JP2007254206A - Method for growing nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the degradation of a single crystal caused by the oxidation of a solution when growing a nitride single crystal by a flux method. <P>SOLUTION: An outer container 4 is disposed inside an atmosphere controlling container 5, and a crucible is disposed inside the outer container 4. A seed crystal is immersed in a solution containing an easily oxidizing substance in the crucible, from which a nitride single crystal is grown. The atmosphere upon growing the nitride single crystal comprises nitrogen supplied from a nitrogen cylinder 19 and a reducing gas supplied from a reducing gas cylinder 21, and preferably the reducing gas contains hydrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a nitride single crystal using sodium or the like as a flux.

Gallium nitride III-V nitride has attracted attention as an excellent blue light-emitting device, and has been put to practical use as a material for light-emitting diodes and semiconductor laser diodes. In addition, gallium nitride III-V nitride is expected as a material for next-generation electronic devices because of its characteristics such as high breakdown voltage due to a wide band gap. As a method for growing a gallium nitride single crystal by the Na flux method, there are methods described in Patent Documents 1, 2, and 3.
JP 2002-293696 A JP 2003-292400 A WO2005-095682 A1

On the other hand, the present applicant disclosed in Patent Document 4 a method for efficiently growing a gallium nitride single crystal under specific conditions using a hot isostatic pressing (HIP) apparatus.
Japanese Patent Application No. 2004-103093

Non-Patent Document 1 describes that when a GaN single crystal is grown by the Na flux method, the GaN single crystal is easily colored black due to the presence of nitrogen defects.
“Journal of Japanese Society for Crystal Growth” Vol. 32, no. 1 2005 “Growth of large and low dislocation GaN single crystals by LPE growth method” Kawamura et al.

Furthermore, in Patent Document 5, first, a raw material such as Ga and Na and a flux are melted to form a solution (melt), then hydrogen is once flowed into the furnace, then hydrogen is stopped, and the solution is heated to a predetermined temperature. Further, the nitride single crystal is grown by heating and pressurizing to a nitrogen pressure.
JP-A-2005-154254

In the method described in Patent Document 5, hydrogen is allowed to flow before growing a single crystal, thereby reducing the surfaces of the reaction vessel, the heater, and the heat insulating material, suppressing the dissolution of oxygen in the solution, and growing the group III nitride crystal. Claims to be promoted. However, it has been surprisingly found that impurities, dislocations, lattice defects, and coloring occur in the nitride single crystal even when hydrogen is allowed to flow through the furnace before the single crystal is grown. These crystallinity imperfections appear macroscopically as a decrease in optical transparency and an increase in the half-value width of the X-ray diffraction peak.

  An object of the present invention is to prevent deterioration of a nitride single crystal due to oxidation of a solution during the growth of the nitride single crystal by a flux method.

  The present invention is a method for growing a nitride single crystal from a solution containing an easily oxidizable substance, wherein the atmosphere when growing the nitride single crystal includes nitrogen and a reducing gas.

  The cause of the above crystal defects is that oxygen is melted into the solution, impurity oxygen contained in the raw material, flux and dopant itself, oxides, crucibles, heaters, and heat insulating materials formed on the raw material, flux and dopant surface at the time of weighing Various factors such as oxygen and moisture adsorbed on the surface of oxygen and the like, oxygen and moisture diffused from the inside of the crucible, heater, heat insulating material, seed crystal, etc. during the growth can be considered. Among these, the diffusion rate of oxygen and moisture inside crucibles, heaters, heat insulating materials, seed crystals, etc. is very slow, so even if hydrogen is allowed to flow sufficiently before growth, it cannot be completely removed, It was found that it gradually dissolved in the solution during the growth.

  Therefore, even if the nitride single crystal was being grown, it was thought that oxygen dissolved in the solution could be removed, and when a single crystal was grown by mixing a reducing gas such as hydrogen in the growth atmosphere, We succeeded in growing a high-quality group III nitride single crystal without adverse effects due to the atmosphere.

  Therefore, the group III nitride single crystal produced using the present invention has a low defect density. Therefore, the light emitting diode and the semiconductor laser diode lead to an improvement in lifetime and light emission efficiency, and the electronic device leads to an improvement in withstand voltage, current density and frequency characteristics.

  In Patent Document 5, hydrogen is allowed to flow into the furnace at a stage where a raw material or the like is melted to form a solution before growing the nitride single crystal, but hydrogen is stopped before entering the single crystal growing stage. This shows that it was recognized that it was sufficient to reduce the inside of the furnace before single crystal growth, and that it was not usually possible to mix hydrogen in the nitrogen atmosphere during growth. .

  In the present invention, the reducing gas is not limited, and examples thereof include hydrogen and carbon monoxide. It is particularly preferred that it contains at least hydrogen.

  In addition, an inert gas such as argon, neon, or helium can be contained in the atmosphere during single crystal growth, and this has the effect of suppressing evaporation of substances constituting the solution, such as sodium. In this case, the upper limit of the partial pressure of the inert gas is not particularly limited, but can be, for example, 200 MPa or less.

  At the time of single crystal growth, the temperature and pressure conditions of each gas are not particularly limited. For example, the nitrogen partial pressure is preferably 1 MPa or more and 200 MPa or less, more preferably 10 MPa or more and 100 MPa or less.

  Further, during the growth of the single crystal, the partial pressure of the reducing atmosphere is preferably 0.05 MPa or more, and more preferably 0.1 MPa or more, from the viewpoint of preventing oxidation of the growth solution and the crystal. Further, when the partial pressure of the reducing atmosphere is increased, the structure of the growing apparatus becomes complicated. Therefore, from the viewpoint of practical use, it is preferably 10 MPa or less, and more preferably 5 MPa or less.

  The growth temperature of the single crystal is not particularly limited because it varies depending on the type of single crystal. In general, the growth temperature of the single crystal is preferably 800 ° C. or higher and 1200 ° C. or lower, and more preferably 900 ° C. or higher and 1100 ° C. or lower.

  In a preferred embodiment, the crucible containing the solution is housed in a pressure vessel and heated under high pressure using a hot isostatic press. At this time, the atmospheric gas containing nitrogen and reducing gas is compressed to a predetermined pressure and supplied into the pressure vessel to control the nitrogen partial pressure and the reducing gas partial pressure.

  FIG. 1 is a schematic diagram showing the configuration of the entire apparatus for carrying out the present invention. Moreover, FIG. 2 is a figure which shows typically the growing part of the apparatus for implementing this invention.

  A furnace material 11 is provided in the pressure vessel 12, and a predetermined heater 13 is provided in the furnace material 11. An atmosphere control container 5 is installed inside the furnace material 11, and an outer container 4 is installed inside the container 5. 5a is a lid. A crucible 1 is further installed inside the outer container 4. A lid 1b is provided in the crucible 1, a solution 7 is generated in the crucible 1, and a seed crystal 6 is immersed therein. The lid 4a of the outer container 4 melts and disappears during heating before the start of growth, and the portion of the lid 4a becomes an opening.

  As shown in FIG. 1, a nitrogen cylinder 19 and a reducing gas cylinder 21 are connected to the outside of the pressure vessel 12 through a supply pipe 20, a joint 16, and a pressure control device 18. The flow rate of each gas is controlled by a valve and a pressure control device 18. Reference numeral 17 denotes a discharge valve.

  The gas cylinders 19 and 21 are filled with nitrogen and a reducing gas, and these gases are mixed and compressed by the pressure control device 18 to obtain a predetermined pressure, and the pressure vessel 12 is passed through the supply pipe 20 as indicated by an arrow A. To supply. Nitrogen in the atmosphere serves as a nitrogen source, and the reducing gas exhibits the above-described action. Note that by mixing an inert gas such as argon gas, evaporation of substances constituting a solution such as sodium can be suppressed.

  When the crucible 1 is heated and pressurized in the pressure vessel 12, all the raw materials, flux, and dopant are dissolved in the crucible 1 as shown in FIG. Here, if a predetermined single crystal growth condition is maintained, nitrogen is stably supplied from the inner space 1 a into the solution 7, and the single crystal film 8 is grown on the seed crystal 6.

  On the other hand, when an easily oxidizable substance such as sodium metal is oxidized, as shown in FIG. 4, for example, during the heat treatment, the oxidized components gather near the liquid surface of the solution 10 and nitrogen is contained in the growing solution. To prevent melting as indicated by arrow B. For this reason, nitrogen flows on the liquid surface of the solution 10 as indicated by an arrow C and is not supplied well into the solution. As a result, a high-quality single crystal film is not formed on the seed crystal 6 with high productivity, and problems such as coloring may occur in the obtained single crystal.

  In the present invention, for example, a glove box can be used when weighing the raw material, flux, and dopant.

  In the present invention, in the single crystal growth apparatus, an apparatus for heating the raw material, flux, and dopant to generate a solution is not particularly limited. This apparatus is preferably a hot isostatic pressing apparatus, but other atmospheric pressure heating furnaces may be used.

  The easily oxidizable substance to which the present invention is applicable is not particularly limited. An easily oxidizable substance means a substance that is easily oxidized when it comes into contact with the atmosphere at room temperature. For example, it means a substance that can be oxidized within one minute. The easily oxidizable substance may be a powder (or a powder mixture) or a molded body.

  In a preferred embodiment, the oxidizable substance is one or more metals selected from the group consisting of alkali metals and alkaline earth metals, or alloys thereof. Examples of the metal include lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, and barium. Lithium, sodium, and calcium are particularly preferable, and sodium is most preferable.

Moreover, the following metals can be illustrated as a substance which forms an alloy with the said easily oxidizable substance.
Gallium, aluminum, indium, boron, zinc, silicon, tin, antimony, bismuth.

By the growth method of the present invention, for example, the following group III metal nitride single crystals can be preferably grown.
GaN, AlN, InN, mixed crystals of these (AlGaInN), BN

  Further, the easily oxidizable substance may behave as a reactant in a predetermined reaction, or may be present as a non-reacting component in a solution.

  The material of the crucible for carrying out the reaction is not particularly limited as long as the material is durable under the intended heating and pressurizing conditions. Such materials include refractory metals such as tantalum, tungsten and molybdenum, oxides such as alumina, sapphire and yttria, nitride ceramics such as aluminum nitride, titanium nitride, zirconium nitride and boron nitride, tungsten carbide and tantalum carbide. Examples include pyrolytic products such as carbides of high melting point metals, p-BN (pyrolytic BN), p-Gr (pyrolytic graphite).

Hereinafter, more specific single crystals and their growth procedures will be exemplified.
(Gallium nitride single crystal growth example)
Using the present invention, a gallium nitride single crystal can be grown using a flux containing at least sodium metal. In this flux, the gallium source material is dissolved. As the gallium source material, a gallium simple metal, a gallium alloy, and a gallium compound can be applied, but a gallium simple metal is also preferable in terms of handling.

  This flux can contain metals other than sodium, such as lithium. The use ratio of the source material such as gallium and the flux such as sodium may be appropriate, but in general, it is considered to use an excess amount of sodium. Of course, this is not limiting.

  The material of the growth substrate for epitaxially growing the gallium nitride crystal is not limited, but sapphire, AlN template, GaN template, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl2O4), LiAlO2, LiGaO2, LaAlO3, LaGaO3 , NdGaO3 and other perovskite complex oxides. The composition formula [A1-y (Sr1-xBax) y] [(Al1-zGaz) 1-u.Du] O3 (A is a rare earth element; D is a kind selected from the group consisting of niobium and tantalum. A cubic system of y = 0.3 to 0.98; x = 0 to 1; z = 0 to 1; u = 0.15 to 0.49; x + z = 0.1 to 2) Perovskite structure composite oxides of the above can also be used. SCAM (ScAlMgO4) can also be used.

(Example of growing AlN single crystal)
The present invention has been confirmed to be effective even when growing an AlN single crystal by pressurizing a solution containing at least aluminum and an alkaline earth in a nitrogen-containing atmosphere under specific conditions.

(Example 1)
A gallium nitride single crystal was grown according to the method referred to with reference to FIGS. 2 g of metal Ga as a Group III material, 2 g of metal Na as a flux, and 2 mg of metal Li were weighed together with a seed crystal 6 in a ceramic crucible 1 having an inner diameter of 2 cm. As the seed crystal, an AlN single crystal thin film epitaxially grown on a sapphire substrate by metal organic vapor phase epitaxy was used. The seed crystal 6 was placed on the bottom so that the growth surface faced upward. The crucible 1 was placed in a metal container 4 having a gas inlet and sealed. A series of operations were performed in an inert gas atmosphere to prevent oxidation of raw materials and flux.

  After the sealed container 4 was placed in an electric furnace having a heater 13, the gas inlet was connected to a nitrogen and hydrogen supply line via a pressure regulator. After the connection, introduction and discharge of nitrogen and hydrogen were repeated, and oxygen and moisture were removed from the inside of the metal container 4 and the surface of the ceramic crucible 1 and the like.

  A gas was introduced into a metal container heated to a temperature of 865 ° C. so that the partial pressure of nitrogen was 3.0 MPa and the partial pressure of hydrogen was 0.1 MPa, and held for 100 hours. Thereafter, the crucible 1 was taken out from the cooled metal container 4, and the flux was reacted with ethanol and removed, whereby the GaN single crystal 8 grown on the seed crystal 6 was collected. The thickness of the GaN single crystal grown on the seed crystal was about 0.5 mm.

  The FWHM of the X-ray diffraction peak of the obtained GaN single crystal showed good values of (0002) surface reflection 33.5 seconds and (10-12) surface reflection 27.2 seconds. FIG. 5 is an appearance photograph of the obtained gallium nitride single crystal.

(Comparative Example 1)
A gallium nitride single crystal was grown according to the method referred to with reference to FIGS. 2 g of metal Ga as a group III material, 2 g of metal Na as a flux, and 2 mg of metal Li were weighed together with a seed crystal 6 in a ceramic crucible 1 having an inner diameter of 2 cm. As the seed crystal, an AlN single crystal thin film epitaxially grown on a sapphire substrate by metal organic vapor phase epitaxy was used. The seed crystal 6 was placed on the bottom so that the growth surface faced upward. The crucible 1 was placed in a metal container 4 having a gas inlet and sealed. A series of operations were performed in an inert gas atmosphere to prevent oxidation of raw materials and flux.

  After the sealed container 4 was placed in an electric furnace having a heater, the gas inlet was connected to a nitrogen and hydrogen supply line via a pressure regulator 18. After the connection, introduction and discharge of nitrogen and hydrogen were repeated, and oxygen and moisture were removed from the inside of the metal container 4 and the surface of the ceramic crucible 1 and the like.

  A gas was introduced into the metal container 4 heated to a temperature of 865 ° C. so that the total pressure became 3.0 MPa only with nitrogen, and the gas was held for 100 hours. Then, the crucible 1 was taken out from the cooled metal container 4, and the GaN single crystal 8 grown on the seed crystal 6 was recovered by removing the flux by reacting with ethanol. The thickness of the GaN single crystal 8 grown on the seed crystal was about 0.5 mm.

  The half-width of the X-ray diffraction peak of the obtained GaN single crystal is (0002) surface reflection 68.7 seconds (10-12) surface reflection 62.7 seconds, which is a large value compared to the case where growth is performed in a hydrogen mixed atmosphere. showed that.

(Example 2)
A gallium nitride single crystal was grown according to the method referred to with reference to FIGS. 2 g of metal Ga as a group III material, 2 g of metal Na as a flux, and 2 mg of metal Li were weighed together with a seed crystal 6 in a ceramic crucible 1 having an inner diameter of 2 cm. As the seed crystal 6, an AlN single crystal thin film epitaxially grown on a sapphire substrate by metal organic vapor phase epitaxy was used. The seed crystal 6 was placed on the bottom so that the growth surface faced upward. The crucible 1 was placed in a metal container 4 having a gas inlet and sealed. A series of operations were performed in an inert gas atmosphere to prevent oxidation of raw materials and flux.

  After the sealed container 4 was placed in an electric furnace having a heater 13, the gas inlet was connected to a nitrogen and hydrogen supply line via a pressure regulator 18. After the connection, introduction and discharge of nitrogen and hydrogen were repeated, and oxygen and moisture were removed from the inside of the metal container 4 and the surface of the ceramic crucible 1 and the like.

  A gas was introduced into the metal container 4 heated to a temperature of 1000 ° C. so that the partial pressure of nitrogen was 45 MPa and the partial pressure of hydrogen was 5 MPa, and was maintained for 100 hours. Thereafter, the crucible 1 was taken out from the cooled metal container 4, and the flux was reacted with ethanol and removed, whereby the GaN single crystal 8 grown on the seed crystal 6 was collected. The thickness of the GaN single crystal 8 grown on the seed crystal 6 was about 1 mm.

  The FWHM of the X-ray diffraction peak of the obtained GaN single crystal showed good values of (0002) surface reflection 43.0 seconds and (10-12) surface reflection 39.2 seconds.

It is a schematic diagram which shows the structure of the whole apparatus for implementing this invention. It is a figure which shows typically the growing part of the apparatus for implementing this invention. 2 is a schematic cross-sectional view showing a state where a single crystal 8 is grown in a crucible 1. FIG. It is typical sectional drawing for demonstrating the single crystal growth in case the growth solution is oxidizing. It is an external appearance photograph of the obtained gallium nitride single crystal.

Explanation of symbols

  1 crucible 4 outer vessel 5 atmosphere control vessel 6 seed crystal 7 solution 8 single crystal film 10 solution containing oxidized components 11 furnace material 12 pressure vessel 13 heater 16 joint 17 discharge control valve 18 pressure control device 19 nitrogen cylinder 20 supply pipe 21 Reducing gas cylinder A, B, C Flow of nitrogen

Claims (4)

A method for growing a nitride single crystal from a solution containing an easily oxidizable substance,
A method for growing a nitride single crystal, wherein an atmosphere when growing the nitride single crystal contains nitrogen and a reducing gas.   The method for growing a nitride single crystal according to claim 1, wherein the reducing gas contains hydrogen.   The method for growing a nitride single crystal according to claim 1 or 2, wherein the nitride single crystal is made of a nitride of a group III metal.   4. The method for growing a nitride single crystal according to claim 3, wherein the nitride single crystal is a gallium nitride single crystal.

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