JP2000068559A - GaN GROUP CRYSTAL MATERIAL AND MANUFACTURE THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN group crystal material which is formed with few dislocations and few cracks and a method of manufacturing the same. SOLUTION: A masking layer 3 is provided on the surface of a base substrate B so as to form a masked region and an unmasked region 4. The masked layer is formed of a material where a GaN group crystal cannot substantially grow. A first GaN crystal layer 1 is grown until it covers the masking layer 3 using the unmasked region 4 as a start point of crystal growth, and a second GaN group crystal layer 2 is grown thereon to provide a GaN group crystal material. At this time, the layer 1 substantially includes no aluminum. Also, the layer 2 includes a part wherein a composition of A1 increases as the distance from the interface with the layer 1 increases. It is preferable that the initial value of the composition of A1 is 0.01 or less, substantially zero at a portion where the composition of A1 of the layer 2 increases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to a technical field for obtaining a GaN-based crystal base material used for a semiconductor light-emitting device (GaN-based light-emitting device) using a GaN-based crystal, and particularly has an Al composition. It relates to a GaN-based crystal.

[0002]

2. Description of the Related Art In recent years, GaN-based light emitting devices have been actively researched with the opportunity of realizing high-intensity light emitting diodes (LEDs), and reports of room-temperature continuous oscillation of semiconductor lasers have been heard. It has become. For example, high brightness LED
Green and blue, and a semiconductor laser (LD) achieves purple.

[0003] Conventionally, InGaN is often used as a material of a light emitting portion of a GaN-based light emitting device. The light emitting portion is, for example, a depletion layer portion of a pn junction or an active layer having a double hetero junction structure in an LED, and a stripe portion of a stripe structure in an LD. InGaN is a material that can emit light of a short wavelength from green to blue and can obtain high luminous efficiency.

[0004] However, with an increase in the density of information signal transmission and recording, a GaN-based light emitting device is required to emit light having a shorter wavelength from blue light to ultraviolet light.
For that purpose, as a material of the light emitting part, InGaN is
It is necessary to reduce the n composition and approach GaN. Along with this, surrounding layers such as a cladding layer confine carriers, transmit light (in the case of LED), and confine light (LD).
), And so on. Therefore, the surrounding layer must be formed of a material having a larger band gap than the light emitting portion, that is, a material having an increased Al composition such as AlGaN (referred to as an AlGaN-based material).

On the other hand, a general method of fabricating a GaN-based light-emitting device is to use a single crystal of sapphire as a crystal substrate, grow various GaN-based crystal layers thereon via a buffer layer, and form a desired GaN-based crystal. That is, a crystal layer is used as a light emitting unit. However, in the GaN-based crystal layer grown by such a method, dislocations due to lattice mismatch with the crystal substrate and the like exist at high density. The dislocation is inherited upward even when the GaN-based crystal grows and the thickness increases, and becomes a continuous defect portion called a dislocation line (threading dislocation), thereby impairing the characteristics of the device.

On the other hand, there has been reported a method for obtaining a low dislocation GaN crystal using a mask layer. Hereinafter, this method will be referred to as a “mask method” and described. The mask method is
As shown in FIG. 2A, first, a material (Si) on which a GaN-based crystal cannot grow
The mask layer 20 made of O ₂ or the like is formed by drawing a specific pattern. Then, a region (non-mask region) 10a where the mask layer 20 is not formed on the base substrate
Is used as a starting surface to grow a GaN-based crystal. If the crystal growth is continued even after the crystal has grown to the height of the mask layer 20, the GaN-based crystal grows not only in the thickness direction but also in the lateral direction along the upper surface of the mask layer 20, as shown in FIG.
As shown in (b), the mask layer 20 is embedded and covered with G.
It becomes the aN-based crystal layer 30. At this time, the GaN-based crystal layer 3
In 0, for example, a low dislocation portion with little propagation of dislocation lines is formed in a specific portion such as the portion 30a above the mask layer.

[0007]

However, when attempting to grow an AlGaN-based material by the mask method, a large amount of the AlGaN-based material starts from the upper surface of the mask layer on the assumption that a GaN-based crystal cannot be grown. There is a problem that the crystal grows crystallographically, the masking process is not achieved, and the crystal quality deteriorates.

[0008] This is because Al is very active and the diffusion length of Al reactive species on the mask layer is short, so that it easily reacts with SiO _{2 of} the mask material, and other reactive species on the mask layer. This is considered to be due to the fact that the nucleus easily reacts with and accumulates, and a portion serving as a nucleus for crystal growth is easily generated on the mask layer.

In the conventional mask method, when growing an AlGaN-based crystal, a GaN surface layer is first placed on a sapphire substrate with a thickness of several μm via a buffer layer in order to improve the crystallinity.
The base substrate is grown by growing AlG on the base substrate.
Usually, an aN-based crystal layer is grown. However, in such a method, even if the crystallinity is improved, the difference in the thermal expansion coefficient between the GaN crystal and the AlGaN-based crystal and the increase and decrease in the temperature repeated until the entire device is completed are caused by these differences. There is a problem that cracks occur in one or both of the layers.

An object of the present invention is to solve the above-mentioned problems and to provide an AlGa film formed in a state of low dislocations and few cracks.
An object of the present invention is to provide a GaN-based crystal substrate having an N-based crystal layer, and to provide a method for producing the same.

[0011]

Means for Solving the Problems The GaN-based crystal base material of the present invention and the method for producing the same have the following features. (1) A mask layer is provided on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region, and the mask layer is substantially Ga from its own surface.
A first GaN-based crystal layer, which is made of a material in which an N-based crystal cannot grow, and is grown to cover the mask layer using a non-mask region as a starting point of crystal growth, and a second Ga layer grown thereon.
A first GaN-based crystal layer, wherein the first GaN-based crystal layer has an Al composition of substantially 0, and the second GaN-based crystal layer has a layer from a boundary with the first GaN-based crystal layer. A GaN-based crystal base material comprising a layered portion in which the Al composition increases as the thickness increases.

(2) The GaN-based crystal base material according to (1), wherein the initial value of the Al composition in the portion where the Al composition of the second GaN-based crystal layer increases is 0.01 or less.

(3) The formation pattern of the mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the strip-shaped mask layer is the first GaN-based crystal layer. The GaN-based crystal substrate according to the above (1), which extends in the <1-100> direction with respect to

(4) The GaN-based crystal substrate according to (1), wherein the first GaN-based crystal layer is a GaN crystal layer, and the second GaN-based crystal layer is an AlGaN crystal layer.

(5) A method for producing a GaN-based crystal substrate according to any one of the above (1) to (4),
A mask layer is provided on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region, and the material of the mask layer can be grown substantially from its own surface. GaN-based crystal is grown using a non-mask region as a starting point for crystal growth, and the Al composition is substantially zero until the GaN-based crystal covers the mask layer.
A method of manufacturing a GaN-based crystal base material, comprising a step of forming, after the GaN-based crystal covers a mask layer, a portion where the Al composition increases as the thickness of the GaN-based crystal layer increases.

(6) The manufacturing method according to the above (5), wherein the Al composition is increased by setting the initial value of the Al composition to 0.01 or less when forming the portion where the Al composition increases.

In the present invention, “GaN-based” refers to In _x G
a _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1,
X + Y + Z = 1). Therefore, “AlGaN-based” in the above equation is 0 <Z ≦ 1.

In the present specification, if a lattice plane of a hexagonal lattice crystal such as a GaN-based crystal or a sapphire substrate is specified by four Miller indices (hkil), for convenience of description, when the index is negative, the index is negative. Is indicated with a minus sign in front of, and the general notation method of the Miller index is used except for the notation method regarding the negative exponent. Therefore, in the case of a GaN-based crystal, there are six prism surfaces (singular surfaces) parallel to the C axis. For example, one of the surfaces is expressed as (1-100), and the six surfaces are grouped as equivalent surfaces. In this case, it is described as {1-100}. Also, planes perpendicular to the {1-100} plane and parallel to the C axis are equivalently collectively denoted as {11-20}. Also, (1-1)
The direction perpendicular to the (00) plane is [1-100], and the set of directions equivalent thereto is <1-100>. The direction perpendicular to the (11-20) plane is [11-20]. The set is described as <11-20>. However, if there is a case where the Miller index is written in the drawing, if the index is negative, the index is indicated by adding a minus sign to the index, and all of the general Miller index notations are followed. The crystal orientations referred to in the present invention are all orientations based on a GaN-based crystal grown on a base substrate.

The "mask region" (ie, the masked region) and the "unmasked region" (ie, the unmasked region) are both regions in the base substrate plane. The region on the upper surface of the mask layer is regarded as being equal to the mask region, and is used in the description as synonymous.

[0020]

When growing a GaN-based crystal using the mask method, the first GaN-based crystal layer covers A until the first GaN-based crystal layer covers the mask layer.
By setting the 1 composition to substantially 0, the polycrystal growth of the crystal on the mask layer is suppressed, a good process of the mask method is achieved, and a low dislocation crystal portion is obtained. After the crystal has covered the mask layer, cracks are formed by providing a portion for increasing the Al composition to a small value of 0.01 or less, preferably substantially from 0 as the layer thickness increases. The AlGaN-based crystal layer having a preferable quality and having suppressed Al is obtained. Hereinafter, a material in which the Al composition is substantially zero will be referred to as GaN, and a material in which the Al composition is increased will be referred to as AlGaN. However, an appropriate In composition may be added to the materials described above.

In order to reduce the occurrence of cracks, it is preferable to reduce the thickness of the GaN crystal covering the mask layer as much as possible. Therefore, in the present invention, it is a preferable embodiment that the Al composition starts increasing when the GaN crystal covers the mask layer.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a GaN-based crystal substrate according to the present invention will be described, and a method of manufacturing the same will be described. As shown in FIG. 1, the GaN-based crystal base material according to the present invention includes a base substrate B, a mask layer 3, a first GaN-based crystal layer (hereinafter, “first layer”) 1, and a second GaN-based crystal layer ( Below, "second layer")
And 2. The mask layer 3 is provided on the substrate surface of the base substrate B so as to form a mask region and a non-mask region 4. The first layer 1 is a layer grown to cover the mask layer using the non-mask region 4 as a starting point for crystal growth.
The composition is substantially zero. The second layer 2 is a layer grown on the first layer 1. The second layer 2 has a structure in which a portion where the Al composition increases as the thickness of the layer increases from a boundary with the first layer 1 to a portion having a predetermined thickness.

The base substrate may be any substrate as long as the GaN-based crystal can grow with the C axis in the thickness direction, and examples thereof include sapphire, quartz, and SiC. Above all, a C-plane, an A-plane of sapphire, and a 6H-SiC substrate, particularly a C-plane sapphire substrate are preferable.

Further, the above substrate is used as a basic crystal substrate,
A substrate provided with a buffer layer on its surface may be used as a base substrate. As the material of the buffer layer, a known material may be used.However, the first layer and the second layer have a smaller thermal expansion coefficient difference to suppress the occurrence of cracks, and also, when a light emitting element is formed, absorb light. Al _X Ga _1-X N
(0 <x ≦ 1) is preferable.

Further, at least the surface layer of the base substrate is G
It may be an aN-based crystal layer. For example, as shown in FIG. 1, a GaN-based crystal layer B3 is grown as a surface layer on a surface of a base crystal substrate B1 such as sapphire via a buffer layer B2, and is used as a base substrate B.

The mask layer is substantially free from its own surface.
A material that does not allow the GaN-based crystal to grow is used. This
Such materials include SiO_Two, SiNx, TiO_Two, Z
rO _TwoAnd the like. Also, the laminated structure of these materials
It is also possible.

The mask layer may be formed in any shape, such as a circle, an ellipse, a star, a hexagon, or the like, having an opening, or a strip, but may be formed in any shape. This is an important factor that has a significant effect on how the line propagates. In particular, the direction of the boundary between the mask region and the non-mask region is important. Next, the direction of this boundary line will be described.

(A) When the boundary between the mask region and the non-mask region is a straight line in the <1-100> direction, Ga that grows in the lateral direction along the upper surface of the mask layer beyond this boundary.
The plane of the N-based crystal is a {11-20} plane. ｛11-2
Face 0 is off-facet, so facet {1}
The GaN-based crystal grows faster in the lateral direction than the -100 ° plane. When the lateral growth rate increases, ｛1-10
It is difficult to form oblique facets such as the 1 ° plane. As a result, the thickness of the GaN-based crystal layer when the mask layer is buried flat can be made smaller than in the case of (b) below. In this case, threading dislocations propagate as they are in the C-axis direction, and low dislocations occur above the mask layer.

(B) When the boundary between the mask region and the non-mask region is a straight line in the <11-20> direction, the facet {1-100} plane grows laterally beyond this boundary. And the growth rate in the lateral direction is reduced. Since the growth rate in the C-axis direction is faster than the lateral growth rate,
An oblique facet such as a 101 ° plane is easily formed, and a pyramid shape is first formed and then flattened. As a result, the GaN-based crystal layer needs to have a certain thickness to bury the mask layer flat. In this case, threading dislocations propagate toward the upper side of the mask layer, and low dislocations occur above the non-mask region.

A stripe pattern is an example of a pattern that remarkably exhibits the effect of the mask layer formation pattern. The striped pattern is a pattern in which strip-shaped mask layers are arranged in a striped manner, and strip-shaped mask areas and strip-shaped non-mask areas are alternately arranged. The longitudinal direction of this band is the direction of the boundary between the mask region and the non-mask region. Hereinafter, a case where the mask layer is formed in a stripe pattern will be described.

The thickness of the mask layer is usually 50 nm to 500 nm.
About nm is preferable. When the formation pattern of the mask layer is a stripe pattern, the width of each band-shaped mask layer is preferably about 0.1 μm to 10 μm, and the width of the band-shaped mask layer and the width of the band-shaped non-mask region are different. The ratio etc.
A conventional mask method may be referred to.

By applying the mask method, the first layer (Al composition
0), the crystal growth method for growing the second layer is HVP
E, MOCVD, MBE, etc. are preferred. When forming a thick film, the HVPE method is preferable, but when forming a thin film, the MOCVD method is preferable.

As the growth atmosphere gas when the mask method is applied, hydrogen, nitrogen, argon, helium, etc. can be used. Hydrogen and nitrogen are desirable for control.

When the growth is performed in a hydrogen atmosphere, the growth rate in the C-axis direction increases. In combination with the stripe pattern, the longitudinal direction of the mask layer is set to <11-2.
In the case of the <0> direction, the thickness is more remarkably required to embed flat. On the other hand, the longitudinal direction of the mask is set to <11−
20> direction, in order to embed flat,
It can be thinner than in the case of the <1-20> direction.

When the growth is performed in a nitrogen atmosphere, the growth rate in the C-axis direction is lower than in the hydrogen atmosphere, so that the growth rate in the lateral direction is relatively higher, and the first layer is thinner on the mask layer. It will be covered in stages. When the longitudinal direction of the mask layer is the <1-100> direction, this effect is remarkable.

By changing the growth conditions in this way, the buried thickness and the low dislocation region forming portion can be controlled, so that the degree of freedom in device design increases. In the present invention, the first layer is preferably as thin as possible because it is better to reduce the difference in thermal expansion coefficient between the first layer and the second layer and suppress the occurrence of cracks. Therefore, the conditions for applying the mask method include:
The longitudinal direction of the mask is set to the <1-100> direction, and the MO
The optimal condition is to use a CVD method and use a nitrogen-rich gas as the atmosphere during crystal growth.

Since the first layer continues to grow in the thickness direction while growing laterally along the upper surface of the mask layer,
The thickness T of the first layer at the moment when the top surface of the mask layer is covered
The (thickness in the non-mask region with respect to the upper surface of the base substrate B) depends on the lateral growth rate of the first layer and the width W of the mask layer. Therefore, the width W of the mask layer
, The value of the thickness T itself decreases, but the ratio of the thickness T of the first layer to the width W of the mask layer can be further reduced according to the above conditions. .

The material of the first layer is a GaN-based material In _x Ga
Of _Y Al _Z N, Al composition may be any of substantially 0. As described below, the second layer is preferably made of AlGaN, in which case the lowermost portion of the second layer is GaN. Therefore, it is preferable that the material of the first layer be GaN in order to reduce the difference in thermal expansion coefficient between the first layer and the second layer.

Since it is preferable that the first layer is as thin as possible, it is preferable that the second layer be formed as soon as the first layer covers the mask layer. The thickness of the first layer (the thickness T in the non-mask region with reference to the upper surface of the base substrate in FIG. 1) may be determined by selecting the width of the mask layer and the crystal growth conditions described above. The thickness is preferably 0.1 μm to 3 μm or less from the viewpoints that cracks do not occur and light absorption does not occur.

The second layer may be made of an AlGaN-based material, but from the viewpoint of suppressing light absorption and reducing the difference in thermal expansion coefficient,
Al _x Ga ₁ -xN (0 <x ≦ 1) is most preferred. The portion where the Al composition increases in the second layer may be secured in the second layer at least on the interface side with the first layer. For example, from the interface with the first layer, the Al composition increases in a predetermined thickness up to a predetermined thickness, and the Al composition is constant or decreases or fluctuates from that portion, and the Al composition increases over the entire thickness of the second layer. May be increased.

The Al composition in the second layer can be increased continuously or steplessly until a desired composition ratio is obtained.
Stepwise Al for each layer obtained by further dividing the second layer into an arbitrary number of layers
The composition may be increased. In any case, the degree of increase in the Al composition may be arbitrarily selected, such as linear or curved. As a method of growing a crystal while continuously and steplessly increasing the Al composition of the second layer, MO is used.
CVD, MBE, etc. are mentioned.

The initial value of the Al composition in the portion where the Al composition of the second layer increases, that is, the initial Al composition when the second layer starts growing on the first layer, is determined by the thermal expansion of the first layer. In order to make the coefficient difference smaller, it is preferable to set the composition ratio to 0.01 or less, particularly to substantially 0. Therefore, a GaN crystal is grown as the first layer, and the second layer starts growing from the GaN crystal.
A combination that increases the Al composition until the composition becomes N is most preferable.

The first layer and the second layer may be configured such that the raw material supply is switched on the spot in the same crystal growth apparatus and no clear interface is provided. Further, the crystal growth method of the first layer and the second layer may be changed according to the purpose.

[0044]

Example 1 In this example, a GaN-based crystal base material in which the first layer was GaN and the second layer was AlGaN was manufactured. [Formation of Base Substrate] As shown in FIG.
On the surface substrate B1, an AlGaN low-temperature buffer layer B2 was grown, and then an n-type Al _0.1 Ga _0.9 N layer B3 was grown at 2 μm to obtain a base substrate B.

[Formation of Mask Layer] An SiO ₂ mask layer m was formed on the substrate surface of the base substrate B by a sputtering apparatus. The formation pattern of the SiO ₂ mask layer was stripe-shaped, and the longitudinal direction of each strip-shaped mask layer was formed so as to be in the <1-100> direction of the crystal of the base substrate surface layer B3. The thickness of the mask layer is 0.1 μm, the width of the mask layer is 4 μm, and the width of the non-mask region is 4 μm.

[Formation of First Layer] This sample was placed in a MOCVD apparatus, and the temperature was raised to 1000 ° C. in a nitrogen atmosphere, TMG, ammonia, and silane were allowed to flow for 30 minutes. The n-GaN layer was grown as the first layer 1. When the growth was continued until the mask layer was covered with GaN, the thickness of the first layer from the top surface of the base substrate in the non-mask region was 1.8 μm.

[Formation of Second Layer] Next, in addition to TMG, ammonia and silane, the flow rate of TMA was set to an initial value of 0 so that the Al composition changed from 0 to 0.2 over the entire layer thickness. The flow rate of TMA is increased and the total layer thickness is set to 3 so that the surface of the second layer becomes Al _0.2 Ga _0.8 N near the surface.
μm to form a second layer.
A base crystal base material was obtained.

The AlGaN crystal of the second layer had a low dislocation region above the mask layer. No crack was observed in the 2-inch wafer surface.

Example 2 In this example, a light-emitting portion was further formed on the GaN-based crystal base material obtained in Example 1 above, and ultraviolet light (370 nm) was formed.
A light emitting device was manufactured. [Formation of DH Structure] The second layer of the GaN-based crystal substrate obtained in Example 1 was used as an n-type cladding layer, and an InGaN layer was formed as an active layer on the surface thereof to a thickness of 50 nm. Subsequently, an Al _0.2 Ga _0.8 N layer was added as a p-type cladding layer to a thickness of _0.1 μm.
1 μm was formed.

[Formation of Electrodes, etc.] On the p-type cladding layer, a p-type Al _0.05 Ga _0.95 N
μm was grown. Forming a p-type electrode on the contact layer,
In addition, the n-type cladding layer (GaN
The second layer of the base crystal base material) was partially exposed to form an n-type electrode, thereby completing the LED.

[Evaluation] This LED was mounted on a To-18 stem base, and the output was measured.
1 mW at 20 mA was obtained.

[0052]

According to the present invention, an AlGaN-based crystal layer (second layer) with low dislocation and few cracks can be obtained. Therefore, if a light emitting element that emits light in the ultraviolet region is configured using the base material, the second layer transmits light (in the case of an LED),
It can be preferably used as a cladding layer that plays a role of confining light (in the case of LD).

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a GaN-based crystal base material according to the present invention. In the figure, the crystal substrate is partially enlarged, and only the mask layer is hatched.

FIG. 2 is a diagram schematically showing how a GaN-based crystal grows by a mask method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First layer 2 Second layer 3 Mask layer 4 Non-mask area B Base substrate

Continued on the front page (72) Inventor Yoichiro Ouchi 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industry Co., Ltd. Itami Works (72) Inventor Masahiro Koto 4-3-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Inside the Itami Works (72) Inventor Kazumasa Hiramatsu 1-4-4, Shibata, Yokkaichi-shi, Mie Prefecture F-term (reference) 4G051 BB05 BC13 HA09 4G077 AA03 BE15 BE47 DB08 EE07 EF01 EF03 TB05 TC13 UA09 5F041 AA03 AA11 CA40 CA23 CA40 CA40 CA74 CB05 5F045 AA04 AA19 AB14 AB17 AB18 AB32 AC01 AC08 AC12 AD14 AF02 AF04 AF09 AF13 AF20 BB12 CA10 DA53 DA58

Claims (6)

[Claims] A mask layer is provided on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region, and the mask layer is substantially GaN-based crystal from its own surface. Is composed of a material that cannot grow, and a first GaN-based crystal layer grown to cover the mask layer using the non-mask region as a starting point for crystal growth, and a second GaN-based crystal layer grown thereon. The first GaN-based crystal layer has an Al composition of substantially 0, and the second GaN-based crystal layer has a thickness increasing from the boundary with the first GaN-based crystal layer. A GaN-based crystal base material comprising a layered portion having an increased Al composition. 2. The GaN-based crystal base material according to claim 1, wherein the initial value of the Al composition in a portion where the Al composition of the second GaN-based crystal layer increases is 0.01 or less. 3. A pattern for forming a mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the strip-shaped mask layer is the first G
The GaN-based crystal substrate according to claim 1, wherein the GaN-based crystal substrate extends in the <1-100> direction with respect to the aN-based crystal layer. 4. The GaN-based crystal base material according to claim 1, wherein the first GaN-based crystal layer is a GaN crystal layer, and the second GaN-based crystal layer is an AlGaN crystal layer. 5. The G according to claim 1, wherein
A method for manufacturing an aN-based crystal base material, comprising: providing a mask layer on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region; A material that does not allow the GaN-based crystal to grow substantially from its own surface. The GaN-based crystal is grown using the non-mask region as a starting point for crystal growth. The Al composition is maintained until the GaN-based crystal covers the mask layer. A GaN-based crystal, wherein the GaN-based crystal covers the mask layer and forms a portion where the Al composition increases as the thickness of the GaN-based crystal layer increases. A method for manufacturing a substrate. 6. The method according to claim 5, wherein, when forming the portion where the Al composition is increased, the initial value of the Al composition is set to 0.01 or less to increase the Al composition.