TWI589017B - Composite substrate and functional components - Google Patents

Description

Composite substrate and functional components

The present invention relates to a composite substrate having a gallium nitride crystal layer and functional elements using the same.

Non-Patent Documents 1 and 2 disclose that a film of InGaN or AlGaN is formed in the middle of forming a gallium nitride crystal layer on a sapphire substrate by MOCVD, and a gallium nitride crystal is grown thereon. At this time, the gallium nitride crystal layer is gently grown, and the compressive stress is weak, so that the bending of the substrate can be reduced.

When the inventors formed a gallium nitride crystal layer on a sapphire substrate by MOCVD, an intermediate layer such as InGaN or AlGaN was formed, and a thick film of gallium nitride crystal was grown thereon by a solvent method ( Flux method ). The layer is formed so that the gallium nitride crystal layer is peeled off from the sapphire substrate, and the self-supporting substrate composed of the gallium nitride crystal is successfully produced (Patent Document 1: JP-A-2009-184847).

(prior technical literature)

(Patent Document 1) Japanese Special Open 2009-184847

(Non-Patent Document 1) Japanese Journal of Applied Physics, Vol. 43, (2004) 8019~8023

(Non-Patent Document 2)

Letters and Telecommunications (Technical Research Report of the Institute of Electronic Information and Communication) 104 (360), 2004 year

The present inventors have made a structure in which a function of an LED or a power device can be realized by a MOCVD method using a low dislocation GaN template fabricated by a Na cosolvent method. the study. The GaN template substrate refers to a substrate in which a seed crystal layer and a gallium nitride crystal layer are provided on a support substrate, and a functional layer is further formed thereon to form a template.

At this time, in the production method disclosed in Patent Document 1, since the gallium nitride crystal layer formed by the Na co-solvent method is naturally peeled off from the sapphire substrate, the GaN template substrate cannot be provided, and thus it is not considered to be a production method.

Specifically, a gallium nitride crystal layer is formed by a MOCVD method or the like on a seed crystal growth substrate having a flat surface to form a seed crystal substrate, and the crystal substrate is further grown thereon by a solvent method. When a gallium nitride crystal layer having a thickness of 300 μm or less is grown at a temperature of 800 ° C to 900 ° C, a GaN template having a gallium nitride crystal layer having a low surface density at the outermost surface can be produced.

The inventors attempted to fabricate an LED structure by MOCVD using the GaN template. However, in this case, when the light-emitting element structure is formed in a high-temperature atmosphere (for example, 1000 ° C or higher), a stripe-shaped portion (striped-like abnormality) which is not formed into a film is formed on the surface of the formed light-emitting element structure. This phenomenon is unknown.

An object of the present invention is to suppress the occurrence of streaky abnormalities in a functional layer when a functional layer composed of a nitride of a group 13 element is formed on a composite substrate, and the composite substrate is a nitrogen including crystal grown on a substrate for growing a seed crystal. Gallium Crystallized layer.

The composite substrate of the present invention includes: a seed crystal growth substrate; a stress relaxation layer provided on the seed crystal growth substrate; a seed crystal layer formed of a gallium nitride crystal formed on the stress relaxation layer; and crystal growth a gallium nitride crystal layer having a thickness of 300 μm or less on the crystal layer; wherein the stress relaxation layer is composed of a group 13 element nitride, and the Young's modulus of the stress relaxation layer is higher than that of the seed layer The modulus is low.

Further, the functional device of the present invention includes: the composite substrate; and a functional layer formed of a group 13 element nitride formed on the gallium nitride crystal layer by a vapor phase method.

The present inventors have inquired about the cause of streaky abnormality in the functional layer when the functional layer is further formed on the composite substrate. The result is the following inference.

That is, it was found that streaky cracks were also formed on the surface of the composite substrate under the functional layer in which streaky abnormalities occurred, and film formation could not be performed directly above it, and streaky abnormalities were generated.

In other words, it is presumed that the gallium nitride crystal layer is grown at a growth temperature of 800 ° C to 900 ° C in the co-solvent method. However, when a functional layer is formed on the composite substrate by a vapor phase method such as MOCVD, the temperature is raised to Above 1000 ° C, the thick film gallium nitride crystal layer cannot withstand the stress between the substrate for seed crystal growth.

Therefore, it has been confirmed that when the composite substrate is held at a temperature higher than the film forming temperature of the gallium nitride crystal layer, for example, at 950 ° C, cracks are actually generated in the composite substrate.

According to the findings, the inventors of the present invention have attempted to form a stress relaxation in which the Young's modulus of the Young's modulus is lower than that of the seed crystal layer between the seed crystal layer composed of the gallium nitride crystal and the seed crystal growth substrate. Floor. As a result, it was found that a gallium nitride crystal layer was formed on the crystal layer, and after the functional layer was formed thereon, the stripe-like anomaly did not occur in the functional layer, and the present invention was achieved.

In a preferred embodiment, a stress relaxation layer having a difference in density and a higher density of the seed crystal layer than the seed crystal layer is formed between the seed crystal layer composed of the gallium nitride crystal and the seed crystal growth substrate. Accordingly, a gallium nitride crystal layer is formed on the crystal layer, and after forming a functional layer thereon, streaky abnormalities are more difficult to occur in the functional layer.

Further, in Patent Document 1, a gallium nitride seed crystal layer is formed on a sapphire substrate, and a thick film gallium nitride crystal layer is grown thereon by a Na cosolvent method, but since the gallium nitride crystal layer is a thick film. The sapphire substrate is naturally peeled off and becomes a free-standing substrate. Therefore, the idea of using a composite substrate including a sapphire substrate as a template is not solved, and the problem of the present invention cannot be solved.

1‧‧‧ kinds of substrates for crystal growth

4‧‧‧ kinds of crystal layers

5‧‧‧ gallium nitride crystal layer

5A‧‧‧ gallium nitride crystal layer

6‧‧‧ functional layer

17‧‧‧Functional components

1(a), (b), (c), and (d) are schematic diagrams showing a manufacturing process of the functional element 17 of the reference example.

2(a), (b), (c), and (d) are schematic views showing a process of fabricating the composite substrate 10 of the present invention.

3(a) and 3(b) are schematic diagrams showing the functional elements 7 formed by forming the functional layer 6 on the composite substrate 10 of Fig. 2(d).

Fig. 4 is a schematic view showing a functional element 7A formed by forming a functional layer 6 on another composite substrate 10A.

Fig. 5 is a schematic view showing a functional element 7B formed by forming a functional layer 6 on another composite substrate 10B.

Fig. 6 is a schematic view showing a functional element 7C formed by forming a functional layer 6 on another composite substrate 10C.

The invention will be described in detail below with reference to the drawings.

First, the composite substrate which the present inventors have posed and the problems thereof will be described. First, as shown in FIG. 1(a), a seed crystal layer 4 is formed on the seed crystal growth substrate 1. Next, as shown in FIG. 1(b), a gallium nitride crystal layer 5 made of gallium nitride is formed on the seed crystal layer 4 by a co-solvent method.

Next, as shown in FIG. 1(c), the gallium nitride crystal layer 5 is polished to form a polished gallium nitride crystal layer 5A as the composite substrate 20. A functional layer 6 is formed on the composite substrate 20 to obtain a functional element 17.

However, even if the surface of the composite substrate 20 is not deformed at the surface, the surface is flattened, but when the functional layer 6 is formed thereon, streaky irregularities appear in the functional layer 6. When the functional layer 6 was confirmed to be under the functional layer 6, it was found that the composite substrate 20 was cracked directly under the stripe-like irregularities of the functional layer 6.

Therefore, in the present invention, for example, a stress relieving layer is formed as shown in FIG. That is, first, as shown in FIG. 2(a), the stress relaxation layer 3 is formed on the seed crystal growth substrate 1. Next, as shown in FIG. 2(b), a seed crystal layer 4 is formed on the stress relaxation layer 3. Next, as shown in FIG. 2(c), a gallium nitride crystal layer 5 is formed on the seed crystal layer 4 by a co-solvent method. In this case, it is assumed that the gallium nitride crystal layer is not crystallized by the seed. The long substrate 1 is naturally peeled off.

Next, as shown in FIG. 2(d), the gallium nitride crystal layer 5 is polished to form a polished gallium nitride crystal layer 5A, which is referred to as a composite substrate 10.

When the functional layer 6 was formed on the composite substrate, it was confirmed that the functional layer 6 did not have streaky irregularities, and the composite substrate under the functional layer 6 did not have cracks.

Here, by minimizing the difference between the seed crystal layers 4, the difference between the gallium nitride crystal layers 5A can be reduced, and the functional layer can be formed by a vapor phase method as a template.

The stress relaxation layer 3 can be directly formed on the surface of the seed crystal growth substrate 1. Alternatively, a primer layer 2 made of a nitride of a group 13 element is provided on the surface of the seed crystal growth substrate 1, and a stress relaxation layer 3 is provided on the underlayer 2.

Next, as shown in FIG. 3(a), the functional layer 6 is formed on the composite substrate 10. Here, the functional layer 6 can form a plurality of layers. For example, in the example of Fig. 3, a light-emitting element structure 6 is formed. According to this, a light-emitting element structure having a small difference in density can be obtained, and the internal quantum efficiency of the light-emitting element 7 can be improved.

The light emitting element structure 6 includes, 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. In the light-emitting element 7 of FIG. 3(b), an n-type contact layer 6a, an active layer 6c, a p-type barrier layer 6d, and a p-type contact layer 6e are formed on the gallium nitride crystal layer 5A to constitute a light-emitting element structure 6. .

Hereinafter, each element of the composite substrate of the present invention will be further described.

(a substrate for crystal growth)

a substrate for crystal growth, as long as it is capable of growing a crystal film and a gallium nitride junction The crystal layer is not particularly limited, and examples thereof include various III-V compounds other than GaN such as sapphire, SiC (tantalum carbide), GaAs, AlN, or AlGaN, and various oxides such as Si, Ge, ZnO, or MgO. material.

In a preferred embodiment, the substrate material for crystal growth of sapphire or the like has a wurtzite structure. The wurtzite structure has a c-plane, an a-plane, and an m-plane. These crystal faces are defined in terms of crystallography. The growth direction of the underlayer, the seed crystal layer, and the gallium nitride crystal layer grown by the co-solvent method may be the normal direction of the c-plane or the normal direction of the a-plane and the m-plane, respectively.

From the viewpoint of the present invention, in order to suppress the peeling of the gallium nitride crystal, it is preferred that the thickness of the seed crystal growth substrate be made thicker than the thickness of the gallium nitride crystal layer. Therefore, the thickness of the seed crystal growth substrate is preferably 200 to 2000 μm, more preferably 300 to 1300 μm, still more preferably 300 to 1000 μm.

(bottom layer)

The formation method of the underlayer is a vapor phase growth method, and may be, for example, a metal organic chemical vapor phase epitaxy (MOCVD) method, a hydride vapor phase growth (HVPE) method, or an MBE (molecular line). Crystal growth method: Molecular Beam Epitaxy method, sublimation method.

The thickness of the underlayer is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.1 μm or more. When the thickness is too thick, the film formation time is too long and the efficiency is poor, so it is preferably 3.0 μm or less, more preferably 1.5 μm or less. Further, the material of the underlayer is preferably a nitride of a group 13 element described later.

(grain layer)

The crystalline layer can be one layer or multiple layers. Further, a preferred example of the method for forming a seed crystal layer is a vapor phase growth method, but may be a metal organic chemical vapor phase epitaxy (MOCVD) method or a hydride vapor phase growth (HVPE) method. PXD (pulsed excitation Deposition) method, MBE method, sublimation method. The organometallic chemical vapor phase growth method is particularly good.

(stress relaxation layer)

The stress relieving layer is a layer applied to the stress between the seed crystal growth substrate and the gallium nitride crystal layer in order to absorb the heat treatment when the functional layer is formed on the composite substrate.

The stress relieving layer is preferably one which does not directly contact the seed crystal growth substrate. In this case, it is particularly preferable to additionally form a primer layer between the stress relaxation layer and the seed crystal growth substrate.

The stress relieving layer is composed of a group 13 element nitride. Group 13 element refers to the Group 13 element of the periodic table developed by IUPAC. Specifically, the group 13 element includes gallium, aluminum, indium, antimony, and the like.

In a preferred embodiment, the stress relaxation layer is made of a material selected from the group consisting of InGaN, AlGaN, InAlN, InN, InAlGaN, GaN, and AlN. Alternatively, the stress relaxation layer is composed of two or more superlattice structures selected from the group consisting of InGaN, AlGaN, InAlN, InAlGaN, InN, GaN, and AlN.

The method for forming the stress relaxation layer is a vapor phase growth method, and other methods such as a metal organic chemical vapor deposition (Hydrogen Vapor Deposition) method, a hydride vapor phase growth (HVPE) method, and a pulse method may be used. Excitation deposition (PXD) method, MBE method, sublimation method.

In the present invention, the Young's modulus of the stress relaxation layer is lower than the Young's modulus of the seed crystal layer. From this point of view, (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) is preferably 0.96 or less, more preferably 0.95 or less, still more preferably 0.94 or less, and still more Good is below 0.090. Further, from the viewpoint of the present invention, (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) is preferably 0.80 or more, more preferably 0.85 or more, still more preferably 0.87 or more.

The Young's modulus of the stress relaxation layer is preferably 285 GPa or less, more preferably 270 GPa or less. Further, the Young's modulus of the stress relaxation layer is preferably 150 GPa or more, more preferably 200 GPa or more.

From the viewpoint of reducing the difference in the discharge density of the gallium nitride crystal layer provided on the seed crystal layer, the difference in the density of the seed crystal layer is preferably low. From this point of view, the difference in density of the seed crystal layer is preferably 7 × 10 ⁸ cm ^-2 or less, more preferably 5 × 10 ⁸ cm ^-2 or less. Further, from the viewpoint of quality, the difference in the density of the seed crystal layers is preferably as low as possible, so there is no lower limit, and in general, it is usually 5 × 10 ⁷ cm ^-2 or more.

In a preferred embodiment, the stress relaxation layer is provided between the sapphire substrate and the seed crystal layer, and has a difference in discharge density of a higher crystal layer.

Here, from the viewpoint of the present invention, the difference density of the stress relaxation layer is preferably 1 × 10 ⁹ cm ^-2 or more, more preferably 2 × 10 ⁹ cm ^-2 or more.

Further, from the viewpoint of the present invention, the ratio (B/A) of the difference density of the stress relaxation layer B to the difference density of the seed crystal layer A is preferably 2 or more, more preferably 10 or more.

A method for determining the Young's modulus of each layer will be described. The Young's modulus was measured using a Nanoindentation Test method. Specifically, The pressing load and depth of the diamond stylus were continuously measured, and the Young's modulus was calculated from the curve of the pressing depth and the load. The pressing depth is set to 10% of the thickness of the measurement target layer (the outermost layer), and is set to a depth that is not affected by the underlayer. The measurement was performed on 9 points in the wafer surface. Specifically, the center point of the wafer is 5 mm inside from the end of the wafer. under. left. The total of the right is 4 points, and the above center point is above. under. left. The measurement was performed at each intermediate point (4 points) between the four right points. The average value of the measured values at 9 points was calculated and set as the Young's modulus of the measurement target layer.

Further, the Young's modulus of the gallium nitride crystal phase was measured by growing a low-temperature GaN buffer layer (30 nm) at 500 ° C on a ψ 2 inch sapphire substrate by MOCVD, and growing a GaN layer (3 μm) at 1080 ° C. The measurement was carried out by a nanoindentation test method.

The Young's modulus of a material other than GaN is measured by growing a low-temperature GaN buffer layer (30 nm) and a GaN layer (1 μm) at 500 ° C on a sapphire substrate by MOCVD, and then growing the crystal to be measured for 30 minutes. 10% of the film thickness was set as the pressing depth of the nanoindentation test stylus, and the Young's modulus was measured.

In addition, the difference in density of each layer was calculated by a direct observation method using a cross-sectional TEM (transmission electron microscope) image. The device is H-9000NAR manufactured by Hitachi Advanced Technology Co., Ltd., and the accelerating voltage is 300 kV. The magnification is adjusted according to the difference in the density of the observed objects, and the magnification accuracy is ±5%. From the cross-sectional TEM image of the flaky sample, the difference between the observed layers was counted, and the difference in discharge density was calculated from the size of the field of view and the thickness of the sample. The thickness of the sample is adjusted in accordance with the state of the observation sample or the difference in the discharge density.

For example, the composite substrate 10A of the functional element 7A of FIG. 4 is of a species A stress relaxation layer 3A having a super lattice structure is formed between the crystal layer 4 and the underlayer 2. The stress relieving layer 3A is formed by, for example, sequentially laminating the first layer 3a and the second layer 3b. The materials and forming methods of the respective layers 3a and 3b are as described above. Further, it is also possible to repeatedly laminate three or more layers. The Young's modulus and the differential discharge density of the stress relaxation layer 3A are measured for the entire stress relaxation layer 3A.

Further, the composite substrate 10B of the functional element 7B of FIG. 5 is provided on the underlayer 2, and first, a stress relaxation layer 13 is provided thereon, and a gallium nitride crystal layer 8 having a low difference in density is provided thereon, and a stress relaxation layer is provided thereon. 3. A seed crystal layer 4 is formed on the stress relaxation layer 3. That is, in this example, two stress relieving layers 3, 13 are formed between the seed crystal layer and the sapphire substrate. The specific contents of the stress relieving layers 3, 13 are as described above.

Further, on the composite substrate 10C of the functional element 7C of Fig. 6, on the underlayer 2, a stress relaxation layer 13A having a super lattice structure is first provided, and a gallium nitride crystal layer 8 having a high Young's modulus is provided thereon. Further, a stress relaxation layer 3A having a super lattice structure is provided, and a seed crystal layer 4 is formed on the stress relaxation layer 3A. The layer 8 having a high Young's modulus and the stress relieving layer 3A having a super-lattice structure can each repeatedly repeat the laminated plurality of layers.

In order to obtain a favorable gallium nitride crystal layer, the average surface roughness of the stress relaxation layer is preferably 10 nm or less, more preferably 4 nm or less. The reason is that the smaller the average surface roughness of the stress relaxation layer, the less the growth of the seed crystal layer is not hindered, and a good seed crystal layer can be obtained, and as a result, a favorable gallium nitride crystal can be obtained.

(gallium nitride crystal layer)

According to the present invention, if natural peeling occurs between the gallium nitride crystal layer and the sapphire substrate, it cannot be used as a composite substrate. Therefore, by setting up GaN The thickness of the crystal layer (thickness at the time of film formation) is 300 μm or less, so that the natural peeling of the gallium nitride crystal layer from the sapphire substrate is less likely to occur. From this point of view, the thickness of the gallium nitride crystal layer is preferably 200 μm or less, more preferably 100 μm or less, still more preferably 50 μm or less.

In addition, the thickness of the gallium nitride crystal layer is preferably 10 μm or more from the viewpoint of eliminating the difference between the seed crystal layers 4 when the gallium nitride is grown by the co-solvent method and the crystallinity of the outermost surface is good. More preferably, it is 20 μm or more.

Further, by grinding and polishing the surface of the gallium nitride crystal layer, the quality of the functional layer thereon can be further improved.

Further, from the viewpoint of the present invention, the thickness of the gallium nitride crystal layer after polishing is preferably 100 μm or less, more preferably 30 μm or less.

The definition of single crystal in the present invention is explained. Although a single crystal of a textbook containing all the atoms in the crystal is arranged in the correct order, it is not limited to this meaning, but is generally distributed in the industrial sense. That is, the crystal may contain a certain degree of defects, internal deformation, impurity infiltration, etc., and a distinction between polycrystals (ceramics), and the so-called single crystals are the same meaning to the user.

The gallium nitride crystal layer in this project was grown by a cosolvent method. In this case, the type of the solvent is not particularly limited as long as the gallium nitride crystal can be grown. In a preferred embodiment, a solvent containing at least one of an alkali metal and an alkaline earth metal, particularly a solvent containing a sodium metal, is preferably used.

The solvent is used by mixing a gallium raw material. The gallium source material may use a gallium monomer metal, a gallium alloy, or a gallium compound, but is preferably used as a gallium monomer metal.

The growth temperature of the gallium nitride crystal in the cosolvent method or the retention time during growth is not particularly limited, and may be appropriately changed depending on the composition of the solvent. For example, when a gallium nitride crystal is grown using a solvent containing sodium or lithium, the growth temperature is preferably 800 to 950 ° C, more preferably 850 to 900 ° C.

In the cosolvent method, the growth of a single crystal is carried out in an atmosphere containing a gas containing a nitrogen atom. The gas is preferably nitrogen, but may also be ammonia. The pressure of the atmosphere is not particularly limited, but from the viewpoint of preventing evaporation of the solvent, it is preferably 10 or more, more preferably 30 or more. However, if the pressure is high, the apparatus becomes large, so the total pressure of the atmosphere is preferably 2000 or less, more preferably 500 or less. The gas other than the nitrogen atom-containing gas in the atmosphere is not particularly limited, but is preferably an inert gas, and argon, helium, and neon are particularly preferable.

Further, from the viewpoint of the promotion of the stress relaxation, the growth temperature at the time of growing the gallium nitride crystal layer by the co-solvent method is preferably higher than the growth temperature of the stress relaxation layer, and the temperature difference is set to 100 ° C or more. better.

(functional layer)

A functional layer is formed on the composite substrate thus obtained by a vapor phase method.

The functional layer can be a single layer or a plurality of layers. Further, the function is a blue LED for high brightness and high color rendering, a blue-violet laser for high-speed high-density optical memory, and a power element for an inverter for a hybrid electric vehicle.

When a semiconductor light-emitting diode (LED) is preferably produced by a vapor phase method on a composite substrate by an organic metal vapor phase epitaxy (MOCVD) method, the difference in density inside the LED is equivalent to that of the composite substrate.

The film formation temperature of the functional layer is preferably 950 ° C or higher, more preferably 1000 ° C or higher, from the viewpoint of film formation speed. Again, suppressing the streak-like appearance The film forming temperature of the functional layer is preferably 1200 ° C or lower, more preferably 1150 ° C or lower.

The material of the functional layer is preferably a nitride of a group 13 element. Group 13 element refers to the 13th element of the periodic table established by IUPAC. Group 13 elements, specifically gallium, aluminum, indium, antimony, and the like.

[Examples]

(Example 1)

A composite substrate and functional elements were produced as illustrated in FIG. 2 .

(made of crystal substrate)

A single-crystal sapphire c-plane substrate 1 having a diameter of 2 inches was placed in an MOCVD furnace (organic metal vapor phase growth furnace), and heated at 1150 ° C for 10 minutes in a hydrogen atmosphere to clean the surface. Next, the substrate temperature was lowered to 500 ° C, and a gallium nitride layer having a thickness of 30 nm was grown using TMG (trimethylgallium) or ammonia as a raw material. Next, the substrate temperature was raised to 1080 ° C, and a gallium nitride layer having a thickness of 1 μm was grown using TMG and ammonia as a raw material to form the underlayer 2 . In this case, the molar ratio (hereinafter referred to as "V/III") of the supply amount of the raw material (ammonia) of the group V element to the raw material (TMG) of the group III element is 4,000.

Next, TMG and ammonia were used as raw materials, and V/III=800 was changed to form a stress relaxation layer 3 having a thickness of 0.1 μm. Next, using TMG and ammonia as raw materials, V/III=4000 is again recovered, and TMG and ammonia are used as raw materials, and hydrogen and nitrogen are used as carrier gases, and the crystal layer 4 composed of gallium nitride is again grown at a temperature of 1080 ° C. A thickness of 2 μm was deposited.

The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. Further, the stress relaxation layer 3 has a difference density of 2 × 10 ⁹ cm ^-2 and a Young's modulus of 283 GP. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) = 0.946.

In addition, since the measurement of the Young's modulus was not performed in the middle of the production of the composite substrate disclosed in Example 1, the same measurement was performed.

(solvent method)

The gallium nitride crystal is grown on the crystal substrate by the Na cosolvent method. The raw materials used for growth are metal gallium and sodium metal. The alumina crucible was filled with 30 g of metal gallium and 44 g of metallic sodium, respectively, and a gallium nitride single crystal was grown at a temperature of 900 ° C and a pressure of 4 Mpa for about 30 hours. As a result of the extraction, a transparent single crystal was grown, and a gallium nitride crystal layer 5 having a thickness of 100 μm was deposited on the entire surface of the substrate.

Next, the surface of the gallium nitride crystal layer 5 was polished with diamond abrasive grains, and the thickness of the ground gallium nitride crystal layer 5A after polishing was set to 25 μm.

(film formation by MOCVD on a composite substrate)

The composite substrate was placed in a MOCVD furnace and heated to 1080 ° C in a mixed atmosphere of hydrogen and ammonia gas. At this temperature, a GaN layer having a thickness of 2 μm was grown using TMG and ammonia as raw materials, and then monodecane was mixed into the raw material gas to grow. 2 μm thick n-GaN layer. Thereafter, the raw material was stopped, and after the substrate temperature was lowered to room temperature, the substrate was taken out.

(assessment)

As a result, the obtained LED structure showed no streaky abnormality and was completely formed into a film.

(Example 2)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer 3 was set to an InGaN layer, the film formation temperature was set to 800 ° C, and the layer thickness was set to 0.2 μm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 2 × 10 ⁹ cm ^-2 and a Young's modulus of 244 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) = 0.816.

As a result, the obtained LED structure showed no streaky abnormality, and the film formation was performed in an all-round manner.

(Example 3)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer was an AlGaN layer (Al composition: 20%), the film formation temperature was 1080 ° C, and the layer thickness was 30 nm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 5 × 10 ⁹ cm ^-2 and a Young's modulus of 285 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.953.

As a result, the obtained LED structure showed no streaky abnormality, and the film formation was performed in an all-round manner.

(Example 4)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer 3 was a GaN layer, the film formation temperature was 800 ° C, and the layer thickness was set to 0.3 μm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 1.5 × 10 ¹⁰ cm ^-2 and a Young's modulus of 279 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.933.

As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner.

(Example 5)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer was a GaN layer, the film formation temperature was 500 ° C, and the layer thickness was set to 0.1 μm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 5 × 10 ¹⁰ cm ^-2 and a Young's modulus of 262 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.876.

As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner.

(Example 6)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer was AlInGaN, and the film formation temperature was set to 900 °C. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 5 × 10 ⁹ cm ^-2 and a Young's modulus of 279 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.933.

As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner.

(Example 7)

A composite substrate and an LED element were produced in the same manner as in Example 1.

The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa.

However, the material of the stress relaxation layer 3 was a GaN layer, the film formation temperature was 980 ° C, and the layer thickness was set to 0.3 μm. As a result, the stress relaxation layer 3 had a difference density of 1 × 10 ⁹ cm ^-2 and a Young's modulus of 282 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.943.

Further, the thickness (before polishing) of the gallium nitride crystal layer formed by the co-solvent method was set to 300 μm.

As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner.

(Comparative Example 1)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the stress relieving layer 3 is not provided. The underlayer 2 and the seed crystal layer 4 have a difference in density of 5 × 10 ⁸ cm ^-2 .

As a result, a streak-like abnormality occurred in the obtained LED structure. In addition, cracks appear on the composite substrate directly under the stripe-shaped anomaly.

(Comparative Example 2)

A composite substrate and an LED element having a high differential density of the seed crystal layer were produced.

A single-crystal sapphire c-plane 1 having a diameter of 2 inches was placed in an MOCVD furnace (organic metal vapor phase growth furnace), and heated at 1150 ° C for 10 minutes in a hydrogen atmosphere to clean the surface. Next, the substrate temperature was lowered to 500 ° C, and a gallium nitride layer having a thickness of 30 nm was grown using TMG (trimethylgallium) or ammonia as a raw material. Next, the substrate temperature was raised to 1080 ° C, and a gallium nitride layer having a thickness of 1 μm was grown using TMG and ammonia as a raw material to form the underlayer 2 . In this case, the molar ratio (hereinafter referred to as "V/III") of the supply amount of the raw material (ammonia) of the group V element to the raw material (TMG) of the group III element is 2,000.

Next, using TMG and ammonia as raw materials, change to V/III=4000. A gallium nitride layer having a thickness of 0.1 μm was formed. Next, using TMG and ammonia as raw materials, V/III = 2000 was again recovered, and hydrogen and nitrogen were used as carrier gases, and the seed crystal layer 4 composed of gallium nitride was again grown at a temperature of 1080 ° C to a thickness of 2 μm.

The underlayer 2 and the seed crystal layer 4 have a difference density of 1 × 10 ⁹ cm ^-2 and a Young's modulus of 286 GPa. The gallium nitride layer held between the underlayer 2 and the seed crystal layer 4 has a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. (Young's modulus of the stress absorbing layer) / (Young's modulus of the seed crystal layer) was 1.045.

Next, in the same manner as in Example 1, a gallium nitride crystal layer 5 was formed by a co-solvent method, and a gallium nitride crystal layer 5A having a thickness of 25 μm was formed by grinding with diamond abrasive grains to obtain a composite substrate.

Next, an LED structure was formed on the composite substrate in the same manner as in the first embodiment. As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner. However, the differential density of the LED structure is 2 × 10 ⁹ cm ^-2 . Further, regarding the internal quantum efficiency of the obtained LED, the LED produced in Example 1 can obtain 80% or more of all the LED elements, whereas Comparative Example 2 is about 50% lower.

(Comparative Example 3)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer was an AlGaN layer (Al composition: 35%), the film formation temperature was 1080 ° C, and the layer thickness was 30 nm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa.

The stress relaxation layer 3 has a difference density of 9 × 10 ⁹ cm ^-2 and a Young's modulus of 322 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 1.077.

In this example, the Young's modulus of the stress relaxation layer is relatively large, and the differential discharge density is relatively large.

As a result, a streak-like abnormality occurred in the obtained LED structure. In addition, cracks appear on the composite substrate directly under the streaky abnormality.

That is, it can be confirmed that the difference density of the stress relaxation layer is high, and when the Young's modulus is also large, streaky irregularities still occur.

(Example 8)

A composite substrate and an LED element were produced in the same manner as in Example 1.

However, the material of the stress relaxation layer was made of InGaN, the film formation temperature was 900 ° C, and the layer thickness was set to 0.2 μm. The underlayer 2 and the seed crystal layer 4 have a difference density of 5 × 10 ⁸ cm ^-2 and a Young's modulus of 299 GPa. The stress relaxation layer 3 has a difference density of 3 × 10 ⁸ cm ^-2 and a Young's modulus of 278 GPa. (Young's modulus of the stress relaxation layer) / (Young's modulus of the seed crystal layer) was 0.930.

In this example, the retardation density of the stress relaxation layer is relatively low, and the Young's modulus is relatively low.

As a result, no streaky abnormality occurred in the obtained LED structure, and film formation was performed in an all-round manner.

That is, it was confirmed that the difference density of the stress relaxation layer was low, and when the Young's modulus was also low, no streaky abnormality occurred.

(use)

The invention can be used in a technical field requiring high quality, such as a high color rendering blue LED called a post fluorescent lamp or a blue purple laser, a hybrid electric vehicle for high speed and high density optical memory. The power components used in the inverter used.

1‧‧‧ kinds of substrates for crystal growth

4‧‧‧ kinds of crystal layers

5‧‧‧ gallium nitride crystal layer

5A‧‧‧ gallium nitride crystal layer

6‧‧‧ functional layer

17‧‧‧Functional components

Claims (10)

A composite substrate comprising: a seed crystal growth substrate; a stress relaxation layer provided on the seed crystal growth substrate; a seed crystal layer formed of the gallium nitride crystal formed on the stress relaxation layer; and crystal growth a gallium nitride crystal layer on the crystal layer; wherein the thickness of the gallium nitride crystal layer is 300 μm or less, and the stress relaxation layer is composed of a nitride of a group 13 element, and a Young's modulus of the stress relaxation layer is higher The Young's modulus of the above-mentioned crystal layer is low, and the ratio (B/A) of the difference density B of the stress relaxation layer to the difference density A of the above-mentioned crystal layer is 2 or more. The composite substrate according to claim 1, wherein the ratio (B/A) of the difference density B of the stress relaxation layer to the difference density A of the seed crystal layer is 10 or more. The composite substrate according to claim 1 or 2, wherein the stress relaxation layer has a difference in density of 1 × 10 ⁹ cm ^-2 or more. The composite substrate according to claim 1 or 2, wherein a ratio of a Young's modulus of the stress relieving layer to a Young's modulus of the above-mentioned crystal layer (Young's modulus of the stress relieving layer/the above kind of crystal) The Young's modulus of the layer is 0.96 or less. The composite substrate according to claim 1 or 2, wherein the stress relaxation layer has a Young's modulus of 285 GPa or less. A composite substrate according to claim 1 or 2, wherein the gallium nitride crystal layer is subjected to grinding. Such as the composite substrate of claim 1 or 2, wherein the above kind of crystal The growth substrate is made of sapphire. The composite substrate according to claim 1 or 2, wherein the stress relaxation layer is made of a material selected from the group consisting of AlInGaN, InGaN, AlGaN, InAlN, InN, GaN, and AlN. The composite substrate according to claim 1 or 2, wherein the stress relieving layer is composed of a superlattice structure composed of a group consisting of AlInGaN, InGaN, AlGaN, InAlN, InN, GaN, and AlN. Two or more materials are selected. A functional element, comprising: a light-emitting element or a power device; comprising: the composite substrate according to any one of claims 1 to 9; and being formed by a vapor phase method on the gallium nitride crystal layer a functional layer composed of a nitride of a group 13 element.