WO2014192904A1 - Method for growing gallium nitride crystal, composite substrate, method for manufacturing light emitting element, and dissolution preventing jig - Google Patents

Abstract

A seed substrate, which is provided with a supporting substrate that is formed of a material that is soluble in a molten alkali metal and a seed crystal film that is formed on the outer surface of the supporting substrate and is formed of a nitride of a group 13 element, is used. A region of the outer surface of the supporting substrate, said region being not covered by the seed crystal film, is covered by a material that is not soluble in the molten alkali metal. After that, a gallium nitride crystal is grown on the seed crystal film by a flux method. Consequently, a gallium nitride film having less defects can be formed at high rate and at low cost.

Description

Method for growing gallium nitride crystal, composite substrate, method for manufacturing light emitting device, and dissolution preventing jig

The present invention relates to a method for growing a gallium nitride crystal, a composite substrate, a method for manufacturing a light emitting element, and a dissolution preventing jig.

白色 White LEDs are being used for various light sources. Low-brightness LEDs such as backlights and light bulbs are already in widespread use, and in recent years, studies on application to high-brightness LEDs such as projectors and headlights have become active. Currently, the mainstream white LEDs are formed by forming a light emitting layer made of a group 13 element nitride on a sapphire base substrate by metal organic chemical vapor deposition (MOCVD: Metal-Organic-Chemical-Vapor-Deposition) method.

White LEDs fabricated on the current mainstream sapphire base substrate have a large difference in material properties between sapphire, which is the base substrate, and gallium nitride, which is the light-emitting layer.・ It is difficult to achieve high efficiency.

There is a hydride vapor phase epitaxy (HVPE method) as a method for producing a self-supporting gallium nitride substrate. When using a gallium nitride substrate fabricated by the HVPE method as the underlying substrate, LED performance can be expected to improve, but the cost of the HVPE method gallium nitride substrate is high and it is difficult to increase the diameter, so it is difficult for LED applications. Adoption is not progressing.

Zinc oxide (ZnO) is a safe and inexpensive compound semiconductor, and is known as a material that is chemically stable and excellent in transparency. It is mainly used in the form of sintered bodies and powders, and is used for sputtering targets, varistors, additives to rubber, cosmetics and the like. The zinc oxide substrate, which has the same hexagonal wurtzite crystal structure as gallium nitride and has a lattice constant and thermal expansion coefficient close to that of gallium nitride, is expected to improve the LED performance by reducing defects in the light emitting layer. As a research and development.

When using zinc oxide as a sintered body, it is known that the characteristics change by orienting the crystal orientation. For example, Patent Document 1 discloses a crystal-oriented zinc oxide sintered body having a (101) crystal orientation ratio within a predetermined range as a sputtering target. Patent Document 2 discloses a (110) crystal-oriented zinc oxide sintered body.

Also, from the viewpoint of reducing the cost of LEDs, it is also considered to use Si, which has a large-diameter substrate exceeding 8 inches, in various semiconductor applications.

L. Lu etal., JAP. 109, 113537 (2011)

Japanese Patent No. 3128861 Japanese Patent No. 4502493

When a zinc oxide substrate is used as the base substrate, the lattice constant and thermal expansion coefficient of zinc oxide are close to those of gallium nitride, so that defects in the light emitting layer are reduced, and LED performance is expected to be improved. However, when an LED structure is actually manufactured, impurities derived from zinc oxide are taken into the functional layer, so that carrier control is difficult and a high-performance LED cannot be manufactured.

In addition, the zinc oxide substrate currently produced is based on the hydrothermal method, but its diameter and cost have not been reduced.

On the other hand, when using a Si single crystal as the base substrate, as in the case of using a sapphire base substrate, the material property difference between Si and gallium nitride, which is the light emitting layer, is large. It is difficult to achieve the high output and high efficiency required by the company.

In order to suppress defects inside the light emitting layer, it is effective to increase the thickness of the n-type nitride layer between the light emitting layer and the stress relaxation layer (Non-Patent Document 1). Is slow and productivity is significantly reduced.

Furthermore, since zinc oxide and Si are easily dissolved in the molten alkali metal used in the flux method, it has not been studied to form a gallium nitride film by applying the flux method.

The present invention uses a seed substrate comprising a support substrate made of a substance that dissolves in a molten alkali metal and a seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate. A region of the outer surface that is not covered with the seed crystal film is covered with a material insoluble in the molten alkali metal, and then a gallium nitride crystal is grown on the seed crystal film by a flux method, The present invention relates to a method for growing a gallium nitride crystal.

The present invention also provides a support substrate made of a substance that dissolves in a molten alkali metal,
A seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate;
A protective film made of a material insoluble in the molten alkali metal that covers a region of the outer surface of the support substrate that is not covered with the group 13 element nitride film, and formed on the seed crystal film by a flux method. The present invention relates to a composite substrate comprising a gallium nitride crystal.

The present invention also relates to a light emitting device having the light emitting layer formed on the composite substrate and the gallium nitride layer.

The present invention also relates to a method for manufacturing a light-emitting element, in which a light-emitting layer is formed on the composite substrate by metal organic vapor phase epitaxy or molecular beam epitaxy.

The present invention also provides a seed substrate comprising a support substrate made of a substance that dissolves in a molten alkali metal and a seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate for the flux method. A melting prevention jig for
The dissolution preventing jig is in close contact with a region of the outer surface of the support substrate that is not covered with the seed crystal film, and prevents the support substrate from coming into direct contact with the molten alkali metal.

According to the present invention, a seed crystal film made of a group 13 element nitride is formed on the outer surface of a support substrate made of a substance that dissolves in a molten alkali metal, and the seed crystal film is coated on the outer surface of the support substrate. A region not formed is covered with a material insoluble in molten alkali metal, and a gallium nitride crystal is grown on the seed crystal film by a flux method. Thereby, at the time of growing the gallium nitride crystal, dissolution of the support substrate due to contact between the melt and the support substrate can be prevented, and inhibition of the growth of the gallium nitride crystal and contamination can be prevented. As a result, gallium nitride crystals can be mass-produced by the flux method using a support substrate made of a substance that can be dissolved in molten alkali metal, which has not been conventionally used, and has great industrial applicability.

(A) is sectional drawing which shows the support substrate 1 typically, (b) is sectional drawing which shows the state which formed the seed crystal film 2 on the support substrate 1, (c) is support substrate 1 It is sectional drawing which shows the state which coat | covered protective film 3A, 3B which consists of a material insoluble in a molten alkali metal on the outer surface of FIG., (D) is the state which formed the gallium nitride crystal 5 on the seed crystal film 2. It is sectional drawing shown. (A) is sectional drawing which shows the state which grind-processed the gallium nitride crystal 5 of FIG.1 (d), and formed the gallium nitride crystal 5A, (b) shows the light emitting layer 7 on the gallium nitride crystal 5A. It is sectional drawing which shows the formed state. (A) is sectional drawing which shows the support substrate 1 typically, (b) is sectional drawing which shows the state which formed the seed crystal film 2 on the support substrate 1, (c) is a seed crystal film 2 is a cross-sectional view showing a state in which a gallium nitride crystal 5 is formed on 2. FIG. FIG. 3A is a cross-sectional view showing a state in which the gallium nitride crystal 5A of FIG. 3C is polished to form a gallium nitride crystal 5A, and FIG. 3B is a cross-sectional view of the light emitting layer 7 on the gallium nitride crystal 5A. It is sectional drawing which shows the formed state. (A) is sectional drawing which shows typically the state which set the seed substrate to the dissolution prevention jig | tool 11, (b) is a top view which shows the state which set the seed substrate to the dissolution prevention jig | tool 11. . FIG. 6 is a schematic diagram showing a state where the seed substrate and the dissolution preventing jig of FIG. 5 are immersed in the melt 16. It is sectional drawing which shows typically the state which set the seed substrate to 11 A of melt | dissolution prevention jig | tools. It is a schematic diagram which shows the state which set the seed board | substrate to the crucible 20 which functions as a melt | dissolution prevention jig | tool.

The present invention will be further described below with reference to the drawings as appropriate.
As shown to Fig.1 (a), the support substrate 1 which consists of a substance which melt | dissolves in a molten alkali metal is prepared. In this example, the outer surface of the support substrate 1 includes a first main surface 1a, a second main surface 1b opposite to the main surface 1a, and a side surface 1c formed between the main surfaces 1a and 1b. Including. Although the planar form of the substrate 1 is not illustrated, it is not particularly limited, and may have any form such as a wafer shape, a polygonal shape, and a circular shape.

Next, as shown in FIG. 1B, a seed crystal film 2 made of a group 13 element nitride is formed on the first main surface 1a. The seed crystal film 2 is preferably formed over the entire main surface 1a, but the seed crystal film 2 may not be formed on the outer edge of the main surface 1a, and the main surface of the support substrate may be exposed.

Next, as shown in FIG. 1C, a protective film made of a material insoluble in molten alkali metal is formed on the second main surface 1b and the side surface 1c of the support substrate 1 that are not covered with the seed crystal film 2. 3A and 3B are coated. As a result, the outer surface of the support substrate 1 is not directly exposed, and the seed substrate 4 is obtained.

Next, the seed substrate 4 is immersed in the melt, and a gallium nitride crystal 5 is grown as shown in FIG. 1 (d) by a flux method. At this time, since the support substrate 1 does not come into contact with the melt, dissolution thereof is prevented, so that the growth of the gallium nitride crystal is not inhibited and no contamination occurs. In this example, it is not necessary to set the support substrate on the dissolution preventing jig.

Using the composite substrate thus obtained, a light emitting layer can be formed thereon. However, in a preferred embodiment, the polished gallium nitride crystal 5A can be formed by polishing the surface of the gallium nitride crystal, as shown in FIG. In this way, the warpage of the composite substrate 6 can be adjusted and the flatness of the surface of the gallium nitride crystal can be improved. In this case, a light emitting element is obtained by forming the light emitting layer 7 on the polished gallium nitride crystal 5A as shown in FIG. 2B.

In another embodiment, a region of the outer surface of the support substrate that is not covered with the seed crystal film is covered with a dissolution preventing jig made of a material insoluble in the molten alkali metal, so that the support substrate is melted. To prevent contact. In this case, it is not necessary to cover a region of the outer surface of the support substrate that is not covered with the seed crystal film with a protective film made of a material insoluble in molten alkali metal, and the outer surface of the support substrate is exposed. However, the effect of the present invention can be obtained.

For example, as shown in FIG. 3A, a support substrate 1 made of a substance that dissolves in a molten alkali metal is prepared. Next, as shown in FIG. 3B, a seed crystal film 2 made of a group 13 element nitride is formed on the first main surface 1a. In the case of this type of substrate, the second main surface 1b and the side surface 1c of the support substrate are exposed.

Next, the seed substrate of FIG. 3B is immersed in the melt, and the gallium nitride crystal 5 is grown by the flux method as shown in FIG. 3C. At this time, in the seed substrate of FIG. 3B, the outer surface of the support substrate is exposed. When this seed substrate is immersed in the melt as it is, the second main surface 1b and the side surface 1c of the support substrate are dissolved in the molten alkali metal in the melt to inhibit the growth of the gallium nitride crystal. Since contamination occurs, when this type of substrate is used, a dissolution preventing jig is used.

Using the composite substrate thus obtained, a light emitting layer can be formed thereon. However, in a preferred embodiment, by polishing the surface of the gallium nitride crystal, as shown in FIG. 4A, a polished gallium nitride crystal 5A can be formed and a composite substrate 9 can be obtained. . Then, as shown in FIG. 4B, the light emitting element is obtained by forming the light emitting layer 7 on the polished gallium nitride crystal 5A.

Here, an example of the dissolution preventing jig will be described.
For example, in the example of FIG. 5, the seed substrate is set on the dissolution preventing jig 11. The dissolution preventing jig 11 has a main surface covering portion 12 that covers the second main surface, a side surface covering portion 13 a that covers the side surface, and an outer edge covering portion 13 b that covers the outer edge of the seed crystal film 2. . In this example, the main surface covering portion 12 is a separate member separated from the side surface covering portion 13a, and the side surface covering portion 13a and the outer edge covering portion 13b constitute an integral member.

Next, as shown in FIG. 6, the dissolution preventing jig and the seed substrate of FIG. 5 are immersed in the melt 16 in the crucible 15. The melt 16 enters the gap 14. At this time, since the entire outer surface of the support substrate 1 is covered with the dissolution preventing jig 11 and the seed crystal film 2, the contact of the support substrate with the melt can be prevented.

In addition, by providing the outer edge covering portion 13b on the jig, the creepage distance until the melt reaches the side surface 1c of the support substrate 1 can be increased, and the contact of the melt with the support substrate can be further suppressed. However, the outer edge covering portion 13b is not always necessary.

Further, the dissolution preventing jig 11A shown in FIG. 7 includes a main surface covering portion 17a that covers the second main surface, a side surface covering portion 17b that covers the side surface, and an outer edge covering portion that covers the outer edge of the seed crystal film 2. 18. In this example, the main surface covering portion 17a and the side surface covering portion 17b constitute an integral member, and the outer edge covering portion 18 is a separate member.

In a preferred embodiment, a crucible for containing the melt functions as a dissolution preventing jig. This eliminates the need to provide a separate jig from the crucible.

For example, in the example of FIG. 8, the melt 16 is accommodated in the crucible 20. The second main surface 1b of the support substrate 1 is placed on the bottom 20c of the crucible 20, and the second main surface 1b is in contact with the bottom surface 20a. Moreover, the seed substrate is accommodated inside the substrate accommodating portion 20d of the crucible 20, and the inner wall surface 20b of the substrate accommodating portion 20d is in contact with the side surface of the seed substrate.

And the melt accommodating part 20f is provided on the board | substrate accommodating part 20d, and the melt 16 is accommodated in the melt accommodating part 20f. As a result, the melt 16 exists on the seed crystal film 2, and a gallium nitride crystal is grown on the seed crystal film. At the same time, the second main surface 1b of the support substrate 1 is in contact with the bottom surface 20a of the crucible, and the side surface 1b of the support substrate 1 is in contact with the inner wall surface 20b of the substrate housing portion. Is prevented from touching.

In this example, a step surface 20e is formed between the substrate housing portion 20d and the melt housing portion 20f, and an outer edge covering portion 21 is provided on the step surface 20e. The outer edge covering portion 21 covers the outer edge of the seed crystal film 2, thereby increasing the creeping distance of the melt to the side surface of the support substrate, and more reliably preventing the melt from contacting the support substrate.

Hereinafter, each element of the present invention will be described in more detail.
The material that dissolves in the molten alkali metal is a material that dissolves in the molten alkali metal constituting the melt used in the flux method. The alkali metal is an alkali metal specified in the periodic table, and sodium is particularly preferable. Moreover, dissolving in a molten alkali metal means the following.

In the present specification, when a substance is brought into contact with a molten alkali metal (molten alkali metal used for growing a gallium nitride crystal) heated to a growth temperature for growing a gallium nitride crystal by a flux method, When the surface is eroded by molten alkali metal at a rate of 12 μm / hour or more, the substance is determined to be dissolved in molten alkali metal used as a flux.

The substance that dissolves in the molten alkali metal is particularly preferably zinc oxide or Si.

A preferred embodiment of the support substrate made of zinc oxide will be further described.
In a preferred embodiment, the support substrate is composed of an oriented polycrystalline zinc oxide sintered body. The zinc oxide crystal has a hexagonal wurtzite structure, and the oriented polycrystalline zinc oxide sintered body is a solid formed by bonding innumerable zinc oxide crystal particles to each other by sintering.

Zinc oxide crystal particles are particles composed of zinc oxide, and may contain dopants and inevitable impurities as other elements, or may be composed of zinc oxide and inevitable impurities. Such other elements may be substituted with hexagonal wurtzite structure Zn sites or O sites, may be included as additive elements that do not constitute a crystal structure, or exist at grain boundaries. It may be a thing. The zinc oxide sintered body may also contain other phases or other elements as described above in addition to the zinc oxide crystal particles, but preferably comprises zinc oxide crystal particles and inevitable impurities.

However, the oriented polycrystalline zinc oxide sintered body may be composed of ZnO mixed with at least one crystal selected from the group consisting of MgO, CdO, ZnS, ZnSe, and ZnTe.

In order to obtain an oriented zinc oxide sintered body, a hot isostatic pressing method (HIP) or a hot press method (HP) can be used.

The average particle diameter of the zinc oxide single crystal particles constituting the oriented polycrystalline zinc oxide sintered body is preferably 1 to 100 μm, more preferably 10 to 80 μm, and still more preferably 20 to 50 μm. Within these ranges, the light emission efficiency, mechanical strength, light scattering properties, reflectivity, etc. are excellent. The average particle size of the sintered particles in the present invention is measured by the following method. That is, a sample of an appropriate size is cut out from the plate-shaped sintered body, the surface perpendicular to the plate surface is polished, etched with nitric acid having a concentration of 0.3 M for 10 seconds, and then an image is obtained with a scanning electron microscope. Take a picture. The visual field range is a visual field range in which straight lines intersecting 10 to 30 particles can be drawn when straight lines parallel and perpendicular to the plate surface are drawn. In three straight lines drawn parallel to the plate surface, the value obtained by multiplying the average of the lengths of the inner line segments of each particle by 1.5 for all particles intersecting with the straight line is defined as a1. In addition, in three straight lines drawn perpendicularly to the plate surface, a value obtained by multiplying the average length of the line segments inside the individual particles by 1.5 for all the particles intersecting the straight lines is a2. , (A1 + a2) / 2 is the average particle size.

The orientation plane orientation of the oriented polycrystalline zinc oxide sintered body is not particularly limited, and may be a (002) plane, a (100) plane, or a (110) plane. Alternatively, it may be the (101) plane or another plane.
As for the degree of orientation, for example, the degree of orientation on the substrate surface is preferably 50% or more, more preferably 65% or more, and further preferably 75% or more. This degree of orientation was measured using an XRD apparatus (for example, product name “RINT-TTR III” manufactured by Rigaku Corporation) and measuring the XRD profile when the surface of the plate-like zinc oxide was irradiated with X-rays. In the case of evaluating a sintered body oriented other than the (110) plane, it can be obtained by calculation according to the following formula.

 
 

 
 

The above formula is an equation assuming that the (110) plane need not be considered. However, when the (110) plane needs to be considered, that is, the sintered body oriented in the (110) plane is evaluated. In this case, I0 (110) and Is (110) corresponding to the diffraction intensity of the (110) plane may be added to the denominators of the second and third expressions, respectively. That is, I0 (110) is ICDDNo. This is the diffraction intensity (integrated value) of the (110) plane in 361451, and Is (110) is the diffraction intensity (integrated value) of the (110) plane in the sample.

By applying crystal orientation technology, we succeeded in producing a large-diameter and highly-oriented ZnO (zinc oxide) polycrystalline substrate. As a result, a large-diameter zinc oxide substrate of 6 inches or more can be produced at low cost.

Furthermore, a large-diameter gallium nitride substrate was realized by producing a gallium nitride (GaN) crystal on a highly oriented zinc oxide substrate by a flux method.

Compared to sapphire, zinc oxide has a lattice constant and thermal expansion coefficient close to that of gallium nitride, so that the crystallinity of gallium nitride is improved and the defect density is reduced. Since the growth temperature of gallium nitride crystals by the flux method (for example, about 850 ° C) is lower than the gallium nitride film formation temperature of 1000 ° C or more by the MOCVD method, contamination of gallium nitride due to decomposition of zinc oxide is suppressed. .
By using this large-diameter gallium nitride substrate as a base and forming a light-emitting layer by MOCVD, it becomes possible to fabricate high-brightness and high-efficiency LEDs.

A large reduction in the cost of the gallium nitride substrate can be expected by using Si, which has a large-diameter substrate exceeding 8 inches in various semiconductor applications, as the base substrate.

By using a flux method for forming gallium nitride on a Si single crystal substrate, a low-defect gallium nitride film can be formed at high speed.
Since Si is easily dissolved in molten Na used for the flux method, it could not be applied to the flux method. However, according to the present invention, the flux method can be applied to the formation of the gallium nitride film on the Si single crystal substrate, and a low-defect gallium nitride film can be formed.

A seed substrate is obtained by providing a seed crystal film made of a group 13 element nitride on the outer surface of the support substrate. The seed crystal film may be a single layer, or may include a buffer layer on the support substrate side.

The group 13 element is a group 13 element according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. The group 13 element nitride is particularly preferably GaN, AlN, InN, or GaAlN. Examples of the additive include carbon, low melting point metals (tin, bismuth, silver, gold) and high melting point metals (transition metals such as iron, manganese, titanium, and chromium).

The method for forming the seed crystal film is preferably a vapor phase growth method, but examples include a MOCVD method, a hydride vapor phase growth (HVPE) method, a pulsed excitation deposition (PXD) method, a molecular beam epitaxy (MBE) method, and a sublimation method. Metalorganic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200 ° C.

In the present invention, a region of the outer surface of the support substrate that is not covered with the seed crystal film is covered with a material insoluble in the molten alkali metal. The term “insoluble in molten alkali metal” is defined as follows.

The rate at which the surface of a substance is eroded when it is brought into contact with a molten alkali metal (molten alkali metal used when growing a gallium nitride crystal) heated to the growth temperature for growing a gallium nitride crystal by the flux method. Is 0.4 μm or less per hour, it is determined that the substance does not dissolve in the molten alkali metal used as the flux.

In a preferred embodiment, the material insoluble in the molten alkali metal is a group 13 element nitride. Examples of the group 13 element nitride include those listed for the seed crystal film.

In a preferred embodiment, the material insoluble in the molten alkali metal is a corrosion-resistant ceramic. As such ceramics, dense alumina, yttria or silicon carbide is preferable.

In a preferred embodiment, the material insoluble in the molten alkali metal is a refractory metal. The refractory metal is a metal having a melting point of 2000 ° C. or higher. This refractory metal is preferably tantalum or tungsten.

Further, as a method for forming a protective film made of a material insoluble in molten alkali metal, a vapor phase growth method is preferable, but an MOCVD method, an HVPE method, a PXD method, an MBE method, and a sublimation method can be exemplified.

Next, a gallium nitride crystal is grown on the seed crystal film by a flux method.
In addition to molten alkali metal, a gallium raw material is mixed in the melt. As the gallium source material, a single metal, an alloy, or a compound can be applied, but a single metal of gallium is preferable from the viewpoint of handling.

In the flux method, a single crystal is grown in an atmosphere containing a gas containing nitrogen atoms. This gas is preferably nitrogen gas, but may be ammonia.
The gas other than the gas containing nitrogen atoms in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable.

∙ Temperature and pressure during growth can be selected as appropriate. In a preferred embodiment, the pressure during growth is preferably 1 MPa to 10 MPa, more preferably 3 MPa to 5 MPa. The temperature during growth is preferably 750 to 950 ° C., more preferably 800 to 900 ° C.

The ratio (mol ratio) of gallium / molten alkali metal in the melt is preferably increased from the viewpoint of the present invention, preferably 18 mol% or more, and more preferably 25 mol% or more. However, if this ratio becomes too large, the crystal quality tends to deteriorate, so 40 mol% or less is preferable.

A functional layer can be provided on the obtained gallium nitride crystal. As functions, it can be used for white LEDs with high luminance and high color rendering, blue-violet laser disks for high-speed and high-density optical memories, power devices for inverters for hybrid vehicles, and the like.

The material of the functional layer is preferably a group 13 element nitride. Group 13 elements are Group 13 elements according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like.

In the structure of the light-emitting element as the functional layer, for example, an n-type semiconductor layer, a light-emitting region provided on the n-type semiconductor layer, and a p-type semiconductor layer provided on the light-emitting region are provided. In addition, the light-emitting element can be further provided with an electrode for an n-type semiconductor layer, an electrode for a p-type semiconductor layer, a conductive adhesive layer, a buffer layer, a conductive support, and the like (not shown).
The film forming temperature of the n-type semiconductor layer is preferably 950 ° C. or higher, and more preferably 1000 ° C. or higher, from the viewpoint of the film forming speed. Further, from the viewpoint of suppressing defects, the film formation temperature of the functional layer is preferably 1200 ° C. or lower, and more preferably 1150 ° C. or lower.

In the light-emitting element, when light is generated in the light-emitting region due to recombination of holes and electrons injected from the semiconductor layer, the light is extracted from the translucent electrode or the gallium nitride crystal side on the p-type semiconductor layer. The translucent electrode is a translucent electrode made of a metal thin film or a transparent conductive film formed on almost the entire surface of the p-type semiconductor layer.

The material of the semiconductor constituting the n-type semiconductor layer and the p-type semiconductor layer is made of a III-V group compound semiconductor, and examples thereof are as follows.
Al _y In _x Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
Examples of the doping material for imparting n-type conductivity include silicon, germanium, and oxygen. Moreover, magnesium and zinc can be illustrated as a dope material for providing p-type conductivity.

As the growth method of each semiconductor layer constituting the light emitting structure, various vapor phase growth methods can be exemplified. For example, a metal organic chemical vapor deposition method (MOCVD method), a molecular beam epitaxy method (MBE method), a hydride vapor phase epitaxy method (HVPE method), or the like can be used. Among them, the MOCVD method can obtain a semiconductor layer with good crystallinity and flatness. In the MOCVD method, alkyl metal compounds such as TMG (trimethyl gallium) and TEG (triethyl gallium) are often used as the Ga source, and gases such as ammonia and hydrazine are used as the nitrogen source. As the atmosphere gas, hydrogen gas, nitrogen gas, or the like is used.

The light emitting region includes a quantum well structure including a barrier layer and a well layer. The material of the well layer is designed so that the band gap is smaller than the materials of the n-type semiconductor layer and the p-type semiconductor layer. The quantum well structure may be a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. The material of a quantum well structure can illustrate the following.

As a preferred example of the quantum well structure, 3 to 10 pairs of In _x Ga _1-x N / GaN multilayer films (x = 0.15) each having a film thickness of 2.5 nm / 10 nm were formed. An MQW structure is mentioned.

(Example 1)
A composite substrate was produced according to the procedure shown in FIGS.
That is, the following procedure was used to produce a uniaxially oriented gallium nitride substrate using a zinc oxide polycrystalline substrate as a support substrate.

First, a c-plane plate-like crystal of zinc oxide was produced by a solution method. Specifically, 173 parts by weight of zinc sulfate heptahydrate (manufactured by Kojundo Chemical Laboratory) and 0.45 parts by weight of sodium gluconate (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 300 parts by weight of ion-exchanged water. The solution thus obtained was placed in a beaker and dissolved by heating to 90 ° C. while stirring with a magnetic stirrer. This solution was kept at 90 ° C., and 49 parts by weight of 25% ammonium water was added dropwise with a microtube pump while stirring. After completion of dropping, the solution was kept at 90 ° C. with stirring for 4 hours, and then the solution was poured into a large amount of ion-exchanged water and allowed to stand. The precipitate deposited on the bottom of the container was separated by filtration, further washed with ion-exchanged water three times, and dried to obtain a white powdered zinc oxide precursor. The obtained zinc oxide precursor was placed on a zirconia setter and calcined in the air in an electric furnace to obtain a zinc oxide plate-like porous powder. The temperature schedule at the time of calcination was raised from room temperature to 900 ° C. at a rate of temperature increase of 100 ° C./h, and then kept at 900 ° C. for 30 minutes to allow natural cooling.

With respect to 100 parts by weight of the obtained zinc oxide plate-like particles, 15 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: di (2-ethylhexyl) phthalate, black 10 parts by weight of Kinkasei Co., Ltd., 3 parts by weight of a dispersant (product name Leodol SP-O30, Kao Corporation) and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 10,000 cP. The slurry thus prepared was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 20 μm. The obtained tape was cut into a sheet having a diameter of 2 inches, 50 pieces of cutting tape were laminated, placed on an aluminum plate having a thickness of 10 mm, and then vacuum packed. This vacuum pack was hydrostatically pressed at a pressure of 100 kgf / cm ² in 85 ° C. warm water to produce a plate-like molded body. The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. for 20 hours. The obtained degreased body was fired at 1400 ° C. for 5 hours under normal pressure in nitrogen to prepare a plate-like ZnO oriented sintered body substrate.

The (002) orientation degree F (002) of the obtained sintered body was measured by XRD. For this measurement, an XRD apparatus (product name “RINT-TTR III” manufactured by Rigaku Corporation) was used to measure the XRD profile when the surface of the plate-like zinc oxide was irradiated with X-rays. evaluated.
The (002) orientation degree of the support substrate measured in this way was 80%.
Further, when the material of the support substrate was brought into contact with molten sodium at 850 ° C., the rate at which the surface of the material of the support substrate was eroded was 50 μm per hour.

 
 

 
 

Next, a seed crystal film 2 made of gallium nitride having a thickness of 3 μm was formed at 800 ° C. in a nitrogen atmosphere on the main surface 1a of the support substrate 1 by MOCVD. Further, the side surface not covered with the seed crystal film 2 and the second main surface were coated with the protective films 3A and 3B made of dense alumina by sputtering, and the seed substrate 4 was obtained. When this dense alumina was brought into contact with molten sodium at 850 ° C., the rate at which the surface of the material was eroded was 0.05 μm per hour.

The obtained seed substrate 4 was placed on the bottom portion of a cylindrical flat bottom alumina crucible having an inner diameter of 80 mm and a height of 45 mm, and then the melt composition was filled in the crucible in a glove box. The composition of the melt composition is as follows.
・ Metal Ga: 60g
・ Metal Na: 60g
・ Germanium tetrachloride: 1.85 g

After placing this alumina crucible in a refractory metal container and sealing it, the alumina crucible was placed on a table that can rotate the crystal growth furnace. The gallium nitride crystal was grown with stirring by rotating the solution while maintaining the temperature for 24 hours after heating and pressurizing to 850 ° C. and 4.0 MPa in a nitrogen atmosphere. After completion of the crystal growth, it was gradually cooled to room temperature over 3 hours, and the growth vessel was taken out of the crystal growth furnace. The melt composition remaining in the crucible was removed using ethanol, and the sample on which the gallium nitride crystal was grown was collected. A Ge-doped gallium nitride crystal was grown on a gallium nitride film formed by MOCVD on the zinc oxide substrate, and the thickness of the crystal was about 0.1 mm. Cracks were not confirmed.

The surface of the sample thus obtained on the gallium nitride crystal side was flattened by grinding with a # 600 and # 2000 grindstone, and then smoothed by lapping using diamond abrasive grains. In the smoothing process, the flatness was improved while gradually reducing the size of the abrasive grains from 3 μm to 0.1 μm. The average surface roughness Ra of the processed gallium nitride was 0.2 nm and the thickness was 15 μm. In this way, a composite substrate made of gallium nitride and zinc oxide was produced.

Next, 1 μm of an n-GaN layer doped with an Si atom concentration of 5 × 10 ¹⁸ / cm ³ at 1050 ° C. was deposited as an n-type layer on the composite substrate by MOCVD. Next, a multiple quantum well structure was deposited at 800 ° C. as a light emitting layer. Specifically, five pairs of InGaN well layers having a thickness of 2.5 nm and GaN barrier layers having a thickness of 10 nm were stacked. Next, a p-GaN layer doped to have a Mg atom concentration of 1 × 10 ¹⁹ / cm ³ at 950 ° C. was deposited as a p-type layer at 200 nm. After that, it was taken out from the MOCVD apparatus and subjected to a heat treatment at 800 ° C. for 10 minutes in a nitrogen atmosphere as an activation process for Mg ions in the p-type layer.

A photolithography process and a vacuum deposition method were used for forming the LED element structure. After forming the electrode, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve the ohmic contact characteristics. The wafer thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting device having a vertical structure.

When electricity was passed between the cathode electrode and the anode electrode and IV measurement was performed, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of 450 nm was confirmed.

Thus, according to the present invention, a large-diameter and high-quality gallium nitride composite substrate for manufacturing a high-luminance LED was realized.
By using crystallographically oriented zinc oxide instead of sapphire for the support substrate, cost reduction of the gallium nitride substrate was realized.
By using the flux method to produce gallium nitride crystals on zinc oxide, contamination of impurities into the gallium nitride crystals was suppressed.

(Example 2)
A light emitting device was fabricated according to the method described with reference to FIGS.
Specifically, first, in the same manner as in Example 1, an oriented zinc oxide substrate (supporting substrate 1) having an orientation degree of 80% was produced. Next, a seed crystal film 2 made of gallium nitride having a thickness of 3 μm was formed at 800 ° C. in a nitrogen atmosphere on the first main surface of the support substrate 1 by MOCVD, thereby obtaining a seed substrate. Next, as shown in FIG. 5, the seed substrate was attached to the dissolution preventing jig 11. The dissolution preventing jig 11 is made of alumina and includes a bottom surface covering portion 12 and a side surface covering portion (ring) 13.
When this alumina was brought into contact with molten sodium at 850 ° C., the rate at which the surface of the material was eroded was 0.2 μm per hour.

As shown in FIG. 6, the seed substrate placed on the dissolution preventing jig 11 was placed on the bottom portion of a cylindrical flat bottom alumina crucible 15 having an inner diameter of 80 mm and a height of 45 mm. Thereafter, in the same manner as in Example 1, crystal growth by a flux method, polishing, and formation of a light emitting functional layer by a MOCVD method were performed to manufacture a vertical light emitting device. When current was passed between the cathode electrode and the anode electrode and IV measurement was performed, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of 450 nm was confirmed.

(Example 3)
A light emitting element was fabricated in the same manner as in Example 2.
However, the support substrate 1 made of 6-inch Si single crystal was used. A seed crystal film 2 made of gallium nitride having a thickness of 3 μm was formed at 800 ° C. in a nitrogen atmosphere on the first main surface 1a of the substrate of the support substrate 1 in a nitrogen atmosphere, thereby producing a seed substrate. This seed substrate was attached to an alumina ceramic dissolution preventing jig 11 similar to that used in Example 2.
When this Si single crystal was brought into contact with molten sodium at 850 ° C., the speed at which the surface of the material was eroded was 1 mm or more per hour.

The seed substrate attached to the dissolution preventing jig 11 is placed on the bottom portion of a cylindrical flat bottom alumina crucible 15 having an inner diameter of 200 mm and a height of 45 mm. Similarly to Example 1, crystal growth by the flux method, polishing processing, and light emission by the MOCVD method. A functional layer was formed to fabricate a vertical light emitting device. When current was passed between the cathode electrode and the anode electrode and IV measurement was performed, rectification was confirmed. Further, when a forward current was passed, light emission with a wavelength of 450 nm was confirmed.

Thus, according to the present invention, a large-diameter and high-quality gallium nitride substrate for manufacturing a high-brightness LED was realized. Since Si is easily dissolved in the molten alkali metal used in the flux method, it cannot usually be applied to the flux method. However, according to the present invention, the flux method can be applied to the formation of the gallium nitride film on the Si single crystal substrate, and a low-defect gallium nitride film can be formed.

According to the present invention, it is possible to apply a Si single crystal, which is a material soluble in molten alkali metal, to the base substrate of the flux method, realizing a large diameter and low cost of the gallium nitride substrate.

Example 4
A light emitting device was manufactured in the same manner as in Example 1.
However, in this example, a support substrate made of Si single crystal was used.
After forming an aluminum nitride film and an aluminum gallium nitride film at about 1000 ° C. in a hydrogen and nitrogen atmosphere on the main surface 1a of the support substrate made of Si single crystal by MOCVD, a seed crystal film 2 made of gallium nitride is formed. A thickness of 3 μm was formed.

Next, a seed substrate 4 was produced by coating the outer surface of the support substrate 1 other than the main surface on which the seed crystal film 2 was formed with the protective films 3A and 3B made of alumina by sputtering. Next, this seed substrate was placed in a crucible together with Ga raw material and Na raw material.

Next, gallium nitride crystal growth was performed on the seed substrate by the flux method. Specifically, it was heated at 850 ° C. for 24 hours in a 4 MPa nitrogen atmosphere. The grown gallium nitride crystal was collected together with the seed substrate, and a composite substrate having a seed substrate and a gallium nitride crystal layer by a flux method was obtained. The surface of the gallium nitride crystal was mirror polished.

A light emitting functional layer was fabricated on the composite substrate by MOCVD. Specifically, 1 μm of an n-GaN layer was deposited at 1050 ° C., then five pairs of quantum well structures were deposited as a light emitting layer at 800 ° C., and a p-GaN layer was deposited at 200 nm at 950 ° C. After the activation treatment of the p-type layer, an LED element structure was formed by photolithography, formed into a chip, and subjected to an energization test. As a result, light emission with a wavelength of 450 nm was confirmed.

Thus, according to the present invention, a large-diameter and high-quality gallium nitride substrate for manufacturing a high-brightness LED was realized.
By using Si single crystal for the base substrate, the cost reduction of the gallium nitride substrate was realized.
By using the flux method to produce gallium nitride crystals on Si single crystals, impurities in the gallium nitride layer were suppressed.
By producing a group 13 element nitride light emitting layer on the flux method gallium nitride crystal, contamination of the light emitting layer with impurities was suppressed.

Claims (16)

Using a seed substrate comprising a support substrate made of a substance that dissolves in molten alkali metal and a seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate, the outer surface of the support substrate Of the gallium nitride crystal, a region not covered with the seed crystal film is covered with a material insoluble in the molten alkali metal, and then a gallium nitride crystal is grown on the seed crystal film by a flux method. Training method. The method according to claim 1, wherein a region of the outer surface of the support substrate that is not covered with the seed crystal film is covered with a protective film made of a material insoluble in the molten alkali metal. The method according to claim 1, wherein a region of the outer surface of the support substrate that is not covered with the seed crystal film is covered with a jig made of a material insoluble in the molten alkali metal. The method according to claim 3, wherein the jig includes an outer edge covering portion that covers an outer edge of the seed crystal film. The jig is a crucible for holding a melt containing the molten alkali metal and a gallium raw material and bringing the melt into contact with the seed crystal film when the flux method is performed. The method according to claim 3 or 4. The method according to any one of claims 1 to 5, wherein the substance dissolved in the molten alkali metal is zinc oxide or Si. The method according to any one of claims 1 to 6, wherein the material insoluble in the molten alkali metal is any one of a group 13 element nitride, a corrosion-resistant ceramic, and a refractory metal. A support substrate made of a substance that dissolves in molten alkali metal,
A seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate;
A protective film made of a material insoluble in the molten alkali metal that covers a region of the outer surface of the support substrate that is not covered with the seed crystal film, and is formed on the seed crystal film by a flux method. A composite substrate comprising a gallium nitride crystal. The composite substrate according to claim 8, wherein the substance dissolved in the molten alkali metal is zinc oxide or Si. The composite substrate according to claim 8 or 9, wherein the material insoluble in the molten alkali metal is any one of group 13 element nitride, corrosion-resistant ceramic, and refractory metal. A light emitting device comprising the composite substrate according to any one of claims 8 to 10 and a light emitting layer formed on the gallium nitride crystal. A method for manufacturing a light-emitting element, wherein a light-emitting layer is formed on a composite substrate according to any one of claims 8 to 10 by metal organic vapor phase epitaxy or molecular beam epitaxy. A dissolution preventing jig for subjecting a seed substrate comprising a support substrate made of a substance dissolved in molten alkali metal and a seed crystal film made of a group 13 element nitride formed on the outer surface of the support substrate to the flux method Because
A dissolution preventing jig that adheres to a region of the outer surface of the support substrate that is not covered with the seed crystal film and prevents the support substrate from coming into direct contact with the molten alkali metal. The dissolution preventing jig according to claim 13, wherein the dissolution preventing jig includes an outer edge covering portion that covers an outer edge of the seed crystal film. The melting preventing jig is a crucible for holding a melt containing the molten alkali metal and a gallium raw material and bringing the melt into contact with the seed crystal film when the flux method is performed. The dissolution preventing jig according to claim 13 or 14. The dissolution preventing jig according to any one of claims 13 to 15, wherein the material insoluble in the molten alkali metal is any one of a group 13 element nitride, a corrosion-resistant ceramic, and a refractory metal.

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