JP2002154900A - Method for growing crystal of gallium nitride-based compound semiconductor and gallium nitride-based compound semiconductor - Google Patents

Abstract

(57) [Problem] To improve the crystallinity of a gallium nitride-based compound semiconductor grown on a buffer layer. A gallium nitride-based compound semiconductor is grown stably and with good yield. SOLUTION: A gallium nitride-based compound semiconductor crystal is grown on a buffer layer by a metalorganic compound vapor phase epitaxy method. This method _(in the range of where 0.5 ≦ X ≦ 1.) The general formula Ga X _Al 1-X _N is grown a buffer layer of more becomes polycrystalline, partially buffer layer then raising the temperature A gallium nitride-based compound semiconductor having a carrier concentration of 2 × 10 ¹⁵ (Example 6) to 1 × 10 ¹⁹ / cm ² (Example 8) is grown using this as a seed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a gallium nitride-based compound semiconductor crystal on a substrate such as sapphire, and more particularly to a method for growing an epitaxial layer of a gallium nitride-based semiconductor compound having excellent crystallinity.

[0002]

2. Description of the Related Art Recently, gallium nitride-based compound semiconductors, for example, having a general formula of [Ga _X Al _1-X N
(However, X is in the range of 0 ≦ X ≦ 1.)]. As a method for growing a crystal of a gallium nitride-based compound semiconductor, an organic metal compound vapor deposition method (hereinafter, referred to as “MOCVD method”) is well known. This method supplies an organometallic compound gas as a reaction gas into a reaction vessel in which a sapphire substrate is installed,
This is a method of growing an epitaxial layer of a compound semiconductor crystal on a substrate while maintaining the crystal growth temperature at a high temperature of about 900 ° C. to 1100 ° C. For example, when growing a GaN epitaxial layer, trimethylgallium is used as a group III gas and ammonia gas is used as a group V gas.

In order to use a gallium nitride-based compound semiconductor epitaxial layer grown as described above as a light emitting device, it is first essential to improve crystallinity.

Further, the surface of, for example, a GaN layer directly grown on a sapphire substrate by using the MOCVD method has a hexagonal pyramid or hexagonal columnar growth pattern, and countless irregularities are formed. Has the drawback of becoming extremely poor. Fabricating a blue light-emitting device using a crystal layer of a semiconductor having extremely inferior surface morphology having innumerable irregularities on the surface has been very poor and almost impossible.

In order to solve such a problem, there has been proposed a method of growing an AlN buffer layer on a substrate before growing a gallium nitride compound semiconductor crystal {Appl. Phys. Lett 48, (1986), 353, (Applied Physics Letters 48, 1986, 353
Page) and JP-A-2-229476. In this method, a growth temperature of 400 to 900 ° C. is applied on a sapphire substrate.
At a low temperature of 100-500 Å
1N of a buffer layer is provided. According to this method, the crystallinity and surface morphology of the GaN semiconductor layer can be improved by growing GaN on the AlN layer serving as the buffer layer.

[0006]

However, in the above method, the growth conditions of the buffer layer are severely limited, and the thickness of the buffer layer must be strictly set to a very thin range of 100 to 500 angstroms. To
It is difficult to uniformly form a uniform film thickness over the entire surface of a large-area sapphire substrate, for example, a sapphire substrate having a diameter of about 50 mmφ. Therefore, it is difficult to improve the crystallinity and surface morphology of the gallium nitride-based compound semiconductor formed on the buffer layer with a good yield, and the crystallinity is still high enough to produce practical light emitting diodes, semiconductor lasers, and the like. However, the crystallinity has been required to be further improved.

The present invention has been made in view of such circumstances, and an object thereof is to improve the crystallinity and surface morphology of a gallium nitride-based compound semiconductor grown on a buffer layer to practical levels. It is another object of the present invention to provide a growth method for growing a gallium nitride-based compound semiconductor in a stable and high yield.

[0008]

The gallium nitride-based compound semiconductor crystal growing method of the present invention is an improved method of growing a gallium nitride-based compound semiconductor crystal by an organometallic compound vapor phase growth method. The method of the present invention, (in the range of where 0.5 ≦ X ≦ 1.) The general formula _Ga X _{Al 1-X} N is grown a buffer layer of polycrystalline consisting. Next, the temperature of the substrate is increased to partially partially crystallize the buffer layer, and the gallium nitride-based compound semiconductor is grown at a temperature higher than the growth temperature of the buffer layer.

Further, in the method for growing a gallium nitride compound semiconductor crystal according to claim 2 of the present invention, the buffer layer is grown on the gallium nitride compound semiconductor layer. Furthermore, in the method for growing a gallium nitride-based compound semiconductor according to claim 3, Si or Mg is doped during the growth of the gallium nitride-based compound semiconductor layer. Claim 4
In the method of growing a gallium nitride-based compound semiconductor described above, the thickness of the buffer layer is set to 0.2 μm or less.

The thickness of the buffer layer is preferably not less than 0.002 μm and not more than 0.2 μm, as shown in FIGS.
Hereinafter, it is more preferably adjusted to the range of 0.01 to 0.2 μm. Its thickness is thinner than 0.002 μm, and
If the thickness is more than 0.2 μm, the surface morphology of the gallium nitride-based compound semiconductor crystal formed on the buffer layer tends to deteriorate.

The growth temperature of the buffer layer is 200 ° C.
The temperature is adjusted in the range of not less than 900 ° C and preferably not more than 400 to 800 ° C. If the temperature is lower than 200 ° C., it is difficult to form a buffer layer, and if the temperature is higher than 900 ° C., the buffer layer tends to be a single crystal, and does not function as a buffer layer described later.

[0012]

FIG. 1 is a cross-sectional view showing the structure of an epitaxial wafer in the case where gallium nitride-based compound semiconductor crystals are grown on Ga _X Al _1-X N as a buffer layer, and FIG. A cross-sectional view showing the structure of an epitaxial wafer when the same crystal is grown thereon as a buffer layer is also shown. Since the buffer layer of the present invention has a larger allowable range of thickness than the conventional buffer layer, the buffer layer and the gallium nitride-based compound semiconductor crystal can be grown with good yield.

A method of growing a gallium nitride-based compound semiconductor crystal using AlN as a buffer layer has been described by Thin.
Solid Films. 163, (1988), 415 (Shin Solid Films 163, 1988, 415), and
Appl. Phys. Lett 48, (1986), 353 (Applied Physics Letters 48, 1986, p. 353) and the like, but the function of the buffer layer described in those documents will be briefly described. And the following:

AlN grown at low temperature (about 600 ° C.) is a polycrystalline layer, and when the temperature of this buffer layer is raised to about 1000 ° C. to grow, for example, GaN, the layer is partially monocrystallized. . The partially single crystallized part is
When GaN is grown at 1000 ° C., a seed crystal having a uniform orientation is formed. From the seed crystal, a GaN crystal grows and a uniform GaN single crystal layer can be grown. When there is no buffer layer, the sapphire substrate itself becomes a seed crystal, so that the crystal of the hexagonal prism of GaN having a large variation in orientation grows.

As in the present invention, Ga _X Al _1-X N (0.
When 5 ≦ X ≦ 1) is formed as the buffer layer, the following is considered as compared with the case where the conventional AlN is used as the buffer layer.

First, as a buffer layer, for example, G of X = 1
Considering the case of forming aN, the melting point of GaN is 110
0 ° C. and the melting point of AlN is 1700 ° C. Therefore, when a GaN buffer layer is formed at 600 ° C., a polycrystalline buffer layer grows. Next, when the temperature is raised to 1000 ° C. in order to grow an epitaxial layer of GaN on the polycrystalline GaN buffer layer, the GaN buffer layer is partially single-crystallized, similar to the case where AlN is used as the buffer layer. Then, it acts as a seed crystal for the GaN epitaxial layer.

In addition, since the melting point is lower than in the case where AlN is formed as the buffer layer, single crystal is easily formed when the temperature is raised. For this reason, even if the thickness of the buffer layer is increased, the effect as the buffer layer can be expected. Since the buffer layer is GaN, when the GaN epitaxial layer is grown thereon, the same material is grown on the same material, so that improvement in crystallinity can be expected. And so on.

In order to confirm the above, AlN, Ga
_0.5 Al _0.5 N, three types of buffer layers of GaN
The half width (FWHM: fuHM) of the double crystal X-ray rocking curve of the GaN epitaxial layer when each is formed on a sapphire substrate at 00 ° C. and a GaN epitaxial layer is grown thereon at 1000 ° C. with a thickness of 4 μm.
FIG. 3 shows a diagram in which the relationship between (ll width at half-maximum) and the thickness of the buffer layer is obtained. The smaller the FWHM, the better the crystallinity.

As shown in FIG. 3, GaN and Ga
_{The 0.5} Al _0.5 N buffer layer has good crystallinity over a wide buffer layer thickness range, and exhibits extremely excellent characteristics as compared with the conventional AlN buffer layer.

FIGS. 4 to 7 show that the thickness of the GaN buffer layer formed on the sapphire substrate was changed,
Ga in the case where an epitaxial layer of N is grown to 4 μm
The micrograph showing the crystal structure of the surface of the N epitaxial layer is shown. 4 to 7, the buffer layer thickness is 0.002 μm, 0.07 μm, 0.20 μm, 0 μm
(No buffer layer).

As can be seen from these figures, when there is no buffer layer, hexagonal columnar crystals appear on the surface as shown in FIG. Although it depends on the conditions when forming the buffer layer, the surface tends to be mirror-finished as the buffer layer is formed. However, if the buffer layer is too thick, the state of the surface (surface morphology) tends to deteriorate.
Therefore, the preferred thickness of the buffer layer is between 0.01 μm and 0.2 μm.

The buffer layer according to the crystal growth method of the present invention may be formed not only on a sapphire substrate but also on any layer having an epitaxial layer of a gallium nitride compound semiconductor. For example, on an n-type GaN epitaxial layer, p-type G doped with Mg as a p-type impurity
When it is desired to form an epitaxial layer of aN, the n-type G
A buffer layer may be formed on the aN epitaxial layer, and a p-type GaN epitaxial layer may be grown on the buffer layer.

[0023]

Embodiments of the present invention will be described below. However, the following examples illustrate a method for embodying the technical idea of the present invention, and the method of the present invention includes the following growth conditions, types of organometallic compound gases, and materials used. It is not specified. The growth method of the present invention can make various changes in the scope of the claims.

Gallium nitride-based system using the apparatus shown in FIG.
Crystal growth of the compound semiconductor was performed. [Example 1] GaN sapphire was formed on a sapphire substrate in the following steps.
A epitaxial layer was grown to a thickness of 4 μm. Susceptor washed 2 inch φ sapphire substrate
Put on top of -2. The air inside the reaction vessel 1 made of stainless steel is exhausted by an exhaust pump.
After evacuating at 6, the inside is further H₂Replace with Then H₂The gas is supplied to the reaction gas injection pipe 4 and the reaction vessel.
1 from the upper sub-injection pipe 5 and into the reaction vessel 1
The susceptor 2 is heated up to 1060 ° C. by the heater 3.
Heat. This state is maintained for 10 minutes, and the sapphire substrate surface
The oxide film is removed. Next, the temperature of the susceptor 2 was lowered to 500 ° C.
Let stand until the temperature is stable. Subsequently, H₂And N₂Supply mixed gas
Then, ammonia gas and H₂Gas
Supply mixed gas. H supplied from sub injection pipe 5 ₂gas
And N₂The gas flow rate was 10 liters / min.
The flow rate of ammonia gas supplied from the
Torr / min, H₂The gas flow rate was 1 liter / min.
Wait until the temperature of the susceptor 2 stabilizes at 500 ° C
One. Then, reactant gas injection to form a buffer layer
Ammonia gas and H from tube 4₂In addition to gas, TMG
2.7 × 10 (trimethylgallium) gas^-5Mol /
Flush for 1 minute. Next, only the TMG gas is stopped to grow the buffer layer.
stop. Here, a buffer layer having a thickness of 0.02 μm is formed.
Wear. The temperature of the susceptor 2 while flowing another gas
To 1000 ° C. After the temperature of the susceptor 2 rises to 1020 ° C,
Ammonia gas and H from reaction gas injection pipe 4₂In addition to gas
And TMG gas is 5.4 × 10^-5 At a flow rate of mol / min
The GaN epitaxial layer was supplied for 4.0 minutes,
It is grown to a thickness of μm. During this time, H₂And N₂Gas as described above
Supply, and the reaction gas is not contaminated in the reaction vessel
Like that. In addition, crystals grow uniformly on the susceptor 2
To rotate the motor 7 at 5 rpm. Note that
Not surprisingly, while the gas is being supplied, the exhaust
The gas supplied from the exhaust pipe 8 branched from the pipe of the pump 6
Release to the outside. Sapphire as above
A GaN buffer layer having a thickness of 0.02 μm on a substrate,
A 4 μm GaN epitaxial layer was grown thereon.

In the step of forming the buffer layer of Comparative Example 1, a 4 μm layer was formed on the AlN buffer layer in the same manner as in Example 1 except that the AlN buffer layer was formed to a thickness of 0.02 μm. A GaN epitaxial layer was grown. When forming the AlN buffer layer, TMA (trimethylaluminum) was added to the reaction gas injection pipe 4 in addition to 2.7 × in addition to ammonia gas and H ₂ gas.
It flowed at ^10-5 mol / min for 1 minute.

After the growth, the hole measurement was performed at room temperature, and the GaN epitaxial layer according to the present invention was compared with the GaN epitaxial layer according to Comparative Example 1.
FIGS. 9 and 10 show the carrier concentration and the mobility of the epitaxial layer, respectively, and the resulting carrier concentration and the in-plane distribution of the mobility are shown in FIGS. The present invention is shown in FIG. 9, the comparative example is shown in FIG. 10, the carrier concentration is indicated by ●, and the mobility is indicated by ○.

When a non-doped crystal is grown, the lower the carrier concentration and the higher the mobility, the better the crystallinity and the lower the impurity concentration.

GaN according to the present invention has a carrier concentration of 4 × 10 ¹⁶ / cm ³ and a mobility of 600 cm as shown in FIG.
^It shows a very good value of ² / V · sec. On the other hand, in Comparative Example 1 in which AlN was used as the buffer layer, the carrier concentration was 1 × 10 ¹⁸
/ Cm ³ , and the mobility was about 90 cm ² / V · sec.

In the step of forming the buffer layer of the second embodiment, the buffer layer of Ga _0.5 Al _0.5 N
A GaN epitaxial layer was grown on the buffer layer in the same manner as in Example 1, except that the buffer layer and the gallium nitride-based compound semiconductor were not formed to have the same composition. When forming the buffer layer, in addition to the ammonia gas and the H ₂ gas from the reaction gas injection pipe 4, TMG was 2.7 × 10 ⁻⁵ mol / min and TMA was 2.
7 × 10 ^{- 5} mol / min was passed respectively 0.5 min. This GaN epitaxial layer also showed an excellent X-ray rocking curve as shown in FIG. 3, and the surface morphology observed by microscopy was equivalent to that of Example 1, and the carrier concentration and mobility were the same as those of Example 1 and Comparative Example 1. It was located in the middle.

Example 3 was the same as Example 1 except that the growth temperature of the buffer layer was set to 600 ° C., the gas flow time was changed to 2.5 minutes, and the thickness of the buffer layer was set to 0.05 μm. Similarly, a GaN epitaxial layer was grown. This GaN epitaxial layer also had the same surface morphology as in Example 1, showed an excellent crystallinity with a half-value width of the X-ray rocking curve of 3 minutes, and was similar to Example 1 in both carrier concentration and mobility.

[Embodiment 4] In the same manner as in Embodiment 1 except that the growth temperature of the buffer layer was set to 800 ° C.
An aN epitaxial layer was grown. This GaN epitaxial layer also has the same surface morphology as that of Example 1, and shows an excellent crystallinity with a half value width of the X-ray rocking curve of 3 minutes.
The carrier concentration and the mobility were the same as in Example 1.

In the step of forming the buffer layer in [Embodiment 5], Ga _{0 . 5} A
A _0.5 N buffer layer was formed with a thickness of 0.02 μm. In addition to the ammonia gas and the H ₂ gas from the reaction gas injection pipe 4, TMA gas was added at 2.7 × 10 ⁻⁵ mol / min. Example 1 was repeated except that a TMG gas was supplied at a flow rate of 2.7 × 10 ⁻⁵ mol / min for 60 minutes to grow a Ga _0.5 Al _0.5 N epitaxial layer to a thickness of 4.0 μm. In the same manner as described above, a film thickness of 0.02 μm is formed on the sapphire substrate.
m Ga _0.5 Al _0.5 N buffer layer, and 4
μm Ga _{0 . A 5} Al _0.5 N epitaxial layer was grown. This Ga _0.5 Al _0.5 N epitaxial layer also had the same surface morphology as that of Example 1.

In Example 6, in addition to ammonia gas, H ₂ gas and TMG gas, Cp ₂ Mg
While flowing (biscyclopentadienyl magnesium) gas, the GaN epitaxial layer is doped with Mg, which is a p-type impurity, to form a p-type GaN epitaxial layer.
It was grown to a thickness of 0 μm. On the sapphire substrate as described above, a GaN buffer layer having a thickness of 0.02 μm, and a Mg layer doped with 10 ²⁰ / cm ³ thereon, having a thickness of 4.0 μm.
Was grown. This p-type GaN epitaxial layer also has the same surface morphology as in Example 1, and has a carrier concentration of 2.0 × 10 ¹⁵ / c.
For the first time, a gallium nitride-based compound semiconductor showed a p-type characteristic with m ³ and a mobility of 9.4 cm ² / V · sec. This means
This shows that the crystallinity of this epitaxial layer is very excellent.

Example 7 A GaN buffer layer having a thickness of 0.02 μm was formed on the GaN epitaxial layer having a thickness of 4 μm obtained in Example 1 in the same manner as in Example 6.
g of 10 ²⁰ / cm ³ and a 4.0 μm-thick p-type G
An aN epitaxial layer was grown. This p-type GaN epitaxial layer also had the same surface morphology as in Example 1, and exhibited the same p-type characteristics as the carrier concentration of 3.5 × 10 ¹⁵ / cm ³ and the mobility of 8.5 cm ² / V · sec.

In Example 8, silane (S) was added in addition to ammonia gas, H ₂ gas, and TMG gas.
While flowing iH ₄ ) gas, the GaN epitaxial layer was doped with Si, which is an n-type impurity, to grow to a thickness of 4.0 μm. As described above, a GaN buffer layer having a thickness of 0.02 μm was formed on the sapphire substrate.
4 μm-thick n-type G doped with about 10 ²⁰ / cm ^{3 of} Si
An aN epitaxial layer was grown. This n-type GaN epitaxial layer also had the same surface morphology as in Example 1, and exhibited a very high carrier concentration of 1.0 × 10 ¹⁹ / cm ³ .

Comparative Example 2 The buffer layer of AlN was 0.0
Except for forming a film having a thickness of 2 μm,
To further grow a 4 μm n-type GaN epitaxial layer on the AlN buffer layer formed on the sapphire substrate. This n-type GaN epitaxial layer has a carrier concentration of 5.0 × 10 ¹⁸ / cm ³ , and the carrier concentration is not as high as that of Comparative Example 1, and it is considered that the n-type GaN epitaxial layer is compensated for by impurities and has a low carrier concentration.

[0037]

As described in the _foregoing, Ga _{X Al 1-X}
By forming N (0.5 ≦ X ≦ 1) in the buffer layer, the crystallinity of the gallium nitride-based compound semiconductor grown thereon is drastically improved. In particular, the crystal growth of the gallium nitride compound semiconductor process of the present invention, the value of X of Ga X _Al 1-X _N is a buffer layer to identify the range of 0.5 ≦ X ≦ 1, further gallium nitride A buffer layer is also grown in a reaction vessel for growing a compound semiconductor. By specifying the range of X of the buffer layer in the range of 0.5 ≦ X ≦ 1, the crystal growth method of the gallium nitride-based compound semiconductor of the present invention, as shown in FIG. The FWHM can be remarkably improved as compared with the gallium nitride compound semiconductor used. FWHM is a parameter indicating crystallinity. Therefore, in addition to growing the buffer layer and the gallium nitride-based compound semiconductor in the same reaction vessel, the method of the present invention specifies gallium nitride by defining the range of X to be 0.5 ≦ X ≦ 1. An extremely excellent feature that crystallinity can be significantly improved, which is most important for a method of growing a crystal of a system compound semiconductor, is realized. Carrier concentration and mobility are also parameters indicating crystallinity. When a non-doped crystal is grown, the lower the carrier concentration and the higher the mobility,
It indicates that the crystallinity is good and the impurity concentration is low. As shown in FIG. 9, the gallium nitride based compound semiconductor prototyped in Example 1 of the present invention has
The carrier concentration is 4 × 10 ¹⁶ / cm ³ and the mobility is 600 cm ²
/ V · sec. This value is a remarkably excellent value in the gallium nitride-based compound semiconductor crystal. Incidentally, a gallium nitride-based compound semiconductor manufactured by a conventional method using AlN as a buffer layer has a carrier concentration of 1 × 10 ¹⁸ / cm ³ and a mobility of about 90 cm ² / V ·.
sec. The gallium nitride-based compound semiconductor grown by the method of the present invention has an excellent carrier concentration of 100 times or more and a mobility of about 7 times. Further, according to the gallium nitride based compound semiconductor crystal growth method of the present invention, by forming a buffer layer, the Mg-doped GaN epitaxial layer grown thereon exhibits p-type without any treatment. This is the first time, and shows how excellent the crystallinity of the gallium nitride-based compound semiconductor grown by the method of the present invention is. Further, n-type GaN doped with Si grown on the buffer layer is also made of Al.
A very high carrier concentration is shown as compared with the case where N is used as the buffer layer. Furthermore, compared to the conventional AlN buffer layer, the conditions for growing the buffer layer are milder in the method of the present invention. That is, the gallium nitride-based compound semiconductor layer grown thereon has good crystallinity over a wide range of the thickness of the buffer layer. Therefore, it is excellent in mass productivity in forming a light emitting element. As described above, by using the technology of the present invention, a gallium nitride-based compound semiconductor crystal is utilized, and a blue light emitting diode is used,
Even for semiconductor lasers, there are very large applications for practical use.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure of an epitaxial wafer according to a crystal growth method of the present invention.

FIG. 2 is a schematic cross-sectional view showing a structure of an epitaxial wafer formed by a conventional crystal growth method.

FIG. 3 is a diagram showing a relationship between a full width at half maximum (FWHM) of a double crystal X-ray rocking curve of a GaN epitaxial layer and a film thickness of a buffer layer.

FIG. 4 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 5 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 6 is a micrograph showing a crystal structure of a GaN epitaxial layer.

FIG. 7 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 8 is a partial schematic sectional view of an apparatus used in the present invention.

FIG. 9 is a diagram showing an in-plane distribution of carrier concentration and mobility based on a hole measurement result of a GaN crystal according to the method of the present invention.

FIG. 10 is a diagram showing an in-plane distribution of carrier concentration and mobility based on a hole measurement result of a GaN crystal according to a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction container 2 ... Susceptor 3 ... Heater 4 ... Reaction gas injection pipe 5 ... Sub injection pipe 6 ... Exhaust pump 7 ... Motor 8 ... Exhaust pipe

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[Procedure amendment]

[Submission Date] October 2, 2001 (2001.10.
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Crystal growth method of gallium nitride-based compound semiconductor and gallium nitride-based compound semiconductor

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a gallium nitride compound semiconductor crystal on a substrate such as sapphire and a gallium nitride compound semiconductor, and more particularly to an epitaxial layer of a gallium nitride semiconductor compound having excellent crystallinity. And a gallium nitride-based compound semiconductor.

[0002]

2. Description of the Related Art Recently, gallium nitride-based compound semiconductors, for example, having a general formula of [Ga _X Al _1-X N
(However, X is in the range of 0 ≦ X ≦ 1.)]. As a method for growing a crystal of a gallium nitride-based compound semiconductor, an organic metal compound vapor deposition method (hereinafter, referred to as “MOCVD method”) is well known. This method supplies an organometallic compound gas as a reaction gas into a reaction vessel in which a sapphire substrate is installed,
This is a method of growing an epitaxial layer of a compound semiconductor crystal on a substrate while maintaining the crystal growth temperature at a high temperature of about 900 ° C. to 1100 ° C. For example, when growing a GaN epitaxial layer, trimethylgallium is used as a group III gas and ammonia gas is used as a group V gas.

In order to use a gallium nitride-based compound semiconductor epitaxial layer grown as described above as a light emitting device, it is first essential to improve crystallinity.

Further, the surface of, for example, a GaN layer directly grown on a sapphire substrate by using the MOCVD method has a hexagonal pyramid or hexagonal columnar growth pattern, and countless irregularities are formed. Has the drawback of becoming extremely poor. Fabricating a blue light-emitting device using a crystal layer of a semiconductor having extremely inferior surface morphology having innumerable irregularities on the surface has been very poor and almost impossible.

In order to solve such a problem, there has been proposed a method of growing an AlN buffer layer on a substrate before growing a gallium nitride compound semiconductor crystal {Appl. Phys. Lett 48, (1986), 353, (Applied Physics Letters 48, 1986, 353
Page) and JP-A-2-229476. In this method, a growth temperature of 400 to 900 ° C. is applied on a sapphire substrate.
At a low temperature of 100-500 Å
1N of a buffer layer is provided. According to this method, the crystallinity and surface morphology of the GaN semiconductor layer can be improved by growing GaN on the AlN layer serving as the buffer layer.

[0006]

However, in the above method, the growth conditions of the buffer layer are severely limited, and the thickness of the buffer layer must be strictly set to a very thin range of 100 to 500 angstroms. To
It is difficult to uniformly form a uniform film thickness over the entire surface of a large-area sapphire substrate, for example, a sapphire substrate having a diameter of about 50 mmφ. Therefore, it is difficult to improve the crystallinity and surface morphology of the gallium nitride-based compound semiconductor formed on the buffer layer with a good yield, and the crystallinity is still high enough to make practical light emitting diodes, semiconductor lasers, etc. However, the crystallinity has been required to be further improved.

The present invention has been made in view of such circumstances, and an object thereof is to improve the crystallinity and surface morphology of a gallium nitride-based compound semiconductor grown on a buffer layer to practical levels. It is another object of the present invention to provide a growth method for growing a gallium nitride-based compound semiconductor in a stable and high yield.

[0008]

The gallium nitride-based compound semiconductor crystal growing method of the present invention is an improved method of growing a gallium nitride-based compound semiconductor crystal by an organometallic compound vapor phase growth method. The method of the present invention, (in the range of where 0.5 ≦ X ≦ 1.) The general formula _Ga X _{Al 1-X} N is grown a buffer layer of polycrystalline consisting. Next, the temperature of the substrate is increased to partially partially crystallize the buffer layer, and the gallium nitride-based compound semiconductor is grown at a temperature higher than the growth temperature of the buffer layer.

Further, in the method for growing a gallium nitride compound semiconductor crystal according to claim 2 of the present invention, the buffer layer is grown on the gallium nitride compound semiconductor layer. Furthermore, in the method for growing a gallium nitride-based compound semiconductor according to claim 3, Si or Mg is doped during the growth of the gallium nitride-based compound semiconductor layer. Claim 4
In the method of growing a gallium nitride-based compound semiconductor described above, the thickness of the buffer layer is set to 0.2 μm or less.

The thickness of the buffer layer is preferably not less than 0.002 μm and not more than 0.2 μm, as shown in FIGS.
Hereinafter, it is more preferably adjusted to the range of 0.01 to 0.2 μm. Its thickness is thinner than 0.002 μm, and
If the thickness is more than 0.2 μm, the surface morphology of the gallium nitride-based compound semiconductor crystal formed on the buffer layer tends to deteriorate.

The growth temperature of the buffer layer is 200 ° C.
The temperature is adjusted in the range of not less than 900 ° C and preferably not more than 400 to 800 ° C. If the temperature is lower than 200 ° C., it is difficult to form a buffer layer, and if the temperature is higher than 900 ° C., the buffer layer tends to be a single crystal, and does not function as a buffer layer described later.

The gallium nitride-based compound semiconductor of the present invention comprises:
Batch grown on the substrate by the organometallic compound growth method
Gallium nitride-based layer grown on the buffer layer
Gallium nitride based compound semiconductor having compound semiconductor layer
A is, the buffer layer is represented by the general formula is _Ga X _{Al 1-X} N
(However, the range is 0.5 ≦ X ≦ 1)
Both are layers having a single crystal, and are a half of a gallium nitride-based compound.
The conductor layer has a carrier concentration of 2 × 10 ¹⁵ to 1 × 10 ¹⁹
/ Cm ² .

[0013]

FIG. 1 is a cross-sectional view showing the structure of an epitaxial wafer in the case where gallium nitride-based compound semiconductor crystals are grown on Ga _X Al _1-X N as a buffer layer, and FIG. A cross-sectional view showing the structure of an epitaxial wafer when the same crystal is grown thereon as a buffer layer is also shown. Since the buffer layer of the present invention has a larger allowable range of thickness than the conventional buffer layer, the buffer layer and the gallium nitride-based compound semiconductor crystal can be grown with good yield.

A method of growing a gallium nitride-based compound semiconductor crystal using AlN as a buffer layer is based on the thin film method.
Solid Films. 163, (1988), 415 (Shin Solid Films 163, 1988, 415), and
Appl. Phys. Lett 48, (1986), 353 (Applied Physics Letters 48, 1986, p. 353) and the like, but the function of the buffer layer described in those documents will be briefly described. And the following:

AlN grown at low temperature (about 600 ° C.) is a polycrystalline layer, and when the temperature of this buffer layer is raised to about 1000 ° C. to grow GaN, for example, the layer is partially monocrystallized. . The partially single crystallized part is
When GaN is grown at 1000 ° C., a seed crystal having a uniform orientation is formed. From the seed crystal, a GaN crystal grows and a uniform GaN single crystal layer can be grown. When there is no buffer layer, the sapphire substrate itself becomes a seed crystal, so that the crystal of the hexagonal prism of GaN having a large variation in orientation grows.

As in the present invention, Ga _X Al _1-X N (0.
When 5 ≦ X ≦ 1) is formed as the buffer layer, the following is considered as compared with the case where the conventional AlN is used as the buffer layer.

First, as a buffer layer, for example, G of X = 1
Considering the case of forming aN, the melting point of GaN is 110
0 ° C. and the melting point of AlN is 1700 ° C. Therefore, when a GaN buffer layer is formed at 600 ° C., a polycrystalline buffer layer grows. Next, when the temperature is raised to 1000 ° C. in order to grow an epitaxial layer of GaN on the polycrystalline GaN buffer layer, the GaN buffer layer is partially single-crystallized, similar to the case where AlN is used as the buffer layer. Then, it acts as a seed crystal for the GaN epitaxial layer.

In addition, since the melting point is lower than in the case where AlN is formed as the buffer layer, single crystal is easily formed when the temperature is raised. For this reason, even if the thickness of the buffer layer is increased, the effect as the buffer layer can be expected. Since the buffer layer is GaN, when growing an epitaxial layer of GaN thereon, the same material is grown on the same material, so that an improvement in crystallinity can be expected. And so on.

In order to confirm the above, AlN, Ga
_0.5 Al _0.5 N, three types of buffer layers of GaN
The half width (FWHM: fuHM) of the double crystal X-ray rocking curve of the GaN epitaxial layer when each is formed on a sapphire substrate at 00 ° C. and a GaN epitaxial layer is grown thereon at 1000 ° C. with a thickness of 4 μm.
FIG. 3 shows a diagram in which the relationship between (ll width at half-maximum) and the thickness of the buffer layer is obtained. The smaller the FWHM, the better the crystallinity.

As shown in FIG. 3, GaN and Ga
_{The 0.5} Al _0.5 N buffer layer has good crystallinity over a wide buffer layer thickness range, and exhibits extremely excellent characteristics as compared with the conventional AlN buffer layer.

FIG. 4 to FIG. 7 show that the thickness of the GaN buffer layer formed on the sapphire substrate is changed,
Ga in the case where an epitaxial layer of N is grown to 4 μm
The micrograph showing the crystal structure of the surface of the N epitaxial layer is shown. 4 to 7, the buffer layer thickness is 0.002 μm, 0.07 μm, 0.20 μm, 0 μm
(No buffer layer).

As can be seen from these figures, when there is no buffer layer, hexagonal columnar crystals appear on the surface as shown in FIG. Although it depends on the conditions when forming the buffer layer, the surface tends to be mirror-finished as the buffer layer is formed. However, if the buffer layer is too thick, the state of the surface (surface morphology) tends to deteriorate.
Therefore, the preferred thickness of the buffer layer is between 0.01 μm and 0.2 μm.

The buffer layer according to the crystal growth method of the present invention may be formed not only on a sapphire substrate but also on any layer having an epitaxial layer of a gallium nitride compound semiconductor. For example, on an n-type GaN epitaxial layer, p-type G doped with Mg as a p-type impurity
When it is desired to form an epitaxial layer of aN, the n-type G
A buffer layer may be formed on the aN epitaxial layer, and a p-type GaN epitaxial layer may be grown on the buffer layer.

[0024]

Embodiments of the present invention will be described below. However, the following examples illustrate a method for embodying the technical idea of the present invention, and the method of the present invention includes the following growth conditions, types of organometallic compound gases, and materials used. It is not specified. The growth method of the present invention can make various changes in the scope of the claims.

Using the apparatus shown in FIG.
Crystal growth of the compound semiconductor was performed. [Example 1]
GaN epitaxial layer on sapphire substrate
m. Susceptor washed 2 inch φ sapphire substrate
Put on top of -2. The air inside the reaction vessel 1 made of stainless steel is exhausted by an exhaust pump.
After evacuating at 6, the inside is further H₂Replace with Then H₂The gas is supplied to the reaction gas injection pipe 4 and the reaction vessel.
1 from the upper sub-injection pipe 5 and into the reaction vessel 1
The susceptor 2 is heated up to 1060 ° C. by the heater 3.
Heat. This state is maintained for 10 minutes, and the sapphire substrate surface
The oxide film is removed. Next, the temperature of the susceptor 2 was lowered to 500 ° C.
Let stand until the temperature is stable. Subsequently, H₂And N₂Supply mixed gas
Then, ammonia gas and H₂Gas
Supply mixed gas. H supplied from sub injection pipe 5 ₂gas
And N₂The gas flow rate was 10 liters / min.
The flow rate of ammonia gas supplied from the
Torr / min, H₂The gas flow rate was 1 liter / min.
Wait until the temperature of the susceptor 2 stabilizes at 500 ° C
One. Then, reactant gas injection to form a buffer layer
Ammonia gas and H from tube 4₂In addition to gas, TMG
2.7 × 10 (trimethylgallium) gas^-5Mol /
Flush for 1 minute. Next, only the TMG gas is stopped to grow the buffer layer.
stop. Here, a buffer layer having a thickness of 0.02 μm is formed.
Wear. The temperature of the susceptor 2 while flowing another gas
To 1000 ° C. After the temperature of the susceptor 2 rises to 1020 ° C,
Ammonia gas and H from reaction gas injection pipe 4₂In addition to gas
And TMG gas is 5.4 × 10^-5 At a flow rate of mol / min
The GaN epitaxial layer was supplied for 4.0 minutes,
It is grown to a thickness of μm. During this time, H₂And N₂Gas as described above
Supply, and the reaction gas is not contaminated in the reaction vessel
Like that. In addition, crystals grow uniformly on the susceptor 2
To rotate the motor 7 at 5 rpm. Note that
Not surprisingly, while the gas is being supplied, the exhaust
The gas supplied from the exhaust pipe 8 branched from the pipe of the pump 6
Release to the outside. Sapphire as above
A GaN buffer layer having a thickness of 0.02 μm on a substrate,
A 4 μm GaN epitaxial layer was grown thereon.

In the step of forming the buffer layer of Comparative Example 1, a 4 μm layer was formed on the AlN buffer layer in the same manner as in Example 1 except that the AlN buffer layer was formed to a thickness of 0.02 μm. A GaN epitaxial layer was grown. When forming the AlN buffer layer, TMA (trimethylaluminum) was added to the reaction gas injection pipe 4 in addition to 2.7 × in addition to ammonia gas and H ₂ gas.
It flowed at ^10-5 mol / min for 1 minute.

After the growth, the hole measurement was performed at room temperature, and the GaN epitaxial layer according to the present invention was compared with the GaN epitaxial layer according to Comparative Example 1.
FIGS. 9 and 10 show the carrier concentration and the mobility of the epitaxial layer, respectively, and the resulting carrier concentration and the in-plane distribution of the mobility are shown in FIGS. The present invention is shown in FIG. 9, the comparative example is shown in FIG. 10, the carrier concentration is indicated by ●, and the mobility is indicated by ○.

When a non-doped crystal is grown, the lower the carrier concentration and the higher the mobility, the better the crystallinity and the lower the impurity concentration.

The GaN according to the present invention has a carrier concentration of 4 × 10 ¹⁶ / cm ³ and a mobility of 600 cm as shown in FIG.
^It shows a very good value of ² / V · sec. On the other hand, in Comparative Example 1 in which AlN was used as the buffer layer, the carrier concentration was 1 × 10 ¹⁸
/ Cm ³ , and the mobility was about 90 cm ² / V · sec.

In the step of forming the buffer layer of [Example 2], the buffer layer of Ga _0.5 Al _0.5 N
A GaN epitaxial layer was grown on the buffer layer in the same manner as in Example 1, except that the buffer layer and the gallium nitride-based compound semiconductor were not formed to have the same composition. When forming the buffer layer, in addition to the ammonia gas and the H ₂ gas from the reaction gas injection pipe 4, TMG was 2.7 × 10 ⁻⁵ mol / min and TMA was 2.
7 × 10 ^{- 5} mol / min was passed respectively 0.5 min. This GaN epitaxial layer also showed an excellent X-ray rocking curve as shown in FIG. 3, and the surface morphology observed by microscopy was equivalent to that of Example 1, and the carrier concentration and mobility were the same as those of Example 1 and Comparative Example 1. It was located in the middle.

Example 3 was the same as Example 1 except that the growth temperature of the buffer layer was set to 600 ° C., the gas flow time was changed to 2.5 minutes, and the thickness of the buffer layer was set to 0.05 μm. Similarly, a GaN epitaxial layer was grown. This GaN epitaxial layer also had the same surface morphology as in Example 1, showed an excellent crystallinity with a half-value width of the X-ray rocking curve of 3 minutes, and was similar to Example 1 in both carrier concentration and mobility.

[Embodiment 4] In the same manner as in Embodiment 1 except that the growth temperature of the buffer layer was set to 800 ° C.
An aN epitaxial layer was grown. This GaN epitaxial layer also has the same surface morphology as that of Example 1, and shows an excellent crystallinity with a half value width of the X-ray rocking curve of 3 minutes.
The carrier concentration and the mobility were the same as in Example 1.

In the step of forming the buffer layer in [Embodiment 5], Ga _{0 . 5} A
A _0.5 N buffer layer was formed with a thickness of 0.02 μm. In addition to the ammonia gas and the H ₂ gas from the reaction gas injection pipe 4, TMA gas was added at 2.7 × 10 ⁻⁵ mol / min. Example 1 was repeated except that a TMG gas was supplied at a flow rate of 2.7 × 10 ⁻⁵ mol / min for 60 minutes to grow a Ga _0.5 Al _0.5 N epitaxial layer to a thickness of 4.0 μm. In the same manner as described above, a film thickness of 0.02 μm is formed on the sapphire substrate.
m Ga _0.5 Al _0.5 N buffer layer, and 4
μm Ga _{0 . A 5} Al _0.5 N epitaxial layer was grown. This Ga _0.5 Al _0.5 N epitaxial layer also had the same surface morphology as that of Example 1.

In the sixth embodiment, in addition to the ammonia gas, the H ₂ gas, and the TMG gas, Cp ₂ Mg
While flowing (biscyclopentadienyl magnesium) gas, the GaN epitaxial layer is doped with Mg, which is a p-type impurity, to form a p-type GaN epitaxial layer.
It was grown to a thickness of 0 μm. On the sapphire substrate as described above, a GaN buffer layer having a thickness of 0.02 μm, and a Mg layer doped with 10 ²⁰ / cm ³ thereon, having a thickness of 4.0 μm.
Was grown. This p-type GaN epitaxial layer also has the same surface morphology as in Example 1, and has a carrier concentration of 2.0 × 10 ¹⁵ / c.
For the first time, a gallium nitride-based compound semiconductor showed a p-type characteristic with m ³ and a mobility of 9.4 cm ² / V · sec. This means
This shows that the crystallinity of this epitaxial layer is very excellent.

Example 7 A GaN buffer layer having a thickness of 0.02 μm was formed on the GaN epitaxial layer having a thickness of 4 μm obtained in Example 1 in the same manner as in Example 6.
g of 10 ²⁰ / cm ³ and a 4.0 μm-thick p-type G
An aN epitaxial layer was grown. This p-type GaN epitaxial layer also had the same surface morphology as in Example 1, and exhibited the same p-type characteristics as the carrier concentration of 3.5 × 10 ¹⁵ / cm ³ and the mobility of 8.5 cm ² / V · sec.

In Example 8, silane (S) was added in addition to ammonia gas, H ₂ gas, and TMG gas.
While flowing iH ₄ ) gas, the GaN epitaxial layer was doped with Si, which is an n-type impurity, to grow to a thickness of 4.0 μm. As described above, a GaN buffer layer having a thickness of 0.02 μm was formed on the sapphire substrate.
4 μm-thick n-type G doped with about 10 ²⁰ / cm ^{3 of} Si
An aN epitaxial layer was grown. This n-type GaN epitaxial layer also had the same surface morphology as in Example 1, and exhibited a very high carrier concentration of 1.0 × 10 ¹⁹ / cm ³ .

Comparative Example 2 The buffer layer of AlN was 0.0
Except for forming a film having a thickness of 2 μm,
To further grow a 4 μm n-type GaN epitaxial layer on the AlN buffer layer formed on the sapphire substrate. This n-type GaN epitaxial layer has a carrier concentration of 5.0 × 10 ¹⁸ / cm ³ , and the carrier concentration is not as high as that of Comparative Example 1, and it is considered that the n-type GaN epitaxial layer is compensated for by impurities and has a low carrier concentration.

[0038]

As described in the _foregoing, Ga _{X Al 1-X}
By forming N (0.5 ≦ X ≦ 1) in the buffer layer, the crystallinity of the gallium nitride-based compound semiconductor grown thereon is drastically improved. In particular, the crystal growth of the gallium nitride compound semiconductor process of the present invention, the value of X of Ga X _Al 1-X _N is a buffer layer to identify the range of 0.5 ≦ X ≦ 1, further gallium nitride A buffer layer is also grown in a reaction vessel for growing a compound semiconductor. By specifying the range of X of the buffer layer in the range of 0.5 ≦ X ≦ 1, the crystal growth method of the gallium nitride-based compound semiconductor of the present invention, as shown in FIG. The FWHM can be remarkably improved as compared with the gallium nitride compound semiconductor used. FWHM is a parameter indicating crystallinity. Therefore, in addition to growing the buffer layer and the gallium nitride-based compound semiconductor in the same reaction vessel, the method of the present invention specifies gallium nitride by defining the range of X to be 0.5 ≦ X ≦ 1. An extremely excellent feature that crystallinity can be significantly improved, which is most important for a method of growing a crystal of a system compound semiconductor, is realized. Carrier concentration and mobility are also parameters indicating crystallinity. When a non-doped crystal is grown, the lower the carrier concentration and the higher the mobility,
It indicates that the crystallinity is good and the impurity concentration is low. As shown in FIG. 9, the gallium nitride based compound semiconductor prototyped in Example 1 of the present invention has
The carrier concentration is 4 × 10 ¹⁶ / cm ³ and the mobility is 600 cm ²
/ V · sec. This value is a remarkably excellent value in the gallium nitride-based compound semiconductor crystal. Incidentally, a gallium nitride-based compound semiconductor manufactured by a conventional method using AlN as a buffer layer has a carrier concentration of 1 × 10 ¹⁸ / cm ³ and a mobility of about 90 cm ² / V ·.
sec. The gallium nitride-based compound semiconductor grown by the method of the present invention has an excellent carrier concentration of 100 times or more and a mobility of about 7 times. Further, according to the gallium nitride based compound semiconductor crystal growth method of the present invention, by forming a buffer layer, the Mg-doped GaN epitaxial layer grown thereon exhibits p-type without any treatment. This is the first time, and shows how excellent the crystallinity of the gallium nitride-based compound semiconductor grown by the method of the present invention is. Further, n-type GaN doped with Si grown on the buffer layer is also made of Al.
A very high carrier concentration is shown as compared with the case where N is used as the buffer layer. Furthermore, compared to the conventional AlN buffer layer, the conditions for growing the buffer layer are milder in the method of the present invention. That is, the gallium nitride-based compound semiconductor layer grown thereon has good crystallinity over a wide range of the thickness of the buffer layer. Therefore, it is excellent in mass productivity in forming a light emitting element. As described above, by using the technology of the present invention, a gallium nitride-based compound semiconductor crystal is utilized, and a blue light emitting diode is used,
Even for semiconductor lasers, there are very large applications for practical use.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure of an epitaxial wafer according to a crystal growth method of the present invention.

FIG. 2 is a schematic cross-sectional view showing a structure of an epitaxial wafer formed by a conventional crystal growth method.

FIG. 3 is a diagram showing a relationship between a full width at half maximum (FWHM) of a double crystal X-ray rocking curve of a GaN epitaxial layer and a film thickness of a buffer layer.

FIG. 4 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 5 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 6 is a micrograph showing a crystal structure of a GaN epitaxial layer.

FIG. 7 is a micrograph showing the crystal structure of the GaN epitaxial layer.

FIG. 8 is a partial schematic sectional view of an apparatus used in the present invention.

FIG. 9 is a diagram showing an in-plane distribution of carrier concentration and mobility based on a hole measurement result of a GaN crystal according to the method of the present invention.

FIG. 10 is a diagram showing an in-plane distribution of carrier concentration and mobility based on a hole measurement result of a GaN crystal according to a conventional method.

[Description of Signs] 1 ... Reaction vessel 2 ... Susceptor 3 ... Heater 4 ... Reaction gas injection pipe 5 ... Sub injection pipe 6 ... Exhaust pump 7 ... Motor 8 ... Exhaust pipe

Continued on front page F term (reference) 4G077 AA03 AB01 BE11 BE15 DB08 EF03 TB05 TC13 TC16 5F041 AA40 CA34 CA40 CA46 CA65 5F045 AA04 AB14 AB17 AC08 AC12 AD08 AD14 AF09 BB12 CA10 CA12 DA53 5F073 CA07 CB05 CB29 DA05 EA

Claims (5)

[Claims] 1. A method for growing a gallium nitride-based compound semiconductor crystal on a buffer layer by an organometallic compound vapor phase epitaxy method, wherein a general formula Ga _X Al ₁ -XN (0.5 ≦ X ≦ 1 Is grown, and then the temperature is increased to partially single-crystallize the buffer layer, and this is used as a seed crystal, and the carrier concentration is 2 × 10 ¹⁵ to 1 × 1.
A gallium nitride-based compound semiconductor crystal growth method comprising growing a gallium nitride-based compound semiconductor at 0 ¹⁹ / cm ² . 2. The method according to claim 1, wherein the buffer layer is grown on the gallium nitride-based compound semiconductor layer. 3. The method of growing a gallium nitride-based compound semiconductor according to claim 1, wherein Si or Mg is doped during the growth of the gallium nitride-based compound semiconductor layer. 4. The method for growing a gallium nitride-based compound semiconductor according to claim 1, wherein the thickness of the buffer layer is 0.2 μm or less. 5. A mobility of 8.5 to 600 cm ² / V · sec.
The gallium nitride-based compound semiconductor crystal growth method according to claim 1, wherein the gallium nitride-based compound semiconductor is grown.