JP2015127298A - Gallium nitride crystal, crystal substrate, and nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an n-type group III nitride single crystal which has high quality and low resistance through simple processes.SOLUTION: A manufacturing method includes: a material feeding process of feeding a substance including at least a group III element, alkali metal, and boron oxide into a reaction vessel; a melting process of melting the boron oxide by heating the reaction vessel up to the fusion point of the boron oxide; a mixed melt forming process of forming a mixed melt including the group III element, the alkali metal, and the boron oxide in the reaction vessel by heating the reaction vessel up to the crystal growth temperature of the group III nitride; a nitrogen dissolving process of dissolving nitrogen in the mixed melt by bringing a gas including the nitrogen into contact with the mixed melt; and a crystal growth process of growing an n-type group III nitride single crystal doped with oxygen in the boron oxide from the group III element, nitrogen, and oxygen dissolved in the mixed melt.

Description

  The present invention relates to a method for producing an n-type group III nitride single crystal, an n-type group III nitride single crystal, and a crystal substrate.

  At present, an InGaAlN-based (Group III nitride) device used as a light source that emits ultraviolet light, violet light, blue light, and green light is formed on a sapphire substrate or silicon carbide (SiC) substrate by MO-CVD (organic). Most of them are manufactured by a manufacturing method including a step of crystal growth of a group III nitride single crystal using a metal chemical vapor deposition method), an MBE method (molecular beam crystal growth method) or the like.

  The problem with using a sapphire substrate or SiC substrate as the substrate is that there are many crystal defects due to the large difference in thermal expansion coefficient and lattice constant between the substrate and group III nitride. Is mentioned. For this reason, there exists a possibility that device characteristics may deteriorate, for example, the lifetime of the group III nitride device which is a light emitting device may become short, or operating power may become large.

  In order to solve these problems, the substrate material and the crystal material grown on the substrate are made the same, and a group III nitride single crystal substrate such as a gallium nitride (GaN) substrate is used for group III nitridation. It is most appropriate to perform crystal growth on a single crystal substrate.

  As a manufacturing method of a GaN substrate, conventionally, after a GaN thick film is grown by a halogenated vapor phase epitaxy (HVPE) method on a base substrate made of a different material such as a sapphire substrate or a GaAs substrate, A GaN substrate having a diameter (φ) of about 2 inches has been manufactured by separating the GaN thick film.

However, in the HVPE method, since a GaN single crystal is heteroepitaxially grown on a base substrate composed of a different material, the GaN single crystal and the base substrate inevitably have a difference in thermal expansion coefficient or lattice mismatch. May occur. Therefore, the GaN substrate manufactured by the HVPE method has a dislocation density as high as about 10 ⁶ cm ^−2, or the GaN substrate warps due to a difference in thermal expansion coefficient from the base substrate. There's a problem. Therefore, a manufacturing method capable of further improving the quality of the GaN substrate is desired.

As one of the methods for producing a high-quality GaN substrate, a flux method in which nitrogen is dissolved in a mixed melt of sodium (Na) and gallium (Ga) to grow a GaN single crystal has been researched and developed. . According to the flux method, it is possible to grow a GaN single crystal at a relatively low temperature of 700 ° C. to 900 ° C., and the pressure in the reaction vessel is relatively low at about 100 kg / cm ^2. It is practical as a manufacturing method.

In Non-Patent Document 1, sodium azide (NaN ₃ ) and Ga are used as raw materials, nitrogen is sealed in a stainless steel reaction vessel, and the reaction vessel is held at a temperature of 600 ° C. to 800 ° C. for 24 hours to 100 hours. Thus, an example of growing a GaN single crystal has been reported. Patent Document 1 discloses a method for growing a GaN columnar crystal using a needle crystal of aluminum nitride (AlN) as a seed crystal as a method for producing a large GaN crystal by a flux method. Furthermore, Patent Document 2 discloses a method for producing an AlN needle crystal used as a seed crystal. Thus, it is a well-known technique to produce a large GaN crystal by crystal growth of a seed crystal by a flux method.

By the way, when a GaN crystal is used as a substrate for an optical device, it is necessary to form an n-side ohmic electrode on the GaN substrate. Therefore, an n-type GaN semiconductor crystal having an n-type carrier concentration of 10 ¹⁷ cm ⁻³ or more. Is needed. Therefore, it has been studied to grow an n-type GaN crystal by adding (doping) a donor such as oxygen or germanium into the GaN crystal by a flux method.

  However, Patent Documents 5 and 6 have problems that when the amount of germanium doped is increased, the crystal growth rate is reduced, or the absorption of visible light is increased and the device characteristics are deteriorated.

Regarding the addition of oxygen, for example, Patent Document 3 discloses a technique of doping a Group III nitride crystal with about 2 × 10 ¹⁷ cm ⁻³ of oxygen using sodium oxide (Na ₂ O) or oxygen gas as a dopant. Yes. Patent Document 4 discloses a technique of doping oxygen of about 10 ¹⁸ to 10 ²⁰ cm ⁻³ by mixing oxygen and moisture into the atmosphere gas in the glove box at the time of raw material charging.

Regarding the addition of germanium, for example, Patent Document 5 discloses a technique of adding germanium of about 2 × 10 ¹⁹ cm ⁻³ to a group III nitride. In Patent Document 6, by adding carbon and germanium simultaneously, germanium of 2 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less is doped, and the electron concentration is 5 × 10 ¹⁹ cm ^−. A technique for producing a low-resistance GaN crystal of about ³ is disclosed.

  However, Patent Document 3 has a problem that crystals having a sufficiently high carrier concentration cannot be obtained, and it is difficult to form a low-resistance ohmic electrode. Moreover, in patent document 4, there exists a subject that a manufacturing process is complicated, such as enclosing oxygen and a water | moisture content in a reaction container in a glove box, and sealing a container. In addition, since the atmosphere of the glove box is temporarily deteriorated, there is a problem that the life of the catalyst for removing oxygen and moisture is shortened, and there is also a problem that it is expensive when mass-producing crystals.

  Thus, in the prior art, oxygen is doped using a gas or an oxide having a melting point higher than the crystal growth temperature. Therefore, it is difficult to efficiently make a crystal having a high carrier concentration by doping oxygen into the crystal. There is a problem. Moreover, in order to obtain a crystal with a high carrier concentration, there is a problem that the apparatus and the manufacturing process become complicated.

  The present invention has been made in view of the above, and an object thereof is to produce an n-type group III nitride single crystal having high quality and low resistance by a simple process.

  In order to solve the above-described problems and achieve the object, a method for producing an n-type group III nitride single crystal according to the present invention includes a substance containing at least a group III element, an alkali metal, A material charging step for charging boron, a melting step for melting the boron oxide by heating the reaction vessel to the melting point of the boron oxide, and heating the reaction vessel to the crystal growth temperature of the group III nitride A mixed melt forming step of forming a mixed melt containing the group III element, the alkali metal, and the boron oxide in the reaction vessel, and a gas containing nitrogen in the mixed melt. From the nitrogen dissolution step of dissolving nitrogen in the mixed melt, the group III element dissolved in the mixed melt, the nitrogen, and oxygen in the boron oxide. There characterized in that it contains crystals and growth step the doped n-type Group III nitride single crystal is grown as a donor, the.

  The n-type group III nitride single crystal of the present invention is an n-type group III nitride single crystal produced by the above-described production method.

  Furthermore, the n-type group III nitride crystal substrate of the present invention is an n-type group III nitride crystal substrate manufactured by processing the above-described n-type group III nitride single crystal.

  According to the present invention, by introducing boron oxide having a melting point lower than the crystal growth temperature of the group III nitride (eg, gallium nitride) into the reaction vessel, the crystal can be easily doped with oxygen. . Therefore, it is possible to efficiently dope oxygen into the crystal by a simple process and to produce an n-type group III nitride single crystal having a high carrier concentration and low resistance.

FIG. 1 is a schematic diagram showing a configuration example of a crystal manufacturing apparatus for manufacturing an n-type group III nitride single crystal according to the present embodiment. FIG. 2 is a schematic diagram for explaining the c-axis and c-plane of a group III nitride single crystal. FIG. 3 is a schematic diagram for explaining the c-plane. FIG. 4 is a process diagram showing a manufacturing process for manufacturing the crystal substrate according to the present embodiment. FIG. 5 is a schematic diagram illustrating the configuration of the crystal manufacturing apparatus according to the third embodiment. FIG. 6 is a graph showing the relationship between the amount of boron oxide added and the concentrations of oxygen and boron in the GaN single crystal.

  Hereinafter, a method for producing an n-type group III nitride single crystal, an n-type group III nitride single crystal and a crystal substrate according to the present embodiment will be described in detail with reference to the accompanying drawings. In the following description, the drawings merely schematically show the shape, size, and arrangement of constituent elements to the extent that the invention can be understood, and the present invention is not particularly limited thereby. In addition, similar components shown in a plurality of drawings are denoted by the same reference numerals, and redundant description thereof may be omitted.

<Crystal production equipment>
FIG. 1 is a schematic diagram illustrating a configuration example of a crystal manufacturing apparatus 1 that manufactures an n-type group III nitride single crystal according to the present embodiment.

  As shown in FIG. 1, the crystal manufacturing apparatus 1 includes a pressure vessel 11 made of, for example, stainless steel that can form a closed space. The pressure vessel 11 can be detached from the crystal manufacturing apparatus 1 at the valve 21 portion. Further, the reaction vessel 12 is installed on the installation table 26 in the pressure vessel 11. The reaction vessel 12 is detachable from the installation base 26.

  The reaction vessel 12 is a vessel for holding the needle-like crystal 25 of the group III nitride, which is a seed crystal, and the mixed melt 24 containing raw materials and additives to grow the needle-like crystal 25. A crucible or the like is used. The material of the reaction vessel 12 is not particularly limited, and BN sintered body, nitrides such as Pyrolytic-BN (P-BN), oxides such as alumina, sapphire, yttrium aluminum garnet (YAG), SiC, etc. Carbide etc. can be used. As a preferred embodiment, a BN sintered body crucible is preferably used.

  Further, as shown in FIG. 1, a heater 13 is disposed in the vicinity of the outer periphery of the pressure vessel 11, and the temperature of the mixed melt 24 can be adjusted by heating the pressure vessel 11 and the reaction vessel 12. Any heater 13 can be used as long as it can heat the pressure vessel 11. For example, a two-sided heating muffle furnace can be used.

The pressure vessel 11 is connected to the internal space 23 of the pressure vessel 11 with a gas supply pipe 14 for supplying nitrogen (N ₂ ) gas and dilution gas, which are the raw materials for the group III nitride crystal. The gas supply pipe 14 branches into a nitrogen supply pipe 17 and a dilution gas supply pipe 20, and can be separated by valves 15 and 18, respectively.

  Nitrogen gas is supplied from a nitrogen supply pipe 17 connected to a gas cylinder of nitrogen gas and the like, and after the pressure is adjusted by the pressure control device 16, the nitrogen gas is supplied to the gas supply pipe 14 through the valve 15. On the other hand, the dilution gas (for example, argon gas) is supplied from a dilution gas supply pipe 20 connected to a gas cylinder of the dilution gas and the pressure is adjusted by the pressure control device 19, and then gas is supplied through the valve 18. It is supplied to the supply pipe 14. The nitrogen gas and the dilution gas whose pressures are adjusted in this way are respectively supplied to the gas supply pipe 14 and mixed.

  A mixed gas of nitrogen and dilution gas is supplied from the gas supply pipe 14 through the valve 21 into the pressure resistant container 11. The gas supply pipe 14 is provided with a pressure gauge 22 so that the pressure in the pressure vessel 11 can be adjusted while the pressure gauge 22 monitors the total pressure in the pressure vessel 11.

  In this embodiment, the nitrogen partial pressure can be adjusted by adjusting the pressures of the nitrogen gas and the dilution gas with the valves 15 and 18 and the pressure control devices 16 and 19 as described above. Further, since the total pressure in the pressure vessel 11 can be adjusted, the total pressure in the pressure vessel 11 can be increased to suppress evaporation of alkali metal (for example, sodium) in the reaction vessel 12.

  In addition, although it is desirable to use argon (Ar) gas as dilution gas, it is not limited to this, You may use other inert gas.

<Crystal production method>
(1) Preparation of raw materials, etc. In the crystal manufacturing method of an n-type group III nitride single crystal according to the present embodiment, a needle-like crystal of group III nitride is used as a seed crystal, and the needle-like crystal is obtained by a flux method. By further growing, a single crystal ingot for manufacturing a nitride crystal substrate is manufactured.

  The operation of introducing the raw materials and additives into the reaction vessel 12 is performed by separating the pressure resistant vessel 11 from the valve 21 and placing the separated pressure resistant vessel 11 in a glove box filled with an inert gas such as argon gas.

In the reaction vessel 12, as a constituent material of the mixed melt 24, a substance containing at least a group III element (for example, gallium), an alkali metal (for example, sodium) used as a flux, and boron oxide (for example, boron trioxide) (B ₂ O ₃ )) is added (material input step).

The melting point of boron oxide is lower than the crystal growth temperature of group III nitride (for example, the crystal growth temperature of gallium nitride is about 700 to 900 ° C.). As an example, the melting point of boron trioxide (B ₂ O ₃ ) is 480 ° C. Accordingly, the boron oxide melts at the crystal growth temperature, and oxygen and boron are added to the mixed melt 24 formed in the reaction vessel 12. As a result, when a group III nitride single crystal grows by the flux method, oxygen and boron, which are n-type dopants, are dissolved in the group III nitride single crystal and the n-type group III nitride single crystal is dissolved. Crystal 27 can be grown.

In this embodiment, since boron oxide which is liquid at the crystal growth temperature is used as the oxygen dopant raw material, a gas (for example, oxygen gas) or a high melting point oxide (for example, sodium oxide) is used as the oxygen dopant raw material. Compared with the case of using (Na ₂ O)), oxygen can be easily dissolved in the mixed melt 24. This makes it possible to efficiently dope oxygen into the crystal, efficiently increase the oxygen concentration in the crystal, and manufacture the n-type group III nitride single crystal 27 having a high carrier concentration and a low resistance. There is an effect that can be done.

  In this embodiment, since boron oxide, which is a compound of boron, which is a group III element, is used as a raw material for the additive, carrier doping can be performed without reducing the n-type carrier concentration.

  In other words, when elements with different valences are dissolved in the crystal, the charge balance (charge neutrality) in the crystal is lost, and oxygen (oxide ions) valence electrons are consumed to maintain the charge balance. Will be. That is, since the oxygen valence electrons are consumed, the carrier concentration decreases, and the resistance of the n-type group III nitride single crystal increases.

  On the other hand, boron added in the present embodiment has the same genus as the group III element (for example, gallium) as a raw material and has the same valence. Therefore, when boron is dissolved in the group III nitride crystal, the charge balance in the crystal is not lost. Accordingly, the valence electrons of oxygen are not consumed for compensating the charge, and the carrier concentration in the crystal can be kept high. In this way, in the present embodiment, an n-type group III nitride single crystal having a high carrier concentration and a low resistance can be produced.

In a preferred embodiment, the amount of boron oxide (B ₂ O ₃ ) is preferably 0.001 mol% or more with respect to the group III element. As a more preferred embodiment, the amount of boron oxide (B ₂ O ₃ ) is preferably 0.01 mol% or more and less than 0.22 mol% with respect to the amount of the group III element. As a more preferred embodiment, the amount of boron oxide (B ₂ O ₃ ) is preferably about 0.01 to 0.1 mol% with respect to the group III element (see Examples).

According to the preferred embodiment described above, in the crystal of the n-type group III nitride single crystal 27, the concentration of oxygen that is an n-type dopant is set to about 10 ¹⁷ cm ⁻³ to 10 ²⁰ cm ^−3. In addition, the n-type group III nitride single crystal 27 having a high carrier concentration of 10 ¹⁷ cm ⁻³ or more and a low resistance can be produced.

  As a material containing at least a group III element as a raw material, for example, a group III element gallium (Ga) is used, but as another example, other group III elements such as aluminum and indium, or a mixture thereof is used. Also good.

  As an alkali metal used as a flux, sodium (Na) or a sodium compound (for example, sodium azide) is used. As other examples, lithium, other alkali metals such as potassium, A compound may be used. A plurality of types of alkali metals may be used.

  The molar ratio of the substance containing the group III element and the alkali metal is not particularly limited, but the molar ratio of the alkali metal to the total number of moles of the group III element and the alkali metal should be 40 to 95%. Is preferred. In a more preferred embodiment, the molar ratio of the group III element (for example, Ga) to the alkali metal (for example, Na) is preferably set to 0.4: 0.6.

In a preferred embodiment, the molar ratio of the group III element to the alkali metal is 0.4: 0.6, and boron oxide (B ₂ O ₃ ) is 0.04 mol% to 0.1 mol% with respect to the group III element. It is preferable to refer to (see Examples).

  Further, a group III nitride needle crystal 25 is placed in the reaction vessel 12 as a seed crystal. As a preferred embodiment, a gallium nitride needle crystal obtained by a flux method is preferably used as a seed crystal. Since the needle crystal 25 manufactured by the flux method has a low dislocation density and a high quality, when the n-type group III nitride single crystal 27 is grown using this seed crystal, the dislocation from the seed crystal is generated. Therefore, high quality crystals can be grown. In addition, about the manufacturing method of the acicular crystal | crystallization by the flux method, the method similar to a prior art can be used.

  FIG. 2 is a schematic diagram showing a group III nitride needle crystal 25 used as a seed crystal in the present embodiment. In the present embodiment, as shown in FIG. 2, an n-type group III nitride single crystal 27 is grown using a group III nitride needle crystal 25 elongated in the c-axis direction as a seed crystal. . In the present embodiment, group III nitride needle-like crystal 25 and n-type group III nitride single crystal 27 have a hexagonal crystal structure. The c-plane is synonymous with the {0001} plane, and the m-plane (see FIG. 3) is synonymous with the {10-10} plane.

  A cross-sectional view of the c-plane orthogonal to the c-axis shown in FIG. 2 is shown in FIG. As shown in FIG. 3, the maximum diameter of the c-plane is referred to as a crystal diameter d. That is, the crystal diameter d is the length of the longest diagonal line of the hexagon forming the c-plane. In the present embodiment, this group III nitride needle crystal 25 is used as a seed crystal, and this needle crystal 25 is grown in the radial direction perpendicular to the c-axis to increase the crystal diameter d, and the c-plane Increase the area of.

  In the present embodiment, the n-type group III nitride single crystal 27 is manufactured by the same flux method as the method of manufacturing the needle crystal 25. Accordingly, the lattice constant and the thermal expansion coefficient are more consistent between the acicular crystal 25 and the n-type group III nitride single crystal 27 than when grown by a method different from the acicular crystal 25. Can do. Further, dislocations that occur when the n-type group III nitride single crystal 27 is grown from the needle-like crystal 25 can be suppressed.

  After introducing the raw materials and the like as described above, the reaction vessel 12 is installed in the pressure vessel 11. In addition, since the operation | work which prepares a raw material is performed in the glove box of inert gas atmosphere, the inert gas is filled into the pressure | voltage resistant container 11. FIG. Then, the pressure vessel 11 is connected to the crystal manufacturing apparatus 1 by operating the valve 21.

(2) Crystal Growth of Group III Nitride Single Crystal After setting the raw materials and the like in the pressure vessel 11 as described above, the heater 13 is energized to heat the pressure vessel 11 and the reaction vessel 12 inside it. Since the melting point of boron oxide is lower than the crystal growth temperature of the present embodiment as described above, the temperature of the reaction vessel 12 reaches the melting point of boron oxide in the process of heating the reaction vessel 12 to the crystal growth temperature. Thus, boron oxide is melted and liquefied (melting step).

  Furthermore, by heating the reaction vessel 12 to the crystal growth temperature, the substance containing at least a group III element, the alkali metal, and the oxide charged into the reaction vessel 12 are dissolved, and the reaction vessel 12 has III A mixed melt 24 containing a group element, an alkali metal, and boron oxide is formed (mixed melt forming step).

  The temperature of the mixed melt 24 in the mixed melt forming step is not particularly limited, but as a preferred embodiment, it is preferable that the temperature is at least 700 ° C. or higher. As a more preferable embodiment, the temperature is preferably about 860 ° C. to 900 ° C. (see Examples).

  Further, the valves 15 and 18 and the pressure control devices 16 and 19 are adjusted to adjust the nitrogen gas and the dilution gas to predetermined gas partial pressures, and the valve 21 is opened to introduce the mixed gas into the pressure resistant vessel 11. . Thereby, nitrogen in the gas which contacts the mixed melt 24 in the pressure vessel 11 is dissolved in the mixed melt 24 (nitrogen dissolving step). The nitrogen gas partial pressure in the gas is not particularly limited, but is preferably at least 0.1 MPa or more. As a more preferred embodiment, it is preferable that the nitrogen partial pressure is about 6 MPa and the total pressure in the internal space 23 in the pressure vessel 11 is about 8 MPa (see Examples).

As a more preferred embodiment, regarding the raw material, the molar ratio of the group III element to the alkali metal is 0.4: 0.6, and boron oxide (B ₂ O ₃ ) is 0.04 mol% with respect to the group III element. With respect to the crystal growth atmosphere, the crystal growth temperature of the mixed melt 24 is about 900 ° C., the nitrogen partial pressure is about 6 MPa, and the total pressure in the internal space 23 in the pressure vessel 11 is about 8 MPa. It is preferred (see the examples).

  By adopting the crystal growth conditions as described above, an n-type group III nitride single crystal 27 in which a group III element dissolved in the mixed melt 24, nitrogen, oxygen, and boron is dissolved is formed as a seed crystal. The crystal is grown using the needle crystal 25 as a starting point for crystal growth (crystal growth step).

  More specifically, oxygen and boron are decomposed into oxide ions and boron ions by boron oxide being decomposed in the mixed melt 24 or in the vicinity of the crystal growth surface (surface) of the n-type group III nitride single crystal 27. Solid solution (dope). In addition, since the crystal is doped with oxygen (oxide oxide) having a divalent negative charge, the group III nitride grown as a crystal becomes an n-type semiconductor crystal.

  In the above description, the n-type group III nitride single crystal 27 is grown using the non-doped group III nitride needle crystal 25 as a seed crystal, but the crystal manufacturing method is not limited to this. As another example, an n-type group III nitride single crystal is produced by generating crystal nuclei from the mixed melt 24 without further setting a seed crystal in the reaction vessel 12 and further growing the crystal nuclei. You may do that. Further, an n-type group III nitride single crystal in which the entire crystal is an n-type semiconductor may be manufactured by performing the same crystal growth process as described above using this as a seed crystal.

  As described above, according to the present embodiment, by introducing boron oxide having a melting point lower than the crystal growth temperature of group III nitride (eg, gallium nitride) into the reaction vessel 12, Can be doped with oxygen. Therefore, it is possible to efficiently dope oxygen into the crystal by a simple process and to produce an n-type group III nitride single crystal having a high carrier concentration and low resistance.

<Manufacturing process of crystal substrate>
By molding the n-type group III nitride single crystal 27 obtained as described above, the n-type group III nitride crystal substrate according to the present embodiment is manufactured. FIG. 4 is a process diagram showing a manufacturing process for manufacturing the crystal substrates 28m and 28c according to the present embodiment (hereinafter referred to as the crystal substrate 28 unless otherwise specified).

  As shown in FIG. 4, when the n-type group III nitride single crystal 27 is sliced in a direction perpendicular to the radial direction of the crystal, that is, in a direction perpendicular to the c-plane, and shaped and polished, the nonpolar surface is obtained. Thus, a large-area crystal substrate 28m having a m-plane ({10-10} plane) as a main surface is obtained.

  On the other hand, when the n-type group III nitride single crystal 27 is sliced in parallel with the radial direction of the crystal, that is, in parallel with the c-plane, and then molded, the surface is polished to obtain a polar c-plane ({0001} plane) Thus, a large-area crystal substrate 28c having a main surface as a surface is obtained.

  As described above, according to the manufacturing process of the present embodiment, a large-sized crystal substrate 28 (28m, 28c) having a practical size that can be used for an optical device or other semiconductor devices can be manufactured. In addition, the crystal substrate 28 can be manufactured for any crystal plane of the m-plane and the c-plane.

  Further, when crystal growth of an n-type group III nitride single crystal is performed in the same manner as described above using the cut crystal substrate 28m or crystal substrate 28c as a seed crystal, the crystal planes of the m-plane and c-plane are high quality and large It becomes possible to mass-produce single crystal wafers of area.

  Further, since the n-type group III nitride single crystal 27 manufactured by the above-described crystal manufacturing method has a low dislocation density and a low resistance, a crystal obtained by processing the n-type group III nitride single crystal 27. The substrate 28 also has a low dislocation density and a low resistance. Therefore, according to the present embodiment, it is possible to manufacture a high-quality and low-resistance n-type group III nitride crystal substrate 28 by a simple process. An ohmic electrode for a low-resistance optical device can be formed.

  EXAMPLES Examples will be shown below to describe the present invention in more detail, but the present invention is not limited to the examples.

Example 1
In this example, an n-type GaN single crystal 27 doped with oxygen was grown using a needle-like crystal 25 of GaN as a seed crystal. The reference numerals correspond to the configuration of the crystal manufacturing apparatus 1 described with reference to FIG.

  First, the pressure vessel 11 was separated from the crystal manufacturing apparatus 1 at the valve 21 portion and placed in a glove box in an Ar atmosphere.

Then, gallium (Ga), sodium (Na), and boron oxide (B ₂ O ₃ ) were put into a reaction vessel 12 made of a BN sintered body and having an inner diameter of 55 mm. In this example, the molar ratio of gallium to sodium was 0.4: 0.6. The amount of boron oxide (B ₂ O ₃ ) added was 0.1 mol% with respect to the amount of gallium.

  A seed crystal was placed in the reaction vessel 12. As a seed crystal, a hexagonal columnar needle-like crystal 25 that is long in the c-axis direction and whose side surface is a {10-10} plane (m-plane) was used. The length of the c-axis of the acicular crystal 25 (the height of the acicular crystal 25) is 20 mm, and the diameter of the cross section perpendicular to the c-axis is 500 μm.

  Next, the pressure vessel 11 was sealed, the valve 21 was closed, and the inside of the reaction vessel 12 was shut off from the external atmosphere. Since a series of operations are performed in a glove box having a high-purity Ar gas atmosphere, the inside of the pressure resistant vessel 11 is filled with Ar gas. Then, the pressure vessel 11 was taken out of the glove box and incorporated in the crystal manufacturing apparatus 1. That is, the pressure vessel 11 was installed at a predetermined position in the heating region of the heater 13 and connected to the nitrogen and argon gas supply pipe 14 at the valve 21 portion.

  Next, the valve 21 and the valve 18 were opened, Ar gas was introduced from the dilution gas supply pipe 20, the pressure was adjusted by the pressure controller 19, the total pressure in the pressure-resistant vessel 11 was adjusted to 0.75 MPa, and the valve 18 was closed. . In addition, nitrogen gas was introduced from the nitrogen supply pipe 17 and the pressure was adjusted by the pressure control device 16, and then the valve 15 was opened to set the total pressure in the pressure resistant vessel 11 to 3 MPa. That is, the partial pressure of nitrogen in the internal space 23 of the pressure vessel 11 is 2.25 MPa. Thereafter, the valve 15 was closed and the pressure control device 16 was set to 8 MPa.

  Next, the heater 13 was energized to raise the temperature of the reaction vessel 12 to 900 ° C., which is the crystal growth temperature. At the crystal growth temperature, gallium and sodium in the reaction vessel 12 are melted to form a mixed melt 24. Note that the temperature of the mixed melt 24 is the same as the temperature of the reaction vessel 12. Further, when the temperature is raised to 900 ° C., the pressure of the gas in the internal space 23 of the pressure vessel 11 increases as the temperature rises in the crystal manufacturing apparatus 1 of the present embodiment, so that the total pressure becomes 8 MPa. That is, the nitrogen partial pressure is 6 MPa.

  Next, the valve 15 is opened and the nitrogen gas pressure is set to 8 MPa. This is because, even when nitrogen is consumed by crystal growth of gallium nitride, nitrogen is supplied from the outside to maintain the nitrogen partial pressure in the pressure vessel 11 at 6 MPa. This state was maintained for 1000 hours, and nitrogen was continuously dissolved in the mixed melt 24 to grow the n-type GaN single crystal 27.

  After 1000 hours, the reaction vessel 12 was cooled to room temperature. When the pressure vessel 11 was opened after the gas pressure in the pressure vessel 11 was lowered, an n-type GaN single crystal 27 was grown in the reaction vessel 12 using the GaN needle crystal 25 as a seed crystal.

  The obtained n-type GaN single crystal 27 was colorless and transparent, the outer diameter was 20 mm, and the c-axis length (the height of the n-type GaN single crystal 27) was 47 mm. The crystal shape of the n-type GaN single crystal 27 is a hexagonal pyramid shape in which the upper part of the crystal is constituted by a {10-11} plane, and the lower part of the crystal is constituted by an m-plane ({10-10} plane). Hexagonal columnar shape.

  Subsequently, from the hexagonal columnar portion of the n-type GaN single crystal 27, a plate crystal having an m plane ({10-10} plane) as a main surface and a plate shape having a c plane ({0001} plane) as a main surface. Crystals were cut out and molded, and then surface polishing was performed to produce GaN crystal substrates 28m and 28c.

  As a result, for the crystal substrate 28m having the m-plane as the main surface, 10 substrates having a vertical and horizontal size of 10 × 20 mm and a thickness of 0.4 mm are produced, and for the crystal substrate 28c having the c-plane as the main surface, Five substrates having an outer diameter of φ16 mm and a thickness of 0.4 mm were produced.

Further, when the crystal substrate 28c was etched with an acidic solution and the etch pits were observed, it was found that the etch pit density was 10 ³ cm ⁻² or less and the dislocation density was low and the substrate was a high quality.

Furthermore, when elemental analysis of the crystal substrate 28 was performed by SIMS (Secondary Ionization Mass Spectrometer), oxygen (O) and boron (B) were detected. The oxygen concentration in the crystal substrate 28 was 3 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ , and the average value was 8 × 10 ¹⁹ cm ⁻³ . The boron concentration was 3 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , and the average value was 1 × 10 ¹⁸ cm ⁻³ .

  Further, when the electrical conductivity of the crystal substrate 28 was measured, it was found that it showed n-type electrical conductivity and low resistance.

(Example 2)
In this example, the amount of boron oxide (B ₂ O ₃ ) added was 0.04 mol% with respect to the amount of gallium, and other experimental conditions were the same as in Example 1 to grow an n-type GaN single crystal.

The obtained GaN single crystal was processed in the same manner as in Example 1 to produce a GaN crystal substrate. When the etch pits were observed in this GaN crystal substrate, the etch pit density was 10 ³ cm ⁻² or less, and it was found that the substrate was a high quality substrate with a low dislocation density. As a result of SIMS analysis, the average value of oxygen concentration in the GaN crystal substrate was 2 × 10 ¹⁹ cm ⁻³ , and the average value of boron concentration was 1 × 10 ¹⁸ cm ⁻³ . Furthermore, as a result of measuring the electric conductivity of the GaN crystal substrate, it was found that the n-type electric conductivity was exhibited and the resistance was low.

(Example 3)
FIG. 5 is a schematic diagram illustrating the configuration of the crystal manufacturing apparatus 2 according to the third embodiment. In this embodiment, five reaction vessels 12 (12a to 12e) having an inner diameter of 17 mm are installed in the pressure vessel 11, and GaN needle crystals 25 (25a to 25e) are installed in the reaction vessels 12a to 12e. Thus, each of the acicular crystals 25a to 25e was grown.

  Although only two reaction vessels 12a and 12b are shown in FIG. 5, reaction vessels 12c, 12d, and 12e that are not actually shown are installed in the pressure resistant vessel 11. Further, as the acicular crystals 25a to 25e, GaN single crystals having the same crystallinity and size as the acicular crystals 25 used in Example 1 were used.

In this example, crystal growth was performed by varying the amount of boron oxide (B ₂ O ₃ ) charged into each of the reaction vessels 12a to 12e. That is, boron oxide is not charged into one of the reaction vessels 12, and the remaining four reaction vessels 12 are respectively 0.01 mol% and 0.04 mol of boron oxide (B ₂ O ₃ ) relative to gallium. %, 0.10 mol%, and 0.22 mol% were added boron oxide.

  The other experimental conditions were the same as in Example 1. The reaction vessels 12a to 12e were held at 900 ° C., which is the crystal growth temperature, for 80 hours, and the GaN single crystals 27 (27a to 27e) of each reaction vessel 12a to 12e were retained. Crystal growth was performed.

  The crystal shapes of the obtained GaN single crystals 27a to 27e are hexagonal pyramidal shapes in which the upper part of the crystal is configured with {10-11} plane, as in Example 1, and the side of the lower part of the crystal is m-plane ({ 10-10} plane).

Further, GaN crystals having a thickness of about several hundred μm are grown on the surfaces of the seed crystals 25 a to 25 e, and the GaN crystals are thicker on the seed crystal 25 as the amount of boron oxide (B ₂ O ₃ ) is increased. It was growing up.

Further, the boron oxide _(B 2 _{O 3)} 0.01 mol%, 0.04 mol%, a GaN single crystal 27 grown by adding 0.10 mol%, without the addition of boron oxide _(B 2 _{O 3)} Each of the grown GaN single crystals 27 was transparent. On the other hand, the GaN single crystal 27 grown by adding 0.22 mol% of boron oxide (B ₂ O ₃ ) was colored black.

  Furthermore, the oxygen concentration and the boron concentration in the crystals of the GaN single crystals 27a to 27e were measured by SIMS. The m-plane ({10-10} plane), which is the side surface of the GaN single crystals 27a to 27e, was analyzed as an inspection plane. In the same GaN single crystal 27, the concentration may be measured multiple times by changing the inspection location.

FIG. 6 is a graph showing the relationship between the amount of boron oxide (B ₂ O ₃ ) added and the concentrations of oxygen (O) and boron (B) in the GaN single crystals 27a to 27e. The horizontal axis of the graph shows the amount of boron oxide (B ₂ O ₃ ) added as a mole fraction of boron oxide (B ₂ O ₃ ) with respect to gallium.

(1) Oxygen concentration in crystal As shown in FIG. 6, the oxygen concentration in the GaN single crystal 27 grown without adding boron oxide (B ₂ O ₃ ) is the oxygen background at the time of this measurement. The value was 8 × 10 ¹⁶ cm ⁻³ or less. Further, when 0.01 mol% of boron oxide (B ₂ O ₃ ) is added, the oxygen concentration in the GaN single crystal 27 is about 10 ¹⁷ cm ⁻³ , and boron oxide (B ₂ O ₃ ) is about 0.17. When 22 mol% was added, the oxygen concentration in the GaN single crystal 27 was 4 × 10 ²⁰ cm ⁻³ . Therefore, by adding 0.01 mol% to 0.22 mol% of boron oxide (B ₂ O ₃ ) and growing the crystal, oxygen is added in the GaN single crystal 27 from 10 ¹⁷ cm ⁻³ to 4 × 10 ²⁰ cm ^−3. It turned out that it can dope to the extent.

Further, as shown in FIG. 6, when boron oxide (B ₂ O ₃ ) is added in an amount less than 0.01 mol%, oxygen is contained in the GaN single crystal 27 in an amount less than about 10 ¹⁷ cm ^−3. It turns out that it can dope. Furthermore, based on the relationship between the added amount of boron oxide (B ₂ O ₃ ) and the oxygen concentration in the GaN single crystal 27 shown in FIG. 6 and the background value of oxygen, for example, boron oxide (B ₂ O ₃₎ ) Is added by about an order of 0.001 mol%, which is an order of magnitude less than 0.01 mol%, it is estimated that about 10 ¹⁶ cm ^{−3 of} oxygen can be doped into the GaN single crystal 27.

(2) Boron concentration in the crystal As shown in FIG. 6, when 0.01 mol% of boron oxide (B ₂ O ₃ ) is added, the boron concentration in the GaN single crystal 27 is about 10 ¹⁷ cm ⁻³ . Yes, when 0.1 mol% of boron oxide (B ₂ O ₃ ) was added, the boron concentration in the GaN single crystal 27 was about 3 × 10 ¹⁸ cm ⁻³ . Accordingly, boron is added in the GaN single crystal 27 by 10 ¹⁷ cm ⁻³ to 3 × 10 ¹⁸ cm ⁻³ by adding 0.01 mol% to 0.22 mol% of boron oxide (B ₂ O ₃ ) and growing the crystal. It turned out that it can dope to the extent.

Boron was also detected at about 6 × 10 ¹⁵ cm ⁻³ in the GaN single crystal 27 grown without adding boron oxide. This is probably because boron (B) eluted from the reaction vessel 12 is taken into the GaN single crystal 27 during crystal growth because the material of the reaction vessel 12 is boron nitride (BN).

Therefore, it can be seen that when boron oxide (B ₂ O ₃ ) is added in an amount less than 0.01 mol%, the GaN single crystal 27 can be doped with boron in an amount less than about 10 ¹⁷ cm ⁻³ . Furthermore, from the relationship between the added amount of boron oxide (B ₂ O ₃ ) shown in FIG. 6 and the boron concentration in the GaN single crystal 27, for example, boron oxide (B ₂ O ₃ ) is one digit less than 0.01 mol%. When about 0.001 mol% is added, it is estimated that about 10 ¹⁶ cm ^{−3 of} boron can be doped into the GaN single crystal 27.

(3) Electric conductivity Furthermore, electric conductivity was measured about the GaN single crystal 27 (27a-27e). As a result, it was found that the GaN single crystal 27 showed n-type electrical conductivity, and the electrical conductivity increased as the amount of boron oxide (B ₂ O ₃ ) increased, resulting in a low resistance. This is considered to be caused by oxygen doped in the GaN single crystal 27 contributing as a donor.

In this example, the GaN single crystal 27 increases with the amount of boron oxide (B ₂ O ₃ ) until the amount of boron oxide (B ₂ O ₃ ) is 0.01 mol%. The resistance tended to decrease obviously. On the other hand, when the amount of boron oxide (B ₂ O ₃ ) added was greater than 0.01 mol%, the tendency for the resistance to decrease (change rate) became moderate. That is, the resistance of the GaN single crystal 27 obtained by adding 0.22 mol% of boron oxide (B ₂ O ₃ ) is the same as that of GaN single crystal obtained by adding 0.01 mol% of boron oxide (B ₂ O ₃ ). Although it decreased slightly from the resistance of the crystal 27, it was a decrease that can be said to be almost the same.

  Thus, in this example, a high-quality and low-resistance n-type group III nitride single crystal could be manufactured by a simple process.

DESCRIPTION OF SYMBOLS 1, 2 Crystal production apparatus 11 Pressure-resistant container 12, 12a, 12b, 12c, 12d, 12e Reaction container 13 Heater 14 Gas supply pipe 15, 18, 21 Valve 16, 19 Pressure control apparatus 17 Nitrogen supply pipe 20 Diluted gas supply pipe 22 Pressure gauge 23 Internal space 24 Mixed melt 25, 25a Needle crystal (seed crystal)
26 Installation base 27, 27a n-type group III nitride single crystal (n-type GaN single crystal)
28, 28m, 28c crystal substrate

JP 2008-94704 A JP 2006-045047 A JP 2005-154254 A JP 2007-246303 A Japanese Patent No. 4223540 JP 2010-1209 A

Chemistry of Materials, Vol. 9 (1997) 413-416

The present invention relates to a gallium nitride crystal , a crystal substrate, and a nitride crystal .

Claims (5)

A material charging step of charging a substance containing at least a group III element, an alkali metal, and boron oxide into the reaction vessel;
A melting step of melting the boron oxide by heating the reaction vessel to the melting point of the boron oxide;
By heating the reaction vessel to the group III nitride crystal growth temperature, a mixed melt is formed in the reaction vessel to form a mixed melt containing the group III element, the alkali metal, and the boron oxide. A liquid forming step;
A nitrogen dissolving step in which a gas containing nitrogen is brought into contact with the mixed melt to dissolve nitrogen in the mixed melt;
Crystal growth for growing an n-type group III nitride single crystal doped with the oxygen as a donor from the group III element dissolved in the mixed melt, the nitrogen, and oxygen in the boron oxide Process,
A method for producing an n-type group III nitride single crystal comprising:   2. The method for producing an n-type group III nitride single crystal according to claim 1, wherein in the crystal growth step, boron in the boron oxide is doped into the n-type group III nitride single crystal.   An n-type group III nitride single crystal produced by the production method according to claim 1. The n-type group III nitride single crystal according to claim ³ , wherein the oxygen concentration in the crystal is 10 ¹⁷ to 10 ²⁰ cm ⁻³ .   A crystal substrate of n-type group III nitride produced by processing the n-type group III nitride single crystal according to claim 3 or 4.