JP4900966B2 - Method for producing gallium hydride gas and method for producing gallium nitride crystal - Google Patents

Description

  The present invention relates to a method for producing a gallium hydride gas and a method for producing a gallium nitride crystal using the gallium hydride gas.

Gallium nitride (GaN) crystals are used for light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LD), and for electronic devices such as field-effect transistors (FETs) and high-electron mobility transistors (HEMTs). Application is expected. In general, in order to obtain high-quality crystals, a method is used in which the crystals are once melted and then recrystallized. However, since gallium nitride needs to be melted at a very high temperature, it is decomposed into gallium (Ga) and nitrogen (N) at normal pressure. In order to obtain a high-purity gallium nitride crystal while preventing such decomposition, conditions of high temperature and high pressure (2530 ° C., 45000 atmospheres or more) are required. Therefore, in order to grow a gallium nitride crystal industrially, conventionally, a metal organic vapor phase epitaxy (MOVPE) method or a hydride vapor phase epitaxy (HVPE) method is used. ₃ ) etc. are used.
The following is a reaction formula for generating a gallium nitride crystal from trimethylgallium and ammonia (NH ₃ ) in the MOCVD method.
(CH ₃ ) 3 Ga + NH ₃ → GaN + 3CH ₄
The following is a reaction formula for producing gallium chloride (GaCl ₃ ) from gallium and hydrogen chloride (HCl) and producing a gallium nitride crystal from the gallium chloride and ammonia in the HVPE method.
Ga + 3HCl → GaCl ₃ + 3 / 2H ₂
GaCl ₃ + NH ₃ → GaN + 3HCl
However, in the MOVPE method using a gallium raw material containing carbon such as trimethylgallium, carbon is mixed in the gallium nitride crystal. Since carbon exhibits both n-type and p-type characteristics, the carrier concentration in a gallium nitride crystal as a semiconductor becomes unstable. In the HVPE method using gallium chloride, the crystal growth apparatus is corroded because chloride is generated.

  As a crystal growth method that replaces the above method, it has been studied to grow a gallium nitride crystal in a melt using a sodium flux method. However, in this method, sodium (Na) may be mixed as an impurity in the crystal.

Therefore, it has been studied to generate a gallium hydride gas by reacting gallium metal and hydrogen (H ₂ ), and to grow a gallium nitride single crystal by reacting the generated gallium hydride gas and ammonia ( Non-patent document 1).

In order to give n-type electrical characteristics to the gallium nitride crystal, silicon (Si) is generally used as an n-type dopant. However, in order to dope silicon, it is necessary to use silane (SiH ₄ ) gas, which is dangerous to handle.

Therefore, when a gallium nitride crystal is grown by the HVPE method or the like, the crystal is doped with oxygen by mixing water (H ₂ O) or oxygen (O ₂ ) into a reaction gas containing chloride, thereby forming an n-type. It has been proposed to have the following electrical characteristics (see Patent Document 1).

Examination of Effects of H2 Concentration in Reactant Gas on GaN Growth by Gallium Hydride Vapor Phase Epitaxy (Mamoru Imade, Fumio Kawamura, Minoru Kawahara, Masashi Yoshimura, Yusuke Mori and Takatomo Sasaki, Japanese Journal of Applied Physics, Vol.45 (2006), (No.33 pp L878-L880) JP 2000-44400 A

  In the conventional reaction in which gallium hydride gas is generated from gallium metal and hydrogen, since the change in free energy is disadvantageous to the reaction, the reaction does not proceed easily, and the amount of gallium hydride gas generated is reduced. Further, since gallium has a low melting point of about 30 ° C. and becomes a liquid at the reaction temperature with hydrogen, the contact area with hydrogen gas is reduced, and the amount of gallium hydride gas generated is also reduced. Thus, when the amount of gallium hydride gas generated is small, the growth rate of the gallium nitride crystal becomes slow. Therefore, it is conceivable to increase the contact area with the hydrogen gas by holding the gallium metal by the carrier. However, since the held gallium metal melts and aggregates due to the high reaction temperature, the contact area cannot be secured, and impurities may be generated by the decomposition of the support and reaction with hydrogen.

  When a gallium nitride crystal is grown by a conventional HVPE method or the like, oxygen is added to the gallium nitride crystal as an n-type dopant by mixing water or oxygen into a reaction gas containing chloride. Equipment may corrode.

  An object of this invention is to provide the manufacturing method of the gallium hydride gas which can contribute to solving the above subjects, and the manufacturing method of a gallium nitride crystal.

The method for producing gallium hydride gas according to the present invention includes a step of generating gallium hydride gas by reacting gallium oxide (Ga ₂ O ₃ ) with hydrogen. In this case, hydrogen gas may be introduced into a reaction vessel containing solid gallium oxide, and gallium oxide and hydrogen may be reacted in the reaction vessel. In order to ensure the amount of gallium hydride gas generated, the reaction between gallium oxide and hydrogen is performed at a high temperature, and in order to prevent decomposition of the generated gallium hydride gas, it is preferable to limit the upper limit temperature, The reaction is preferably performed at a temperature of 600 ° C to 1200 ° C, more preferably 700 ° C to 1100 ° C, and even more preferably 800 ° C to 1000 ° C. Specific examples of the gallium hydride gas generated in this way include, for example, GaH ₃ and Ga ₂ H ₆ .
The present invention is based on the discovery that a gallium nitride crystal can be grown by generating gallium hydride gas by reducing gallium oxide with hydrogen and reacting the gallium hydride gas with a nitrogen-containing compound. . That is, a reaction formula for generating gallium hydride gas by reacting gallium oxide with hydrogen is expressed as follows.
XGa ₂ O ₃ + (Y + 3X) H ₂ → 2Ga _X H _Y + 3XH ₂ O
Here, X = 1 to 2, Y = 1 to 6 in Ga _X H _Y.
On the other hand, a reaction equation for generating gallium hydride gas by reacting gallium metal with hydrogen is represented by the following.
XGa + 1 / 2YH ₂ → Ga _X H _Y
The reaction between gallium oxide and hydrogen generates not only gallium hydride but also water as a by-product, so free energy compared to the conventional case where gallium hydride gas is generated by the reaction between gallium metal and hydrogen. Since the change in is advantageous for the reaction, the reaction is likely to proceed.

  In addition, gallium metal has a low melting point and thus becomes liquid at the reaction temperature with hydrogen, whereas gallium oxide has a high melting point of about 1900 ° C. and therefore becomes solid even at the reaction temperature with hydrogen. Thereby, the contact area of a gallium oxide and hydrogen gas can be enlarged, without using a thing like a support body. Therefore, it is preferable to react gallium oxide with hydrogen in the form of powder or pellets in order to increase the contact area between gallium oxide and hydrogen gas. When gallium oxide is powdered, for example, the median particle size is set to 1 to 100 μm. In addition, by making powdered gallium oxide into a pellet and increasing the bulk density, the amount charged into the contact area with hydrogen gas can be increased. When gallium oxide is formed into a pellet, it is formed into a cylindrical shape having a diameter of 1 to 10 mm, for example.

  The method for producing a gallium nitride crystal of the present invention comprises a step of growing a gallium nitride crystal by reacting the gallium hydride gas produced according to the present invention with a nitrogen-containing compound. Since the reaction between gallium oxide and hydrogen is easier to proceed than the conventional reaction between gallium metal and hydrogen, the growth rate of the gallium nitride crystal can be improved. The gallium nitride is epitaxially grown on a crystal growth substrate, whereby a single crystal can be obtained. As the crystal growth substrate, for example, a sapphire, silicon carbide, gallium nitride, gallium arsenide, silicon, gallium oxide, or zinc oxide substrate can be used. In order to promote the decomposition of nitrogen-containing compounds and ensure crystal quality, the reaction between gallium hydride gas and nitrogen-containing compounds is performed at a high temperature, and the maximum temperature is limited to prevent decomposition of the grown gallium nitride crystals. Therefore, the reaction is preferably performed at a temperature of 800 ° C. to 1200 ° C., more preferably 900 ° C. to 1100 ° C.

In the method for producing a gallium nitride crystal according to the present invention, oxygen derived from water molecules generated with the generation of the gallium hydride gas is doped into the gallium nitride crystal as an n-type dopant in the step of growing the gallium nitride crystal. It is preferable to do this. In order to secure oxygen derived from the water molecules, it is preferable that the reaction between gallium oxide and hydrogen and the reaction between gallium hydride gas and nitrogen-containing compound are performed at a high temperature as described above.
Thereby, oxygen can be doped into the gallium nitride crystal as an n-type dopant without supplying a new oxygen source from the outside, so that no chloride is generated as in the conventional HVPE method. In the present invention, since the gallium nitride crystal raw material does not contain carbon, the carbon concentration as an impurity in the reaction region can be extremely low, and the carbon concentration in the gallium nitride crystal can be reduced to 1 × 10 ¹⁷ cm ^−3. It is possible to: As a result, in a gallium nitride crystal as a semiconductor, oxygen can perform the function as an n-type carrier according to a substantially concentration without being inhibited by carbon, and obtain a carrier concentration according to the amount of oxygen to be doped. Can do. In this case, the oxygen concentration in the gallium nitride crystal is preferably 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ .

  An apparatus used for growing a gallium nitride crystal according to the present invention comprises a first reaction vessel, a second reaction vessel, a gas flow path connecting both reaction vessels, and a heating device in each reaction vessel, A solid gallium oxide mounting portion, a hydrogen gas inlet, and a gallium hydride gas outlet connected to the gas flow path are provided in the first reaction vessel, and crystal growth is provided in the second reaction vessel. It is preferable that a substrate mounting portion, a gallium hydride gas introduction port connected to the gas flow path, a nitrogen-containing compound gas introduction port, and an exhaust gas discharge port are provided. Thereby, gallium oxide and hydrogen are reacted at a high temperature in the first reaction vessel, and the generated gallium hydride gas and a nitrogen-containing compound are reacted at a high temperature in the second reaction vessel to grow a gallium nitride crystal on the substrate. be able to. The gallium hydride gas generated in the first reaction vessel is preferably conveyed to the second reaction vessel by an inert gas that does not react with gallium hydride and hydrogen. It is preferable that the temperature in each reaction vessel can be independently controlled by a heating device. Gallium hydride gas inlet and nitrogen-containing compound gas inlet so that the gallium hydride gas flows along the surface of the crystal growth substrate and the nitrogen-containing compound flows so as to be sprayed onto the surface of the crystal growth substrate. Is preferably disposed relative to the crystal growth substrate.

  According to the present invention, the generation reaction of gallium hydride gas can be promoted, the growth rate of the gallium nitride crystal can be improved, and by doping oxygen into the gallium nitride crystal as an n-type dopant, impurities having a desired carrier concentration can be produced. Less gallium nitride crystals can be obtained without causing corrosion of the crystal growth apparatus.

  The crystal growth apparatus 1 according to the embodiment of the present invention shown in FIG. 1 includes a first reaction vessel 2 for generating gallium hydride gas, a second reaction vessel 3 for growing a gallium nitride crystal, and both reactions. Pipes constituting the gas flow path 4 connecting the containers 2 and 3, a first heating device 5 for heating the inside of the first reaction vessel 2, a second heating device 6 for heating the inside of the second reaction vessel 3, and a gas A third heating device 7 for heating the flow path 4 is provided.

The first reaction vessel 2 is configured by covering both ends of the quartz tube 2a with stainless lids 2b and 2b '. The raw material stand 2c provided in the quartz tube 2a is used as a mounting portion for the solid gallium oxide 10. The raw material stand 2c can be composed of, for example, quartz integrated with the quartz tube 2a and a crucible or alumina boat placed thereon. The lids 2b and 2b 'have a flange portion protruding from the outer periphery of the quartz tube 2a, and are cooled by cooling water flowing through a water channel formed there, and a sealing O-ring between the lids 2b and 2b' and the quartz tube 2a. Deterioration is prevented. One end of a pipe inserted into one lid 2b is a gas inlet 2d, and one end of the pipe is connected to a supply source of hydrogen gas and carrier gas. One end of the pipe inserted into the other lid 2b ′ is a gas outlet 2e, and the pipe constituting the gas outlet 2e constitutes the gas flow path 4. Hydrogen gas diluted with carrier gas is introduced into the first reaction vessel 2 from the gas inlet 2d, and gallium hydride gas generated in the first reaction vessel 2 flows out of the gas outlet 2e together with the carrier gas. As the carrier gas, it is preferable to use an inert gas such as argon (Ar), nitrogen (N ₂ ), and helium (He) that does not react with gallium hydride and hydrogen.

  The second reaction vessel 3 is configured by covering both ends of the quartz tube 3a with stainless lids 3b and 3b '. A susceptor 3 c provided in the quartz tube 3 a is used as a placement portion for the crystal growth substrate 11. The type of the crystal growth substrate 11 is not particularly limited, although a sapphire substrate is used for epitaxial growth of gallium nitride in this embodiment. The structure of the susceptor 3c is not particularly limited. For example, a well-known structure that makes the film thickness uniform by supporting the substrate 11 so as to be inclined with respect to the horizontal direction or rotating the substrate 11 can be employed. The lids 3b and 3b 'have flange portions projecting from the outer periphery of the quartz tube 3a, and are cooled by cooling water flowing through the water passages formed there, and a sealing O-ring between the lids 3b and 3b' and the quartz tube 3a. Deterioration is prevented. A pipe whose one end is the gas outlet 2e is inserted into one lid 3b, and the other end of the pipe is a first gas inlet 3d. Also, a pipe different from the pipe is inserted into one lid 3b, one end of the pipe is a second gas inlet 3e, and the other end is connected to a nitrogen-containing compound supply source. In this embodiment, ammonia gas is used as the nitrogen-containing compound. One end of the pipe inserted into the other lid 3b 'is a gas discharge port 3f. Thereby, the gallium hydride gas generated in the first reaction vessel 2 is introduced into the second reaction vessel 3 from the first gas introduction port 3d together with the carrier gas. The nitrogen-containing compound is introduced into the second reaction vessel 3 from the second gas inlet 3e. The gas that did not participate in the crystal growth reaction in the second reaction vessel 3 and the by-product gas of the crystal growth reaction flow out as exhaust gas from the gas discharge port 3f together with the carrier gas.

  As shown in FIGS. 2 and 3, the first gas introduction port 3d is disposed laterally away from the crystal growth substrate 11 placed on the susceptor 3c, and the second gas introduction port 3e is directed upward. Placed apart. Thus, the gallium hydride gas introduced from the first gas introduction port 3d flows along the surface of the substrate 1, and the nitrogen-containing compound introduced from the second gas introduction port 3e is sprayed on the surface of the substrate 1. Flowing. Thereby, poor mixing of the gallium hydride gas and the nitrogen-containing compound on the substrate 11 can be prevented, and the quality of gallium nitride can be prevented from being lowered and yellowing due to insufficient nitrogen.

  The configuration of each of the heating devices 5, 6, and 7 is not particularly limited, and for example, an alumina heater or a high frequency heating device can be used. Each of the heating devices 5, 6 and 7 can be controlled independently so that the internal temperature of each reaction vessel 2 and 3 and the temperature of the gas flow path 4 can be controlled independently.

  The flow rate of the hydrogen gas introduced into the first reaction vessel 2, the flow rate of the carrier gas, and the flow rate of the nitrogen-containing compound introduced into the second reaction vessel 3 can be controlled independently by a non-illustrated mass flow controller (MFC). It is said that. Further, the gas discharge port 3f is connected to a suction pump (not shown) so that the inside of the apparatus 1 can be purged or depressurized. The gallium nitride crystal is preferably grown under normal pressure or reduced pressure, and in particular, by reducing the pressure, it is possible to prevent the crystal growth from being suppressed due to gas retention on the growth substrate and to improve the growth rate of the crystal.

  The first reaction vessel 2 and the second reaction vessel 3 can be opened and closed by providing, for example, an open / close valve for the gas flow path 4 so that the first reaction vessel 2 can be opened independently to replenish gallium oxide. Also good. Thereby, the gallium oxide 10 can be additionally charged into the first reaction vessel 2 during the crystal growth in the second reaction vessel 3, and the crystal growth can be continuously performed.

  According to the crystal growth apparatus 1, the solid gallium oxide 10 is placed on the raw material table 2 c in the first reaction vessel 2, and hydrogen gas diluted with a carrier gas is introduced into the first reaction vessel 2. By reacting gallium oxide 10 and hydrogen in the first reaction vessel 2, gallium hydride gas can be generated in the first reaction vessel 2. By reacting the gallium oxide 10 with hydrogen in the form of powder or pellets, the contact area with the hydrogen gas can be increased without using a carrier, and the amount charged on the raw material table 2c is increased by using pellets. Can be made.

  When the temperature in the first reaction vessel 2 decreases, the amount of gallium hydride gas generated decreases, and when it increases, the generated gallium hydride gas decomposes into gallium and hydrogen. For this reason, the temperature in the first reaction vessel 2 is preferably set to 600 ° C. to 1200 ° C. by the first heating device 5, more preferably 700 ° C. to 1100 ° C., and further preferably 800 ° C. to 1000 ° C. .

  When the concentration of hydrogen gas to be reacted with gallium oxide in the first reaction vessel 2 decreases, the amount of gallium hydride gas generated decreases, and when it increases, excess hydrogen reacts with the gallium nitride crystal growing in the second reaction vessel 3. As a result, the growth rate of the gallium nitride crystal decreases. Therefore, the hydrogen gas concentration introduced into the first reaction vessel 2 is preferably 1 to 50 vol%, more preferably 5 to 30 vol%.

  Gallium hydride gas generated in the first reaction vessel 2 is introduced into the second reaction vessel 3 from the first gas introduction port 3d through the gas flow path 4, and ammonia gas as a nitrogen-containing compound from the second gas introduction port 3e. Is introduced into the second reaction vessel 3, and the gallium hydride gas and the ammonia gas are reacted to grow a gallium nitride crystal on the substrate 11. The ammonia gas may be diluted using, for example, argon, nitrogen, helium, hydrogen, or the like. In this crystal growth step, oxygen derived from water molecules generated with the generation of gallium hydride gas in the first reaction vessel 2 is doped into the gallium nitride crystal as an n-type dopant. Since the reaction between gallium oxide 10 and hydrogen is easier than the conventional reaction between gallium metal and hydrogen, the growth rate of the gallium nitride crystal can be improved.

  When the temperature in the second reaction vessel 3 is low, the decomposition of ammonia is suppressed and the generation of nitrogen is suppressed, and the migration of molecules on the substrate 11 is suppressed. The gallium nitride crystal is decomposed into gallium and nitrogen, and the crystal growth rate becomes slow. Therefore, it is preferable that the temperature in the second reaction vessel 3 is set to 800 ° C. to 1200 ° C., more preferably 900 ° C. to 1100 ° C. by the second heating device 6.

  Since the third heating device 7 heats the gas flow path 4, it is possible to prevent a temperature drop of the gallium hydride gas in the gas flow path 4.

  If the ratio M1 / M2 of the molar concentration M1 of ammonia gas introduced into the second reaction vessel 3 and the molar concentration M2 of gallium hydride gas diluted with the carrier gas introduced into the second reaction vessel 3 is low, nitrogen Due to the shortage, defects in the gallium nitride crystal increase and yellow, and if it is high, the gallium nitride crystal is generated even on the substrate 11 and the growth rate of the gallium nitride crystal on the substrate 11 decreases. Therefore, the molar concentration ratio M1 / M2 is preferably 100 to 10,000, and more preferably 3000 to 6000.

  By doping the gallium nitride crystal with oxygen derived from water molecules as the gallium hydride gas is generated in the first reaction vessel 2 as an n-type dopant, it is not necessary to supply a new oxygen source from the outside. No chloride is generated as in the HVPE method. In order to secure oxygen derived from water molecules as a dopant, it is preferable to perform the reaction between gallium oxide and hydrogen and the reaction between gallium hydride gas and nitrogen-containing compound at a high temperature as described above.

Further, according to the above embodiment, since the raw material of the gallium nitride crystal does not contain carbon, the impurity concentration of carbon in the reaction region of gallium hydride and the nitrogen-containing compound can be extremely low, The carbon concentration can be reduced to 1 × 10 ¹⁷ cm ⁻³ or less. Thereby, in gallium nitride as a semiconductor, oxygen can exhibit the function as an n-type carrier according to a substantially concentration without being inhibited by carbon, and a carrier concentration corresponding to the amount of oxygen to be doped can be obtained. it can. On the oxygen doped into a gallium nitride crystal functions as an n-type dopant is preferably the oxygen concentration is ^{1 × 10 16 cm -3 ~1 ×} 10 20 cm -3 in the crystal, 1 × 10 ¹⁸ ~ More preferably, it is 1 × 10 ²⁰ cm ⁻³ . The concentration of the doped oxygen can be controlled by adjusting the concentration of the diluted hydrogen gas introduced into the first reaction vessel 2. For example, if the hydrogen gas concentration is increased, the concentration of the doped oxygen is increased. If the gas concentration is lowered, the oxygen concentration to be doped tends to be lowered.

When a gallium nitride crystal is grown by the crystal growth apparatus 1 of the above embodiment, gallium oxide vapor or gallium vapor generated by decomposition of gallium oxide is present in the first reaction vessel 2, and these are It was confirmed whether or not it was involved in the growth of gallium nitride single crystals. That is, the gallium nitride crystal was grown in a state where the gas flow path 4 was kept at room temperature without heating so that only the gallium hydride gas generated in the first reaction vessel 2 reached the second reaction vessel 3. As a result, gallium nitride crystals grew on the substrate 11, and the growth rate did not change significantly.
From this, it was confirmed that only the gallium hydride gas generated in the first reaction vessel 2 was involved in the growth of gallium nitride crystals in the second reaction vessel 3.

  Using the crystal growth apparatus 1 of the above embodiment, the oxygen-doped gallium nitride crystals according to Examples 1 to 3 grown on the substrate 11 according to the present invention and the oxygen-doped according to the comparative example using gallium metal instead of gallium oxide The gallium nitride crystal was comparatively evaluated using X-ray diffraction (XRD), scanning electron microscope (SEM), and secondary ion mass spectrometry (SIMS).

The implementation conditions of Example 1 were as follows.
1.0 g of gallium oxide powder having a purity of 99.999 wt% was placed in a quartz crucible constituting the raw material table 2 c of the first reaction vessel 2. The crucible size was 30 mm in inner diameter and 10 mm in depth. A sapphire substrate as a crystal growth substrate 11 was placed on the susceptor 3c of the second reaction vessel 3 with the C surface (0001 surface) as the upper surface. The inside of the apparatus 1 is evacuated, and the impurities in the apparatus 1 are removed by substituting the inside air of the apparatus 1 with an inert gas (argon gas). The temperature inside the one reaction vessel 2 is raised to 970 ° C., the temperature inside the second reaction vessel 3 is raised to 1100 ° C. by the alumina heater which is the second heating device 6, and the gas flow path is caused by the alumina heater which is the third heating device 7. 4 was heated to 700 ° C. After the temperature in the apparatus 1 is increased, hydrogen gas diluted to a concentration of 5 vol% with argon gas as a carrier gas is introduced into the first reaction vessel 2 at a flow rate of 2000 ml / min, and the purity is 99.9995 vol% as a nitrogen-containing compound. Of ammonia gas was introduced into the second reaction vessel 3 at a flow rate of 3000 ml / min. As a result, the operation of generating gallium hydride gas in the first reaction vessel 2 and growing gallium nitride crystals on the substrate 11 in the second reaction vessel 3 was carried out for 2 hours.

  The execution conditions of Example 2 were the same as Example 1 except that the concentration of diluted hydrogen gas was 10 vol%.

  The implementation conditions of Example 3 were the same as those of Example 2 except that the pressure in the apparatus 1 was slightly reduced to 66.66 kPa (500 torr) and pellets were formed so that gallium oxide was not easily scattered.

  The implementation condition of Comparative Example 1 was that gallium metal having a purity of 99.999 wt% was used instead of gallium oxide, and the weight of gallium metal was changed to 0.7 g so that the amount of gallium was equal to 1.0 g of gallium oxide. Was the same as in Example 3.

(Crystallinity evaluation)
When the gallium nitride crystals grown according to the respective examples and comparative examples were evaluated by X-ray diffraction, each crystal was a single crystal oriented on the C axis of the sapphire substrate.

(Crystal growth rate measurement)
Table 1 below shows the result of calculating the growth rate per hour by measuring the film thickness of the grown gallium nitride single crystal with a scanning electron microscope.

From Table 1 above, the growth rate of Example 2 relative to the growth rate of Example 1 was about 1.3 times. This is because in Example 2, the amount of gallium hydride gas generated was increased by increasing the hydrogen gas concentration.
The growth rate of Example 3 was improved with respect to the growth rate of Example 2. This is because, in Example 3, the apparatus 1 was slightly reduced in pressure to suppress gas stagnation on the substrate 11 and to facilitate crystal growth on the substrate 11.
The growth rate of Example 3 was about 10 times that of Comparative Example 1. This is because the reaction between gallium oxide and hydrogen is easier to proceed than the reaction between gallium metal and hydrogen, and the contact area between gallium oxide and hydrogen gas is larger than the contact area between gallium metal and hydrogen gas. Therefore, the amount of gallium hydride gas generated is large.

(Impurity concentration measurement)
Table 2 below shows the results of measuring the impurity concentration in the grown gallium nitride single crystal by secondary ion mass spectrometry.

As a result of comparing the impurity concentration of the gallium nitride single crystal according to the present invention grown according to Examples 1 to 3 and the impurity concentration of the gallium nitride single crystal grown according to Comparative Example 1, the hydrogen concentration, carbon concentration, and silicon concentration are There was no significant difference, and the carbon concentration was as low as 1 × 10 ¹⁷ cm ⁻³ or less. Further, the concentration of oxygen functioning as an n-type dopant is 1 × 10 ²⁰ cm ⁻³ in Examples 1 to 3 compared to 2 × 10 ¹⁷ cm ⁻³ in Comparative Example 1, which is appropriate. The dopant concentration. That is, according to the present invention, it has been confirmed that the concentration of oxygen functioning as an n-type dopant in the gallium nitride single crystal can be made higher than that of the comparative example in a state where other impurity concentrations are lowered.

Configuration explanatory diagram of a crystal growth apparatus according to an embodiment of the present invention The figure which shows the relative arrangement | positioning of the board | substrate for crystal growth which concerns on embodiment of this invention, and a gas inlet III-III sectional view of FIG.

Explanation of symbols

10 ... Gallium oxide 11 ... Substrate for crystal growth

Claims (4)

  A method for producing gallium hydride gas comprising a step of generating gallium hydride gas by reacting gallium oxide with hydrogen.   The method for producing gallium hydride gas according to claim 1, wherein the gallium oxide is reacted with the hydrogen in a powder or pellet state.   A method for producing a gallium nitride crystal comprising a step of growing a gallium nitride crystal by reacting the gallium hydride gas produced by the method according to claim 1 or 2 with a nitrogen-containing compound.   4. The gallium nitride crystal according to claim 3, wherein oxygen derived from water molecules generated along with the generation of the gallium hydride gas is doped into the gallium nitride crystal as an n-type dopant in the step of growing the gallium nitride crystal. Production method.

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