Crystalline group-iii nitride and production method therefor

Abstract

Provided is a crystalline Group-III nitride which can be produced in an improved yield. The crystalline Group-III nitride is one formed on a seed substrate by crystal growth, and comprises: a base portion formed by crystal growth from the seed substrate and extending to a growth surface having growth pits as recesses; and a filling portion formed by filling the growth-pit recesses in the growth surface with the crystalline Group-III nitride.

Description

Group III nitride crystal and method for producing same

[0001] The present disclosure relates to Group III nitride crystals and methods for making the same.

[0002] Vertical GaN power devices require GaN substrates with low resistivity and low dislocation density. For example, when fabricating n-type low resistivity GaN substrates, pits have been formed during growth to improve carrier concentration and reduce dislocation density (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-50107

[0004] However, the manufacturing method described in Patent Document 1 suffers from the problem that breakage and cracks occur when the temperature is lowered after growth, resulting in a low production yield of the Group III nitride crystal. The occurrence of breakage and cracks is due to the fact that the growth surface is covered with pits (growth pits) and there is a difference in the thermal expansion coefficient between the seed substrate and the growth layer.

[0005] FIG. 1(a) is a schematic cross-sectional view showing the vertical cross-sectional structure at high temperature immediately after GaN crystal growth on a seed substrate by OVPE, and FIG. 1(b) is a schematic cross-sectional view showing the vertical cross-sectional structure after cooling to room temperature. When low-resistivity n-type GaN is fabricated by adding oxygen at a higher concentration than that of the seed substrate using the OVPE method described in Patent Document 1, the thermal expansion coefficient of the n-type low-resistivity GaN is greater than that of the seed substrate. In this case, as shown in FIG. 1(b), the growth layer shrinks more than the seed substrate during cooling after growth, resulting in deformation into a downward convex shape. Furthermore, if pits are present on the surface, the stress generated on the surface is greater than that in a flat case, as indicated by the arrows in FIG. 1(b). Therefore, the probability of fractures and cracks occurring increases.

[0006] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a Group III nitride crystal and a method for manufacturing a Group III nitride crystal that can improve the production yield when manufacturing the Group III nitride crystal.

[0007] A Group III nitride crystal according to the present disclosure is a Group III nitride crystal grown on a seed substrate, and has a base portion extending from the seed substrate to a growth surface having a growth pit formed in a recess, and a buried portion in which the recess of the growth pit is buried by the Group III nitride crystal within the growth surface.

[0008] A method for producing a Group III nitride crystal according to the present disclosure includes the steps of preparing a seed substrate, supplying a Group III element oxide gas and a nitrogen-containing gas onto the seed substrate to grow a Group III nitride crystal three-dimensionally on the seed substrate, and growing the Group III nitride crystal two-dimensionally and filling growth pits on the surface of the Group III nitride crystal to smooth the surface.

[0009] According to the Group III nitride crystal and the method for manufacturing the same according to the present disclosure, the production yield when manufacturing Group III nitride crystal can be improved, and high-quality Group III nitride crystal can be manufactured.

[0010] 1A is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane at a high temperature immediately after GaN crystal has been grown on a seed substrate by OVPE, and FIG. 1B is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane after cooling to room temperature following FIG. 1A is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane of a Group III nitride crystal at a high temperature immediately after GaN crystal has been grown on a seed substrate by OVPE, and FIG. 1B is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane of a Group III nitride crystal in which a smoothing step has been performed following FIG. 1A to form a buried portion by filling growth pits in recesses in the growth surface in a Group III nitride crystal manufacturing method according to a first embodiment. 1A is a chronological flowchart of a Group III nitride crystal manufacturing method according to a first embodiment, and FIG. 1B is a diagram showing, as steps, the functional units from upstream to downstream within a manufacturing apparatus used in this manufacturing method. 1B is a schematic cross-sectional view of a Group III nitride crystal manufacturing apparatus according to a first embodiment. 1C is a graph showing the relationship between oxygen concentration and stress generated in the buried portion during the smoothing step.

[0011] A Group III nitride crystal according to a first aspect is a Group III nitride crystal grown on a seed substrate, and has a base portion extending from the seed substrate to a growth surface having growth pits in recesses, and a buried portion in which the recesses of the growth pits are buried by Group III nitride crystal within the growth surface.

[0012] A Group III nitride crystal according to a second aspect is the same as in the first aspect, wherein the growth pits are filled with Group III nitride crystal, and the oxygen concentration in the substrate portion is 1×10 ２０ atoms / cm ３ It may be more than that.

[0013] A Group III nitride crystal according to a third aspect is any of the first and second aspects, wherein the growth pits are filled with Group III nitride crystal, and the oxygen concentration in the substrate portion is 1×10 ２１ atoms / cm ３ The oxygen concentration in the buried portion is 4.8×10 ２０ atoms / cm ３ It may be more than that.

[0014] A Group III nitride crystal according to a fourth aspect is any one of the first to third aspects, wherein the growth pits are filled with Group III nitride crystal, and the dislocation density is 5×10 ５ cm －２ It may be the following:

[0015] A method for producing a Group III nitride crystal according to the fifth aspect includes the steps of preparing a seed substrate, supplying a Group III element oxide gas and a nitrogen-containing gas onto the seed substrate to grow a Group III nitride crystal three-dimensionally on the seed substrate, and growing the Group III nitride crystal two-dimensionally and filling in recesses in growth pits on the surface of the Group III nitride crystal to smooth the surface.

[0016] A method for producing a Group III nitride crystal according to a sixth aspect may be the same as the fifth aspect, in which the surface smoothing step is carried out by controlling the Group III element oxide gas and nitrogen-containing gas that are supplied to make the V / III ratio five or more.

[0017] A seventh aspect of the method for producing a Group III nitride crystal is the fifth aspect described above, wherein the surface smoothing step may be carried out by raising the substrate temperature by 50° C. or more higher than in the growth step.

[0018] A method for producing a Group III nitride crystal according to an eighth aspect is any one of the fifth to seventh aspects, wherein in the step of smoothing the surface of the Group III nitride crystal, the oxygen concentration in the region where the surface irregularities have been filled is 4.8×10 ２０ atoms / cm ３ It may be more than that.

[0019] Group III nitride crystals and methods for producing the same according to embodiments will be described in detail below with reference to the accompanying drawings, although the present disclosure is not limited to these embodiments.

[0020] 2A is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane at a high temperature immediately after GaN crystal growth on a seed substrate by OVPE, and FIG. 2B is a schematic cross-sectional view showing the cross-sectional structure of a vertical plane of a Group III nitride crystal in which a smoothing step has been performed after FIG. 2A in the method for producing a Group III nitride crystal according to the first embodiment, thereby forming buried portions that fill growth pits in recesses in the growth surface. An overview of the Group III nitride crystal according to the first embodiment will be described with reference to FIG. 2 . The Group III nitride crystal according to the first embodiment is a Group III nitride crystal grown on a seed substrate. This Group III nitride crystal has a base portion that grows from the seed substrate to a growth surface having growth pits in recesses, and a buried portion in which the recesses in the growth pits are filled with Group III nitride crystal within the growth surface. Note that filling the growth pits requires switching the growth mode of the Group III nitride crystal to two-dimensional growth. Methods for switching from the three-dimensional growth mode in normal crystal growth to the two-dimensional growth mode include, for example, increasing the growth temperature compared to that during growth of the substrate portion shown in FIG. 2B or increasing the V / III ratio (ratio of group V source to group III source). Methods for increasing the V / III ratio include increasing the supply rate of the group V source or decreasing the supply rate of the group III source. By controlling the growth conditions of the buried portion, the oxygen concentration in the buried portion can be controlled, and the difference in thermal expansion coefficient between the buried portion and the substrate portion can be controlled.

[0021] The first effect of forming the buried portion is that it can reduce stress concentration when a load is applied to the substrate portion by smoothing the surface irregularities formed by growth pits. For example, when a Group III nitride crystal is grown on a seed substrate while rotating during the growth process, contact with the substrate susceptor is unavoidable, and a load is applied from the substrate susceptor to the growing crystal. Therefore, forming the buried portion can suppress breakage and cracking. Furthermore, as a second effect, by forming a buried portion whose thermal expansion coefficient difference with the substrate portion is close, it can reduce stress concentration during cooling caused by the difference in thermal expansion coefficients. Therefore, providing a buried portion whose thermal expansion coefficient difference is close can further suppress breakage and cracking.

[0022] <Outline of III-nitride crystal manufacturing method> Figure 3(a) is a chronological flowchart of a III-nitride crystal manufacturing method according to the first embodiment, and (b) shows, as steps, the functional units from upstream to downstream within a manufacturing apparatus used in this manufacturing method. Figure 4 is a schematic cross-sectional view of a III-nitride crystal manufacturing apparatus according to the first embodiment. An outline of the III-nitride crystal manufacturing method according to the first embodiment will be described with reference to the flowchart of Figure 3 and Figure 4. The III-nitride crystal manufacturing method includes the steps of preparing a seed substrate, supplying a III-element oxide gas and a nitrogen-containing gas to grow III-nitride crystal on the seed substrate, and filling growth pits and smoothing the surface in the latter part of the III-nitride crystal growth step.

[0023] In the seed substrate preparation step of preparing the seed substrate 116, the seed substrate 116 is placed on a substrate susceptor 117. In this embodiment, the method for producing a Group III nitride crystal also includes a temperature-raising step. In the temperature-raising step, the growth chamber 111 is heated to 100°C or higher and lower than 500°C in an inert gas atmosphere. In this embodiment, the method for producing a Group III nitride crystal also includes a decomposition protection temperature-raising step 1. In the decomposition protection temperature-raising step 1, NH ３ The temperature of the growth chamber 111 is increased to 500° C. or higher and lower than 1100° C. in a gas atmosphere.

[0024] In this embodiment, the method for producing a group III nitride crystal includes a decomposition protection temperature increase step 2. In the decomposition protection temperature increase step 2, NH ３ Gas and Ga ２ The growth chamber 111 is heated to a temperature of 1100° C. or higher and lower than 1500° C. in an O gas atmosphere.

[0025] In the growth step of growing a Group III nitride crystal on the seed substrate 116, a Group III element oxide gas is generated in the source chamber 100 and supplied to the growth chamber 111, and a nitrogen-containing gas is also supplied to the growth chamber 111, thereby growing a Group III nitride crystal on the seed substrate 116.

[0026] The growth step further comprises a reactive gas supply step, a Group III element oxide gas generation step, a Group III element oxide gas supply step, a nitrogen-containing gas supply step, a Group III nitride crystal generation step, and a residual gas exhaust step. Note that each step included in the growth step may be carried out simultaneously within the Group III nitride crystal manufacturing apparatus.

[0027] In the reactive gas supply step, a reactive gas is supplied to the raw material reaction chamber, and in the Group III element oxide gas generation step, the starting Group III element source is reacted with the reactive gas (a reducing gas if the starting Group III element source is an oxide, and an oxidizing gas if the starting Group III element source is a metal) to generate a Group III element oxide gas.

[0028] In the Group III element oxide gas supplying step, the Group III element oxide gas produced in the Group III element oxide gas producing step is supplied to the growth chamber.

[0029] In the nitrogen-containing gas supplying step, a nitrogen-containing gas is supplied to the growth chamber, and in the Group III nitride crystal generating step, the Group III element oxide gas supplied into the growth chamber in the Group III element oxide gas supplying step and the nitrogen-containing gas supplied into the growth chamber in the nitrogen-containing gas supplying step are reacted with each other to grow a Group III nitride crystal on the seed substrate.

[0030] In the residual gas exhaust step, unreacted gases that do not contribute to the formation of group III nitride crystals are exhausted to the outside of the chamber.

[0031] In this embodiment, the method for manufacturing a Group III nitride crystal includes a surface smoothing step, which promotes two-dimensional growth of the Group III nitride crystal (in the case of growth on the +c plane, growth that exposes the +c plane) and reduces surface irregularities in order to smooth the surface of the Group III nitride crystal grown on seed substrate 116.

[0032] In this embodiment, the method for producing a Group III nitride crystal includes a decomposition protection temperature-lowering step. In the decomposition protection temperature-lowering step, in order to suppress the decomposition of the Group III nitride crystal grown on the seed substrate 116, NH ３ While supplying the gas, the temperatures of the source chamber 100 and the growth chamber 111 are lowered to 500°C.

[0033] In this embodiment, the method for producing a group III nitride crystal includes a temperature-lowering step in which the temperatures of the source chamber 100 and the growth chamber 111 are lowered to below 100° C. in an inert gas atmosphere.

[0034] In this embodiment, the method for producing a group III nitride crystal includes an unloading step in which seed substrate 116 on which group III nitride crystal has been grown is unloaded from growth chamber 111.

[0035] <Outline of Group III Nitride Crystal Manufacturing Apparatus> An outline of the manufacturing apparatus used in the method for manufacturing a Group III nitride crystal according to the first embodiment will be described with reference to FIG. 4 . In FIG. 4 , the size, ratio, etc. of each component may differ from the actual one. The Group III nitride crystal manufacturing apparatus has a source material reaction chamber 101 disposed within a source material chamber 100, and a source material boat 104 carrying a starting Group III element source 105 disposed within the source material reaction chamber 101. A reactive gas supply pipe 103 is connected to the source material reaction chamber 101, and supplies a gas that reacts with the starting Group III element source 105. The source material reaction chamber 101 has a Group III element oxide gas outlet 107 for discharging the generated Group III element oxide gas. When the starting Group III source is an oxide, a reducing gas is used as the reactive gas. When the starting Group III source is a metal, an oxidizing gas is used as the reactive gas. A first carrier gas supply port 102 for supplying a first carrier gas is connected to the source chamber 100, and the first carrier gas supplied from the first carrier gas supply port 102 and the Group III element oxide gas discharged from the Group III element oxide gas discharge port 107 flow from the gas discharge port 108 through a connecting pipe 109 to the growth chamber 111, and are supplied into the growth chamber 111 from a gas supply port 118 connected to the growth chamber 111. The growth chamber 111 has a gas supply port 118, a third carrier gas supply port 112, a nitrogen-containing gas supply port 113, a second carrier gas supply port 114, and an exhaust port 119. The growth chamber 111 is equipped with a substrate susceptor 117 on which a seed substrate 116 is placed.

[0036] <Details of Manufacturing Method and Manufacturing Apparatus> A method for manufacturing a Group III nitride crystal according to the first embodiment will be described in detail with reference to Figures 3 and 4. In this embodiment, metal Ga is used as the starting Group III element source 105, but this is not limiting and, for example, Al or In may also be used. First, a seed substrate 116 is prepared. Examples of the seed substrate 116 include gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, and ScAlMgO. ４In this embodiment, gallium nitride is used as the seed substrate 116. In the temperature-raising step, the temperature of the growth chamber is raised in an inert gas atmosphere to a temperature at which decomposition of the seed substrate 116 does not occur. In the production of Group III nitride crystals by the OVPE method, an inert gas (e.g., N ２ Heating is carried out in a gas atmosphere.

[0037] In the decomposition protection temperature increase step 1, the temperature is increased in a nitrogen-element-containing gas atmosphere while suppressing the decomposition of the seed substrate 116. In the production of Group III nitride crystals by the OVPE method, the temperature is increased in a nitrogen-element-containing gas atmosphere up to 500°C or higher but lower than 1100°C by using an inert gas and a nitrogen-element-containing gas NH ３ Heating is carried out in a state where the gas is mixed with NH ３ The reason for mixing H is to prevent the seed substrate 116 from being decomposed due to the detachment of N atoms. ２ Heating may be carried out in a state where the gas is further mixed.

[0038] In the decomposition protection temperature increase step 2, the temperature is increased in an atmosphere of a group III oxide gas and a nitrogen element-containing gas while suppressing the decomposition of the seed substrate 116. In the production of group III nitride crystals by the OVPE method, the temperature is increased to 1100°C or higher but lower than 1500°C by H ２ gas, inert gas, Group III element oxide gas, and nitrogen element-containing gas NH ３ Heating is performed in a state where the gas is mixed with a group III element oxide gas. The reason for mixing a group III element oxide gas is that decomposition cannot be suppressed with a nitrogen-containing gas alone. By providing a driving force for the growth of group III nitride crystals, it becomes possible to suppress decomposition.

[0039] In the growth step, a Group III element oxide gas is generated in the source chamber 100 and supplied to the growth chamber 111, and a nitrogen-containing gas is also supplied to the growth chamber 111, to grow a Group III nitride crystal three-dimensionally on the seed substrate 116. Specifically, the growth step includes a reactive gas supply step, a Group III element oxide gas generation step, a Group III element oxide gas supply step, a nitrogen-containing gas supply step, a Group III nitride crystal generation step, and a residual gas exhaust step.

[0040] In the reactive gas supply step, a reactive gas is supplied from the reactive gas supply pipe 103 to the raw material reaction chamber 101 in the raw material chamber 100. As described above, the reactive gas may be a reducing gas or an oxidizing gas, as required. In this embodiment, metal Ga is used as the group III element source 105, and therefore H is used as the reactive gas. ２ O gas is used.

[0041] In the Group III element oxide gas generation step, the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supply step reacts with Ga, which is the starting Group III element source 105, to produce Ga, which is a Group III element oxide gas. ２ O gas is generated. Ga ２ The O gas is discharged from the source reaction chamber 101 to the source chamber 100 via the Group III element oxide gas discharge port 107. ２ The O gas is mixed with the first carrier gas supplied from the first carrier gas supply port 102 to the source chamber, and is supplied to the gas exhaust port 108. In this embodiment, the source chamber 100 is heated by the first heater 106. When the source chamber 100 is heated, the temperature of the source chamber 100 is controlled by the Ga ２ From the viewpoint of the boiling point of O gas, the temperature is preferably 800°C or higher. The temperature of the source chamber 100 is preferably lower than that of the growth chamber 111. When the growth chamber is heated by a second heater 115 as described below, the temperature of the source chamber 100 is preferably lower than 1800°C, for example. The starting Group III element source 105 is placed in a source boat 104 disposed in the source reaction chamber 101. The source boat 104 preferably has a shape that can increase the contact area between the reactive gas and the starting Group III element source. For example, the source boat 104 preferably has a multi-tiered dish shape to prevent the starting Group III element source 105 and the reactive gas from passing through the source reaction chamber 101 without contacting each other.

[0042] Methods for generating a Group III element oxide gas are roughly classified into a method for reducing the starting Group III element source 105 and a method for oxidizing the starting Group III element source 105. For example, in the reduction method, an oxide (e.g., Ga２ O ３ ), a reducing gas (e.g., H ２ Gas, CO gas, CH ４ Gas, C ２ H ６ Gas, H ２ S gas, SO ２ On the other hand, in the oxidation method, a non-oxide (e.g., liquid Ga) is used as the starting group III element source 105, and an oxidizing gas (e.g., H ２ O gas, O ２ Gas, CO gas, CO2 gas, NO gas, N ２ O gas, NO ２ In addition to the starting group III element source 106, an In source or an Al source can be used as the starting group III element. As the first carrier gas, an inert gas, H ２ Gas or the like can be used.

[0043] In the Group III element oxide gas supply step, Ga generated in the Group III element oxide gas generation step is ２ O gas is supplied to the growth chamber 111 via the gas outlet 108, the connecting pipe 109, and the gas supply port 118. When the temperature of the connecting pipe 109 connecting the source chamber 100 and the growth chamber 111 drops below the temperature of the source chamber 100, a reverse reaction of the reaction for producing the Group III element oxide gas occurs, and the starting Ga source 105 precipitates in the connecting pipe 109. Therefore, it is preferable that the connecting pipe 109 be heated by the third heater 110 to a temperature higher than that of the first heater 106 so that the temperature does not drop below that of the source chamber 100.

[0044] In the nitrogen-containing gas supply step, a nitrogen-containing gas is supplied to the growth chamber 111 from a nitrogen-containing gas supply port 113. An example of the nitrogen-containing gas is NH ３ Gas, NO Gas, NO ２ Gas, N ２ O gas, N ２ H ２ Gas, N ２ H ４ Includes gas.

[0045] In the Group III nitride crystal growth process, the source gases supplied into the growth chamber through each supply process are reacted to grow a Group III nitride crystal on the seed substrate 116. The growth chamber 111 is preferably heated by the second heater 115 to a temperature at which the Group III element oxide gas and the nitrogen-containing gas react. At this time, the temperature of the growth chamber 111 is preferably controlled so that it does not fall below the temperature of the source chamber 100, in order to prevent a reverse reaction of the reaction that generates the Group III element oxide gas. The temperature of the growth chamber 111 heated by the second heater 115 is preferably 1000°C or higher and 1800°C or lower. In addition, the Ga generated in the source chamber 100 is preferably heated to a temperature at which the Ga ２ In order to suppress temperature fluctuations in the growth chamber 111 due to the O gas and the first carrier gas, it is desirable that the second heater 115 and the third heater 111 have the same temperature.

[0046] By mixing the Group III element oxide gas supplied to the growth chamber 111 via the Group III element oxide supply step and the nitrogen element-containing gas supplied to the growth chamber 111 via the nitrogen element-containing gas supply step upstream of the seed substrate 116, it is possible to grow a Group III nitride crystal on the seed substrate 116.

[0047] The reactive gas supplying step, the Group III element oxide gas generating step, the Group III element oxide gas supplying step, the nitrogen-containing gas supplying step, the Group III nitride crystal generating step, and the residual gas exhausting step, which are included in the growth step, may be performed simultaneously.

[0048] The second carrier gas may be an inert gas or H ２ In the residual gas exhaust step, the unreacted Group III element oxide gas and nitrogen-containing gas, as well as the first carrier gas, second carrier gas, and third carrier gas are exhausted from the exhaust port 119.

[0049] Furthermore, from the viewpoint of increasing the carrier concentration, the substrate portion of the Group III nitride crystal formed by the growth step has an oxygen concentration of 1×10 ２０ atoms / cm ３It is preferable that the oxygen concentration is 1×10 or more. ２１ atoms / cm ３ It is preferable that this is equal to or greater than this.

[0050] Furthermore, the growth pits generated during the growth process have the effect of coalescing and eliminating dislocations in the seed substrate. Therefore, from the viewpoint of improving the quality of the base material, the density of the growth pits is set to 5×10 ５ cm －２ It is preferable that the ratio is 1×10 or less, and more preferably 1×10 ５ cm －２ It is preferable that:

[0051] In the surface smoothing step, two-dimensional growth of the Group III nitride crystal is promoted rather than three-dimensional growth toward the end of the growth process in order to smooth out irregularities such as growth pits that occurred during the growth process. By promoting two-dimensional growth, irregularities such as growth pits are filled in, forming buried portions, and the surface is smoothed. There are two main methods for promoting two-dimensional growth. One is to increase the growth temperature. The other is to increase the V / III ratio (the ratio of Group V source to Group III source). By implementing either or both of these methods, the surface irregularities can be filled in. Specifically, it is desirable to increase the V / III ratio by five times or more. Furthermore, it is desirable to perform the growth at a substrate temperature that is 50°C or higher than that of the growth process described above. These conditions may be used selectively, or may be used in combination.

[0052] In the decomposition protection temperature-lowering step, the temperature is lowered in a nitrogen-containing gas atmosphere while suppressing decomposition of the Group III nitride crystal. ３ In the temperature-lowering step, the temperature is lowered in an inert gas atmosphere to a temperature at which the Group III nitride crystal can be removed from the growth chamber.

[0053] In this embodiment, seed substrate 116 on which Group III nitride crystal has grown is removed from growth chamber 111 after the temperature-lowering step.

[0054] (Relationship between oxygen concentration in the buried portion and stress in the buried portion) The relationship between the oxygen concentration in the buried portion and the stress caused by the difference in thermal expansion coefficient occurring in the region where the growth pits are buried (buried portion) is shown in FIG. 5. The results in FIG. 5 are analytical values ​​from a thermal stress analysis, and are calculated when the oxygen concentration in the substrate is 1×10 ２１ atoms / cm ３ The dotted line in FIG. 5 represents the stress in the growth pit portion when the surface smoothing step is not implemented. As can be seen from this, when the oxygen concentration in the buried portion is 4.8×10 ２０ atoms / cm ３ From the viewpoint of suppressing the stress caused by the difference in the thermal expansion coefficient, it is found that the oxygen concentration in the buried portion is 4.8×10 ２０ atoms / cm ３ It is preferable to set the above. Note that the embedding is more effective in suppressing breakage and cracking. Therefore, it can be seen that simply forming the embedding portion is effective in suppressing the load on the growing crystal and reducing breakage and cracking. The reason for this is that the substrate (growing crystal) is rotated during growth and temperature reduction to equalize the gas partial pressure on the surface of the growing crystal. Therefore, as the growing crystal rotates, it may come into contact with the substrate susceptor. This contact puts a load on the growing crystal, and breakage and cracking are more likely to occur when the embedding portion is not formed.

[0055] According to the Group III nitride crystals according to the present disclosure, the production yield during the manufacture of Group III nitride crystals can be improved, and high-quality Group III nitride crystals can be manufactured.

[0056] 100 Source chamber 101 Source reaction chamber 102 First carrier gas supply port 103 Reactive gas supply pipe 104 Source boat 105 Starting Group III element source 106 First heater 107 Group III element oxide gas outlet 108 Gas outlet 109 Connecting pipe 110 Third heater 111 Growth chamber 112 Third carrier gas supply port 113 Nitrogen-containing gas supply port 114 Second carrier gas supply port 115 Second heater 116 Seed substrate 117 Substrate susceptor 118 Gas supply port 119 Exhaust port

Claims

1. A III-nitride crystal grown on a seed substrate, the III-nitride crystal comprising: a base portion from the seed substrate to a growth surface having growth pits in recesses; and a buried portion in which the recesses of the growth pits are buried within the growth surface with III-nitride crystal.

2. The growth pit is filled with a group III nitride crystal, and the oxygen concentration of the substrate is 1×10 ２０ atoms / cm ３ The Group III nitride crystal according to claim 1 .

3. The growth pit is filled with a group III nitride crystal, and the oxygen concentration of the substrate is 1×10 ２１ atoms / cm ３ or more, and the oxygen concentration of the buried portion is 4.8×10 ２０ atoms / cm ３ The Group III nitride crystal according to claim 1 .

4. The growth pits are filled with Group III nitride crystals, and the dislocation density is 5×10 ５ cm －２ 2. The Group III-nitride crystal of claim 1 , wherein:

5. A method for producing a Group III nitride crystal, comprising the steps of: preparing a seed substrate; supplying a Group III element oxide gas and a nitrogen-containing gas onto said seed substrate to grow a Group III nitride crystal three-dimensionally on said seed substrate; and growing the Group III nitride crystal two-dimensionally and filling in recesses in growth pits on the surface of the Group III nitride crystal to smooth the surface.

6. A method for producing a Group III nitride crystal as set forth in claim 5, wherein the surface smoothing step is carried out by controlling the supplied Group III element oxide gas and nitrogen-containing gas to set the V / III ratio at 5 or more.

7. The method for producing a Group III nitride crystal as set forth in claim 5, wherein the surface smoothing step is carried out by increasing the temperature of the substrate by 50° C. or more higher than that of the growth step.

8. In the step of smoothing the surface of the Group III nitride crystal, the oxygen concentration in the region where the surface irregularities have been filled is 4.8×10 ２０ atoms / cm ３ The method for producing a Group III nitride crystal according to any one of claims 5 to 7, wherein the method is as described above.