DE1667709A1 - Process for making gallium arsenide - Google Patents

Description

Process for making gallium arsenide

Some optical devices in which semiconductor bodies are used as optically effective parts, and their mode of action on the optical properties of the semiconductor bodies used due to the specific semiconductor properties are based already known (see e.g. the one announced on May 24, 1956 German patent application S 40 619 IX / 42h). The semiconductor body can be used, e.g. as a lens or lens system, as a prism, Filter, window, vessel or mirror can be designed.

The semiconductor bodies should generally have the greatest possible light permeability - in a wavelength range peculiar to them. The latter increases, inter alia, with the decrease in the number of free charge carriers per "volume unit of the semiconductor body (charge carrier concentration in the onr). Semiconductor bodies that have transmission ranges in the infrared are useful for many of the above-mentioned application examples if their charge carrier concentration is below 10 cm ^J.

A semiconductor material with a large permeability range is gallium arsenide (GaAs). If this substance carries a charge

16 - ¹ ^ ger concentration of less than 10 cm, it has a practically straight-line optical transmittance of 0.9 to 18 μ of about $ 55. The latter can be increased considerably by tempering with a reflection-reducing layer.

In addition to its large permeability range, it stands out GaAs also because of its insensitivity to dust and humidity the end. Therefore, in contrast to previously used infrared-permeable substances, such as eel-colored substances (e.g. NaCl), plastics or glasses, in? other than Mafc <jrLal for optical lenses and DMlbet 'in baiapiüluwüUie infrared

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-Spectrophotometers and their expansion units (reflection accessories, Bundle condensers etc.) are suitable. Another advantage of GaAs is its high resistance to aggressive chemicals Add substances, especially when choosing pen materials for (infrared) cuvettes of all kinds these properties gain the greatest importance of GaAs. Among other things, measurements can be carried out without difficulty! neutral, acidic and basic inorganic aqueous solutions in any concentration, just such organic aqueous solutions or phases, chemically highly aggressive liquids (concentrated or anhydrous sulfuric acid, hydrochloric acid, trifluoroacetic acid, etc.) and gases (Sulfur trioxide, sulfur halides, hydrogen fluoride, free halogens, etc.), alkali-halide-dissolving and plastic-changing organic substances or solvents (polar ethers, aromatic ring compounds, highly aggressive organometallic compounds of all Art and their solutions). GaAs with a low charge carrier concentration, i.e. high permeability, is also excellent as Starting material suitable for light emitting diodes. GaAs can also be used for solar cells. GaAs solar cells have one higher efficiency than cells made of silicon and are more radiation-resistant, especially when used on artificial earth satellites as Si cells, especially when the cell layer to be irradiated is η-conductive.

Although it is largely unimportant for the optical properties, whether the GaAs is monocrystalline or polycrystalline, however - as said - it is important that the GaAs have a small charge carrier concentration (less than 10 cm) that it is extremely pure.

Many attempts have been made to produce such pure GaAs. However, so far both physical cleaning processes, e.g. the zone drawing, as well as the cleaning of the GaA3 by chemical means, e.g. the conversion of purified Ga ₂ O with "purified AaH", mainly because of the normally normal effort ,) and -, ve yen of the low yield

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GaAs with a sufficiently low charge carrier concentration is considered unsatisfactory. The invention is therefore based on the object of creating an uncomplicated method according to the above-mentioned method High purity GaAs, especially continuously, can be produced.

The invention relates to a method for producing

16 -3 gallium arsenide with charge carrier concentrations below 10 cm,

8 15-3
cm, in particular 10-10 .The invention is that powdered gallium-alkoxy-halide at temperatures between about 300 ⁰ C and 800 ⁰ O with arsine - is whirled AsH-- in the heating zone of a fluidized bed furnace and brought to reaction and that the resulting gallium arsenide powder is converted into a coherent crystalline form.

The process according to the invention allows gallium alkoxy halides (alkoxy group = <3H ~ 0-, halogen = X = 01 or Br), which have a gallium: halogen ratio of 1: 1 or 2: 3 in the molecule the fluidized bed process at 300 to 800 ⁰ O, in particular 600 to 80 ⁰ C with high-purity arsine in a hydrogen atmosphere quantitatively convert to powdered gallium arsenide. The gallium arsenide represented in this way is of special purity and serves as a starting material for the production of optical materials for the iiifraroten spectral range of 0.9-18μ.

The gallium alkoxy halides can preferably be the methoxy compounds or the corresponding xthoxy compounds Act. The methoxy compounds have so far proven to be the best.

Gallium alkoxy halides can be prepared according to a further invention a) by reducing alkanol, e.g. methanol or ethanol, with gallium (I) halides in excess alkanol or a inert organic solvents (such as benzene or hexane), for example according to the equation:

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(1) Ga ¹ CGa ¹¹¹ X ₄ ) + 2 CH ₃ OH ^ H ₂ + (OH ₃ O) ₂ GaX + GaX _?

b) by reaction of gallium (III) halides with alkali metal Alkanolates, especially methanolates, in excess alkanol or an inert organic solvent, e.g. Benzene or hexane, for example according to

(2) GaX ₃ + 2 MeOCH ₃ >> 2 MeX + (CH ₃ O) ₂ GaX; Me = Li, ITa, K

c) by electrolysis of an alcohol (alkanol) solution, in particular an approximately 50% methanolic solution, of Ga-III halide, especially GaCl ,, with elemental gallium as electrode material, for example

(3) GaCl, Ηο + white, insoluble substance, with Ga and Cl in a ratio of about 2: 3

d) by thermal decomposition of the gallium (III) chloride phase and alkanol, for example something like this:

(4) GaCl ₃ «2 CH ₃ OH - ^^ Cl / C ^ -OC ^ (= 8: 2) + white

insoluble powder Ga: Cl = 2: 3.

All of the novel gallium alkoxy halides described above can be used according to the invention. They are white, extremely finely divided amorphous powdery substances that are insoluble in all common organic solvents, against air and humidity They are insensitive and thermally stable up to higher temperatures without melting and without decomposition. they are easy to isolate from the respective reaction mixtures by filtration or centrifugation and can be washed out can be obtained in high purity with any inert or polar organic solvents. The gallium alkoxy halides are polymer.

Gallium alkoxy halide can be used without any problems its properties mentioned and because of the possibility of pure preparation of the starting materials, in particular in one purity produce, which can also be described as extraordinarily high in terms of semiconductor technology.

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Since arsine (AsH,) can be produced with the same purity, it arises in the inventive method a GaAs, from which by melting and crystal pulling without difficulty and other measures

16 8

GaAs crystals with far less than 10, e.g. between 10 and

ic 12 15 ¹ ^

10, in particular 10 to 10, free charge carriers per cm can be generated.

In the first stage of the process according to the invention, the powdered gallium alkoxy halide at temperatures between 300 and 800 ° 0 with; Arsine implemented. The reaction temperatures are chosen so that the arsine does not decompose essentially thermally, but chemically with the gallium alkoxy halide reacted. At low temperatures, arsine is thermally stable, but the speed of the chemical reaction mentioned is generally too small. At high temperatures, at which the reaction rate per se would greatly increase, ultimately predominates the thermal decomposition of arsine is so severe that the yield of GaAs would again be too low.

It has therefore proven to be very useful to place the pulverulent gallium alkoxy halide in an elongated upright fluidized bed reaction furnace, in the heating zone of which the temperature rises from the bottom to the top from about 300 ° 0 to about 800 ⁰ O, with the help of arsine blown in from below swirled up in such a way that the gallium-alkoxy-halide-Teilohen are kept in suspension in a kind of "dust column" in the heating zone.

Every gallium alkoxy halide molecule reacts in this column with arsine, if hydrogen is used as the carrier gas for the latter, for example according to the formula for the methoxy compound:

(6) (CH ₃ O) ₂ GaX + AsH ₃ + 2 H ₂ ^ GaAs + 2H ₂ O + 2 OH. + HX +

energy

The resulting GaAs is powdery. The halogen X can preferably Be chlorine or bromine.

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Since the substances on the right-hand side of equation (6) have high formation energies the reaction is practically quantitative. Except for the GaAs, all of these substances are gaseous. Bs can do it generally about water vapor, hydrocarbons, alcohols, hydrogen halides and their substitution and addition products, provided they are at least at the specified high temperatures are gaseous, act. The gaseous substances mentioned are expediently blown off through an exhaust gas opening in the upper part of the furnace.

As a carrier gas, instead of hydrogen - as in equation (6) specified - an inert gas, e.g. nitrogen or argon, can also be used. This has no influence on the formation of the GaAs. However, in many cases it is cheaper to use hydrogen. The choice of hydrogen as the carrier gas eliminates any deposition of carbon avoided because organic decomposition products occur immediately saturated and volatile removed from the reaction zone. Without the use of hydrogen carrier gas small amounts of carbon may get into the GaAs.

Because gallium arsenide is specifically heavier than gallium methoxy halide is, the GaAs falls from the material whirled up in the furnace after it has arisen down. The GaAs then settles in the lower end of the furnace, especially on a sieve, through the the arsine may be blown together with a carrier gas. If the GaAs forming in the fluidized bed falls on such a sieve, So it is advisable to leave a GaAs layer of approximately constant thickness on the sieve so that the gallium-alkoxy-halide powder is swirled up is always exposed to approximately the same static arsine pressure (from below). It is therefore particularly cheap, yes initially applying a GaAs layer to the screen and removing the GaAs from the furnace as it is formed. The removal of the GaAs can take place at certain time intervals or continuously. At the same time, the gallium alkoxy halide be supplemented accordingly. This material can in particular be introduced into the furnace from above.

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The resulting gallium arsenide will, especially if it is too optical Effective semiconductor bodies are to be processed, then melted and then in the form of crystalline bars or rods stiffens. This can be done using a drawing process in the horizontal boat, e.g. using the Bridgman method, or by Crystal pulling, e.g. carried out according to the Czochralski method will. The G-aAs powder can also be used as a starting material for epitaxial growth.

Since the GaAs consists of two elements with very different vapor pressures at the melting point, an atmosphere of the more volatile arsenic is usually maintained above the melt with such a partial pressure that a depletion of arsenic in the melt - i.e. an unstoichiometry of the GaAs - is expediently maintained in this process. cannot occur. This arsenic partial pressure is about 0.9 atm (above the GaAs melt at approx. 1238 ^{° C.).}

It has hitherto been absolutely necessary in the manufacture of GaAs held to maintain at least this arsenic partial pressure over the GaAs melt, so that gallium and arsenic in the Melt remains stoichiometrically composed and, for example, with arsenic negative pressure, there are no macroscopic Form gallium inclusions in the crystal. Such gallium inclusions can prove to be very useful in many applications of GaAs as electrical semiconductor components, e.g. tunnel diodes or lasers harmful effects. The GaAs according to the invention can also be processed in this known manner - that is to say at an excess pressure of arsenic above the GaAs melt will.

However, it has been found that at least a slight instoichiometry of the GaAs melt in the production of GaAs -Crystals, especially those for optical applications, not only do not interfere, but even significantly improve contributes to the properties of the GaAs compared to GaAs crystals produced in a known manner; especially is by one low arsenic deficiency the permeability of GaAs (in the permeability range) increased by a few percent.

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Therefore, especially when pulling GaAs crystals for optical Apparatus, according to a further invention, an arsenic pressure is maintained above the melt, which is less than that of Temperature of the melt corresponding arsenic vapor pressure of about 0.9 atm. Suitable arsenic partial pressures in this sense are e.g. 0.6 to 0.8 atm, especially about 0.8 atm.

Based on the schematic drawing, further details of the method according to the invention are shown using the example of the Methoxy compounds illustrated; show it:

1 shows a fluidized bed reaction furnace and Fig. 2 shows a crystal pulling apparatus.

In a vertically arranged fluidized bed reaction furnace (reactor), as shown schematically in FIG. 1, the inventive reaction of the gallium methoiy halide with arsenic can be carried out continuously. The reactor wall 1 consists, for example, of quartz glass. The heater surrounding the roughly tubular reactor is denoted by 2. It can, for example, be set so that approx. 300 ^° C. and approx. 800 ° C. prevail in the lower part of the reactor. Gallium methoxy halide powder 4 can, for example, be introduced into this heating zone of the reactor from above through the feed 3, for example by starting the fan 5. At the same time, 7 arsine can be blown so from the bottom through the feeder 6 with a blower that its static pressure in the heating zone is approximately between 300 ⁰ C and 800 ° C mark in the balance holds the gallium-methoxy-halide powder . A carrier gas, such as hydrogen, nitrogen or argon, can be added to the arsine through a further line 8, the amount of which can possibly be controlled by means of a valve 9. If the arsine (+ carrier gas) pressure is set correctly, the powder 4 introduced into the reactor is in dynamic equilibrium in a "dust column" 10 (shown in dotted lines) in the heating zone of the reactor.

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In the heating zone then - as explained above - finely powdered GaAs formed, which due to its relatively high specific weight is not kept in suspension by the arsine flow and therefore falls down. There it can be caught e.g. by a sieve 11 through which arsine flows in the opposite direction will. The arsine gas flow is not uncontrollable through the GaAs powder layer To influence 12, it is expedient to maintain a GaAs layer 12 of approximately constant thickness. In addition a GaAs layer of the desired thickness can be applied to the sieve 11 even before the start of the reaction and this is then renewed Forming GaAs, in particular continuously, removed from the reactor will. An opening 13 in the reactor, for example, is suitable for this purpose. It is very advantageous to have the sieve 11 (Sieve plate) with a cooling device 14 (e.g. water flow cooler) to prevent premature decomposition of the arsine (Arsine) to prevent.

In addition to the solid, powdery GaAs in the implementation of the Gallium methoxy halide with the arsine formed by-products (e.g. water, hydrocarbons, hydrogen halides and their Fission products) are all volatile and can be gaseous through an exhaust gas opening 15, which may be provided with a control valve 16 is to be removed from the reactor. Unreacted arsenic is expediently condensed on the cold finger 17.

The process according to the invention can, as described, continuously, but can also be operated discontinuously. In the latter case, it can initially be in a vertically arranged fluidized bed reactor 1 according to Pig. 1 on the sieve plate 11 are a given amount of the gallium methoxy halide to be converted.

Then - as with the continuous process - initially by slowly flowing through hydrogen from below (line 8) any atmospheric oxygen is displaced from the system and then the reaction space is set to the desired level by an external heater 2 Reaction temperature are brought. If this is achieved, will

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the spine is adjusted by increasing the flow rate of the hydrogen (the respective vertebral points are included to be determined experimentally beforehand depending on the substance) and arsine is added in any proportions. In the case of the discontinuous Procedure, the upper filler neck 3 and the outlet line 13 (Fig. 1) are not required.

The extremely fine division of the reaction material introduced allows the respective vortex point to be set with relatively low flow velocities. In both the continuous and the discontinuous process ψ, this results in an optimal temperature equalization within the reaction mixture, on the one hand, and an almost quantitative reaction with the partner supplied due to an increased "hit probability" on the other.

The gallium arsenide formed is collected on the sieve plate 11; should the reaction not have been carried out quantitatively, it can be freed from unreacted methoxide in a simple manner by treating it with warm water.

The powdery GaAs obtained in accordance with the invention in the reactor can are then melted and converted into the crystalline phase, e.g. by crystal pulling. In Fig.2 is a fc example of a crystal pulling device drawn schematically. The GaAs melt 20 is in a high-frequency induction coil 21 heated crucible 22 (e.g. made of graphite). The grown crystal rod 23 is held at 24 and with the Pulling apparatus 25 pulled upwards (from the melt). Suitable drawing speeds are in the order of mm / min. The pulling device can be a magnetic pulling device Act. This can e.g. consist of a soft iron core 31 surrounded by graphite 30 and a movable magnet 32, the movement of which the pulling device follows.

13 claims
2 figures - 10 -

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Claims (13)

VPA 67/1210 JU claims 1. Process for producing gallium arsenide with charge carrier Concentrations below 10 cm, especially between 10 and 1R - ¹ ^
10 cm, characterized in that pulverulent gallium alkoxy halide is ^{whirled up and reacted at temperatures between about 300 0} C and about 800 ⁰ C with arsine in the -AsH, - heating zone of a fluidized bed furnace and that the gallium arsenide powder which is formed is in a coherent crystalline 3? orm is transferred. 2. The method according to claim 1, characterized in that chlorine or bromine is used as halogen. 3. Process according to Claims 1 and 2, characterized in that the methoxy or ethoxy compound is used as the gallium alkoxy halide is used. 4. Process according to claims 1 to 3, characterized in that pulverulent gallium alkoxy halide in the fluidized bed reaction furnace by arsine blown in from below, in particular with a carrier gas such as hydrogen or inert gas, mixed in a column in which the temperature is from below rises upwards from about 300 ⁰ C to about 800 ⁰ C, whirled up and held in suspension. 5. The method according to claims 3 and 4, characterized in that the gallium-alkoxy halide is heavy and im lower part of the furnace, especially on one of the arsine gas stream traversed sieve, settling gallium arsenide is continuously removed from the furnace. 6. The method according to claims 3 to 5, characterized in that apart from the gallium arsenide, all of the reaction in the furnace forming substances, such as water vapor, hydrocarbons, alcohols and hydrogen halide, by a located above the heating zone Exhaust opening can be removed. - 11 - 109828 / U68 VPA 67/1210 7. The method according to claims 1 to 6, characterized in that in the Vortex reaction furnace during the reaction powdered gallium alkoxy halide refilled from above will. 8. The method according to claims 1 to 7, characterized in that the pulverulent gallium arsenide is melted and that from the melt at a lower arsenic partial pressure than the arsenic vapor pressure of the melt, in particular at about 0.8 Atm arsenic partial pressure, a gallium arsenide crystal pulled will. 9. The method according to claim 1, characterized in that the gallium alkoxy halide by reduction of alkanol, in particular Methanol or ethanol with gallium (I) halides in excess alkanol or an inert organic solvent, such as benzene or hexane. 10. The method according to claim 1, characterized in that the gallium alkoxy halide by reaction of gallium (III) halides with alkali metal alkanolates, in particular Metha nolaten, in excess alkanol or an inert organic solvent such as benzene or hexane, will be produced. 11. The method according to claim 1, characterized in that the gallium alkoxy halide by electrolysis of an alkanol solution, in particular an approximately 50 # Lgen methanolic solution of Gallium (III) halide, such as GaOl ,, with elemental gallium is produced as an electrode material. 12. The method according to claim 1, characterized in that the gallium-alkoxy-halide by thermal decomposition of the phase gallium (III) chloride and alkanol, eg gaol, .2 CH ₅ OH is prepared at about 125 ⁰ C. - 12 - 109828 / U68 VPA 67/1210 13. Use of the gallium arsenide bodies produced by the method according to one or more of the preceding claims for windows of infrared cuvettes, for infrared permeable lenses, lens systems, prisms, filters and vessels as well as for infrared mirrors. - 13 - 1Q9828 / U68 Le e rs e ι te