JP2002367909A - Nitride semiconductor film and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor film where crystal defects existing in the nitride semiconductor layer as a lower layer is controlled to be extended to the nitride semiconductor layer as an upper layer, and a method of manufacturing the same film. SOLUTION: There are provided a method of manufacturing a nitride semiconductor film. In the method, etch pit is formed by selective etching of crystal defects existing on the upper surface of a nitride semiconductor layer, and a new nitride semiconductor layer is grown on the nitride semiconductor layer in the manner that the etch pits are not filled perfectly. Two layers of nitride semiconductor layers are laminated wherein the etch pits are formed in the side of the nitride semiconductor layer as the lower layer at the interface of two layers, and density of crystal defects of the nitride semiconductor layer as the upper layer is lower than that of the nitride semiconductor layer as the lower layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor film and a method for manufacturing the same, and further relates to a semiconductor device including the nitride semiconductor film.

[0002]

2. Description of the Related Art A GaN-based III-V compound semiconductor (hereinafter, referred to as a GaN-based semiconductor), which is a direct transition semiconductor having a band gap of 1.9 eV to 6.2 eV, emits light in a visible region to an ultraviolet region. In recent years, the development of semiconductor laser diodes (LDs) and light-emitting diodes (LEDs) has been actively carried out to enable the realization of semiconductor light-emitting elements such as light-emitting diodes (LEDs). In particular, in the field of optical recording, in order to improve the recording density of an optical disc or the like, practical use of a blue-violet semiconductor LD capable of obtaining light having a light emission wavelength of about 400 nm is required. In addition, the emission wavelength 46
A blue semiconductor LD of about 0 nm is expected to be applied to a laser display, and an ultraviolet semiconductor LD having an emission wavelength of 380 nm or less is expected to be applied to a phosphor excitation light source.

In the GaN-based semiconductor light emitting device described above, crystal defects, particularly threading dislocations propagating in the thickness direction of the film, are detrimental to a device active layer formed near the film surface. Works as a luminescence center,
It is known to impair the electrical and optical properties of the device. Therefore, in order to manufacture a GaN-based semiconductor light-emitting device, it is necessary to reduce crystal defects, particularly threading dislocations, as much as possible. In recent years, as a method for reducing crystal defects, particularly threading dislocations, ELO (Epitaxial Latera 10 vergrowth)
A method using lateral growth for epitaxial growth typified by the method is adopted. Specifically, "JP-B-6-105797", "JP-A-10-312971", "TS Zheleva et
a1., MRS Internet J. Nitride Semicond.Res.4Gl, G3.3
8 (1999) ", etc., discloses a crystal defect density reduction technique using this technique.

In the conventional GaN-based blue semiconductor laser device utilizing the lateral growth, a sapphire substrate is mainly used because there is no suitable substrate having good lattice matching with GaN. However, the sapphire substrate has poor lattice matching with GaN, has a large difference in thermal expansion coefficient, has low thermal conductivity, and is liable to have poor cleavage surface formation. There is.

As one of the promising solutions, mass production of a conductive GaN substrate and fabrication of a laser structure thereon have been proposed. "A. Usui et al., Jpn. J. Ap
pl.Phys. 36 (1997) L899 "and JP-A-10-312971, HVPE (Hydride Vapor Phase Epitaxial
Growth) using a GaN substrate. Also, an attempt to fabricate a laser structure on the GaN substrate was described in "M. Kuramoto et al., Jpn. J. App1. Phys.
38 (1999) L184 ".

However, GaN obtained by the HVPE method
When manufacturing a GaN-based blue semiconductor laser device on a substrate, the heat dissipation characteristics are better than when a sapphire substrate is used, and the end face can be formed favorably by the cleavage method. G
There is a problem that the crystal defect density is higher than the crystal defect density (the lowest case) in the aN epitaxial film.

In order to solve such a problem, it is desired to further reduce the defect of the GaN substrate obtained by the HVPE method. A GaN substrate by the HVPE method is obtained by forming a GaN thick film having a thickness of several hundred microns on a heterogeneous substrate such as a sapphire substrate or a GaAs substrate. In this case, an ELO method is used in combination to reduce the crystal defect density. Methods are known. However, the HVP is still higher than the crystal defect density (in the lowest case) of the GaN epitaxial film formed on the sapphire substrate by using the ELO method.
The crystal defect density of the GaN substrate by the E method has a high value.
Although a method using the ELO method in multiple stages is conceivable, it is practically impossible to obtain a large-area substrate due to problems such as warpage when forming a thick film. As described above, H
It has been difficult to reduce the crystal defect density of the GaN substrate obtained by the VPE method and obtain a practical GaN substrate.

Therefore, GaN obtained by the HVPE method
When growing a GaN epitaxial film on a substrate, GaN
In order to reduce the number of defects in the device by suppressing the expansion of crystal defects in the substrate to the GaN epitaxial film, it is conceivable to use the ELO method for epitaxial growth. "S. Nakamura et al., Jpn. J. App1.Phys.V
ol. 39 (2000) L647 ", a GaN-based semiconductor laser manufactured using this method has an estimated life of 1500 hours at 60 ° C., which is a sufficiently practical life.

However, as disclosed in FIG. 2 (c) of the above document, the region along the edge of the stripe-shaped mask or the upper portion of the center by the ELO method has a high crystal defect density. This is because "A. Sakai et al., Appl. Phy
s. Lett., vol. 73 p. 481 (1998) '' and `` S. Tomiya et a1.,
App1. Phys. Lett., Vol. 77 p. 636 (2000) ”, the crystal axis on the striped mask is tilted compared to the crystal axis in the window region between the masks. This is due to the occurrence of various crystal defects.

As described above, when a GaN-based film is epitaxially grown using a GaN substrate obtained by the HVPE method to manufacture a GaN-based semiconductor device such as a GaN-based semiconductor laser, the crystal defect density of the GaN substrate is reduced. This is practically difficult, and when growing a GaN epitaxial film on such a GaN substrate, Ga
Since the crystal defects of the N substrate expand or new crystal defects are generated, there is a problem that the crystal defect density is increased in the entire device.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a nitride semiconductor film in which expansion of crystal defects existing in a lower nitride semiconductor layer to an upper nitride semiconductor layer is suppressed, and a method of manufacturing the same. It is still another object of the present invention to provide a semiconductor device using the nitride semiconductor film and having a low crystal defect density over the entire surface. Another object of the present invention is a method for selectively removing crystal defects on the upper surface of a nitride semiconductor layer, and epitaxially growing a nitride semiconductor layer having a lower crystal defect density on the nitride semiconductor layer using the method. It is to provide a method.

[0012]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, selectively etched a crystal defect existing on the upper surface of the nitride semiconductor layer to form an etch pit. By growing a new nitride semiconductor layer on the nitride semiconductor layer so that the etch pits are not completely buried, the crystal defects existing in the lower nitride semiconductor layer can be removed from the upper nitride semiconductor layer. I obtained an unexpected finding that the expansion of the system can be suppressed. In a semiconductor device having a nitride semiconductor film obtained by such a method, crystal defects are reduced over the entire surface. As a result, the semiconductor device has better electrical and optical characteristics than the conventional device without impairing the electrical and optical characteristics.

The process that led to the above finding will be described in detail below. The present inventors evaluated a GaN epitaxial film epitaxially grown on a GaN substrate or a GaN thin film (hereinafter, referred to as a “lower GaN layer”) by an ELO method using a conventional method. Conventionally, to obtain such a GaN epitaxial film, the lower GaN layer is masked with a silicon oxide film, a silicon nitride film, or the like, the mask is partially removed to provide a plurality of windows, and the exposed lower GaN layer is removed. As a seed, a method has been adopted in which a GaN single crystal is epitaxially grown continuously in a direction parallel to the surface of the lower GaN layer from the seed portion, and further joined to and integrated with an epitaxially grown portion grown from an adjacent seed portion.

The present inventors have analyzed the above two-layer nitride semiconductor film and found that the lower GaN layer is partially etched at the interface between the lower GaN layer and the mask. Furthermore, the present inventors have carefully analyzed the nitride semiconductor film and found that crystal defects are selectively etched. Figure 1 shows this situation.
Is shown schematically in FIG. The present inventors have conducted intensive studies on such a phenomenon, and found that the above phenomenon is observed.
This is because the high-temperature ammonia gas or high-temperature hydrogen gas used during crystal growth selectively etched the crystal defects through the mask material because the bonding state of the crystal defects existing in the lower GaN layer was weaker than the surrounding crystals. Obtained knowledge.

Further, the present inventors have found that in the above nitride semiconductor film, although the etching amount is smaller than the crystal defects of the lower GaN layer, the thickness of the mask material is also reduced. From the analysis results, the present inventors have also obtained the knowledge that the high-temperature ammonia gas and the high-temperature hydrogen gas used for crystal growth simultaneously etch not only the crystal defects of the lower GaN layer but also the mask material.

Based on the above two findings, the present inventors
According to the following method, an unexpected finding was obtained that crystal defects existing in the lower nitride semiconductor layer can be suppressed from expanding to the upper nitride semiconductor layer. That is, such a method means that a mask material is deposited on a lower GaN layer, and a high-temperature ammonia gas or a high-temperature hydrogen gas used for crystal growth is allowed to act through the mask material, whereby the nitride semiconductor at the interface between the nitride semiconductor layer and the mask material is Selectively etch the crystal defects of the layer, and also etch the mask material with the high-temperature gas, and then add a new nitride semiconductor layer on the nitride semiconductor layer so that the etch pits are not completely filled. It is a method of growing.

The present inventors have further studied and obtained the above findings at the beginning of this section, and have completed the present invention.

That is, according to the present invention, (1) an etch pit is formed by selectively etching a crystal defect existing on an upper surface of a nitride semiconductor layer, and the etch pit is completely formed on the nitride semiconductor layer. A method of manufacturing a nitride semiconductor film, wherein a new nitride semiconductor layer is grown without being buried; (2) a mask material is deposited on the upper surface of the nitride semiconductor layer before etching, and the mask material is etched (3) The method for manufacturing a nitride semiconductor film according to (1), wherein the nitride semiconductor layer on which the mask material is deposited may be doped with an n-type or p-type impurity. The method for producing a nitride semiconductor film according to the above (2), which is a GaN crystal substrate or a GaN epitaxial film, (4) the selective etching of crystal defects is performed by a high-temperature gas. (5) The method for producing a nitride semiconductor film according to (2), wherein the high-temperature gas is a high-temperature ammonia gas and / or a high-temperature hydrogen gas. And a method of manufacturing a nitride semiconductor film.

The present invention also provides (6) a method for producing a nitride semiconductor film according to (4), wherein the mask material is also removed by using a high-temperature gas.
(6) The method for manufacturing a nitride semiconductor film according to (6), wherein the high-temperature gas is high-temperature ammonia gas and / or high-temperature hydrogen gas. (8) The mask material is a silicon oxide film or a silicon nitride film. (9) The method for manufacturing a nitride semiconductor film according to the above (2), wherein
(2) The growth of a new nitride semiconductor layer is performed under the condition that the growth rate in the direction parallel to the growth direction in the direction parallel to the growth rate in the direction perpendicular to the lower nitride semiconductor layer is higher. )).

The present invention also provides (10) a structure in which two nitride semiconductor layers are stacked, and an etch pit is formed on the lower nitride semiconductor layer side at the interface between the two layers. (11) a nitride semiconductor film characterized in that the crystal defect density in the upper nitride semiconductor layer is lower than that in the lower nitride semiconductor layer; (11) the lower nitride semiconductor layer has n-type or p-type impurities; (10) The nitride semiconductor film according to (10), which is a GaN crystal substrate or a GaN epitaxial film which may be doped, wherein the upper nitride semiconductor layer is n-type or p-type.
The nitride semiconductor film according to (11), wherein the nitride semiconductor film is a GaN layer that may be doped with a type impurity.

The present invention also provides (13) the above (10).
(14) A semiconductor device comprising the nitride semiconductor film described in (10) as a component, (14) a plurality of nitride semiconductor layers laminated on the nitride semiconductor film described in (10). (15) The semiconductor device according to (14), which is a nitride semiconductor light emitting device including a double hetero structure, (1)
6) The semiconductor device according to (15), which is a nitride semiconductor laser.

Further, according to the present invention, (17) a mask material is deposited on the upper surface of the nitride semiconductor layer, and a crystal defect of the nitride semiconductor layer at an interface between the nitride semiconductor layer and the mask material is selectively etched to perform etching. Forming a pit, then removing the mask material, and then growing a new nitride semiconductor layer on the nitride semiconductor layer so that the etch pit is not completely filled. A method for producing a nitride semiconductor film comprising a nitride semiconductor layer, (18)
Depositing a mask material on the upper surface of the nitride semiconductor layer, selectively etching crystal defects of the nitride semiconductor layer at the interface between the nitride semiconductor layer and the mask material to form etch pits, and then removing the mask material; Thereafter, a new nitride semiconductor layer is grown on the nitride semiconductor layer so that the etch pits are not completely buried. The nitride semiconductor having a lower crystal defect density is formed on the nitride semiconductor layer. (19) depositing a mask material on the upper surface of the nitride semiconductor layer and applying a high-temperature gas through the mask material to form a bond between the nitride semiconductor layer and the nitride semiconductor layer at the interface between the mask material and the mask material; A method for selectively removing crystal defects on the upper surface of the nitride semiconductor layer, characterized by selectively etching a weak portion.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, an etch pit is formed by selectively etching a crystal defect existing on an upper surface of a nitride semiconductor layer, and the etch pit is completely buried on the nitride semiconductor layer. A method of manufacturing a nitride semiconductor film including two nitride semiconductor layers, characterized in that a new nitride semiconductor layer is grown without causing the growth. In addition,
The “upper surface of the nitride semiconductor layer” refers to a surface that becomes a growth substrate when a new nitride semiconductor layer is grown on the nitride semiconductor layer.

[0024] In the present invention, a nitride semiconductor, the chemical formula _{In x Al y Ga z N (} x, y, z ≧ 1, x + y + z
= 1), it is basically based on semiconductors containing semiconductors of all compositions in which the composition ratios x, y and z are changed within the respective ranges. For example, InGaN (x = 0.4, y = 0, z =
0.6) is also included in the “nitride semiconductor”. In addition, III
Examples include those in which some of the group elements In, Al, and Ga are replaced with B (boron), and those in which some of the group V elements N are replaced with As (arsenic) or P (phosphorus). On this occasion,
Group III elements include the above three elements (In, Al, G
Any one of a) and the group V element always contain N (nitrogen). The GaN-based semiconductor is a concept included in a nitride semiconductor.

In the method for manufacturing a nitride semiconductor film according to the present invention, "etching pits are formed by selectively etching crystal defects existing on the upper surface of the nitride semiconductor layer."
As a method, a method of depositing a mask material on the upper surface of the nitride semiconductor layer, selectively etching crystal defects of the nitride semiconductor layer at the interface between the nitride semiconductor layer and the mask material, and forming etch pits is preferable. An example is given.

A nitride semiconductor layer on which a mask material is deposited, that is, a nitride semiconductor layer (hereinafter, referred to as a lower layer) which is a lower layer in a nitride semiconductor film including two nitride semiconductor layers according to the present invention.
As the “lower nitride semiconductor layer”, a substrate made of a nitride semiconductor can be mentioned. Above all, the substrate may be made of G which may be doped with n-type or p-type impurities.
It is preferable to use an aN crystal substrate, and it is more preferable to use a c-plane GaN crystal substrate doped with an n-type impurity such as Si. Further, the lower nitride semiconductor layer also includes a nitride semiconductor epitaxial film grown on a substrate having a different lattice constant or thermal expansion coefficient. The substrate having a different lattice constant or thermal expansion coefficient is not particularly limited, but may be a sapphire substrate, SiC, Si, GaAs, spinel, or ZnO.
And the like.

The material used for the mask material is not particularly limited as long as the nitride semiconductor layer does not grow on the protective film or has a property that it is difficult to grow. For example, SiO _x , SiN _x , TiN , TiO, W and the like. Above all, it is preferable to use a silicon oxide film represented by SiO _x or a silicon nitride film represented by SiN _x as a mask material.

In order to selectively etch crystal defects of the lower nitride semiconductor layer at the interface between the lower nitride semiconductor layer and the mask material to form an etch pit, the lower nitride semiconductor layer on which the mask material is deposited is used as a mask material. Through the hot gas. The part where the crystal has a defect has a weaker bonding state than the surrounding part, and thus the above processing selectively etches the crystal defect to form an etch pit.

The temperature condition of the high-temperature gas cannot be unconditionally determined because it depends on the crystal defect density of the nitride semiconductor layer and the like, but it is preferably about 100 to 2000 ° C., and about 500 ° C.
About 1500 ° C., more preferably about 700 to 1200 ° C.
C is more preferred. Instead of the high-temperature gas, a gas whose kinetic energy is increased by generating high-frequency discharge or irradiating light may be used.

It is preferable to use a high-temperature ammonia gas and / or a high-temperature hydrogen gas as the high-temperature gas.
In particular, about 900 to 1100 ° C., more preferably about 1 to about 1100 ° C.
It is more preferable to use ammonia gas and / or hydrogen gas heated to about 000 ° C.

As described above, the crystal defects of the lower nitride semiconductor layer at the interface between the lower nitride semiconductor layer and the mask material are selectively etched to form etch pits in the lower nitride semiconductor layer. Remove material. A known method may be used as a method for removing the mask material. Among them,
Similarly to the above, a method of etching a mask material with a high-temperature gas is suitably used.

Next, a new nitride semiconductor layer (hereinafter, referred to as “upper nitride semiconductor layer”) is grown on the lower nitride semiconductor layer on which the etch pits are formed. The method for growing the upper nitride semiconductor layer is not particularly limited.
For example, metalorganic vapor phase epitaxy (MOCVD), halide vapor phase epitaxy, or molecular beam evitaxy (Molecular Beam)
A known method such as the Epitaxy (MBE) method may be used. Especially, it is preferable to use the MOCVD method.

When growing the upper nitride semiconductor layer, the etch pits formed on the surface of the lower nitride semiconductor layer are not completely filled. Therefore, it is preferable that the growth of the upper nitride semiconductor layer is performed under the condition that the growth speed in the direction parallel to the growth direction in the direction perpendicular to the growth direction of the lower nitride semiconductor layer is higher. In addition,
"The etch pit is not completely filled" means that the etch pit is not completely buried and disappears, and includes not only a case where the etch pit is not completely buried but also a case where it is partially buried.

The manufacturing method according to the present invention will be described with reference to FIG.
Will be described in detail. As shown in FIG.
Semiconductor substrate or nitride semiconductor epitaxial film, etc.
A silicon oxide film or silicon film is formed on the lower nitride semiconductor layer.
A mask material such as a con nitride film is deposited. Then, this
To a hot gas, preferably ammonia (N
H ₃) Gas and / or hydrogen (H₂Exposure to gas
As a result, as shown in FIG.
The lower nitride semiconductor layer at the interface between the conductor layer and the mask material
Crystal defects such as damaged portions 23b and passing dislocations 23a
Selectively etched to form etch pits 25
You.

Further, by exposing the sample to a high-temperature gas, preferably an ammonia (NH ₃ ) gas and / or a hydrogen (H ₂ ) gas, the shape of the etch pit is increased, and at the same time, the mask material is also etched. The mask material can be eliminated (FIG. 2C). In this step, the mask material may diffuse into the lower nitride semiconductor layer. However, when the mask material is a silicon oxide film, its constituent elements silicon and oxygen act as n-type impurities in the nitride semiconductor crystal, so that only the lower nitride semiconductor layer becomes an n-type nitride semiconductor layer. There is no particular problem. When the mask material is a silicon nitride film, silicon acts as an n-type impurity in the nitride semiconductor crystal,
Since nitrogen is a constituent element of the nitride semiconductor crystal, there is no particular problem similarly to the above. Thereafter, the upper nitride semiconductor layer is epitaxially grown under a growth condition in which the lateral growth rate is faster than the vertical growth rate so that the etch pits are not completely filled. Thus, an upper nitride semiconductor layer having a low crystal defect density can be obtained.

Hereinafter, a specific embodiment of the method for manufacturing a nitride semiconductor film according to the present invention will be described in more detail with reference to FIG. Such a specific embodiment is a preferred embodiment of the method for manufacturing a nitride semiconductor film according to the present invention, but the present invention is not limited to this. After sufficiently cleaning the c-plane GaN crystal substrate 31 doped with the n-type impurity, the substrate is transported into an electron beam evaporation apparatus, and a mask material 32 made of a silicon oxide film is deposited to about 5 nm (FIG. 3A). Subsequently, the sample was subjected to MOCVD (Metal Organic Chemical V
apor Deposition (organic metal vapor phase epitaxy)
In the MOCVD furnace, while heating the sample to a temperature of about 1000 ° C., a mixed gas of ammonia (NH ₃ ) gas and hydrogen (H ₂ ) and nitrogen (N ₂ ) necessary for GaN-based epitaxial growth is simultaneously supplied. In this step, these gases penetrate through the mask material 32, thereby
Etch pits 35 are formed on N crystal substrate 31 (FIG. 3).
(B)).

Further, this process is continued until the mask material 32 is etched by the high-temperature mixed gas and disappears (FIG. 3C). At the same time that the mask material 32 almost disappears, for example, trimethylgallium ((CH ₃ ) ₃ Ga,
By flowing TMG) into the MOCVD apparatus, Ga
Initiate N epitaxial growth. At this time, the GaN epitaxial growth is performed under the condition that the lateral growth rate is high, that is, under the condition that the c-axis growth rate is low.
So that the etch pit 35 is not completely buried,
A GaN epitaxial film 34 is obtained (FIG. 3D).

As described above, the method for manufacturing a nitride semiconductor film according to the present invention has an advantage that crystal defects existing in the lower nitride semiconductor layer can be substantially prevented from expanding to the upper part. . As a result, when the method for manufacturing a nitride semiconductor film according to the present invention is used, etch pits are formed on the lower nitride semiconductor layer side at the interface between the two nitride semiconductor layers, and the crystal in the upper nitride semiconductor layer is formed. The nitride semiconductor film according to the present invention is characterized in that the defect density is lower than that in the lower nitride semiconductor layer.

The thus obtained nitride semiconductor film according to the present invention has an advantage that the crystal defect density is reduced over the entire film. In addition, since the mask material is removed, it is possible to suppress the failure of the cleavage end face at the time of cleavage in the formation of the end face due to the mask material remaining in the film. Further, in the nitride semiconductor film according to the present invention, since a nitride semiconductor substrate can be used, the conventional problem of a decrease in laser performance due to the use of substrates having different lattice constants and thermal expansion coefficients can be solved.

A semiconductor device according to the present invention is characterized by having the above nitride semiconductor film according to the present invention. The semiconductor device according to the present invention includes a semiconductor device in which a plurality of nitride semiconductor layers are stacked on the nitride semiconductor film according to the present invention. More specifically, for example, a nitride semiconductor light emitting device such as a nitride semiconductor laser or an LED, or an electron transit device such as an FET is exemplified. The semiconductor device according to the present invention may have a known structure known in the art, and can be easily manufactured by a method known per se.

As a semiconductor device according to the present invention, a nitride semiconductor laser will be specifically described below in detail with reference to FIG. The nitride semiconductor laser according to the present invention,
A GaN layer 43 having a thickness of about 2 μm is laminated on a c-plane of a substrate 41 made of GaN to which Si is added. The GaN layer 43 is made of n-type GaN to which Si is added as an n-type impurity. n-type GaN substrate 4
An etch pit 42 is formed at the interface between 1 and the n-type GaN layer 43, and is formed to prevent crystal defects in the n-type GaN substrate from expanding to the upper part.
On this n-type GaN layer 43, an n-side cladding layer 44, an n-side light guide layer 45, and an active layer 4 are formed as nitride semiconductor layers.
6, a cap layer 47, a p-side light guide layer 48, a p-side cladding layer 49, and a p-side contact layer 50 are sequentially laminated.

The n-side cladding layer 44 has a thickness of about 1 μm and is made of an n-type AlGaN mixed crystal to which Si is added as an n-type impurity. The n-side light guide layer 45 has a thickness of about 0.1 μm and is made of n-type GaN to which Si is added as an n-type impurity. The active layer 46 has a multiple quantum well (MQ) having a well thickness of about 3 nm and a barrier layer of about 4 nm.
W) It is composed of a GaInN mixed crystal having a structure. The cap layer 47 is also referred to as a deterioration prevention layer, and is provided to prevent the active layer 7 from being deteriorated when an upper structure including the p-side light guide layer is formed on the active layer 7.
It is composed of an AlGaN mixed crystal having a thickness of about 20 nm.

The p-side light guide layer 48 has a thickness of about 0.1 μm.
m, and is made of p-type GaN to which Mg is added as a p-type impurity. p-side cladding layer 49
Has a thickness of about 0.5 μm and is made of a p-type AlGaN mixed crystal to which Mg is added as a p-type impurity. Further, the p-side cladding layer 49 may have a superlattice structure including an AlGaN layer and a GaN layer. The p-side contact layer 50 has a thickness of about 0.1 μm
And the p-type impurity added Mg as a p-type impurity.
It is composed of type GaN. The upper portion of the p-side cladding layer 50 and the p-side contact layer 51 may be processed into a stripe-shaped upper mesa structure with a tapered cross section in order to confine current.

An insulating layer 51 made of an insulating material such as silicon dioxide (SiO ₂ ) and a p-side electrode 52 are formed on the p-side contact layer 50 through an opening provided in the insulating layer 51. I have. The p-side electrode 52 is formed of palladium (Pd), platinum (Pt) from the p-side contact layer 50 side.
And gold (Au) are sequentially laminated.
The p-side electrode 52 is formed in a narrow band shape (a band shape extending in a direction perpendicular to the drawing in FIG. 4) to narrow the current. Further, the n-type GaN substrate 4
1, titanium (Ti), aluminum (Al) and gold (Au) are sequentially stacked from the substrate 41 side.
A side electrode 43 is provided. Although not shown, the nitride semiconductor laser is provided with a mirror layer on a pair of side surfaces perpendicular to the length direction of the p-side electrode 52 (that is, the resonator length direction).

The method of manufacturing the nitride semiconductor laser according to the present invention will be described below. n-type GaN substrate 41
The method for growing the n-type GaN layer 43 via the etch pits 42 is the same as described above. The semiconductor film obtained in this manner is carried into a MOCVD apparatus, and under the condition that lateral growth occurs, an n-side cladding layer 44 made of n-type AlGaN, an n-side light guide layer 45 made of n-type GaN, an active layer 46, a cap layer 47, a p-side light guide layer 48 made of p-type GaN, and a p-side clad layer 4 made of p-type AlGaN
9. A p-side contact layer 50 made of p-type GaN is sequentially laminated.

As a growth material for these nitride semiconductor layers, for example, trimethyl gallium ((CH ₃ ) ₃ Ga; TMG) using group III element Ga as a raw material and group III element A
The raw material of l is trimethylaluminum ((C
H ₃ ) ₃ Al; TMAl) was used as a raw material of In as a group III raw material, and trimethyl indium ((CH ₃ ) ₃ In;
It is preferable to use ammonia (NH ₃ ) as TMIn) as a raw material of N of the group V element. As the carrier gas, for example, a mixed gas of hydrogen (H ₂ ) and nitrogen (N ₂ ) is preferably used. The dopant is, for example, monosilane (SiH ₄ ) as an n-type dopant, and bis = methylcyclopentanedienyl magnesium ((CH ₃ C ₅ H ₄ ) ₂ Mg; MeCp ₂ M as a p-type dopant.
g) or bis = cyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg; Cp ₂ Mg) is preferably used.

Next, the substrate on which the nitride semiconductor layer has been grown is removed from the MOCVD apparatus, and an insulating layer 51 made of SiO ₂ is formed on the p-type GaN contact layer 50 by, eg, CVD. Next, a resist film (not shown) is applied on the insulating layer 51, and a mask pattern corresponding to the formation position of the p-side electrode 52 is formed by photolithography. Thereafter, etching is performed using this as a mask, and the insulating layer 51 is selectively removed to form an opening corresponding to the formation position of the p-side electrode 52.

Subsequently, for example, palladium (Pd), platinum (Pt), and gold are formed on the entire surface (ie, on the p-type GaN contact layer 50 from which the insulating layer 51 is selectively removed and on the resist film (not shown)). (Au) is sequentially deposited, and a resist film (not shown) is removed together with palladium, platinum, and gold deposited on the resist film (lift-off) to form a p-side electrode 52.

Next, under the n-type GaN substrate 41, titanium, aluminum and gold are selectively vapor-deposited sequentially to form an n-type GaN substrate.
The side electrode 53 is formed. After forming the n-side electrode 53,
The substrate 41 is cleaved with a predetermined width perpendicular to the length direction (resonator length direction) of the p-side electrode 52, and a reflecting mirror layer is formed on the cleavage plane. Thus, the nitride semiconductor laser according to the present invention shown in FIG. 4 is formed. In the above manufacturing method, the growth method has been described as being limited to the MOCVD method. However, a halide vapor phase growth method and molecular beam epitaxy (Molecular Beta) are used.
am Epitaxy (MBE) method may be used.

[0050]

The present invention provides a method for growing a nitride semiconductor layer having a lower crystal defect density on a nitride semiconductor layer. By using such a method, it is possible to use a nitride semiconductor substrate which has not been used conventionally because of a high crystal defect density. As a result, conventional problems caused by using a substrate having a different lattice constant or coefficient of thermal expansion from a nitride semiconductor, such as a sapphire substrate, are eliminated, for example, degradation of device performance due to lattice mismatch or a difference in coefficient of thermal expansion. it can.

Further, in the nitride semiconductor film according to the present invention, since the crystal defects existing in the lower nitride semiconductor layer are suppressed from expanding to the upper part by the etch pits, the crystal defect density is reduced over the entire surface. It has the advantage of being able to. As a result, the semiconductor device according to the present invention using such a nitride semiconductor film has a low density of crystal defects acting as a current leak portion or a non-emission center, so that electrical or optical characteristics are improved. This has the advantage that the life of the device is extended.

Further, for example, in the production of a nitride semiconductor laser, conventionally, when forming a laser stripe,
A process of aligning a mask with a region having a low crystal defect density was required. On the other hand, in the nitride semiconductor laser including the nitride semiconductor film according to the present invention, since the crystal defect density is reduced over the entire surface, the mask alignment process is substantially unnecessary, and as a result, the nitride semiconductor Lasers can be mass-produced inexpensively.

[Brief description of the drawings]

FIG. 1. ELO on GaN substrate or GaN thin film
FIG. 2 is a schematic cross-sectional view showing an etch pit observed under a mask material in a GaN epitaxial film epitaxially grown by a method.

FIG. 2 is a schematic cross-sectional view of the nitride semiconductor film for describing a method for manufacturing a nitride semiconductor film according to the present invention.

FIG. 3 is a schematic cross-sectional view of the nitride semiconductor film for describing a specific embodiment of the method for manufacturing a nitride semiconductor film according to the present invention.

FIG. 4 is a schematic diagram of a cross section perpendicular to a cavity length direction of a nitride semiconductor laser which is a semiconductor device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 GaN substrate or GaN thin film 2 Mask material 3 Crystal defect (threading dislocation) 4 GaN epitaxial film 5 Etch pit 21 Lower nitride semiconductor layer 22 Mask material 23a Crystal defect (threading dislocation) 23b Crystal defect (damaged part) 24 Crystal defect density Lower nitride semiconductor layer 25 etch pit 31 n-type GaN substrate 32 mask material 34 GaN epitaxial film 35 etch pit 41 n-type GaN substrate 42 etch pit 43 low defect n-type GaN layer 44 n-side cladding layer 45 n-side light guide Layer 46 active layer 47 cap layer 48 p-side light guide layer 49 p-side cladding layer 50 p-side contact layer 51 insulating layer 52 p-side electrode 53 n-side electrode

Continued on the front page F term (reference) 5F004 AA16 BD04 DA00 DA24 DB00 DB03 5F045 AA02 AA04 AC08 AC12 DB09 HA03 5F073 AA13 AA74 BA06 BA09 CA07 CB02 CB22 DA05 DA21

Claims (19)

[Claims] An etching pit is formed by selectively etching a crystal defect present on an upper surface of a nitride semiconductor layer, and a new etching pit is not completely buried on the nitride semiconductor layer. A method for manufacturing a nitride semiconductor film, comprising growing a nitride semiconductor layer. 2. The method according to claim 1, wherein a mask material is deposited on the upper surface of the nitride semiconductor layer before the etching, and the mask material is removed after the etching. 3. A nitride semiconductor layer on which a mask material is deposited, wherein the nitride semiconductor layer may be doped with an n-type or p-type impurity.
3. The method for producing a nitride semiconductor film according to claim 2, wherein the method is an aN crystal substrate or a GaN epitaxial film. 4. The method for producing a nitride semiconductor film according to claim 2, wherein the selective etching of the crystal defects is performed by using a high-temperature gas. 5. The high-temperature gas is a high-temperature ammonia gas and / or a high-temperature hydrogen gas.
3. The method for producing a nitride semiconductor film according to 1. 6. The method of manufacturing a nitride semiconductor film according to claim 4, wherein the mask material is removed by using a high-temperature gas. 7. The high-temperature gas is a high-temperature ammonia gas and / or a high-temperature hydrogen gas.
3. The method for producing a nitride semiconductor film according to item 1. 8. The method for manufacturing a nitride semiconductor film according to claim 2, wherein the mask material is a silicon oxide film or a silicon nitride film. 9. The growth of a new nitride semiconductor layer is performed under the condition that the growth rate in a direction parallel to the direction perpendicular to the lower nitride semiconductor layer is faster than the growth rate in a direction perpendicular to the lower nitride semiconductor layer. The method for producing a nitride semiconductor film according to claim 2. 10. A structure in which two nitride semiconductor layers are stacked, wherein an etch pit is formed on a lower nitride semiconductor layer side at an interface between the two layers, and A nitride semiconductor film having a crystal defect density lower than that of a lower nitride semiconductor layer. 11. The nitride semiconductor film according to claim 10, wherein the lower nitride semiconductor layer is a GaN crystal substrate or a GaN epitaxial film which may be doped with n-type or p-type impurities. . 12. The nitride semiconductor film according to claim 11, wherein the upper nitride semiconductor layer is a GaN layer that may be doped with an n-type or p-type impurity. 13. A semiconductor device comprising the nitride semiconductor film according to claim 10 as a component. 14. The semiconductor device according to claim 13, wherein a plurality of nitride semiconductor layers are stacked on the nitride semiconductor film according to claim 10. 15. The semiconductor device according to claim 14, which is a nitride semiconductor light emitting device having a double hetero structure. 16. A nitride semiconductor laser.
3. The semiconductor device according to claim 1. 17. A mask material is deposited on an upper surface of the nitride semiconductor layer, and a crystal defect of the nitride semiconductor layer at an interface between the nitride semiconductor layer and the mask material is selectively etched to form an etch pit. Removing a material, and then growing a new nitride semiconductor layer on the nitride semiconductor layer such that the etch pits are not completely buried. Of manufacturing a semiconductor film. 18. A mask material is deposited on an upper surface of the nitride semiconductor layer, and a crystal defect of the nitride semiconductor layer at an interface between the nitride semiconductor layer and the mask material is selectively etched to form an etch pit. Removing a material, and then growing a new nitride semiconductor layer on the nitride semiconductor layer so that the etch pits are not completely buried. To grow a nitride semiconductor layer having a low density. 19. A mask material is deposited on the upper surface of the nitride semiconductor layer, and a high-temperature gas is applied through the mask material to select a portion of the interface between the nitride semiconductor layer and the mask material where the bonding of the nitride semiconductor layer is weak. A method for selectively removing crystal defects on the upper surface of a nitride semiconductor layer, characterized by selectively etching.