JP4907476B2 - Nitride semiconductor single crystal - Google Patents

Description

  The present invention relates to a nitride semiconductor single crystal made of gallium nitride (GaN), aluminum nitride (AlN), or the like suitably used for a light emitting diode, a laser light emitting element, an electronic element capable of high-speed and high-temperature operation, and the like.

  Nitride semiconductors typified by GaN and AlN have a wide band gap, and are compound semiconductors having excellent characteristics such as high electron mobility and high heat resistance. It is a material that is expected to be applied to high temperature operable electronic devices.

Since the nitride semiconductor has a high melting point and a very high equilibrium vapor pressure of nitrogen, bulk crystal growth from the melt is not easy. For this reason, a single crystal is produced by heteroepitaxial growth on a heterogeneous substrate.
Conventionally, a GaN (0001) or AlN (0001) single crystal film has been formed on a substrate of sapphire (0001), 6H—SiC (0001), Si (111) or the like via a buffer layer.

Among these substrates, the Si substrate is excellent in crystallinity, obtained in a large area, and low in price as compared with other substrates. It was supposed to be.
Moreover, since the formation of the nitride semiconductor film on the Si substrate can inherit the current silicon technology, it is required to be put into practical use also from the advantage in the development cost of industrial technology.

  However, when the nitride semiconductor single crystal is formed on the Si substrate, the nitride semiconductor single crystal film is cracked due to the difference in thermal expansion coefficient between Si and the nitride semiconductor. Due to the difference in the crystal lattice constant, a large number of crystal defects occur, and it was difficult to form a single crystal film having a thickness of 1 μm or more.

For this reason, when forming a nitride semiconductor single crystal on a Si substrate, it is necessary to form it through an appropriate buffer layer.
As such a buffer layer, for example, when 3C-SiC (111) is formed on a Si (110) substrate, the lattice defect between Si and 3C-SiC is less than when the Si (111) substrate is used. It is known that the matching is relaxed and the crystallinity of 3C—SiC (111) is improved (see, for example, Patent Document 1).
It has also been proposed to employ a superlattice structure of AlN and GaN or a 3C—SiC (111) layer.

Non-Patent Document 1 shows that when GaN (10-12) is formed on a Si (001) substrate, the orientation is exhibited by setting the off-cut angle of the Si substrate to 2 to 6 °. It is disclosed.
JP 2005-223206 A Applied Physics Letters, vol.84, No.23, July 7, 2004, p. 4747-4749

  However, when a nitride semiconductor is used for a light-emitting device, even if the above-described substrate or buffer layer is adopted, the (0001) -plane nitride semiconductor single crystal has a hole hole of electrons. The recombination is hindered by the spontaneous polarization of the crystal, resulting in a problem that the luminous efficiency is lowered.

  In addition, GaN (10-12) described in Non-Patent Document 1 does not pass through a buffer layer, and the orientation is not good.

  For this reason, from the viewpoint of improving the light emission efficiency, the nitride semiconductor single crystal suitable for the light-emitting device is a (10-10) or (11-20) plane that is a nonpolar crystal plane, or a semipolar plane. (10-1m) or (11-2n) (where m is a natural number, n is a natural number of 2 or more; the same shall apply hereinafter) or the like.

  On the other hand, when forming nitride semiconductor films such as GaN (10-1 m) and AlN (10-1 m), the present inventors have formed a substrate on which the above-described Si (100) is cut off. Focusing on the use of the formed 3C—SiC or BP buffer layer, the inventors have found that the nitride semiconductor film can be formed with a thickness of 1 μm or more.

  That is, the present invention has been made to solve the above technical problem, and a (10-1 m) -plane nitride semiconductor film having a thickness of 1 μm or more is formed on a Si substrate. An object of the present invention is to provide a nitride semiconductor single crystal that can be suitably used for a light emitting device.

The nitride semiconductor single crystal according to the present invention is either SiC or BP on a Si substrate having an off-cut angle from <100> to <110> direction of 1 to 35 ° with respect to Si (100). It is formed through one or more buffer layers and an AlN buffer layer, and is characterized by being made of GaN (10-1 m), AlN (10-1 m) or InN (10-1 m) (m: natural number).
According to the above configuration, a nitride semiconductor single crystal having a thickness of 1 μm or more and excellent in crystallinity (10-1 m) can be formed on a Si substrate.

Moreover, the nitride semiconductor single crystal according to another aspect of the present invention is formed on a Si substrate having an off-cut angle from <100> to the <110> direction of 1 to 35 ° with respect to Si (100). It is formed through a buffer layer composed of at least one of SiC and BP and an AlN buffer layer, and has a superlattice structure of GaN and AlN.
Thus, the crystallinity of the nitride semiconductor single crystal can be further improved by forming a superlattice structure of GaN and AlN.
Preferably, the Si substrate has an off-cut angle of 7 to 9 °.

As described above, according to the present invention, a GaN, AlN, or InN single crystal film excellent in crystallinity of a (10-1 m) plane which is a semipolar crystal plane can be obtained on a Si substrate with a thickness of 1 μm or more. Can do.
Furthermore, the crystallinity of the nitride semiconductor single crystal can be further improved by forming a superlattice structure of GaN and AlN.
Therefore, the nitride semiconductor single crystal according to the present invention can be suitably used for a light-emitting diode, a laser light-emitting element, an electronic element capable of high-speed and high-temperature operation, and is particularly suitable for a light-emitting device. Can be achieved.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
1 to 3 show an outline of an example of a layer structure when forming a nitride semiconductor single crystal according to the present invention.
The nitride semiconductor single crystal shown in FIG. 1 is a GaN, AlN or InN single crystal 4 formed on a Si single crystal substrate 1 via a SiC buffer layer 2a and an AlN buffer layer 3.
The nitride semiconductor single crystal shown in FIG. 2 has the same configuration as that of FIG. 1 except that a BP buffer layer 2b is formed instead of the SiC buffer layer 2a.
Further, the nitride semiconductor single crystal shown in FIG. 3 has a SiC buffer layer 2a and a BP buffer layer 2b, and the other configuration is the same as that of FIG.

These nitride semiconductor single crystals use, as a Si single crystal substrate, a substrate that is cut from 1 to 35 ° in the normal <100> to <110> directions with respect to Si (100). In addition, a (10-1 m) -plane single crystal having excellent crystallinity can be obtained by forming a buffer layer made of at least one of 3C—SiC and BP.
Further, this (10-1 m) -plane nitride semiconductor single crystal is formed on a Si substrate, so that it can utilize the apparatus and technology used in the conventional Si semiconductor manufacturing process, and has a large diameter. In addition, it has an advantage that it can be obtained at low cost.

  The manufacturing method of the Si single crystal substrate used in the present invention is not particularly limited. Those produced by the Czochralski (CZ) method or those produced by the floating zone (FZ) method may be used. An epitaxially grown crystal layer (Si epi substrate) may be used.

The off-cut angle of the Si substrate is preferably 1 to 35 ° in the <100> to <110> direction.
When the off-cut angle is less than 1 °, the nitride grown via the SiC or BP buffer layer is not oriented in the nonpolar plane, but is (0001) oriented.
On the other hand, when the off-cut angle exceeds 35 °, it is substantially Si (111), and the nitride grown through the buffer layer of SiC or BP is oriented to (0001).

The off-cut angle is preferably 8 ° ± 1.0 °, that is, 7-9 °.
More preferably, it is 8 °, but in consideration of machining accuracy, ± 1.0 ° is an allowable range.
By using such a Si substrate, cracks and crystal defects of the nitride semiconductor single crystal film on the entire surface can be suppressed, and the thickness of the (10-1 m) plane nitride semiconductor single crystal having excellent crystallinity can be reduced. It can be obtained at 1 μm or more.
Note that m = 2 at this off-cut angle.

  The Si (100) off-cut substrate is cleaned by removing a natural oxide film on the surface by cleaning with hydrogen gas or the like before forming a buffer layer made of at least one of SiC and BP on the Si (100) off-cut substrate. It is preferable to keep it in a state.

Furthermore, it is preferable that the surface of the Si substrate is carbonized by heat treatment at 1000 to 1350 ° C. using a hydrocarbon-based gas such as propane.
By performing such carbonization in advance, it is possible to prevent Si from being detached from the surface of the Si substrate when forming the SiC buffer layer.

  In addition, the buffer layer made of one or more of SiC and BP formed on the Si (100) off-cut substrate is only the SiC layer 2a as shown in FIG. 1, or as shown in FIG. Only the BP layer 2b may be used, or alternatively, as shown in FIG. 3, the SiC layer 2a and the BP layer 2b may be used.

When two types of SiC and BP are selected in the buffer layer, it is preferable to form the SiC layer 2a after forming the BP layer 2b as shown in FIG.
Since BP has an intermediate lattice constant between Si and SiC, the effect as a buffer layer can be improved by arranging the BP between the Si (100) off-cut substrate and the SiC layer. Can be efficiently formed as a film having a low defect density.

Further, an AlN buffer layer 3 is formed on the SiC or BP buffer layer.
The AlN buffer layer 3 serves to alleviate crystal lattice mismatch between the substrate 1 and the SiC 2a or BP buffer layer 2b and the GaN, AlN or InN single crystal 4 formed thereon.

The thickness of the AlN buffer layer is preferably as thin as possible from the viewpoint of manufacturing cost. However, the substrate and the SiC or BP buffer layer as described above, and GaN (10-1 m), AlN formed thereon are preferable. (10-1m) or InN (10-1m) is formed to such an extent that the effect of relaxing the crystal lattice mismatch with the single crystal is sufficiently obtained. Specifically, the thickness is preferably about 1 to 500 nm.
The AlN buffer layer can be formed, for example, by epitaxial growth on the SiC or BP buffer layer by vapor deposition.

  Then, a GaN (10-1m), AlN (10-1m) or InN (10-1m) single crystal is epitaxially grown on the AlN buffer layer, so that these nitride semiconductor single crystals have a thickness of 1 μm or more. It can be formed as a film having excellent crystallinity.

Further, FIG. 4 shows another aspect of the layer structure when the nitride semiconductor single crystal according to the present invention is formed.
As shown in FIG. 4, GaN (10-1 m) is formed on the SiC or BP buffer layer 2a (2b) and the AlN buffer layer 3 formed in the same manner as any of FIGS. Further, by forming the superlattice structure 5 in which AlN (10-1m) is alternately laminated as a thin film, the crystallinity of these nitride semiconductor single crystals can be further improved.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
With respect to Si (100), an Si substrate having an off-cut angle of 8 ° from the <100> to the <110> direction is set in a growth region in the reaction tube, and while supplying hydrogen as a carrier gas, the Si substrate The substrate was heated to 1100 ° C. to clean the substrate surface.
Then, propane was supplied, the substrate temperature was set to 1000 to 1350 ° C., and the surface of the Si substrate was carbonized, and then propane and silane were supplied to form a SiC buffer layer having a thickness of 10 to 10,000 nm.
Next, trimethylaluminum (TMA) and ammonia were supplied as raw materials while maintaining the substrate temperature, and an AlN buffer layer having a thickness of 1 to 500 nm was formed on the SiC layer.
Further, the substrate temperature was lowered to about 1000 ° C., trimethylgallium (TMG) and ammonia were supplied as raw materials, and a GaN single crystal layer was formed.
Even when the GaN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 2]
In the same manner as in Example 1, a SiC buffer layer and an AlN buffer layer were formed on a Si substrate with an off-cut angle from the <100> to the <110> direction of 8 ° with respect to Si (100). .
Then, the substrate temperature was raised to 1200 ° C. or higher, TMA and ammonia were supplied as raw materials, and an AlN single crystal layer was formed.
Even when the AlN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 3]
In the same manner as in Example 1, a SiC buffer layer and an AlN buffer layer were formed on a Si substrate with an off-cut angle from the <100> to the <110> direction of 8 ° with respect to Si (100). .
Then, the substrate temperature was raised to 500 ° C. or higher, and trimethylindium (TMIn) and ammonia were supplied as raw materials to form an InN single crystal layer.
Even when the InN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 4]
PH ₃ gas and B ₂ H ₆ gas were supplied onto a Si substrate cleaned in the same manner as in Example 1 to form a BP buffer layer having a thickness of 10 to 500 nm.
An AlN buffer layer and a GaN single crystal layer were formed on the BP buffer layer in the same manner as in Example 1.
Even when the GaN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 5]
In the same manner as in Example 4, a BP buffer layer and an AlN buffer layer were formed on a Si substrate with an off-cut angle from the <100> to the <110> direction of 8 ° with respect to Si (100). .
An AlN single crystal layer was formed on the AlN buffer layer in the same manner as in Example 2.
Even when the AlN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 6]
In the same manner as in Example 4, a BP buffer layer and an AlN buffer layer were formed on a Si substrate with an off-cut angle from the <100> to the <110> direction of 8 ° with respect to Si (100). .
An InN single crystal layer was formed on the AlN buffer layer in the same manner as in Example 3.
Even when the InN single crystal layer was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 7]
In the same manner as in Example 1, a SiC buffer layer and an AlN buffer layer were formed on a Si substrate with an off-cut angle from the <100> to the <110> direction of 8 ° with respect to Si (100). .
Then, the substrate temperature is lowered to about 1000 ° C., TMG and ammonia are supplied as raw materials, a GaN single crystal layer having a thickness of 1 to 500 nm is formed on the AlN buffer layer, and the substrate temperature is maintained. Then, TMA and ammonia were supplied as raw materials, and an AlN single crystal layer having a thickness of 1 to 500 nm was formed on the GaN single crystal layer. In the same manner, a plurality of the GaN single crystal layers and AlN single crystal layers were alternately stacked to form a superlattice structure.
Even when the superlattice structure was formed to a thickness of 1 μm or more, a flat surface was obtained, and no cracks or defects were observed. The orientation direction was <10-12>.

[Example 8]
In the same manner as in Example 1, an SiC buffer layer, an AlN buffer layer, and a GaN single crystal were formed on a Si substrate having an off-cut angle of 4 ° from the <100> to the <110> direction with respect to Si (100). Layers were deposited.
In the GaN single crystal layer, a flat surface could not be obtained in a part of the in-plane region, but no crack or defect was observed in other regions, and the orientation direction was <10-12>. It was.

[Comparative Examples 1 and 2]
Similar to Example 1, with respect to Si (100), on an Si substrate with an off-cut angle from the <100> to the <110> direction being 0 ° (Comparative Example 1) or 45 ° (Comparative Example 2) Then, an SiC buffer layer, an AlN buffer layer, and a GaN single crystal layer were formed.
None of the GaN single crystal layers could obtain a generally flat surface.

It is a schematic sectional drawing which shows an example of the layer structure at the time of forming the nitride semiconductor single crystal concerning this invention. It is a schematic sectional drawing which shows an example of the layer structure at the time of forming the nitride semiconductor single crystal concerning this invention. It is a schematic sectional drawing which shows an example of the layer structure at the time of forming the nitride semiconductor single crystal concerning this invention. It is a schematic sectional drawing which shows an example of the layer structure at the time of forming the nitride semiconductor single crystal concerning this invention.

Explanation of symbols

1 Si substrate 2a SiC buffer layer 2b BP buffer layer 3 AlN buffer layer 4 GaN, AlN or InN single crystal 5 Superlattice structure

Claims (3)

  A buffer layer and an AlN buffer layer made of at least one of SiC and BP on a Si substrate having an off-cut angle of 1 to 35 degrees from <100> to <110> with respect to Si (100) A nitride semiconductor single crystal formed of GaN (10-1 m), AlN (10-1 m), or InN (10-1 m) (m: natural number).   A buffer layer and an AlN buffer layer made of at least one of SiC and BP on a Si substrate having an off-cut angle of 1 to 35 degrees from <100> to <110> with respect to Si (100) A nitride semiconductor single crystal formed through a superlattice structure of GaN and AlN.   The nitride semiconductor single crystal according to claim 1 or 2, wherein an off-cut angle of the Si substrate is 7 to 9 °.

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