JP2003078163A - Method for growing nitride semiconductor - Google Patents

Abstract

(57) [Summary] [Purpose] Crystallinity of nitride semiconductor grown on substrate
LED, LD, etc. with high reliability
You. [Structure] In vapor deposition_aAl_bGa
_1-abN (0 ≦ a, 0 ≦ b, a + b ≦ 1)
Method for epitaxial growth of nitride semiconductor on substrate
Then, use SiC for the substrate, and place it on the SiC substrate.
Al whose composition is graded so that the X value gradually decreases_XGa
_1-XAn N (0 ≦ X ≦ 1) layer is grown and its Al _XGa
_1-XBy growing a nitride semiconductor on the N layer
To reduce the strain due to lattice mismatch of nitride semiconductors.
Dramatically improves crystallinity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nitride semiconductor In _a Al _b Ga _1-a-b N (0≤a, 0≤b,
It relates to a method of growing a crystal of a + b ≦ 1) on a substrate.

[0002]

2. Description of the Related Art Nitride semiconductors are metal organic chemical vapor deposition (M
OVPE), molecular beam vapor phase epitaxy (MBE), halide vapor phase epitaxy (HDVPE) and the like are used to epitaxially grow on the substrate. In general, for epitaxial growth of a compound semiconductor, it is common knowledge that a substrate with a lattice constant that matches that of the compound semiconductor will yield good crystallinity. It was always grown on sapphire substrates with a lattice constant difference of as much as 13%.

In the case of a sapphire substrate, it is known that before growing a nitride semiconductor, a buffer layer made of AlN or GaN is first grown on the sapphire substrate and then the nitride semiconductor is grown on the buffer layer. . For example, Japanese Examined Patent Publication No. 59-48794 and Japanese Examined Patent Publication No. 4-15200 describe a method of using AlN as a buffer layer, and Japanese Laid-Open Patent Publication Nos. 60-173829 and 4-297023 disclose GaN as a buffer layer. How to do is described. Among them, the method disclosed in JP-A-4-297023 is one of the core technologies of the nitride semiconductor LEDs currently put into practical use.

Other substrates for growing nitride semiconductors include ZnS (Japanese Patent Laid-Open No. 4-68579) and MnO (Japanese Patent Laid-Open No. 4-19859).
209577), ZnO (JP-A-4-236477),
Many proposals have been made, such as SiC (Japanese Patent Laid-Open No. 4-223330). In particular, Japanese Patent Laid-Open No. 4-223330 discloses a technique of forming a SiC buffer layer on the surface of a SiC substrate and growing a nitride semiconductor on the buffer layer. It is shown.

[0005]

Currently, blue LEDs, blue-green LEDs, etc. are practically used for nitride semiconductors grown on a sapphire substrate, but in the future, they will have higher brightness and excellent reliability. In order to realize advanced light emitting devices such as LEDs and LDs, it is necessary to further improve the crystallinity of the nitride semiconductor. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to improve the crystallinity of a nitride semiconductor grown on a substrate and realize a highly reliable LED, LD, or the like. To do.

[0006]

A method of growing a nitride semiconductor according to the present invention is a vapor phase epitaxy method of In _a Al _b Ga _{1-.
In a} method of epitaxially growing a nitride semiconductor represented by abN (0 ≦ a, 0 ≦ b, a + b ≦ 1) on a substrate, SiC is used for the substrate, and the X value is gradually decreased on the SiC substrate. Compositionally graded Al _X Ga _1-X
A N (0 ≦ X ≦ 1) layer is grown and its Al _X Ga _1-X is grown.
The nitride semiconductor is grown on the N layer.

In the growth method of the present invention, the vapor phase growth method is, for example, the MOVPE method or the MBE method as described above.
Method, HDVPE method, etc. can be adopted, but MOV is preferable.
By growing by the PE method, a semiconductor layer with good crystallinity can be obtained.

For the SiC substrate, a single crystal SiC substrate is used. SiC has various crystal structures such as 4H, 6H, and 3C, but is not particularly limited. Preferably 6H
-SiC (0001) plane, 3C-SiC (111) plane
A nitride semiconductor with good crystallinity can be obtained by growing it on the surface.

Al with a composition gradient_XGa_1-XWhat is N layer?
l The mixed crystal ratio decreases as the distance from the SiC substrate increases.
Al configured as_XGa_1-XThis is the N layer and this Al_X
Ga _1-XThe N layer is composed of a single layer with a composition gradient.
Or multiple Al as described later._XGa
_1-XEach layer is composed of a multilayer film with N layers stacked.
Al with a smaller Al mixed crystal ratio with increasing distance from SiC
_XGa_1-XIt may be N.

The Al _X Ga _1-X N layer is preferably grown to a thickness of 5 nm to 5 μm, more preferably 5 n.
Adjust to m to 3 μm. If it is thinner than 5 nm, it is difficult to form a compositionally graded layer, and if it is thicker than 2 μm, Al _X G
This is because cracks are likely to occur in the a1 _- XN layer itself. Further, it is more desirable that the outermost surface of the compositionally graded AlXGa1-XN layer is GaN. When GaN is used, the crystallinity of the nitride semiconductor layer grown thereon is particularly good.

Next, the growth method of the present invention is carried out according to the above-mentioned Al _X Ga.
_An AlN layer is grown between the _1- XN layer and the substrate. By growing this AlN layer, the crystallinity of the Al _X Ga _1-X N layer formed thereon is further improved. Therefore, the crystallinity of the nitride semiconductor layer grown on the Al _X Ga _1-X N layer is also improved. The thickness of the AlN layer is 1 nm
It is desirable to form the film with a thickness of 0.1 μm. 0.1
If it is thicker than μm, the AlN layer itself tends to be cracked, so that an Al _X Ga _1-X N layer having good crystallinity is difficult to grow on it. The AlN layer can be grown under the usual vapor phase growth conditions. For example, with the MOVPE method,
It can be grown by supplying an organometallic gas containing Al and a hydride of nitrogen to the surface of the SiC substrate heated in the range of 400 ° C to 1200 ° C. In this case, 900
AlN grown at a temperature of ℃ or below becomes a crystal containing amorphous AlN, and AlN grown at a temperature of about 900 ℃ becomes a crystal close to a single crystal. good _{Al X Ga 1-X} N layer can be grown.

Next, the Al _X Ga _1-X N layer is characterized by being formed of a multi-layer film in which layers having different X values are laminated. That is, on the SiC substrate side, AlGa with a large Al mixed crystal ratio
An N layer is formed on which AlGaN with a small Al mixed crystal ratio is formed.
Layers are formed to form a multilayer film in which AlGaN layers each having a gradually lower Al composition ratio are stacked. There is no particular problem even if the number of layers of the multilayer film is laminated, but as described above, the total thickness of the AlGaN layer is 5 n.
It is desirable to adjust to the range of m to 5 μm.

[0013]

When the compositionally graded AlGaN layer is formed on the SiC substrate, the AlGaN layer can reduce dislocations, strains and the like due to lattice mismatch with the substrate. It can be inferred that this is because the AlGaN layer having a large Al mixed crystal ratio is close to the lattice constant of SiC. Therefore, the compositionally graded Al
If the AlN layer is grown first before the GaN layer is grown, the crystallinity of AlGaN is improved. Moreover, Al
By reducing the mixed crystal ratio, the lattice defects of the AlGaN layer having a large Al mixed crystal ratio formed first are gradually relaxed, and the AlGaN layer having good crystallinity is gradually grown. If an AlGaN layer with good crystallinity can be grown, the nitride semiconductor grown on it will be the AlGaN layer previously formed.
Since the layer serves as a lattice-matched substrate, the crystallinity of the nitride semiconductor is dramatically improved.

[0014]

EXAMPLES The growth method of the present invention by the MOVPE method will be described below.

Hydrogen gas was used as a carrier gas on the (0001) plane of the 6H-SiC substrate heated to 1050 ° C.
TMA (trimethylaluminum) and ammonia gas are supplied to grow a thin film of AlN to a thickness of 50 nm. This AlN thin film can be grown in the range of 400 ° C. to 1200 ° C., and when it is grown at about 900 ° C. or lower, a crystal containing amorphous AlN grows,
Although a single crystal AlN thin film tends to grow when grown at 900 ° C. or higher, either an amorphous AlN thin film or a single crystal AlN thin film may be grown.

Subsequently, while maintaining the substrate at 1050 ° C., in addition to TMA gas, TMG (trimethylgallium) gas is gradually flowed to grow a compositionally graded AlGaN layer. The gas flow rates of TMG and TMA are controlled by a mass flow controller, the gas flow rate of TMG gas is gradually increased with the passage of time, and at the same time, the flow rate of TMA gas is gradually decreased to obtain the total gas of TMG gas and TMA gas. The AlGaN layer is grown by always adjusting the amount to be almost the same. Finally, the TMA gas is stopped so that the GaN layer grows. Al having a composition gradient as described above
A GaN layer is grown to a film thickness of 2 μm. Gradient composition A
Although the uppermost layer of the lGaN layer is made of GaN, it is not necessary to make the uppermost layer of GaN as long as it has a graded composition.
Preferably, the uppermost layer is Al _X G having an X value of less than 0.5.
The a _{1 -X} N layer, and more preferably 0.3 or less, can grow a nitride semiconductor layer with good crystallinity on the Al _X Ga _1-X N layer.

Then, the TMA gas was completely stopped, and the TMG was removed.
Gas, ammonia gas at 1050 ℃ 3μ GaN layer
Grow with a film thickness of m.

After growth, the substrate was taken out and the full width at half maximum (FWHM) of the double crystal X-ray rocking curve was used to evaluate the crystallinity of the obtained GaN layer.
It was found that the crystallinity was extremely excellent at 1.5 minutes. When the mobility of the crystal was measured with a Hall measuring device, it showed an excellent value of 900 cm ² / V · sec. Note that the smaller the FWHM, the better the crystallinity, and the larger the mobility, the better the crystallinity. For example, a non-doped GaN single crystal layer grown on a sapphire substrate using GaN as a buffer layer has a mobility of 3 to 5 minutes and a mobility of 500 to 600 cm ² / V · sec.

[Embodiment 2] The same as in Embodiment 1 except that the AlN thin film is not grown on the SiC substrate.
When the N layer was grown, the FWHM was 2 minutes and the mobility was 80.
It was 0 cm ² / V · sec, and the crystallinity was slightly inferior to that of Example 1.

Example 3 In Example 1, after the AlN thin film was grown, the temperature was kept at 1050 ° C.
First, Al _0.9 Ga _0.1 is adjusted by adjusting the gas flow rates of A and TMG.
The N layer is grown to 0.2 μm. Then Al _0.8 Ga _0.2 N
Layer is 0.2 μm, Al _0.7 Ga _0.3 N layer is 0.2 μm ..
... Al _0.2 Ga _0.8 N layer 0.2 μm, Al _0.1 Ga
Nine _0.9 N layers are laminated in the order of 0.2 μm to grow a compositionally graded AlGaN multilayer film with a thickness of 1.8 μm. Thereafter, in the same manner as in Example 1, Ga was formed on the Al _0.1 Ga _0.9 N layer.
When the N layer was grown to 2 μm, the crystallinity of the obtained GaN layer showed almost the same value as in Example 1.

[Embodiment 4] In Embodiment 1, after the AlGaN layer having the graded composition is grown, the same temperature is set to 10.
While maintaining the temperature at 50 ° C., an Al _0.2 Ga _0.8 N layer is grown to 2 μm with TMA, TMG and ammonia gas. This A
FWHM of _0.2 Ga _0.8 N layer is 2 minutes, mobility is 800 cm
² / V · sec, which shows that AlGaN has very good crystallinity.

[Embodiment 5] FIG. 1 is a schematic sectional view showing the structure of a laser device obtained by the method of the present invention.
Embodiment 5 will be described below with reference to this drawing.

An AlN thin film 2 having a thickness of 50 nm is formed on the (0001) plane of a 6 H—SiC substrate 1 having a thickness of 500 μm.
2 μm of n-type AlGaN layer 3 with composition gradient up to GaN
With the same film thickness as in Example 1, the layers are stacked. Note that the compositionally graded AlGaN layer 3 was doped with Si in order to obtain a preferable n-type, and was grown while being doped with silane gas as a Si source while flowing a source gas.

Next, the substrate temperature is set to 800 ° C., and TMI (trimethylindium) gas, TMG, ammonia, and silane gas are used as source gases, and n-type In _0.05 Ga _0.95 N is used.
Layer 4 was grown to a film thickness of 0.1 μm.

Subsequently, the flow rate of TMI was increased to form a non-doped In _0.2 Ga _0.8 N layer 5 with a film thickness of 2 nm as an active layer so that a single quantum well structure was formed.

Next, the TMI is stopped and the temperature of the substrate is changed to 1050.
℃, the source gas TMG, TMA, ammonia, p
Cp ₂ Mg (cyclopentadienylmagnesium) is used as a type impurity gas, and Mg-doped p-type Al _0.15 Ga
_{A 0.85} N layer 6 was grown to a thickness of 0.1 μm.

Subsequently, the flow rate of TMA was increased to grow the Mg-doped p-type Al _0.3 Ga _0.7 N layer 7 to a thickness of 0.1 μm.

Finally, TMA was stopped and Mg-doped p-type Ga was used.
The N layer 8 was grown to 0.5 μm.

The wafer on which the nitride semiconductor layers are laminated as described above is taken out of the reaction container, and the composition gradient n-AlGa is formed from the uppermost p-GaN layer 8 by an etching apparatus.
Etching is performed until the N layer 3 is exposed. After etching, the negative electrode 10 is provided on the exposed n-AlGaN layer 3,
Striped positive electrodes 11 were provided on the uppermost p-GaN layer.

After the electrode is installed, the wafer is cleaved in a direction perpendicular to the stripe of the positive electrode, and a reflective film made of a dielectric multilayer film is formed on the cleaved surface by a conventional method to obtain a laser device. FIG. 1 shows a sectional view of an element cleaved in a direction perpendicular to the stripe-shaped positive electrode 11. This laser device showed laser oscillation at room temperature at a threshold current density of 500 mA / cm ² and an output of 5 mW. This is because the nitride semiconductor grown on the compositionally graded AlGaN layer has good crystallinity, and the cleavage plane of the substrate facilitates the formation of a resonance surface.

This laser device has the following advantages. First of all, when SiC is used as the substrate, since the SiC substrate has conductivity, a normal negative electrode is provided in contact with the SiC substrate. That is, the positive electrode and the negative electrode face each other. However, SiC and nitride semiconductor are heteroepitaxial. Therefore, since a barrier caused by heteroepitaxial exists at the interface between the SiC and the nitride semiconductor layer, V _f (forward voltage) of the device increases. On the other hand, the laser device according to the present invention has a structure in which the negative electrode is not provided on the substrate side but the nitride semiconductor is intentionally etched to be provided on the same surface side, although the conductive substrate of SiC is used. Therefore, since no current flows through the interface between SiC and the nitride semiconductor layer, V _f
Can be suppressed. Secondly, compositionally graded AlGaN
By growing the layer 3 to a thickness of 1 μm or more, it becomes a contact layer for forming a negative electrode and a clad layer for confining light emission of the active layer. Thirdly, Si
Unlike the conventional sapphire substrate, C has a cleavability. Therefore, by utilizing the cleavage property of SiC, it is very convenient to use the cleavage surface of the nitride semiconductor as the optical resonance surface of the laser element.

[0032]

As described above, according to the method of the present invention, a nitride semiconductor layer having good crystallinity can be obtained. For example, in the hole measurement of crystals, the mobility is 900 cm ² / V · se
The value of c is a very excellent value for a nitride semiconductor.
Further, according to the present invention, a nitride semiconductor having good crystallinity can be obtained. Therefore, when a light emitting device is produced as in Example 5, a device having a high light emission output can be obtained, and its industrial utility value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor laser device obtained by a method according to an embodiment of the present invention.

[Explanation of symbols]

1 ... SiC substrate 2 ... AlN thin film 3 ... Si-doped n-type AlGaN layer 4 ... Si-doped n-type In _0.05 Ga _0.95 N layer 5 ... Non-doped In _0.2 Ga _0.8 N active layer 6 ... Mg-doped p-type Al _0.15 Ga _0.85 N layer 7 ...- Mg-doped p-type Al _0.3 Ga _0.7 N layer 8 ... p-type GaN layer 10 ... Negative electrode 11 .... Positive electrode

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[Procedure amendment]

[Submission date] September 17, 2002 (2002.9.1)
7)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

[Means for Solving the Problems]
The growth method is vapor phase growth_aAl_bGa_1
-AbN (0 ≦ a, 0 ≦ b, a + b ≦ 1)
Method for epitaxially growing a nitride semiconductor on a substrate
In, using SiC for the substrate, on the SiC substrate
The composition was graded so that the X value gradually decreased.Si dope
ofAl_XGa_{1- X}N (0 ≦ X ≦ 1) layersThe outermost surface is Ga
To be NGrown and its Al_XGa _1-XN layers
It is characterized in that the nitride semiconductor is grown thereon.

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Claims (3)

[Claims] 1. In _a Al _b Ga by a vapor phase growth method.
_In a method of epitaxially growing a nitride semiconductor represented by _1-a-bN (0 ≦ a, 0 ≦ b, a + b ≦ 1) on a substrate, SiC is used as the substrate and the SiC substrate is
Al _X Ga compositionally graded so that the X value gradually decreases
_1-X N (0 ≦ X ≦ 1) layer is grown and its Al _X Ga
_A method for growing a nitride semiconductor, which comprises growing the nitride semiconductor on a _1- XN layer. 2. The method for growing a nitride semiconductor according to claim 1, wherein an AlN layer is grown between the Al _X Ga _1-X N layer and the substrate. 3. The growth of the nitride semiconductor according to claim 1, wherein the Al _X Ga _1-X N layer is formed of a multilayer film in which layers having different X values are stacked. Method.