JP5212333B2 - Method for producing group III nitride crystal - Google Patents

Description

  The present invention relates to a method for producing a group III nitride crystal, and more particularly to a method for producing a group III nitride crystal having a high crystal growth rate of the group III nitride crystal.

Since group III nitrides such as GaN have a decomposition temperature at normal pressure lower than the melting temperature, it is difficult to obtain crystals of these group III nitrides by a melting method at normal pressure. 1500 ° C. in a high temperature and 1GPa~2GPa about high nitrogen (N ₂₎ dissolved nitrogen in Ga melt under pressure performing crystal growth high N ₂ pressure solution method has been used.

  In recent years, as an effective method capable of crystal growth under milder conditions, sodium is used for crystal growth by dissolving nitrogen in a Ga—Na melt at a temperature of about 600 ° C. to 800 ° C. and a nitrogen gas pressure of about 5 MPa. (Na) flux methods have been proposed (for example, Patent Documents 1 to 5).

  However, in the conventional sodium flux method described above, the dissolution and diffusion of nitrogen into the Ga—Na melt was slow, and the crystal growth rate of the GaN crystal was low. Therefore, development of a method for producing a group III nitride crystal having a high crystal growth rate has been strongly desired in the industrial world.

US Pat. No. 5,868,837 JP 2001-58900 A JP 2001-102316 A JP 2001-64098 A JP 2001-128857 A

  In view of the above situation, an object of the present invention is to provide a method for producing a group III nitride crystal having a high crystal growth rate.

  The present invention includes a melt forming step of forming a melt containing at least a group III element and a catalyst agent around a seed crystal in a reaction vessel, a step of removing a surface oxide layer of the melt, And a crystal growth step of growing a group III nitride crystal on the seed crystal by supplying a nitrogen-containing material.

The method of manufacturing a group III nitride crystal according to the present invention may be a III-nitride obtained by irradiating a nitrogen plasma on the surface of the melt containing at least group III element and nitrogen content.

  In the method for producing a group III nitride crystal according to the present invention, the silicon concentration in the group III nitride crystal can be adjusted by further adding silicon as a dopant to the melt. Further, by adding an oxygen-containing material as a dopant to the melt or the nitrogen-containing material, the oxygen concentration in the group III nitride crystal can be adjusted. In addition, a group III nitride crystal substrate can be used as the seed crystal.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a group III nitride crystal with a large crystal growth rate can be provided.

It is a schematic diagram which shows the manufacturing method of one group III nitride crystal concerning this invention. (A) is a schematic diagram which shows a manufacturing apparatus. (B) is a schematic diagram which shows a melt formation process. (C) is a schematic diagram showing a crystal growth step. It is a schematic diagram which shows the manufacturing method of the other group III nitride crystal concerning this invention. (A) is a schematic diagram which shows a melt formation process. (B) is a schematic diagram which shows the process of removing the surface oxidation layer of a melt. (C) is a schematic diagram showing a crystal growth step. It is a schematic diagram which shows the manufacturing method of the further another group III nitride crystal concerning this invention. It is a schematic diagram which shows the manufacturing method of the further another group III nitride crystal concerning this invention.

  Hereinafter, embodiments of the present invention will be specifically described. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

(Embodiment 1)
FIG. 1 shows a method for producing a group III nitride crystal according to the present invention. With reference to FIG. 1A, a manufacturing apparatus used in this manufacturing method includes at least a reaction vessel 21, a heater 23 for heating the reaction vessel (low temperature heater 23a, high temperature heater 23b), and a heat insulating material 24. A nitrogen-containing material supply device 31 and a nitrogen-containing material supply pipe 32 that are stored in the outer container 22 and supply the nitrogen-containing material to the reaction container 21 are disposed.

  In one method for producing a group III nitride crystal according to the present invention, referring to FIG. 1 (b), a melt 1 containing at least a group III element and a catalyst agent is placed in a reaction vessel 21 as a seed crystal 2. And a crystal growth step in which a nitrogen-containing material 3 is supplied to the melt 1 to grow a group III nitride crystal 4 on the seed crystal 2 with reference to FIG. Furthermore, in this crystal forming step, the temperature of the melt 1 is changed from the interface 13 between the nitrogen-containing material 3 and the melt 1 to the interface 12 between the seed crystal 2 and the melt 1 or the seed crystal 2. The temperature is controlled so as to decrease toward the interface 14 between the group III nitride crystal 4 and the melt 1 that have grown to a high temperature.

  Since the solubility of nitrogen in the nitrogen-containing material in the melt increases with an increase in temperature, in the melt, a seed crystal or a group III nitride crystal grown on the seed crystal from the interface with the nitrogen-containing material is used. Concentration at which the concentration of nitrogen dissolved in the melt decreases from the interface with the nitrogen-containing material to the interface with the seed crystal or the group III nitride crystal grown on the seed crystal by providing a temperature gradient in which the temperature decreases toward the interface A gradient occurs, and this nitrogen concentration gradient causes the nitrogen to be continuously diffused and supplied to the seed crystal or the interface with the group III nitride crystal grown on the seed crystal, so that the group III nitridation on the seed crystal Growth of physical crystals is promoted.

  Here, in the melt forming step shown in FIG. 1 (b), 1) the group III element and the catalyst agent are accommodated in the reaction vessel 21 and heated to obtain the melt 1; 2. Method of introducing seed crystal 2 into 1 2) Group III element, catalyst agent, and seed crystal 2 are accommodated in the reaction vessel 21, and these are heated to form III around the seed crystal 2. Any method of forming a melt 1 containing a group element and a catalyst agent can be used.

  Preferred examples of the group III element contained in the melt include Al, Ga, and In. Further, the catalyst agent contained in the melt is one that melts together with the group III element and promotes the reaction between the group III element and nitrogen, and preferred examples include alkali metal elements and transition metal elements. When Ga is used as a group III element, Na, which is an alkali metal element, is preferably used as a catalyst agent. When Al is used as a group III element, Fe, Mn, Cr, which are transition metal elements, as a catalyst agent. Etc. are preferably used. Further, the ratio of the mol% of the group III element to the mol% of the catalyst agent in the melt is not particularly limited, but is preferably a group III element: catalyst agent = 5: 95 to 90:10. When the mol% of the group III element in the melt is small, the supply of the group III element is insufficient and the growth of the group III nitride crystal is suppressed. When the mol% of the catalyst agent is small, the amount of nitrogen dissolved in the melt is small. Therefore, the supply of nitrogen is insufficient, and the growth of the group III nitride crystal is suppressed. From such a viewpoint, the ratio of the mol% of the group III element to the mol% of the catalyst agent in the melt is more preferably group III element: catalyst agent = 10: 90 to 75:25.

Further, in the crystal growth step shown in FIG. 1C, the nitrogen-containing material supplied to the melt is a nitrogen source that is dissolved in the melt and grows a group III nitride crystal. In addition to the nitrogen-containing gas such as nitrogen gas and ammonia gas, NaN ₃ , group III nitride and the like are also included. This embodiment is suitable for supplying a nitrogen-containing gas as a nitrogen-containing material. Further, the supply pressure of the nitrogen-containing gas is preferably 0.1 MPa to 10.0 MPa. When the pressure of the nitrogen-containing gas is less than 0.1 MPa, nitrogen is not sufficiently supplied into the melt, and thus the growth of the group III nitride crystal is suppressed. On the other hand, when the pressure of the nitrogen-containing gas exceeds 10.0 MPa, the reaction apparatus becomes complicated. From this viewpoint, the pressure of the nitrogen-containing gas is more preferably 1.0 MPa to 5.0 MPa.

  1C, the temperature of the melt 1 is changed from the interface 13 between the nitrogen-containing material 3 and the melt 1 to the interface 12 between the seed crystal 2 and the melt 1 or on the seed crystal. There is no particular limitation on the method of controlling the temperature so as to decrease toward the interface 14 between the group III nitride crystal 4 and the melt 1 grown on the substrate. For example, two types of heaters, a low temperature heater 23a and a high temperature heater 23b, are used. The heating temperature can be changed locally.

In the method for producing a group III nitride crystal of the present embodiment, the temperature T _{N at} the interface 13 between the nitrogen-containing material 3 and the melt 1 and the seed crystal are further increased during the crystal growth step shown in FIG. 2 at the interface 12 between the melt 1 and the temperature T _{C at} the interface 14 between the group III nitride crystal 4 and the melt 1 grown on the seed crystal 2, and the nitrogen-containing material 3 dissolved in the melt 1. temperature but such that the temperature difference T _N -T _C of relationship between the temperature T ₀ is T _N> T ₀ ≧ T _C, and T _N and T _C precipitated as a group III nitride crystal 4 is 10 ° C. to 300 ° C. It is preferable to control. The temperature was measured by inserting a thermocouple protected by an alumina tube at the corresponding location.

By setting T _N > T ₀ , group III nitride crystals are not precipitated in the vicinity of the interface 13 between the nitrogen-containing material 3 and the melt 1, so that nitrogen can sufficiently diffuse into the melt. it can. Furthermore, by setting T ₀ ≧ T _C , a group III nitride crystal can be efficiently grown on the seed crystal. Therefore, by making T _N > T ₀ ≧ T, the growth of the group III nitride crystal on the seed crystal is further promoted. Here, it is possible to promote the growth of T ₀ -T _C is too large III-nitride crystal, T ₀ -T _C is larger the group III other than on the seed crystal in the melt nitride crystal The possibility of precipitation also increases.

Moreover, it is preferable to control the temperature so that _TN - _TC is 10 ° C to 300 ° C. If T _N -T _C is less than 10 ° C., the temperature gradient from the interface with the nitrogen-containing material in the melt to the interface with the seed crystal or the group III nitride crystal grown on the seed crystal becomes small, and crystal growth The supply of nitrogen to the portion is reduced and the crystal growth rate is reduced. On the other hand, if T _N -T _C exceeds 300 ° C., excess nitrogen is supplied into the melt, and the possibility that Group III nitride crystals will precipitate in addition to the seed crystals increases. From this viewpoint, the lower limit of T _N -T _C is preferably not less than 50 ° C., more preferably above 100 ° C., the upper limit of T _N -T _C is preferably 250 ° C. or less, more preferably 200 ° C. or less.

Here, T _N and T _C can be set to a temperature suitable for the group III element and a catalyst agent used in the Group III nitride crystal. For example, when growing a GaN crystal or an AlN crystal, which is a group III nitride crystal, using Ga or Al as a group III element and alkali metal Na as a catalyst, _TN is set to 700 ° C. to 1000 ° C., _C is preferably set to 500 ° C to 800 ° C. Further, when an AlN crystal that is a group III nitride crystal is grown using Al as the III metal element and transition metal elements Fe, Mn, Cr, etc. as the catalyst agent, T _N is 900 ° C. to 1600 ° C. T _C is preferably set to 700 ° C. to 1400 ° C..

  In the group III nitride crystal manufacturing method of the present embodiment, it is preferable that the seed crystal 2 is further locally cooled during the crystal growth step shown in FIG. By locally cooling the seed crystal, the temperature of the interface 12 between the seed crystal 2 and the melt 1 or the interface 14 between the group III nitride crystal 4 grown on the seed crystal and the melt 1 is further reduced, The growth of the group III nitride crystal can be further promoted.

Here, the method for locally cooling the seed crystal is not particularly limited. However, as shown in FIG. 1 (c), it is preferable that the seed crystal 2 is brought into contact with the coolant 42 to release heat. As the coolant, a material having a high thermal conductivity or a material having a high infrared transmittance is preferably used. Materials having high thermal conductivity such as various metals and AlN polycrystals can release the heat of the seed crystal to the outside of the reaction vessel by heat conduction. A material having high infrared transmittance, such as sapphire or quartz, can release the heat of the seed crystal out of the reaction vessel by heat radiation. In particular, a material having a high infrared transmittance such as sapphire is preferably used as the coolant. By using the sapphire rod as a coolant, the temperature T _C at the interface between the seed crystal and the melt can be lowered to a temperature lower by 300 ° C. or more than the temperature T _{N at} the interface between the nitrogen-containing material and the melt.

  In FIG. 1, the coolant 42 for locally cooling the seed crystal 2 is provided in the reaction vessel 21, but the coolant 42 is provided so as to reach the outer vessel 22 outside the reaction vessel 21. You can also. By bringing the coolant into contact with the outer container, the heat of the seed crystal can be directly released out of the outer container 22, so that the cooling effect of the seed crystal can be further increased.

  The material of the reaction vessel used in the present embodiment and the outer vessel that accommodates the reaction vessel is not particularly limited. However, from the viewpoint of high heat resistance and less contamination of impurities, the reaction vessel may be alumina, pyronic BN, Platinum or the like is preferable, and stainless steel, Inconel, or the like is preferable as the outer container. Moreover, although there is no restriction | limiting in particular in the material of a heater and a heat insulating material, From a viewpoint similar to the above, a graphite etc. are preferable.

(Embodiment 2)
As shown in FIG. 1, another Group III nitride crystal manufacturing method according to the present invention includes at least a reaction vessel 21 having an opening, a heater 23, and a heat insulating material 24 in an outer vessel 22. 23 and a heat insulating material 24 using a manufacturing apparatus made of graphite, as shown in FIG. 1 (b), in a reaction vessel 21, a group consisting of at least a group III element, an alkali metal element, and a transition metal element. A melt forming step of forming a melt 1 containing one or more selected elements around the seed crystal 2, and supplying a nitrogen-containing material 3 to the melt 1 as shown in FIG. A crystal growth step of growing a group III nitride crystal 4 on the substrate 2. By using a material with a small surface area such as graphite for the heater and the heat insulating material, it is possible to suppress dissolution of oxygen and / or water vapor mainly generated from the heater, the heat insulating material, etc. in the melt in the reaction vessel when the temperature is raised. Thus, the dissolution of nitrogen into the melt is promoted, and the growth of group III nitride crystals is promoted. From this point of view, it is more preferable that the graphite has a higher purity. For example, it is desired that the impurity concentration is 10 ppm or less.

(Embodiment 3)
Another method for producing a group III nitride crystal according to the present invention is described with reference to FIG. 1, a step of removing moisture by preheating the reaction vessel 21 as shown in FIG. As shown in 1 (b), in the reaction vessel 21 from which water has been removed, a melt 1 containing at least a group III element and one or more elements selected from the group consisting of alkali metal elements and transition metal elements is seeded. A melt forming step formed around the crystal 2 and a crystal growth in which a nitrogen-containing material 3 is supplied to the melt 1 to grow a group III nitride crystal 4 on the seed crystal 2 as shown in FIG. Process. By removing heat from the reaction vessel 21 by heat treatment in advance, the dissolution of water vapor in the melt 1 is reduced, the dissolution of nitrogen in the melt 1 is promoted, and the growth of group III nitride crystals is promoted. The Here, the heat treatment conditions are not particularly limited as long as the water in the reaction vessel can be removed. However, it is preferable to perform the heat treatment at 100 Pa or lower and 100 ° C. or higher for 1 hour or longer while evacuating.

(Embodiment 4)
FIG. 2 shows another method for producing a group III nitride crystal according to the present invention. In this manufacturing method, a manufacturing apparatus similar to the manufacturing apparatus of FIG. 1 can be used. Referring to FIG. 2 (a), another method for producing a group III nitride crystal according to the present invention comprises at least a group III element and an alkali metal element and a transition metal element as a catalyst in a reaction vessel 21. A melt forming step of forming a melt 1 containing one or more elements selected from the group around the seed crystal 2, and the surface of the melt 1 with reference to FIGS. 2 (a) and 2 (b) A step of removing the oxide layer 11 and a crystal growth step of growing a group III nitride crystal 4 on the seed crystal 2 by supplying the nitrogen-containing material 3 to the melt 1 with reference to FIG. Including.

  By removing the surface oxide layer 11 of the melt 1, the dissolution of nitrogen into the melt 1 is promoted, and the growth of group III nitride crystals is promoted. Here, in addition to the oxide of the melt, impurities such as B and Al derived from the material of the reaction vessel are taken into the surface oxide layer. Therefore, by removing the surface oxide layer, a higher quality group III A nitride crystal is obtained. Although there is no restriction | limiting in particular in the method of removing the surface oxidation layer of a melt, The method of attracting | sucking a surface oxidation layer etc. is mentioned preferably. Here, the thickness of the surface oxide layer of the melt is less than 10% with respect to the height of the melt, even if it is thick, according to the observation from the cross-section of the melt of the melt without taking special anti-oxidation measures. Therefore, the surface oxide layer can be removed by removing 10% or more of the surface layer with respect to the height of the melt from the surface of the melt.

  Here, in the second to fourth embodiments, by providing the same temperature gradient of the melt as in the first embodiment during the crystal growth step, the dissolution of nitrogen in the melt is further promoted, and the group III The growth of nitride crystals is further promoted.

(Embodiment 5)
FIG. 3 shows still another method for producing a group III nitride crystal according to the present invention. As in the manufacturing apparatus shown in FIGS. 1 and 2, the manufacturing apparatus used in this manufacturing method includes at least a reaction vessel 21, a heater 23 for heating the reaction vessel (low temperature heater 23a, high temperature heater 23b), and heat insulation. The material 24 is stored in the outer container 22, and a nitrogen-containing material supply device 31 that supplies the nitrogen-containing material 3 to the reaction container 21 and a nitrogen-containing material supply pipe 32 are disposed.

  However, in the production apparatus shown in FIGS. 1 and 2, the main surface for crystal growth of the seed crystal 2 is arranged at the bottom of the reaction vessel 21 so that the melt 1 in the reaction vessel 21 is vertically oriented. A low-temperature heater 23a and a high-temperature heater 23b are installed so as to provide a temperature gradient, and a group III nitride crystal 4 is grown above the seed crystal 2. On the other hand, in the manufacturing apparatus shown in FIG. 3, the main surface for crystal growth of the seed crystal 2 is placed sideways on the side surface portion of the reaction vessel 21, and the melt in the reaction vessel 21 extends in the lateral direction. The low temperature heater 23 a and the high temperature heater 23 b are installed so as to provide a temperature gradient, and the group III nitride crystal 4 is grown in the lateral direction of the seed crystal 2.

  Also in this embodiment, it is not limited to the growth direction of the group III nitride crystal, and in the melt, on the seed crystal or the seed crystal from the interface with the nitrogen-containing material, as in the first to fourth embodiments. By providing a temperature gradient in which the temperature decreases toward the interface with the grown group III nitride crystal, the growth of the group III nitride crystal on the seed crystal can be promoted.

  Also in the present embodiment, the heater 23 and the heat insulating material 24 are made of graphite as shown in the second embodiment, and the reaction vessel is preheated as shown in the third embodiment to remove moisture. In addition, by removing the surface oxide layer of the melt as shown in the fourth embodiment, the growth of the group III nitride crystal on the seed crystal can be promoted.

Further, in the first to fifth embodiments, an inert gas such as argon gas flows into and out of the outer container during the melt forming step and adheres to the reaction container, heater, and heat insulating material in the outer container. It is preferable to remove oxygen and / or water vapor. Here, the flow rate of the inert gas is preferably 1 cm ³ / min or more per 10 cm ³ of the outer container. Further, it is preferable to reduce the surfaces of the reaction vessel, the heater and the heat insulating material in the outer vessel by flowing a reducing gas such as hydrogen gas in and out after the melt forming step and before the crystal growth step. Here, the flow rate of the reducing gas is preferably 1 cm ³ / min or more per 10 cm ³ of the outer container. By taking such means, dissolution of oxygen and / or water vapor into the melt in the reaction vessel can be further suppressed, and the growth of group III nitride crystals is further promoted.

(Embodiment 6)
FIG. 4 shows still another method for producing a group III nitride crystal according to the present invention. Referring to FIG. 4, the manufacturing apparatus used in this manufacturing method includes at least a reaction vessel 21, a heater 23 for heating the reaction vessel (low temperature heater 23a, high temperature heaters 23b and 23c), and a heat insulating material 24 on the outside. It is stored in the container 22. In this embodiment is suitable when used as the NaN _3, III Group solid such as a nitride as a nitrogen-containing compound serving as a nitrogen source.

  In the present embodiment, in the melt forming step, a melt 1 containing a group III element and a catalyst agent is formed around the seed crystal 2 and the solid nitrogen-containing material 3 in the reaction vessel 21, In the growth process, the nitrogen-containing material 3 is dissolved in the melt, and a group III nitride crystal is grown on the seed crystal 2. Here, the method for forming the melt 1 containing the group III element and the catalyst agent in the reaction vessel 21 around the seed crystal 2 and the solid nitrogen-containing material 3 is not particularly limited. The seed crystal 2 is arranged on one side of the vessel 21, the nitrogen-containing material 3 is arranged on the other side of the reaction vessel 21, and a group III element and a catalyst agent are accommodated between them, and then these are heated to bring the group III element and From the viewpoint of workability, it is preferable to form the melt 1 containing the catalyst agent.

  In the present embodiment, the temperature of the melt 1 is adjusted from the interface 13 between the nitrogen-containing material 3 and the melt 1 by adjusting the temperature of the low-temperature heater 23a and the high-temperature heaters 23b and 23c. Thus, a temperature gradient can be formed that decreases toward the interface 12 between the crystal layer 3 and the interface 14 between the group III nitride crystal 4 grown on the seed crystal and the melt 1.

  In the method for producing a group III nitride crystal of the present embodiment, it is preferable to use a group III nitride obtained by irradiating the surface of a melt containing a group III element with nitrogen plasma as the nitrogen-containing material. Group III nitride powders usually sold as reagents are obtained by chemical reaction of group III elements or group III element oxides with ammonia, and have low purity and high cost. By using such a group III nitride, a high purity group III nitride crystal can be obtained at a high crystal growth rate. Here, the nitrogen plasma is obtained, for example, by applying a microwave or a high frequency pulse to nitrogen gas. By irradiating the molten liquid with such nitrogen plasma, high purity group III nitride powder can be obtained efficiently at low cost.

Here, the seed crystal used in the first to sixth embodiments is not particularly limited, and is a SiC crystal substrate, a sapphire crystal substrate, a substrate in which a thin film of a group III nitride crystal is formed on a sapphire crystal, III Examples thereof include group nitride crystal substrates. Among these, a group III nitride crystal substrate is preferable from the viewpoint of rapidly growing a high-quality group III nitride crystal. Furthermore, from the viewpoint of rapidly growing a high-quality group III nitride crystal, the group III nitride crystal substrate used as a seed crystal preferably has a dislocation density of 5 × 10 ⁹ pieces / cm ³ or less. Further, when a group III nitride crystal substrate is used as a seed crystal, a flat GaN crystal on the (0001) plane (Ga plane) is likely to grow at a high speed, so the (0001) plane may be used as the seed crystal surface. More preferred.

In Embodiments 1 to 6, the silicon concentration in the group III nitride crystal can be adjusted by further adding silicon to the melt. By adjusting the concentration of silicon which is a dopant of the group III nitride crystal, a group III nitride crystal according to the purpose can be obtained. For example, a group III nitride crystal having a silicon concentration exceeding 1 × 10 ¹⁷ pieces / cm ³ has an increased conductivity and is suitable for manufacturing an optical device. In addition, a group III nitride crystal having a silicon concentration of 1 × 10 ¹⁷ pieces / cm ³ or less has a reduced conductivity and is suitable for manufacturing an electronic device.

In Embodiments 1 to 6, the oxygen concentration in the group III nitride crystal can be adjusted by further adding an oxygen-containing material to the melt or nitrogen-containing material. Here, the oxygen-containing material is not particularly limited as long as oxygen can be supplied into the group III nitride crystal, and examples thereof include oxygen gas and sodium oxide (Na ₂ O). By adjusting the oxygen concentration which is a dopant of the group III nitride crystal, a group III nitride crystal corresponding to the purpose can be obtained. For example, III-nitride crystal having an oxygen concentration exceeds 1 × 10 ¹⁷ / cm ³ is conductive is increased, are suitable for the manufacture of the optical device. In addition, a group III nitride crystal having an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ or less has reduced conductivity and is suitable for manufacturing an electronic device.

Example 1
Referring to FIG. 1B of FIG. 1, a GaN crystal substrate is installed as a seed crystal 2 on a sapphire rod that is a coolant 42 of the reaction vessel 21, and Ga as a group III element is further added to the reaction vessel 21. A Ga—Na melt was formed around the GaN crystal substrate by containing Na as a catalyst agent in a mole ratio of 50:50 in the melt and heating. At this time, the Ga—Na melt has a surface temperature (corresponding to T _N ) of 850 ° C., and the temperature at the interface between the Ga—Na melt and the GaN crystal substrate (corresponding to T _C ) is 800 ° C. The amount of heat of the high temperature heater 23b and the low temperature heater 23a was adjusted to have a gradient.

Next, with reference to FIG.1 (c), nitrogen gas was supplied to the said Ga-Na melt as the nitrogen containing material 3 so that nitrogen gas pressure might be set to 1.0 MPa. At this time, the precipitation temperature (T ₀ ) of the GaN crystal in the Ga—Na melt is 830 ° C. By supplying nitrogen gas to the surface of the Ga—Na melt having the temperature gradient, crystals grew only on the GaN crystal substrate as the seed crystal 2. The crystal growth rate of this crystal was 3.2 μm / hour. When the obtained crystal was measured by XRD (X-ray diffraction), it was confirmed from the lattice constant that it was a GaN crystal. The results are summarized in Table 1.

(Comparative Example 1)
A GaN crystal was grown in the same manner as in Example 1 except that the temperature of the entire Ga—Na melt was changed to 800 ° C. without providing a temperature gradient of the Ga—Na melt. The GaN crystal grew not only on the GaN crystal substrate as a seed crystal but also on the Ga—Na melt surface and the interface between the Ga—Na melt and the reaction vessel. The results are summarized in Tables 1 and 4.

(Example 2 to Example 7)
Referring to FIG. 1, the surface temperature of melt 1 (corresponding to _TN ), melt 1 and seed crystal 2 using group III elements, catalyst agent, seed crystal 2 and nitrogen-containing material 3 shown in Table 1. After forming the melt 1 around the seed crystal 2 so that the interface temperature (T _C ) with the temperature shown in Table 1 becomes nitrogen gas or ammonia gas as the nitrogen-containing material 3 The pressure was supplied so as to be 1.0 MPa. In any of Examples 2 to 7, Group III nitride crystals grew only on the seed crystals. The results are summarized in Table 1. The results of Example 2 are also shown in Table 4.

(Comparative Example 2)
An AlN crystal was grown in the same manner as in Example 7 except that the temperature of the entire Al—Fe melt was set to 800 ° C. without providing a temperature gradient of the Al—Fe melt. The results are summarized in Table 1.

(Example 8)
Referring to FIG. 3, the low temperature heater is arranged so that the main surface for crystal growth of seed crystal 2 faces sideways and is disposed on the side surface of reaction vessel 21, and a temperature gradient is provided in the lateral direction of the melt in reaction vessel 21. A GaN crystal was grown in the same manner as in Example 1 except that the group 23a and the high-temperature heater 23b were installed and the group III nitride crystal 4 was grown in the lateral direction of the seed crystal 2. The results are summarized in Table 1. In the present embodiment, the temperature T _{N at} the interface between the nitrogen-containing material and the melt refers to the temperature of the region farthest from the seed crystal at the interface between the nitrogen-containing material and the melt.

As can be seen from Table 1, the crystal growth rates of GaN crystals in Examples 1 to 3 and Example 8 in which the melt has a temperature gradient of T _N > T _C are comparative examples in which there is no temperature gradient in the melt. 1 was larger than the crystal growth rate of the GaN crystal. Moreover, the crystal growth rate increased as T _N -T _C increased (Examples 1 to 3). In addition to the growth of GaN crystals as well as the growth of AlN crystals, the crystal growth rate of AlN crystals was increased by providing a temperature gradient of T _N > T _{C in} the melt (Example 7, Comparative Example 2). ).

(Example 9 to Example 11)
Referring to FIG. 1, as shown in Table 2, Ga as a group III element, Na as a catalyst, Si or Na ₂ O (sodium oxide) as a dopant, and a GaN crystal substrate as a seed crystal 2 The melt 1 containing the dopant was formed around the seed crystal 2 by being accommodated in the reaction vessel and heated. At this time, the amount of heat of the heater was adjusted so that the surface temperature (corresponding to _TN ) of the melt 1 was 850 ° C., and the interface temperature (T _C ) between the melt 1 and the seed crystal 2 was 700 ° C. Next, nitrogen gas was supplied to the melt 1 as nitrogen-containing material 3 so that the gas pressure became 1.0 MPa. In any of Examples 9 to 11, a GaN crystal containing silicon or oxygen grew only on the seed crystal. The results are summarized in Table 2. Here, the concentration of silicon or oxygen in the GaN crystal was measured by SIMS (Secondary Ion Mass Spectrometry).

(Example 12)
Referring to FIG. 1, as shown in Table 2, Ga as the Group III element, Na as the catalyst, and GaN as the seed crystal 2 are contained in a reaction vessel and heated to heat the melt 1 as the seed crystal 2. Formed around. At this time, the amount of heat of the heater was adjusted so that the surface temperature (corresponding to _TN ) of the melt 1 was 850 ° C., and the interface temperature (T _C ) between the melt 1 and the seed crystal 2 was 700 ° C. Next, in this melt, a mixed gas of nitrogen gas as a nitrogen-containing substance and oxygen gas as a dopant (the ratio of N ₂ mol% to O ₂ mol% in the mixed gas is 99.9: 0.1). ) Was supplied so that the mixed gas pressure was 1.0 MPa, and a GaN crystal containing oxygen grew only on the seed crystal. The results are summarized in Table 2.

  As can be seen from Table 2, a group III nitride crystal having a desired dopant concentration was obtained by adding a dopant to the melt or nitrogen-containing material.

(Example 13 to Example 15)
Referring to FIG. 4, a GaN crystal substrate is installed as seed crystal 2 on a sapphire rod that is coolant 42 of reaction vessel 21, and 50 mol% Ga as a group III element is added to reaction vessel 21 and a catalyst agent. As a seed crystal, GaN crystal substrate as a seed crystal is heated by containing 50 mol% of Na and III-nitride powder as nitrogen-containing material 3 so that the molar ratio to Group III element is 1. A Ga-Na melt was formed. At this time, the Ga—Na melt is a temperature at the interface (corresponding to _TN ) between the Ga—Na melt and the group III nitride powder, and the interface between the Ga—Na melt and the GaN crystal substrate. The amounts of heat of the high-temperature heaters 23b and 23C and the low-temperature heater 23a were adjusted so as to have a temperature gradient so that the temperature (corresponding to T _C ) becomes a temperature as shown in Table 3. As dissolution of the Group III nitride powder into the melt progressed, GaN crystals grew on the seed crystals. Note that the Group III nitride powders in Examples 13 to 15 irradiate a 1000 ° C. Ga melt with nitrogen plasma obtained by applying a microwave of 250 W with a frequency of 2.45 GHz to nitrogen gas. The GaN powder obtained by this was used. The results are summarized in Table 3.

As can be seen from Table 3, even when Group III nitride is used as the nitrogen-containing material for supplying nitrogen to the melt, T _N > T in the melt as in Examples 1 to 3. By providing the temperature gradient of _C , the crystal growth rate of the group III nitride crystal was increased.

(Example 16)
Referring to FIG. 1, as shown in FIG. 1A, the reaction vessel 21 is evacuated with a vacuum pump 33 in advance and heat treated at 100 Pa and 100 ° C. for 1 hour to remove moisture, and then FIG. As shown in b), a GaN crystal substrate is installed as a seed crystal 2 on a sapphire rod, which is a coolant 42 in the reaction vessel 21 from which water has been removed, and Ga and a catalyst are added to the reaction vessel 21 as a group III element. The Na—as the agent was contained in the mol% shown in Table 3 and heated to form a Ga—Na melt around the GaN crystal substrate. At this time, the Ga—Na melt has a surface temperature (corresponding to T _N ) of 850 ° C., and the temperature at the interface between the Ga—Na melt and the GaN crystal substrate (corresponding to T _C ) is 700 ° C. The amount of heat of the high temperature heater 23b and the low temperature heater 23a was adjusted to have a gradient. Next, as shown in FIG. 1C, nitrogen gas was supplied as a nitrogen-containing material 3 to the Ga—Na melt to grow a GaN crystal on the seed crystal 2. The results are summarized in Table 4.

(Example 17)
Referring to FIG. 2, a GaN crystal substrate as a seed crystal 2 is placed on a sapphire rod, which is a coolant 42 in the reaction vessel 21, as shown in FIG. A Ga—Na melt having the same temperature gradient as in Example 16 was formed around the GaN crystal substrate by containing Ga as an element and Na as a catalyst agent in mol% shown in Table 3 and heating. . Next, as shown in FIGS. 2 (a) to 2 (b), by removing the layer from the surface of the Ga-Na melt to a depth of up to 10% with respect to the height of the melt by suction. The surface oxide layer 11 of the Ga—Na melt was removed. Next, as shown in FIG. 2C, a GaN crystal was grown on the seed crystal 2 by supplying nitrogen gas as a nitrogen-containing material 3 to the Ga—Na melt. The results are summarized in Table 4.

(Example 18)
After the reaction vessel 21 was preheated at 100 ° C. for 1 hour to remove moisture, a GaN crystal was grown in the same manner as in Example 17. The results are summarized in Table 4.

In Table 4, when Example 2 is compared with Examples 16 to 18, as a means for preventing oxidation of the melt, the reaction vessel is preheated before the melt forming step to remove moisture, or the melt It can be seen that the crystal growth rate of the GaN crystal is increased by removing the surface oxide layer of the melt after the formation step and before the crystal growth step. A GaN crystal having an oxygen concentration of 1 × 10 ¹⁷ atoms / cm ³ or less was obtained.

(Example 19 to Example 22)
Referring to FIGS. 1 and 2, as shown in Table 5, at least one of preheating the reaction vessel before the melt forming step and removing the surface oxide layer of the melt after the melt forming step and before the crystal growth step are performed. Crystal growth of GaN crystals was carried out in the case where two melt antioxidant means and a temperature gradient of the melt were provided and various dopants were added to the melt or nitrogen-containing material. These results are summarized in Table 5.

  As can be seen from Table 5, even when the melt antioxidant means and the temperature gradient of the melt are provided, a GaN crystal having a desired dopant concentration can be obtained by adding a dopant to the melt or nitrogen-containing material. Obtained.

  In Examples 1 to 22 and Comparative Examples 1 and 2, the reaction vessel is made of pyronic BN, the outer vessel is made of stainless steel, and the heater and the heat insulating material are made of graphite (impurity concentration of 10 ppm or less). Using.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be widely used for a group III nitride crystal having a high crystal growth rate, a method for producing the same, and a group III nitride crystal production apparatus.

  DESCRIPTION OF SYMBOLS 1 Melt, 2 seed crystal, 3 Nitrogen-containing substance, 4 group III nitride crystal, 11 Surface oxidation layer, 12 Interface between seed crystal and melt, 13 Interface between nitrogen-containing substance and melt, 14 On seed crystal Interface between Group III nitride crystal grown on melt and melt, 21 reaction vessel, 22 outer vessel, 23 heater, 23a low temperature heater, 23b, 23c high temperature heater, 24 heat insulating material, 31 nitrogen content supply device, 32 nitrogen content Material supply pipe, 33 vacuum pump, 42 coolant.

Claims (5)

  In the reaction vessel, a melt forming step of forming a melt containing at least a group III element and a catalyst agent around the seed crystal, a step of removing a surface oxide layer of the melt, and the melt containing nitrogen And a crystal growth step of supplying a product to grow a group III nitride crystal on the seed crystal. The method for producing a group III nitride crystal according to claim 1, wherein the nitrogen-containing material is a group III nitride obtained by irradiating a surface of a melt containing at least the group III element with nitrogen plasma. 3. The method for producing a group III nitride crystal according to claim 1, wherein the silicon concentration in the group III nitride crystal is adjusted by further adding silicon as a dopant to the melt. By adding oxygenates as further dopant to the melt or the nitrogen-containing substance, according to any one of claims 1 to 3, wherein adjusting the oxygen concentration of the group III nitride crystal A method for producing a group III nitride crystal of The method for producing a group III nitride crystal according to any one of claims 1 to 4 , wherein a group III nitride crystal substrate is used as the seed crystal.

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