JP2000114599A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high yield and reproducible crystal growth of a group III-V nitride single crystal compound semiconductor layer on a substrate of a different material system with good crystallinity on a substrate of a different material. The present invention provides a semiconductor light emitting device having high quality and high reliability and realizing planar light emission using the same. SOLUTION: A group III-V nitride-based semiconductor light-emitting device comprises:
A plurality of single crystal semiconductor growth layers made of at least one kind of II-V nitride-based compound semiconductor material are laminated on a substrate made of a constituent material other than the III-V nitride-based material. It has a laminated structure. The bulk lattice constant a ₁ of the first growth layer closest to the substrate in the stacked structure and the bulk lattice constant a of the second growth layer having the largest thickness in the stacked structure ₂ satisfies the relationship a ₂ <a ₁ ≦ 1.005a ₂ when the coefficient of thermal expansion of the substrate is larger than the coefficient of thermal expansion of these layers, and the coefficient of thermal expansion of the substrate is If the coefficient of thermal expansion is smaller than 0.95, the relationship 0.995a ₂ ≦ a ₁ <a ₂ is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device made of a group III-V nitride compound semiconductor material.

[0002]

2. Description of the Related Art In recent years, high-luminance blue light-emitting diodes using III-V nitride-based compound semiconductor materials, for example, GaN-based compound semiconductor materials, have been commercialized.
Group nitride-based compound semiconductor materials are greatly expected as constituent materials of light emitting devices.

In general, the crystal growth of a group III-V nitride compound semiconductor material layer is performed by a hydride vapor phase epitaxy (HVP).
E), metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or the like.
On the other hand, as a substrate on which a group III-V nitride compound semiconductor material is grown, a substrate made of a constituent material other than the group III-V nitride compound semiconductor material, for example, a sapphire substrate or a SiC substrate is used. . Ideally, the substrate for crystal growth is originally composed of the same material system as the grown film, but it is difficult to obtain a large-area single-crystal substrate of a III-V nitride-based compound semiconductor material. Therefore, a substrate made of such a heterogeneous material system is used.

[0004]

SUMMARY OF THE INVENTION On the GaN layer, AlG
When growing a hetero-grown layer made of aN or InGaN, unlike a case of growing a group III-V compound semiconductor layer other than nitride, a grown film having a thickness exceeding the critical film thickness obtained from the calculation is obtained. Coherent growth (i.e., growth with the lattice constant in the growth plane coincident),
It has been reported so far (for example, Mat. Res. Soc. Sy.
mp. Proc., Vol. 449, p. 1143).

However, when a substrate made of a material other than III-V nitride, such as a sapphire substrate or a SiC substrate, is used, the distance between the substrate and the III-V nitride-based compound semiconductor layer grown thereon is increased. Due to the large lattice mismatch of
A single-crystal III-V nitride-based compound semiconductor layer cannot be satisfactorily grown directly on a substrate. In such a case, a non-single crystal buffer layer is first grown on the substrate,
On this buffer layer, a III-V nitride-based single crystal compound semiconductor layer is grown (for example, Japanese Journey).
nal of Applied Physics, Vol. 30, page L1705).

Further, the effect of the relationship between the coefficient of thermal expansion between the substrate and the grown film on the lattice constant has been reported so far (for example, Journal of the Japan Society for Crystal Growth, Vol. 23, No. 49).
See page.)

In general, a sapphire substrate has a larger coefficient of thermal expansion than a group III-V nitride compound semiconductor layer such as GaN. For this reason, the GaN single crystal film grown on the sapphire substrate via the buffer layer as described above has a growth direction at a temperature lower than the crystal growth temperature.
A compressive stress is applied in an in-plane direction (a-axis direction) perpendicular to the (c-axis direction), and the lattice constant in the in-plane direction becomes smaller than the bulk lattice constant. On the other hand, the SiC substrate has a smaller coefficient of thermal expansion than the group III-V nitride compound semiconductor layer. Therefore, the GaN single crystal film grown on the SiC substrate by the above method is pulled at a temperature lower than the crystal growth temperature in an in-plane direction (a-axis direction) perpendicular to the growth direction (c-axis direction). Under the stress, the lattice constant in the in-plane direction becomes larger than the bulk lattice constant. In the specification of the present application, the term “bulk lattice constant” is not a lattice constant value in a state of being incorporated in an element structure and being strained, but an original lattice constant value of a material in a state formed without distortion. Point to.

Further, in many cases, an active layer used for manufacturing a semiconductor light emitting device is formed of an IGaN layer such as an InGaN layer.
A layer containing n is used. Since InGaN has a larger bulk lattice constant than GaN, InGaN particularly has a thermal expansion coefficient of III.
-Growing a GaN single crystal film on a substrate (for example, a sapphire substrate) larger than a group V nitride-based compound semiconductor layer by the method described above, and further forming an active layer containing In (for example,
When a GaN active layer is grown, the lattice mismatch in the in-plane direction of the active layer with respect to the GaN single crystal film becomes larger than that in the bulk crystal. This is because the GaN single crystal film receives compressive stress from the substrate at a temperature lower than the crystal growth temperature, and the lattice constant in the in-plane direction becomes smaller than the bulk lattice constant. For this reason, in order to obtain an active layer having good crystallinity, the active layer must be formed into a thin film (for example, in the case of In _0.3 Ga _0.7 N, a thickness of several nm is used, depending on the In concentration). Sa). The efficiency of incorporation of In into such a thin InGaN active layer is lower than that of an InGaN layer grown under the same conditions on a GaN film grown on a GaN single crystal substrate. Further, In is not uniformly taken into the InGaN active layer, and a part having a high In concentration and a part having a low In concentration are mixed in the active layer. As a result, the semiconductor light-emitting device manufactured as described above emits light in the form of a collection of bright spots, and an element exhibiting planar light emission cannot be obtained.

On the other hand, a GaN single crystal film is grown on a substrate (for example, a SiC substrate) having a smaller coefficient of thermal expansion than a group III-V nitride compound semiconductor layer by the above-described method, and further an In Active layer containing (for example, InGaN active layer)
Is grown, the lattice mismatch in the in-plane direction of the active layer with respect to the GaN single crystal film is smaller than that in the bulk crystal. This is because the GaN single crystal film receives tensile stress from the substrate at a temperature lower than the crystal growth temperature, and the lattice constant in the in-plane direction becomes larger than the bulk lattice constant.
However, also in this case, the underlying GaN single crystal film is subjected to lattice distortion, and a high quality GaN single crystal film cannot be obtained. Therefore, the InGaN active layer grown on the GaN film has a high quality. It is difficult to form.

[0010] In the crystal growth by the method as described above, a slight shift in the growth conditions changes the mixed crystal ratio and the lattice mismatch of the active layer.
The GaN active layer cannot be grown.

As an attempt to solve such a problem, Japanese Patent Application Laid-Open No. 8-264833 describes that an InGaN buffer layer having a lattice constant close to the lattice constant of an AlInGaN active layer is grown on a sapphire substrate. That is,
It is intended to reduce the lattice distortion of the active layer by making the lattice constants of the active layer and the buffer layer close to each other.
However, when a group III-V nitride based single crystal semiconductor layer is grown on a substrate other than a nitride, the lattice strain is mainly caused by a difference in thermal expansion coefficient between the substrate and the single crystal epitaxial growth layer. Lattice distortion cannot be sufficiently removed only by improving the layer, and it is still difficult to obtain a high-quality InGaN active layer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to form a group III-V nitride single crystal compound semiconductor layer on a substrate of a material different from the above. It is an object of the present invention to provide a semiconductor light emitting device which has high crystal quality and high reproducibility and has high quality and high reliability and realizes planar light emission by using the crystal growth with good crystallinity and good yield.

[0013]

According to the present invention, there is provided a group III-V nitride semiconductor light emitting device comprising a plurality of single crystal semiconductor growth layers comprising at least one kind of group III-V nitride compound semiconductor material. A laminated structure which is formed by being laminated on a substrate made of a constituent material other than the III-V nitride-based material, wherein the substrate has a thermal expansion coefficient of The first growth layer located closest to the first growth layer and the thermal expansion coefficient of the second growth layer having the largest thickness of the laminated structure, and the first growth of the laminated structure The bulk lattice constant a ₁ of the layer and the bulk lattice constant a ₂ of the second growth layer satisfy a relationship of a ₂ <a ₁ ≦ 1.005a ₂ , whereby the object is achieved. .

In another III-V nitride semiconductor light emitting device of the present invention, a plurality of single crystal semiconductor growth layers comprising at least one kind of III-V nitride compound semiconductor material are provided.
A laminated structure that is formed by being laminated on a substrate made of a constituent material other than the III-V nitride-based material,
The coefficient of thermal expansion of the substrate is the coefficient of thermal expansion of the first growth layer closest to the substrate in the laminated structure, and the second growth layer having the largest thickness of the laminated structure. And the bulk lattice constant a _{1 of the first} growth layer and the bulk lattice constant a ₂ of the second growth layer of the laminated structure are 0.995a ₂ ≦ a ₁ <a ₂ . The relationship is satisfied, thereby achieving the above objectives.

[0015] In one embodiment, a non-single-crystal buffer layer is further formed between the substrate and the laminated structure.

Hereinafter, the operation of the present invention will be described.

According to the present invention, between the bulk lattice constant a ₁ of the first growth layer closest to the substrate and the bulk lattice constant a ₂ of the second growth layer having the largest thickness in the laminated structure. ,
The thermal expansion coefficient of the substrate is more than the thermal expansion coefficient of the III-V nitride-based compound semiconductor material constituting the laminated structure (more specifically, the thermal expansion coefficient of the first growth layer and the thermal expansion coefficient of the second growth layer). When it is larger than the thermal expansion coefficient), the relationship a ₂ <a ₁ ≦ 1.005a ₂ is satisfied. As a result, the first growth layer receives a compressive stress and generates a compressive strain at a lower temperature than the crystal growth. As a result, the lattice constant of the first growth layer in the in-plane direction (a-axis direction) becomes smaller than the bulk lattice constant of the first growth layer, and approaches the bulk lattice constant of the second growth layer.

Alternatively, the coefficient of thermal expansion of the substrate is higher than the coefficient of thermal expansion of the III-V nitride compound semiconductor material constituting the laminated structure (more specifically, the coefficient of thermal expansion of the first growth layer and When it is smaller than the thermal expansion coefficient of the second growth layer), the relationship of 0.995a ₂ ≦ a ₁ <a ₂ is satisfied. As a result, the first growth layer receives tensile stress at a temperature lower than that of crystal growth, and generates tensile strain. As a result, the first growth layer moves in the in-plane direction.
The lattice constant in the (a-axis direction) becomes larger than the bulk lattice constant of the first growth layer and approaches the bulk lattice constant of the second growth layer.

As described above, according to the present invention, whether the thermal expansion coefficient of the substrate is higher or lower than the thermal expansion coefficient of the laminated structure (the thermal expansion coefficients of the first and second growth layers) Also, the lattice distortion of the second growth layer is reduced, and the crystallinity of the second growth layer is improved. As a result, the crystallinity of the active layer is improved, and a high-quality active layer with good yield and good reproducibility can be obtained.

Further, when the thermal expansion coefficient of the substrate is larger than the thermal expansion coefficient of the first growth layer closest to the substrate and the thermal expansion coefficient of the second growth layer having the maximum film thickness in the laminated structure, Since the active layer formed on the second growth layer grows coherently on the a-axis of the second growth layer which is the underlying layer,
An active layer having a lattice constant equal to the lattice constant strain of the second growth layer can be formed. As a result, the lattice distortion of the active layer is reduced, and an active layer having a sufficient thickness can be grown.
In addition, the efficiency of incorporation of In into the active layer can be improved, and the in-plane uniformity of the In concentration in the active layer can be improved. As a result, a high-quality thick active layer with improved yield and reproducibility can be grown. become. As a result, a group III-V nitride-based single crystal semiconductor light emitting device exhibiting planar light emission with high luminance is realized.

Further, by appropriately selecting the constituent material, composition ratio, and thickness of the first growth layer, the lattice constant in the in-plane direction of the first growth layer is made to match the bulk lattice constant of the second growth layer. Becomes possible. In such a case, it is possible to grow a strain-free and high-quality group III-V nitride-based single crystal compound semiconductor layer as the second growth layer.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) As a first embodiment of the present invention, a configuration in which an LED (light emitting diode) element is formed on a sapphire substrate will be described.

FIG. 1 is a sectional view schematically showing the structure of the LED element 100 according to the present embodiment.

In the LED element 100, sapphire (00
01 surface) In the substrate 10_0.01Ga _0.99N buffer layer
11 is formed, and further, In_0.01Ga_0.99N
First growth layer 12 (about 0.5 μm), Si-doped n-type GaN
Second growth layer (maximum thickness layer) 13 (about 5 μm), In_0.35Ga
_0.65N active layer 14 (about 2 nm), Al_0.1Ga_0.9N layer 15
(About 10 nm), and Mg-doped p-type GaN layer 16 (about 10 nm).
0.4 μm). Bag
The total film thickness from the pha layer 11 to the GaN layer 16 is about 5.9.
μm. Where Al_0.1Ga_0.9The N layer 15 is made of In
_0.35Ga_0.65Prevents evaporation of In from N active layer 14
It is an evaporation prevention layer.

A part of the device structure is partially cut away until the Si-doped n-type GaN second growth layer 13 is exposed, and an n-type electrode 17 is formed on the exposed surface. On the other hand, on the Mg-doped p-type GaN layer 16, p
A mold electrode 18 is formed.

Here, the coefficient of thermal expansion (7.50 × 10 ⁻⁶ / deg) of the sapphire substrate 10 is the same as the coefficient of thermal expansion (GaN) of the laminated structure composed of the group III-V nitride single crystal semiconductor layer. Has a thermal expansion coefficient larger than 5.45 × 10 ⁻⁶ / deg). In addition, In _{0. 01} Ga _0.99 N first growth layer 1
2 bulk lattice constant a ₁ and Si-doped n-type GaN second growth layer (maximum film thickness layer) 13 a bulk lattice constant a ₂ of is a ₁ = 3.193A and a ₂ = 3.189 Å, respectively,
The relationship a ₂ <a ₁ ≦ 1.005a ₂ is satisfied.

Hereinafter, a method for manufacturing the LED element 100 will be described.
The measurement results of the device characteristics will be described.

First, In _0.01 on the sapphire substrate 10.
A Ga _0.99 N buffer layer 11 is grown, and further thereon,
In _0.01 Ga _0.99 N first growth layer 1 at a substrate temperature of about 900 ° C.
Grow 2. Thereafter, the substrate temperature is raised to about 1100 ° C. while growing a GaN layer on the In _0.01 Ga _0.99 N first growth layer 12, and finally the substrate temperature is increased to about 11100 ° C.
The Si-doped GaN second growth layer 13 is grown at 00 ° C. Next, after lowering the substrate temperature to about 760 ° C.,
An n _0.35 Ga _0.65 N active layer 14 is grown, and an Al _0.1 Ga _0.9 N layer 15 is further grown thereon at the same temperature. Thereafter, the substrate temperature is raised to about 1050 ° C., and the Mg-doped GaN layer 16 is grown. In the above-mentioned growth process, for example, the MOCVD method is used.

The device structure formed as described above was analyzed by X-ray analysis and transmission electron microscope (TEM) analysis to obtain a second Si-doped GaN growth layer 13, In _0.35 Ga
_0.65 N active layer 14, Al _0.1 Ga _0.9 N layer 15, and Mg
The lattice constant of each of the doped GaN layers 16 was analyzed. As a result, the lattice constant of the Si-doped GaN second growth layer 13 and the Mg-doped GaN layer 16 is equal to the bulk lattice constant of GaN, and the grown GaN layers 13 and 16 are lattice-relaxed and have no strain. There was found. On the other hand, In
_0.35 Ga _0.65 N active layer 14 and Al _0.1 Ga _0.9 N layer 15
Has a lattice constant in the a-axis direction that matches the bulk lattice constant of GaN, and these layers 14 and 15 are strained in the in-plane direction (a-axis direction) while the Si-doped GaN second growth layer 13
It turns out that it is growing coherently.

The above phenomenon is considered to be caused by the following mechanism.

When the substrate temperature decreases from the crystal growth temperature,
Laminated structure and In_0.01Ga_0.99N buffer layer 11
Due to the difference in the coefficient of thermal expansion between the fire substrate 10 and
In _0.01Ga_0.99N buffer layer 11 and sapphire substrate 1
Stress occurs at the interface with zero. This stress is sapphire-based
The plate 10 has a larger coefficient of thermal expansion than the laminated structure.
Thus, it is a compressive stress. On the other hand, the laminated structure and In_0.01
Ga_0.99The same III-V nitride based N buffer layer 11
, They have almost the same coefficient of thermal expansion.
Therefore, the above-mentioned compressive stress is In_0.01Ga_0.99N
Sapphire in the laminated structure via the buffer layer 11
In closest to the substrate 10_0.01Ga_0.99N first
Propagation to the long layer 12. From this, In_0.01Ga_0.99Nth
1 growth layer 12 is subjected to compressive stress, and its lattice constant is
Smaller than the Lattice lattice constant,
It is almost equal to the child constant.

Further, when the Si-doped GaN second growth layer 13 is grown on such an In _0.01 Ga _0.99 N first growth layer 12, the underlying In _0.01 Ga _0.99 N first growth layer 1 is formed.
Since 2 has a lattice constant substantially equal to the bulk lattice constant of the GaN layer, the occurrence of lattice distortion in the Si-doped GaN second growth layer 13 is reduced, and preferably the lattice is relaxed. Further, since the In _0.35 Ga _0.65 N active layer 14 is coherently grown on the Si-doped GaN second growth layer 13 having the maximum thickness, it is formed so as to have a lattice constant substantially equal to the bulk lattice constant of the GaN layer. obtain. In addition, this I
Al _0.15 formed on the n _0.35 Ga _0.65 N active layer 14
The Ga _0.9 N layer 15 and the Mg-doped GaN layer 16 are similarly formed by coherent growth to have a lattice constant substantially equal to the bulk lattice constant of the GaN layer.

Next, in order to activate Mg as a p-type dopant, the substrate having the above-described element structure formed thereon is annealed in a nitrogen atmosphere at about 800 ° C. for about 20 minutes. After that, S from the upper surface of the Mg-doped GaN layer 16
A portion reaching the inside of the i-doped GaN second growth layer 13 is partially removed by etching to expose a partial surface of the second growth layer 13. Next, an n-type electrode 17 is formed on the exposed surface of the n-type GaN layer 13, and a p-type electrode 18 is formed on the surface of the p-type GaN layer 16, respectively. Thus, the LED element 100 is manufactured.

When the luminance of the LED element 100 of this embodiment was measured, the emission current was 470 nm at a driving current of 20 mA.
m, and a luminance of 3.5 cd, which was 1.5 times the luminance of the related art. Further, when the light emission pattern of the LED element 100 was observed with a microscope, it was confirmed that uniform planar light emission was realized. On the other hand, for comparison, In _0.01 G
a _0.99 N The first growth layer 12 was omitted, and the light emission pattern of a comparative LED element manufactured in the same manner as described above was observed with a microscope, and it was found that the light emission was caused by a collection of bright spots. did.

Further, several comparative LEDs manufactured in the same manner as described above except that the thickness of the Si-doped GaN second growth layer 13 as the maximum thickness layer in the laminated structure was changed variously. The luminance of the devices was measured. FIG. 2 shows the measurement results.

As shown in FIG. 2, when the thickness of the second growth layer (maximum thickness layer) 13 is 1 μm or more, I shown by a dotted line in FIG.
LE in which n _0.01 Ga _0.99 N first growth layer 12 was not formed
The luminance was higher than the value in the D element. Thus, when the thermal expansion coefficient of the substrate is larger than the thermal expansion coefficient of the multilayer structure as in the present embodiment, the thickness of the second growth layer 13 needs to be set to 1 μm or more.

In addition, the first growth layer 12 and the second growth layer 1
By changing the constituent materials and / or composition ratios of Sample No. 3 variously, their lattice constants were changed, and the brightness of some comparative LED elements manufactured in the same manner as above was measured. FIG. 3 shows the measurement results. Specifically, these comparative LED elements are the first
The layer is composed of InGaN, the second layer is composed of GaN, and I
It was prepared by changing the mixed crystal ratio of nGaN.

In FIG. 3, the theoretical bulk between the first growth layer 12 (bulk lattice constant: a ₁ ) and the second growth layer (maximum thickness layer) 13 (bulk lattice constant: a ₂ ) is shown. Lattice mismatch ε
Is defined as ε = (a ₁ −a ₂ ) / a ₁ × 100, and the bulk lattice mismatch rate ε is used as a parameter.

FIG. 3 shows that within the range of 0 <ε ≦ 0.5, that is, within the range of a ₂ <a ₁ ≦ 1.005a ₂ , In _0.01 Ga _0.99 as the first layer shown by the dotted line in the figure. The luminance was higher than that of the LED element in which the N first growth layer 12 was not formed.

Thus, when the thermal expansion coefficient of the substrate is larger than the thermal expansion coefficient of the laminated structure as in the present embodiment,
The brightness of the LED element was improved within the range of a ₂ <a ₁ ≦ 1.005a ₂ .

Note that InGaN in the above embodiment is used.
Is not limited to the specific value described above, and Ga _x Al _y In _z N (x, y, z ≧ 0, x + y + z
= 1).

The substrate is not limited to the sapphire substrate, but may be any substrate made of a material having a larger coefficient of thermal expansion than the group III-V nitride compound semiconductor material constituting the laminated structure.

Further, in the growth process of each layer, the MO
It has been confirmed that the same effect as that of the present embodiment can be obtained by using other well-known processes used in semiconductor technology, such as the MBE method and the HPPE method, instead of the CVD method.

(Second Embodiment) As a second embodiment of the present invention, a configuration in which LED elements are formed on a SiC substrate will be described.

FIG. 4 is a cross-sectional view schematically showing the structure of the LED element 200 of the present embodiment.

The LED element 200 is made of SiC (0001 surface)
An Al _0.01 Ga _0.99 N buffer layer 21 is formed on a substrate 20, and an Al _0.01 Ga _0.99 N first growth layer 22 (about 0.3 μm) and a Si-doped n-type GaN second growth layer are further formed thereon.
(Maximum thickness layer) 23 (about 4 μm), In _0.35 Ga _0.65 N active layer 24 (about 2 nm), Al _0.1 Ga _0.9 N layer 25 (about 10 n
m), and Mg-doped p-type GaN layer 26 (about 0.4 μm)
Is formed. The total film thickness from the buffer layer 21 to the GaN layer 26 is about 4.7 μm.
Here, the Al _0.1 Ga _0.9 N layer 25 is made of In _0.35 Ga _0.65
This is an evaporation prevention layer for preventing In from evaporating from the N active layer 24.

A part of the device structure is partially cut out until a part of the Si-doped n-type GaN second growth layer 23 is exposed, and an n-type electrode 17 is formed on the exposed surface. ing. On the other hand, the p-type electrode 18 is formed on the Mg-doped p-type GaN layer 26.

Here, the thermal expansion coefficient of the SiC substrate 20
(5.0 × 10^-6/ Deg) is the above group III-V nitride
Coefficient of thermal expansion of laminated structure composed of oxide single crystal semiconductor layer
(The coefficient of thermal expansion of GaN is 5.45 × 10^-6/ Deg)
Small. In addition, Al_0.01Ga _0.99N first growth layer 2
Bulk lattice constant a of 2₁And Si-doped n-type GaN second component
Bulk lattice constant a of long layer (maximum thickness layer) 23_TwoAnd it
A₁= 3.188Åa_Two= 3.189Å
0.995a_Two≤a₁<A_TwoRelationship is satisfied.

Hereinafter, a method of manufacturing the LED element 200 will be described.
The measurement results of the device characteristics will be described.

First, Al _0.01 Ga is formed on the SiC substrate 20.
_{A 0.99} N buffer layer 21 is grown, and an Al _0.01 Ga _0.99 N first growth layer 22 is further formed thereon at a substrate temperature of about 1100 ° C.
Grow. Then, on the Al _0.01 Ga _0.99 N first growth layer 22, at a substrate temperature of about 1100 ° C.,
The second growth layer 23 is grown. Next, the substrate temperature is reduced to about 76
After the temperature is lowered to 0 ° C., the In _0.35 Ga _0.65 N active layer 24 is formed.
Is grown thereon, and further, at the same temperature, Al _0.1 Ga _0.9 N
Grow layer 25. Thereafter, the substrate temperature is set to about 1050 ° C.
To grow the Mg-doped GaN layer 26.
In the above-mentioned growth process, for example, the MOCVD method is used.

The device structure formed as described above was analyzed by X-ray analysis and TEM analysis to obtain a Si-doped Ga.
N second growth layer 23, In _0.35 Ga _0.65 N active layer 24, A
l _{0. 1} Ga _0.9 N layer 25, and were analyzed each lattice constant of Mg-doped GaN layer 26. As a result, Si-doped Ga
The lattice constants of the N second growth layer 23 and the Mg-doped GaN layer 26 are equal to the bulk lattice constant of GaN as in the case of the first embodiment, and the grown GaN layers 23 and 26 are strained due to lattice relaxation. Was found to be in a state without any. On the other hand, the In _0.35 Ga _0.65 N active layer 24 and the Al _0.1 Ga _0.9
The lattice constant in the a-axis direction of the N layer 25 matches the bulk lattice constant of GaN, and these layers 24 and 25 are in the in-plane direction.
It was found that the strain was coherently grown on the Si-doped GaN second growth layer 23 while being distorted in the (a-axis direction).

The above phenomenon is considered to be caused by the following mechanism.

When the substrate temperature decreases from the crystal growth temperature,
Laminated structure, Al _0.01 Ga _0.99 N buffer layer 21 and S
The difference in the coefficient of thermal expansion between the iC substrate 20
Stress occurs at the interface between the _0.01 Ga _0.99 N buffer layer 21 and the SiC substrate 20. This stress is a tensile stress because the SiC substrate 20 has a smaller coefficient of thermal expansion than the laminated structure. On the other hand, the laminated structure and Al _0.01 Ga _0.99
Since the N buffer layer 21 is made of the same group III-V nitride-based material, it has substantially the same coefficient of thermal expansion. Therefore,
The tensile stress as described above is applied to the SiC substrate 20 in the laminated structure via the Al _0.01 Ga _0.99 N buffer layer 21.
Al _0.01 Ga _0.99 N first growth layer 22 located closest to
Propagate to As a result, the Al _0.01 Ga _0.99 N first growth layer 22 receives a tensile stress, and its lattice constant becomes larger than the bulk lattice constant and becomes substantially equal to the bulk lattice constant of the GaN layer.

Further, when the Si-doped GaN second growth layer 23 is grown on such an Al _0.01 Ga _0.99 N first growth layer 22, the underlying Al _0.01 Ga _0.99 N first growth layer 2 is formed.
Since 2 has a lattice constant substantially equal to the bulk lattice constant of the GaN layer, the occurrence of lattice distortion in the Si-doped GaN second growth layer 23 is reduced, and preferably the lattice is relaxed. Further, since the In _0.35 Ga _0.65 N active layer 24 is coherently grown on the Si-doped GaN second growth layer 23 having the maximum thickness, it is formed so as to have a lattice constant substantially equal to the bulk lattice constant of the GaN layer. obtain. In addition, this I
Al _0.15 formed on the n _0.35 Ga _0.65 N active layer 24
The Ga _0.9 N layer 25 and the Mg-doped GaN layer 26 are similarly formed by coherent growth to have a lattice constant substantially equal to the bulk lattice constant of the GaN layer.

Next, in order to activate Mg as a p-type dopant, the substrate having the above-described element structure is annealed in a nitrogen atmosphere at about 800 ° C. for about 20 minutes. After that, S from the upper surface of the Mg-doped GaN layer 26
A portion reaching the inside of the i-doped GaN second growth layer 23 is partially removed by etching to expose a partial surface of the second growth layer 23. Next, an n-type electrode 17 is formed on the exposed surface of the n-type GaN layer 23, and a p-type electrode 18 is formed on the surface of the p-type GaN layer 26, respectively. Thus, the LED element 200 is manufactured.

When the luminance of the LED element 200 of this embodiment was measured, the emission current was 470 nm at a drive current of 20 mA.
m, and a luminance of 3.4 cd, which was 1.5 times the luminance of the related art. Furthermore, when the light emission pattern of the LED element 200 was observed with a microscope, it was confirmed that uniform planar light emission was realized. On the other hand, for comparison, Al _0.01 G
a _0.99 N The first growth layer 22 was omitted, and the light emission pattern of the comparative LED element manufactured in the same manner as described above was observed with a microscope. did.

Further, several comparative LEDs manufactured in the same manner as described above except that the thickness of the Si-doped GaN second growth layer 23 as the maximum thickness layer in the laminated structure was changed variously. The luminance of the devices was measured. FIG. 5 shows the measurement results.

FIG. 5 shows that when the thickness of the second growth layer (maximum thickness layer) 23 is 0.5 μm or more, the Al _0.01 Ga _0.99 N first growth layer 22 shown by the dotted line in the figure is not formed. The brightness was higher than the value of the LED element that had failed. Thus, when the thermal expansion coefficient of the substrate is smaller than the thermal expansion coefficient of the laminated structure as in the present embodiment, the second growth layer 2
The film thickness of No. 3 needs to be set to 0.5 μm or more.

In addition, the first growth layer 22 and the second growth layer 2
By changing the constituent materials and / or composition ratios of Sample No. 3 variously, their lattice constants were changed, and the brightness of some comparative LED elements manufactured in the same manner as above was measured. FIG. 6 shows the measurement results. Specifically, these comparative LED elements are the first
The layer is composed of AlGaN, the second layer is composed of GaN, and A
It was prepared by changing the mixed crystal ratio of lGaN.

In FIG. 6, as in the first embodiment, the first growth layer 22 (bulk lattice constant: a ₁ ) and the second growth layer (maximum thickness layer) 23 (bulk lattice constant: a ₂ ) the theoretical bulk lattice mismatch ε = (a ₁ −a ₂ ) / a ₁
× 100 is used as a parameter.

FIG. 6 shows that within the range of -0.5 ≦ ε <0, that is, within the range of 0.995a ₂ ≦ a ₁ <a ₂ , Al _0.01 Ga as the first layer shown by the dotted line in the figure. _The luminance was higher than that of the LED element in which the _0.99 N first growth layer 22 was not formed.

Accordingly, when the coefficient of thermal expansion of the substrate is smaller than the coefficient of thermal expansion of the laminated structure as in the present embodiment,
The brightness of the LED element was improved within the range of 0.995a ₂ ≦ a ₁ <a ₂ .

Note that the InGaN in the above embodiment is
Is not limited to the specific value described above, and Ga _x Al _y In _z N (x, y, z ≧ 0, x + y + z
= 1).

The substrate is not limited to a sapphire substrate, but may be any substrate made of a material having a larger coefficient of thermal expansion than the group III-V nitride compound semiconductor material constituting the laminated structure.

Further, in the growth process of each layer, MO
It has been confirmed that the same effect as that of the present embodiment can be obtained by using other well-known processes used in semiconductor technology, such as the MBE method and the HPPE method, instead of the CVD method.

Third Embodiment As a third embodiment of the present invention, a configuration in which an LD (laser diode) element is formed on a sapphire substrate will be described.

FIG. 7 is a cross-sectional view schematically showing the configuration of the LD element 300 of this embodiment.

In the LD element 300, sapphire (000
In _0.01 Ga _{0. 99} N buffer layer 3 on the one side) substrate 30
1 is further formed thereon, and an In _0.01 Ga _0.99 N first growth layer 32 (about 0.5 μm), a Si-doped n-type GaN contact second growth layer (maximum thickness layer) 33 (about 5 μm, : About 1 × 10 ¹⁸ cm ⁻³ ), Si-doped n-type Al _0
.1 Ga _0.9 N clad layer 34 (about 0.4 μm), Si-doped n-type GaN optical guide layer 35 (about 0.1 μm, carrier concentration: about 1 × 10 ¹⁸ cm ⁻³ ), In _0.35 Ga _0.65 N (about 2
nm) / In _0.05 Ga _0.95 N (approximately 4 nm) consisting of 10 periods of a multiple quantum well active layer 36 (approximately 60 nm in total thickness), A
l _0.1 Ga _0.9 N layer 37 (about 10 nm), Mg-doped p-type G
aN optical guide layer 38 (about 0.1 μm, carrier concentration: about 1 × 10 ¹⁸ cm ⁻³ ), Mg-doped p-type Al _0.1 Ga _0.9 N
Cladding layer 39 (about 0.4 μm) and Mg-doped p-type G
A laminated structure including the aN contact layer 40 (about 0.5 μm) is formed. The total thickness from the buffer layer 31 to the GaN contact layer 40 is about 7.1 μm. Here, the Al _0.1 Ga _0.9 N layer 37 is formed of the multiple quantum well active layer 3.
6 is an evaporation preventing layer for preventing evaporation of In from 6.

A part of the device structure is partially cut out until the Si-doped n-type GaN contact second growth layer 33 is exposed, and an n-type electrode 41 is formed on the exposed surface. . On the other hand, a p-type electrode 42 is formed on the Mg-doped p-type GaN contact layer 40.

Here, the coefficient of thermal expansion (7.50 × 10 ⁻⁶ / deg) of the sapphire substrate 30 is determined by the coefficient of thermal expansion (GaN) of the above-mentioned laminated structure composed of the group III-V nitride-based single crystal semiconductor layer. Has a thermal expansion coefficient larger than 5.45 × 10 ⁻⁶ / deg). In addition, In _{0. 01} Ga _0.99 N first growth layer 3
2 bulk lattice constant a ₁ and Si-doped n-type GaN contact second growth layer (maximum film thickness layer) 33 a bulk lattice constant a ₂
Are a ₁ = 3.193Å and a ₂ = 3.189, respectively.
Å, and the relationship a ₂ <a ₁ ≦ 1.005a ₂ is satisfied.

Hereinafter, a method of manufacturing the LD element 300 and measurement results of the element characteristics will be described.

First, the In _0.01 Ga _0.99 N buffer layer 31, the In _0.01 Ga _0.99 N first growth layer 32, the Si-doped n-type GaN contact second growth layer 33, and the Si _0.01 Ga _0.99 N buffer layer 31 are formed on the sapphire substrate 30 by, eg, MOCVD. Doped n-type Al _0.1 Ga _0.9 N cladding layer 34, Si-doped n-type Ga
N light guide layer 35, In _0.35 Ga _0.65 N (about 2 nm) / I
n _0.05 Ga _0.95 N (about 4 nm), a multiple quantum well active layer 36 composed of 10 periods, an Al _0.1 Ga _0.9 N layer 37, a Mg-doped p-type GaN optical guide layer 38, a Mg-doped p-type Al _0.1
Ga _0.9 N cladding layer 39 and Mg-doped p-type GaN
The contact layer 40 is formed by sequentially laminating.

Next, in order to activate Mg as a p-type dopant, the substrate having the above-described element structure is annealed at about 800 ° C. for about 20 minutes in a nitrogen atmosphere. Thereafter, a portion from the upper surface of the p-type GaN contact layer 40 to the inside of the Si-doped GaN contact second growth layer 33 is removed by etching into a stripe shape having a width of about 200 μm, and a partial surface of the second growth layer 33 is formed. To expose. Next, the n-type electrode 4 is placed on the exposed surface of the n-type GaN layer 33.
1, and a p-type electrode 42 is formed on the surface of the p-type GaN contact layer 40, respectively. Thus, the LD element 3
00 is produced.

The LD device 300 of this embodiment oscillates at room temperature. The oscillation threshold current and the threshold voltage are about 160 mA and about 5.8 V, respectively. On the other hand, for the sake of comparison, the In _0.01 Ga _0.99 N first growth layer 32 was omitted, and other than that, the comparison L
When the D element was manufactured, no laser oscillation occurred.

(Fourth Embodiment) As a fourth embodiment of the present invention, a configuration in which an LD element is formed on a SiC substrate will be described.

FIG. 8 is a cross-sectional view schematically showing the configuration of the LD device 400 of the present embodiment.

In the LD element 400, an Al _0.01 Ga _0.99 N buffer layer 51 is formed on a SiC (0001 plane) substrate 50, and an Al _0.01 Ga _0.99 N first growth layer 5 is further formed thereon.
2 (about 0.7 μm), Si-doped n-type GaN contact second growth layer (maximum thickness layer) 53 (about 5 μm, carrier concentration:
About ^{1 × 10 18 cm -3),} Si -doped n-type Al _0.1 Ga _{0. 9}
N cladding layer 54 (about 0.4 μm), Si-doped n-type Ga
N light guide layer 55 (about 0.1 μm, carrier concentration: about 1
× 10 ¹⁸ cm ^-3 ), In _0.35 Ga _0.65 N (about 2 nm) / I
A multiple quantum well active layer 56 (total thickness of about 60 nm) consisting of 10 periods of n _0.05 Ga _0.95 N (about 4 nm), Al _0.1 Ga
_0.9 N layer 57 (about 10 nm), Mg-doped p-type GaN optical guide layer 58 (about 0.1 μm, carrier concentration: about 1 × 10
¹⁸ cm ⁻³ ), a laminated structure including a Mg-doped p-type Al _0.1 Ga _0.9 N clad layer 59 (about 0.4 μm) and a Mg-doped p-type GaN contact layer 60 (about 0.5 μm) is formed. . From the buffer layer 51 to the GaN contact layer 60
Is about 7.3 μm. Where Al
_{The 0.1} Ga _0.9 N layer 57 is an evaporation preventing layer for preventing In from evaporating from the multiple quantum well active layer 56.

A part of the above device structure is partially cut out until a part of the Si-doped n-type GaN second growth layer 53 is exposed, and an n-type electrode 41 is formed on the exposed surface. ing. On the other hand, a p-type electrode 42 is formed on the Mg-doped p-type GaN contact layer 60.

Here, the thermal expansion coefficient of the SiC substrate 50
(5.0 × 10^-6/ Deg) is the above group III-V nitride
Coefficient of thermal expansion of laminated structure composed of oxide single crystal semiconductor layer
(The coefficient of thermal expansion of GaN is 5.45 × 10^-6/ Deg)
Small. In addition, Al_0.01Ga _0.99N first growth layer 5
Bulk lattice constant a of 2₁And Si-doped n-type GaN contour
Lattice constant a of the second growth layer (maximum thickness layer) 53_Two
Means a₁= 3.188 ° and a_Two= 3.189
９５ and 0.995a_Two≤a₁<A_TwoRelationship is satisfied
Have been.

Hereinafter, a method of manufacturing the LD element 400 and measurement results of the element characteristics will be described.

First, for example, an MOC
By the VD method, an Al _0.01 Ga _0.99 N buffer layer 51,
Al _0.01 Ga _0.99 N first growth layer 52, Si-doped n-type G
aN contact second growth layer 53, Si-doped n-type Al
_0.1 Ga _0.9 N clad layer 54, Si-doped n-type GaN optical guide layer 55, In _0.35 Ga _0.65 N (about 2 nm) / In _0.
The multiple quantum well active layer 56 composed of 10 periods of ₀₅ Ga _0.95 N (about 4 nm), the Al _0.1 Ga _0.9 N layer 57, and the Mg-doped p
Type GaN optical guide layer 58, Mg-doped p-type Al _{0 .1} Ga
_{A 0.9} N clad layer 59 and a Mg-doped p-type GaN contact layer 60 are sequentially laminated.

Next, in order to activate Mg as a p-type dopant, the substrate having the above-described element structure is annealed in a nitrogen atmosphere at about 800 ° C. for about 20 minutes. Thereafter, a portion from the upper surface of the p-type GaN contact layer 60 to the inside of the Si-doped GaN contact second growth layer 53 is removed by etching into a stripe shape having a width of about 200 μm, and a partial surface of the second growth layer 53 is formed. To expose. Next, the n-type electrode 4 is placed on the exposed surface of the n-type GaN layer 53.
1, and a p-type electrode 42 is formed on the surface of the p-type GaN contact layer 60, respectively. Thus, the LD element 4
00 is produced.

The LD device 400 of this embodiment oscillates at room temperature. The oscillation threshold current and the threshold voltage are about 150 mA and about 5.5 V, respectively. On the other hand, for the sake of comparison, the In _0.01 Ga _0.99 N first growth layer 52 was omitted, and other than that, the comparison L
When the D element was manufactured, no laser oscillation occurred.

Note that in the configuration of each of the above embodiments,
The buffer layer formed between the substrate and the stacked structure (first growth layer) does not need to be a single crystal layer, and may be a non-single crystal layer such as a polycrystal layer.

The effects of the present invention described above are particularly remarkable when the total thickness of the buffer layer and the laminated structure formed on the substrate is about 100 μm or less.

[0086]

As described above, in the III-V nitride semiconductor light emitting device of the present invention, when a substrate having a larger thermal expansion coefficient than that of the III-V nitride compound semiconductor material is used, Another III-V nitride compound semiconductor layer having a larger bulk lattice constant than the maximum thickness layer is inserted between the III-V nitride compound semiconductor layer having the maximum thickness and the substrate. When a substrate having a smaller coefficient of thermal expansion than the group III-V nitride-based compound semiconductor layer is used,
Another group III-V nitride compound semiconductor layer having a smaller bulk lattice constant than the maximum thickness layer is inserted between the III-V nitride compound semiconductor layer having the maximum thickness layer and the substrate. Thereby, the influence of lattice distortion from the substrate on the maximum thickness layer is suppressed, and the crystallinity of the active layer is improved.
-V-nitride-based compound semiconductor layers and semiconductor light-emitting devices using the same can be manufactured.

As described above, according to the present invention, a III-V nitride-based semiconductor light emitting device having improved yield and reproducibility, having high quality and high reliability, and realizing planar light emission is realized. Is done.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a configuration of an LED element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between the thickness of a second growth layer (maximum thickness layer) and luminance in the LED element of FIG.

FIG. 3 shows a first growth layer and a second growth layer in the LED device of FIG. 1;
Bulk lattice mismatch ε between the growth layer (the maximum thickness layer) and
It is a figure showing the relation with brightness.

FIG. 4 is a cross-sectional view schematically illustrating a configuration of an LED element according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between the thickness of a second growth layer (maximum thickness layer) and luminance in the LED element of FIG.

FIG. 6 shows a first growth layer and a second growth layer in the LED element of FIG.
Bulk lattice mismatch ε between the growth layer (the maximum thickness layer) and
It is a figure showing the relation with brightness.

FIG. 7 is a cross-sectional view schematically illustrating a configuration of an LD element according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view schematically illustrating a configuration of an LD element according to the first embodiment of the present invention.

[Explanation of symbols]

 10, 30 Sapphire substrate 20, 50 SiC substrate 11, 21, 31, 51 Buffer layer 12, 32 InGaN first growth layer 22, 52 AlGaN first growth layer 13, 23, 33, 53 n-type GaN second growth layer 14 , 24, 36, 56 Active layer 15, 25, 37, 57 Evaporation preventing layer 16, 26, 40, 60 p-type GaN contact layer 34, 54 n-type AlGaN cladding layer 35, 55 n-type GaN guide layer 38, 58 p -Type GaN guide layer 39, 59 p-type AlGaN cladding layer 17, 41 n-type electrode 18, 42 p-type electrode 100, 200 LED element 300, 400 LD element

Claims (3)

[Claims] A plurality of single crystal semiconductor growth layers made of at least one kind of III-V nitride-based compound semiconductor material are stacked on a substrate made of a constituent material other than the III-V nitride-based material. II with a laminated structure composed of
A group IV nitride semiconductor light-emitting device, wherein the thermal expansion coefficient of the substrate is the thermal expansion coefficient of a first growth layer located closest to the substrate in the multilayer structure and the multilayer structure. Larger than the coefficient of thermal expansion of the second growth layer having the largest thickness of the body, and the bulk lattice constant a _{1 of the first} growth layer and the bulk lattice constant a ₂ of the second growth layer of the laminated structure And a ₂ <a ₁ ≦ 1.
005a ₂ becomes to satisfy the relationship, III-V nitride-based semiconductor light-emitting device. 2. A plurality of single crystal semiconductor growth layers made of at least one kind of III-V nitride-based compound semiconductor material are stacked on a substrate made of a constituent material other than the III-V nitride-based material. II with a laminated structure composed of
A group IV nitride semiconductor light-emitting device, wherein the thermal expansion coefficient of the substrate is the thermal expansion coefficient of a first growth layer located closest to the substrate in the multilayer structure and the multilayer structure. Smaller than the coefficient of thermal expansion of the second growth layer having the largest thickness of the body, the bulk lattice constant a _{1 of the first} growth layer and the bulk lattice constant a ₂ of the second growth layer of the laminated structure Is 0.995a ₂ ≦
A group III-V nitride-based semiconductor light emitting device that satisfies the relationship a ₁ <a ₂ . 3. The group III-V nitride single crystal semiconductor light emitting device according to claim 1, further comprising a non-single crystal buffer layer formed between said substrate and said laminated structure.