JP2006265162A - Method for producing trialkylgallium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a trialkylgallium, capable of producing the trialkylgallium in a high yield, by reacting gallium, magnesium, and an alkyl halide, without using a gallium-magnesium alloy. <P>SOLUTION: This method for producing the trialkylgallium comprises reacting the gallium, the magnesium, and at least one of the alkyl halide in at least one kind of ether compound and diluting the reaction system with at least one of the ether compound in the course of the reaction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing trialkylgallium useful as a material for forming a compound semiconductor thin film such as GaN by epitaxial crystal growth using a MOCVD (Metal-Organic Chemical Vapor Deposition) method or the like.

  Due to recent advances in mobile phones and optical communication technologies, demand for compound semiconductors is increasing such as high electron mobility transistors (HEMTs) and heterobipolar transistors (HBTs) used in mobile phones. It is growing rapidly in applications such as high-speed electronic devices, semiconductor lasers used in optical communications and DVDs, and optical devices such as white and blue ultra-high brightness LEDs used in displays.

  In general, as organometallic compounds (MO: Metal Organics) used as raw materials for compound semiconductors, alkyl metal compounds of Group II elements and III elements of the periodic table, particularly methyl compounds and ethyl compounds are frequently used. Among them, the group III alkylgallium in the periodic table is in great demand as a material for producing a compound semiconductor by MOCVD together with elements of the group V of the periodic table such as nitrogen and arsenic.

As a typical synthesis method of alkylgallium, a method of reacting a gallium-magnesium mixture or a gallium-magnesium alloy with an alkyl halide is known. This method is useful in that high-purity metallic gallium and metallic magnesium, which are commercially available products, can be used as they are as starting materials, and a reagent that requires labor is not required.
Examples of reports on these methods are shown below. In the conventional method, since a method using a gallium-magnesium alloy as a raw material yields trialkylgallium in a higher yield than a method using a gallium-magnesium mixture as a raw material, a gallium-magnesium alloy was used. There are more reports.

In Patent Document 1 (US Pat. No. 5,248,800), in a method of synthesizing trialkylgallium by a reaction between a gallium-magnesium alloy and alkyl iodide, the Mg / Ga molar ratio is 1.6 to 2.4. It is described that trialkyl gallium can be obtained with a high yield of 80 to 90% by setting the range. Patent Document 1 describes that the yield of trialkylgallium by a reaction using a gallium-magnesium mixture is 15%. That is, Patent Document 1 clearly shows that the method using a gallium-magnesium alloy as a raw material yields trialkylgallium in a higher yield than the method using a gallium-magnesium mixture as a raw material.
Patent Document 2 (UK Patent No. 2123423) also describes a method of synthesizing a trialkylgallium compound by reacting a gallium-magnesium alloy and an alkyl iodide in the presence of an ether compound.

However, in the method using a gallium-magnesium alloy, an extra step of preparing the alloy by heating is necessary, and it is difficult to prepare a uniform gallium-magnesium alloy. There is also a report that the reproducibility of the yield of trialkylgallium cannot be obtained due to this (Non-patent Documents 1 and 2) (AC Jones, DJ Cole-Hamilton, AK). .Holliday, M.J.Mahmad, J.Chem.Soc., Dalton Trans., 1047 (1983), K.B.Starowieski, K.J.Klabunde, Appl.Organomet.Chem., 3, 219 (1989) ).

  Therefore, it is desirable to use a gallium-magnesium mixture, which is a simpler raw material, from the viewpoint of simplification of the manufacturing process and stable productivity.

  In this regard, Patent Document 3 (Soviet Union Patent No. 388563) discloses that a gallium-magnesium mixture or a gallium-magnesium alloy and an alkyl halide are converted into ether compounds such as dibutyl ether, diisoamyl ether, or diethyl ether. The synthesis of a trialkylgallium compound by reacting in the presence of a Lewis base represented by

Non-Patent Document 3 (LI Zakharkin, V. V. Gavrirenko, N.P. Fattyshina, Russ. Chem. Bull., 46 , 379 (1997) includes a gallium-magnesium mixture, methyl iodide, and A method of directly synthesizing trimethylgallium by ball milling under heating is described, and Non-Patent Document 3 discloses a gallium-magnesium-iodine mixture in the absence of a solvent or in the presence of hexane. A method for synthesizing triethylgallium by reacting with ethyl iodide after heating and vacuum degassing is described in Non-Patent Document 3. Powdered magnesium is used.

Non-Patent Document 4 (VI Bregadze, LM Golubinskaya, BI Kozyrkin, J. Clust, Sci., 13 , 631 (2002) includes a gallium-magnesium mixture, methyl iodide, and In the presence of isoamyl ether, trimethylgallium is obtained in a high yield of 80 to 90% .Non-patent document 4 also uses powdered magnesium.
However, when a gallium-magnesium mixture is used, the yield is lower than when a gallium-magnesium alloy is used. Moreover, when it is going to obtain a high yield using a gallium-magnesium mixture, the shape of magnesium which can be used is limited to a powder form like a nonpatent literature 3 and 4.

  An object of the present invention is to provide a method capable of producing trialkylgallium in a high yield by a reaction of gallium, magnesium and an alkyl halide without using a gallium-magnesium alloy.

  In order to solve the above-mentioned problems, the present inventors have intensively studied, reacting gallium, magnesium, and at least one alkyl halide in at least one ether compound, and at least reacting the reaction system during the reaction. It has been found that trialkylgallium can be produced in good yield by diluting with one ether compound to lower the magnesium concentration.

  The present invention has been completed based on this finding, and provides the following method for producing trialkylgallium.

  Item 1. A method for producing trialkylgallium, wherein gallium, magnesium and at least one alkyl halide are reacted in at least one ether compound, and the reaction system is diluted with at least one ether compound during the reaction. how to.

  Item 2. Item 2. The method according to Item 1, wherein the magnesium concentration in the reaction system is 5 moL / L or more at the start of the reaction, and the total magnesium concentration in the reaction system is 4 moL / L or less.

  Item 3. Item 3. The gallium, magnesium, and at least one alkyl halide are reacted by introducing at least one alkyl halide into a mixture of gallium, magnesium, and at least one ether compound. Method.

  Item 4. Item 4. The method according to Item 3, wherein at least one alkyl halide is introduced dropwise into a mixture of gallium, magnesium and at least one ether compound.

  Item 5. Items 1 to 4 for diluting the reaction system for Ts ± 30 minutes from the time (Ts) when alkylmagnesium halide and magnesium halide are precipitated in the reaction system and the temperature rise of the reaction system is stopped. The method according to any one.

  Item 6. Item 6. The method according to any one of Items 1 to 5, wherein 1 to 10 mol of magnesium is used per 1 mol of gallium.

  Item 7. Item 7. The method according to any one of Items 1 to 6, wherein the magnesium is in the form of a ribbon, a chip, a chip, or particles.

  Item 8. Item 8. The method according to any one of Items 1 to 7, wherein the at least one alkyl halide is at least one alkyl halide selected from the group consisting of alkyl iodide and alkyl bromide.

  Item 9. Item 9. The method according to any one of Items 1 to 8, wherein at least one alkyl halide has an alkyl group having 1 to 10 carbon atoms.

  Item 10. Item 10. A trialkylgallium obtained by the method according to any one of Items 1 to 9.

  Item 11. Item 11. A gallium compound formed by epitaxial growth using the trialkylgallium according to Item 10 and at least one group III element-containing compound selected from the group consisting of a nitrogen-containing compound, a phosphorus-containing compound, and an arsenic-containing compound. A gallium compound semiconductor device comprising a semiconductor thin film.

  According to the present invention, there has been provided a method for producing trialkylgallium in a high yield by reacting a mixture of gallium and magnesium, which is a simpler raw material, with an alkyl halide without using a gallium-magnesium alloy. This makes it possible to synthesize trialkylgallium with high reproducibility and high yield, without requiring time-consuming alloy preparation.

  In the method of the present invention, high reactivity can be obtained by using magnesium having a shape such as a chip shape or a chip shape that is easy to handle without using a powdery magnesium raw material. Rate is obtained.

Hereinafter, the present invention will be described in detail.
In the method for producing trialkylgallium according to the present invention, gallium, magnesium and at least one alkyl halide are reacted in at least one ether compound, and the reaction system is diluted with at least one ether compound during the reaction. Is the method.
material
<Gallium>
As the gallium, a commercial product having a purity of 99.9% (3N) or higher can be used, and gallium having a purity of up to 7N is commercially available.

  The electrical characteristics and optical characteristics of the compound semiconductor produced by MOCVD are greatly influenced by the purity of the organometallic compound as a raw material. Therefore, it is required to synthesize high-purity trialkylgallium also in the method of the present invention. Since the purity of the generated trialkylgallium depends on the purity of gallium as a raw material, it is desirable that the gallium is highly pure.

In the present invention, the purity of gallium is preferably 99.999% (5N) or more, and more preferably 99.9999% (6N) or more. High purity gallium of 5N or more is commercially available as described above, but can be obtained by refining a commercially available product of 3N or 4N purity by recrystallization, vacuum purification, electrolytic refining or the like.
<Magnesium>
A commercially available product having a purity of 99% (2N) to 99.9999% (6N) can be used. However, since magnesium having a purity of 5N or higher is very expensive, it is sufficient to use a magnesium having a purity of 2N to 4N purified by vacuum distillation, vacuum sublimation, or the like. The purity of magnesium used in the method of the present invention is preferably 3N or more.

  The shape of magnesium is not particularly limited. For example, ribbons, shavings, chips (scraping smaller than shavings), powders, granules, and the like that are generally used in Grignard reagent synthesis can be used. In the present invention, powdered magnesium refers to magnesium having an average particle size of 500 μm or less. In the present invention, the average particle diameter is a value measured by a laser diffraction method.

  In general, the powdery form is more reactive with alkyl halides than the larger form, but according to the method of the present invention, the reactivity is high even when magnesium other than the powder form is used. can get. Although powdered magnesium needs to be handled and stored, it is not always necessary to use such powdered magnesium in the method of the present invention. For this reason, ribbon-shaped, shaved-shaped, chip-shaped, and granular magnesium are preferable, and among them, a shaved-shaped or chip-shaped one is preferable in terms of high reactivity with alkyl halide and easy handling.

The surface of magnesium is more or less covered with an oxide film. If this oxide film is thick, the induction period of the reaction becomes longer. Therefore, before the reaction, mechanical stirring, pulverization, addition of a small amount of iodine or bromine, washing with dilute hydrochloric acid, etc. are performed on the surface to activate the surface. It is generally performed. In addition, a method of activating magnesium by adding a small amount of methyl iodide, ethyl iodide, 1,2-dibromoethane or the like has been performed (DE Peason, D. Cowan, JD Beckler, J Org.Chem., 24 , 504 (1959)). According to the method of the present invention, magnesium shows sufficient reactivity without such activation treatment, but the reaction time can be further shortened by carrying out such activation treatment before the reaction. .
<Solvent>
Usable ether compounds are not particularly limited, and known ether compounds used for trialkylgallium synthesis may be used. For example, aliphatic ether compounds such as diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether, di-sec-butyl ether, diisopentyl ether (diisoamyl ether); anisole, methylanisole Aromatic ether compounds such as benzyl methyl ether, ethyl anisole, dimethyl anisole, isopropyl anisole, and phenetole can be used.

  Since the ether compound forms an adduct with the product trialkylgallium compound, the ether adduct is thermally decomposed by distillation as described later after the synthesis step to isolate the trialkylgallium compound. It is preferable to do. For this reason, the ether compound is preferably a compound having a boiling point higher than that of trialkylgallium. Also, when the thermal decomposition temperature of the trialkylgallium ether adduct is higher than the thermal decomposition temperature of the trialkylgallium compound, the decomposition of the trialkylgallium compound also proceeds due to the thermal decomposition of the ether adduct. It is preferable to select an ether compound whose temperature is lower than the decomposition temperature of trialkylgallium.

An ether compound can be used individually by 1 type or in mixture of 2 or more types. However, it is preferable to use one kind of ether alone because the resulting trialkylgallium can be easily purified.
<Alkyl halide>
As the alkyl halide, an alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms may be used. The alkyl halide having an alkyl group having the above carbon number is rich in reactivity, and by using these, a trialkylgallium having sufficient volatility as a MOCVD raw material can be obtained.

  Also, any of alkyl chloride, alkyl bromide, and alkyl iodide can be used, but alkyl bromide and alkyl iodide are preferred from the viewpoint of relatively high reactivity.

  Specific examples of the alkyl halide having an alkyl group having 1 to 4 carbon atoms include methyl chloride, ethyl chloride, n-propyl chloride, isopropyl chloride, n-butyl chloride, isobutyl chloride, sec-butyl chloride, and tert-butyl chloride. Alkyl chlorides such as; bromides such as methyl bromide, ethyl bromide, n-propyl bromide, isopropyl bromide, n-butyl bromide, isobutyl bromide, sec-butyl bromide, tert-butyl bromide Alkyl; alkyl iodides such as methyl iodide, ethyl iodide, n-propyl iodide, isopropyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, and tert-butyl iodide. . Among them, methyl bromide such as methyl bromide, ethyl bromide, n-propyl bromide, isopropyl bromide, n-butyl bromide, isobutyl bromide, sec-butyl bromide, tert-butyl bromide; Alkyl iodides such as methyl, ethyl iodide, n-propyl iodide, isopropyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, tert-butyl iodide are preferred.

Alkyl halides can be used singly or in combination of two or more. When mixing 2 or more types, you may mix and use the thing from which the kind of halogen differs, and the kind from which an alkyl group differs.
Reaction producing trialkyl gallium by reaction with use ratio gallium over magnesium mixture and an alkyl halide, 2Ga + aMg + (a + 3) is considered to follow the following equation (1) RX
→ 2GaR ₃ + 3MgX ₂ + (a-3) RMgX (1)
(In the formula, R represents an alkyl group, X represents a halogen atom, and a represents a positive integer.)
Thus, it is considered that alkylmagnesium halide (RMgX), that is, Grignard reagent is involved in the generation of trialkylgallium.

  Regarding the molar ratio of magnesium to gallium, the molar ratio of magnesium to 1 mol of gallium is preferably about 1 to 10 mol, more preferably about 1 to 5 mol, and about 1 to 3 mol. Even more preferred. If it is the said range, the reaction of a gallium, magnesium, and an alkyl halide can be advanced practically enough efficiently, and a trialkyl gallium will be obtained with a high yield.

As shown in the formula (1), the alkyl halide has an amount equivalent to (a + 3) / 2 mol for the synthesis of trialkylgallium with respect to 1 mol of gallium and a / 2 mol of magnesium. Necessary and varies depending on the number of moles of gallium used and the mole ratio of gallium to magnesium. The amount of the halogenated alkyl used is usually about 50 to 200% of (a + 3) / 2 mol shown in Formula (1), and preferably about 70 to 150% of (a + 3) / 2 mol. If it is the said range, a trialkyl gallium will be obtained with a high yield.
Synthesis reaction step In the present invention, the synthesis reaction is carried out in an inert gas atmosphere such as nitrogen, helium, neon, argon, krypton, or xenon. The purity of these inert gases is preferably 99.99% (4N) or more, particularly preferably 99.9999% (6N) or more.

  In particular, moisture and oxygen in the atmospheric gas not only reduce the yield of trialkylgallium, but can also cause a decrease in purity, so it is desirable to use atmospheric gas from which moisture and oxygen have been removed as much as possible. The reaction atmosphere gas preferably has a dew point of −80 ° C. or lower and an oxygen concentration of 100 ppb or lower, particularly preferably a dew point of −100 ° C. or lower and an oxygen concentration of 10 ppb or lower. Such a high purity inert gas can be obtained by a membrane separation method, a catalytic reaction method, a liquefaction rectification method, a PSA (Pressure Swing Adsorption) method, or the like.

  The reaction is carried out by placing gallium, magnesium, alkyl halide, and ether in a reaction vessel under an inert gas atmosphere. The order of introduction of these compounds into the reaction vessel is not particularly limited, but gallium, magnesium, and ether are first placed in the reaction vessel, and then the alkyl halide is introduced into the reaction vessel, because it is easy to introduce into the reaction vessel. It is preferable. In this case, the alkyl halide is preferably introduced slowly and more preferably added dropwise.

  The method of the present invention is characterized in that the reaction system is diluted with an ether compound during the reaction. The ether compound used for the dilution may be the same kind as the ether compound in the reaction system or may be a different kind, but it is preferable to use the same kind.

  In the method of the present invention, the magnesium concentration in the reaction system at the start of the reaction is usually 5 moL / L or more, preferably 6 moL / L or more, more preferably 7 moL / L or more. This is because the magnesium in the reaction system is concentrated and the reaction of magnesium, gallium, and alkyl halide is reliably started and progressed. If the magnesium concentration is too high, vigorous heat generation is caused and stirring becomes difficult, so the upper limit of the magnesium concentration at the start of the reaction is usually about 10 moL / L.

  After dilution, the total magnesium concentration in the reaction system is preferably 4 moL / L or less, and more preferably 3 moL / L or less.

  Since the reaction does not proceed easily even if the magnesium concentration is too low, the lower limit of the total magnesium concentration in the diluted reaction solution may be about 0.1 moL / L. “Total magnesium” refers to the total amount of magnesium alone, magnesium halide, and alkylmagnesium halide.

  Dilution may be performed by adding the ether compound at once, or the ether compound may be added slowly.

 As the reaction proceeds, supersaturated alkylmagnesium halide and by-product magnesium halide precipitate. At this time, it may be diluted by adding an ether compound to the reaction system. Specifically, the temperature rise of the reaction system stops as the precipitation proceeds. It is preferable to dilute for about Ts ± 30 minutes, more preferably for about Ts ± 20 minutes, relative to the point in time when the temperature increase stops (Ts).

When adding a small amount of alkyl halide to a mixture of gallium, magnesium and ether, the temperature of the reaction system rises due to the addition of the alkyl halide, and further addition of the alkyl halide increases the alkyl halide. Magnesium and magnesium halide precipitate, and the temperature rise stops. At this time, an ether compound may be added to the reaction system.
The reaction temperature may be a temperature at which the reaction proceeds efficiently in consideration of the type of ether compound used and the alkyl halide. When gallium, magnesium, an ether compound and an alkyl halide are mixed, the temperature of the reaction system rises, the temperature rise stops as the precipitation proceeds, and the temperature rises due to dilution of the reaction system. Thereafter, the reaction may be carried out by setting the temperature of the reaction system to about 0 to 200 ° C., preferably about 40 to 160 ° C., more preferably about 60 to 120 ° C. In the case where the alkyl halide is gradually added, the reaction may be performed at the above temperature after adding the entire amount of the alkyl halide.

  Trialkyl gallium is usually produced by reacting at the above temperature for about 3 to 30 hours.

The synthesis reaction pressure is not particularly limited, and the synthesis reaction can be performed under atmospheric pressure, reduced pressure, or increased pressure.
The trialkyl gallium obtained after the completion of the purification step reaction contains trialkyl gallium to which an ether compound or an alkyl halide is added. Therefore, by distilling the reaction solution, these adducts can be decomposed and the trialkylgallium can be isolated by fractional distillation. The heating temperature is preferably lower than the decomposition temperature of the trialkyl gallium and higher than the decomposition temperature of the trialkyl gallium ether adduct or halogenated alkyl adduct. Distillation may be performed at normal pressure, but vacuum distillation may be performed.

  Furthermore, by purifying by precision distillation, sublimation or the like, a trialkylgallium having a purity of 99.999% (5N) or more that can be used as a MOCVD raw material is obtained.

The purification step is also usually performed in an inert gas atmosphere.
Gallium-based compound semiconductor device Using trialkylgallium obtained by the method of the present invention and at least one group III element-containing compound selected from the group consisting of nitrogen-containing compounds, phosphorus-containing compounds, and arsenic-containing compounds as raw materials, for example, MOCVD The gallium-based compound semiconductor thin film of the gallium-based compound semiconductor device can be formed by epitaxial growth. A typical example of the gallium compound semiconductor thin film is a gallium nitride compound semiconductor thin film formed using trialkylgallium and a nitrogen-containing compound such as ammonia as raw materials.

  Examples of the semiconductor structure include a MIS (Metal Insulator Semiconductor) junction, a homostructure having a PIN junction or a pn junction, a heterostructure, or a double heterostructure. Various emission wavelengths can be selected depending on the material of the semiconductor layer and the degree of mixed crystal. In addition, a single quantum well structure or a multiple quantum well structure in which the semiconductor active layer is formed in a thin film in which a quantum effect is generated can be used.

  If the gallium nitride compound semiconductor thin film is described as an example, materials such as sapphire, spinel, SiC, Si, ZnO, and GaN are preferably used for the gallium nitride compound semiconductor substrate. In order to form a nitride semiconductor with good crystallinity with high productivity, it is preferable to use a sapphire substrate. A gallium nitride compound semiconductor can be formed on the sapphire substrate by MOCVD or the like. A buffer layer of GaN, AlN, GaAIN or the like is formed on the sapphire substrate, and a nitride semiconductor having a pn junction is formed thereon.

  As an example of a light emitting device having a pn junction using a gallium nitride compound semiconductor, a first contact layer formed of n-type gallium nitride and a first cladding layer formed of n-type aluminum nitride / gallium on a buffer layer A double hetero structure in which an active layer formed of indium gallium nitride, a second cladding layer formed of p-type aluminum nitride / gallium, and a second contact layer formed of p-type gallium nitride are sequentially stacked. It is done.

The gallium nitride compound semiconductor exhibits n-type conductivity without being doped with impurities. When forming a desired n-type nitride semiconductor, for example, to improve luminous efficiency, it is preferable to appropriately introduce Si, Ge, Se, Te, C, etc. as an n-type dopant. On the other hand, when forming a p-type gallium nitride compound semiconductor, p-type dopants such as Zn, Mg, Be, Ca, Sr, and Ba are doped. Since the gallium nitride compound semiconductor is difficult to be p-type only by being doped with a p-type dopant, it is preferable to lower the resistance by heating in a furnace, plasma irradiation, or the like after introduction of the p-type dopant. After the electrodes are formed, a light emitting element made of a nitride semiconductor can be obtained by cutting the semiconductor wafer into chips.
EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[Example 1] Synthesis of trimethylgallium A nitrogen-substituted four-necked flask with a capacity of 300 mL was filled with diisoamyl ether of 10.00 g (143 mmol) of gallium, 9.53 g (392 mmol) of ground magnesium, and molecular sieves. Add 52 mL and bring the magnesium slurry concentration in diisoamyl ether to 7.54 mol / L.

  The purity of gallium is 6N, and the purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

  After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 101.5 g (715 mmol) of methyl iodide separately weighed is dropped into the solution in the flask over about 1 hour with stirring. When methyl iodide is dropped, magnesium iodide crystals are precipitated, and further, supersaturated methyl magnesium iodide is precipitated. As precipitation of methylmagnesium iodide proceeds, the temperature rise in the flask stops. At this time, 104 mL of diisoamyl ether sufficiently dehydrated with molecular sieves is further added to the flask. The total amount of diisoamyl ether added to the reaction system is 156 mL, and the magnesium slurry concentration in diisoamyl ether is diluted to 2.51 mol / L.

  The supersaturated methylmagnesium iodide is redissolved, and the temperature in the flask rises again with the addition of methyl iodide. All methyl iodide is added, and the temperature inside the flask is kept at 110 ° C., and the mixture is heated and stirred for 18 hours.

  After completion of the reaction, a large amount of white magnesium iodide is precipitated. The crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column packed with glass beads from the reaction mixture with diisoamyl ether boiling.

  13.8 g (84.0% yield in terms of gallium) of crude trimethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer (ICP-AES: Inductively Coupled Plasma Atomic Emission Spectrometer).

[Example 2] Synthesis of trimethylgallium A nitrogen-substituted 300 mL glass autoclave was charged with 10.00 g (143 mmol) of gallium, 9.41 g (387 mmol) of ground magnesium, and 50 mL of diisoamyl ether sufficiently dehydrated with molecular sieves at room temperature. In addition, the magnesium slurry concentration in diisoamyl ether is 7.74 moL / L.

  The purity of gallium is 6N, and the purity of magnesium is 3N. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

  After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 67.4 g (710 mmol) of methyl bromide separately weighed is bubbled into the solution in the flask for about 2 hours while stirring. As methyl bromide is bubbled, magnesium bromide crystals begin to precipitate, and supersaturated methyl magnesium bromide also precipitates. As precipitation of methylmagnesium bromide proceeds, the temperature rise in the flask stops. At this time, 100 mL of diisoamyl ether sufficiently dehydrated with molecular sieves is further added to the flask. The total amount of diisoamyl ether added to the reaction system is 150 mL, and the magnesium slurry concentration in diisoamyl ether is diluted to 2.58 mol / L.

  The supersaturated methylmagnesium bromide is redissolved and the temperature in the flask rises again with the addition of methyl bromide. When all the methyl bromide is bubbled and the reflux of methyl bromide is not carried out, the autoclave internal temperature is kept at 110 ° C. and the mixture is heated and stirred for 18 hours.

  After completion of the reaction, a large amount of white magnesium bromide precipitates. Crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column packed with glass beads from the reaction mixture in a state where diisoamyl ether is boiling.

10.2 g (62.0% yield in terms of gallium) of crude trimethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer.
[Comparative Example 1] Synthesis of trimethylgallium (no intermediate dilution with isoamyl ether)
Trimethylgallium is synthesized in the same manner as in Example 1 except that the amount of diisoamyl ether added before the reaction is 156 mL and diisoamyl ether is not added during the reaction.

By gallium quantification using an inductively coupled plasma emission spectrometer, 3.3 g of crude trimethylgallium (19.8% yield in terms of gallium) is obtained by fractional distillation.
[Comparative Example 2] Synthesis of trimethylgallium (using powdered magnesium)
Use of 9.41 g (387 mmol) of powdered magnesium having an average particle size of 45 μm (measured using a Mastersizer 2000 manufactured by Marvern) instead of 9.41 g (387 mmol) of ground magnesium, and use of diisoamyl ether added before the reaction Trimethylgallium is synthesized in the same manner as in Example 1 except that the amount is 156 mL and diisoamyl ether is not added during the reaction.

  13.5 g of crude trimethylgallium (82.0% yield in terms of gallium) is obtained by fractional distillation by gallium quantification using an inductively coupled plasma emission spectrometer.

[Comparative Example 3] Synthesis of trimethylgallium (using gallium-magnesium alloy)
In place of the mixture of gallium and machined magnesium, 20.5 g of a gallium-magnesium alloy (molar ratio: gallium / magnesium = 2/5) was used, and the amount of diisoamyl ether added before the reaction was 156 mL. The trimethylgallium was synthesized in the same manner as in Example 1 except that diisoamyl ether was not added.

  14.5 g of crude trimethylgallium (84.0% yield in terms of gallium) is obtained by fractional distillation by gallium quantification using an inductively coupled plasma emission spectrometer.

As a result, in Comparative Example 1, since the magnesium concentration is not lowered during the reaction, the yield is very low, which is not practical at all. In Comparative Example 2, a high yield can be obtained without diluting magnesium during the reaction, but since powdered magnesium is used, handling thereof is complicated. In Comparative Example 3, since a gallium-magnesium alloy is used, a high yield can be obtained, but it takes time to prepare the alloy. Alloy preparation is a very difficult process. In addition, since the alloy is used, the reproducibility of the yield of trialkylgallium cannot be obtained.

On the other hand, in Examples 1 and 2 of the present invention, trialkylgallium can be synthesized in high yield without using a gallium-magnesium alloy and by using shaved magnesium that is easy to handle.

[Example 3] Manufacture of gallium nitride compound semiconductor device A substrate made of sapphire (C-plane) was set in a reaction vessel of MOVPE (Metal Organic Vapor Phase Epitaxy), and the temperature of the substrate was increased to 1050 ° C while flowing hydrogen. Raise the substrate and clean the substrate.
(Buffer layer)
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, ammonia is used as a source gas, and trimethyl gallium obtained in the above-described Example 1 is further purified. Grow with angstrom thickness. This reaction is represented by the following formula.

Ga (CH ₃ ) ₃ + NH ₃ → GaN + 3CH ₄
(Undoped GaN layer)
After growing the buffer layer, only trimethylgallium is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., trimethylgallium and ammonia gas are similarly used as source gases, and an undoped GaN layer is grown to a thickness of 1.5 μm.
(N-side contact layer)
Subsequently, at 1050 ° C., an n-side contact layer made of GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si using TMG and ammonia gas as source gases and silane gas as impurity gas, with a thickness of 2.25 μm. Grow.
(N-side first multilayer film layer)
Next, the silane gas alone was stopped, and an undoped GaN layer was grown to a thickness of 75 Å at 1050 ° C. using trimethyl gallium and ammonia gas. Subsequently, silane gas was added at the same temperature to add Si to 4.5 × 10 ^18. A / cm ³ -doped GaN layer is grown to a thickness of 25 Å. In this way, a pair consisting of an A layer composed of an undoped GaN layer of 75 angstroms and a 25 angstrom B layer having an Si doped GaN layer is grown. Then, 25 pairs are stacked to have a thickness of 2500 Å, and an n-side first multilayer film made of a multilayer film having a superlattice structure is grown.
(N-side second multilayer film layer)
Next, a second nitride semiconductor layer made of undoped GaN is grown at a similar temperature by 40 Å, and then at a temperature of 800 ° C., using trimethylgallium, trimethylindium, and ammonia, and using undoped In _0.13 Ga. _A first nitride semiconductor layer made of _0.87 N is grown by 20 Å. Then, these operations are repeated, and 10 layers are alternately stacked in the order of 2 + 1 and finally, the n-side formed of a multi-layer film having a superlattice structure in which a second nitride semiconductor layer made of GaN is grown by 40 angstroms. A second multilayer layer is grown to a thickness of 640 angstroms.
(Active layer)
Next, a barrier layer made of undoped GaN is grown to a thickness of 200 angstroms, followed by a temperature of 800 ° C. and a well made of undoped In _0.4 Ga _0.6 N using trimethylgallium, trimethylindium, and ammonia. The layer is grown to a thickness of 30 angstroms. Then, an active layer having a multiple quantum well structure with a total film thickness of 1120 angstroms is formed by alternately laminating five barrier layers and four well layers in the order of barrier + well + barrier + well. Grow.
(P-side multilayer clad layer)
Next, a ^{third layer of} p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg using trimethyl gallium, trimethyl aluminum, ammonia, biscyclopentadienyl magnesium at a temperature of 1050 ° C. The nitride semiconductor layer is grown to a thickness of 40 Å, and then the temperature is set to 800 ° C., and Mg is doped with 1 × 10 ²⁰ / cm ³ using trimethylgallium, trimethylindium, ammonia, and biscyclopentadienylmagnesium. A fourth nitride semiconductor layer made of In _0.03 Ga _0.97 N is grown to a thickness of 25 Å. Then, these operations are repeated, and 5 layers are alternately stacked in the order of 3 + 4, and finally, the third nitride semiconductor layer is grown to a thickness of 40 angstroms and is formed of a superlattice multilayer film. A side multilayer cladding layer is grown to a film thickness of 365 angstroms.
(P-side GaN contact layer)
Subsequently, at 1050 ° C., a p-side contact layer made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 700 Å using trimethylgallium, ammonia, and biscyclopentadienylmagnesium.

  After completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

  After annealing, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer, and etching is performed from the p-side contact layer side with a reactive ion etching (RIE) apparatus. To expose the surface of the n-side contact layer.

  After etching, a translucent p-electrode 10 containing Ni and Au having a thickness of 200 angstroms is formed on almost the entire surface of the p-side contact layer on the uppermost layer, and a p-pad electrode made of Au for bonding is formed on the p-electrode. It is formed with a film thickness of 0.5 μm. On the other hand, an n-electrode containing W and Al is formed on the surface of the n-side contact layer exposed by etching to form a gallium nitride compound semiconductor device.

  This gallium nitride-based compound semiconductor device emits pure green light of 520 nm at a forward current of 20 mA.

Trimethylgallium can also be used for a gallium nitride compound semiconductor device having another configuration. For example, ammonia and trimethyl gallium are used as source gases, and a buffer layer made of GaN is grown on the substrate. On the first buffer layer made of GaN, a second buffer layer made of undoped GaN, an n-side contact layer made of Si-doped GaN, an active layer made of a multiple quantum well structure, a single Mg-doped Al _{0. For example, a 1} Ga _0.9 N layer and a p-side contact layer made of Mg-doped GaN are sequentially stacked.

  The trialkylgallium obtained by the method of the present invention can be suitably used as a raw material for forming a gallium compound semiconductor thin film by epitaxial crystal growth.

Claims (11)

  A method for producing trialkylgallium, wherein gallium, magnesium and at least one alkyl halide are reacted in at least one ether compound, and the reaction system is diluted with at least one ether compound during the reaction. how to.   The method according to claim 1, wherein the dilution is performed so that the magnesium concentration in the reaction system is 5 moL / L or more at the start of the reaction and the total magnesium concentration in the reaction system is 4 moL / L or less.   3. The gallium, magnesium and at least one alkyl halide are reacted by introducing at least one alkyl halide into a mixture of gallium, magnesium and at least one ether compound. the method of.   4. The process according to claim 3, wherein at least one alkyl halide is introduced dropwise into a mixture of gallium, magnesium and at least one ether compound.   5. The reaction system is diluted within Ts ± 30 minutes from the time (Ts) when alkylmagnesium halide and magnesium halide are precipitated in the reaction system and the temperature rise of the reaction system stops (Ts). The method in any one of.   The method according to claim 1, wherein 1 to 10 mol of magnesium is used per 1 mol of gallium.   The method according to any one of claims 1 to 6, wherein the magnesium is in the form of a ribbon, a chip, a chip, or a granule.   The method according to claim 1, wherein the at least one alkyl halide is at least one alkyl halide selected from the group consisting of alkyl iodide and alkyl bromide.   The method according to claim 1, wherein at least one alkyl halide has an alkyl group having 1 to 10 carbon atoms.   A trialkylgallium obtained by the method according to claim 1.   A gallium-based material formed by epitaxial growth using the trialkylgallium according to claim 10 and at least one group III element-containing compound selected from the group consisting of a nitrogen-containing compound, a phosphorus-containing compound, and an arsenic-containing compound. A gallium compound semiconductor device comprising a compound semiconductor thin film.