an electrical current between the seed and the melt whereby the tip of the seed melts, contacting the surface of the melt with the molten tip of the seed and withdrawing the seed and an attached dendrite from the melt.

Other objects of the present invention will, in part, be ovious and will, in part, appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawings, in which:

IGURE 1 is a view in elevation, partly in cross section, of a crystal growing apparatus suitable for use in accordance with the teachings of this invention;

lee

FIG. 2 is a greatly enlarged fragmentary view of a dendritic seed crystal;

FIG. 3 is an enlarged planned view of a dendritic crystal;

FIG. 4 is a fragmentary view in elevation;

FIG. 5 is a side view of a dendritic crystal grown in accordance with the prior art; and

FIG. 6 is a side view of a dendritic crystal being grown in accordance with the process of this invention.

In accordance with the present invention and in attainment of the foregoing objects there is provided a process for growing a thin flat elongated dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, which comprises the steps of establishing a supercooled melt of the material to be grown as a dendritic crystal, disposing adjacent the surface of the melt a suitably oriented seed having two or more twin planes and having a molten tip produced by any suitable means, contacting the melt surface with the molten tip of the seed crystal, and withdrawing the seed from the melt at a speed of from 0.25 inch to 25 inches per minute while maintaining the melt at the supercooled temperature, whereby a dendritic crystal is grown from the melt as an isomorphous direct prolongation of the seed crystal. The tip of the seed is preferably melted by passing an electrical current between the tip and the supercooled melt.

The present invention is particularly applicable to solid materials crystallizing in the diamond cubic lattice or zinc blend structure. Examples of such materials are the elements silicon and germanium. Likewise, stoichiometric compounds having an average of four valence electrons per atom respond satisfactorily to the crystal growing process of this invention. Such compounds which have been processed with excellent results comprise substantially equal molar proportions of an element from group III of the periodic table, particularly aluminum, gallium and indium, combined with an element from group V of the periodic table, particularly phosphor, arsenic and antimony. Compounds comprising stoichiometric proportions of group II and group VI elements, for example, zinc selenide (ZnSe) and zinc sulfide (ZnS), can be processed in accordance with this invention. These materials crystallizing in the diamond cubic lattice or zinc blend structure are particularly satisfactory for various semiconductor applications. Furthermore, the diamond cubic lattice structure materials may be intrinsic or they may be doped with one or more impurities to produce n-type or p-type semiconductor materials. The crystal growing process of this invention may be applied to all these difierent materials.

For a better understanding of the practice of this invention, reference should be had to FIG. 1 of the drawings wherein there is illustrated apparatus 10 suitable for use in the practice of this invention. The apparatus comprises a base 12 carrying a metal support 14 for a crucible 16 of a suitable refractory metal such as graphite to hold a melt of the material from which the fiat dendritic crystals are to be drawn. Molten material 1%, for example germanium, is maintained Within the crucible 16 in the molten state by a suitable heating means such, for example, as an induction heating coil 20 disposed about the crucible. Controls, not shown, are employed to supply an alternating electrical current to the induction coil 2% to maintain a closely controllable temperature in the body of the melt 18. The temperature should be readily controllable to provide a temperature in the melt a few degrees above the melting point to prevent premature solidification, and also to reduce heat input so that the temperature drops to a temperature at least one degree below the melting temperature and preferably to supercool the melt from 5 C. to 15 C., or lower. A cover 22 closely fitting the top of the crucible 16 may be provided in order to maintain a low thermal gradient in the dendrite immediately above the top of the melt. Passing through an aperture 24 in the cover 22 is a seed crystal 26, having at least two internal twin planes and preferably having three internal twin planes and being oriented crystallographically as will be disclosed in detail hereinafter. The crystal 26 is fastened to a pulling rod 28 by means of a screw 30 or the like. The pulling rod 28 is actuated by suitable mechanism to control its upward movement at a desired uniform rate, ordinarily in excess of one inch per minute and normally 5. to 12 inches per minute or even more. A protective enclosure 32 of glass or other suitable material is disposed about the crucible with a cover 34 closing the top thereof except for an aperture 36 through which the pulling rod 28 passes.

Within the interior of enclosure 32 is provided a suitable portective atmosphere entering through a conduit 4d and, if necessary, a vent 42 may be provided for circulating a current of such protective atmosphere. Depending on the crystal material being processed in the apparatus, the protective atmosphere may comprise a noble gas such as helium or argon, or a reducing gas such as hydrogen or mixtures of hydrogen and nitrogen, or nitrogen or the like or mixtures of two or more gases.

In the event that the process is applied to compounds having one component with a high vapor pressure at the temperature of the melt, a separate suitably heated vessel containing the one component may be disposed in the enclosure 32 to maintain therein the vapor of such com: pound at a partial pressure sufiicient to prevent impoverishing the melt or the grown crystal with respect to the component. The temperature of the separate vessel containing the said one component is heated so that the vapor pressure of the component is substantially equal to the vapor pressure of the component'from the supercooled melt. Thus, an atmosphere of arsenic may be provided when crystals of gallium arsenide are being pulled. Enclosure 32 may be suitably heated, for example, by an electrically heated cover, to maintain the walls thereof at a temperature above the temperature of the separately heated vessel containing the arsenic in order to prevent condensation of arsenic thereon.

In order to melt the tip of the seed, an electrical current source is connected thereto, for example, a direct current power source 44 is connected in series by an electrical conductor 46 with an impedance such as a resistance, 48, a switch 50, the crucible support 14 and the pull rod 28. In FIG. 1, the conductor 46 is illustrated as passing through an electrically insulating seal 52 in the enclosure 32 and making contact with the crucible support 14. The conductor 46 makes contact with the pull rod 28 through a sliding or brush type contact 54. It will be understood that the method of establishing electrical contact wlth the melt 18 and the pull rod 28 is not critical, and such contact may be made in any number of appropriate ways. For example, a metal plate may be inserted in the base 12 in contact with the metal support member 14. In FIG. 1, the crucible support 14 and therefore the melt is illustrated as being biased positive relative to the pull rod 28 and the seed 26, since this is the preferred directlon of current flow for reasons which will be discussed later herein. Howeven it is not critical, and the pull rod and seed may be biased positive to themelt. In some cases alternating current may be employed. It will be understood that current passes from the crucible support 14, which maybe comprised of any suitable electrical conducting material to the graphite crucible 16 and thence to the melt 18.

It will also be understood that current flows from the pull rod 28 to the seed crystal 26.

Referring to FIG. 2 of the drawing, there is'illustrated, in greatly enlarged view, a section of a seed crystal 26 having the preferred structure of three

internal twin planes

50, 51, and 52, respectively. The seed crystal may and indium antimonide.

be obtained in various ways, for example, by supercooling a melt of the solid material to a temperature at which a portion thereof solidifies, at which time a mass of dendritic material will be formed and may be removed from the melt. Selection and study of each dendrite may result in one being found that has three or more twin planes. While these selected dendritic crystals may not be uniform, they are suitable. for seed purposes. Also, one can cut from a previously prepared large crystal having twin planes a section suitable for. use as a seed crystal. The seed crystal 26 comprises two relatively fiat faces 54 and 56. Examination will show that the crystallographic structure of the preferred seed on both

faces

54 and 56 is that indicated by the crystallographic direction arrows at the right and left faces, respectively, of FIG. 2. It will be noted that the horizontal directions perpendicular to the flat faces 54 and 56 and parallel to the melt surface are 111. The direction of growth of dendritic crystal will be in a 2l1 crystallographic direction. If the faces'54 and 56 0f the dendritic crystal 26 were to be etched preferentially to the (111) planes, they will both exhibit equilateral triangular etch pitch 58 whose vertices 60 will point upwardly while their bases 62 will be parallel to the surface of the melt. It is an important fea ture of the preferred embodiment of the present invention that the etch pits on both

faces

54 and 56 of seed crystal 26 have their vertices 60 pointing upwardly. It will be understood that while FIG. 2 illustrates a preferred embodiment of the seed crystal, that is one having three twin planes, the process of this invention may be practiced with a seed crystal having any odd number of interior twin planes; Satisfactory results have been achieved, under certain conditions, when seed crystals having an even number of interior twin planes have been employed. Reference should be had to U.S. patent application Serial No. 844,288, identified further hereinabove, for a more complete discussion of suitable seed crystals.

Referring again to FIG. 1, in the practice of the process of this invention the melt 18 comprised of the material from which the dendritic crystal is to be drawn is prepared in crucible 16. After the melt 18 is formed, the electrical power provided to coil 20 is reduced and the melt 18 is supercooled to a temperature ranging from 5 C. to 40 C. below its melting point. In practice, super cooling the melt from 5 C. to 20 C. below its melting point has given good results with, for example, germanium -A greater degree of supercooling may be employed. However, with a greater degree of supercooling, much higher rates of crystal withdrawal from the melt are necessary, and these higher rates may introduce operational difiiculties. After supercooling of the melt 1-8, the tip of seed crystal 26 is brought into close proximity /s inch'or less) with surface 19 ofthe melt 18. The switch 50 is then closed and a potential established between the melt 18 and the seed crystal 26; The potential between the melt18 and the seed crystal 26 results in the ionization of the gaseous atmosphere within the enclosure 32 which results in the melting of at least the tip 25 of seed crystal 26. When a molten drop appears on the tip 25 of the seed crystal 26 the seed crystal is brought in contact with at least the surface 19 of the melt. The drop on the tip of the seed crystal coalesces with the melt and conveniently and automatically terminates the gaseous discharge. The switch 50 may also be opened at the instant of contact to terminate the gaseous discharge. Dendritic growth will immediately commence on the seed as a crystalline continuation of the seed and parallel to the seed axis. The pull mechanism is immediately activated and the seed is withdrawn from the melt 18 whereby a dendritic crystal of the melt material is formed as an actual isomo 'phous linear prolongation of the seed crystal.

The voltage and current necessary to effect the gaseous discharge between the melt and the seed tip will depend, among other things, upon the distance between the surface 19 of the melt 18 and the seed 26 at the time of the gaseous discharge. Satisfactory results have been achieved using a voltage of from 300 to 1000 volts and a current of the order of 1 to milliamperes. A voltage of approximately 700 volts and a current of the order of 1 to 10 milliamperes is preferred.

The impedance member 4-8 serves to provide a constant current variable voltage between the melt and the seed crystal. The impedance member also serves to decrease the current provided by the source 44 without a substantial decrease in voltage. While any suitable impedance member may be used satisfactory results have been realized when a vacuum tube triode with the plate and grid connected together to make a diode has been used as the impedance member.

It is the preferred embodiment of the process of this invention that the seed be biased negative relative to the melt since in a gaseous discharge the negative electrode is heated more than the positive electrode. However, the polarity may be reversed in carrying out the process of this invention. If, however, the melt is biased negative relative to the seed, care must be taken that the resultant heating of the melt does not prevent maintenance of the desired degree of supercooling within the melt.

Referring to FIG. 3 of the drawing, there is illustrated a portion of dendrite crystal 26 which is produced in accordance with the successful practice of the invention. The faces of the dendritic crystal will comprise atomically flat planes, parallel to each other, while the sides will exhibit a serrated appearance. A fiat surface of the dendrite is scored lightly with for example a diamond scribe to-provide two parallel transverse grooves 7t} and 72 defining therebetween a desired square 74. The dendrite is placed on a flat surface with end 76 beyond score mark 70 projecting beyond the edge of the surface and flexed lightly by applying a tweezer or the like to the end and the end will break oif at the score mark 7%. In a similar manner, the die 74 is severed from the main body of the dendrite 26. The die 74 has a perfect lll orientation and may be employed in the fabrication of a semiconductor device.

Referring to FIG. 4 of the drawing, there is illustrated a suitable mechanism for pulling a dendritic crystal of indefinite length. The dendrite crystal 80 being withdrawn from the melt 18 is disposed between

rotating rollers

82 and 84 which are flexibly mounted to grip the dendritic crystal between them and whose speed of rotation is collated to the supercooling of the melt 18 such that the desired thickness of dendritic crystal is withdrawn continuously. The portion of the crystal 80 above the

rollers

82 and 84 may be coiled on a wide diameter spool or it may be severed from time to time into suitable lengths. Reference should be had to U.S. patent application Serial No. 829,069, filed July 23, 1959, the assignee of which is the same as that of the present invention, for a detailed explanation of a process of pulling a continuous dendrite of indefinite lengths.

A further advantage of the process of this invention over that set forth in US. patent application Serial No. 844,288, identified above, can be understood with references to FIGS. 5 and 6. In FIG. 5 there is shown two dendritic crystals which tend to grow from a flat seed crystal employed in accordance with the teaching of the prior application Serial No. 844,288. The seed 1% has a spike-like growth 112 formed at one end thereof as a result of the seed being brought into stationary contact with a melt while the melt is at a temperature above its melting point and maintaining it in contact with the melt while the melt is supercooled. Thereafter, as the seed is pulled from the supercooled melt two dendrites 114- and 116 form upon the extremities of spike 112 and extend downwardly therefrom. While there is no objection to pulling two dendrites simultaneously, when the length L becomes relatively great compared to the distance D, sur- 6 face tension tends to pull the

dendrites

114 and 116 together whereby they coalesce and terminate the uniform growing process. Therefore efforts are usually made to terminate growth of one of the dendrites growing from the spike 112.

With reference to FIG. 6, there is illustrated the manner in which the melt solidifies on the seed in a direct prolongation thereof by following the procedure set out herein. The melt 218 solidifies in the form of a single fiat dendritic crystal joined to the seed 226 at a point 230. In contrast to the growth illustrated in FIG. 5, it will be observed that there are no spike-like lateral growths (denoted as 112 in FIG. 5) in the process of this invention, and that only a single flat dendritic crystal is grown in a direct actual isomorphous prolongation of the seed.

The following examples are illustrative of the practice of this invention:

Example I An apparatus similar to that shown in FIG. 1 a graphite crucible containing a quantity of intrinsic germanium is heated by the induction coil to a temperature several degrees above the melting point of germanium the temperature of the melt being about 938 C., until the entire quantity forms a molten pool. After the formation of the molten pool the temperature of the germanium melt is lowered to approximately 928 C. in a period of approximately 5 seconds.

A dendrite seed crystal having three interior twin planes and oriented as illustrated in FIG. 2 of the drawing, held vertically in a holder, is lowered until its lower end is within approximately /s inch of the surface of the molten germanium.

As illustrated in FIG. 1, the germanium melt is biased positive relative to the seed crystal by an electrical concluctor. A direct current power source, comprised of two Hewlett-Packard power supplies, each set at a maximum voltage of 350 volts to 450 volts and connected together in series, an impedance, comprised of a Heinz- Kaufman vacuum triode tube in which the plate and grid were connected to make a diode and in which the filament was operated at 6 volts, and a knife switch were connected in series with the seed and melt.

With the seed disposed approximately /8 inch above the surface of the germanium melt the knife switch was closed, whereby a gaseous discharge was initiated which resulted in the melting of the lower tip of the seed. The seed was then lowered until it contacted the surface of the melt, whereby the gaseous discharge was automatically terminated. Upon termination of the gaseous discharge the knife switch was opened. The seed crystal was removed from the melt at a rate of approximately 7 inches per minute. As the seed crystal leaves the melt at single dendritic crystal is observed growing on the seed as a direct actual prolongation of the seed. The grown crystal has a thickness of 7 mils and is approximately 2 millimeters in width. The grown dendrite crystal has substantially fiat and highly parallel faces from end to end with (111) orientation. The germanium dendritic crystal so grown is found to have no surface imperfections, except for a number of substantially atomically flat faces difiering by about 50 angstroms, and was of a quality suitable for semiconductor applications.

Example 11 The procedure of Example I is repeated except that the melt is comprised of germanium and 1.5 10'- by weight, arsenic. The pull rate employed is 12 inches per minute. The resultant single dendritic crystal grown is a prolongation of the seed and is approximately 3.5 mils in thickness and is of a width of about 30 mils. The surface perfections and flatness are exceptional. The grown crystal is of a quality suitable for semiconductor application and had an n-type semiconductivity.

Equally satisfactory results can be realized in employing the process of this invention to grow dendritic crystals 7 of silicon and from melts comprised of equal molar pro portions of elements of group III and group V of the periodic table.

'While the invention has been described with reference to particular embodiments and examples it will be understood, that modifications, substitutions and the like may be made therein without departing from its scope.

I claim as my invention:

1. In the process of growing a thin flat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the steps comprising establishing a poten tial between a supercooled melt of the material to be grown into a dendritic crystaland a suitable seed crystal within a gaseous atmosphere, said seed crystal being cient magnitude to cause a gaseous discharge between the melt and the seed crystal when one is moved in close proximity to the other, whereby a tip portion of the seed crystal is melted, contacting the surface of the supercooled melt with the molten portion of the seed crystal and thereafter withdrawing the seed from the melt at a speed of from 0.25 inch to inches per minute while maintaining the melt atthe supercooled temperature, whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal. I

2. In the process of growing a thin flat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the steps comprising establishing a potential between a supercooled melt of the materialto be grown into a dendritic crystal and a suitable seed crystal within a gaseous atmosphere, said seed crystal being biased negative relative to said melt, said potential being of sufiicient magnitude to cause a gaseous discharge between the melt of the seed when one is moved within a close proximity with the other, whereby, a portion of the seed crystal is melted, contacting at least the surface of the supercooled melt with the molten portion of the seed crystal and thereafter withdrawing the seed from the melt at a speed of from 0.25 inch to 25 inches per rninutewhile maintaining the melt at the supercooled temperature, whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal.

3. In the process of growing a thin flat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the steps comprising establishing a potential of from 300 to 1000 volts and a current of the order of l to 10 milliamperes between a supercooled melt of the material to be grown into a dendritic crystal and a suitable seed crystal within a gaseous atmosphere, said seed being biased negative relative to said melt, said potential being of suflicient magnitude to cause a gaseous discharge between the melt and the seed crystal when one is moved Within a close proximity with the other, whereby, a portion of the seed crystal is melted, contacting at least 7 the surface of the supercooled melt with the molten portion of the seed crystal and thereafter withdrawing the seed from the melt to the speed of from 0.25 inch to 25 inches per minute while maintaining the melt at the supercooled temperature, whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal.

4; In the process of growing a thin flat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the steps comprising establishing a potential between a supercooled melt comprised of a material selected from the group consisting of silicon, germa nium,.and stoichiometric compounds of elements of group 6 III and elements of group V of the periodic table and a suitable seed crystal spaced from the surface of the melt within a gaseous atmosphere, said potential being of sufficient magnitude to cause a gaseous discharge between the melt and the seed crystal, whereby, a tip portion of the seed crystal is melted, contacting the surface of the supercooled melt with the molten portion of the seed crystal and thereafter withdrawing the seed from the melt at a speed of from 0.25 inch to 25 inches per minute while maint ining t e melt at the supercooled temperature,

8 whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal.

5. In the process of growing a thin flat dendritic crystal of a solidtmaterial crystallizing in the diamond cubic lattice structure, the steps comprising establishing a potential between a supercooled melt comprised of a material selected from the group consisting of silicon, germanium, and stoichiometric compounds of elements of group III and elements of group V of the periodic. table and at least one suitable doping material therefor, and a suitable seed crystal within a gaseous atmosphere, said potential being of sufiicient magnitude to cause a gaseous discharge between the melt and the seed crystal when one is moved within a close proximity with the other, whereby, a portion of the seed crystal is melted, contacting at least the surface of the supercooled melt with the molten portion of the seed crystal, and thereafter withdrawing the seed from the melt ata speed of from 0.25 inch to 25 inches per'minute while maintaining the melt at the supercooled temperature, whereby, a dendritic crystal is grown from the melt as a'direct prolongation of the seed crystal. 7

6. In the process of growing a thin fiat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the steps comprising establishing a potential between a supercooled melt comprised of a material selected from the group consisting of silicon, germanium, and stoichiometric compounds of elements of group III and elements of group V of the periodic table and a suitable seed crystal spaced from the surface of the melt within a gaseous atmospheresaid seed crystal having at least two interior twin planes, said seed crystal having a 1l1 direction parallel to the surfaces of the melt and a 211 direction perpendicular to the surface of the melt, the seed crystal when etched exhibiting triangular etch pits on both faces with the vertices of the triangular pits being directed upward with respect to the melt and the base of each etch pit being parallel to the surface of the melt, said potential being of 'sufiicient magnitude to cause a gaseous discharge between the melt and the seed crystal whereby, a tip portion of the seed crystal is melted, contacting the surface ofthe supercooled melt with the molten portion of the seed crystal and thereafter withdrawing the seed from the melt at a speed of from 0.25 inch to 25 inches per minute while maintaining the melt at the supercooled temperature, whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal.

7. In the process of growing a thin flat dendritic crystal of a solid material crystallizing in the diamond cubic lattice structure, the, steps comprising establishing a potential between a supercooled melt comprised of a material selected from the group consisting of silicon, germanium, and stoichiometric compounds of elements of group III and elements of group V of the periodic table and a suitable seed crystal spaced from the surface of the melt within a gaseous atmosphere, said seed crystalhaving an odd numberof interior twin planes, said seed crystal having a 111 direction parallel to the surface of the melt and a 2l1 direction perpendicular'tothe surface of the melt, the seed crystal when etched exhibiting triangular etch pits on both faces with the vertices of the triangular pits being directed upward with respect to the melt and the base of each etch pit being parallel to the surface of the melt, said potential being of sufiicient magnitude to cause a gaseous discharge between the melt and the seed crystal whereby, a tip portion of the seed crystal is melted, contacting the surface of the supercooled melt with the molten portion of theseed crystal and thereafter withdrawing the seed from the melt at a speed of from 0.25 inch to 25 inches per minute while maintaining the melt at the supercooled temperature, whereby, a dendritic crystal is grown from the melt as a direct prolongation of the seed crystal.

(References on following page) 10 References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Growth of Monocrystals etc., Billig, Proceedings of the 2,631,356 Sparks et a1 Mali 17, 19 3 Royal 500., A, vol. 229, pp. 346663 (1955)- 2,842,467 Landauer et a1 July 1958 5 Growth Twins in Germanium, Bolling et a1., Canadian FOREIGN PATENTS J our. of Physics, v01. 34 January-June 1956, pp. 234-240.

769,426 Great Britain Mar. 6, 1957

Claims

4. IN THE PROCESS OF GROWING A THIN FLAT DENDRITIC CRYSTAL OF A SOLID MATERIAL CRYSTALLIZING IN THE DIAMOND CUBIC LATTICE STRUCTURE, THE STEPS COMPRISING ESTABLISHING A POTENTIAL BETWEEN A SUPERCOOLED MELT COMPRISED OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICON, GERMANIUM, AND STOICHIOMETRIC COMPOUNDS OF ELEMENTS OF GROUP III AND ELEMENTS OF GROUP V OF THE PERIODIC TABLE AND A SUITABLE SEED CRYSTAL SPACED FROM THE SURFACE OF THE MELT WITHIN A GASEOUS ATMOSPHERE, SAID POTENTIAL BEING OF SUFFICIENT MAGNITUDE TO CAUSE A GASEOUS DISCHARGE BETWEEN THE MELT AND THE SEED CRYSTAL, WHEREBY, A TIP PORTION OF THE SEED CRYSTAL IS MELTED, CONTACTING THE SURFACE OF THE SUPERCOOLED MELT WITH THE MOLTEN PORTION OF THE SEED CRYSTAL AND THEREAFTER WITHDRAWING THE SEED FROM THE MELT AT A SPEED OF FROM 0.25 INCH TO 25 INCHES PER MINUTE WHILE MAINTAINING THE MELT AT THE SUPERCOOLED TEMPERATURE WHEREBY, A DENDRITIC CRYSTAL IS GROWN FROM THE MELT AS A DIRECT PROLONGATION OF THE SEED CRYSTAL.