JPH11219904A - Compound semiconductor substrate and manufacture of the same, and compound semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound semiconductor substrate and a compound semiconductor light-emitting element capable of reducing difficulties generated in a semiconductor element preparing process, in a compound semiconductor substrate having a buffer layer for growing an epitaxyal layer and a method for manufacturing this substrate, and a compound semiconductor light-emitting element formed by the use of this substrate. SOLUTION: This compound semiconductor substrate is provided with a base mono-crystalline substrate 11, a first buffer layer 12 of a compound semiconductor having the variations of the width which is formed on the base mono- crystalline substrate 11, a second buffer layer 13 of the compound semiconductor the composition of which is different from that of the first buffer layer 12, formed on the first buffer layer 12. The first buffer layer 12 is formed of materials having features for more easily absorbing distortions than those of the second buffer layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor substrate, a light emitting device, and a method for manufacturing the same, and more particularly, to a compound semiconductor substrate having a buffer layer for epitaxial layer growth, a method for manufacturing the same, and formation using the substrate. And a compound semiconductor light-emitting device.

[0002]

2. Description of the Related Art There are many direct semiconductors among compound semiconductors of the III-V group, II-VI group and the like, and their use as light emitting devices and the like is progressing. Compound semiconductors having high mobility are also used as high-speed operation devices.

Many compound semiconductor devices utilize an epitaxial layer grown on a base single crystal as a device layer. Epitaxial growth is a method of growing a crystal layer in accordance with the crystal axis of a base single crystal. In the process of crystal growth, it is said that, for example, growth nuclei are first generated on the base surface, the growth nuclei grow into islands, and the islands are combined to form a layer.

[0004] G, one of III-V compound semiconductors,
aN has a wide direct-transfer bandgap of 3.4 eV, and has characteristics suitable for a short-wavelength light-emitting element such as blue. When trying to epitaxially grow GaN, G
A base single crystal substrate having a lattice constant close to the lattice constant of aN and a thermal expansion coefficient close to that of GaN is desired.

However, it is currently difficult to obtain a base single crystal substrate suitable for epitaxial growth of GaN. Therefore, a c-plane sapphire substrate is widely used as a substrate for GaN epitaxial growth. However, there is about 13.8% lattice mismatch between the c-plane sapphire substrate and GaN. It is difficult to grow a good quality GaN crystal layer directly on a sapphire substrate.

When GaN is epitaxially grown directly on a sapphire substrate, GaN grows in a hexagonal column shape, and a uniform and high-quality GaN single crystal film cannot be obtained. When epitaxially growing a GaN layer on a sapphire substrate, a buffer layer for relaxing lattice distortion is often used.

[0007] Amano et al. Formed an AlN buffer layer or a low-temperature deposited GaN buffer layer comprising a large number of micro-growth nuclei and an amorphous layer on a sapphire substrate, and vapor-phase epitaxially grown a GaN-based compound semiconductor thereon. Proposal (Advanced Electronics I-1, "II
Group IV compound semiconductors "edited by Isamu Akasaki, Baifukan, 1994
335-337).

Through the AlN or GaN buffer layer, the density of growth nuclei generated in the early stage of GaN epitaxial growth is increased, and lateral growth and coalescence of islands are promoted in the process of growing nuclei into island-like crystals.
This enables flat film growth without pits.

However, even when this method is used, the quality of the crystal greatly depends on the growth conditions of the buffer layer,
In order to obtain an aN layer, the growth conditions of the buffer layer must be strictly controlled. Also, the epitaxial layer on the buffer layer must be grown to a thickness of about 4 μm or more in order to obtain a good quality semiconductor layer.

When the GaN epitaxial layer is made thicker, there is a problem that the substrate is warped due to a difference in physical properties from the sapphire substrate. Therefore, growth conditions such as temperature,
There is a problem that the uniformity and the like are different, so that a device having uniform characteristics cannot be obtained, and a problem arises in that the yield is reduced due to poor handling in a process of manufacturing a semiconductor device by forming a chip after forming a wafer.

Instead of using a sapphire substrate, ZnO, MnO, MgF ₂ or the like having a physical constant relatively close to GaN is used as a base single crystal substrate, or an attempt is made to use a buffer layer made of another single material. JP-A-5-29653
JP-A-5-283744, JP-A-5-29161
8 and JP-A-6-61527. By using these materials, a light-emitting element layer can be formed over a buffer layer.

[0012]

As described above, various difficulties arise when a compound semiconductor layer such as GaN is epitaxially grown on a base single crystal substrate having a different lattice constant, and then a semiconductor device is manufactured.

An object of the present invention is to provide a compound semiconductor substrate or a compound semiconductor light emitting device capable of reducing the difficulty that occurs in a semiconductor device manufacturing process.

Another object of the present invention is to provide a method of manufacturing a compound semiconductor substrate which is of good quality and hardly causes difficulties in a semiconductor device manufacturing process.

Still another object of the present invention is to provide a crystal growth technique capable of relaxing strain and growing an epitaxial layer with few defects.

[0016]

According to one aspect of the present invention, a base single crystal substrate, a first buffer layer of a compound semiconductor formed on the base single crystal substrate and having a thickness variation, A first buffer layer formed on the first buffer layer;
And a second buffer layer of a compound semiconductor having a different composition from the first buffer layer, wherein the first buffer layer is formed of a material having a property of absorbing strain more easily than the second buffer layer. A semiconductor substrate is provided.

According to another aspect of the present invention, a base single crystal substrate, a first buffer layer of a compound semiconductor formed on the base single crystal substrate and having a thickness variation, and the first buffer A second buffer layer of a compound semiconductor having a composition different from that of the first buffer layer, and a pn layer formed epitaxially on the second buffer layer.
A compound semiconductor light-emitting element layer including a junction;
A compound semiconductor light-emitting device having such a property that the buffer layer has a property of absorbing strain more easily than the second buffer layer.

According to still another aspect of the present invention, a first compound semiconductor having a thickness variation on an underlying single crystal substrate.
Growing a second buffer layer of a compound semiconductor having a composition different from that of the first buffer layer on the first buffer layer; and forming a second buffer layer of the compound semiconductor on the second buffer layer. Epitaxially growing a compound semiconductor element layer.

When a first buffer layer made of a material having a thickness variation and having a property of easily absorbing strain is formed on a base single crystal substrate, and a second buffer layer is formed thereon, The characteristics of the epitaxial layer formed thereon are improved.

For example, the first buffer layer is an InN layer, the second buffer layer is a GaN layer, and the epitaxial layer formed thereon is a GaN layer.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have found that when a GaN epitaxial layer is grown on a sapphire substrate via a buffer layer, it is necessary to form the epitaxial layer as thick as about 4 μm or more. Also in this case, the cause of the warping of the substrate and the like were considered.

It is conceivable that strong distortion occurs as a cause of these. There is a lattice mismatch of up to 13.8% between the sapphire substrate and the GaN epitaxial layer. By growing the buffer layer, the epitaxial layer grows from a nucleus to an island crystal in the growth of the epitaxial layer, and the lateral growth and the coalescence of the islands are promoted. It is considered that the distortion due to the mismatch remains.

There is also a difference in the coefficient of thermal expansion between the sapphire substrate and the GaN layer. Epitaxial growth is
It is performed at a high temperature of about 1000 ° C. Even if the sapphire substrate and the epitaxial layer have the same dimensions at this temperature, when the temperature is lowered to room temperature, it is considered that a strong distortion occurs between the two due to a difference in thermal expansion coefficient. It is believed that the thicker the epitaxial layer, the stronger the strain.

Therefore, the present inventors have studied how to form a compound semiconductor element layer with less distortion on a base single crystal substrate. In order to alleviate or absorb the strain, it is considered preferable to form a buffer layer made of a material that easily absorbs the strain on the single crystal base substrate. The material having the property of easily absorbing strain will be a material that can be deformed flexibly with an external force.

In the group III-V compound semiconductor, I
It is known that a group III-V compound semiconductor containing n as a group III element is a relatively soft material as compared with other materials. Further, InN has a weak bond between In and N, and has flexibility as compared with GaN. For example, the binding energies of AlN, GaN, and InN are 11.52 eV / atom, 8.92 eV / atom, respectively.
7,72 eV / atom.

In the compound semiconductor, the fact that the binding energy of the constituent elements is small means that the relative relationship between the two is easily changed, and it is considered that the compound semiconductor has higher flexibility (deformability).

When considering the hardness, it is generally said that the smaller the atoms are and the closer the interatomic distance is, the higher the hardness is. When the interatomic distance is short, the cohesive force between the atoms tends to increase accordingly. The lattice constants of AlN, GaN, and InN are 3.110, 3.160, and 3,5446, respectively. Assuming that the atomic radii of N are the same, the atomic radius of In is larger than the atomic radii of Al and Ga. This aspect also suggests that InN is a softer material than AlN or GaN.

Therefore, when growing a GaN epitaxial layer on a sapphire substrate, first, an In
It is conceivable to form an N buffer layer. here,
When a sapphire c-plane substrate is used, the lattice mismatch of the InN layer is larger than that of the GaN layer.

The present inventors consider that a buffer layer for epitaxial growth needs a strain relaxation function and an orientation propagation function. Various difficulties can be expected to achieve these two functions with a single buffer layer. It was considered that the buffer layer may be formed by laminating a plurality of layers, and that both functions may be more easily realized by the laminated buffer layer. Also, when growing the GaN epitaxial layer, it was considered that a material having similar physical and chemical properties to GaN is preferable as the underlayer.

First, when InN and GaN were selected as candidates and these materials were grown on a heterogeneous single crystal base substrate, it was observed how crystal growth occurs.

A sapphire c-plane substrate was used as the base single crystal substrate. After washing the sapphire c-plane substrate, it was set in an organic molecular chemical vapor deposition (MOCVD) apparatus. Thereafter, the substrate was thermally annealed at a high temperature. The condition of the thermal annealing is a process of holding the film at 1050 ° C. for 10 minutes in a reduced-pressure hydrogen atmosphere.

A buffer layer was grown on the base single-crystal sapphire substrate thus prepared.

In the case of an InN buffer layer, the growth conditions were set as follows. Substrate temperature: 530 ° C., Source gas: TMIn 9 μmol / min, NH ₃ 1.1
3 l / min, carrier gas: hydrogen 5.5 l / min, atmospheric pressure: 700 Torr

In the case of a GaN buffer layer, 9 μm of TMGa is used as a Ga material instead of TMIn which is an In material.
ol / min, and other conditions were the same as those for InN.

InN and G are deposited on a sapphire substrate for 1 hour.
aN was grown, and the growth state was observed by cross-sectional observation.

As a result, it was confirmed that GaN showed so-called layer growth, and InN was a mixture of layer growth and island growth, but it was confirmed that the growth of island growth was strong.

Generally, as a mode of epitaxial growth of a thin film, Volmer-Webe is used.
r) Style, Frank-Fan der Amelbe (Frank-
van der Merwe) style, Stranski-Krastanov
The style is known.

[0038] Volmer-Web
The er) style is a growth style in which three-dimensional growth occurs from the initial stage of the epitaxial layer formation. That is, first, islands of three-dimensional clusters are formed on the substrate, and these islands gradually grow and coalesce with each other to form a continuous film.

[0039] Frank Van der Melve
The -van der Merwe) mode is a mode in which a two-dimensional cluster of monoatomic layers is first formed on a substrate, grows gradually along a plane, merges with each other to form a layer, and performs layer growth.

Stranki Klasnov (Stran)
In the ski-krastanov style, after growing two-dimensionally in the initial stage of growth as in the Frank van der Melbe style, a three-dimensional island is formed thereon and grown as in the Borma-Weber style. Style.

According to the above classification, the GaN buffer layer is
In the Frank van der Melbe style, the InN buffer layer is in the Stranki-Krastanov style. In
In the case of the N buffer layer, the thickness of the N buffer layer has a variation of about the cluster level, that is, about several tens of degrees at the beginning of growth.

The following four types were prepared as samples for forming a gallium nitride layer on a sapphire c-plane substrate. The time in parentheses indicates the growth time.

Sample 1: sapphire c-plane substrate / GaN
Epitaxial layer, Sample 2: Sapphire c-plane substrate / GaN buffer layer (60 seconds) / GaN epitaxial layer, Sample 3: Sapphire c-plane substrate / InN buffer layer (30 seconds) / GaN buffer layer (60 seconds) / GaN epitaxial layer Sample 4: sapphire c-plane substrate / InN buffer layer (30 seconds) / GaN buffer layer (30 seconds) / GaN epitaxial layer.

In the above samples, the formation of the InN buffer layer and the GaN buffer layer was performed under the same conditions as the above-described growth of the InN layer and the GaN layer except for the growth time. The growth of the InN buffer layer has a growth time of 30 seconds and a film thickness of about 10 to 50 °. The growth time of the GaN buffer layer is about 200 ° with a growth time of 60 seconds.

The growth of the GaN epitaxial layer is performed at a growth temperature of about 1030 ° C., using a source gas of trimethylgallium (TM).
Ga) 18 μmol / min, NH ₃ 2.83 slm,
Carrier gas (H ₂ ) 5.5 slm, ambient pressure 700
torr. The growth time is about 40 minutes,
The thickness is about 2 μm. After growing the GaN epitaxial layer having a desired thickness, the supply of TMGa is stopped to stop the growth of the epitaxial layer, other source gases are stopped, and the substrate is cooled to room temperature.

For the four samples thus prepared, the following 4
Kind measurement and observation were performed. Measurement of Orientation of Light-Emitting Element Layer: The orientation of the crystal was measured by measuring the half-width (FWHM) of an x-ray diffraction rocking curve (XRC).

Observation of surface roughness: Surface morphology was observed with a differential interference microscope. Electrical characteristics of light-emitting element layer: Hall measurement shows Hall
The l mobility was measured and the electrical characteristics were observed.

Optical characteristics of light emitting element layer: Optical characteristics of the light emitting element layer were measured by photoluminescence (PL) measurement. The PL measurement was performed by measuring the emission intensity at the band edge and the emission intensity at a deep level.

The following results were obtained from these measurements. XRC FWHM: Sample 1 rocking curve is broad. And the diffraction intensity is very weak. This suggests that the GaN light emitting element layer is polycrystalline and has poor crystallinity.

The FWHM of Samples 2, 3, and 4 were 234 seconds, 223 seconds, and 234 seconds, respectively. It is considered that the decrease in FWHM in Sample 3 in which a thin InN layer was inserted as compared to Sample 2 suggests an improvement in crystallinity, and suggests that the strain may be relaxed by the InN layer.

Observation of surface morphology: In sample 1, surface morphology having irregularities of about several μm suggesting polycrystalline growth was observed. Sample 2 showed mirror growth. Samples 3 and 4 showed mirror growth as a whole, and a facet portion reflecting the plane orientation of the substrate and the crystal structure of the buffer layer was observed. It is presumed that the insertion of the InN layer may alleviate the distortion.

Mobility: The mobilities of samples 1, 2, 3, and 4 were 11, 333, 475, and 364 cm ² / cm, respectively.
V · sec. In addition, these holes (Hal
l) The mobility is a result of a hall measurement at room temperature by a van der Pauw method.

When GaN epitaxial growth was performed directly on the underlying sapphire c-plane substrate, the mobility was 11 μ ·
cm ² / V · sec, which is an extremely low value, but by inserting a single GaN buffer layer, the mobility is 333 μm.
cm ² / V · sec. In sample 3 in which the two-layer buffer layer was inserted, the mobility was further improved by about 40%. However, when the thickness of the GaN layer, which is the second buffer layer, is reduced to about half, the improvement in mobility is limited to about 10%.

Therefore, the InN first buffer layer showing the best mobility in the measured sample (growth time: 30 seconds),
With the GaN second buffer layer (growth time 60 seconds) as the center, the first buffer layer growth time and the second buffer layer growth time were changed, and how the mobility changed was further observed.

FIG. 2A shows a measurement result when the growth time of the second buffer layer is fixed to 60 seconds and the growth time of the InN first buffer layer is changed from 0 seconds to 120 seconds. When the first buffer layer is grown for 30 seconds as compared with the mobility 333 when the first buffer layer is not formed, the mobility is improved by about 40% as described above.
Even if it is extended to 120 seconds, it is almost 400μ · cm ² / V · se
An increase in mobility of c and about 20% is observed.

FIG. 2B is a graph showing a change in mobility when the growth time of the first buffer layer is fixed at 30 seconds and the growth time of the second buffer layer is changed. When the growth time of the second buffer layer changes from 30 seconds to 60 seconds, the mobility increases from 364 to 475. However, when the growth time further increases to 90 seconds, the mobility shows a gradual decrease.

The mobility is considered to represent the reciprocal of the degree of carrier scattering in the crystal. The more disordered the crystal, the lower the mobility is expected. Therefore, an increase in mobility can be interpreted as meaning an improvement in crystallinity.

The InN first buffer layer improves the crystallinity by being inserted. Its thickness is about 30
The best result is shown in seconds, but the mobility is improved even when thicker than in the absence of the first buffer layer.

When the GaN second buffer layer is thick to some extent, the effect becomes remarkable. According to the above experiment, the best result is obtained when the growth time is 60 seconds (about 200 ° in terms of thickness). When the second buffer layer is made thicker, the effect is considered to be gradually reduced.

The PL measurement was performed at a wavelength of 3 for emission at the band edge.
A 25 nm He-Cd laser beam was used for deep level light emission, and a 325 nm wavelength He-Cd laser beam was used. The excitation light intensity was 1 mW. The PL emission of Sample 1 showed a broad peak, and the intensities were 36 and 23 for band-edge emission and deep-level emission, respectively.

For sample 2, the emission at the band edge and the emission at the deep level were 52 and 99, respectively. An increase in the intensity of the band edge emission means an improvement in the crystallinity, but an increase in the emission in the deeper order suggests that many undesirable deep levels are formed.

For sample 3, the emission at the band edge and the emission at the deep level were 46 and 26, respectively. For sample 4, the band edge emission and the deep level emission were 38 and 17, respectively. It is conspicuous that samples 3 and 4 using the two-layer buffer layer have significantly reduced emission at deep levels. In this regard,
It is considered that the crystallinity was improved and the deep level was reduced. However, it appears that the band edge emission is slightly reduced compared to the case of the single buffer layer.

In the above experiments, the growth of the buffer layer was performed at a substrate temperature of 530 ° C., but the growth of the epitaxial layer was performed at 1030 ° C., which was much higher. That is, the buffer layer once grown is then subjected to a temperature raising process. InN has a low binding energy and is known as a soft material, but it is considered that it is released by exposure to high temperatures. To confirm this possibility, after growing the buffer layer, a heating process was performed, and the microscope observation was performed.

After the growth of the InN layer, the temperature is changed from room temperature to 1100.
A temperature raising experiment was performed in the range of ° C. As a result, it was confirmed that the surface morphology deteriorated around 650 ° C. G
When a similar experiment was performed, the aN layer showed only a slight surface change even at a temperature around 1000 ° C. InN first
When a similar experiment was performed with the GaN second buffer layer formed on the buffer layer, only a slight surface change was observed.

From these results, it is presumed that when the GaN second buffer layer is formed on the InN first buffer layer, the decomposition and dissociation of the InN first buffer layer are protected even when a high-temperature heat treatment is performed.

Considering these results, the InN first buffer layer preferably has a thickness of about 5 to 100 °, and the GaN second buffer layer formed thereon has a thickness of 1 to 100 °.
It is preferable to have about 50 to 500 °. The thickness of the entire buffer layer including the first buffer layer and the second buffer layer is preferably about 50 to 600 °, more preferably 150 to 500 °.
It is expected that the degree will be more favorable.

The buffer layer is preferably not too thick because it is necessary to propagate the orientation of the underlying single crystal substrate to the epitaxial layer. From this viewpoint, the thickness of the buffer layer may preferably be 1000 ° or less.

Further, as compared with the case where a single buffer layer was used, the variation in the mobility in the substrate plane was reduced to about 1/3 when the stacked buffer layer was used. From this, it is considered that the use of the stacked buffer layer alleviates the growth condition dependency of the epitaxial layer.

In the case where the above-mentioned laminated buffer layer was used, even if the epitaxial layer was formed thick, the substrate was hardly warped. On the other hand, since a favorable crystal layer can be obtained even if the epitaxial layer is thinned, the thickness of the epitaxial layer can be reduced. For this reason, substrate separation,
The yield can be improved in a cutting step, a step of thinning a substrate by polishing, or the like.

An experiment using GaInN instead of InN as the first buffer layer was also performed. GaInN first
The buffer layer was made of TMGa of 4.5 μm as a source gas.
ol / min, 4.5 μmol / min of TMIn, N
H ₃ flushed 1.13Slm, except that the growth time was 90 seconds, was prepared under the same conditions as sample 4. Note that the GaInN first buffer layer has a growth time of 90 seconds,
It grew 0Å. In this sample, sample 3,
No smooth GaN epitaxial layer excellent in crystallinity as in No. 4 was obtained.

GaInN is a crystal in which GaN and InN are mixed in a phase-separated state (miscibility), and is known not to form a so-called mixed crystal. As a precautionary measure, the free energy was thermodynamically calculated as to whether the prepared GaInN was a non-mixed crystal material.

FIG. 3 shows the calculated free energy values as a function of composition. As shown in the figure, up to around 1000 ° C., the free energy ΔF does not have a minimum value, indicating that the crystal does not become a mixed crystal.

Therefore, it is preferable that the first buffer layer is made of a single material or a mixed crystal material, which is soft and has a variation in thickness.

FIG. 1 is a schematic sectional view showing a GaN-based light-emitting device according to an embodiment of the present invention based on the above-described experimental results. On the surface of the sapphire c-plane single crystal substrate 11, an InN first buffer layer 12 having a thickness of about 10 to 50 ° is grown at a substrate temperature of about 530 ° C., and a GaN second buffer layer is further formed thereon at a substrate temperature of about 530 ° C. Grows about 200 mm thick. On this laminated buffer layer, an n-type GaN layer 1 doped with Si
4. GaInN light emitting layer 15, Mg-doped p-type AlGaN cladding layer 16, Mg-doped p-type Ga
An N layer 17 is grown to form a double hetero structure.

Thereafter, the p-type layer and part of the light emitting layer are removed, an Al negative electrode 22 is formed on the exposed surface of the n-type layer 14, and a Ni layer and an Al layer are formed on the surface of the p-type layer 17. A positive electrode 21 composed of a laminate is formed. By causing a current to flow from the positive electrode to the negative electrode, light emission occurs from the light emitting layer 16,
Functions as a light emitting diode.

When compared with a light emitting diode having a double hetero structure using a GaN single buffer layer as shown in Sample 2, the light emitting diode of this embodiment has the same thickness even when the active layer is thinned. Electro-optical properties are obtained.
Further, in-plane uniformity is improved.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these.

For example, a single hetero structure or a multiple quantum well structure may be used instead of the double hetero structure. The structure of the light emitting element layer is not limited to these.

In the above embodiment, the semiconductor layer is grown by the MOCVD method, but other growth methods can be used. For example, a vapor phase growth method such as an MBE method or a halide method may be employed. Further, a liquid crystal growth method can be applied.

Although the case where the GaN-based light emitting element layer is formed on the sapphire substrate has been described, a sapphire substrate other than the c-plane or a single crystal substrate of another material such as SiC, Si, or GaAs can be used.

The light emitting element layers are also GaN, GaInN, Ga
Not limited to gallium nitride-based compounds such as AlN and GaAlInN, a III-V compound semiconductor layer such as GaAlInP or a II-VI compound semiconductor layer can also be used.

When a buffer layer is formed and epitaxial growth is performed, the buffer layer is usually deposited at a low temperature. When the epitaxial layer is grown at a high temperature, the buffer layer may be single-crystallized when the temperature is raised from the formation temperature to the growth temperature of the epitaxial layer. The crystal state of the buffer layer in the product may be any of amorphous, polycrystalline, and single crystal.

Although the case where the first buffer layer is formed of InN and the second buffer layer is formed of GaN has been described, the first buffer layer and the second buffer layer may be formed of any material having desired properties. Not limited to things. For example, the first buffer layer may be made of InP, InAs, ZnTe, CdTe.
Or the second buffer layer is made of AlN, GaAlN,
ZnO, GaAs, AlGaAs, GaP, ZnSe,
ZnS or the like can also be used. Here, the first buffer layer will need to have a property of forming an uneven surface, being softer than the second buffer layer, and not being completely miscible with the second buffer layer.

Considering the above experimental results from another viewpoint, an InN layer having a larger lattice mismatch with the sapphire c-plane as the underlying crystal is grown as a first buffer layer, and a lattice mismatch is formed thereon. Good results have been obtained when a smaller GaN layer is grown as the second buffer layer. From the viewpoint of strain relaxation, it is presumed that it would be effective to grow a layer having a large lattice mismatch as the first buffer layer and grow a layer having a reduced lattice mismatch as the second buffer layer thereon.

It will be apparent to those skilled in the art that various other modifications, improvements, combinations, and the like can be made.

[0086]

As described above, according to the present invention,
By using a multilayer buffer layer, a high-quality compound semiconductor crystal layer can be formed thereon. The uniformity and electro-optical characteristics of the epitaxial layer are improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a structure of a light emitting diode according to an embodiment of the present invention.

FIG. 2 is a graph showing experimental results on which the present invention is based.

FIG. 3 is a graph showing the free energy of GaInN formation with respect to a change in composition.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Single crystal substrate 12 1st buffer layer 13 2nd buffer layer 14, 15, 16, 17 Light emitting element layer 21, 22 Electrode

Claims (13)

[Claims] An underlying single-crystal substrate; a first buffer layer of a compound semiconductor formed on the underlying single-crystal substrate and having a thickness variation; and a first buffer layer formed on the first buffer layer; A first buffer layer and a second buffer layer of a compound semiconductor having a different composition from the first buffer layer, wherein the first buffer layer is formed of a material having a property of absorbing strain more easily than the second buffer layer. Compound semiconductor substrate. 2. The method according to claim 1, wherein the first buffer layer is formed of I
2. The compound semiconductor substrate according to claim 1, wherein the substrate is made of a II-V compound semiconductor. 3. The compound semiconductor according to claim 1, wherein the first buffer layer is a layer grown in a Volma-Weber style or a Stranki-Krastanov style. 4. The method according to claim 1, wherein the thickness of the first buffer layer is different from the thickness of the second buffer layer.
The compound semiconductor according to any one of claims 1 to 3, wherein the sum of the thickness and the thickness of the buffer layer is 200 nm or less. 5. The method according to claim 1, wherein a lattice mismatch between the first buffer layer and the underlying single crystal substrate is larger than a lattice mismatch between the second buffer layer and the underlying single crystal substrate. Compound semiconductor substrate. 6. The compound semiconductor substrate according to claim 1, further comprising a compound semiconductor element layer formed epitaxially on said second buffer layer. 7. The compound semiconductor substrate according to claim 6, wherein said first buffer layer is formed of InN, said second buffer layer is formed of GaN, and said compound semiconductor element layer includes a GaN layer. 8. A base single crystal substrate, a first buffer layer of a compound semiconductor formed on the base single crystal substrate and having a thickness variation, and a first buffer layer formed on the first buffer layer. A second buffer layer of a compound semiconductor having a different composition from the first buffer layer; and a second buffer layer formed epitaxially on the second buffer layer;
a compound semiconductor light-emitting element layer including a pn junction, wherein the first buffer layer has a property of absorbing strain more easily than the second buffer layer. 9. The compound semiconductor light-emitting device according to claim 8, wherein the first buffer layer is a layer grown in a Volma-Weber style or a Stranki-Klastanov style. 10. The compound semiconductor light emitting device according to claim 8, wherein a sum of a thickness of said first buffer layer and a thickness of said second buffer layer is 200 nm or less. 11. The first buffer layer is formed of InN, the second buffer layer is formed of GaN, and the compound semiconductor light emitting device layer includes a GaN layer.
0. The compound semiconductor light-emitting device according to any one of 0 to 0. 12. A step of growing a first buffer layer of a compound semiconductor having a thickness variation on a base single crystal substrate; and a step of forming a first buffer layer on the first buffer layer, A method of manufacturing a compound semiconductor substrate, comprising: growing a second buffer layer of a different compound semiconductor; and epitaxially growing a compound semiconductor element layer on the second buffer layer. 13. The compound semiconductor substrate according to claim 12, wherein the first buffer layer is grown in a Volma-Weber style or a Stranki-Krasnov style, and the second buffer layer is grown in a Frank van der Melbe style. Manufacturing method.