JP4774776B2 - Method for producing trialkylgallium - Google Patents

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, the 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 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 trialkylgallium, a reaction between gallium trichloride and trialkylaluminum has been reported. This method is generally a method for obtaining high-purity trialkylgallium having industrial quality.

For example, Non-Patent Document 1 (KK Fukin, IA Frolov, Tr. Khim. Khim. Tekhnol., 4 , 40 (1973)) describes trimethylgallium by the reaction of gallium trichloride and trimethylaluminum. The results of various studies on the molar ratio of trimethylaluminum to gallium trichloride (Al / Ga molar ratio) at this time are described. Assuming that this reaction proceeds stoichiometrically, it is represented by the following formula (1).

GaCl ₃ + AlMe ₃ → GaMe ₃ + AlCl ₃ (1)
Accordingly, the reaction should proceed stoichiometrically when the Al / Ga molar ratio is 1, but Non-Patent Document 1 shows that the yield of trimethylgallium is 1 when the Al / Ga molar ratio = 1. Reported to be ~ 2%. Further, when the Al / Ga molar ratio = 2 when the amount of trimethylaluminum used is increased, the yield of trimethylgallium is 10 to 12%. When the Al / Ga molar ratio = 3, the yield of trimethylgallium is 55%. It is reported that it is 58%.

Under such circumstances, Non-Patent Document 2 (D. F. Gaines, J. Borlin, E. P. Fody, Inorg. Synth., 15 , 203 (1974)) increases the yield of trimethylgallium. Therefore, it has been reported that trimethylgallium is synthesized by reacting gallium trichloride with trimethylaluminum under the condition of Al / Ga molar ratio = 6. However, since this method uses a large excess of trimethylaluminum with respect to gallium trichloride, there is a problem that the cost is increased and a large amount of organoaluminum compound is by-produced in addition to trimethylgallium.

Non-Patent Document 3 (K. B. Staroweyski, A. Chwownowski, K. Jankowski, J. Lewinski, J. Zachara, Appl. Organomet. Chem., 14 , 616 Al (Ga)). = 3, gallium trichloride is reacted with trimethylaluminum to synthesize trimethylgallium. At this time, by adding inorganic salts such as sodium chloride and potassium fluoride, the yield is 80 to 90%. It has been reported that trimethylgallium is formed.

Non-Patent Document 3 describes the consideration that trimethylgallium is generated by the reactions shown in the following formulas (2) and (3). That is, when Al / Ga molar ratio = 3 and no such inorganic salt is added, the reaction proceeds according to the following formula (2), and in addition to the target trimethylgallium, a double nucleus of aluminum and gallium Complexes (AlGaMe ₄ Cl ₂ ) and organoaluminums (AlMe ₂ Cl) are generated.

GaCl ₃ + 3AlMe ₃
→ 0.5AlGaMe ₄ Cl ₂ + 2AlMe ₂ Cl
+0.5 AlMe ₃ +0.5 GaMe ₃ (2)
When inorganic salts are added to the reaction system of the formula (2), the inorganic salts decompose a binuclear complex of aluminum and gallium according to the following formula (3) to generate trimethylgallium.

0.5AlGaMe ₄ Cl ₂ + 2AlMe ₂ Cl + 0.5AlMe ₃
+0.5 GaMe ₃ + KCl
→ 3K [AlMe ₂ Cl ₂ ] + GaMe ₃ (3)
However, organoaluminums (KAlMe ₂ Cl ₂ ) are also produced by this method.

  Thus, in order to obtain trialkylgallium in a practically sufficient yield by the reaction of gallium trichloride and trialkylaluminum, a large excess of trialkylaluminum is required relative to gallium trichloride, which increases the cost. become.

In addition, when a large excess of trialkylaluminum is used, in addition to the target trialkylgallium, a large amount of spontaneously ignitable third-class hazardous material AlR ₂ Cl is produced as a by-product. Moreover, in order to obtain the same yield by using inorganic salts, the amount of trialkylaluminum used can be slightly reduced, but it is not sufficient. Furthermore, even if inorganic salts are used, a large amount of K [AlMe ₂ Cl ₂ ], which is an organoaluminum compound, is by-produced.

  The present invention is a method for synthesizing trialkylgallium by reaction of gallium trichloride and trialkylaluminum, and produces trialkylgallium in a high yield even if the amount of trialkylaluminum used relative to gallium trichloride is reduced. It is an object to provide a method that can be used.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and in the absence of a solvent or in at least one hydrocarbon solvent, the reaction of gallium trichloride with at least one trialkylaluminum results in a trialkylgallium. At this time, the molar ratio of at least one trialkylaluminum to gallium trichloride is set to about 1 to 4, and gallium trichloride and at least one trialkylaluminum are contacted for about 10 to 60 minutes. After that, it was found that trialkylgallium can be produced in a high yield by reacting at a temperature higher than that at the time of contact.

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

Item 1. A first step of contacting the gallium trichloride with at least one trialkylaluminum for 10 to 60 minutes in a solvent-free manner at a molar ratio of trialkylaluminum to gallium trichloride of 1 to 4;
And a second step of synthesizing trialkylgallium by reacting gallium trichloride with the trialkylaluminum at a temperature higher than that in the first step.

  Item 2. Item 2. The method according to Item 1, wherein in the first step, gallium trichloride and at least one trialkylaluminum are contacted at a temperature of 50 ° C or lower.

  Item 3. Item 3. The method according to Item 1 or 2, wherein in the first step, gallium trichloride and at least one trialkylaluminum are brought into contact with stirring.

  Item 4. Item 4. The method according to any one of Items 1 to 3, wherein, in the second step, gallium trichloride and at least one trialkylaluminum are reacted at a temperature of 50 to 150 ° C.

  Item 5. Item 5. The method according to any one of Items 1 to 4, wherein the reaction is performed for 1 to 10 hours in the second step.

  Item 6. Item 4. The method according to any one of Items 1 to 3, wherein the trialkylaluminum has an alkyl group having 1 to 4 carbon atoms.

  According to the present invention, in the method of synthesizing trialkylgallium by the reaction of gallium trichloride and trialkylaluminum, even if the amount of trialkylaluminum used is greatly reduced as compared with the conventional method, the practically sufficient yield is obtained. A way to obtain rates was provided.

  Thus, since the usage-amount of a trialkylaluminum can be reduced, the production amount of the pyrophoric organoaluminum compound which is a by-product can also be reduced simultaneously.

  Moreover, since the usage-amount of excess trialkylaluminum decreases, manufacturing cost can be held down.

  Hereinafter, the present invention will be described in detail.

In the method for producing trimethylgallium according to the present invention, the molar ratio of trialkylaluminum to gallium trichloride is about 1 to 4 in at least one hydrocarbon solvent or without solvent, and gallium trichloride and at least one trimethylgallium are used. It is a method including a first step of contacting alkylaluminum for about 10 to 60 minutes, and a second step of reacting gallium trichloride and the trialkylaluminum at a temperature higher than that of the first step.
material
<Gallium trichloride>
As gallium trichloride, a commercially available product having a purity of 99.9% (3N) to 99.999% (5N) can be used.

  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 trichloride as a raw material, it is desirable that the gallium trichloride has a high purity.

High purity gallium trichloride exceeding 4N is commercially available, but can be obtained by refining the above 3N or 4N purity commercial product by recrystallization, vacuum purification, electrolytic refining or the like. In the present invention, the purity of gallium trichloride is preferably 99.999% (5N) or more, and more preferably 99.9999% (6N) or more.
<Trialkylaluminum>
As the trialkylaluminum, an alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms may be used. The trialkylaluminum having an alkyl group having the carbon number is rich in reactivity, and by using these, a trialkylgallium having sufficient volatility as a MOCVD raw material can be obtained.

  Specific examples of the trialkylaluminum having an alkyl group having 1 to 4 carbon atoms include trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-sec-butyl. Aluminum, tri-tert-butylaluminum. In particular, trimethylaluminum and triethylaluminum are preferable.

  Trialkylaluminum can be used alone or in combination of two or more.

As the trialkylaluminum compound, a commercially available product for use in electronic materials having a purity of 5N or 6N can be used as it is, or a product obtained by purifying a commercially available product for polymerization with a purity of 2N or less by distillation purification can be used. Also, for example, “Comprehensive Organometallic Chemistry, The Synthesis, Reactions and Structures of Organometallic Compounds Vol. 1”, ed. S. G. Wilkinson, F.M. G. A. Stones, E .; W. Abel, Pergamon Press Ltd. , (1982), Chapter 6) can be used after being purified by distillation purification or the like. As the trialkylaluminum, those having a purity of 99.999% (5N) or more are preferably used, and it is more preferable to use a high-purity product having 99.9999% (6N) or more for electronic materials.
<Solvent>
When using a hydrocarbon compound as a reaction solvent, the kind is not specifically limited. For example, saturated aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane; saturated alicyclic hydrocarbons such as cyclohexane, cycloheptane; toluene, xylene, trimethylbenzene, ethylbenzene, ethyltoluene, Aromatic hydrocarbons such as indene can be used.
The hydrocarbon compound is preferably one that can be easily separated from the product trialkylgallium. In general, hydrocarbon compounds having a large boiling point difference from trialkylgallium are preferred. However, even if the difference in boiling point is sufficiently large, if a hydrocarbon compound having a lower boiling point than trialkylgallium is used, the yield decreases due to a small amount of azeotrope. It is desirable to select. However, since a hydrocarbon compound that is solid at room temperature is troublesome to handle, it is preferable to select a hydrocarbon compound having a lower boiling point than such a hydrocarbon compound.

  A hydrocarbon 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 hydrocarbon compound alone in that the resulting trialkylgallium can be easily purified.

The use ratio of gallium trichloride to trialkylaluminum (trialkylaluminum / gallium trichloride) is about 1 to 4 in molar ratio. Especially, about 1-3 are preferable, about 2-3 are more preferable, and about 2.5-3 are still more preferable. If it is the said range, while being able to obtain a practically sufficient yield, the by-product amount of a pyrophoric organoaluminum compound can be reduced significantly compared with the conventional method.
1st process (contact process)
Contact between gallium trichloride and trialkylaluminum is performed 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, and more preferably 99.9999% (6N) or more.

  In particular, since moisture and oxygen in the atmospheric gas not only reduce the yield of trialkylgallium, but can also cause a decrease in purity, 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 an inert gas having a high purity can be obtained using a membrane separation method, a catalytic reaction method, a liquefaction rectification method, or a PSA (Pressure Swing Adsorption) method.

  The reaction between gallium trichloride and trialkylaluminum can be carried out without solvent or in a hydrocarbon compound. Whether the reaction is performed in the absence of a solvent or in a hydrocarbon compound can be arbitrarily selected in consideration of the type of trialkylaluminum used and other conditions.

  In contacting gallium trichloride and trialkylaluminum, they may be mixed and contacted as they are in an inert gas atmosphere and in the absence of a solvent. When using a hydrocarbon compound solvent, gallium trichloride, trialkylaluminum, and solvent can be mixed in any order under an inert gas atmosphere, but usually under an inert gas atmosphere. In this reaction vessel, gallium trichloride and, if necessary, a hydrocarbon compound are put, and then trialkylaluminum is slowly introduced into the mixture. Moreover, when using a hydrocarbon compound, you may dilute trialkylaluminum with a hydrocarbon compound previously.

  When a hydrocarbon compound solvent is used, the amount of the solvent used means the concentration (mole number relative to 1 L of the solvent) immediately after the contact between gallium trichloride and trialkylaluminum. ) Is preferably about 0.01 to 10 mol / L, more preferably about 0.1 to 5 mol / L. If it is the said density | concentration range, the reactivity and by extension, a trialkylgallium yield will become high enough.

  The temperature at the time of contact between gallium trichloride and trialkylaluminum is not particularly limited as long as it is lower than the temperature at the subsequent high-temperature reaction, but is preferably 50 ° C. or less, more preferably 40 ° C. or less. The lower limit of the temperature at the time of contact is usually about 20 ° C. If it is the said temperature range, the fall of the reactivity by crystallization of a gallium trichloride and an organoaluminum compound is avoided.

  In bringing them into contact with each other, they may be mixed and allowed to stand, or the contact state may be maintained under stirring. Stirring is preferable for efficient reaction. Stirring may be performed by a known method such as stirring with a magnetic stirrer or induction stirring.

The contact time is about 10 to 60 minutes, preferably about 20 to 50 minutes, and more preferably about 30 to 40 minutes. By contacting for the above time, trialkylgallium can be synthesized in a sufficient yield. This contact time is a time starting from the time when all the materials are mixed. For example, in the case where trialkylaluminum is dropped into a mixture of gallium trichloride and a hydrocarbon solvent, from the time when dropping of the trialkylaluminum is completed. Is the time.
Second step (high temperature reaction step)
Subsequently, the reaction between gallium trichloride and trialkylaluminum proceeds at a temperature higher than that in the contact step under an inert gas atmosphere. The reaction temperature is preferably about 50 to 150 ° C, more preferably about 70 to 130 ° C, and still more preferably about 80 to 120 ° C. If it is the said temperature range, a sufficiently high yield will be obtained practically and the produced trialkylgallium will not be decomposed.

  The reaction time at this high temperature is not particularly limited, but is preferably about 1 to 10 hours, and more preferably about 2 to 5 hours. Due to the high temperature reaction for the above time, the yield can be increased practically and the produced trialkylgallium is not decomposed.

  It is preferable to stir the reaction solution for efficiently advancing the reaction even at a high temperature reaction.

The first step and the second step are not particularly limited, and the synthesis reaction can be performed under atmospheric pressure, reduced pressure, or increased pressure.
Purification step By the above reaction, in addition to the target trialkylgallium, for example, a binuclear complex of aluminum and gallium such as AlGaR ₄ Cl ₂ (R represents an alkyl group), AlR ₂ Cl (R is an alkyl group) In some cases, an organoaluminum compound such as Therefore, the trialkylgallium may be separated and purified by distilling the reaction solution. 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 element 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 or plasma irradiation after introducing 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, but the present invention is not limited to these examples.
[Reference Example 1]
Into a 500 mL four-necked flask purged with nitrogen, 25.09 g (142 mmol) of gallium trichloride and 201 mL of toluene sufficiently dehydrated with molecular sieves are added at room temperature. A dry ice condenser is attached to the flask and the internal temperature is adjusted to 20 ° C., and then a solution obtained by diluting 30.97 g (430 mmol) of trimethylaluminum with 49 mL of toluene is dropped into the solution in the flask over about 1 hour. During this time, the temperature in the flask is adjusted to a range of 45 to 50 ° C. After completion of dropping, the reaction solution is kept at 45 ° C. for 30 minutes while stirring.

  The purity of gallium trichloride is 5N, and the purity of trimethylaluminum is 5N. The molar ratio of trimethylaluminum to gallium trichloride is 3.0. Further, the concentration of gallium trichloride in the solvent immediately after mixing is 0.57 mol / L, and the concentration of trimethylaluminum is 1.72 mol / L (respectively, the number of moles relative to 1 liter of solvent, the same applies hereinafter). Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

  Next, the temperature of the reaction solution is raised to 100 ° C., and the reaction solution is kept at 100 ° C. for 3 hours by heating while stirring.

Crude trimethylgallium is fractionated from the reaction mixture in a state where toluene is boiling, using a column having a length of 30 cm and a diameter of 1.5 cm filled with glass beads.
By gallium quantification using an inductively coupled plasma atomic emission spectrometer (ICP-AES) Inductively Coupled Plasma Atomic Emission Spectrometer, 14.35 g (87.9% yield in terms of gallium) of crude trimethylgallium is obtained.
[Example 1]
25.07 g (114 mmol) of gallium trichloride is added to a 100 mL four-necked flask purged with nitrogen at room temperature. A dry ice condenser is attached to the flask and the internal temperature is adjusted to 20 ° C., and 24.78 g (344 mmol) of trimethylaluminum is dropped into the solution in the flask over about 1 hour and stirred. During this time, the temperature in the flask is adjusted to a range of 45 to 50 ° C. After completion of dropping, the reaction solution is kept at 45 ° C. for 30 minutes while stirring.

  The purity of gallium trichloride is 5N, and the purity of trimethylaluminum is 5N. The molar ratio of trimethylaluminum to gallium trichloride is 3.0. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

  Next, the temperature of the reaction solution is raised to 100 ° C., and the reaction solution is kept at 100 ° C. for 3 hours by heating while stirring.

  From the reaction mixture, crude trimethylgallium is fractionated using a column having a length of 30 cm and a diameter of 1.5 cm filled with glass beads.

By gallium quantification using an inductively coupled plasma emission spectrometer, 12.06 g (92.0% yield in terms of gallium) of crude trimethylgallium is obtained.
[Reference Example 2]
To a 500 mL four-necked flask purged with nitrogen is added 22.58 g (128 mmol) of gallium trichloride at room temperature. After attaching a dry ice condenser to this flask and adjusting the internal temperature to 20 ° C., a solution obtained by diluting 44.12 g (378 mmol) of triethylaluminum with 220 mL of hexane sufficiently dehydrated with molecular sieves was added to the solution in the flask over about 1 hour. Stir dropwise. During this time, the temperature in the flask is adjusted to a range of 45 to 50 ° C. After completion of dropping, the reaction solution is kept at 45 ° C. for 30 minutes while stirring.

  The purity of gallium trichloride is 5N, and the purity of triethylaluminum is 5N. The molar ratio of triethylaluminum to gallium trichloride is 3.0. The concentration of gallium trichloride in the solvent immediately after mixing is 0.58 mol / L, and the concentration of triethylaluminum is 1.72 mol / L. Nitrogen has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb.

  Next, the temperature of the reaction solution is raised to 65 ° C., and the reaction solution is kept at 65 ° C. for 3 hours by heating with stirring.

  From the reaction mixture, hexane and crude triethylgallium are fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads. First, hexane is fractionally distilled (39 to 41 ° C.) under a reduced pressure of 300 Torr, and then crude triethylgallium is fractionally distilled (107 to 109 ° C.).

16.05 g (80.0% yield in terms of gallium) of crude triethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer.
[Comparative Example 1]
The same operation as in Example 1 is performed except that the heating reaction step of heating the reaction solution to 100 ° C. and heating and stirring for 3 hours is not performed.

By gallium quantification using an inductively coupled plasma emission spectrometer, 8.28 g (50.7% yield in terms of gallium) of crude trimethylgallium is obtained.
[Comparative Example 2]
All the same operations as in Example 3 are performed except that the heating reaction step of heating the reaction solution to 65 ° C. and heating and stirring for 3 hours is not performed.
By gallium quantification using an inductively coupled plasma emission spectrometer, 8.32 g (41.5% yield in terms of gallium) of crude triethylgallium is obtained.

In Example 1, where gallium trichloride and trimethylaluminum are mixed and then subjected to a heating reaction at 100 ° C. for 3 hours, the yield is 87.9%, but a comparative example is a corresponding comparative example in which this heating reaction is not performed. In No. 1, the yield is 50.7%.

  Similarly, in Example 3, in which gallium trichloride and triethylaluminum are mixed and then subjected to a heating reaction at 65 ° C. for 3 hours, the yield is 80.0%. In a corresponding comparative example in which this heating reaction is not performed, In Comparative Example 2, the yield is 41.5%.

From this, it can be seen that the yield is greatly improved by carrying out the heating reaction.

[Example 2] Manufacture of gallium nitride based 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 is used, using trimethyl gallium, ammonia gas as source gas, and silane gas as impurity gas, and a film thickness of 2.25 μm. Grow in.
(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 (6)

A first step of contacting the gallium trichloride with at least one trialkylaluminum for 10 to 60 minutes in a solvent-free manner at a molar ratio of trialkylaluminum to gallium trichloride of 1 to 4;
And a second step of synthesizing trialkylgallium by reacting gallium trichloride with the trialkylaluminum at a temperature higher than that in the first step. The method according to claim 1, wherein in the first step, gallium trichloride and at least one trialkylaluminum are contacted at a temperature of 50 ° C. or lower. The method according to claim 1 or 2, wherein in the first step, gallium trichloride and at least one trialkylaluminum are brought into contact with stirring. The method according to any one of claims 1 to 3, wherein in the second step, gallium trichloride and at least one trialkylaluminum are reacted at a temperature of 50 to 150C. The method according to any one of claims 1 to 4, wherein the reaction is performed for 1 to 10 hours in the second step. The method according to any one of claims 1 to 3, wherein the trialkylaluminum has an alkyl group having 1 to 4 carbon atoms.