JP4774774B2 - 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 a trialkylgallium compound which has been conventionally reported, a synthesis method by the following reactions (a) to (g) can be mentioned.
(A) Reaction of gallium halide compound with Grignard reagent (for example, Patent Document 1 (US Pat. No. 4,604,473))
(B) Reaction of a gallium halide compound with a trialkylaluminum compound (for example, Non-Patent Document 1 ((KK Fukin, IA Frolov, Tr. Khim. Khim. Tekhnol., 4 , 40 (1973) )
(C) Reaction of a gallium halide compound with an alkyl lithium compound (for example, Non-Patent Document 2 (RA Kovar, H. Derr, D. Brandau, J. O. Calloway, Inorg. Chem., 14 , 2809 ( 1975))
(D) Reaction of a gallium halide compound with a dialkylzinc compound (for example, Non-Patent Document 3 (C. A. Claus, FE Tounder, Proc. Natl. Acad. Sci. USA, 19 , 192 (1933))
(E) Reaction of gallium with dialkyl mercury (for example, Non-Patent Document 4 (GE Coates, J. Chem. Soc., 2003 (1951))
(F) Reaction of gallium-magnesium mixture and alkyl halide compound (for example, Patent Document 2 (US Pat. No. 325847)
(G) Reaction of gallium-magnesium alloy with alkyl halide compound (for example, Patent Document 3 (US Pat. No. 5,248,800))
Thus, gallium halide or gallium is used as the gallium raw material. However, there is no known practical method for synthesizing trialkylgallium with good yield using other gallium raw materials.

  An object of the present invention is to provide a method capable of producing trialkylgallium with high yield by using a new gallium raw material not conventionally used as a raw material for producing trialkylgallium.

In order to solve the above-mentioned problems, the present inventors have intensively studied, and the following general formula (1)
_{Ga 2 R m X 6-m} (1)
(In the formula, R represents a methyl group or an ethyl group, X represents a halogen atom, and m represents an integer of 1 to 5).
It was found that a trialkyl gallium compound can be produced in a high yield by reacting at least one alkyl gallium compound represented by the formula (1) with at least one alkyl metal compound as an alkylating agent.

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

Item 1. The following general formula (1)
_{Ga 2 R m X 6-m} (1)
(In the formula, R represents a methyl group or an ethyl group, X represents a halogen atom, and m represents an integer of 1 to 5).
A trialkylgallium compound by reacting at least one halogenated alkylgallium compound represented by the formula: at least one alkyl metal compound selected from the group consisting of a lithium-containing compound, a magnesium-containing compound, and a zinc-containing compound. A method of producing trialkylgallium for synthesizing
Item 2. Item 2. The method according to Item 1, wherein the at least one alkyl metal compound is at least one compound selected from the group consisting of alkyl lithium compounds, halogenated alkyl magnesium compounds, and dialkyl zinc compounds.
Item 3. Item 3. The method according to Item 1 or 2, wherein the at least one alkyl metal compound is at least one compound selected from the group consisting of a methyl metal compound and an ethyl metal compound.
Item 4. Any one of Items 1 to 3, wherein at least one alkyl metal compound is used in an amount of 0.5 to 2 times the number of moles of the stoichiometric composition ratio with respect to 1 mole of the compound represented by the general formula (1). The method described in 1.

 According to the present invention, the trimethyl gallium compound of the general formula (1), which is a new gallium raw material that has not been conventionally used, is alkylated with an alkyl metal compound in a practically high yield with a simple method. It has been found that alkyl gallium compounds can be obtained. The present invention has opened a new path for trialkylgallium synthesis.

  Hereinafter, the present invention will be described in detail.

The method for producing trialkylgallium according to the present invention synthesizes trialkylgallium by reacting at least one alkylgallium halide compound represented by the general formula (1) with at least one alkylmetal compound. It is a method to do.
material
<Gallium compound>
Although the kind of halogen atom in the halogenated alkylgallium compound of the general formula (1) is not particularly limited, it may be usually a chlorine atom, a bromine atom, or an iodine atom. Of these, alkyl gallium iodide and alkyl gallium bromide are preferable in terms of high reactivity, and alkyl gallium iodide is most preferable.

  In the general formula (1), R is preferably a methyl group in view of the large demand for trimethylgallium as an MOCVD raw material.

Specific examples of the compound represented by the general formula (1) are Ga ₂ MeCl ₅ , Ga ₂ Me ₂ Cl ₄ , Ga ₂ Me ₃ Cl ₃ , Ga ₂ Me ₄ Cl ₂ , Ga ₂ Me ₅ Cl; Ga ₂ MeClBr. ₅ , Ga ₂ Me ₂ Br ₄ , Ga ₂ Me ₃ Br ₃ , Ga ₂ Me ₄ Br ₂ , Ga ₂ Me ₅ Br; Ga ₂ MeClI ₅ , Ga ₂ Me ₂ I ₄ , Ga ₂ Me ₃ I ₃ , Ga _{2 Me 4 I 2, Ga 2 Me} 5 I; Ga 2 EtCl 5, Ga 2 Et 2 Cl 4, Ga 2 Et 3 Cl 3, Ga 2 Et 4 Cl 2, Ga 2 Et 5 Cl; Ga 2 EtClBr 5, Ga 2 _{Et 2 Br 4, Ga 2 Et} 3 Br 3, Ga 2 Et 4 Br 2, Ga 2 Et 5 Br; Ga 2 EtClI 5, Ga 2 Et 2 I 4, Ga 2 Et Is _{I 3, Ga 2 Et 4 I} 2, Ga 2 Et 5 I. Among these, Ga ₂ Me ₂ Br ₄ , Ga ₂ Me ₃ Br ₃ , Ga ₂ Me ₄ Br ₂ , Ga ₂ Me ₅ Br; Ga ₂ Me ₂ I ₄ , Ga ₂ Me ₃ I ₃ , Ga ₂ Me ₄ I ₂ , _{Ga 2 Me 5 I; Ga 2} Et 2 Br 4, Ga 2 Et 3 Br 3, Ga 2 Et 4 Br 2, Ga 2 Et 5 Br; Ga 2 Et 2 I 4, Ga 2 Et 3 I 3, Ga 2 Et ₄ I ₂ and Ga ₂ Et ₅ I are preferable, and Ga ₂ Me ₂ I ₄ , Ga ₂ Me ₃ I ₃ , Ga ₂ Me ₄ I ₂ , and Ga ₂ Me ₅ I are more preferable.

  The compound represented by General formula (1) can be used individually by 1 type or in combination of 2 or more types.

The halogenated alkylgallium compound of the general formula (1) can be synthesized by a known method in which gallium and an alkyl halide are reacted. For example, Ga ₂ R ₃ X ₃ is M.M. J. et al. S. Gynane, I .; J. et al. Worall, J. et al. Organomet. Chem. , 40 , C59 (1972), and Ga ₂ R ₂ I ₄ can be synthesized according to M.M. Wilkinson, I.D. J. et al. Worall, J. et al. Organomet. Chem. , 93 , 39 (1975), and Ga ₂ RBr ₅ can be synthesized by the method described in W.W. Lind, I .; J. et al. Worall, J. et al. Organomet. Chem. , 36 . 35 (1972) and W.W. Lind, I .; J. et al. Worall, J. et al. Organomet. Chem. , 40 . 35 (1972). Other compounds included in the general formula (1) can be produced by those skilled in the art according to the methods described in the above documents. Moreover, the compound of General formula (1) can also be synthesize | combined by the well-known method of making a gallium halide and an alkyl metal compound react.
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 trialkyl gallium to be generated also depends on the purity of the raw material compound, it is desirable that the compound of the general formula (1) has a high purity.
What is necessary is just to use what was synthesize | combined using the high purity gallium or a gallium halide as a raw material for the compound of the said General formula (1). As the gallium or gallium halide, a commercially available gallium product having a purity of 99.9% (3N) to 99.99999% (7N) may be used. Although high purity gallium or gallium halide exceeding 4N is commercially available, it can be obtained by refining a commercially available product of 3N or 4N purity by recrystallization, vacuum purification, electrolytic refining or the like. The purity of the raw material gallium or gallium halide is preferably 99.999% (5N) or more, and more preferably 99.9999% (6N) or more.
<Alkyl metal compound>
An alkyl metal compound is a compound having a bond between an alkyl group and a metal. The kind of alkyl metal compound is not particularly limited. Of these, alkyl lithium compounds, alkyl magnesium compounds, alkyl aluminum compounds, and alkyl zinc compounds are preferred. In addition, the alkyl group is usually a methyl group or an ethyl group, and a methyl group is preferred in that there is a great demand for trimethylgallium as a MOCVD raw material.

  Examples of the alkyl metal compound include a halogenated alkyl magnesium compound (Grignard reagent), an alkyl lithium compound, a trialkyl aluminum compound, and a dialkyl zinc compound having a methyl group or an ethyl group as an alkyl group. Among these, a halogenated alkylmagnesium compound and a trialkylaluminum compound are more preferable because the safety of the trialkylgallium production process is high and the obtained trialkylgallium is easily purified.

Specific examples of the halogenated alkylmagnesium compound (Grignard reagent) include methylmagnesium chloride, ethylmagnesium chloride, methylmagnesium bromide, ethylmagnesium bromide, methylmagnesium iodide, and ethylmagnesium iodide. In particular, methylmagnesium iodide and ethylmagnesium iodide are preferable in terms of high reactivity.
Specific examples of the alkyl lithium compound include methyl lithium and ethyl lithium. Specific examples of the trialkylaluminum compound include trimethylaluminum and triethylaluminum. Specific examples of the dialkyl zinc compound include dimethyl zinc and diethyl zinc.

  A method for producing an alkylmagnesium halide is well known and can be synthesized by reacting magnesium with an alkyl halide in a solvent such as ether. In addition, a halogenated alkylmagnesium compound (Grignard reagent) having a methyl group or an ethyl group as an alkyl group is commercially available.

  A method for producing an alkyl lithium compound is well known and can be synthesized, for example, by reacting an alkyl chloride or alkyl bromide with lithium metal in an ether compound. Methyl lithium and ethyl lithium are also commercially available.

  Methods for producing trialkylaluminum are well known, see, for example, “Comprehensive Organometallic Chemistry, The Synthesis, Reactions and Structures of Organic Compounds, Vol. S. G. Wilkinson, F.M. G. A. Stones, E .; W. Abel, Pergamon Press Ltd. , (1982), Chapter 6. Trimethylaluminum and triethylaluminum are also commercially available.

  A method for producing a dialkylzinc compound is well known and can be synthesized, for example, by reacting alkyl iodide with zinc metal in an ether or hydrocarbon solvent. Dimethyl zinc and diethyl zinc are also commercially available.

  Explaining the purity of the alkyl metal compound, as for the trialkylaluminum compound and the dialkylzinc compound, commercially available products having a purity of 5N or 6N for electronic materials can be used as they are, or commercially available products of a general grade of purity 2N can be used. It can be used after being purified by distillation purification. As the halogenated alkylmagnesium compound and the alkyllithium compound, since there are no commercially available products with high purity, those synthesized from 3N or more magnesium or lithium as a raw material can be used. Magnesium and lithium with a purity of 3N or more are commercially available, but since higher purity magnesium and lithium are expensive, they are synthesized by purifying commercially available products of 2N to 4N by vacuum distillation, vacuum sublimation, etc. Alkylmagnesium halide compounds and alkyllithium compounds prepared can be used.

An alkyl metal compound can be used individually by 1 type or in combination of 2 or more type within the range of the same compound. For example, two or more types can be used in combination as long as they are within the range of the alkyl lithium compound. For example, it is difficult to use a combination of an alkyl lithium compound and a trialkylaluminum compound.
<Solvent>
The synthesis reaction of the present invention can be carried out without solvent when the alkyl metal compound is a liquid, but usually a solvent may be used. In addition, since commercially available products of halogenated alkylmagnesium compounds (Grignard reagents) and commercially available products of alkyllithylum compounds are usually sold as solutions in solvents, when using such alkyl metal compounds, the solvent must be There is no need to use it separately.

  The kind of the solvent is not particularly limited except for a compound having active hydrogen that reacts with the product trialkylgallium compound, such as an alcohol compound or a thiol compound. For example, known solvents such as ether compounds, hydrocarbon compounds, and amine compounds can be used. Among these, an ether compound and an amine compound are preferable in that the reactivity of trialkylgallium synthesis is high.

  Examples of hydrocarbon compounds include saturated aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane; saturated alicyclic hydrocarbons such as cyclohexane and cycloheptane; toluene, xylene, and trimethylbenzene. And aromatic hydrocarbons such as ethylbenzene, ethyltoluene, and indene.

  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.

  Examples of ether compounds include aliphatic ether compounds such as diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether, di-sec-butyl ether, and diisopentyl ether (diisoamyl ether). An aromatic ether compound such as anisole, methylanisole, benzylmethyl ether, ethylanisole, dimethylanisole, isopropylanisole, and phenetole;

  Since the ether compound forms an adduct with the product trialkylgallium compound, the ether adduct of trialkylgallium is thermally decomposed by distillation as described later after the synthesis step, so that the trialkylgallium is obtained. It is preferred to isolate the compound. 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.

  As the amine compound, for example, a tertiary amine compound can be used. Specifically, aliphatic tertiary amine compounds such as trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, tri-sec-butylamine, tri-tert-butylamine; pyridine And heterocyclic tertiary amine compounds such as pyrrole, pyrimidine, pyrazine, pyridazine, 1,3,5-triazine, and hexahydrotriazine.

  Since the amine compound forms an adduct with the product trialkylgallium compound, after the synthesis reaction, the trialkylgallium compound is pyrolyzed by pyrolyzing the amine adduct of trialkylgallium by distillation as described later. It is preferred to isolate. For this reason, when the thermal decomposition temperature of the amine adduct of trialkylgallium is higher than the thermal decomposition temperature of the trialkylgallium compound, the decomposition of the trialkylgallium compound also proceeds. It is preferable to select an amine compound that is lower than the decomposition temperature.

A solvent can be used individually by 1 type or in combination of 2 or more types. However, it is preferable to use one kind of solvent alone because the resulting trialkylgallium can be easily purified.
Usage Ratio The usage ratio of the alkylgallium halide compound represented by the general formula (1) and the alkyl metal compound varies depending on the type of the alkyl metal compound.

  When the alkyl metal compound is a halogenated alkyl magnesium compound, the trialkylgallium synthesis reaction can be represented by the following formula (2).

_{Ga 2 R m X 6-m} + (6-m) RMgX
→ 2GaR ₃ + (6-m) MgX ₂ (2)
From the formula (2), the stoichiometric composition ratio is a halogenated alkylmagnesium compound (6-m) mole per 1 mole of the halogenated alkylgallium compound of the general formula (1). Therefore, it is preferable to use about 0.5 (6-m) to 2 (6-m) mole of alkylmagnesium halide with respect to 1 mole of the compound of the general formula (1). ) To 1.5 (6-m) moles are more preferable.

  Further, when the alkyl metal compound is an alkyl lithium compound, the trialkylgallium synthesis reaction can be represented by the following formula (3).

_{Ga 2 R m X 6-m} + (6-m) RLi
→ 2GaR ₃ + (6-m) LiX (3)
From the formula (3), the stoichiometric composition ratio is an alkyllithium compound (6-m) mole with respect to 1 mole of the halogenated alkylgallium compound of the general formula (1). Therefore, it is preferable to use about 0.5 (6-m) to 2 (6-m) moles of an alkyl lithium compound with respect to 1 mole of the compound of the general formula (1), and 0.7 (6-m) It is more preferable to use about ~ 1.5 (6-m) mol.

  When the alkyl metal compound is a trialkylaluminum compound, the trialkylgallium synthesis reaction can be represented by the following formula (4).

_{Ga 2 R m X 6-m} + (6-m) / 3AlR 3
→ 2GaR ₃ + (6-m) / 3AlX ₃ (4)
From the formula (4), the stoichiometric composition ratio is trialkylaluminum compound (6-m) / 3 mol with respect to 1 mol of the halogenated alkylgallium compound of the general formula (1). Therefore, it is preferable to use about 0.5 [(6-m) / 3] to 2 [(6-m) / 3] mol of trialkylaluminum with respect to 1 mol of the compound of the general formula (1). It is more preferable to use about 0.7 [(6-m) / 3] to 1.5 [(6-m) / 3] mole.

  Further, when the alkyl metal compound is a dialkyl zinc compound, the trialkyl gallium synthesis reaction can be represented by the following formula (5).

_{Ga 2 R m X 6-m} + (6-m) / 2ZnR 2
→ 2GaR ₃ + (6-m) / 2ZnX ₂ (5)
From the formula (5), the stoichiometric composition ratio is dialkylzinc compound (6-m) / 2 mol with respect to 1 mol of the halogenated alkylgallium compound of the general formula (1). Therefore, it is preferable to use about 0.5 [(6-m) / 2] to 2 [(6-m) / 2] moles of dialkyl zinc with respect to 1 mole of the compound of the general formula (1). It is more preferable to use about 0.7 [(6-m) / 2] to 1.5 [(6-m) / 2] mol.

In the case of using any alkyl metal compound, the reaction can sufficiently proceed within the above range. Moreover, even if the usage ratio of the alkyl metal compound is too high, no further effect can be obtained. On the other hand, the amount of waste increases and post-treatment takes time and costs are increased. If so, such a problem will not occur.
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. When synthesizing a halogenated alkylgallium compound or an alkyl metal compound, it is carried out in an inert gas atmosphere. 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.

  In the reaction, the halogenated alkylgallium compound of the general formula (1) and the alkyl metal compound are brought into contact with each other in an ordinary solvent in an inert gas atmosphere. The order of addition of these compounds into the reaction vessel is not particularly limited, but it is usually preferable to add a solvent and an alkyl gallium halide compound and then add an alkyl metal compound. When the reactivity between the halogenated alkylgallium compound and the alkyl metal compound is high, the alkyl metal compound may be added in small portions. If the reactivity is low, the whole amount can be added at once.

  The amount of the solvent used is not particularly limited, but the alkylgallium halide concentration and the alkylmetal concentration in the solvent at the end of the preparation of the alkylmetal compound (each means the number of moles relative to 1 L of the solvent; the same applies hereinafter). In any case, an amount of about 0.01 to 10 moL / L is preferable, and an amount of about 0.1 to 5 moL / L is more preferable. When the concentration is within the above range, the reactivity and thus the yield of trialkylgallium are sufficiently high, and the reaction can be easily controlled, that is, the reaction proceeds suddenly, or the reaction is in progress due to precipitation of the generated alkylmagnesium halide. It does not end with, and stirring is difficult due to the by-product magnesium halide.

  The reaction temperature may be a temperature at which the reaction proceeds efficiently in consideration of the halogenated alkylgallium compound, the alkyl metal compound, the type of solvent, and other conditions. Usually, the reaction may be performed at a temperature of about 0 to 200 ° C, preferably about 40 to 160 ° C, more preferably about 60 to 120 ° C. Under this temperature, trialkylgallium is usually produced by a reaction of 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 a method such as precision distillation or sublimation, 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. However, the present invention is not limited to these examples.
[Example 1] Synthesis of trimethylgallium
(1) Synthesis of Ga ₂ Me ₃ I ₃ A magnetic stirrer chip is placed in a 100 mL capacity glass autoclave substituted with nitrogen, and at room temperature, 5.00 g (72 mmol) of 6N gallium and 22.78 g (161 mmol) of methyl iodide are used. ). The temperature inside the autoclave is raised to 90 ° C., and the mixture is heated and stirred at the same temperature for 24 hours. All the gallium is dissolved and becomes a yellow liquid. The identification of the product is J. et al. S. Gynane, I .; J. et al. Worral, J. et al. Organomet. Chem. , 40 , C59 (1972) with reference to the description of IR spectrum and Raman spectrum.
(2) Synthesis of methylmagnesium iodide To a 300 mL capacity four-necked flask purged with nitrogen, 4.01 g (167 mmol) of 3N-purified magnesium having a purity of 3N at room temperature and 68 mL of diisoamyl ether sufficiently dehydrated with molecular sieves are added. After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 27.89 g (197 mmol) of methyl iodide is dropped into the solution in the flask over about 2 hours. During this time, the temperature in the flask is adjusted so as not to exceed 40 ° C. After completion of dropping, the mixture is stirred at room temperature for 12 hours.

The resulting reaction mixture is filtered. As a result of measurement by the Gilman double titration method (method described in H. Gilman, FK Cantledge, J. Organomet. Chem., 2 , 447 (1964)), it was found that the iodine was 97.0% yield (162 mmol). Methyl magnesium chloride is formed.
(3) Reaction of Ga ₂ Me ₃ I ₃ with methylmagnesium iodide Into a nitrogen-substituted 300 mL four-necked flask, the total amount of Ga ₂ Me ₃ I ₃ synthesized above at room temperature and diisoamyl sufficiently dehydrated with molecular sieves Add 48 mL of ether. A dry ice condenser is attached and the internal temperature is adjusted to 20 ° C., and then the synthesized diisoamyl ether solution equivalent to 56 g (114 mmol) of methylmagnesium iodide is slowly added dropwise. After completion of dropping, the temperature in the autoclave is increased to 90 ° C., and the mixture is stirred for 6 hours.

Nitrogen used in the synthesis of Ga ₂ Me ₃ I ₃ , methylmagnesium iodide, and trialkylgallium has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The concentration of Ga ₂ Me ₃ I _{3 in} the solvent at the end of the preparation of methylmagnesium iodide is 0.31 mol / L, and the concentration of methylmagnesium iodide is 0.97 mol / L (respectively, the number of moles relative to 1 liter of solvent. ,the same.).

After completion of the reaction, crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture in a state where diisoamyl ether is boiling.
By gallium quantification using an inductively coupled plasma optical emission spectrometer (ICP-AES) Inductively Coupled Plasma Atomic Emission Spectrometer, 6.09 g (73.5% yield in terms of gallium) of crude trimethylgallium is obtained.
[Example 2] Synthesis of trimethylgallium
Reaction of Ga ₂ Me ₃ I ₃ and trimethylaluminum Put a magnetic stirrer chip in a 100 mL capacity glass autoclave with nitrogen substitution, and molecular sieves are sufficient for the total amount of Ga ₂ Me ₃ I ₃ synthesized in Example 1 at room temperature. Add 50 mL of dehydrated toluene. Next, 8.36 g (116 mmol) of commercially available trimethylaluminum is added and heated and stirred at 120 ° C. for 20 hours.

The nitrogen used has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The Ga ₂ Me ₃ I ₃ concentration in the solvent at the end of the trimethylaluminum charge is 0.50 mol / L, and the trimethylaluminum concentration is 1.61 mol / L.

After completion of the reaction, crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture in a state where toluene is boiling.
6.74 g (81.5% yield in terms of gallium) of crude triethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer.
[Example 3] Synthesis of trimethylgallium
(1) Synthesis of Ga ₂ Me ₃ Br ₃ A magnetic stirrer chip was placed in a 100 mL glass autoclave purged with nitrogen, and 5.00 g (72 mmol) gallium having a purity of 6N at room temperature and 14.73 g (155 mmol) methyl bromide. Is introduced. The inside of the autoclave is heated to 90 ° C. and stirred for 24 hours. All the gallium is dissolved and becomes a yellow liquid.

The identification of the product is J. et al. S. Gynane, I .; J. et al. Worral, J. et al. Organomet. Chem. , 40 , C59 (1972) with reference to the description of IR spectrum and Raman spectrum.
(2) Reaction of Ga ₂ Me ₃ Br ₃ and methylmagnesium iodide A 300-mL four-necked flask purged with nitrogen was thoroughly dehydrated with Ga ₂ Me ₃ Br ₃ synthesized as described above and molecular sieves at room temperature. Add 48 mL of diisoamyl ether. After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., a diisoamyl ether solution equivalent to 56 g (114 mmol) of methylmagnesium iodide synthesized in Example 1 is slowly added dropwise. After completion of dropping, the temperature in the autoclave is increased to 90 ° C., and the mixture is stirred for 6 hours.

Nitrogen used in the synthesis of Ga ₂ Me ₃ Br ₃ , methylmagnesium iodide, and trialkylgallium has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The Ga ₂ Me ₃ Br ₃ concentration in the solvent at the end of the preparation of methylmagnesium iodide is 0.32 mol / L, and the concentration of methylmagnesium iodide is 1.02 mol / L.

  After completion of the reaction, crude trimethylgallium is fractionated using a 30 cm × 1.5 cm column packed with glass beads from the reaction mixture in a state where diisoamyl ether is boiling.

By quantifying gallium with an inductively coupled plasma emission spectrometer, 5.92 g (71.5% yield in terms of gallium) of crude trimethylgallium is obtained.
[Example 4] Synthesis of triethylgallium
(1) Synthesis of Ga ₂ Et ₃ I ₃ A magnetic stirrer chip was placed in a 100 mL glass autoclave purged with nitrogen, and 5.00 g (72 mmol) gallium having a purity of 6N and 24.11 g (155 mmol) ethyl iodide at room temperature. Is introduced. The inside of the autoclave is heated to 90 ° C. and stirred for 24 hours. All the gallium is dissolved and becomes a yellow liquid. The identification of the product is J. et al. S. Gynane, I .; J. et al. Worral, J. et al. Organomet. Chem. , 40 , C59 (1972) with reference to the description of IR spectrum and Raman spectrum.
(2) Synthesis of ethylmagnesium iodide To a 300 mL capacity four-necked flask purged with nitrogen is added 4.17 g (174 mmol) of 3N-purified magnesium having a purity of 3N at room temperature and 68 mL of diethyl ether sufficiently dehydrated with molecular sieves. After attaching a dry ice condenser and adjusting the internal temperature to 20 ° C., 29.65 g (190 mmol) of ethyl iodide is dropped into the solution in the flask over about 2 hours. During this time, the temperature in the flask is adjusted so that diethyl ether boils lightly. After completion of dropping, the mixture is stirred at room temperature for 12 hours.

The resulting reaction mixture is filtered. As a result of measurement by the Gilman double titration method (the method described in H. Gilman, FK Cantledge, J. Organomet. Chem., 2 , 447 (1964)), it was found to be 98.0% yield (171 mmol). Ethyl magnesium bromide is formed.
(3) Reaction of Ga ₂ Et ₃ I ₃ and ethyl magnesium iodide In a 300 mL capacity four-necked flask purged with nitrogen, the total amount of Ga ₂ Et ₃ I ₃ synthesized as described above and molecular sieves are sufficient. Add 48 mL of dehydrated diethyl ether. A dry ice condenser is attached to the flask and the internal temperature is adjusted to 20 ° C., and then a diethyl ether solution equivalent to 56 g (114 mmol) of ethylmagnesium iodide synthesized as described above is slowly added dropwise. After completion of dropping, the mixture is heated and refluxed for 6 hours.

Nitrogen used during the synthesis of Ga ₂ Et ₃ I ₃ , ethylmagnesium iodide and trialkylgallium has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The Ga ₂ Et ₃ I ₃ concentration in the solvent at the end of the preparation of ethyl magnesium iodide is 0.30 mol / L, and the concentration of ethyl magnesium iodide is 0.96 mol / L.

  After completion of the reaction, diethyl ether is first fractionated at normal pressure using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture. Next, crude triethylgallium is fractionally distilled at a reduced pressure of 100 Torr (79 to 81 ° C.).

By gallium quantification using an inductively coupled plasma optical emission spectrometer, 7.90 g (69.9% yield in terms of gallium) of crude triethylgallium is obtained.
[Example 5] Synthesis of trimethylgallium
Reaction of Ga ₂ Et ₃ I ₃ and Ethyl Lithium A nitrogen-substituted 300 mL four-necked flask was charged with total amount of Ga ₂ Et ₃ I ₃ synthesized in Example 4 and 48 mL of diethyl ether sufficiently dehydrated with molecular sieves at room temperature. Add. A dry ice condenser is attached to the flask and the internal temperature is adjusted to 20 ° C., and then 72 mL (equivalent to 72 mmol) of a commercially available diethyl ether solution of ethyllithium (1.0 mol / L) is slowly added dropwise. After completion of dropping, the mixture is heated and refluxed for 6 hours.

The nitrogen used has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The Ga ₂ Et ₃ I ₃ concentration in the solvent at the end of the ethyllithium charge is 0.27 mol / L, and the ethyllithium concentration is 0.54 mol / L.

After completion of the reaction, diethyl ether is first fractionated at normal pressure using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture. Next, crude triethylgallium is fractionally distilled at a reduced pressure of 100 Torr (79 to 81 ° C.).
9.20 g (81.5% yield in terms of gallium) of crude triethylgallium is obtained by gallium quantification using an inductively coupled plasma emission spectrometer.
[Example 6] Synthesis of trimethylgallium
Reaction of Ga ₂ Me ₃ I ₃ and dimethylzinc A nitrogen-substituted (100) mL glass autoclave was charged with a magnetic stirrer chip and synthesized in Example 1 at room temperature, and molecular sieves were added to the total amount of Ga ₂ Me ₃ I _3. Add 50 mL of toluene dehydrated sufficiently. Next, 5.73 g (60 mmol) of commercially available dimethyl zinc is added, and the mixture is heated and stirred at 120 ° C. for 20 hours.

The nitrogen used has a purity of 6N, a dew point of −110 ° C., and an oxygen concentration of 1 ppb. The Ga ₂ Me ₃ I ₃ concentration in the solvent at the end of the dimethylzinc charge is (0.52) moL / L, and the dimethylzinc concentration is (0.87) moL / L.

After completion of the reaction, crude trimethylgallium is fractionated using a 30 cm long, 1.5 cm diameter column filled with glass beads from the reaction mixture in a state where toluene is boiling.
By gallium quantification with an inductively coupled plasma emission spectrometer, 7.08 g (85.7% yield in terms of gallium) of crude triethylgallium is obtained.

From the above, it can be seen that trialkylgallium can be obtained in a yield of about 70% or more, which is practically sufficient, by alkylating the halogenated alkylgallium compound with an alkyl metal compound.

[Example 7] 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 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 (4)

The following general formula (1)
_{Ga 2 R m X 6-m} (1)
(In the formula, R represents a methyl group or an ethyl group, X represents a halogen atom, and m represents an integer of 1 to 5).
A trialkylgallium compound by reacting at least one halogenated alkylgallium compound represented by the formula: at least one alkyl metal compound selected from the group consisting of a lithium-containing compound, a magnesium-containing compound, and a zinc-containing compound. A method of producing trialkylgallium for synthesizing At least one alkyl metal compound, alkyl lithium compounds, alkylmagnesium halide compounds, method according to claim 1 is at least one compound selected from the group consisting 及 beauty dialkylzinc compound. The method according to claim 1 or 2 , wherein the at least one alkyl metal compound is at least one compound selected from the group consisting of a methyl metal compound and an ethyl metal compound. Relative to 1 mol of the compound represented by the general formula (1), one of the at least one alkyl metal compound in the stoichiometric composition ratio and used 0.5 to 2 times the number of moles of formed of claims 1-3 The method of crab.