JP4245822B2 - Method for producing group III nitride crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a blue-violet light source for optical disks, an ultraviolet light source (LD or LED), a blue-violet light source for electrophotography, a group III nitride electronic device, a group III nitride crystal that can be used for LED lighting equipment, etc.To the manufacturing methodRelated.
[0002]
[Prior art]
  Currently, most of InGaAlN-based (group III nitride) devices used as purple-blue-green light sources are formed on a sapphire substrate or SiC substrate by MO-CVD (metal organic chemical vapor deposition) or MBE. It is fabricated by crystal growth using a method (molecular beam crystal growth method) or the like. When sapphire or SiC is used as a substrate, crystal defects due to large difference in thermal expansion coefficient and difference in lattice constant from group III nitride increase. For this reason, there is a problem that the device characteristics are poor, for example, it is difficult to extend the life of the light emitting device, or the operating power is increased.
[0003]
  Furthermore, in the case of a sapphire substrate, since it is insulative, it is impossible to take out the electrode from the substrate side as in the conventional light emitting device, and it is necessary to take out the electrode from the surface of the group III nitride semiconductor where the crystal has grown. It becomes. As a result, there is a problem that the device area is increased, leading to high costs. Further, the group III nitride semiconductor device fabricated on the sapphire substrate is difficult to separate the chip by cleavage, and it is not easy to obtain the resonator end face required for the laser diode (LD) by cleavage. For this reason, at present, resonator end faces are formed by dry etching, or after the sapphire substrate is polished to a thickness of 100 μm or less, resonator end faces are formed in a form close to cleaving. It is impossible to easily separate a resonator end face such as an LD from a chip in a single process, resulting in a complicated process and an increase in cost.
[0004]
  In order to solve these problems, it has been proposed to reduce crystal defects by performing selective lateral growth and other devices on a sapphire substrate for a group III nitride semiconductor film.
[0005]
  For example, the document “Japanese Journal of Applied Physics Vol. 36 (1997) Part 2, No. 12A, L1568-1571” (hereinafter referred to as the first prior art) includes a laser diode (LD) as shown in FIG. It is shown. In the laser diode of FIG. 10, the GaN low-temperature buffer layer 2 and the GaN layer 3 are sequentially grown on the sapphire substrate 1 by an MO-VPE (metal organic vapor phase epitaxy) apparatus, and then SiO 2 for selective growth.₂A mask 4 is formed. This SiO₂The mask 4 is formed by another CVD (chemical vapor deposition) apparatus using SiO.₂After the film is deposited, it is formed through photolithography and etching processes. Next, this SiO₂A GaN film 3 ′ having a thickness of 20 μm is again grown on the mask 4 by the MO-VPE apparatus, so that GaN is selectively grown in the lateral direction and crystal defects are compared with the case where selective lateral growth is not performed. Is reduced. Furthermore, by introducing a modulation-doped strained superlattice layer (MD-SLS) 5 formed thereon, it is possible to prevent crystal defects from extending to the active layer 6. As a result, the device lifetime can be extended as compared with the case where the selective lateral growth and modulation-doped strained superlattice layer is not used.
[0006]
  In the case of this first prior art, it is possible to reduce crystal defects compared to the case where a GaN film is not selectively grown in the lateral direction on the sapphire substrate. The aforementioned problems with cleavage still remain. Furthermore, SiO₂There is a new problem that the crystal growth by the MO-VPE apparatus is required twice with the mask formation process in between, and the process becomes complicated.
[0007]
  As another method, for example, in the document “Applied Physics Letters, Vol. 73, No. 6, p. 832-834 (1998)” (hereinafter referred to as second prior art), a GaN thick film substrate is applied. It has been proposed to do. In this second prior art, after the selective lateral growth of 20 μm in the first prior art described above, a 200 μm thick GaN film is grown by an H-VPE (hydride vapor phase epitaxy) apparatus, and then this The GaN substrate is fabricated by polishing the GaN film grown to a thickness of 150 μm from the sapphire substrate side. By using the MO-VPE apparatus on this GaN substrate, the crystal growth necessary for the LD device is sequentially performed to produce the LD device, thereby reducing crystal defects and using the sapphire substrate. It becomes possible to solve the above-mentioned problems relating to the insulation and cleavage by. Incidentally, Japanese Patent Laid-Open No. 11-4048 has been proposed as the same as the second prior art, and FIG. 11 shows a semiconductor laser of Japanese Patent Laid-Open No. 11-4048.
[0008]
  However, the process of the second prior art is more complicated than the first prior art, and the cost is further increased. In addition, when a GaN thick film having a thickness of about 200 μm is grown by this second prior art method, the stress accompanying the difference in lattice constant and thermal expansion coefficient from the sapphire substrate increases, There is a new problem of warping and cracking.
[0009]
  In order to avoid this problem, Japanese Patent Application Laid-Open No. 10-256662 proposes that the thickness of the original substrate (sapphire and spinel) on which the thick film is grown be 1 mm or more. In this way, by using a substrate having a thickness of 1 mm or more, even when a GaN film having a thickness of 200 μm is grown, the substrate is not warped or cracked. However, such a thick substrate has a high cost of the substrate itself and needs to spend a lot of time for polishing, leading to an increase in the cost of the polishing process. That is, when a thick substrate is used, the cost is higher than when a thin substrate is used. When a thick substrate is used, the substrate is not warped or cracked after the thick GaN film is grown, but stress is relaxed in the polishing process, and warping or cracking occurs during polishing. For this reason, even if a thick substrate is used, a GaN substrate having a high crystal quality cannot be easily produced with a large area.
[0010]
  On the other hand, in the document “Journal of Crystal Growth, Vol.189 / 190, p.153-158 (1998)” (hereinafter referred to as “third prior art”), a bulk crystal of GaN is grown, and it is used as a homoepitaxial substrate. It has been proposed to be used as The third prior art is a technique for crystal growth of GaN from liquid Ga at a high temperature of 1400 to 1700 ° C. and an ultrahigh pressure of several tens of kbar. In this case, a group III nitride semiconductor film necessary for the device can be grown using the bulk-grown GaN substrate. Therefore, the GaN substrate can be provided without complicating the process as in the first and second conventional techniques.
[0011]
  However, in the third prior art, there is a problem that crystal growth at high temperature and high pressure is required, and a reaction vessel that can withstand the growth becomes extremely expensive. In addition, even with such a growth method, there is a problem that the size of the obtained crystal is at most about 1 cm, which is too small for practical use of the device.
[0012]
  As a technique for solving this problem of GaN crystal growth under high temperature and high pressure, the document “Chemistry of Materials Vol.9 (1997) p.413-416” (hereinafter referred to as “fourth prior art”) describes Na. There has been proposed a GaN crystal growth method that uses γ as a flux. This method uses sodium azide (NaN_Three) And metal Ga as raw materials, sealed in a nitrogen atmosphere in a stainless steel reaction vessel (inner vessel dimensions; inner diameter = 7.5 mm, length = 100 mm), and the reaction vessel is heated at a temperature of 600 to 800 ° C. for 24 to 100 By maintaining the time, the GaN crystal is grown. In the case of the fourth prior art, crystal growth at a relatively low temperature of about 600 to 800 ° C. is possible, and the pressure in the container is at most 100 kg / cm.²The point is that the pressure can be lowered compared with the third prior art. However, the problem of the fourth prior art is that the size of the obtained crystal is small enough to be less than 1 mm. This size is too small to put the device to practical use, as in the third prior art.
[0013]
  Japanese Laid-Open Patent Publication No. 2000-327495 (hereinafter referred to as “fifth prior art”) proposes a technique that combines the above-described fourth prior art with an epitaxial method using a substrate. In the fifth prior art, a substrate obtained by previously growing GaN or AlN on the substrate surface is used as a substrate, and a GaN film is epitaxially grown thereon using the fourth prior art. However, this fifth prior art is basically epitaxial growth, and does not lead to the solution of the crystal defect problem as in the first and second prior arts. Furthermore, since a GaN film or an AlN film is grown on the substrate in advance, the process becomes complicated, leading to high costs.
[0014]
  Recently, Japanese Patent Laid-Open Nos. 2000-12900 and 2000-22212 (hereinafter referred to as sixth prior art) have proposed a method for producing a GaN thick film substrate using a GaAs substrate. 12 and 13 show a method of manufacturing a GaN thick film substrate according to the sixth prior art. First, referring to FIG. 12, SiO 2 is formed on a (111) GaAs substrate 60 as in the first prior art.₂Using the film or SiN film as a mask 61, a GaN film 63 is selectively grown to a thickness of 70 μm to 1 mm (FIGS. 12 (1) to (3)). This crystal growth is performed by H-VPE. Thereafter, the GaAs substrate 60 is etched and removed with aqua regia to produce a GaN free-standing substrate 63 (FIG. 12 (4)). Based on this GaN free-standing substrate 63, a GaN crystal 64 having a thickness of several tens of mm is vapor-phase grown again by H-VPE (FIG. 13 (1)). The GaN crystal 64 having a thickness of several tens of mm is cut into a wafer shape by a slicer to produce a GaN wafer (FIGS. 13 (2) and (3)).
[0015]
  In the sixth prior art, a GaN free-standing substrate 63 is obtained, and a GaN crystal 64 having a thickness of several tens of mm can be obtained. However, the sixth prior art has the following problems. That is, SiN film or SiO₂Since the film is used as a selective growth mask, the manufacturing process becomes complicated and the cost is increased. Further, when a GaN crystal having a thickness of several tens of millimeters is grown by H-VPE, a GaN crystal (single crystal or polycrystal) having a similar thickness or amorphous GaN is deposited in the reaction vessel. There is a problem with mass productivity. Further, since the GaAs substrate is etched and removed as a sacrificial substrate for each growth, the cost is increased. In addition, regarding the crystal quality, there still remains a problem that the defect density is high due to the lattice irregularity and the difference in thermal expansion coefficient, which are basically caused by crystal growth on a heterogeneous substrate called GaAs.
[0016]
[Problems to be solved by the invention]
  The present invention does not complicate the process that is the problem of the first, second, fifth, or sixth prior art, and uses an expensive reaction vessel that is the problem of the third prior art. And a practical size for producing a device such as a high-performance light-emitting diode or LD without reducing the size of the crystal, which is a problem of the third and fourth prior arts, Group III nitride crystals that can grow low-cost, high-quality group III nitride crystalsManufacturing methodIt is intended to provide.
[0017]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1A step in which Na having a purity of 99.9% or more and 99.95% or less and Ga having a purity of 99.9999% are put in a container made of BN and held as a mixed melt, and a substance containing nitrogen is added to the mixed melt. Supplying from the surface to the inside, from the mixed melt and a substance containing nitrogen, III Composed of group metals and nitrogen III Crystal growth of group nitridesIt is a feature.
[0018]
  The invention according to claim 2 is the group III nitride crystal according to claim 1.Manufacturing methodInNitrogen gas, ammonia gas or sodium azide is used for the substance containing nitrogen.It is characterized by that.
[0019]
  The invention according to claim 3 is the group III nitride crystal according to claim 1 or claim 2.Manufacturing methodInThe reaction vessel is formed of sintered BN.Na is used as the alkali metal.
[0020]
  Further, the invention according to claim 4 is the group III nitride crystal according to claim 1 or claim 2.Manufacturing methodInThe reaction vessel is made of pyrolytic BNIt is characterized by that.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the present invention.UsedIt is a figure which shows the structural example of a group III nitride crystal growth apparatus.
[0022]
  Referring to FIG. 1, a mixed melt holding container 102 that holds a mixed melt of a substance containing an alkali metal (for example, Na) and at least a group III metal (for example, Ga) is installed in the reaction container 101. ing.
[0023]
  The substance containing an alkali metal and at least a group III metal may be supplied from the outside, or may exist in the reaction vessel 101 from the beginning.
[0024]
  The reaction vessel 101 is made of, for example, stainless steel.
[0025]
  The reaction vessel 101 is provided with a nitrogen supply pipe 104 for supplying a substance containing at least nitrogen (for example, nitrogen gas, ammonia gas, or sodium azide) to the space 108 in the reaction vessel 101. Nitrogen as used herein refers to nitrogen molecules or atomic nitrogen produced from nitrogen molecules or nitrogen-containing compounds, and atomic groups and molecular groups containing nitrogen. In the present invention, nitrogen refers to this Suppose that
[0026]
  The nitrogen supply pipe 104 is provided with a pressure adjusting mechanism 105 for adjusting the pressure of the nitrogen gas. The pressure adjustment mechanism 105 includes a pressure sensor and a pressure adjustment valve.
[0027]
  Further, the reaction vessel 101 is provided with a heating device 106 for controlling the inside of the reaction vessel 101 to a temperature at which a group III nitride (eg, GaN) can be grown. That is, the temperature control function by the heating device 106 can raise the temperature inside the reaction vessel 101 to a temperature at which crystal growth is possible, lower it to a temperature at which crystal growth stops, and hold the temperature at those temperatures for an arbitrary time. It is possible.
[0028]
  In the group III nitride crystal growth apparatus of FIG. 1, the temperature in the reaction vessel 101 and the effective nitrogen partial pressure are set to the conditions under which the group III nitride crystal grows, thereby starting the group III nitride crystal growth. Be able to.
[0029]
  Such group III nitride crystal growth device, group III nitride crystalManufacturing ofIn the method, in a predetermined container, a mixed melt of an alkali metal and a substance containing at least a group III metal is formed, and the mixed melt and a substance containing at least nitrogen are comprised of a group III metal and nitrogen. Since the group III nitride is crystal-grown, a high-quality group III nitride crystal can be obtained at low cost without requiring a complicated process as in the first or second prior art.
[0030]
  Furthermore, since it is possible to grow group III nitride crystals under conditions where the growth temperature is as low as 1000 ° C. or less and the pressure is as low as about 100 atm or less, it is possible to achieve ultra-high pressure and high temperature as in the third prior art. There is no need to use an expensive reaction vessel that can be tolerated. As a result, a group III nitride crystal can be produced at a low cost.
[0031]
  By the way, in the group III nitride crystal growth apparatus as shown in FIG. 1, when a predetermined container containing an alkali metal, a group III metal, a substance containing nitrogen, or a mixed melt contains a large amount of impurities, Impurities become nuclei or cause a catalytic action, so that the solid material covers the surface of the mixed melt composed of an alkali metal and a substance containing at least a group III metal. If the surface of the mixed melt is covered with the solid material, the subsequent dissolution of nitrogen into the mixed melt is hindered, and the crystal growth of the group III nitride crystal does not proceed.
[0032]
  The inventor of the present application believes that the cause of the generation of the solid material covering the surface of the mixed melt is based on group III nitride (the solid material is polycrystalline or non-crystalline).CrystalGroup III nitride), impurities contained in alkali metals, and / or impurities contained in substances containing at least group III metals, and / or impurities contained in substances containing nitrogen, and / or It has been found that it is caused by impurities in a predetermined container that contains the mixed melt (impurities coming out from the surface of the predetermined container or the inside of the predetermined container).
[0033]
  The present invention has been made based on the above findings by the inventors of the present application, and in a predetermined container, a mixed melt of an alkali metal and a substance containing at least a group III metal is formed, and the mixed melt When a group III nitride composed of a group III metal and nitrogen is grown from a substance containing at least nitrogen, the surface of the mixed melt is brought into a state in which nitrogen can be introduced into the mixed melt, and the group III It is characterized by growing nitride.
[0034]
  More specifically, the present invention relates to impurities contained in alkali metals and / or impurities contained in substances containing at least Group III metals and / or impurities contained in substances containing nitrogen and / or mixed fusion. It is intended to prevent the entire surface of the mixed melt from being covered with solid substances based on impurities in a predetermined container that contains the liquid (impurities coming out of the surface of the predetermined container or inside the predetermined container). ing.
[0035]
  For this reason, in the present invention, the purity of the alkali metal and / or the purity of the substance containing a group III metal and / or the purity of the substance containing nitrogen is determined so that at least a part of the surface of the mixed melt is polycrystalline or NonCrystalIt has the purity necessary to be in a state not covered with high-quality group III nitride.
[0036]
  Specifically, as a result of experiments by the inventors of the present application, it has been found that when the purity of the alkali metal is less than 99%, the solid surface covers the surface of the mixed melt. On the other hand, when the purity of the alkali metal is 99% or more, the solid matter is less likely to cover the surface of the mixed melt.
[0037]
  Furthermore, as a result of experiments by the inventors of the present application, it has been found that when the purity of the alkali metal is 99.9% or more, the surface of the mixed melt is extremely less covered with the solid material.
[0038]
  Further, it was found that when the purity of the alkali metal is 99.95% or more, the mixed melt surface is hardly covered with a solid material. Note that 99.95% has the highest purity as the currently available high purity alkali metal.
[0039]
  In addition, the purity of a substance containing a Group III metal and the purity of a substance containing nitrogen are preferably increased.
[0040]
  Furthermore, it is preferable to use a predetermined material with few impurities for the predetermined container for storing the mixed melt.
[0041]
  For example, the predetermined container can be formed of BN.
[0042]
  Alternatively, the predetermined container can be formed of AlN.
[0043]
  Alternatively, the predetermined container can be formed of pyrolytic BN.
[0044]
  Here, as the material of the predetermined container, BN is preferable because it contains fewer impurities than AlN. In addition, pyrolytic BN has fewer impurities than AlN and BN, and is more preferable.
[0045]
  The pyrolytic BN is also called PBN (Pyrolytic Boron Nitride), and is usually synthesized by CVD (Chemical Vapor Deposition) of boron chloride and ammonia. Compared with BN produced by generally popular sintering (Hot Press), there are few impurities and it is highly purified. In other words, the BN of the sintered body is B₂O_Three, CaO, SiO₂In general, pyrolytic BN has a small content of these impurities.
[0046]
  According to the experiment by the inventors of the present application, when pyrolytic BN is used even under the same condition that the solid melt covers the surface of the mixed melt when BN of sintered body is used as the material of the predetermined container, It was found that the solid surface was suppressed from covering the melt surface.
[0047]
  Thus, according to the present invention, impurities contained in alkali metals and / or impurities contained in substances containing at least Group III metals and / or impurities contained in substances containing nitrogen and / or mixed fluxes are included. Reduce the amount of impurities (impurities coming out of the surface of the predetermined container or the inside of the predetermined container) from the predetermined container that contains the liquid so that the entire surface of the mixed melt is not covered by the solid matter. Thus, continuous dissolution of nitrogen into the mixed melt proceeds, and crystal growth of the group III nitride crystal can be continued. Furthermore, since the group III metal constituting the solid material is reduced, the consumption of the group III metal on the surface of the mixed melt can be reduced, and a large amount of the group III metal is added to the group III nitride crystal in the mixed melt. It becomes possible to supply. As a result, it is possible to grow a large crystal up to a desired group III nitride crystal.
[0048]
(First reference example)
  FirstReference exampleThen, as shown in FIG. 2, the mixed melt holding container 102 contains a mixed melt 103 composed of Ga as a group III metal and Na as an alkali metal.
[0049]
  FirstReference exampleIn the example of FIG. 2, Ga as a Group III metal has a purity of 99.9999%, and Na as an alkali metal has a purity of 99%.
[0050]
  In the first embodiment (example in FIG. 2), the purity of the nitrogen gas supplied from the nitrogen supply pipe 104 is 99.999%.
[0051]
  The material of the mixed melt holding container 102 is BN (nitrogen boron) of a sintered body.
[0052]
  When a group III nitride crystal is grown by the group III nitride crystal growth apparatus having the configuration as shown in FIG.Reference exampleThen, the pressure of the nitrogen gas in the reaction vessel 101 is set to 50 atm, the temperature in the reaction vessel 101 is raised to a temperature of 750 ° C. at which crystal growth starts, and this growth condition is maintained for a certain time. As shown in FIG. 2, a GaN crystal 109 that is a group III nitride grows in the mixed melt holding container 102. At this time, the surface of the mixed melt 103 is covered with the solid material 110, but the holes 111 are opened in places of the solid material 110, and the solid material 110 does not cover the entire surface of the mixed melt 103. Thereby, nitrogen can be dissolved in the mixed melt 103 through the hole 111. As described above, the inventor of the present application determines that the degree to which the solid material 110 covers depends on the purity of Na, the purity of Ga, the purity of nitrogen gas, or the material of the mixed melt holding container 102. It was found by the experiment. Of these, it was found that the extent to which the solid material 110 was covered had the greatest influence due to the purity of Na. Further, as a result of the analysis, the solid material 110 covering the surface of the mixed melt 103 is polycrystalline GaN or non-crystalline.CrystalIt was found that quality GaN is the main constituent.
[0053]
  As in the above example, the purity of Na is 99%, the purity of Ga is 99.9999%, the purity of nitrogen gas is 99.999%, and the material of the mixed melt holding vessel 102 is sintered BN. As shown in FIG. 2, the solid object 110 has a shape in which a hole 111 is partially opened. Nitrogen dissolves into the mixed melt 103 through the hole 111, whereby a single crystal 109 of GaN as a group III nitride can be grown in the mixed melt 103.
[0054]
  (FirstEmbodiment)
  FirstThe first embodiment is also the firstReference exampleAs in FIG. 1, the same group III nitride crystal growth apparatus as in FIG.Reference exampleThe crystal is grown by the same method as in the above.
[0055]
  Here, the purity of Ga as a group III metal is 99.9999%, the purity of nitrogen gas is 99.9999%, and the material of the mixed melt holding vessel 102 is BN of a sintered body. Growth conditions such as temperature and pressure are the firstReference exampleIt is the same.
[0056]
  FirstReference exampleIs different from the firstReference exampleThen, Na as an alkali metal has a purity of 99%,FirstIn this embodiment, the purity of Na as an alkali metal is 99.9%. In this case, the state in the mixed melt holding container 102 is as shown in FIG.
[0057]
  That is,FirstThe first embodiment is also the firstReference exampleThe GaN single crystal 109, which is a group III nitride, is grown in the mixed melt 103 by setting the nitrogen gas pressure and temperature in the same manner as described above and maintaining the growth conditions constant.FirstIn the embodiment, the surface of the mixed melt 103 in the mixed melt holding container 102 is covered with about half of the mixed melt 103 by the solid material 110. The ratio of the solid material 110 covering the surface of the mixed melt 103 may be about half, or may be larger or smaller than that, depending on the growth lot, but at least in the first embodiment. It is not in the state that the hole is opened.
[0058]
  Nitrogen dissolves into the mixed melt 103 through the region 111 where the solid melt 110 does not cover the surface of the mixed melt 103, and the crystal growth of the GaN crystal 109 proceeds.FirstIn the embodiment, the region 111 where the solid material 110 does not cover the surface of the mixed melt 103 is the first.Reference exampleAs a result, the larger GaN single crystal 109 can be grown. That is, polycrystalline GaN or non-CrystalSince the generation of the solid material 110 in which the quality GaN is the main constituent material is small, Ga in the mixed melt 103 can contribute to the growth of the desired GaN single crystal 109 more efficiently. Furthermore, since the rate of nitrogen dissolution is high, the generation of a large number of nuclei can be prevented, and nitrogen can be preferentially taken into large nuclei, allowing the growth of large GaN single crystals.
[0059]
  As aboveFirstIn this embodiment, the purity of Na is 99.9%, which is higher than that in the first embodiment, so that the solid material 110 covering the surface of the mixed melt 103 is reduced, and a larger GaN single crystal 109 is crystallized. It becomes possible to grow.
[0060]
  (SecondEmbodiment)
  SecondThe embodiment ofFirst reference example, firstIn the same manner as in the embodiment, using the same group III nitride crystal growth apparatus as in FIG.First reference example, firstThe crystal is grown by the same method as in the embodiment.
[0061]
  Here, the purity of Ga as a group III metal is 99.9999%, the purity of nitrogen gas is 99.9999%, and the material of the mixed melt holding vessel 102 is BN of a sintered body. Growth conditions such as temperature and pressure areFirst reference example, firstThis is the same as the embodiment.
[0062]
  First reference example, firstThe difference from the embodiment ofSecondIn this embodiment, the purity of Na as an alkali metal is 99.95% or more. In this case, the state in the mixed melt holding container 102 is as shown in FIG.
[0063]
  That is,SecondEven in the embodiment ofFirst reference example, firstIn the same manner as in the embodiment, by setting the nitrogen gas pressure and temperature and maintaining the growth conditions constant, the GaN single crystal 109, which is a group III nitride, grows in the mixed melt 103. In the third embodiment, the solid object 110 is only scattered on a part of the surface of the mixed melt 103 in the mixed melt holding container 102. The ratio of the solid material 110 covering the mixed melt 103 is at most about 10%. This is the firstReference exampleThe ratio of the area covered by the solid object 110 and the area not covered (area with holes) 111 is almost opposite.
[0064]
  Nitrogen dissolves into the mixed melt 103 through the region 111 where the solid melt 110 does not cover the surface of the mixed melt 103, and crystal growth of the GaN crystal 109 proceeds. In the third embodiment, the region 111 where the solid material 110 does not cover the surface of the mixed melt 103 is the first region.Reference exampleAndFirstWhen the number is larger than that in the embodiment, a larger GaN single crystal 109 can be grown. That is, polycrystalline GaN or non-CrystalSince the generation of the solid material 110 in which the quality GaN is the main constituent material is small, Ga in the mixed melt 103 can contribute to the growth of the desired GaN single crystal 109 more efficiently. Furthermore, since the rate of nitrogen dissolution is high, the generation of a large number of nuclei can be prevented, and nitrogen can be preferentially taken into large nuclei, allowing the growth of large GaN single crystals.
[0065]
  As aboveSecondIn the embodiment, the purity of Na is 99.95% and the firstReference example, Number1By making the height higher than in the case of the embodiment, the solid material 110 covering the surface of the mixed melt 103 becomes small, and a larger GaN single crystal 109 can be grown.
[0066]
  (ThirdEmbodiment)
  ThirdThe first embodiment is also the firstReference example, No. 1 Embodiment and secondAs in the first embodiment, the same group III nitride crystal growth apparatus as in FIG.Reference example, No. 1 Embodiment and secondThe crystal is grown by the same method as in the embodiment.
[0067]
  Here, the purity of Ga as a group III metal is 99.9999%, and the purity of nitrogen gas is 99.9999%. Growth conditions such as temperature and pressure are the firstReference example, No. 1 Embodiment and secondThis is the same as the embodiment.
[0068]
  FirstReference example, No. 1 Embodiment and secondThe difference from the embodiment ofThirdIn the embodiment, the purity of Na as an alkali metal is 99.95% or more, and the material of the mixed melt holding container 102 is pyrolytic BN. In this case, the state in the mixed melt holding container 102 is as shown in FIG.
[0069]
  That is,ThirdThe first embodiment is also the firstReference example, No. 1 Embodiment and secondIn the same manner as in the embodiment, by setting the nitrogen gas pressure and temperature and maintaining the growth conditions constant, the GaN single crystal 109, which is a group III nitride, grows in the mixed melt 103. FirstThreeIn the embodiment, the surface of the mixed melt 103 in the mixed melt holding container 102 has a firstReference example, No. 1 Embodiment and secondThere is no solid material 110 present in this embodiment. That is, thisThirdIn the case of this embodiment, there is no solid material 110 that blocks the penetration of nitrogen into the mixed melt 103. Therefore, the crystal growth of the GaN crystal 109 can proceed more smoothly.
[0070]
  in this way,ThirdIn this embodiment, since there is no solid material 110, a larger GaN single crystal 109 can be grown. That is, polycrystalline GaN or non-CrystalSince there is no generation of the solid material 110 whose main constituent material is GaN, Ga in the mixed melt 103 can contribute to the growth of the desired GaN single crystal 109 more efficiently. Furthermore, since the rate at which nitrogen dissolves is large, the generation of a large number of nuclei is prevented, and nitrogen is preferentially taken into large nuclei, thereby enabling growth of a large GaN single crystal.
[0071]
  As aboveThirdIn the embodiment, the purity of Na is 99.95% or more and the first.Reference example, No. 1 Embodiment and secondAnd by using pyrolytic BN as the material of the mixed melt holding container 402, the solid material 110 covering the surface of the mixed melt 103 is eliminated, and a larger GaN single crystal 109 is formed. Crystal growth is possible. Moreover, since pyrolytic BN is used and Na purity is high, impurities contained in the mixed melt 103 are reduced, and the crystal quality of the obtained GaN single crystal 109 is improved.
[0072]
  In the above-described example, Na is used as the alkali metal, but it is also possible to use an alkali metal such as K (potassium) in addition to Na. In the above-described example, Ga is used as the substance containing at least a group III metal. However, it is also possible to use a GaNa alloy or another group III metal such as Al or In. In the above-described example, nitrogen gas (N₂), But in addition to nitrogen gas, ammonia gas and sodium azide (NaN)_Three) Etc. can also be used.
[0073]
  Further, the mixed melt holding container 102 has the firstReference example, no. 1 The third to third embodimentsIn the embodiment, a material made of BN is used, but for example, AlN can be used instead of BN. However, BN is better than AlN as the material of the mixed melt holding container 102. Further, the material of the mixed melt holding container 102 is more than BN.ThirdPyrolytic BN is better as in the embodiment.
[0074]
  In other words, the group III nitride crystal growth apparatus of the present invention is provided with a mixed melt holding container 102 that holds a mixed melt of an alkali metal and a substance containing at least a group III metal, and a mixed melt holding container 102. And at least nitrogen introduction means (104, 105) for introducing a substance containing at least nitrogen into the reaction vessel 101, and the mixed melt is mixed with the mixed melt holding vessel 102. The contact region is characterized by having a sufficient purity with few impurities.
[0075]
  As described above, in the present invention, the region where the mixed melt is in contact with the mixed melt holding container 102 has sufficient purity with few impurities, so that the entire surface of the mixed melt is not covered by the solid matter. As a result, continuous dissolution of nitrogen into the mixed melt proceeds, and crystal growth of the group III nitride crystal can be continued. Furthermore, since the group III metal constituting the solid material is reduced, the consumption of the group III metal on the surface of the mixed melt can be reduced, and a large amount of the group III metal is added to the group III nitride crystal in the mixed melt. It becomes possible to supply. As a result, it is possible to grow a large crystal up to a desired group III nitride crystal. Moreover, the impurities contained in the mixed melt are reduced, and the crystal quality of the obtained group III nitride single crystal is improved.
[0076]
  Further, as shown in FIG. 6, a group III nitride 115 (for example, GaN) of the same type as a group III nitride (for example, GaN) crystal-grown by a group III nitride crystal growth apparatus inside the mixed melt holding container 102. ) Can be applied (coated) in advance. In this case, impurities can be further reduced, and a higher-quality group III nitride crystal (for example, GaN) can be grown.
[0077]
  In the example of FIG. 1, the mixed melt holding container 102 is provided separately from the reaction container 101, but the reaction container 101 and the mixed melt holding container 102 may be integrated. FIG. 7 is a diagram showing another configuration example of the group III nitride crystal growth apparatus according to the present invention. In FIG. 7, the same parts as those in FIG. Referring to FIG. 7, in this group III nitride crystal growth apparatus, the reaction vessel and the mixed melt holding vessel of FIG. 1 are configured as an integral unit. That is, the reaction vessel 200 includes a vessel outer wall 201 and a vessel inner wall 202 for substantially holding the mixed melt.
[0078]
  Here, the container outer wall 201 corresponds to the reaction container 101 of FIG. 1 and is made of, for example, stainless steel.
[0079]
  The container inner wall 202 corresponds to the mixed melt holding container 102 of FIG. 1 and is formed of BN, AlN, or pyrolytic BN. However, as described above, BN is better than AlN as the material of the container inner wall 202, and pyrolytic BN is better than BN.
[0080]
  In the case of the configuration shown in FIG. 7, the nitrogen supply pipe 104 is introduced into the reaction vessel 200 from the top or side of the reaction vessel 200. Also in FIG. 7, as in FIG. 1, the nitrogen supply pipe 104 is provided with a pressure adjusting mechanism 105 for adjusting the pressure of the nitrogen gas.
[0081]
  In the group III nitride crystal growth apparatus having the configuration shown in FIG. 7, a mixed melt of an alkali metal (for example, Na) and a substance containing at least a group III metal (for example, Ga) is contained in the inner wall 202 of the reaction vessel 200. A group III composed of a group III metal and nitrogen is formed by supplying a material containing at least nitrogen (for example, nitrogen gas, ammonia gas or sodium azide) from the nitrogen supply pipe 104 to the space 208 in the reaction vessel 200. A crystal of nitride (eg, GaN) is grown.
[0082]
  At this time, as described above, the purity of the alkali metal and / or the purity of the substance containing the Group III metal and / or the purity of the substance containing nitrogen is increased at least on a part of the surface of the mixed melt. Crystal or nonCrystalThe purity is such that it is not covered with quality III-nitride.
[0083]
  Specifically, the first mentioned above.Reference examples, 1st to 3rdEmbodiment ofOne ofIn the same manner as described above, a group III nitride (for example, GaN) can be grown.Reference examples, 1st to 3rdOf the embodimenteitherThe same effect can be obtained.
[0084]
  In other words, the group III nitride crystal growth apparatus of FIG. 7 includes a reaction vessel 200 that holds a mixed melt of an alkali metal and a substance containing at least a group III metal, and a substance containing at least nitrogen in the reaction vessel 200. At least a nitrogen introducing means (104, 105) for introducing the reaction vessel 200. The reaction vessel 200 is constituted by a vessel outer wall 201 and a vessel inner wall 202 for substantially holding the mixed melt. The region where the melt is in contact with the container inner wall 202 is characterized by having a sufficient purity with few impurities.
[0085]
  As described above, in the group III nitride crystal growth apparatus of FIG. 7, the region where the mixed melt is in contact with the inner wall 202 of the container has sufficient purity with few impurities. As a result, the nitrogen can be continuously dissolved into the mixed melt, and the crystal growth of the group III nitride crystal can be continued. Furthermore, since the group III metal constituting the solid material is reduced, the consumption of the group III metal on the surface of the mixed melt can be reduced, and a large amount of the group III metal is added to the group III nitride crystal in the mixed melt. It becomes possible to supply. As a result, it is possible to grow a large crystal up to a desired group III nitride crystal. Moreover, the impurities contained in the mixed melt are reduced, and the crystal quality of the obtained group III nitride single crystal is improved.
[0086]
  Further, as shown in FIG. 8, in the group III nitride crystal growth apparatus of FIG. 7, the same kind as the group III nitride (for example, GaN) crystal-grown by the group III nitride crystal growth apparatus inside the inner wall 202 of the container. The group III nitride 215 (for example, GaN) can be applied (coated) in advance. In this case, impurities can be further reduced, and a higher-quality group III nitride crystal (for example, GaN) can be grown.
[0087]
  As described above, according to the present invention, a group III nitride crystal having a practical size, low cost, and high quality for manufacturing a device such as a high performance light emitting diode or LD is manufactured and provided. can do.
[0088]
  Therefore, a high-quality group III nitride semiconductor device having a high quality and high performance can be produced using the high-quality group III nitride crystal having a practical size thus obtained. The high performance mentioned here is, for example, a semiconductor laser or a light emitting diode, which has a high output and a long life that has not been realized in the past, and in the case of an electronic device, low power consumption, low noise, It can operate at high speed and high temperature, and in the case of a light receiving device, it has low noise and long life.
[0089]
  For example, a semiconductor light emitting device that emits light with a wavelength shorter than 400 nm can be manufactured as a group III nitride semiconductor device. That is, in the prior art, light emission from a deep order is dominant in the emission spectrum of the GaN film, and there is a problem that device characteristics are poor at a wavelength shorter than 400 nm, but the present invention has good characteristics even in the ultraviolet region. A light emitting device can be provided. That is, by using the high-quality group III nitride crystal obtained by the present invention for the substrate, a group III nitride semiconductor device with few crystal defects and impurities can be realized, and as a result, light emission from a deep order is suppressed. Thus, it is possible to realize a highly efficient light emission characteristic.
[0090]
  FIG. 9 is a diagram showing an example of a group III nitride semiconductor device manufactured using the group III nitride crystal obtained by the present invention. In the example of FIG. 9, the group III nitride semiconductor device is a semiconductor laser. It is configured. Referring to FIG. 9, this group III nitride semiconductor device includes an n-type AlGaN cladding layer 502, an n-type AlGaN clad layer 502 on an n-type GaN substrate 501 manufactured using a group III nitride crystal (GaN) obtained by the present invention. A type GaN guide layer 503, an InGaN MQW (multiple quantum well) active layer 504, a p-type GaN guide layer 505, a p-type AlGaN cladding layer 506, and a p-type GaN contact layer 507 are sequentially grown to form a stacked structure. Yes. As this crystal growth method, a thin film crystal growth method such as MO-VPE (metal organic chemical vapor deposition) method or MBE (molecular beam epitaxy) method can be used.
[0091]
  A ridge structure is formed in the laminated structure, and SiO₂The insulating film 508 is formed in a state where only the region of the contact layer 507 is removed, and a p-side ohmic electrode Al / Ni 509 is formed on the contact layer 507. An n-side ohmic electrode Al / Ti 510 is formed on the back surface of the substrate 501.
[0092]
  In this semiconductor laser, laser is oscillated by injecting current from the p-side ohmic electrode Al / Ni 509 and the n-side ohmic electrode Al / Ti 510, and laser light is emitted in the direction of the arrow in the figure.
[0093]
  Since this semiconductor laser uses the GaN crystal obtained by the present invention as the substrate 501, there are few crystal defects in the semiconductor laser device, and it has a large output operation and a long life. Further, since the GaN substrate 501 is n-type, electrodes can be directly formed on the substrate 501, and two electrodes on the p side and the n side can be formed only from the surface as in the first prior art (FIG. 10). There is no need to take out, and the cost can be reduced. Further, the light emitting end face can be formed by cleaving, and in combination with chip separation, a high-quality device can be realized at low cost.
[0094]
  In the example of FIG. 9, InGaN MQW is the active layer 504, but the emission wavelength can be shortened by using AlGaN MQW as the active layer 504. In any case, in the example of FIG. 9, since the GaN substrate 501 has few defects and few impurities, light emission from a deep order is reduced, and a highly efficient light-emitting device is possible even when the wavelength is shortened. That is, it becomes easy to manufacture a light emitting device having a shorter emission wavelength.
[0095]
  In the above example, the application of the group III nitride crystal obtained by the present invention to an optical device has been described. However, the group III nitride crystal obtained by the present invention can also be applied to an electronic device. In other words, by using a GaN substrate with few defects, the GaN-based thin film epitaxially grown on the GaN substrate has few crystal defects. A high-performance device can be realized.
[0096]
【The invention's effect】
  As explained above, claims 1 to4According to the described invention,99.9% purity More than 99.95% Na and 99.9999% Ga are put in a container made of BN and held as a mixed melt, and a substance containing nitrogen is supplied from the surface of the mixed melt to the inside. From the mixed melt and a substance containing nitrogen, III Composed of group metals and nitrogen III Crystal growth of group nitridesTherefore, it is possible to grow a group III nitride crystal having a practical size, low cost, and high quality for producing a device such as a high performance light emitting diode or LD. In other words, by allowing the surface of the mixed melt to be in a state where nitrogen can be introduced into the mixed melt and growing the group III nitride, nitrogen can be efficiently dissolved in the mixed melt. The group III nitride single crystal continues to grow in the mixed melt, and a large group III nitride crystal can be obtained.
[Brief description of the drawings]
FIG. 1 shows the present invention.UsedIt is a figure which shows the structural example of a group III nitride crystal growth apparatus.
FIG. 2 shows the first of the present inventionReference exampleIt is a figure for demonstrating.
FIG. 3 of the present inventionFirstIt is a figure for demonstrating embodiment of this.
FIG. 4 shows the first aspect of the present invention.2It is a figure for demonstrating embodiment of this.
FIG. 5 shows the first of the present invention.3It is a figure for demonstrating embodiment of this.
6 is a group III nitride crystal growth apparatus of FIG. 1 in which a group III nitride of the same type as the group III nitride crystal grown by the group III nitride crystal growth apparatus is previously placed inside the mixed melt holding vessel. It is a figure which shows the structure to apply | coat
FIG. 7 shows the present invention.UsedIt is a figure which shows the other structural example of a group III nitride crystal growth apparatus.
8 is a group III nitride crystal growth apparatus of FIG. 7 in which a group III nitride of the same type as the group III nitride crystal grown by the group III nitride crystal growth apparatus is applied in advance to the inner wall of the container. FIG.
FIG. 9 is a diagram showing an example of a group III nitride semiconductor device manufactured using a group III nitride crystal obtained by the present invention.
FIG. 10 is a diagram showing a conventional laser diode.
FIG. 11 is a diagram showing a conventional semiconductor laser.
FIG. 12 is a diagram showing a method of manufacturing a GaN thick film substrate according to a sixth conventional technique.
FIG. 13 is a diagram showing a method of manufacturing a GaN thick film substrate according to a sixth conventional technique.
[Explanation of symbols]
101 reaction vessel
102 Mixed melt holding container
103 Mixed melt
104 Nitrogen supply pipe
105 Pressure adjustment mechanism
106 Heating device
108 Space in reaction vessel
109 Group III nitride (GaN) crystals
115 Group III nitride
200 reaction vessel
201 Container outer wall
202 Container inner wall
208 Space in reaction vessel
215 Group III nitride
501 n-type GaN substrate
502 type AlGaN cladding layer
503 n-type GaN guide layer
504 InGaN MQW active layer
505 p-type GaN guide layer
506 p-type AlGaN cladding layer
507 p-type GaN contact layer
508 SiO₂Insulationfilm
509 p-side ohmic electrode
510 n-side ohmic electrode

Claims (4)

A step of holding Na having a purity of 99.9% or more and 99.95% or less and Ga having a purity of 99.9999% in a container made of BN and holding it as a mixed melt;
  Supplying a substance containing nitrogen from the surface of the mixed melt to the inside;
  From the mixed melt and a substance containing nitrogen, III Composed of group metals and nitrogen III Characterized by crystal growth of group nitrides III A method for producing a group nitride crystal. The method for producing a group III nitride crystal according to claim 1, wherein nitrogen-containing material, ammonia gas, or sodium azide is used as the substance containing nitrogen . The said reaction container is formed with BN of the sintered compact, The Claim 1 or 2 characterized by the above-mentioned. III A method for producing a group nitride crystal. Before SL reaction vessel, method for producing a group III nitride crystal according to claim 1 or 2, characterized in that it is formed by pyrolytic BN.

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