US3498894A

US3498894A - Preparation of compound semiconductors by fused salt electrolysis

Info

Publication number: US3498894A
Application number: US609084A
Authority: US
Inventors: Jerome J Cuomo; Richard J Gambino
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1967-01-13
Filing date: 1967-01-13
Publication date: 1970-03-03
Anticipated expiration: 1987-03-03
Also published as: DE1719496C3; NL6717359A; FR1552289A; GB1173939A; CH500763A; DE1719496B2; DE1719496A1; SE337580B; BE707014A

Description

March 3,1970

CURRENT 'JIJ; cU b b ET AL 3,498,894

PREPARATION OF COMPOUND sfimcombucfons .BY FUSED SALT ELEcTRoLYsIs v Filed Jan. 13, 1967 VOLTAGE VOLTAGE-"- mvzmons mm J. cuono mum J. ammo ATTORNEY United States Patent US. Cl. 204-61 24 Claims ABSTRACT OF THE DISCLOSURE Techniques are presented for both synthesis and epitaxial crystal growth of compound semiconductors. Zinc blende structure IIIV and IIVI compounds and IIV I compounds are synthesized and epitaxially deposited by fused salt electrolysis. Illustratively, a fused salt solution for the synthesis of gallium phosphide (GaP) is a single crystal layer of GaP was produced epitaxially i on the l11 face of a silicon single crystal using this composition. Electroluminescent diodes have been produced by selectively doping the GaP layer during deposition.

Illustratively, when the electrolytic cell was operated at a temperature of 800 C. with a cathode current density of 50 milliamperes/cmP, a 100 micron thick layer was produced in 20 hours.

INTRODUCTION This invention relates generally to preparation of compounds by fused salt electrolysis, and it relates more particularly to both synthesis and epitaxial growth of compound semiconductors thereby.

There is a general body of literature relating to synthesis of compounds by electrolysis from fused salt melts. Illustratively, the literature includes the 1958 Ph.D. thesis of P. N. Yocum, The Preparation of Transition Metal Phosphides by Fused Salt Electrolysis, published by University Microfilms, Ann Arbor, Mich., 1960; and the book Electrochemistr of Fused Salts by IU K. Delimarskii et al., published by The Sigma Press, Washington, DC, 1961.

Heretofore, single crystals of compound semiconductors have been grown by chemical vapor deposition, by

recrystallization from a melt, or precipitation from metal solution. Each of these prior techniques for growing or depositing compound semiconductor crystals has several disadvantages. Vapor growth of compound semiconductors requires extremely careful control of growth parameters and expensive and elaborate apparatus. Further, the

reactant gases are often toxic; and it is sometimes impossible to incorporate desired dopant impurities into the crystal during growth. Recrystallization of compound semiconductors from the melt requires heating of the compound to its melting point which often causes contamination of the melt from the crucible. Compound semiconductors usually dissociate measurably at their melting points; and to retain desired stoichiometry and semiconducting properties, it is usually necessary to oppose the dissociation pressure of the compound by at least an equal partial pressure of the metalloid. As the required pressure may be many times atmospheric pressure, crystal growth must be carried out in a heated and pressurized container. Growth of compound semiconductor crystals from metal solutions usually yields dendritic crystals which have limited suitability for device fabrication because of their small sizes and irregular shapes.

It is desirable that there be available a technique without the disadvantages of the noted prior art which produces both synthesis and epitaxial growth of suitably doped single crystals, which employs relatively simple apparatus and which yields crystals of suitable shape and crystalline perfection for fabrication of semiconductor devices. The zinc blende compounds are important semiconductors which have been extensively investigated in the prior art for semiconductor devices of which electroluminescent diodes and injection lasers are exemplary. Illustratively, electroluminescent p-n diodes of GaP have especially suitable characteristics. However, technology has not provided a practical means for production of crystalline layers of GaP which are suitably doped and sufiiciently pure for the fabrication of desirable electronic devices.

It is desirable that the following semiconductor compounds be prepared by a technique which does not have the disadvantages of the prior art techniques:

(a) III-V crystalline semiconductor zinc blende compounds including a metal from the group consisting of Ga, Al, and In with a metalloid from the group consisting of P, As, and Sb.

(b) IIVI crystalline semiconductor zinc blende compounds including a metal from the group consisting of Zn, Cd, and Hg with a metalloid from the group consisting of S, Se, and Te.

(c) IIV crystalline semiconductor compounds including a metal from the group consisting of Zn, Cd, and Hg with a metalloid from the group consisting of P, As, and Sb. It has been generally considered in the prior art that: neither the synthesis of semiconductor compounds could be achieved by fused salt electrolysis, nor that the desirable quality and quantity of crystalline deposits by fused salt electrolysis would be suflicient to permit its use for provision of semiconductor compounds useful for semiconductor devices and especially for semiconductor compounds of the zinc blende structure. I

It is an object of this invention to provide preparation of compound semiconductors by fused salt electrolysis.

It is another object of this invention to provide both synthesis and epitaxial growth of III-V, IIV, and IIVI semiconductor compounds by the electrolysis of fused salt solutions.

It is another object of this invention to provide crystalline gallium phosphide of desirable purity and property by fused salt electrolysis.

It is another object of this invention to dope a semiconductor crystalline deposit during fused salt electrodeposition thereof. I

It is another object of this invention to provide by fused salt electrolysis an overgrowth of one charge carrier type semiconductor on a substrate of another charge carrier type semiconductor.

It is another object of this invention to produce semiconductor devices from III-V, IIV, and IIVI compounds by fused salt electrolysis.

It is another object of this invention to provide electroluminescent solid state devices by fused salt electrolysis.

It is another object of this invention to provide photoluminescent devices by fused salt electrolysis.

Among the advantages of the practice of this invention are its operability at atmospheric pressure and relatively low temperatures and the controllability of crystal growth by the electrolysis parameters voltage and current-density. Another advantage obtained by the practice of this invention for the preparation of zinc blende structure semiconductor compounds of which the III-V compounds are exemplary, is their epitaxial crystal growth of suflicient crystalline perfection and purity such that electroluminescence can be achieved.

Another advantage obtained by the practice of this invention is the preparation of compound semiconductors without excessive overpressure of the metalloid.

Another advantage obtained by the practice of this invention is the preparation of compound semiconductors with uniform doping of the deposited crystals during growth.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of a 'preferred embodiment of the invention, as illustrated in the accompanying drawing.

FIG. 1 is a schematic drawing partially in section illustrating an electrolytic cell useful for obtaining epitaxial growth of a semiconductor compound by fused salt electrolysis according to the practice of this invention.

FIGS. 2A and 2B present current-voltage curves for the codeposition of two exemplary elements useful for an understanding of the theory of this invention.

DESCRIPTION OF INVENTION Generally, this invention provides for both synthesis and epitaxial growth of semiconductor compounds by fused salt electrolysis. More specifically, crystalline deposits of zinc blende structure III-V and II-VI semiconductor compounds and II-V semiconductor compounds are obtained by fused salt electrolysis from a melt containing ions in suificiently electrochemically active form of each of the constituents of the compound. Illustratively, this invention provides crystalline layers of GaP from fused salt melts having a composition including:

(a) NaPO NaF, and Ga (b) LiCl, KC], Ga O and NaPO or (0) NaCl, KC], Ga O and NaPO Gallium phosphide (GaP) is a specific example of a III-V semiconductor compound which is more generally characterized as one including a metal from the group consisting of Al, Ga, and In with a metalloid from the group consisting of P, As and Sb, i.e., GaP, GaAs, and GaSb; AlP, AlAs, and AlSb; InP, InAs, and InSb, or solid solutions thereof. In the fused salt solution, com pared to the procedures for GaP in which phosphates are used to produce a phosphide, arsenates are used to produce arsenides, and antimonates are used to produce antimonides- When the Al or In compounds, analogous to the Ga compounds are desired, those elements in the form of their oxides or halides replace the Ga O in the solution.

The practice of this invention makes it possible to dope the product crystals p-ty-pe or n-type during the growth of the crystal by incorporating the appropriate impurities into the fused salt solution. Crystals with grown in p-n junctions are produced by adding sequentially compound sources of either p-type or n-type dopants to the solution during growth. Alternatively, a layer of p-type material is grown in one fused salt solution, followed by the over-growth of a second layer in a separate fused salt solution which contains an n-type dopant. Junctions can also be produced by solution regrowth through the practice of this invention on a crystalline layer which may be produced by another technique. Illustratively, a layer of GaP doped with Se, i.e., n-ty'pe, can be electroplated on a layer of GaP doped with Zn, i.e., p-type, and vice versa.

The nature and operation of experimental apparatus and control parameters therefor will be described in reference to the figures. The apparatus shown in FIG. 1 consists of an atmosphere chamber of quartz glass heated by electrical windings 12 in insulation 13. Within the chamber 10 there is placed a graphite anode crucible 14 in which the fused salt solution 16 is established. A single crystal silicon substrate 18 is appended to rod 20 and is immersed in the fused salt melt 16. Current is applied between the anode crucible 14 and the silicon substrate 18 via terminals 22 and 24. Voltage source 26 is 4 connected via variable resistance 28 to terminals 22 and 24 to establish terminal 24 positive and terminal 22 negative. The electrolytic cell voltage is measured between terminals 22 and 24 and cell current is measured by ammeter 25 in the series path.

The solution 16 can also be maintained in the molten tate by other conventional techniques such as radio frequency heating or internal resistance heating. Crucible 14 may be of any material that is not attacked by the molten salt solution such as tantalum or quartz coated with pyrolytic graphite. The main function of the atmosphere chamber 10 is to protect the crucible 14 and other graphite parts 20 from oxidation by surrounding them with an inert gas atmosphere. For the synthesis of a semiconductor compound, a graphite rod or other inert conductor may be used as a cathode; the silicon or other crystalline substrate is required only if epitaxial crystal growth is desired.

The fused salt electrolysis approach of this invention to preparation of semiconductor crystals utilizes readily controlled parameters of voltage and current density which illustratively permits regulation of growth rate, dopant concentration, and deposit location.

The general problem of the electrolytic codeposition of two elements will now be discussed with reference to FIGS. 2A and 2B. In FIG. 2A, the solid curve, labeled a+b, represents the current-voltage characteristics of the cathode deposition reactions observed in the electrolysis of a solution containing two ions A+ and B+. This curve is interpreted as being essentially a composite of two curves shown in FIG. 2A by the dashed lines labeled a and b, which represent hypothetical currentvoltage characteristics for the independent electrolytic reactions from the same solution A++e A and B++e B. Although only composite curve a+b can be observed experimentally, the curves a and b for the individual ions can be approximated by observing the currentvoltage characteristics for the deposition of A in the absence of B and for the deposition of B in the absence of A. As shown in FIG. 2A, above some voltage V a current is observed which is due to the discharge of A ions at the cathode if element A is deposited or evolved there. Between voltages V and V the curves a+b and a coincide, i.e., the observed current is solely due to the electrolytic deposition of A. At the voltage V the discharge of ions B begins, and this reaction contributes a current which adds to the current contributed by the discharge of ions A. Thus, the observed current curve a+b, increases more rapidly with increasing voltage for voltages greater than V This voltage V at which an abrupt change in the curve a+b is observed is the minimum voltage for codeposition. If the voltage is increased beyond V the rate of deposition of the two elements increases, but not proportionately. Where curve a intersects curve b at voltage V the currents contributed by the discharge of both A ions and B ions are equal. Since both reactions involve the same number of electrons, the rates of deposition are equal.

For the codeposition represented by FIG. 2B, curves a and b never intersect so there is no voltage at which the discharges A+ and B+ contribute equally to the current. The voltage V' at which a break occurs in curve a+b also corresponds to the lowest voltage at which codeposition can occur. Either type of codeposition illustrated by FIG. 2A or FIG. 2B can occur in electrolytic deposition of a compound dependent on such parameters as the nature and concentration of the ions, and the composition and temperature of the solution.

The formation of a binary compound AB by an electrolytic reaction is in some respects similar to the codeposion of two elements. The current-voltage curve for such a reaction may be substantially the same shape as curve a+b in FIGS. 2A or 2B. The voltage V now represents the minimum voltage necessary for the formation of the compound AB. Between V and V in FIG. 2A,

compound AB and excess of element A is deposited.

At V only the compound AB is liberated and beyond V the compound AB and excess B are liberated.

With regard to the electrolytic formation of III-V compounds, and more particularly with regard to the formation of GaP, a current-voltage characteristic similar in shape to curve a+b in FIGS. 2A and 2B is observed. Above some critical voltage, the slope of the currentvoltage curve increases with an abrupt change in slope. Below this critical voltage, only phosphorous is liberated at the cathode; slightly beyond this critical voltage, GaP formation occurs at a relatively low rate. At still higher voltages, GaP formation occurs at a relatively high rate. At the temperature of operation of the electrolytic cell, elemental phosphorous is extremely volatile whereas the dissociation pressure of GaP is very low. Therefore, phosphorous in excess of that consumed in the formation of GaP evolves as a gas at the cathode. If the cell voltage is higher than the voltage at which equiatomic amounts of Ga and P are liberated, the deposit consists of GaP and Ga metal which is nonvolatile at the temperature of the fused salt electrolysis.

The minimum voltage necessary for the deposition of a compound in the practice of this invention depends on the composition of the fused salt melt, the temperature of the electrolytic cell operation, and the composition and surface condition of the cathode. This minimum voltage corresponds to the voltage at which an abrupt change in slope in the current-voltage curve occurs so it is readily determined experimentally. In the preparation of compounds by fused salt electrolysis, electrode reactions with certain characteristics are advantageous, i.e., both of the constituent elements should deposit at the cathode at approximately the same voltage. It is desirable that at least one of the constituent elements be a volatile element and that the compound be nonvolatile. It is advantageous for high current efiiciencies if the current-voltage deposition curves for the individual elements intersect so that at some voltage they deposit at equal rates, i.e., the behavior shown in FIG. 2A. The foregoing desirable conditions for the practice of this invention for both synthesis and epitaxial crystal growth of semiconductor compounds can readily be achieved for:

(a) III-V crystalline semiconductor zinc blende compounds including a metal from the group consisting of Ga, Al, and In with a metalloid from the group consisting of P, As, and Sd.

b) II-VI crystalline semiconductor zinc blende compounds including a metal from the group consisting of Zn, Cd, and Hg with a metalloid from the group consisting of S, Se, and Te.

(c) II-V crystalline semiconductor compounds including a metal from the group consisting of Zn, Cd, and Hg With a metalloid from the group consisting of P, As, and Sb.

The metal and metalloid elements of a compound must have deposition potentials such that they codeposit cathodically from a fused salt solution or fused salt eutectic solution system.

Fused salt solutions for the synthesis and epitaxial crystal growth of compound semiconductors by fused salt electrolysis in the practice of this invention consist of three types of constituents: solvents and solvent modi fiers; sources of metal ions; and sources of metalloid ions. Illustratively, a solution for the synthesis of GaP consists of 2 moles NaPO /2rn0le NaF, and mole Ga O in which NaPO serves both as the solvent and as the source of the metalloid P, NaF is a solvent modifier which lowers the melting point and viscosity of NaPO and Ga O is the source of Ga ions. Other solvents which can be used are fused alkali halides or their mixtures. Other compounds can be used as a source of phosphorous producing ions, e.g. P phosphates other than NaPO or fluoro-phosphates of the alkali metals. The source of gallium ions can also be from one of its halides, or from an alkali metal gallate or from a halogallate.

Fused salt mixture for the practice of this invention should be maintained during the electrolysis at a temperature which is suflicient to melt the solvent and dissolve the metal and metalloid source compounds. The lower temperature limit is determined by the nature of the salt mixture, i.e., the solvents melting point. The solvents melting point is modified by the addition of the solute. A further factor which influences the temperature is the solubility of the solute in the solvent. The upper temperature limitation is determined by the vaporization or the decomposition of any one of the components present in the fused salt solution and also by the stability of and by the dissociation temperature of the semiconductor compound being deposited. The atmosphere over the solution during the fused salt electrolysis desirably should not be reactive with it or with the crucible it is contained in. Inert gases such as argon or helium are suitable as Well as nitrogen, forming gas or air diluted with nitrogen. As stated hereinbefore the electrolytic cell voltage necessary for the synthesis of GaP, is the voltage at which the two elements Ga and P codeposit at the cathode. When NaPO is used as solvent and source of phosphorous in the solution the minimum voltage is approximately 0.4 volt. With this type solution, the situation represented by FIG. .2B is applicable so that any voltage up to the deposition potential of sodium may be used without codepositing elemental gallium. The upper limit voltage is the deposition potential of the other ions in the solution such as the alkali metals. The synthesis of GaP is readily carried out by the practice of this invention over a wide range of current densities. For epitaxial growth of a high quality crystal, a low rate of deposition is usually required; and it can be obtained by the use of a low current density.

The solvent in which a fused salt for the practice of this invention is established desirably forms an ionicliquid on melting in which compounds of the desired metals and metalloids are soluble yielding ions which are reduced to the constituent elements at the cathode on electrolysis of the solutionso that they are codeposited. In addition, the solvent should not decompose on evaporation at an excessive rate at the temperature of solution in the electrolytic cell. The solvent should not contain any ions other than those desired in the product com pound, which have cathodic deposition potentials lower than or equal to the potential at which the product compound deposits at the cathode of the electrolytic cell. The solution should desirably be electrolyzcd at a cell potential sufficient to codeposit the constituent elements of the resultant compound but low enough that the nonvolatile metal element is not deposited in excess of the stoichiometry of the desired compound or that other undesired elements in the solution are deposited cathodically.

When an epitaxial single crystal layer of the product compound is desired, a crystalline substrate cathode is provided on which epitaxy can occur. The substrate cathode should desirably have a crystal structure and crystalline orientation such that epitaxy is possible for the crystal structure and lattice constants of the desired product compound. Further, the substrate cathode must be an electrical conductor at the temperature of operation of the electrolytic cell and should desirably be non-reactive with the fused salt solution at the cathodic potential at which the product compound deposits.

For the practice of this invention, the temperature of operation of the electrolytic cell should desirably be suflicient to melt the solvent and produce a solution of the compounds which acts as source of the metal ions and metalloid ions. The conductivity of the product com- 7; pound at the temperature of' codepositi'on should 'desirably be such that the potential at the growth surface of the crystal can be maintained at the deposition potential of the compound without inducing electrical breakdown in the product crystal.

Another solution suitable for synthesizing GaP in the practice of this invention is an alkali-halide solution of NaCl-l-KCl to which is added a gallium containing compound and a phosphorous containing compound such as .Ga O and NaPO respectively, i.e., v

Eutectic solution systems are suitable for the practice of this invention. Illustratively, a suitable eutectic solution for the-preparation of GaP by fused salt electrolysis is KCl+LiCl to which is added a gallium containing compound such as Ga O and a phosphorous containing compound such as NaPO e.g.,

1.2LiCl+ 0.8KC1+0.05Ga O +0.lNaPO In the practice of this invention, doping of crystals during fused salt electrolysis epitaxial growth is readily achieved by addition of the dopant ion to the fused salt solution. Illustratively, the addition of ZnO to a melt of 2NaPO +0.5NaF+0.25Ga O provides crystalline GaP which is uniformly doped p-type. Further, the addition to the fused salt solution of Se ions or Te ions in the form of Na SeO or Na TeO respectively, provides crystals of GaP that are doped n-type. By alternately using Zn and Se, a p-n junction is readily produced.

EXPERIMENTAL DATA GaP crystals prepared through the practice of this invention by a fused salt electrolysis are epitaxial deposits with color which ranges from yellow to amber. X-ray diffraction analysis indicates a Laue pattern for a single crystal. For other than optimum control parameters of the melt, there may be obtained a dendritic overgrowth on an original epitaxial layer. By adjustment of the operational parameters, a continuous epitaxial layer of from microns to 100 microns is readily obtained.

Exemplary photoluminescence measurements for Zn doped GaP produced by the practice of this invention at both 77 K. and 42 K. provide the characteristic red light of 6840 A. wavelength with relatively high efficiency of energy transformation.

Exemplary electroluminescence measurements of the Zn doped GaP produced by the practice of this invention provides red-orange light with somewhat less officiency of energy transformation than the noted photoluminescence measurements.

An optimum temperature range for the metaphosphate fused salt solution 2NaPO -l-O.5NaF+0.25 Ga O is 750 C. to 950 C. For the eutectic fused salt solution and by the dissociation of the materials being deposited.

The following are illustrative examples of the practice of thisinvention wherein compound semiconductors with the zinc blende structure are synthesized and/or grown epitaxially. EXAMPLE 1 The GaP was deposited on a single crystal'silicon cathode (chemically polished 111 orientation disk) at a temperature of 925 C. from a melt consisting of 2NaPO /2NaF, and AGa O at a potential of 1.5 volts and a current density of approximately 100 ma./cm. Theproduct formed as a golden 'yellow single crystal layer to microns thick which was in turn covered by a thicker polycrystalline layer. w p

EXAMPLE 2 A mixture of Ga O ,.l IaPO and Na]? was melted in a graphite crucible and the solution was electroplated using the graphite crucible as an anode and a graphite rod as the cathode. Apolycrystalline deposit of GaP formed the c ode.

. EX E 3 A :mixture 'with the composition l6NaPO 4NaF, and 1621 0 was heated to 850 C. in; a resistance furnace. A potential of -5 volts-was applied to thecell with a current of 5 amperes for 1 hour. GaP deposited .as yellow microcrystals at thecathode. The product was identified by X- ray diffraction analysis. The lattice constant was found to be 5.47 A. as compared to 5.45 A. reported in the literature. i 1

EXAMPLE 4 In this example, a sodium metaphosphate electrolyte was used with melt composition of: gallium to phosphorous ratio 0.125 to 0.25 and molality of Ga O solute in 2NaPO /2NaF solvent equals 0.05 to 0.1. The temperature range was, 800 C. to 1050 C.; and the electrical conditions were 0.40 to 6.0 volts, current equals. to 5000 milliamperes with current density range of 12.5 to 625 ma./cm. for an electrode area of 8 cm.

The electrodes were polycrystalline graphite; single crystalline 100 and 111 Si, single crystalline 1,11 'Ge,.and polycrystalline Ge.

For this example, the optimum results were obtained using a substrate of single crystalline 111 Si with melt temperature of 800 0, cell voltage of 1.5 volts and current density of 50 ma./cm. After a time of 20 hours, a single crystal layer of 100 microns was obtained.

EXAMPLE 5 This example provided GaP dendritic crystals and oriented triangles as evidence of epitaxial growth. An electrolyte alkali-halide system of sodium chloride was used. The composition of the melt was 1 molar NaCl, 1 molar KCl, 1 to 0.33 molar ratio Ga/P. Current density was 12 mat/cm. for-voltage of 1.2 volts to 1.8 volts.

EXAMPLE 6 The following are exemplary data on the synthesis of All, whichis a III- V, zinc blen'de compound semiconductor. A solution with the composition 2NaPO 0.5NaF, and 025181 03 was electrolyz'ed at 900 C. with an applied potential of 0.6 volt. A white powder deposited at the cathode. The cathode product was insoluble in water, but dis solved slowly in" acid yielding phosphine gas and a solution containing aluminum-ions. These reactions confirm the presence of AIF in the cathode product.

EXAMPLE 8 The following are exemplary data on ZnSe which is a II-VI zinc blendeflcpmpound semiconductor. A solution with the composition 43 mole percentKCl, 57 mole percent LiCl to which was added a 1:1 molar ratio mixture ,of SeCl; and ZnCl The solution was operated at 500 C. The'cell voltage was 0.96 viand the current was ma.

9 Epitaxial microcrystals of ZnSe deposited on the single crystal Si cathode.

The following are illustrative examples of procedures whereby semiconductor doping of the epitaxially grown semiconductor compound by the practice of this invention was obtained by adding a dopant to the melt.

EXAMPLE 9 The dopant zinc was added to sodium metaphosphate electrolyte as ZnO in a concentration of 2.5 X molar. A deposit of uniformly doped p-type GaP of 100 microns thickness was obtained after hours on a substrate of single crystalline 111 Si. The operational parameters were temperature of 800 C., cell voltage 0.9 volt, and current density of 50 ma./cm. The total surface area of the crystal was 8 cm. with areas up to 0.5 cm. free of cracks.

EXAMPLE 10 With dopants ZnO and -Na SeO in a sodium metaphosphate electrolyte, there resulted a thickness of GaP of microns after 20 hours on a substrate of single crystalline 111 Si. The operational parameters were temperature 805 C., cell voltage of 0.9 volt, and current density of 62 ma./cm. The resultant layer of GaP was doped by both Zn and Se as revealed by photoluminescence.

EXAMPLE 11 The following is a description of an exemplary procedure for growing p-n junctions in a compound semiconductor in the practice of this invention. Two fused salt melts were used. A single crystal of p-type GaP was grown from a solution containing ZnO as the source of Zn bearing ions by electrolysis at a cell voltage of 0.9 volt for 20 hours. After this period of time, the cathode was withdrawn from the p-type dopant solution and transferred to the n-type dopant solution which contained Na SeO as a source of selenium bearing ions. A layer of n-type GaP was deposited over the p-type layer by further electrolysis for 2 hours. The p-n junction thus formed was suitable for electroluminescent diodes and emitted red light on the passage of an electric current.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Method of synthesizing a semiconductor compound with the zinc blende structure comprising the steps of:

establishing a fused salt solution having respective ion sources therein of the members of said compound, said solution having an electrolysis current-voltage characteristic exhibiting a first portion and a second portion wherein said first portion exhibits a given slope over a low range of applied voltage and after a critical voltage said second portion exhibits a slope greater than the slope of said first portion for greater applied voltages;

electrolyzing said fused salt solution at an electrolysis voltage within said second portion of said electrolysis current-voltage characteristic of said solution; and

depositing said compound cathodically in accordance with said electrolysis current-voltage characteristic of said solution.

2. Method of synthesizing a semiconductor compound with the zinc blende structure comprising the steps of:

establishing a fused salt solution having first and second ion sources therein containing respectively the members of said compound said solution having an electroylsis current-voltage characteristic exhibiting a first portion and a second portion wherein said first portion exhibits a given slope over a low range of applied voltage and after a critical voltage said second portion exhibits a slope greater than the slope of said first portion for greater applied voltages;

3. Method according to claim 2 wherein said semiconductor compound is of the III-V class.

4. Method according to claim 2 wherein said semiconductor compound is of the II-IV class.

5. Method according to claim 2 wherein said semiconductor compound is of the II-V class.

6. Method of synthesizing a solid solution with the zinc blende structure of a plurality of semiconductor compounds comprising the steps of:

establishing a fused salt solution having ion sources therein containing the members of sad compounds; electrolyzing said fused salt solution; and depositing said solid solution cathodically.

7. Method of synthesizing binary compound GaP comprising the steps of:

establishing a fused salt solution having first and second ion sources therein containing respectively Ga and P;

electrolyzing said fused salt solution; and

depositing said compound GaP cathodically.

8. Method of depositing a layer of a semiconductor compound including a metal from the group consisting of Ga, Al, and In and a metalloid from the group consisting of P, As, and Sb comprising the steps of:

establishing a fused salt solution having a metallic ion from said metal group and a metalloid bearing ion from said metalloid group;

electrolyzing said fused salt solution; and

depositing said semiconductor compound cathodically.

9. Method of depositing a layer of a semiconductor compound including a metal from the group consisting of Zn, Cd, and Hg and a metalloid from the group consisting of S. Se, and Te comprising the steps of:

establishing a fused salt solution having a metallic ion from said metal group and a metalloid bearing ion from said metalloid group; electrolyzing said fused salt solution; and

depositing said semiconductor compound cathodically.

10. Method of depositing a layer of a semiconductor compound including a metal from the group consisting of Zn, Cd, and Hg and a metalloid from the group consisting of P, As, and Sb comprising the steps of:

electrolyzing said fused salt solution; and

depositing said semiconductor compound cathodically.

11. Method of growing epitaxially a crystalline layer of a semiconductor compound characterized by the steps of:

establishing a fused salt solution having first and second ion sources therein containing respectively the members of said semiconductor compound; electrolyzing said fused salt solution; and

depositing said semiconductor compound cathodically on a crystalline substrate cathode suitable for the epitaxy of said compound crystalline layer. 12. Method of growing epitaxially a crystalline layer of GaP comprising the steps of:

electrolyzing said fused salt solution; and

depositing said crystalline layer of GaP cathodically on a crystalline substrate cathode.

11 13. Method of claim 12 wherein said crystalline substrate is single crystalline silicon.

14. The method of Claim 12 wherein said fused salt solution consists of 2NaPO +0.5NaF+0.25Ga O 15. The method of claim 12 wherein said fused salt solution consists of 16. The method of claim 12 wherein said fused salt solution consists of 17. Method of growing epitaxially a doped crystalline layer of a semiconductor compound comprising the steps of:

establishing a fused salt solution having first and second ion sources therein containing respectively the members of said semiconductor compound;

introducing a dopant ion source into said fused salt solution,

electrolyzing said fused salt solution, and

depositing said doped crystalline layer cathodically.

18. Method of claim 17 wherein said fused salt solution has ion sources of Ga and P therein.

19. Method of claim 17 wherein said dopant is Zn and said dopant ion source is ZnO.

20.. Method of claim 17 wherein said dopant is Se and said dopant ion source is Na SeO 21. Method of claim 17 wherein said dopant is Te and said dopant ion source is Na TeO 22. Method of epitaxially growing a p-n junction in a crystalline region comprising the steps of:

establishing a fused salt solution having first and second ion sources therein containing respectively the members of a first semiconductor compound;

introducing a first dopant ion source containing a first dopant of one charge carrier type into said fused salt solution;

electrolyzing said fused salt solution;

depositing a first layer of said first semiconductor compound cathodically;

establishing a second fused salt solution having third and fourth ion sources therein containing respectively the members of a second semiconductor compound;

introducing a second dopant ion source containing a second dopant of a second charge carrier type into said second fused salt solution;

electrolyzing said second fused salt solution; and

depositing a second layer of said second semiconductor compound cathodically over said first layer of said first semiconductor compound obtained from said fused salt solution.

23. Method as set forth in claim 22 wherein said first and second semiconductor compounds are GaP.

24. Method as set forth in claim 23 wherein said first dopant ion source is ZnO, said first dopant is Zn, said sec- 0nd dopant ion source is Na SeO and said second dopant JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner