JP2002128587A - Method and apparatus for crystal growth, group iii nitride crystal, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride crystal whose size is usable for manufacturing a device such as a high-performance light emitting diode, a high- performance laser diode(LD), etc., without complicating its producing method, without using an expensive reaction vessel, and without allowing the crystal size to become smaller, and to provide the method and apparatus for crystal where such a group III nitride crystal can be grown. SOLUTION: A group III nitride composed of a group III metal and nitrogen is grown to crystal from a mixture melt, in which an alkaline metal and a substance containing at least a group III are mixed, and from a substance containing at least nitrogen. A mixture melt-holding container 102 for holding a mixture melt 103 is installed inside a reaction vessel. The inner shape 102a of the container 102 is so formed that a local density distribution of dissolved nitrogen is generated in the mixture melt 103.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crystal growth method and a crystal growth apparatus, a group III nitride crystal, and a group III nitride semiconductor device.

[0002]

2. Description of the Related Art InGaAlN-based (group III nitride) devices currently used as violet-blue-green light sources are:
Most of them are MO on sapphire or SiC substrate.
-It is manufactured by crystal growth using a CVD method (metal organic chemical vapor deposition method), an MBE method (molecular beam crystal growth method), or the like. When sapphire or SiC is used as a substrate, crystal defects due to a large difference in thermal expansion coefficient and lattice constant from group III nitrides increase. For this reason, there are problems in that the device characteristics are poor, for example, it is difficult to extend the life of the light emitting device, and the operating power increases.

Further, in the case of a sapphire substrate, since it is insulative, it is impossible to take out an electrode from the substrate side as in a conventional light emitting device. Required. As a result, there is a problem in that the device area increases and the cost increases. In addition, II fabricated on a sapphire substrate
In the group I nitride semiconductor device, it is difficult to separate a chip by cleavage, and it is not easy to obtain a cavity facet required for a laser diode (LD) by cleavage. For this reason, at present, cavity end face formation by dry etching,
Alternatively, after the sapphire substrate is polished to a thickness of 100 μm or less, a resonator end face is formed in a form close to cleavage. Also in this case, it is impossible to easily separate the end face of the resonator from the chip as in the conventional LD in a single process, and the process becomes complicated, which leads to an increase in cost.

In order to solve these problems, it has been proposed to reduce the crystal defects by selectively growing a group III nitride semiconductor film on a sapphire substrate in a lateral direction or by taking other measures.

[0005] For example, the document "Japanese Journal of Applie"
d Physics Vol.36 (1997) Part 2, No.12A, L1568-157
"1" (hereinafter, referred to as a first conventional technique) shows a laser diode (LD) as shown in FIG. FIG.
In the laser diode of (1), a GaN low-temperature buffer layer 2 and a GaN layer 3 are sequentially grown on a sapphire substrate 1 by an MO-VPE (metal organic chemical vapor deposition) apparatus,
An iO ₂ mask 4 is formed. The SiO ₂ mask 4 is formed through a photolithography and etching process after depositing a SiO ₂ film by another CVD (chemical vapor deposition) apparatus. Next, the MO ₂ is again placed on the SiO ₂ mask 4.
By growing the GaN film 3 having a thickness of 20 μm with a −VPE device, GaN is selectively grown in the lateral direction, and crystal defects are reduced as compared with the case where selective lateral growth is not performed. Further, by introducing the 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 the modulation-doped strained superlattice layer are not used.

In the case of the first prior art, it is possible to reduce crystal defects as compared with a case where a GaN film is not selectively grown in a lateral direction on a sapphire substrate. The aforementioned problems with regard to insulation and cleavage still remain. Furthermore, SiO
_The crystal growth by the MO-VPE apparatus is required twice with the _two mask forming steps interposed therebetween, which causes a new problem that the steps become complicated.

As another method, for example, the document “Appl
ied Physics Letters, Vol. 73, No. 6, P. 832-834 (199
8) "(hereinafter referred to as a second prior art) proposes to apply a GaN thick film substrate. In the second prior art, after the 20 μm selective lateral growth of the first prior art, a 200 μm thick GaN film is grown by an H-VPE (hydride vapor phase epitaxy) apparatus. By polishing the grown GaN film from the sapphire substrate side to a thickness of 150 μm,
Make a substrate. Using an MO-VPE apparatus, crystal growth necessary for an LD device is sequentially performed on this GaN substrate to produce an LD device. As a result, in addition to the problem of crystal defects, it is possible to solve the above-mentioned problems relating to insulation and cleavage caused by using a sapphire substrate.

[0008] However, the second prior art has a more complicated process than the first prior art, resulting in higher cost. In addition, the second prior art method uses
When a GaN thick film having a thickness of as large as 00 μm is grown, a stress due to a difference in lattice constant and a difference in thermal expansion coefficient from sapphire, which is a substrate, becomes large, and a new problem arises in that the substrate is warped or cracked. Further, even if such a complicated process is performed, the crystal defect density can be reduced to only about 10 ⁶ / cm ² , and a practical semiconductor device cannot be obtained.

To avoid this problem, Japanese Patent Application Laid-Open No.
Japanese Patent No. 2566662 discloses a substrate on which a thick film is grown (Japanese Patent Laid-Open No.
No. 0-256662 describes that sapphire and spinel are most desirable). By using a substrate having a thickness of 1 mm or more, even if a thick GaN film is grown to a thickness of 200 μm, no warping or cracking of the substrate occurs. However, such a thick substrate has a high cost of the substrate itself,
In addition, it is necessary to spend much time for polishing, which leads to an increase in the cost of the polishing process. That is, by using a thick substrate, the cost is higher than when using a thin substrate. When a thick substrate is used, the substrate does not warp or crack after growing a thick GaN film, but stress is relaxed in the polishing step, and warpage or cracks occur during polishing. For this reason, even if a thick substrate is used, a GaN substrate with high crystal quality cannot be easily formed with a large area.

On the other hand, the literature "Journal of Crystal Growth,
Vol.189 / 190, p.153-158 (1998) "(hereinafter referred to as a third conventional technique) proposes growing a GaN bulk crystal and using it as a homoepitaxial substrate. . This technique uses liquid Ga at high temperatures of 1400-1700 ° C. and nitrogen pressures as high as tens of kbar.
This is a technique for growing GaN from a crystal. In this case, a group III nitride semiconductor film required for a device can be grown using the bulk-grown GaN substrate. Therefore, a GaN substrate can be provided without complicating the process unlike the first and second prior arts.

However, the third prior art has a problem in that crystal growth at a high temperature and a high pressure is required, and a reaction vessel capable of withstanding the growth is extremely expensive. In addition, even with such a growth method, the size of the obtained crystal is at most about 1 cm, which is too small for practical use of the device.

As a method for solving the problem of the GaN crystal growth at a high temperature and a high pressure, the literature "Chemistry of Materi
als Vol. 9 (1997) P. 413-416 ”(hereinafter referred to as a fourth conventional technique) proposes a GaN crystal growth method using Na which is an alkali metal as a flux. According to this method, a reaction vessel made of stainless steel (inside dimensions: inner diameter = 7.5 mm, length = 100 mm) using sodium azide (NaN ₃ ) and metal Ga as flux and raw materials.
In a nitrogen atmosphere, and the reaction vessel is 600 to 800
C. for 24 to 100 hours.
This is for growing an N crystal. 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.
^The feature is that the pressure can be reduced as compared with the ^second prior art, which is about ^two . However, a problem with this method is that the size of the obtained crystal is small to less than 1 mm. Such a size is too small, as in the case of the third prior art, to make the device practical.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to a first and a second invention.
Without complicating the process which is a problem of the prior art, without using an expensive reaction vessel which is a problem of the third conventional technology, and without using a crystal which is a problem of the third or fourth conventional technology. The present invention provides a group III nitride crystal of a practical size for manufacturing high-performance light-emitting diodes and devices such as LDs without reducing the size of
It is an object of the present invention to provide a crystal growth method and a crystal growth apparatus capable of growing a group II nitride crystal, and to provide a high-performance group III nitride semiconductor device.

[0014]

According to a first aspect of the present invention, an alkali metal and a substance containing at least a group III metal form a mixed melt in a reaction vessel. Generating a local concentration distribution of dissolved nitrogen in the mixed melt when growing a Group III nitride composed of a Group III metal and nitrogen from the mixed melt and a substance containing at least nitrogen. It is characterized by.

According to a second aspect of the present invention, there is provided the crystal growth method according to the first aspect, wherein the local shape of dissolved nitrogen in the mixed melt is determined by the shape of the mixed melt holding container holding the mixed melt. The characteristic feature is that a typical concentration distribution is generated.

According to a third aspect of the present invention, in the crystal growth method according to the second aspect, the shape of the inner wall of the mixed melt holding container is such that the cross-sectional area decreases as it goes downward. It is characterized in that a local concentration distribution of dissolved nitrogen is generated in the mixed melt by using the same.

According to a fourth aspect of the present invention, there is provided the crystal growth method according to the second aspect, wherein the mixed melt holding vessel has a portion having a small cross-sectional area in a part of an inner wall thereof. Thus, a local concentration distribution of dissolved nitrogen is produced in the mixed melt.

According to a fifth aspect of the present invention, in the crystal growth method of the second aspect, the mixed melt holding container is
The shape in the container, the cross-sectional area becomes smaller as going downward, and from the middle, the cross-sectional area becomes uniform, or using a shape whose cross-sectional area becomes larger as going down, It is characterized in that a local concentration distribution of dissolved nitrogen is generated in the mixed melt.

Further, according to the present invention, the alkali metal and the substance containing at least a group III metal form a mixed melt in the reaction vessel, and the mixed melt is mixed with the substance containing at least nitrogen. , Consisting of Group III metals and nitrogen
A crystal growth apparatus for growing a group II nitride crystal, wherein a mixed melt holding vessel for holding a mixed melt is provided in a reaction vessel, and the mixed melt holding vessel has a mixed shape in the vessel. It is characterized in that it has a shape that produces a local concentration distribution of dissolved nitrogen in the melt.

According to a seventh aspect of the present invention, in the crystal growth apparatus according to the sixth aspect, the mixed melt holding container is
It is characterized in that the shape of the inner wall is such that the cross-sectional area decreases as it goes downward.

The invention according to claim 8 is the crystal growth apparatus according to claim 6, wherein the mixed melt holding container is
It is characterized in that a part of the inner wall has a small cross-sectional area.

According to a ninth aspect of the present invention, in the crystal growth apparatus according to the sixth aspect, the cross-sectional area of the mixed melt holding container becomes smaller as the shape of the container goes downward, and , The cross-sectional area is uniform, or
It is characterized in that the cross-sectional area increases as it goes downward.

The invention according to claim 10 is the invention according to claim 7.
Alternatively, in the crystal growth apparatus according to the eighth aspect, a heating apparatus is further provided so that the inside of the reaction vessel 101 can be controlled to a temperature at which a crystal can be grown.

Further, the invention described in claim 11 is the same as the ninth invention.
The crystal growth apparatus according to claim 1, wherein the first heating device and the second heating device
Is further provided, and the first heating device and the second heating device determine a heating temperature of an upper portion of the mixed melt holding container and a heating temperature of a lower portion of the mixed melt holding container. It is characterized in that a predetermined temperature difference is set between them.

The invention according to claim 12 is the first invention.
A group III nitride crystal grown using the crystal growth method according to any one of claims 1 to 5.

The invention of claim 13 is the first invention.
A semiconductor device manufactured using the group III nitride crystal according to item 2.

The invention according to claim 14 is the first invention.
The semiconductor device described in 3 is a light emitting device that emits light at a wavelength shorter than 400 nm.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. The present invention provides, in a reaction vessel, a mixed melt of an alkali metal and a substance containing at least a group III metal, and is composed of a group III metal and nitrogen from the mixed melt and a substance containing at least nitrogen. A group III nitride crystal is grown, characterized in that when growing a group III nitride crystal, a local concentration distribution of dissolved nitrogen is produced in the mixed melt.

Here, a local concentration distribution of dissolved nitrogen in the mixed melt can be generated by the shape of the mixed melt holding container for holding the mixed melt.

The method for growing a group III nitride crystal according to the present invention will be described more specifically. That is, in the reaction vessel,
There are substances containing alkali metals and at least Group III metals, and substances containing at least nitrogen. These substances may be supplied from the outside or may be present in the reaction vessel from the beginning. Further, the reaction vessel is provided with a temperature control mechanism. The temperature inside the reaction vessel can be raised to a temperature at which crystal growth can be performed, and the temperature can be lowered to a temperature at which crystal growth is stopped, and the temperature can be raised for any time. It is possible to hold. By setting the temperature in the reaction vessel and the effective nitrogen partial pressure to the conditions under which the group III nitride crystal grows, the crystal growth of the group III nitride can be started.

When the temperature is set to a predetermined value by the temperature control mechanism, the alkali metal and the substance containing at least the group III metal form a mixed melt. Nitrogen is dissolved in the mixed melt. The term “dissolved” as used herein means that nitrogen is present in the mixed melt in a dissolved state.

In the present invention, at this stage, a spatial (local) distribution is generated in the concentration of the dissolved nitrogen in the mixed melt. Note that the local concentration distribution of dissolved nitrogen in the mixed melt is such that nitrogen moves from the surface of the mixed melt toward the inside of the mixed melt in the mixed melt holding vessel at a predetermined temperature. However, at this time, it is considered that this is caused by the fact that the mixed melt holding container has an inner shape as described later.

Then, by generating a local concentration distribution of dissolved nitrogen in the mixed melt, it becomes possible to grow a group III nitride crystal in a specific region of the mixed melt. That is, crystal nuclei are generated at the initial stage of the crystal growth start, but if there is a local distribution of the dissolved nitrogen concentration in the mixed melt, the generation of the crystal nuclei is limited to a part of the mixed melt. With this crystal nucleus at the center, the crystal growth of the group III nitride can proceed.

After the crystal is grown to a desired size, the temperature of the reaction vessel is lowered to a temperature at which the crystal can be taken out.

In the above description and in the following description, nitrogen refers to nitrogen molecules or atomic nitrogen produced from nitrogen molecules or compounds containing nitrogen, and atomic groups and molecular groups containing nitrogen. It is.

As described above, in the present invention, depending on the internal shape of the mixed melt holding container for holding the mixed melt,
A local concentration distribution of dissolved nitrogen is produced in the mixed melt.

FIG. 1 is a diagram showing a configuration example of a crystal growth apparatus of the present invention. The crystal growth apparatus of the present invention, in a reaction vessel,
An alkali metal and a substance containing at least a group III metal (for example, Ga) form a mixed melt. The mixed melt is made of a group III metal and nitrogen from a substance containing at least nitrogen (N). It is configured to grow a group III nitride crystal.

That is, referring to FIG.
Inside 01, a mixed melt holding container 102 is provided. Here, the material of the mixed melt holding container 102 is, for example, BN (boron nitride). The mixed melt holding container 102 is a mixed melt 10 composed of a group III metal (eg, Ga) and an alkali metal (eg, Na).
3 is held.

Referring also to FIG. 1, the reaction vessel 101
Is provided with a heating device 106 so that the inside of the reaction vessel 101 can be controlled to a temperature at which a crystal can be grown. Further, a nitrogen supply pipe 10 is provided in a space area 108 in the reaction vessel 101.
4, a nitrogen gas is supplied from outside the reaction vessel 101. In order to adjust the nitrogen pressure, FIG.
In the device described above, a pressure adjusting mechanism 105 is provided. This nitrogen pressure adjusting mechanism 105 is constituted by a pressure sensor, a pressure adjusting valve, and the like.

In the present invention, the mixed melt holding container 102 is
The inside shape of the container is a shape that causes a local concentration distribution of dissolved nitrogen in the mixed melt.

FIG. 2 is a view showing an example of the mixed melt holding container 102. The inner wall 102a of the mixed melt holding container 102 in FIG. 2 has a shape in which the inner volume (cross-sectional area) decreases downward. Here, the shape in which the cross-sectional area becomes smaller as the shape of the inner wall 102a of the mixed melt holding container 102 goes downward is defined as that the shape of the inner wall 102a of the mixed melt holding container 102 is conical or pyramidal, Is a shape having a vertex of the weight at the top. That is, in the example of FIG.
Three-dimensionally, it is held at a portion surrounded by an inner wall 102a shaped like a cone with its apex down.

In the crystal growth apparatus having the structure shown in FIGS. 1 and 2, the nitrogen pressure in the reaction vessel 101 is set to 50 atm, and the temperature is increased to 750 ° C. at which the crystal growth starts. By keeping these growth conditions for a certain period of time, the group III nitride crystal (for example, GaN crystal) 109 is mixed with the mixed melt holding container 10.
Growing into 2 At this time, at the initial stage of crystal growth, III
A nucleus of a group III nitride crystal (for example, GaN crystal) 109 is generated, and crystal growth proceeds based on the nucleus. A region where a group III nitride crystal (for example, GaN crystal) 109 grows is shown in FIG. This is only the inclined upper part of the inner wall 102a of the melt holding container 102.

When the shape of the inner wall 102a of the mixed melt holding container 102 is not a shape as shown in FIG. 2 (a shape such as a cone or a pyramid) but a column or a prism, III Group nitride crystal (for example, GaN crystal) 109
Grows on the entire inner wall 102a of the mixed melt holding vessel 102, and the single crystal group III nitride crystal (for example, GaN crystal) 109 does not grow. On the other hand, when the shape of the inner wall 102 a of the mixed melt holding container 102 is as shown in FIG. 2, nucleation of the group III nitride crystal (for example, GaN crystal) 109 is caused by the mixed melt 103. Group III metals (for example, G
a) can be efficiently used for growing a group III nitride single crystal (for example, a GaN single crystal), and a crystal having a large crystal shape can be obtained.

This is considered to be due to the following mechanism. That is, the nitrogen from the nitrogen gas filled in the space region 108 of the reaction vessel 101 dissolves into the mixed melt 103 from the surface 103a of the mixed melt 103 (from the surface 103a of the mixed melt 103 to the For example by diffusion). When the shape of the inner wall 102a of the mixed melt holding container 102 is as shown in FIG.
The direction of movement of nitrogen in the mixed melt 103
The cross-sectional shape of the inner wall 102a of the mixed melt holding container 102 in a direction perpendicular to the direction (that is, the direction from above to below) that moves by diffusion from the surface 103a to the inside of the mixed melt 103 changes. are doing. for that reason,
A spatial difference (distribution) occurs in the dissolved nitrogen concentration in the mixed melt 103, and a group III nitride crystal (for example, a GaN crystal)
The crystal nucleus 109 forms the inner wall 102 of the mixed melt holding vessel 102.
Occurs in part of a.

That is, when the cross-sectional area of the inner wall 102a of the mixed melt holding container 102 is changed (when the cross-sectional area of the mixed melt 103 is changed according to the shape of the inner wall 102a of the container 102), the dissolved melt is dissolved in the mixed melt 103. A local distribution of the nitrogen concentration will result. As a result, generation of crystal nuclei of the group III nitride crystal (for example, GaN crystal) 109 is limited to a part of the mixed melt 103. Centering on the generated crystal nuclei, furthermore, a group III nitride crystal (for example, GaN
Although the growth of the crystal (crystal) 109 proceeds, the crystal nucleus generated once proceeds more preferentially than the region having no crystal nucleus. At this time, the temperature of the mixed melt holding container 102 and the temperature of the mixed melt 103 therein are uniform. Therefore, II
Nitrogen, which is a Group V source material of Group I nitride crystal (eg, GaN crystal) 109, moves by diffusion from surface 103a of mixed melt 103, and forms a crystal nucleus of Group III nitride crystal (eg, GaN crystal) 109. Will be consumed. As a result, the group III nitride crystal (for example, GaN crystal) 109 grows only on a part of the inner wall 102a of the mixed melt holding vessel 102, and the group III nitride crystal (for example, G
aN crystal) 109 can be grown.

FIG. 3 is a view showing another example of the mixed melt holding container 102. In the example of FIG. 3, the mixed melt holding container 102 has protrusions 12 on the inner wall 102a of the mixed melt holding container 102 below the surface 103a of the mixed melt 103.
6 is provided.

Using the mixed melt holding vessel 102 of FIG.
When growing a group I nitride crystal (for example, GaN crystal) 109, the nucleus of the group III nitride crystal (for example, GaN crystal) 109 is formed around the tip of the protrusion 126 on the inner wall 102a of the mixed melt holding vessel 102. appear. The generation of nuclei of the group III nitride crystal (for example, GaN crystal) 109 is dominant in the mixed melt 103 in a region near the tip of the projection 126. Therefore, the crystal nucleus in this region becomes the center, the growth of the group III nitride crystal (for example, GaN crystal) 109 proceeds, and it becomes possible to grow a crystal having a large crystal shape.

In the crystal growth apparatus having the structure shown in FIGS. 1 and 3, the nitrogen pressure in the reaction vessel 101 is set to 50 atm, and the temperature is increased to 750 ° C. at which the crystal growth starts. By keeping these growth conditions for a certain period of time, the group III nitride crystal (for example, GaN crystal) 109 is mixed with the mixed melt holding container 10.
Growing into 2 At this time, at the initial stage of crystal growth, III
A nucleus of a group III nitride crystal (for example, GaN crystal) 109 is generated, and crystal growth proceeds based on the nucleus. A region where a group III nitride crystal (for example, GaN crystal) 109 grows is shown in FIG. Projection 12 on inner wall 102a of melt holding container 102
6 is only the area near the tip.

This is considered to be due to the following mechanism. That is, the nitrogen from the nitrogen gas filled in the space region 108 of the reaction vessel 101 dissolves into the mixed melt 103 from the surface 103a of the mixed melt 103 (from the surface 103a of the mixed melt 103 to the For example by diffusion). In the case of the example of FIG. 3, since the projection 126 is provided on the inner wall 102 a of the mixed melt holding container 102, the mixed melt holding container 102 in a direction perpendicular to the moving direction of the nitrogen in the mixed melt 103. Is changed in the cross section. Therefore, the mixed melt 103
Difference (distribution) in the concentration of dissolved nitrogen in
A crystal nucleus of a group I nitride crystal (for example, a GaN crystal) 109 is generated around the protrusion 126. Centering on the generated crystal nucleus, further, a group III nitride crystal (for example, GaN
Although the growth of the crystal (crystal) 109 proceeds, the crystal nucleus generated once proceeds more preferentially than the region having no crystal nucleus. At this time, the temperature of the mixed melt holding container 102 and the temperature of the mixed melt 103 therein are uniform. Therefore III
Nitrogen, which is a Group V material of Group III nitride crystal (eg, GaN crystal) 109, moves by diffusion from surface 103 a of mixed melt 103 and is consumed by crystal nuclei of Group III nitride crystal (eg, GaN crystal) 109. Will be done. As a result, the group III nitride crystal (for example, GaN crystal) 109 grows only on a part of the inner wall 102a of the mixed melt holding vessel 102, and the group III nitride crystal (for example, G
aN crystal) 109 can be grown.

In the example shown in FIG. 3, the mixed melt holding container 1
02 is provided with the protrusion 126 on the inner wall 102a.
Means alternative to 6 can also be provided. That is, the mixed melt holding container 102 may have a portion having a small cross-sectional area in a part of the inner wall 102a.

FIG. 4 is a diagram showing another example of the structure of the crystal growth apparatus of the present invention. In FIG. 4, the same reference numerals are given to portions corresponding to FIG. In the crystal growth apparatus shown in FIG. 4, a first heating apparatus 116 and a second heating apparatus are provided so that a group III nitride crystal (for example, a GaN crystal) 109 can be controlled to a temperature at which the crystal can be grown in the reaction vessel 101. 117 are provided. Here, the first heating device 116 and the second heating device 117 can be individually temperature-controlled.

FIG. 5 is a view showing another example of the mixed melt holding container 102. The mixed melt holding container 102 of FIG. 5 is adapted to be used in the crystal growth apparatus of FIG. Referring to FIG. 5, the mixed melt holding vessel 102 has an inner wall formed by an upper inner wall 102a and a lower inner wall 102b, and the inner volume (cross-sectional area) of the upper inner wall 102a decreases downward. It has such a shape. The lower inner wall 102b has a uniform cross-sectional area. That is, the three-dimensional shape of the inner wall of the mixed melt holding container 102 in FIG. 5 is a shape in which a conical shape with a vertex cut down is cut off in the middle and a columnar shape is positioned therebelow.

In the crystal growth apparatus having the structure shown in FIGS. 4 and 5, the nitrogen pressure in the reaction vessel 101 is set to 50 atm, and the upper part (10
The temperature of 2a) is increased to 750 ° C. at which crystal growth starts. Further, the temperature of the lower portion (102b) of the mixed melt holding container 102 is set to 780 ° C. by the second heating device 117. By maintaining these growth conditions for a certain period of time, a group III nitride crystal (for example, GaN crystal) 109 grows in the mixed melt holding container 102. At this time, at the initial stage of crystal growth, a group III nitride crystal (for example, GaN crystal) 10
Nine nuclei are generated, and crystal growth proceeds based on these nuclei. II
The region where the group I nitride crystal (for example, GaN crystal) 109 grows is only the inclined upper part of the inner wall of the mixed melt holding vessel 102 in FIG. 5 (only a part of the upper inner wall 102a).

Group III nitride crystal (for example, GaN crystal)
The crystal nucleus 109 is generated only on a part of the inner wall of the mixed melt holding container 102 as in the case of the example of FIG. Here, the difference between the mixed melt holding container of FIG. 5 and the mixed melt holding container of FIG. 2 is that the shape of the inner wall of the mixed melt holding container 102 has a uniform cross-sectional area from the middle. It is that you are. As described above, when the inner wall of the mixed melt holding container has a cylindrical or prismatic shape, the nucleus of the group III nitride crystal (for example, GaN crystal) 109 grows on the entire inner wall of the mixed melt holding container. In addition, the single crystal group III nitride crystal (for example, GaN crystal) 109 does not increase. On the other hand, when the mixed melt holding container has the shape shown in FIG. 5, nucleation occurs only partially, and the group III metal (eg, Ga) in the mixed melt is converted into a group III nitride single crystal (eg, Ga). , GaN single crystal) 109 can be efficiently used and a crystal having a large crystal shape can be obtained. Moreover, the mixed melt holding container 1
Since the cross-sectional area of the inner wall of No. 02 becomes uniform from the middle (that is, the cross-sectional area of the lower inner wall 102b is uniform), the region of the lower inner wall 102b has III.
Growth of the group III nitride crystal (eg, GaN crystal) 109 is suppressed, and the group III metal (Ga) and the alkali metal (eg,
The mixed melt composed of Na) is held. Therefore,
The region of the lower inner wall 102b is made of a group III metal (eg, Ga) of a group III nitride crystal (eg, GaN crystal) 109.
And a group III metal (for example, Ga) can be continuously supplied, and the crystal can be grown to a sufficient size.

Further, in the crystal growth apparatus shown in FIGS.
Due to the temperature difference between the upper part and the lower part of the mixed melt holding container 102, convection occurs in the mixed melt 103. Due to this convection, the group III metal (for example, Ga) contains the mixed melt holding vessel 1.
02, and nitrogen, which is a Group V raw material, is supplied from the upper portion, thereby enabling efficient crystal growth.

In the example of the crystal growth apparatus shown in FIG. 5, the cross-sectional area of the inner wall of the mixed melt holding vessel 102 becomes smaller as it goes downward, and the cross-sectional area becomes uniform from the middle. However, the shape of the inner wall of the mixed melt holding container 102 may be such that the cross-sectional area becomes smaller as going downward, and the cross-sectional area becomes larger as going down from the middle. .

Further, the internal shape of the mixed melt holding container 102 does not need to be the shape shown in FIGS. 2, 3 and 5. Any shape can be used as long as the shape is generated. Further, the mixed melt holding container 10
It is assumed that the inner shape of the container 2 includes not only the shape of the inner wall of the container but also the shape of the object such as a jig or a mechanical device other than the container 102 when the object is installed in the container 102.

In each of the above examples, Na is used as the metal (alkali metal) having a low melting point and a high vapor pressure.
Potassium (K) or the like can be used instead of Na. That is, as the alkali metal, any alkali metal can be used as long as it becomes a melt at the temperature at which the group III nitride crystal is grown.

In the above example, Ga is used as the substance containing at least the group III metal element. However, other than Ga, a simple metal such as Al or In, or a mixture or alloy thereof may be used. Etc. can also be used.

In the above-described example, nitrogen gas is used as a substance containing at least nitrogen element. However, other than nitrogen gas, a gas such as NH ₃ can be used.

By growing a group III nitride crystal using the above-described crystal growth method and crystal growth apparatus of the present invention, the group III nitride crystal has high crystal quality and is large enough to manufacture a device. Crystals can be provided at low cost.

As an example of the method of growing a group III nitride crystal according to the present invention, Ga is used as a group III metal, nitrogen gas is used as a nitrogen source, Na is used as a flux, the temperature of the reaction vessel and the flux vessel is 750 ° C. Pressure 5
It is kept constant at 0 kg / cm ² G. Under these conditions,
A GaN crystal can be grown.

Further, the growth was performed by the growth method of the present invention.
A group III nitride semiconductor device can be manufactured using a group III nitride crystal.

FIG. 6 is a diagram showing a configuration example of a semiconductor device according to the present invention. In the example of FIG. 6, the semiconductor device is configured as a semiconductor laser. Referring to FIG. 6, this semiconductor device comprises an n-type AlGaN cladding layer 302, an n-type G layer, and an n-type GaN substrate 301 using a group III nitride crystal grown in the manner described above.
aN guide layer 303, InGaN MQW (multiple quantum well) active layer 304, p-type GaN guide layer 305, p-type A
lGaN cladding layer 306, p-type GaN contact layer 3
07 are sequentially grown. As the crystal growth method, MO-VPE (metal organic chemical vapor deposition) method and MBE
A thin film crystal growth method such as a (molecular beam epitaxy) method can be used.

Next, GaN, AlGaN, InGaN
The ridge structure is formed on the laminated film of, SiO ₂ insulating film 308
Is formed in a state where only the contact region is perforated, and a p-side ohmic electrode Al / Ni 309 and an n-side ohmic electrode Al / Ti 310 are formed on the upper and lower parts, respectively.
The semiconductor device (semiconductor laser) of FIG. 6 is configured.

The p-side ohmic electrode A of this semiconductor laser
1 / Ni 309 and n-side ohmic electrode Al / Ti
By injecting a current from 310, this semiconductor laser oscillates and can emit laser light in the direction of arrow A in FIG.

Since this semiconductor laser uses the group III nitride crystal (GaN crystal) of the present invention as the substrate 301, it has few crystal defects in the semiconductor laser device, and has a large output operation and a long life. I have. Further, since the GaN substrate 301 is n-type, the electrode 310 can be formed directly on the substrate 301, and the first conventional technology (FIG. 7)
It is not necessary to take out the two electrodes on the p-side and the n-side only from the surface as in the above, and the cost can be reduced.

Further, in the semiconductor device shown in FIG. 6, the light emitting end face can be formed by cleavage, and together with the separation of the chips, a low-cost and high-quality device can be realized.

In the above example, InGaN MQW
Is used as the active layer, but it is also possible to shorten the emission wavelength by using AlGaN MQW as the active layer. In the present invention, since the defects and impurities of the GaN substrate are small, light emission from a deeper order is reduced, and a highly efficient light emitting device can be realized even if the wavelength is shortened.

Specifically, a light-emitting device that emits light at a wavelength shorter than 400 nm (a light-emitting device having good characteristics even in the ultraviolet region) can be provided as a group III nitride semiconductor device. That is, in the prior art, GaN
The emission spectrum of the film is dominant in emission from deeper order, and there is a problem that device characteristics are poor at a wavelength shorter than 400 nm. However, according to the present invention, it is possible to provide a light emitting device having good characteristics even in an ultraviolet region. it can.

Further, in the above example, application to an optical device has been described, but application to an electronic device is also possible. In other words, by using a GaN substrate having few defects, the GaN-based thin film epitaxially grown thereon has few crystal defects. As a result, it is possible to suppress the leak current, to enhance the effect of confining carriers in a quantum structure, High performance devices can be realized.

[0072]

As described above, according to the first to eleventh aspects of the present invention, in the reaction vessel, the alkali metal and the substance containing at least the group III metal form a mixed melt. When a group III nitride composed of a group III metal and nitrogen is crystal-grown from the mixed melt and a substance containing at least nitrogen, a local concentration distribution of dissolved nitrogen is generated in the mixed melt. Therefore, without complicating the process which is a problem of the first and second conventional techniques, and without using an expensive reaction vessel which is a problem of the third conventional technique,
In addition, 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.
A group III nitride crystal of a practical size for fabricating a device such as the above can be grown.

Further, the growth temperature is as low as 1000 ° C. or less, and the crystal growth of the group III nitride can be performed under the condition that the pressure is as low as about 100 atm or less. There is no need to use expensive reaction vessels that can withstand extremely high temperatures. As a result, a low-cost group III nitride crystal and a device using the same can be realized.

Further, in the inventions according to the first to eleventh aspects, the local concentration distribution of the dissolved nitrogen is generated in the mixed melt, so that the nucleation of the group III nitride crystal can be reduced in the mixed melt. It is possible to limit to a part, and a group III nitride crystal having a large crystal shape can be grown.

According to the fifth and ninth aspects of the present invention, the cross-sectional area of the mixed melt holding container becomes smaller as it goes downward, and the cross-sectional area becomes uniform from the middle. Alternatively, since the cross-sectional area increases in the downward direction, the mixed melt is held in this region. As a result, the group III metal can be continuously supplied to the region where the growth nucleus has been generated, and a larger group III nitride crystal can be grown.

According to the twelfth aspect of the present invention, the crystal is a group III nitride crystal grown by the crystal growth method of any one of the first to fifth aspects. Group III nitride crystals of high quality (less crystal defects) and large enough to produce devices
It can be provided at low cost.

According to the thirteenth aspect of the present invention, since the semiconductor device is manufactured using the group III nitride crystal according to the twelfth aspect, a high-performance group III nitride semiconductor device is provided at low cost. can do. The term “high performance” as used herein means, for example, a semiconductor laser or a light emitting diode that has a high output and a long life, which cannot be realized conventionally, and an electronic device that has low power consumption, low noise, and high speed. It can operate and operate at high temperatures, and the light receiving device has low noise and long life.

According to a fourteenth aspect of the present invention, the semiconductor device according to the thirteenth aspect is a light emitting device that emits light at a wavelength shorter than 400 nm, and provides a device that emits light with high efficiency even in this wavelength range. Can be. That is, the semiconductor device according to the thirteenth aspect is a group III nitride semiconductor device having few crystal defects and impurities. As a result, it is possible to realize high-efficiency light emission characteristics in which light emission from a deep order can be suppressed. Becomes

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a crystal growth apparatus according to the present invention.

FIG. 2 is a diagram illustrating an example of a mixed melt holding container.

FIG. 3 is a diagram illustrating an example of a mixed melt holding container.

FIG. 4 is a diagram showing another configuration example of the crystal growth apparatus according to the present invention.

FIG. 5 is a diagram showing an example of a mixed melt holding container.

FIG. 6 is a diagram showing a configuration example of a semiconductor device according to the present invention.

FIG. 7 is a diagram showing a conventional laser diode.

[Explanation of symbols]

Reference Signs List 101 Reaction vessel 102 Mixed melt holding vessel 103 Mixed melt 104 Nitrogen gas supply pipe 105 Nitrogen pressure adjusting mechanism 106 Heating device 108 Spatial region in reaction vessel 109 Group III nitride (GaN) crystal 103a Mixed melt surface 126 Mixed melt Protrusion of liquid holding container 116 First heating device 117 Second heating device 301 n-type GaN substrate 302 n-type AlGaN cladding layer 303 n-type GaN guide layer 304 InGaN MQW active layer 305 p-type GaN guide layer 306 p-type AlGaN cladding Layer 307 p-type GaN contact layer 308 SiO ₂ insulating film 309 p-side ohmic electrode 310 n-side ohmic electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Maoto Aoki 3-3-1 Aoyama, Rifu-cho, Miyagi-gun, Miyagi F-term (reference) 4G077 AA02 BE15 CC01 EA06 EC08 EG01 HA01 LA01 LA03 LA05 5F041 AA40 CA05 CA34 CA40 CA65 CA66 CA82 CA92 5F073 AA11 AA13 AA45 AA74 CA07 DA02 DA05 DA06 EA05

Claims (14)

[Claims] 1. In a reaction vessel, an alkali metal and a substance containing at least a Group III metal form a mixed melt,
From the mixed melt and a substance containing at least nitrogen, when growing a Group III nitride composed of a Group III metal and nitrogen, a local concentration distribution of dissolved nitrogen in the mixed melt may be generated. Characteristic crystal growth method. 2. The method for growing a crystal according to claim 1, wherein
A crystal growth method, wherein a local concentration distribution of dissolved nitrogen is generated in the mixed melt by a shape of the mixed melt holding container holding the mixed melt. 3. The method for growing a crystal according to claim 2, wherein
As the mixed melt holding container, the shape of the inner wall thereof is such that the cross-sectional area becomes smaller as it goes downward, thereby causing a local concentration distribution of dissolved nitrogen in the mixed melt. Characteristic crystal growth method. 4. The crystal growth method according to claim 2, wherein
As the mixed melt holding container, a container having a portion having a small cross-sectional area on a part of an inner wall thereof is used to generate a local concentration distribution of dissolved nitrogen in the mixed melt. Crystal growth method. 5. The method for growing a crystal according to claim 2, wherein
As the mixed melt holding container, the cross-sectional area decreases as the shape inside the container goes downward, and the cross-sectional area becomes uniform from the middle, or the cross-sectional area increases as going downward. A crystal growth method, wherein a local concentration distribution of dissolved nitrogen is produced in a mixed melt using a shape melt. 6. In a reaction vessel, an alkali metal and a substance containing at least a Group III metal form a mixed melt,
A crystal growth apparatus for growing a group III nitride composed of a group III metal and nitrogen from the mixed melt and a substance containing at least nitrogen, wherein a mixed melt holding the mixed melt is provided in a reaction vessel. A liquid growth container is provided, and the mixed melt holding container has a shape in which the shape of the container is such that a local concentration distribution of dissolved nitrogen is generated in the mixed melt. apparatus. 7. The crystal growth apparatus according to claim 6, wherein
The crystal growth apparatus according to claim 1, wherein the mixed melt holding container has an inner wall having a shape in which a cross-sectional area decreases as it goes downward. 8. The crystal growth apparatus according to claim 6, wherein
A crystal growth apparatus, wherein the mixed melt holding container has a portion having a small cross-sectional area on a part of an inner wall thereof. 9. The crystal growth apparatus according to claim 6, wherein
In the mixed melt holding container, the cross-sectional area becomes smaller as the shape in the container goes downward, and the cross-sectional area becomes uniform from the middle, or the cross-sectional area becomes larger as going downward. A crystal growth apparatus having a shape. 10. The crystal growth apparatus according to claim 7, further comprising a heating device so that the inside of the reaction vessel 101 can be controlled to a temperature at which crystal growth is possible. . 11. The crystal growth apparatus according to claim 9, further comprising a first heating device and a second heating device, wherein the first heating device and the second heating device provide the first heating device and the second heating device. A crystal growth apparatus, wherein a predetermined temperature difference is set between a heating temperature of an upper portion of a mixed melt holding container and a heating temperature of a lower portion of the mixed melt holding container. 12. A group III nitride crystal grown using the crystal growth method according to claim 1. Description: 13. A semiconductor device manufactured using the group III nitride crystal according to claim 12. 14. The semiconductor device according to claim 13,
A semiconductor device, which is a light emitting device that emits light at a wavelength shorter than 400 nm.