Isothermal solution mixing growth of solids
United States Patent 1191 Grandia et al.  
 [ 1 Apr. 29, 1975 1 1 ISOTIIERMAL SOLUTION MIXING GROWTH OF SOLIDS International Business Machines Corporation. Armonk. NY.  
 [22] Filed: May 15. 1973 [21] Appl. No.: 360.518  
 Related U.S. Application Data [631 Continuation-in-part of Ser. No. 84.523. Augv 17.  
 1971. abandoned.  
 [73] Assignee:  
 Prinuu&#39;y l:&#39;.\&#39;umim&#39;rMichael F. Esposito Attorney. Agenl. or Finn-Bernard N. Wiener [57} ABSTRACT It has been discovered for the practice of this invention that when two melts at the same temperature which were separately and simultaneously saturated are mixed. the combined melt is supersaturated and crystal growth occurs isothermally. Mixing of different melts is caused to occur so as to control both composition and amount of growth of the resultant solid substance. A new technique for heterojunction growth has been discovered for the practice of this invention. The method has the capability for growing multilayered structures over a wide range of thicknesses and especially for layer thicknesses substantially less than 1 micron.  
 Generally. the practice of this invention provides solutions to several problems associated with the liquid phase epitaxy method. Specifically. it provides for the maintenance of GaAs surface in suitable form for high quality growth of a layer thereon and for the facility of controllably changing the layer composition in the ease of semiconductor materials with more than two components.  
 Important features of the invention are: a partitioned crucible of isolating two or more melts; a window in each melt compartment which exposes the melt to the substrate when correctly aligned; and a substrate holder which can be positioned to allow contact with one melt and then repositioned to allow contact with one or more other melts without the loss of a solidliquid interface. In the preferred embodiment of the invention. the windows are opened on the walls of an inner crucible; the substrate is held in two slots on a ground face of a cylindrical rod which can be rotated from one window to the next.  
 24 Claims, 13 Drawing Figures PLTENTEBmzsms 3,881.03?  
 sum 36? e FIG. 3A  
 MOLE FRACTION Al As mollllllllllllill DISTANCE ALONG GROWTH AXIS IN MICRONS PATENTEDAPRZSIQYS mil u [I 6 mm 0 I a a a a a a b8 0 s O mzomez a I 2 295 68. 26ml T mmoE 2058 6 I 8 wzomuim I 2 I O. O O O O 0.... O O 0 ll O O O O o 0 0 o o 0 0 0 I. O O O l 2 O I. O O C 0 o o 0 00 0 2 0 0.0 A  
  20:04am M402 PATENTEUA 2 881 .037  
 SHEET 6 OF 6 FIG.5  
 sk xx,  
 ISOTHERMAL SOLUTION MIXING GROWTH OF SOLIDS This is a continuation-inpart of copending application Ser. No. 84.523, filed Aug. 17. 197]. now abandoned.  
 BACKGROUND OF THE INVENTION The liquid phase epitaxial method of growth has heretofore been shown to produce some superior device properties over vapor growth methods for lll-V compound materials. lllustratively. GaP light emitting diodes, GaAs lasers and Si doped GaAs light emitting diodes have superior properties when formed by liquid phase epitaxy method. Recently. Ga ,Al,As has been shown to have more desirable properties when made by the liquid phase epitaxy method.  
  The liquid phase epitaxial growth of Ga .,Al,As layers has been used to realize desirable threshold current densities for injection lasers. Generally. this has been due to the use of GaAs and Ga ,Al,As heterojunction structures. The prior art has provided a l p. (1 micron l Angstrom units) thick Si doped p-type GaAs layer sandwiched between an n-type and a p-type Ga .Al As layer with 0.2 s X s 0.5. lmproved performance of such devices is expected if the thickness of the p-type GaAs layer were reduced even more. Heretofore. layers 1 p. thick were grown using an apparatus in which melts of different composition were brought into contact with the surface of a substrate layer which was mechanically wiped clean of the previous melt.  
  The following are exemplary references which provide background material of interest for the practice of this invention:  
 l. Appl. Phys. Letters ll, 8l (1967), H. Rupprecht et al. 2. IEEE J. Quantum Electron. QE-4. (1968), H.  
 Rupprecht. et al.  
 3. IEEE J. Quantum Electron. QE-5. 211 (1969), l.  
 Hayashi et al.  
 4. lEEE J. Quantum Electron. QE-S. 2 l0 1969), M.  
 B. Panish et al.  
 5. RCA Review 30, 106 (1969). H. Kressel et al.  
 6. Appl. Phys. Letters 16. 326 (1970), M. B. Panish et al.  
 7. J. Phys. Chem. Solids. 30, I29 1969), M. H. Panish et al.  
 8. I968 Symposium on GaAS. Dallas. Texas, M. ll-  
 legems et al.  
 9. J. Electrochem. Soc. l I6. 899 (1969), J. M.  
 Woodall.  
  The background of this invention will now be discussed in greater detail. This invention relates generally to crystal growth, and it relates more particularly to crystallization of solids from liquid solutions. Precipitation from liquid solutions can occur in various ways. Common to the various ways of precipitation is supersaturation in which the liquid solution becomes super saturated with respect to the precipitating solid. Supersaturation can occur by cooling a melt; by evaporation of a solvent; by a combination of cooling and solvent evaporation or by the change of concentration of species in a solution at a constant temperature.  
  Examples of crystal growth from solution by cooling alone are the liquid phase epitaxy method and the flux solution growth technique. An example of solvent evaporation is the growth of alum crystals from water solution. lllustratively, the combination of cooling and concentration change in a melt has been used in germanium transistor technology wherein an indium dot is heated on a germanium wafer surface for causing the germanium to go into solution. When the germanium is slowly cooled. it precipitates out of solution doped with indium. As the melt cools, it slowly changes in concentration as the germanium precipitates on the germanium wafer surface. This form of alloying has been highly developed to provide growth over very large areas and is generally termed liquid phase epitaxy. An exemplary prior art application ofliquid phase epitaxy has been growth of gallium arsenide crystal on gallium arsenide substrate. In this technique a gallium melt is saturated with gallium arsenide source at a given temperature and the melt is then cooled on a gallium arsenide substrate causing the precipitation of a gallium arsenide layer. An illustrative background article which describes the growth of a germanium layer on a germanium wafer by liquid phase epitaxy is RCA Re view, page 603, December 1963. H. Nelson.  
 In the liquid phase epitaxy technique of the prior art.  
 cooling of a melt system has been a critical require-&#39; ment. Also involved in the prior art practice has been the combination of both cooling and concentration changes in the melt which naturally occur during cooling. For the liquid phase epitaxial growth of gallium arsenide on gallium arsenide substrate, the concentrations of gallium and arsenic in the liquid are constrained to change naturally as gallium arsenide is lost to the solid phase as the melt is cooled. Similarly. in solvent evaporation crystal growth. there are thermodynamic constraints on the liquid solution composition which is allowed for a given temperature as the solid crystallizes from solution.  
  For crystal growth of ternary compound semiconductors e.g.. gallium aluminum arsenide. Ga AI As. another degree of freedom for controlling solid composition was utilized. Liquid phase epitaxial growth of ternary compounds with a continuous range of compositions. e.g., Ga, ,Al,As, is disclosed in co-pending application Ser. No. 646,315. filed June [5, 1967, by H. Rupprecht et al and commonly assigned, now U.S. Pat. No. 3.773.571 issured Nov. 20, 1973. and is also described in the noted article by Rupprecht et al. Appl. Phys. Letters ll 8l (1967) which relates to the contribution of the noted patent application Ser. No. 646.315 now U.S. Pat. No. 3,773,571. These references describe use of melts of predetermined composition which have been saturated and then cooled at some cooling rate to cause precipitation of some solid, e.g., gallium aluminum arsenide. Essentially, the composition of the solid has been determined or fixed by the cooling rate selected and the initial composition of the melt.  
  ln copending application Ser. No. 860,316 filed Sept. 23. 1969. by S. E. Blum et al and commonly assigned, now U.S. Pat. No. 3,628,998 issued Dec. 2l. l97l, a liquid is sandwiched between two solids which have the same composition. When the temperature of one solid is raised above that of the other solid. the solid at the higher temperature interface goes into solution and diffuses across the liquid phase and precipitates out at the other interface.  
  ln another type of crystal growth procedure, material is introduced into a melt in such a manner as to change the composition of the melt. The introduction of a solid phase from external to a melt system to change melt compositions is described in co-pending application Ser. No. 860.355. filed Sept. 23. l969, by M. Lorenz and commonly assigned. now U.S. Pat. No. 3.677.836 issued July 18. 1972.  
 SUMMARY OF THE lNVENTlON It has been discovered for the practice of this invention that when two melts at the same temperature which were separately and simultaneously saturated are mixed. the combined melt is supersaturated and crystal growth occurs isothermally. Mixing of different melts is caused to occur so as to control both composition and amount of growth of the resultant solid substance. A further technique for heterojunction growth has been discovered for the practice of this invention. The method of this invention has the capability for growing multi-layered structures with layer thicknesses substantially less than one micron.  
  An exemplary apparatus for the practice of this invention has a partitioned crucible which can contain two melts M and M respectively, and a cylindrical substrate holder made of high purity and high density pyrolytic graphite. Each substrate can be brought into contact with either melt M or M by a rotation of the holder such that the substrate is aligned with one of the windows on the inner wall of the crucible. This apparatus can be used in either the normal liquid phase epitaxial growth mode or the isothermal solution mixing growth mode or both. For the isothermal mode of growth. a predetermined amount of one melt is trapped in the holder as it is rotated into the other melt. This trapped melt becomes supersaturated as it mixes with the other melt causing crystal growth.  
  lllustratively. A Ga-Al melt is saturated with As using a rectangular bar of undoped GaAs with a mass in excess of that required for saturation. Sufficient time should be preferably allowed for complete saturation to occur before rotating the substrate into the melt which is illustratively approximately 1 hour and l5 minutes at 830C. If the substrate is brought into contact with the melt before this time, complete dissolution of the substrate can result.  
  Exemplary advantages of the invention are: the substrate wafer can be stored in the out of a window position with a small amount of melt to protect it from pitting during heat up; the growth can be interrupted by rotating the wafer to a new melt for the formation of a pn junction. a heterojunction. or a graded band gap structure without a loss of the solid-liquid interface. a feature particularly important for the growth of Ga Al As structures; and a periodic variation in properties can be achieved for a superlattice structure, as described by L. Esaki et al in IBM Journal ofResearc/z and Development, l4. 61 1970); and presented in copending applications Ser. No. 8ll.870 and Ser. No. 811,871. filed Apr. 1. 1969. and commonly assigned, now US. Pat. Nos. 3.626.328 and 3.626.257. respectively, issued Dec. 7, 197].  
  It is an object of this invention to provide apparatus and method for growing a crystalline layer by solution growth procedure.  
  It is another object of this invention to provide apparatus and method for growing a crystalline layer of a semiconductor compound by liquid phase epitaxy.  
  It is another object of this invention to provide apparatus and method for growing a crystalline layer of a multicomponent semiconductor compound having more than two components with a continuous range of compositions by liquid phase epitaxy.  
  It is another object of this invention to provide apparatus and method for growing a crystalline layer of a multicomponent semiconductor compound through non-equilibrium growth by mixing of two melt systems at equilibrium at common temperatures.  
  It is another object of this invention to provide method and apparatus for obtaining a solid substance by non-isothermal mixing of at least two melt systems.  
  It is another object of this invention to provide apparatus and method for the isothermal mixing of two saturated melts to cause precipitation of a solid substance.  
  It is another object of this invention to provide apparatus and method for the isothermal mixing of at least two melt systems for obtaining a solid substance wherein the solid substance may be polycrystalline. amorphous or single crystal where these can be either alternating layers homogeneous in doping or alternating layers homogeneous in composition; wherein the solid substance may be semiconductor material where the semiconductor material may be elemental. two component or more than two component. where the two component system may be a compound or an alloy; wherein the two component system may be a compound or a mixed crystal system of the type lll-V or llVl or a non-compound type alloy.  
  It is another object of this invention to provide apparatus and method for growing a layered structure including a plurality of continuous and sequential layers of a multicomponent compound having a continuous range of compositions. This is accomplished by establishing a given multicomponent compound having a particular composition in a melt system and establishing another multicomponent compound having another particular composition in another melt system and thereafter sequentially and alternately causing a solid substrate to be transferred between said mixed melt systems to cause deposition from each said mixed melt system respectively of a solid phase consisting of the non-equilibrium combination of quantities of melts from each said system.  
  It is another object of this invention to provide apparatus and method for controlling the composition and structure of a solid layer.  
  The foregoing and other objects. features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FlGS. 1A, 1B and 1C illustrate apparatus of a preferred embodiment of this invention for growing a multi-layered structure by isothermal solution mixing wherein two isolated melt systems are capable of being intermixed by transfer of a small incremental volume from each to the other; wherein FIGS. 1A and 1B show the apparatus in vertical section and in horizontal section. respectively; and wherein FlG. 1C shows a partially sectioned perspective view of an entire device during assembly.  
  FIGS. 2A and 2B present data graphs illustrating the growth of a multi-layered structure in accordance with the principles of this invention. indicating the mole fraction composition versus distance along the growth axis for two different modes of operation of the invention.  
  FIGS. 3A and 3B present an idealized thermal phase diagram for the mixed crystal system Ga .,Al,As wherein FIG. 3A shows a liquidus line for a given temperature and FIG. 3B shows a portion of 3A enlarged.  
  FIGS. 4A, 4B, 4C, 4D and 4E show an illustrative rendition of FIG. 1B for showing how a multilayered structure is provided by the isothermal solution mixing wherein sequential positions of the substrate holder are indicated respectively.  
  FIG. 5 is an exploded assembly drawing of apparatus for practice of another embodiment of this invention.  
 PREFERRED EMBODIMENT OF THE INVENTION The preferred embodiment of this invention will be described with reference to FIGS. 1A, 1B and 1C. Through the description of the nature of these figures, the method and apparatus in accordance with the principles of this invention will be made clear. The apparatus of the preferred embodiment is presented somewhat schematically in vertical section in FIG. 1A and in horizontal section in FIG. 1B; and is presented in a detailed assembly in FIG. 1C shown during an initial phase of the procedure. With reference to FIGS. 1A and 18, there is a crucible l4 and a substrate holder 16 rotatably mounted therein. The crucible 14 has outer wall 18, inner wall 20, windows 22 and bottom 19. Partitions 24a and 24b divide the entire crucible into two separate compartments 25a and 25b. Substrate holder 16 comprises cylinder 30 and substrate holder mount area 32 which supports substrate 34. Slot 36 in substrate holder 16 into which a pin through hole 22a or 2212 holds substrate holder 16 into place but allows rotation in crucible 14. Vertical slot 29 allows venting of area 32. Crucible l4 and substrate holder 16 are accessed by fastening shaft 40 to outside the system by using nut 38 onto screw 39. The crucible 14 contains melt M of one composition and melt M of another composition. For operation of the apparatus of the preferred embodiment of this invention, substrate holder 16 is inserted into the volume 43 on the inside of inner wall 20. The substrate area mount 32 is such that with proper rotation it lines up window area 22 such that melt M or M comes in contact with substrate 34. Substrate holder 16 can be rotated such that substrate 34 can be aligned with window 22b in melt M or with window 22a in melt M The operation of the apparatus of the preferred embodiment will now be described for the practice of this invention. Substrate 34 is loaded into slot 32 substrate holder 16 is then inserted adjacent to wall and is fastened into place by pinning through hole 42 into slot 36. Melt M is loaded into chamber b and melt M, is loaded into chamber 42a. Gallium arsenide sources 44a and 44b are placed into the bottoms of chambers 25a and 25b and pinned thereon, by pins not shown. Cylinder is rotated such that substrate wafer 34 is not in contact or not aligned with window area 22a or 22b. The assemby illustrated in FIGS. 1A and 1B is established in a vacuum chamber not shown in these figures but shown in detail in FIG. 1C.  
  With reference to FIG. 1C, the chamber 150 contains crucible apparatus 10, and has inlet port 154. outlet port 152, doping tubes 156a and 156/), shaft tube 160 and holding slots 162a and 1621). The crucible assembly is loaded into quartz tube 150, gas inlet supplies are attached to inlet port 154 and a vacuum system is attached to outlet port 152. The gas inlets provide high purity hydrogen gas to the system and the vacuum system provides a vacuum of approximately 1 micron of mercury or less. The apparatus is assembled so that there are doping tubes 156a and 156b which have vacuum seals at openings 167a and 1671). The shaft 40 is connected to the outside of the chamber through shaft tube 160 through a vacuum seal at shaft tube 160. The entire system is then either flushed with hydrogen or vacuum baked at some temperature below growth temperature and subsequently flushed with hydrogen.  
  The nature of operation of the apparatus of the preferred embodiment for the growth of multi-layered structures in accordance with the principles of this invention will now be described in greater detail with reference to FIG. 1C which shows an assembly drawing of the apparatus as it is being assembled for operation.  
  The crucible consists of two pieces: a cylindrical piece 14 has three chambers in it, 25a, 25b and 43; a barrel shaped piece 16 fits into the center of the chamber 43. The cylinder 14 has two separate melt chambers 25a and 25b. The melt chambers 25a and 25b are connected to the center chamber 43 by windows 22a and 22b. Two key ways 162a and 16212 on the outside of the holder 14 hold it with respect to the quartz tube 150. Two threaded holes 19a and 19b and two pin screws 220 not shown are used to hold source materials not shown in place in the respective chamber 25a and 25b. The cylindrical barrel section 16 fits into the center chamber 43 and has an area 32 thereon to hold the substrate wafer 34 in place. A slot 36 on substrate holder 16 allows rotation but restricts vertical movement by an insert pin, not shown. There is a threaded portion attaching shaft 40 via nut 38 to the substrate holder 16. A vent slot 31 allows venting of the wafer chamber. The prepared substrate wafer 34 is inserted into the area 32. The substrate wafer 34 is positioned so that it faces the partition area. The source material is appropriately cleaned and positioned so that the pin screws can hold the source material bars in place during the run.  
  Appropriate materials are placed into the chambers 25a and 25b. Doping may be added at this time or dropped in later via tubes 156a and l56b. With the pin screws in place, the substrate holder 16 is free to rotate but is not free to move vertically with respect to the crucible 14. The shaft 40 is then connected by nut 38 to the assembled crucible and the entire assembly lowered into the chamber 151 so that the key ways 102a and l02b on the quartz tube 150 are engaged in key way slots 162a and 162b on the crucible. This allows rotation of the center barrel l6 and prevents rotation of the outer crucible 14. With the substrate wafer 34 in the neutral position, i.e., it is interfacing section 24, the system is evacuated, baked at a low temperature, and then back filled with hydrogen. The hydrogen flush is continued throughout the entire growth schedule in accordance with the principles of this invention. The system is then heated to appropriate temperature between 750C and 950C and an appropriate soak time is allowed to let the solutions M and M equilibriate. The substrate holder 16 is rotated 90 into one of the windows 220 or 22b. Melt from the particular crucible chamber 25a or 2517 flows into the substrate chamber and growth is initiated by cooling the furnace at an appropriate rate, e.g., between 0.03C/min. and  
 30C/min. When a desired first growth has been accomplished. cooling may be continued after rotating the crucible holder into the other window or cooling may be ceased and isothermal growth may be continued by sequential rotations from window 22a to window 22h. After desired growth is accomplished. the substrate holder 16 is rotated to a neutral position. i.e.. it faces the area 24 of the crucible. and the power is turned off to the furnace winding 104 via terminals 106 and 108. The crucible assembly is normally left in this condition until it has cooled to room temperature.  
  FIG. 2A shows the composition profile of mole fraction of AlAs vs distance in microns as measured along the growth axis of an exemplary layer grown by liquid phase epitaxy in accordance with the principles of this invention in which there was only one rotation between melt M. and melt M The zero position of this plot at zero microns corresponds to the interface between the gallium arsenide substrate and the GaAlAs epitaxial layer. The layer profile is broken up into three regions designated I. ll and Ill. Region I was grown out ofa relatively low aluminum composition melt. region ll was grown out of a relatively high composition aluminum, and region lll which results from cooling the region ll at a higher than equilibrium cooling rate. It should be noted that region I is homogeneous in composition and region ll is relatively homogeneous in composition. whereas region lll has a large variation in composition. In accordance with the principles enunciated in copending application Ser. No. 646.315 filed June 15. 1967 and commonly assigned. now US. Pat. No. 3.773.57l issued Nov. 20. 1973. when the furnace is shut off. the cooling rate starts out slowly and goes through some maximum value as the furnace cools faster and faster. Therefore. the aluminum concentration drops off strongly with increasing cooling rates as shown in region lll.  
  Region l is accomplished by normal cooling. region ll is accomplished by normal cooling after rotation from melt M and melt M and region lll is the result of extremely fast cooling to room temperature after ro tation from melt M to storage position. The 80 micron position is the surface edge of the final growth layer. The data was obtained by using a conventional electron beam probe analyzer which X-ray fluoresces a sample with an electron beam with a dimension of approximately 1% to 2 microns resolution. The X-ray fluorescent data is recorded on a counter which is then converted through calibration factors into mole fraction AlAs.  
  FIG. 28 presents data representation of mole fraction AlAs plotted vs. distance in microns in the growth direction for a layered structure grown by the isothermal melt mixing procedure of this invention in which there are peaks which correspond to the compositions which occur as a result of rotation from M into M and valleys which correspond to the composition of the layer which is formed by a rotation of M into M ldeally. the interface ofthe sequential layers begins at the average composition between the peaks and the valleys so that all of the area under the average value represents a layer of M and everything above the average value represents a layer of M This demonstrates that the growth occurs as a result of the mixing of two melts since the temperature was held constant for approximately revolutions. FIG. 2B is not an idealized square wave profile because of the resolution of the electron beam probe. Both the amplitude and the peak and valley compositions approach each other as the result of dilution of the melts M. by melt M and of melt M by melt M upon rotation ofthe substrate holder 16 which causes the melt mixing.  
 PRACTlCE OF THE INVENTION The composition profiles along the growth axis for two types of growth procedure according to the principles of this invention are shown in FIGS. 2A and 2B. FlG. 2A shows the profile of a layer which was grown from two different melts at a growth rate of O.lC/min. with the apparatus shown in FIGS. 1A. 1B and 1C. The layer was grown on the face of an undoped GaAs substrate 34. The first part of the layer was grown from an As saturated melt M containing 30 gms Ga with an Al/Ga weight ratio of 3 X 10*. and cooled from 862C to 852Cv The substrate was then rotated into a melt M containing 30 gms Ga with an Al/Ga weight ratio of5 X 10&#34;&#34;. and cooled between 852C and 842C. The composition profile is very flat for the part of the growth which occurs in each melt. The decrease in Al concentration which occurs near the end of the profile is due to fast freezing of the melt which is trapped in the substrate holder when the furnace is turned off.  
  PK]. 28 shows the composition profile of a multilayer structure grown in the isothermal solution mixing mode of this invention by several rotations between two melts. M and M,,. The layers have a periodic variation in Al concentration along the growth axis with an overall decrease in amplitude along the growth axis. The peak-to-peak spacing is about 3 microns and each sub layer is about 1.5 microns thick. One melt M had an Al/Ga ratio of l0 and the other melt M had a ratio of 5 X 10 Rotation was accomplished by rotating the substrate holder 16 in less than 1 see. time period from one melt to the other melt and holding thereat for approximately 3 minutes. In other experiments it was found that the thickness and spacing of the sub-layer structure was independent of cooling rate in the range between zero and 0.lC/min. and of rotation cycle time between melts M and M,, in the range be tween 3 min/melt and 30 sec/melt. This is evidence that the growth of the substrate is due to the supersaturation which occurs during the mixing of the trapped melt which is brought over by the substrate holder in contact with the other melt.  
  The volume ratio of the melt in compartment 2521 or 25b to the melt trapped in the holder and transferred from one melt compartment to the other is 25. By the proper selection of this volume ratio. the growth temperature and the melt volume. it is possible to grow any desired thickness of a sublayered structure. lllustratively. the apparatus and method of this invention have been utilized to grow a heterojunction layered structure in which the Ga, ,.Al ,As layers are l micron thick and the GaAs p-type layer is 1 micron. This structure has produced lasing thresholds of 3.600 A/cm at room temperature at a 10&#39; duty cycle and 6.000 A/cm at a l()&#34;- duty cycle.  
 EXPLANATlON OF THE lNVENTlON A theoretical explanation of the isothermal solution mixing epitaxial growth according to the principles of this invention follows from recognition of certain isothermal phase boundary-composition relations in the Ga,- ,.Al,As system. The phase diagram for the Ga Al,As ternary mixed crystal system has been discussed in the literature of which the following are exemplary articles:  
 a. J. Phys. Chem. Solids. 30. 129(1969). M. H. Panish. et al.  
 b. I968 Symposium on GaAs. Dallas. Texas. M. II  
 legems et al.  
  With reference to the ternary phase diagram of FIG. 3A examination of the Ga rich portion of this system shows that a solid-liquid phase boundary I22 exists over a large solid composition range I26, and that an isothermal liquidus curve I22 is such that when two melts M and M having different composition on the liquidus line are mixed. the mixed melt will be supersaturated and hence crystallization can occur. FIG. 3B schematically presents the Ga-Al-As liquidus line I22 at constant temperature T at the Ga rich corner of the phase diagram. The points A and B represent two melts M and M of different composition at solid-liquid equilibrium. Under equilibrium conditions, the composition of the liquid melt can change along path P, of liquidus line 122 between points A and B. When the melts M and M are mixed. the final composition of the mixed melt will lie at some point along path P indicated as line 124 connecting points A and B, the actual point depending on the volume ratio of the two melts. However. any point along path P along line 124 at temperature T except for points A and B lies in a region of supersaturation. This supersaturation is relieved by the growth ofGa, ,Al,As crystal. In FIG. 2A. for a melt of composition A the corresponding solid is indicated as A; and for a melt of composition B. the corresponding solid is indicated as B.  
  As will be described in detail hereinafter with reference to FIGS. 4A, 4B, 4C. 4D and 4E. the composition of the solid which grows during isothermal melt mixing at one chamber more closely corresponds to the melt transported from the other chamber than to the melt at the growth window.  
  The operation of this invention can be visualized by considering an idealized set of circumstances shown schematically in FIGS. 4A. 4B. 4C. 4D and 4E. These figures show in somewhat schematic form the horizontal view of the apparatus of FIG. 1B in five different sequential positions.  
  When the apparatus of FIGS, 1A. 1B and 1C is used in the isothermal melt mixing mode according to the principles of this invention, the flow of the solution of melt mixing that occurs and resulting crystal growth can be visualized by considering a sequence of events illustrated in FIGS 4A, 4B. 4C, 4D and 4E. At the beginning, as shown in FIG. 4A, the substrate wafer 34 is aligned in contact with melt M at window 220. The composition of the melt M is homogeneous in all regions of the crucible compartment a since the melts M and M have been established in equilibrium at the temperature for the isothermal melt mixing. The solid composition corresponding to melt M is represented by circles I40. The solid composition corresponding to melt M is represented by the dots I42. The crucible holder 16 is then rotated into the position shown in FIG. 48 where a volume 17a of melt M is trapped between the substrate holder l6 and the wall of the compartment 24a. The volume 170 of melt M is then moved by substrate holder 16 to window 22b in contact with melt M in chamber 25b, as shown in FIG. 4C.  
  At first. the melt M has an interface with the volume 1711 of melt M which has been moved to window 2212. Since melt M has a different concentration than volume 17a of melt M an interdiffusion mechanism occurs; i.e., melt M that was transported by the substrate holder I6 starts mixing with the bulk of the melt M in crucible chamber 25b. As this occurs. the melt M which is next to the substrate wafer 34 becomes supersaturated which is relieved by crystal growth having a composition I40 on the substrate surface. It has been determined that the composition I40 of the layer 34a which deposits on the substrate 34 corresponds to the composition to be expected from equilibrium growth from a melt having the composition M After the volume 17a of melt M has completely mixed with the melt M in the crucible chamber 25b, there is a stable system in crucible chamber 25b and no further crystal growth occurs. The incremental amount that melt M has changed in concentration depends on the volume of the melt M present therein and the composition of the melt M, which was transported by crucible holder 16 from chamber 250.  
  Ideally, only melt M is deposited as layer 34a. Actually, a certain amount of melt M has mixed with the melt M in crucible chamber 25b. A volume 17b of melt M is shown in FIG. 4D partially transported toward crucible chamber 250. Finally. the substrate holder 16 is shown rotated in FIG. 4E such that another layer 34b with composition I42 has deposited on layer 3411. It has been determined that the composition 142 of layer 34b corresponds to the composition of the liquid trapped in volume 17b shown in FIG. 4D.  
  The graph shown in FIG. 2B substantiates the foregoing explanation of isothermal melt mixing of multilayered structures in accordance with the principles of this invention. The graph has the appearance of a damped sine wave. As noted hereinbefore, the concentration profile is actually more closely that of a rectangular wave pattern. The damping characteristic indicates that the sequential layers being deposited begin to have an increasing amount of content of the melt at the crucible chamber where growth is occurring as a consequence of a prior transport thereof to the other crucible chamber. The process may be repeated so long as there remains a distinct characteristic to the melts M and M When equilibrium has occurred for both melt systems no further crystal growth without cooling is observed.  
 ALTERNATIVE EMBODIMENT The further practice of this invention will be described with reference to FIG. 5 which presents an alternative apparatus for the practice of this invention. It includes three melt chambers and a rotating substrate holder in a horizontal plane whereby the growth of the layered structure in accordance with the practice of this invention is accomplished isothermally without regard for any temperature gradients in the vertical axis of the growth chamber.  
  The apparatus illustrated in FIG. 5 comprises a outer crucible 200 with inner volume 205, feet 2620 and 262b, a tapped hole 201 and retaining screw 202. The outer crucible 200 fits into the bottom of the quartz chamber 260 and does not rotate with respect thereto. It also houses the other components of the crucible. The substrate wafer holder 204 consists of a flat disk structure with a depression 207 to house the wafer. two  
 tapped holes with retaining screws 210a and 21017. a bottom projection not shown which rides in cylindrical depression 203 in the bottom of outer crucible 200, a venting slot 211, and a vertical shaft 208 ending in threaded portion 212. The substrate wafer retainer and spacer 216 has center hole 224 which fits over shaft 208, a through window 218 slightly smaller than the wafer. two through holes 220 which are l80 apart and are 90 from the through window. and a vent slot 222. Barrel 230 with center hole 242 fits over shaft 208. it has three melt chambers, 232a. 232b and 2320 with key slots 236 which extend approximately two-thirds of the way down the barrel. Retaining screw 240 stops a source material bar 238 from rising in the melt after it has been inserted in the slto 236. A vent slot 246 extends the length of the barrel 230 and a vent hole is positioned at one of the four 90 positions on the same radius as the melt chambers 232a. 232b and 2320. A stop slot 244 which receives stop screw 202 and maintains the position of the barrel so that it does not rotate with respect to part 200. A nut 214 is fastened to the top of shaft 208 and holds the crucible turning quartz rod 40 to shaft 208.  
  The growth chamber within which the growth apparatus is established will now be described. A quartz cylinder 260 with a flat bottom. has with two stop rods 264a and 264b at the bottom to hold the outer crucible with respect to itself. An inlet tube 266 and exit tube 268 are attached to the quartz cylinder. This is then fit ted with a vacuum seal fitting 263. The quartz rods 264a and 264b are parallel to the bottom of the quartz tube 260 and are spaced so projections 262a and 262!) from the outer retainer crucible 200 fit between the rods and do not allow rotation of the outer crucible. The vacuum seal fitting 263 has four smaller vacuum connectors on the top thereof: one seal 271 at the center and the other three seals 271a, 2711; and 2710 are placed 90 apart from each other on the same radius as the melt chambers in barrel 230. The vacuum seal fitting is oriented so that the dopant drop tubes 272a, 272b and 2720 via seals 271a. 2711) and 2710 respec tively are above the desired respective chambers 232a. 232b and 2320.  
  The manner in which the apparatus shown in exploded form in FIG. 5 is assembled for operation for growth of a layered structure in accordance with the principles of this invention will now be described. The prepared substrate wafer is placed in the wafer cham&#39; her 207 on the surface of wafer support 204. The wafer retainer and spacer 216 is positioned over the shaft 208 so that the window 218 is over the wafer and retains it and forms the melt storage volume equivalent to volume 17 in FIG. 4. The two stop screws 210 are brought flush to the surface of the wafer retainer and spacer 216. Care must be taken that the stop screws 210 do not extend above the plane of the surface 217 of spacer 216 where they would interfere with the rotation thereof relative to the barrel 230. The barrel 230 with its center hole 242 slides over shaft 208 and is positioned such that the vent hole 234 is above the wafer 219 and the wafer window 207.  
  The source materials 238a, 2381) and 21380 are put in the appropriate slots 23601, 23617 and 2360 and are retained below the surface of the melt by retaining screw 2400. 240b and 2400. respectively. The subassembly parts 204, shaft 208, substrate support 216 and the barrel 230 are then placed in the cylindrical opening 205 of outer crucible 200 and retained there by the retaining screw 202 in the threaded hole 201 via slot 244 in barrel 230. As assembled. the barrel 230 and the outer crucible 200 are fixed with respect to each other. The 5 shaft 208. wafer holder 204 and the retaining spacer 216 are immobile with respect to each other but free to turn with respect to the barrel 230 and the outer crucible 200. When the vent hole 234 is aligned with the wafer window 218 and wafer 219, there is then an entire vent slot consisting of partial vent slots 246, 222 and 211. The entire vent slot formed by partial vent slots 246, 222 and 211 allows the bottom cylindrical opening 203 under substrate support 204 to be vented. The wafer-holding support 204, shaft 208, spacer retainer 216 and barrel assembly 231 are placed into the hole 205 of the outer crucible 200. The screw 202 is then inserted into slot 244 of barrel 230 and prevents rotation of barrel 230 with respect to outer crucible 200.  
  The quartz rod 40 is connected to the crucible assembly and is used to lower the assembled crucible into the chamber 261 of quartz container 260. The appropriate melts are placed in the respective melt chambers 232a. 232b and 2320 and the crucible assembly is ready to be inserted into the quartz container 260. When the crucible assembly is in the bottom of the chamber 261, two quartz rods 264a and 264b position it and keep it from turning with respect to the quartz ware. The fitting and seal 263 for the top of the quartz container 260 is then placed in position, with the drop tubes 2720, 272b and 2720 being loaded with the appropriate dopants over the respective melt chamber 2320. 232b and 2320. The system inlet and outlet ports 265 and 267 are then fastened to the hydrogen input and the vacuum line. not shown. After the appropriate flush time has elapsed. the hydrogen line is turned off and the vacuum line opened so that the entire system including the hydrogen line is evacuated. During this period, the vent hole 234 is positioned over the wafer 219 and venting of the chamber 203 volume is accomplished. The slots 246, 222 and 211 were previously aligned so that the venting of the entire crucible assembly is now possible. When the vacuum pressure reaches approximately one of micron Hg. the entire unit is heated to between 200-250C by furnace windings 280 which one electrically energized via input and output terminals 281 and 282 from a power source, not shown. Temperature of the apparatus is maintained for approximately l5 minutes and the vacuum line is then closed and the system is back filled with hydrogen and a hydrogen flush is maintained throughout the entire run. The furnace 280 is then brought to temperature and the crucible assembly 259 and growth materials in chambers 232a. 232b and 2320 are soaked for an appropriate length of time. usually about an hour to an hour and one half. After this period the first rotation is accomplished. The shaft 40 via knob 276 is rotated 90 so that the wafer holder 204 and the spacer retained 216 are moved into the first melt position. if desired at this time, dopants could be added to the first melt.  
  The furnace is now cooled at approximately 0.lC per minute for an appropriate period of time. depending on the thickness of the desired layer. The heating and cooling cycle program is then shut off and the rotations of shaft 40 are initiated for isothermal solution growth according to the principles of this invention. lllustratively. there is a rotation of 90 into the second melt at chamber 23217 where there is a hold for seconds to three minutes depending on the amount of growth selected, and then a rotation back to the melt at chamber 232a. This mode of rotation is continued until the selected number of layers is achieved. After the final rotation back to chamber 232a, a cooling program is then continued for approximately 30 minutes at a rate of 0.lC/min. After this cooling period. the wafer 219 is rotated to a neutral position. e.g. a 45 rotation, and the power turned off to terminal 281 and 282 of the furnace 280.  
  For another mode of growth, the cooling program is not shut off after the initial cooling period. but continued during rotation of the substrate holder 204 into the second melt. Dopant may now be dropped in the second melt. After an appropriate cooling time in the second melt, the wafer is rotated to a neutral position. For still another mode of solid growth three melts in chambers 232a, 232h and 2320 may be utilized after the growth is finished in the second melt. There is rotation of the substrate holder 204 into the third melt for a short period of time with finally there is rotation into a neutral position and turning off of the power to the furnace. The thir melt is used to terminate growth so that a fast growth layer does not appear on the surface of the multi-layer structure. After the termination of the run, the crucible assembly and quartz container 260 are normally left in the furnace windings 280 under hydrogen flush until both have cooled to room temperature.  
 EXEMPLARY DESIGN CONSIDERATIONS As disclosed for the concept of this invention, in a ternary liquid system it is often possible to find two different compositions. both of which are on the liquidus curve at a given common temperature, such that when these two compositions are mixed the melt will become supersaturated. For the gallium aluminum arsenide system, if at the same temperature. a ternary alloy of gallium aluminum arsenide containing a greater amount of gallium arsenide is mixed with a similar alloy containing a greater amount of aluminum arsenide, growth of the alloy, gallium aluminum arsenide, will take place on a substrate provided for this growth.  
  Clearly to one of ordinary skill in the art of crystal growth, the principles of this invention have a wider range of application. Through knowledge of the phase diagrams of other lll-lll-V materials, it is recognized that the isothermal solution mixing growth of materials may be accomplished according to the principles of this invention for all these materials. For those lll-lll-V systems for which the phase diagrams have not actually been observed in the laboratory, calculations exist which show that they have the same type of phase diagrams. Examples of these lll-lll-V alloys are Ga, ln,As and Ga ,Al,P. Antimony can be substituted for phosphorous. Therefore, ll1&#39;lll-V materials can be grown by the process of this invention. Other semiconductor alloy materials which obey the same relationship are the ll-ll-Vl materials. An example of such materials is Zn Cd Se. The selenium can be substituted with either sulfur or tellurium thereby forming a class of such materials.  
  It is also clear to one of ordinary skill in the art of crystal growth that the principles of this invention are not limited to the growth of semiconductor materials. There are also many electrooptic materials which are ternary alloys. An example is the KNbO LiNbO BaNb O system for which the ternary phase diagram has been published by E. A. Giess et al, Materials Research Bull. 5. l09l 16 (1970). especially FIG. 1. The liquidus curves show sufficient curvature that it is clear that a high degree of supersaturation can be obtained upon the mixing of two appropriate liquid components. Thus, crystal growth will occur by the method of this invention in this and similar materials. Similar behavior is predictable in the Na O-BaO-Nb O system published by E. A. Giess et al, Jv Am. Ceramic Soc. 53, 14-17 (1970). especially FIG. 1.  
  Magnetic metal oxide systems have been described in the literature in considerable detail such as the Fe O Y O -Al O system as published by H. J. van Hook, J. Am. Ceramic Soc. 46, 121-124 1963), especially FIG. 1. The garnet and orthoferrite phases show substantial curvature of the liquidis curves. Hence, it is predictable according to the principles of this invention that they may be grown by the isothermal solution mixing growth process of this invention. The liquidus curves for the spinel and corundum phases show much less curvature and hence the principles of this invention would be somewhat less applicable to their growth.  
  Another example for the practice of this invnention is the Fe O -Feo-YFeO system as published by H. J. van Hook, J. Am. Ceramic Soc. 45. 162-165 (1962), especially FIG. 4. The garnet phase shows considerable curvature. The magnetite phase shows even greater curvature. The orthoferrite phase shows some curvature and the hematite phase very little, if any. curvature. Therefore. the garnet and magnetite phases can be easily grown according to the principles of this invention. The orthoferrite phase can be grown with some difficulty, but the hematite phase cannot be grown. However, these statements apply only within the range of temperatures measured, i.e. less than 1.600C.  
  It is recognized from the foregoing recitation of ex emplary design considerations that the practice of this invention has several aspects.  
  1n the practice of one aspec of this invention, there is the method for growing a solid structure comprising the steps of: established respective regions of two liquid substances each at thermal equilibrium at a respective temperature, said liquid substances being different members of a multicomponent compound system with more than two components and with a continuous range of compositions, and when mixed providing a supersaturated solution; establishing a substrate adjacent one said liquid substance at a solid-liquid interface: transferring an incremental volume of said one liquid substance adjacent to said substrate at said solid-liquid interface together with said solid thereat to a liquidliquid interface with said region of said other liquid substance; and depositing said solid structure on said solid-liquid interface by isothermal solution mixing of said incremental volume of said one liquid substance with said region of said other liquid substance. 1n greater detail, the respective regions of said two liquid substances are each at thermal equilibrium with respect to a respective solid phase with a related composition at a given temperature. Further, the multicomponent compound system can be the lll-lll-V ternary semicon ductor compound system. ln particular. the multicomponent compound system is Ga C AI As where 0 X l.  
  In the practice of another aspect of this invention. there is the method for growing a solid structure comprising the steps of: establishing respective regions of two liquid substances each at thermal equilibrium with respect to a respective solid phase with a related composition at a respective temperature. said liquid substances being different members of a multicomponent compound system with more than two components and with a continuous range of compositions. and when mixed providing a supersaturated solution; establishing a substrate adjacent one said liquid substance at a solidliquid interface; transferring an incremental volume of said one liquid substance adjacent to said substrate at said solid-liquid interface together with said solid thereat to a liquid-liquid interface with said region of said other liquid substance; and depositing said solid structure with substantially said solid phase composition related to said one liquid substance on said solidliquid interface by solution mixing of said incremental volume of said one liquid substance with said region of said other liquid substance which provides a supersaturated solution from which said solid structure is deposited.  
  We claim: 1. Method for growing a solid structure comprising the steps of:  
 establishing respective regions of two liquid substances each at thermal equilibrium with respect to a respective solid phase with a related composition at a respective temperature, said liquid substances being different members of a multicomponent compound system with more than two components and with a continuous range of compositions, and when mixed providing a supersaturated solution;  
 establishing a substrate adjacent one said liquid substance at a solid-liquid interface;  
 transferring an incremental volume of said one liquid substance adjacent to said substrate at said solidliquid interface together with said solid thereat to a liquid-liquid interface with said region of said other liquid substance; and  
 depositing said solid structure with substantially said solid phase composition related to said one liquid substance on said solid-liquid interface by isothermal solution mixing of said incremental volume of said one liquid substance with said region of said other liquid substance which provides a supersaturated solution from which said solid structure is deposited.  
  2. Method for growing a solid structure comprising the steps of:  
 establishing respective regions of two liquid substances each at thermal equilibrium at a respective temperature, said liquid substances being different members of a multi-component compound system with more than two components and with a continuous range of compositions, and when mixed providing a supersaturated solution;  
 establishing a substrate adjacent one said liquid substance at a solid-liquid interface;  
 transferring an incremental volume of said one liquid substance adjacent to said substrate at said solidliquid interface together with said solid thereat to a liquid-liquid interface with said region of said other liquid substance; and  
 depositing said solid structure on said solid-liquid interface by isothermal solution mixing, of said incremental volume of said one liquid substance with said region of said other liquid substance.  
  3. Method as set forth in claim 2 wherein said liquid substances are dilute solutions.  
  4. Method as set forth in claim 2 wherein said respective regions of said two liquid substances are each at thermal equilibrium with respect to a respective solid phase with a related composition at a given temperature.  
  5. Method as set forth in claim 2 wherein said substrate is crystalline and said deposited solid structure is crystalline.  
  6. Method as set forth in claim 5 wherein said substrate has a compatible lattice constant with said multicomponent compound system.  
  7. Method as set forth in claim 4 wherein said multicomponent compound system is a ternary semiconductor compound.  
  8. Method as set forth in claim 7 wherein said ternary compound is a lll-lllV compound.  
  9. Method as set forth in claim 8 wherein said Ill-lll- V compound is Ga ,Al,As where 0 X 1.  
 10. Method as set forth in claim 9 wherein said substrate is GaAs.  
  11. Method as set forth in claim 9 wherein said X of one said compound is approximately 0.7 and X of said other compound is approximately 0.5.  
  12. Method as set forth in claim 5 including the additional steps of:  
 transferring a second incremental volume of said other liquid region adjacent to said deposited crystalline solid structure together with said crystalline solid to said one liquid region at a liquid-liquid interface therewith; and  
 depositing another crystalline solid structure on said second solid-liquid interface by isothermal solution mixing, whereby there is grown a layered crystalline structure. 13. Method as set forth in claim 12 wherein said layered crystalline structure comprises a heterojunction formed by said one solid structure and said another solid structure.  
  14. Method as set forth in claim 13 wherein said heterojunction is a p-n junction.  
  15. Method for growing a solid structure comprising the steps of:  
 establishing respective regions of two liquid substances each at thermal equilibrium with respect to a respective solid phase with a related composition at a respective temperature, said liquid substances being different members of a multicomponent compound system with more than two components and with a continuous range of compositions. and when mixed providing a supersaturated solution;  
 establishing a substrate adjacent one said liquid substance at a solid-liquid interface;  
 transferring an incremental volume of said one liquid substance adjacent to said substrate at said solidliquid interface together with said solid thereat to a liquid-liquid interface with said region of said other liquid substance; and  
 depositing said solid structure with substantially said solid phase composition related to said one liquid substance on said solid-liquid interface by solution mixing of said incremental volume of said one liquid substance with said region of said other liquid substances which provides a supersaturated solution from which said solid structure is deposited.  
  16. Method as set forth in claim 15 wherein said substrate is crystalline and said deposited solid structure is crystalline.  
  17. Method as set forth in claim 16 wherein said substrate has a compatible lattice constant with said multicomponent compound system.  
  18. Method as set forth in claim 16 wherein said multicomponent compound system is a ternary semiconductor compound.  
  19. Method as set forth in claim 17 wherein said multicomponent compound is a lll-lll-V semiconductor compound.  
  20. Method as set forth in claim 19 wherein said lll- Ill-V compound is Ga, ,Al,As where X l.  
  21. Method as set forth in claim 17 wherein said substrate in GaAs and said multicomponent compound system is Ga, ,Al,As where 0 X l.  
  22. Method as set forth in claim including the additional steps of:  
 transferring a second incremental volume of said other liquid substance adjacent to said deposited solid structure at said solid-liquid interface together with said solid structure thereat to a liquidliquid interface with said region of said one liquid substance; and  
 depositing another solid structure with substantially said solid phase composition related to said other liquid substance on said solid-liquid interface by solution mixing of said incremental volume of said other liquid substance with said region of said one liquid substance which provides a supersaturated solution from which said another solid structure is deposited, whereby there is grown a layered crystalline structure.  
  23. Method as set forth in claim 22 wherein said layered crystalline structure comprises a heterojunction formed by said one solid structure and said another solid structure.  
 24. Method as set forth in claim 23 wherein said heterojunction is a p-n junction.