JPH08181070A - Epitaxial wafer and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide a high-performance epitaxial wafer that can be used for, for example, a light-emitting device and a method for industrially manufacturing the same. [Structure] A compound semiconductor substrate 1 selected from the group consisting of GaAs, GaP, InAs and InP, a buffer layer 2 made of GaN having a thickness of 100Å to 800Å formed on the substrate 1, and formed on the buffer layer 2. GaN
And an epitaxial layer 3 including. Buffer layer 2
Is a metal-organic chloride vapor phase epitaxy method,
The epitaxial layer 3 is formed at the first temperature, and is formed at a second temperature higher than the first temperature by the organometallic chloride vapor phase epitaxy growth method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer and a method for manufacturing the same, and more particularly to an epitaxial wafer used for a blue light emitting device or various ultraviolet devices and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 10 shows a GaN-based blue light-emitting device (LE) using a sapphire substrate which is now commercially available.
It is sectional drawing which shows the structure of the epitaxial wafer used for D).

Referring to FIG. 10, this epitaxial wafer includes a sapphire substrate 11, a gallium nitride (GaN) buffer layer 12 formed on substrate 11, and a hexagonal GaN layer formed on GaN buffer layer 12. It is composed of an epitaxial layer 13. In this epitaxial wafer, the GaN buffer layer 12 is provided to reduce strain due to the difference in lattice constant between the sapphire substrate 11 and the GaN epitaxial layer 13.

FIG. 11 is a sectional view showing the structure of a GaN-based blue light emitting device using the epitaxial wafer shown in FIG.

With reference to FIG. 11, this blue light emitting element is
On the epitaxial wafer shown in FIG. 10, the cladding layer 1 is formed.
4, the light emitting layer 15, the cladding layer 16 and the GaN epitaxial layer 17 are sequentially formed, and ohmic electrodes 18 and 19 are formed on the GaN epitaxial layers 13 and 17, respectively.

Referring to FIGS. 10 and 11, this epitaxial wafer uses insulating sapphire as substrate 11. Therefore, when an element is formed by forming electrodes, patterning by photolithography is performed twice. This is required more than once, and the nitride layer needs to be etched by reactive ion etching, which requires complicated steps. Further, since sapphire has high hardness, it is difficult to handle. Furthermore, since this sapphire cannot be cleaved, it cannot be applied to a laser diode having a cleaved end face as an optical resonator, which is a problem in light emitting device application.

Therefore, an attempt has been made to use conductive GaAs as a substrate in place of sapphire which has such drawbacks. However, if the substrate is GaA
If s was changed to s, under the same conditions as when the sapphire substrate was used, it was not possible to obtain an epitaxial wafer comparable to that when the sapphire substrate was used.

Therefore, various studies have been conducted on the production of epitaxial wafers using GaAs as a substrate.

Among these, for example, the Journal of the Crystal Growth Society of Japan, Vol. 20 No. 5 (1994) Supplement
In S409 to S414 (hereinafter referred to as "reference 1"),
An epitaxial wafer as shown in FIG. 12 is disclosed.

Referring to FIG. 12, this epitaxial wafer has a GaAs substrate 21, a GaAs buffer layer 22 formed on this substrate 21, and the surface of this GaAs buffer layer 22 is nitrided to form arsenic (As). ) Is replaced with nitrogen (N) to obtain a GaN film 23, and a GaN epitaxial layer 24 formed on the GaN film 23.

Further, in forming the GaN epitaxial layer 24 in the manufacture of this epitaxial wafer, OMV is used.
The PE method (metalorganic vapor phase epitaxy method) is used. This OMVPE method uses trimethylgallium (TM) while heating only the substrate in the reaction chamber by high frequency heating.
This is a method in which a first gas containing Ga) and a second gas containing ammonia (NH ₃ ) are introduced into the reaction chamber to vapor-deposit a GaN epitaxial layer on the substrate.

Further, for example, in Jpn. J. Appl.
Phys. Vol. 33 (1994) pp. 1747 ~
1752 (hereinafter referred to as "reference 2") discloses an epitaxial wafer as shown in FIG.

With reference to FIG. 13, this epitaxial wafer has a cubic GaN buffer layer 32 formed on its surface in advance by a GS-MBE method (gas source molecular beam epitaxy method). A crystalline GaN epitaxial layer 33 is formed.

A hydride VPE method (vapor phase epitaxy method) is used to form the GaN epitaxial layer 33 in the manufacture of this epitaxial wafer.
In this hydride VPE method, a substrate and a G
a) A source boat containing metal is installed, and a first gas containing hydrogen chloride (HCl) and a second gas containing ammonia (NH ₃ ) are heated from the outside by a resistance heater while heating the entire reaction chamber. It is a method of introducing and performing vapor phase growth of a GaN epitaxial layer on a substrate.

[0015]

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention
The epitaxial wafer disclosed in US Pat.
A GaN epitaxial layer is grown by the MVPE method. Ga is formed on a GaAs substrate by this OMVPE method.
In the case of growing the N epitaxial layer, the film growth rate is extremely reduced as compared with the case of growing it on the sapphire substrate. Specifically, even if a film forming rate of about 3 μm / hour is obtained when forming a film on a sapphire substrate, the film forming rate is not changed when forming a film on a GaAs substrate under the same conditions. It decreases to about 0.15 μm / hour. Therefore, for example, in order to use this epitaxial wafer for a light emitting device, GaN having a thickness of about 4 μm is used.
Although it is necessary to form an epitaxial layer, this method requires nearly one day to manufacture. Therefore, the production of the epitaxial wafer by this method cannot reduce the cost, and there is a problem that it is not suitable for industrialization.

Further, according to this method, the processing temperature cannot be made too high when growing the GaN epitaxial layer. Therefore, there is a limit in improving the characteristics of the obtained GaN epitaxial layer.

On the other hand, in the epitaxial wafer disclosed in Document 2, in order to form a GaN epitaxial layer, a substrate having a GaN buffer layer formed on its surface by the GS-MBE method must be prepared in advance. This G
The formation of the GaN buffer layer on the GaAs substrate by the S-MBE method has a slow growth rate and is not suitable for industrialization.

Further, since the hydride VPE method is used, it is difficult to carry out hetero growth requiring a plurality of sources or growth of a large number of sheets, and it cannot be said to be a method suitable for practical use. Moreover, in order to manufacture an epitaxial wafer by this method, the growth methods of the buffer layer and the epitaxial layer are different, so that two reaction chambers are required, and surface contamination due to growth interruption may be a problem. .

Further, in Reference 2, Ga with high characteristics is used.
The manufacturing conditions and the like for obtaining the N epitaxial layer have not been particularly studied.

An object of the present invention is to solve the above-mentioned problems and to provide a high-performance epitaxial wafer which can be used, for example, as a light-emitting device, and a method for industrially manufacturing the same.

[0021]

The epitaxial wafer according to the present invention comprises GaAs, GaP, InAs and I.
A compound semiconductor substrate selected from the group consisting of nPs, a buffer layer made of GaN having a thickness of 100Å to 800Å formed on the substrate, and an epitaxial layer containing GaN formed on the buffer layer.

Preferably, the buffer layer has a thickness of 200.
Å ~ 600Å is good. Further, the method for manufacturing an epitaxial wafer according to the present invention includes GaAs, GaP, I
On a compound semiconductor substrate selected from the group consisting of nAs and InP, a first gas containing an organometallic raw material containing hydrogen chloride and gallium and a second gas containing ammonia are reacted while externally heating the entire reaction chamber. A step of forming a buffer layer made of GaN at a first temperature by a method of performing vapor phase growth on a substrate installed in a reaction chamber and heating the entire reaction chamber from the outside on the buffer layer. While introducing a first gas containing an organometallic raw material containing hydrogen chloride and gallium and a second gas containing ammonia into the reaction chamber to perform vapor phase growth on a substrate placed in the reaction chamber, Forming a epitaxial layer containing GaN at a second temperature higher than the temperature of 1.

As the organometallic raw material containing gallium, for example, trimethylgallium, triethylgallium, etc. are used.

Preferably, the first temperature is 300 ° C to 70 ° C.
It is good that the temperature is 0 ° C. and the second temperature is 750 ° C. or higher.

More preferably, the first temperature is 400 ° C.
It is good that it is ˜600 ° C.

[0026]

The epitaxial wafer according to the present invention has a buffer layer made of GaN having a thickness of 100Å to 800Å.

A buffer layer made of GaN was formed also in an epitaxial wafer using a conventional sapphire substrate. This buffer layer mainly relaxes strain due to a difference in lattice constant between the sapphire substrate and the GaN epitaxial layer. It was working. On the other hand, the buffer layer in the invention of the present application has a function as a heat resistant coating in addition to such a function of relaxing strain.

That is, it is necessary to perform epitaxial growth of GaN at a very high temperature of 800 ° C. to 1100 ° C.
No heat damage was caused even at a high temperature of 0 ° C or higher. However, the GaAs, GaP, InAs, and InP substrates lose the function of As and P at a high temperature of 800 ° C. or higher, and cannot serve as a substrate. Therefore, GaAs, GaP, InAs
Further, in order to form a GaN epitaxial layer on the InP substrate, it is necessary to apply a heat resistant coating. In the present invention, the GaN buffer layer formed at a lower temperature than the GaN epitaxial layer also functions as such a heat resistant coating.

The thickness of this GaN buffer layer is 100Å
~ 800Å. This is because if the thickness is less than 100Å, the buffer layer is partially interrupted during the temperature rise for forming the epitaxial layer, and the epitaxial layer formed on the buffer layer peels off. On the other hand, if it is thicker than 800 Å, nucleus growth is mixed with low-temperature growth of the flat buffer layer, and the epitaxial layer grows in a pyramid shape centering on this nucleus.

Further, according to the method of manufacturing the epitaxial wafer according to the present invention, the GaN buffer is formed on the compound semiconductor substrate selected from the group consisting of GaAs, GaP, InAs and InP at a temperature lower than the growth temperature of the GaN epitaxial layer. Forming layers.

Therefore, a high-quality cubic GaN epitaxial layer can be grown without damaging the substrate crystal.

The temperature at which the buffer layer made of GaN is formed is preferably 300 ° C to 700 ° C. 300 ° C
This is because if it is lower, the buffer layer made of GaN does not grow. On the other hand, if the temperature is higher than 700 ° C., the substrate will be damaged by heat and the epitaxial layer formed thereon will peel off.

Further, according to the present invention, in forming the GaN buffer layer and the GaN epitaxial layer, the first gas containing the organometallic raw material containing hydrogen chloride and gallium and ammonia are heated while heating the entire reaction chamber from the outside. Second
And a gas of (4) are introduced into the reaction chamber to carry out vapor phase growth on a substrate placed in the reaction chamber (hereinafter referred to as "organic metal chloride vapor phase epitaxy growth method"). This organometallic chloride vapor phase epitaxy growth method has a high growth rate and is capable of obtaining a steep hetero interface.

Further, according to the present invention, the buffer layer and the epitaxial layer are formed by the same organometallic chloride vapor phase epitaxy method. Therefore, it is possible to grow consistently in the same chamber.

[0035]

【Example】

(Embodiment 1) FIG. 1 is a sectional view showing the structure of an example of an epitaxial wafer according to the present invention.

Referring to FIG. 1, in this epitaxial wafer, a GaN buffer layer 2 is formed on a GaAs substrate 1, and a GaN epitaxial layer 3 is further formed thereon.

Next, a method of manufacturing an epitaxial wafer having such a structure will be described below.

FIG. 2 is a diagram showing a schematic structure of a vapor phase growth apparatus used for manufacturing an epitaxial wafer using the organometallic chloride vapor phase epitaxy method according to the present invention. Referring to FIG. 2, this apparatus heats a reaction chamber 54 having a first gas introduction port 51, a second gas introduction port 52, and an exhaust port 53, and the inside of the reaction chamber 54 from the outside thereof. And a resistance heater 55 for heating.

An epitaxial wafer was manufactured as follows using the apparatus thus constructed.

Referring to FIG. 2, first, a gallium arsenide GaAs (100) plane substrate 1 pretreated with a normal H ₂ SO ₄ type etching solution was placed in a reaction chamber 54 made of quartz.

Next, the inside of the chamber is externally heated by the resistance heater 55 and the substrate 1 is kept at 500 ° C., and trimethylgallium (TMGa) as a group III raw material is supplied from the first gas inlet 51. Hydrogen chloride (H
Cl) partial pressure of 8 × 10 ^-4 atm and 8 × 10 ^-4 a, respectively.
At the same time, ammonia gas (NH ₃ ) as a group V raw material is introduced from the second gas inlet 52 at a partial pressure of 1.6 × 1.
It was introduced at 0 ^-1 atm. Under these conditions, epitaxial growth was performed for 15 minutes to form a GaN buffer layer 2 having a thickness of 300Å.

FIG. 3 is a photograph of the crystal structure of the GaN buffer layer 2 thus formed, observed from a cleavage plane by an SEM (scanning electron microscope).

It can be seen from FIG. 3 that the white-looking GaN buffer layer 2 is formed very uniformly on the substrate with a thickness of about 300 Å.

Next, the temperature of the substrate 1 on which the GaN buffer layer 2 is thus formed is set to 8 by the resistance heater 55.
After the temperature was raised to 50 ° C., the partial pressures of TMGa, HCl, and NH ₃ were 8 × 10 ⁻⁴ atm, 8 × 10 ⁻⁴ atm, respectively.
Epitaxial growth was performed for 60 minutes under the condition of 1.6 × 10 ^-1 atm.

As a result, a mirror-like GaN epitaxial layer 3 having a thickness of 2 μm was formed on the GaN buffer layer 2. In the photoluminescence (PL) spectrum of this GaN epitaxial layer 3, strong emission with a peak wavelength of 360 nm was observed. As a result of X-ray diffraction, it was confirmed that a cubic GaN epitaxial layer containing no hexagonal crystal was grown.

FIG. 4 is a photograph of the crystal structure of the GaN epitaxial layer thus formed, observed by SEM from the cleavage plane.

Referring to FIG. 4, it can be seen that a very flat GaN epitaxial layer 3 is formed on the GaN buffer layer 2 formed on the GaAs substrate 1.

Example 2 GaN buffer layer 2 and G
The growth conditions of the aN epitaxial layer 3 were changed as follows, and other conditions were the same as in Example 1 to fabricate an epitaxial wafer having the structure shown in FIG.

Growth conditions of GaN buffer layer Substrate temperature: 400 ° C. TMGa partial pressure: 1 × 10 ⁻⁴ atm HCl partial pressure: 1 × 10 ⁻⁴ atm NH ₃ partial pressure: 5 × 10 ⁻³ atm Growth time: 40 minutes Growth condition of GaN epitaxial layer Substrate temperature: 900 ° C. TMGa partial pressure: 3 × 10 ⁻⁴ atm HCl partial pressure: 3 × 10 ⁻⁴ atm NH ₃ partial pressure: 8 × 10 ⁻² atm Growth time: 60 Min. In the thus obtained epitaxial wafer, a thickness of 8 μm was formed on the GaN buffer layer 2 having a thickness of 400 Å.
The mirror-like GaN epitaxial layer 3 having a thickness of μm was formed.

In the PL spectrum of this GaN epitaxial layer 3, strong emission with a peak wavelength of 360 nm was observed. As a result of X-ray diffraction, it was confirmed that a cubic GaN epitaxial layer containing no hexagonal crystal was grown.

Comparative Example 1 In order to investigate the difference in the characteristics of the GaN epitaxial layer depending on the presence or absence of the GaN buffer layer, the GaN epitaxial layer was directly grown on the GaAs substrate. The growth conditions of the GaN epitaxial layer were the same as in Example 1.

FIG. 5 shows the GaN thus formed.
It is the photograph which observed the crystal structure of the epitaxial layer by SEM from the cleavage plane.

Referring to FIG. 5, when the GaN buffer layer is not provided in this way, the surface of the GaAs substrate is damaged by the high temperature to form irregularities, and the G formed thereon is formed.
It can be observed that the aN epitaxial layer has peeled off from the substrate.

Further, in order to compare the difference in the characteristics depending on the presence or absence of the buffer layer, the roughness of the GaN epitaxial surface of the epitaxial wafers obtained in Example 1 and Comparative Example 1 was measured by a surface roughness meter, and X was measured. The results of line diffraction and PL measurements were compared.

As a result, a large difference was observed in the unevenness of the GaN epitaxial layer surface, and it was found that the surface homology was remarkably improved by providing the GaN buffer layer. Also, regarding the results of X-ray diffraction and PL measurement, only for the example in which the GaN buffer layer was provided,
A very sharp peak was observed.

(Example 3) In order to study the optimum thickness of the GaN buffer layer, various thicknesses of GaN are formed on a GaAs substrate.
A buffer layer was formed, a GaN epitaxial layer was grown on the buffer layer, and the characteristics of the obtained GaN epitaxial layers were compared.

The growth conditions for the GaN buffer layer and the GaN epitaxial layer were the same as in Example 1.

FIG. 6 shows the thickness of the GaN buffer layer and Ga.
Full width at half maximum of X-ray peak of N epitaxial layer (FWHM)
It is a figure which shows the relationship with. In FIG. 6, the horizontal axis is GaN
The thickness (nm) of the buffer layer is shown, and the vertical axis shows the full width at half maximum (FWHM) (minutes) of the X-ray peak.

FIG. 7 is a diagram showing the relationship between the thickness of the GaN buffer layer and the surface roughness of the GaN epitaxial layer. In FIG. 7, the horizontal axis represents the thickness (nm) of the GaN buffer layer, and the vertical axis represents the surface unevenness (μm). The surface unevenness is the difference between the highest point of the convex portion and the lowest point of the concave portion.

As is clear from FIGS. 6 and 7, if the thickness of the buffer layer is too thin or too thick, the crystal characteristics of the GaN epitaxial layer grown thereon will deteriorate. Therefore, the thickness of the GaN buffer layer is 100
Å ~ 800 Å is preferred, more preferably 200 Å ~
It turns out that 600Å is good.

FIG. 8 is a photograph of the crystal structure of an epitaxial wafer in which a GaN epitaxial layer is formed on a GaN buffer layer having a thickness of 80Å, observed by SEM from the cleavage plane.

Referring to FIG. 8, if the buffer layer is too thin as described above, the GaN buffer layer is partially cut off when the substrate is heated from 500 ° C. to 850 ° C. to form the GaN epitaxial layer. , The GaN epitaxial layer formed on that portion is peeled off. As a result, it can be observed that holes are partially formed.

FIG. 9 is a photograph of the crystal structure of an epitaxial wafer in which a GaN epitaxial layer is formed on a GaN buffer layer having a thickness of 900Å, which is observed by SEM from the cleavage plane.

Referring to FIG. 9, if the buffer layer is too thick, nucleation occurs on the GaN buffer layer, and G
It can be observed that the aN epitaxial layer grows in a pyramid shape centering on this nucleus.

Example 4 Ga was used instead of the GaAs substrate
A P substrate was used to form a GaN buffer layer under the same conditions as in Example 1, and further a GaN epitaxial layer was formed thereon under the same conditions as in Example 1.

The thus-obtained epitaxial wafer was subjected to PL measurement and X-ray diffraction measurement of the GaN epitaxial layer. As a result, a good peak was obtained as in Example 1.

Example 5 In instead of the GaAs substrate
A P substrate was used to form a GaN buffer layer under the same conditions as in Example 1, and further a GaN epitaxial layer was formed thereon under the same conditions as in Example 1.

With respect to the epitaxial wafer thus obtained, PL measurement and X-ray diffraction measurement of the GaN epitaxial layer were performed. As a result, a good peak was obtained as in Example 1.

Example 6 TMGa as Group III Raw Material
Using TEGa (triethylgallium) instead of
A GaN buffer layer was formed under the same conditions as in Example 1, and TEGa was further used to form a GaN epitaxial layer under the same conditions as in Example 1.

With respect to the epitaxial wafer thus obtained, PL measurement and X-ray diffraction measurement of the GaN epitaxial layer were performed. As a result, a good peak was obtained as in Example 1.

[0071]

As described above, according to the present invention, an epitaxial wafer in which a high quality cubic GaN epitaxial layer is formed using a GaAs substrate can be obtained. Therefore, the epitaxial wafer according to the present invention can be applied to blue light emitting devices, various ultraviolet devices, and the like.

Further, according to the present invention, it is possible to manufacture an epitaxial wafer at a high growth rate and in the same chamber, and at the same time, it is possible to grow hetero wafers and a large number of wafers. Therefore, the method according to the present invention can be sufficiently applied to industrial production.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of an example of an epitaxial wafer according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a vapor phase growth apparatus used for manufacturing an epitaxial wafer using the organometallic chloride vapor phase epitaxy growth method according to the present invention.

FIG. 3 is a photograph of a crystal structure of a GaN buffer layer formed on a substrate according to the present invention, observed by SEM from a cleavage plane.

FIG. 4 is a photograph of a crystal structure of an example of an epitaxial wafer according to the present invention observed by SEM from a cleavage plane.

FIG. 5 is a photograph of the crystal structure of an example of an epitaxial wafer produced without providing a GaN buffer layer, observed by SEM from the cleavage plane, for comparison.

FIG. 6 is a diagram showing a relationship between a thickness of a GaN buffer layer and a full width at half maximum (FWHM) of an X-ray peak of a GaN epitaxial layer.

FIG. 7 is a diagram showing the relationship between the thickness of the GaN buffer layer and the surface roughness of the GaN epitaxial layer.

FIG. 8 is a photograph of a crystal structure of an example of an epitaxial wafer manufactured by using a GaN buffer layer having a thickness of 80 Å, which is observed by SEM from a cleavage plane for comparison.

FIG. 9 is a photograph of a crystal structure of an example of an epitaxial wafer manufactured by using a GaN buffer layer having a thickness of 900Å for comparison, which is observed by SEM from a cleavage plane.

FIG. 10 is a cross-sectional view showing a structure of an example of a conventional epitaxial wafer.

11 is a cross-sectional view showing the structure of a blue light emitting device using the epitaxial wafer shown in FIG.

FIG. 12 is a sectional view showing the structure of another example of a conventional epitaxial wafer.

FIG. 13 is a cross-sectional view showing the structure of still another example of a conventional epitaxial wafer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 GaN buffer layer 3 GaN epitaxial layer 51 First gas inlet 52 Second gas inlet 53 Exhaust outlet 54 Reaction chamber 55 Resistance heater 55 In each drawing, the same reference numerals indicate the same or corresponding parts. .

Front page continuation (72) Inventor Masato Matsushima 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Kan Seki 3-21-12 Nanyodai, Hachioji, Tokyo ( 72) Inventor Akihaku 2-4-13, Sachimachi, Fuchu, Tokyo

Claims (5)

[Claims] 1. GaAs, GaP, InAs and In
A compound semiconductor substrate selected from the group consisting of P, a buffer layer made of GaN having a thickness of 100Å to 800Å formed on the substrate, and an epitaxial layer containing GaN formed on the buffer layer. Equipped with an epitaxial wafer. 2. The buffer layer has a thickness of 200Å to 6
The epitaxial wafer according to claim 1, which is 00Å. 3. GaAs, GaP, InAs and In
On a compound semiconductor substrate selected from the group consisting of P, a first gas containing an organometallic raw material containing hydrogen chloride and gallium and a second gas containing ammonia are placed in a reaction chamber while heating the entire reaction chamber from the outside. Forming a buffer layer made of GaN at a first temperature by a method of introducing and performing vapor phase growth on a substrate installed in the reaction chamber; and heating the entire reaction chamber from the outside on the buffer layer. While introducing a first gas containing an organometallic raw material containing hydrogen chloride and gallium and a second gas containing ammonia into the reaction chamber to perform vapor phase growth on a substrate placed in the reaction chamber, At a second temperature higher than the temperature of 1, G
forming an epitaxial layer containing aN. 4. The first temperature is 300 ° C. to 700 ° C., and the second temperature is 750 ° C. or higher.
A method for manufacturing an epitaxial wafer according to the above. 5. The method for manufacturing an epitaxial wafer according to claim 4, wherein the first temperature is 400 ° C. to 600 ° C.