US3170861A - Apparatus for producing hyperpure gallium - Google Patents

Description

Feb. 23, 1965 s. LEIBENZEDER APPARATUS FOR PRODUCING HYPERPURE GALLIUM Original Filed Sept. 28, 1961 3,170,861 APPARATUS FOR PRODUCING HYPERPURE GALLIUM Siegfried Leibenzeder, Erlangen, Germany, assignor to Siemens Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt and Erlangen, Germany, a corporation of Germany Original application Sept. 28', man-sea No. 141,381.

Divided and this application May 6, 1964, Ser. No.

370,749 H I Claims priority, applicgtlgaaGgrmanyfsept. 30, 1960,

y 1 Claim., (Cl. got- 239 i p This applicationiisa division of application Serial No. 141,381,, filed September. 23 1961.

{ 'My-invention'relates"to apparatus for the productiori'oi hyperpure gallium, su'ch'asf'required for the production of electronic semiconductors from gallium compounds, for example, GaP, GaA s, GaSb', 'or 'as required foruse as doping or contact substance for semiconductor bodies.

' Hyperpure gallium is also used, for example, in high temperature thermometers and as a metallic heat-exgchange liquid in cooling systems.

Various methods have become known for extreme puri tion of gallium bromide complex. Commercially'aval ficationof gallium} Past investigations have mainly been directed to refinement'of gallium by electrolytic processes. Among the. known refining methods are the precipitation from aqueous medium, as well as the molten-bath electrolysis. The first-mentioned method has only a slight purifyingefiect, .in contrast to molten-bath. electrolysis which affords a high purity of the separated gallium, this purity'beingdependent-1o a great extent upon accurate control of electric-potentials; It is an object of my invention to devise a method and apparatus for the" production of hyperpure gallium on electrolytic principles in which the refining action is independent, within a wide range, of accurately constant potentials and, under otherwise comparable conditions, permits a considerable increase in' yield'by operation at increased"electrolyticlcell voltages. V

To achieve these objects and accordancewith my invention, I employ as electrolyte for electrolytic precipitation, the solution of a gallium, complex'of, the type Ga(GaX in a non-aqueous organicsolvent, wherein X denotes a halogen element, which as used herein is understood to be chlorine, bromine and 'iodine. Particularly suitable as the non-aqueous organic solvent are benzene, toluene and xylene, and as gallium complexes are G'a(GaCl Ga(GaBr )and Ga(GaI over the just-mentioned known methods, namely the'fact that the purifying action-does not depend upon the separation potential so that relatively high cell voltages can be used and a highly purified gallium is readily obtained with a single separation process, satisfying toa great extent the exact impurity requirements of electronic semiconductor techniques. 7

The invention involves the observation that the gallium complexes of the above-mentioned type possess good solubility as Well as electric conductivity in non-aqueous 3,170,861 I P nt Feb. 33,1965

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Ga(GaB r in benzene; at 20 l C. is approximately 1200 g./li ter, and is only .slightlyless than the solubility in toluene and xylene. The specific electric conductivities S in ohm-l cm. ).;of the electrolytes used according to; the invention is indicated in the following Table l.

\ Table'l V 3 1 I Qoneen ,tration in 1 percent by ,Anotherivadvantage over:the methods heretofore known resides in, the production of tliel'ectrolyte. Theprepafaa tion of-the gallium complex-{to be employed aecording to the invention is efieeted in known manner through the reduction of GaX (wherein X -denotes a halogen element) with'gallium in accordance. withthe following reexample of the technique is given' by tainingfthehighpurifying action apparent 'frorn-Table'li t Table- 2 Concentration Concentrationof I p of the foreign the foreign eleelements of the "merits-of the 1 Element anodic Gain catho'dieally pre p.p.m. (10- eipitatedGa in percent) 1 p.p .m (10- percent) '491 10. H H a 3.3 Not detectable. 2.4 Do.

By asecond refining operation,--the purir' yi ilgeffect-can aromatic organic solvents, for example benzene, toluene and xylene, and that the use otsuch solutions as an "electrolyte results in the precipitation of gallium. This was all the lessexpectable as :the above-mentioned complexes have a salt-like structure.

In fact, however, it has beenfound that, for example, a solubility of Ga(GaCl and begstill furtherincreased to a considerable extent, as ap parenttromTable 1.; i f.

As 'isfurther apparent from the apparatus described hereinafter, the above-mentioned extreme purity of the refined product is obtained with the minimum in equipment and with a good yield per unit of time.

When performing the method according to my invention, it is significant that no gas development occurs during the-electrolysis so that theprocess can'be carried out in a completely closed vessel. This excludes the danger of contamination from the ambient atmosphere. In the electrolytic cells, the contamination can also be avoided to a great extent because the electrolysis can be performed at a temperature of about 50 C. and the electrolyte is only slightly aggressive.

To further describe the invention, reference is made to the drawing and the specific example hereinbelow.

The drawing shows a schematic and sectional view'of an electrolysis device for performing the above-described method. The anode is formed by molten gallium located at 1 on the bottom of the electrolytic cell. Current is supplied to the anode by a platinum wire 2 which is immersed at its lower end into the molten gallium. The cathode is denoted by 3 and a collector funnel by 4. The funnel 4 is connected with a receiving vessel 5 through a 14. Simultaneously, the condensers and 12 are put into operation, the anode current supply lead 2 is inserted, thus closing the opening of the nipple 17, and the cathode 3 is inserted through nipple 20. A voltage of from about to about v. is applied to the cell between cathode and anode. This results in the flow of an average current value of about 0.4 amp. Precipitation of about 1 g./hour of hyper-pure gallium takes place with a current yield of about 100%.

Aside'from the addition of the anode gallium and the removal of the cathodically precipitated gallium, the device operates practically automatically, continuously and free of maintenance over a long period of time.- After starting the process, the platinum wire of the cathode becomes coated with gallium melt, until a drop of gallium is formed at the lower end and drips into the collecting funnel 4. v This is repeated continually.

The precipitation is preferably carried out with a high a cathode current density which preferably should not capillary fi. The electrolyte 7 covers the anode 1 and i forms-part of a thermosiphon system which serves to maintain the electrolyte in circulation. This system comprises the two legs 8 and 9 which are interconnected by transverse portion 13. 'Leg 9 is surrounded by a cooler 10. Leg 8 has its lowerend widened to form an inverted funnel portion at 11 abovethe cathode 3 and in upwardlyspaced relation to the funnel 4. Connected to the circulation system of the electrolyte is a reflux condenser 12. The suction nipple of the reflux condenser 12 is denoted by 14. To prevent contamination, the nipple 14 is closed by a protective cover 15 during operation of the device.' A stop-cock is provided at 16. The cell vessel is further provided at 17 withaconical ground nipple through which the anode current-supply lead enters into the vessel. The nipple 17 also serves to supply the vessel with electrolyte. The receiving vessel 5 for the purified gallium 19 is sealed by a stoppered ground nipple 18. Conically ground junctions at 21 connect the lower portion of.the electrolytic cell with the upper portion thatcontains the above-described entire electrolyte-circulating system.

- The quantity of cathode gallium required for starting the process is supplied through the receiving vessel 5 so that the capillary 6 and the receiving funnel 4 are filled with gallium. The anode gallium 1 is supplied through the central nipple 17 in a quantity sufficient to bring the level of the anode gallium to a height of at most a few millimeters below the lower end of the tube 9. Thereafter, the electrolyte is filled into the vessel through the same nipple 17. Since the electrolyte mustnot be subjected to moisture, the filling must be done in a sealed container through a siphon or pump with the aid of a dry inert gas, for example, nitrogen. The electrolyte, for exbe below 200 amperes/de'cimeter This is aided by the fact that the cathode surface is very small in comparison with the anode surface.

However, if the cathode current density is considerably lowered below the above-mentioned amount, then, according to another embodiment of the invention, the

gallium becomes precipitated as a fine pulverulent metal.

ample, is composed of 50% by weight of Ga(GaBr and This powder is suitable, for example, for the production of gallium containing semiconducting sinter materials,

which have been recently employed for thermoelectric purposes. 7

The performance of the electrolyte circulation system involves thethermosiphon principle. That is, the electrolyte heated by the heating bath rises in the leg 8 and passes through the cooled leg 9 back to the lower portion i loules heat which occurs in the vicinity of the cathode in the electrolyte is advantageously used to amplify the thermosiphon effect.

The circulatory system prevents the occurrence of a solid bottom body of Ga(GaX on top of the anode gallium. Such a body would considerably increase the ohmic resistance of the cell and, for the same cell voltage, would result in a reduction of the current density.

' I claim? Apparatus for producing hyperpure gallium for electronic purposes by electrolytic precipitation, which comprises a closed vessel having a gallium anode, a cathode,

a collecting funnel, and a thermosiphon circulatory system, said cathode being located above said funnel so that hyperpure gallium electrolytically precipitating on said cathode drops into said funnel, said thermosiphon system comprising two interconnected inlet and outlet legs, said inlet leg being located above said cathode and said outlet leg being located above said anode at a location removed from said cathode, said outlet leg having cooling means in conjunction therewith.

No references cited.

JOHN H. MACK, Primary Examiner,

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