JP2003060231A - Iii-v compound semiconductor and light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-crystallinity high-quality nitride-based III-V compound semiconductor and a light-emitting element which uses the semiconductor. SOLUTION: (1) A nitride-based III-V compound semiconductor has an interface between two layers having lattice mismatching, an intermediate layer having a thickness of >=25 nm, and a single Inx Gay Alz N quantum well layer (where x+y+z=1, 0<x<=1, 0<=y<1, and 0<=z<1), sandwiched between two barrier layers in this order. (2) The thickness of the quantum well layer of the III-V compound semiconductor described in (1) is adjusted to 5-90 Å. (3) The light emitting element uses the III-V compound semiconductor described in (1) or (2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride-based 3-5 group compound semiconductor, and more specifically to a general formula In _x Ga _y Al _z.
N (however, x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦
The present invention relates to a nitride-based 3-5 group compound semiconductor represented by 1, 0 ≦ z ≦ 1).

[0002]

2. Description of the Related Art As a material for a light emitting device such as an ultraviolet or blue light emitting diode or an ultraviolet or blue laser diode, the general formula InxGayAlzN (provided that x + y
+ Z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), and a nitride-based 3-5 group compound semiconductor is known.
Hereinafter, x, y, and z in this general formula may be referred to as an InN mixed crystal ratio, a GaN mixed crystal ratio, and an AlN mixed crystal ratio, respectively. Among the 3-5 group compound semiconductors, those containing InN in a mixed crystal ratio of 10% or more can adjust the emission wavelength in the visible region according to the InN mixed crystal ratio, and are particularly important for display applications.

By the way, when a light emitting layer is composed of a plurality of layers in a semiconductor light emitting device, if the layers do not have exactly the same structure, the emission spectrum will be a superposition of different spectra of the layers, so that it will spread as a whole. Become. That is, the color purity of the emission color is lowered. On the contrary, when a single light emitting layer is used, such a problem can be avoided. In addition, in the case of application to a laser, when the light emitting layer is a multi-layer, the thickness of the entire light emitting layer increases, so that light absorption by the light emitting layer itself also increases. Therefore, by using a single light emitting layer, the minimum current required for laser oscillation can be reduced.

On the other hand, in the nitride-based 3-5 group compound semiconductor, a crystal of high quality and large area that can be used for crystal growth has not been obtained. Therefore, so-called hetero-epitaxial growth is generally performed on a different type of substrate. That is, an amorphous or microcrystalline thin film called a buffer layer is first grown using a substrate having a relatively close lattice constant, such as sapphire or SiC, and crystal growth of the compound semiconductor is performed thereon. However, it is general that the crystals thus obtained also have very high density dislocations of about 10 ⁸ cm ⁻² .
For these reasons, it is very difficult to form a highly uniform thin film with the compound semiconductor, and it is difficult to achieve high luminous efficiency with a single light emitting layer.
Therefore, in a light emitting device using a nitride compound semiconductor,
It is the actual situation that the so-called multiple quantum well, which is used by stacking a plurality of light emitting layers, is used to enhance the light emission efficiency.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a nitride-based Group 3-5 compound semiconductor having a high quality single quantum well layer with high crystallinity and a light emitting device using the same. Especially.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in view of such a situation, as a result of providing a specific laminated structure between a single quantum well layer and a substrate, The inventors have found that the crystallinity of an overlying layer is remarkably improved and have reached the present invention. That is, the present invention provides (1) a general formula In _x Ga _y Al sandwiched between an interface between two layers having at least one lattice mismatch, an intermediate layer having a film thickness of 25 nm or more, and two barrier layers. _z N (however, x + y + z =
1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1), and a single quantum well layer in this order. Is. The present invention also provides (2) a light emitting device characterized by using the above compound semiconductor.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail.
The nitride-based 3-5 group compound semiconductor in the present invention has an interface between two layers having a lattice mismatch, an intermediate layer and a single quantum well layer on a substrate in this order. here,
The quantum well layer is a general formula InxGayAlzN (however,
x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <
1), which has a larger band gap than that of the general formula Inx'Gay'Alz'N (wherein 0≤x'≤1, 0≤y ').
≦ 1, 0 ≦ z ′ ≦ 1, x ′ + y ′ + z ′ = 1) means a layer sandwiched and in contact with two layers. The thickness of the quantum well layer is usually 5 Å or more and 90 Å or less. Hereinafter, the layer sandwiching the quantum well layer may be simply referred to as a barrier layer, and the quantum well layer may be simply referred to as a well layer. The quantum well layer and the barrier layer may be collectively referred to as a quantum well structure. Note that x ′, y ′, and z ′ in the two barrier layers may be the same or different from each other.

The difference in bandgap between the barrier layer and the well layer is preferably 0.1 eV or more. When this band gap difference is smaller than 0.1 eV, carriers are not sufficiently confined in the well layer, and the light emission efficiency is reduced when used as a light emitting device. More preferably, it is 0.3 ev or more. However, if the bandgap of the barrier layer exceeds 5 eV, the voltage required for charge injection increases, so the bandgap of the barrier layer is preferably 5 eV or less.

Next, the intermediate layer in the present invention is a layer sandwiched between the well layer and the interface between the two layers having the lattice mismatch closest to the well layer, and may be composed of a plurality of layers. Good, the total film thickness is 25 nm or more.
More preferably, it is 30 nm or more. The thickness of the intermediate layer is 2
If it is less than 5 nm, the effects of the present invention may not be exhibited. The intermediate layer may be in contact with the well layer, and in this case, it also serves as the barrier layer. Further, the intermediate layer may form an interface with the other layer having a lattice mismatch, and in this case, it serves as the well layer side layer of the two layers forming the interface. Further, the intermediate layer may be in contact with the well layer and form an interface with the other layer having a lattice mismatch, and in this case, the intermediate layer is the barrier layer and the two layers forming the interface. It will also serve as the layer on the well layer side.

In the present invention, it is necessary that at least one interface between two layers having a lattice mismatch exists. Here, “having a lattice mismatch” means that the two layers have different lattice constants in the bonding surface direction, and when two layers having a lattice mismatch are joined, they are drawn into each other's lattice constant. As described above, the lattice strain is generated, that is, the stress applied to the crystal generally causes the crystal to have a lattice constant different from the original lattice constant. When two layers having a lattice mismatch are in contact with each other and each of the two layers has an original lattice constant in the joining direction, there is no lattice strain, and when the lattice strain is completely relaxed. .
Further, when two layers having a lattice mismatch have exactly the same lattice constant in the direction of the joint surface, there is no relaxation of lattice strain. When two layers having a lattice mismatch are joined and the lattice strain is partially relaxed, the lattice constant in the joining surface direction is different between the two layers, but it is different even when there is no lattice strain and is completely relaxed. It has an intermediate lattice constant between the case and the case where it is not relaxed at all.

As a preferred magnitude of the lattice mismatch in the present invention, specifically, the absolute value is 0.01% or more and 5
% Or less. Here, the size of the lattice mismatch is calculated by dividing the lattice constant difference in the joining surface direction of the layers stacked on the substrate by the lattice constant in the joining surface direction of the substrate on the reference side. To be done. Even if the absolute value of the lattice mismatch is smaller than 0.01% or larger than 5%, the effect of the present invention is not remarkable.

Of the compound semiconductors, it is generally difficult to grow a high-quality thick film for a mixed crystal containing a Group 3 element other than Ga, particularly for In. Therefore, in the present invention, at least one of the layers constituting the interface of the layer having the lattice mismatch is GaN or GaN.
It is preferable that the mixed crystal has a lattice match with. Further, in the layer forming the interface having the lattice mismatch of the present invention, the case where the compressive strain is applied due to the lattice mismatch is more remarkable than the case where the tensile strain is applied, and thus it is preferable. The effect of the present invention is particularly large when one of the layers forming the interface having a lattice mismatch is GaN and the other layer has a laminated structure with a layer having a larger lattice constant than GaN. The band gap of the layer forming the interface having a lattice mismatch is preferably larger than the band gap of the well layer because it does not hinder charge injection into the well layer. Specifically, when the InGaN quantum well layer is used as a light emitting layer, each layer forming an interface having a lattice mismatch is A
lGaN, GaN, InN having a mixed crystal ratio smaller than that of the light emitting layer I
nGaN, InGa having a band gap larger than that of the light emitting layer
It is preferably composed of AlN. In order to grow these layers, the raw material supply method may be adjusted or the growth temperature may be adjusted. Especially in the case of InGaN, I
Since the nN mixed crystal ratio strongly depends on the growth temperature, for example, I
In order to grow a layer having a small nN mixed crystal ratio, the growth temperature can be increased and adjusted.

1 of the structure of the 3-5 group compound semiconductor of the present invention
An example is shown in FIG. In the example of FIG. 1, the buffer layer 2, the GaN layer 3, the InGaN layer 4, the GaN layer 5, the InG are formed on the substrate 1.
The aN layer 6 and the GaAlN layer 7 are laminated in this order. Interface between GaN layer 3 and InGaN layer 4, and I
The interface between the nGaN layer 4 and the GaN layer 5 is the interface between the two layers having the lattice mismatch of the present invention, the GaN layer 5 is the intermediate layer, the InGaN layer 6 is the well layer, and the GaN layer 5 and AlGaN. Layer 7 is the barrier layer. The GaN layer 5 constitutes one of two layers having a lattice mismatch, and also serves as an intermediate layer and a further barrier layer. The thickness of the GaN layer 5, which is the intermediate layer, is 30 nm or more. In addition, In which is a well layer
The film thickness of the GaN layer 6 is not less than 5Å and not more than 90Å.

Although the example shown in FIG. 1 describes a case of a simple structure in order to simply explain the contents of the present invention, it may have a more complicated structure without departing from the contents of the present invention. For example, the constituent elements of each layer are two such as GaN or three such as GaAlN and InGaN, but a mixed crystal generally represented by InGaAlN can be used. Although the GaN layer 5 as the intermediate layer and the InGaN layer 6 as the well layer are in direct contact with each other, one or more layers may be provided between them. Further, although the interface between the two layers having the lattice mismatch and the GaN layer 5 which is the intermediate layer are in direct contact with each other, at least one or more layers are provided between the interface between the intermediate layer and the two layers having the lattice mismatch. Layers may be provided. In the example of FIG. 1, the interface between the two layers having the lattice strain is the interface between the GaN layer 3 and the InGaN layer 4 and the interface between the InGaN layer 4 and the GaN layer 5, but one or three interfaces. One or more may be formed. Examples of two or more interfaces having two layers having a lattice strain include a superlattice structure in which GaN and InGaN are alternately laminated, or a superlattice structure in which GaN and AlGaN are alternately laminated.

The degree of relaxation of the lattice mismatch depends on the size of the lattice mismatch, the thickness of each layer forming the interface of the layer having the lattice mismatch, and the physical properties such as elastic modulus. Since relaxation generally accompanies the generation of dislocations, it is preferably as small as possible.

Next, the substrate and the growth method used in the present invention will be described. Substrates for crystal growth of the Group 3-5 compound semiconductor include sapphire, ZnO, GaAs, and S.
i, SiC, NGO (NdGaO3), spinel (Mg
Al2O4), GaN, etc. are used. Sapphire is especially important because it is transparent and high-quality crystals with a large area can be obtained.

As the method for producing the Group 3-5 compound semiconductor, a molecular beam epitaxy (hereinafter sometimes referred to as MBE) method, a metal organic chemical vapor deposition (hereinafter sometimes referred to as MOVPE) method, Hydride vapor phase growth (hereinafter, HV
Sometimes referred to as PE. ) Law and the like. In addition,
When the MBE method is used, the nitrogen source is nitrogen gas,
Gas source molecular beam epitaxy (hereinafter, referred to as a method of supplying ammonia and other nitrogen compounds in a gaseous state)
Sometimes referred to as GSMBE. ) Method is commonly used. In this case, the nitrogen raw material is chemically inactive, and the nitrogen atom may be difficult to be taken into the crystal. In that case, by exciting the nitrogen raw material by a microwave or the like to supply it in an activated state, it is possible to improve the nitrogen uptake efficiency.

[0018]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto.

Example 1 A group 3-5 compound semiconductor having the structure shown in FIG. 2 was produced by the MOVPE method. As the substrate 1, a sapphire C surface mirror-polished was used after organic cleaning. As a growth method, a two-step growth method using GaN as a low temperature growth buffer layer was used. The temperature of the susceptor on which the substrate is placed is set to 550 ° C., and the GaN buffer layers 2 and 1060 having a thickness of about 50 nm
An n-type layer 8 made of GaN doped with Si and having a thickness of about 3 μm and a non-doped GaN layer 9 having a thickness of 150 nm were grown using hydrogen as a carrier gas.

Next, the susceptor temperature is 825 ° C., the carrier gas is nitrogen, and the carrier gas, TEG, TMI, and silane and ammonia diluted to 1 ppm with nitrogen are used as the raw materials. The InGaN layer 4 having no lattice relaxation was grown by repeating 3 nm and 4 times. The InN mixed crystal ratio of the InGaN layer is 1
At 0%, it has a lattice mismatch of 1.1% with respect to GaN in the a-axis direction. Further, the susceptor temperature is set to 785 ° C., the Si-doped GaN layer 5 as the intermediate layer is 100 nm, the InGaN layer 6 as the well layer is 3 nm, and the Al as the barrier layer.
The GaN layer 7 was grown to 6.5 nm. After the growth, the sample was taken out and the photoluminescence using a He-Cd laser (325 nm) as an excitation light source was measured at room temperature. Light emission from the well layer was observed as a spectrum having a peak at 457 nm, and the peak intensity was 2.06 times that of the standard sample and 6.87 times that of the sample of Comparative Example 1.
In the photoluminescence measurement, a peak from the InGaN layer of the underlayer grown at 825 ° C. was also observed at 406 nm, and its intensity was 2.26 times that of the standard sample and 7.53 of that of the sample of Comparative Example 1. It was double.

Comparative Example 1 In Example 1, a non-doped layer was grown at 1060 ° C., and then a GaN layer and an InGaN layer were not grown at 825 ° C., and a GaN layer and a well layer were directly doped with Si at 785 ° C. InGaN and AlGaN as a barrier layer were grown. This sample has the same structure as Example 1 except that there is no interface between the two layers having lattice mismatch. When this was evaluated for photoluminescence in the same manner as in Example 1,
The light emission from the well layer showed only a peak intensity 0.3 times that of the standard sample.

Comparative Example 2 Example 1 except that the thickness of the intermediate layer was 17 nm.
A sample was prepared in the same manner as in. When photoluminescence was evaluated in the same manner as in Example 1, the peak intensity of light emission from the well layer was 0.41 with respect to the standard sample.
The strength of the sample of Comparative Example 1 was only 1.37 times.

Example 2 A sample was prepared in the same manner as in Example 1 except that after growing undoped GaN at 1060 ° C., all InGaN layers, GaN layers and GaAlN layers were grown at a susceptor temperature of 785 ° C. It was made. When photoluminescence was evaluated in the same manner as in Example 1, the peak intensity was 3.94 times that of the standard sample and 13.1 times that of the sample of Comparative Example 1. This photoluminescence intensity includes a contribution from InGaN in the underlayer and a contribution from the quantum well on the outermost surface. InGa of this embodiment
The N layer has not undergone lattice relaxation, and its InN mixed crystal ratio is 17%.
Thus, GaN has a lattice mismatch of 1.9% in the a-axis direction. The photoluminescence intensity of the InGaN layer in the underlayer in Example 1 was 2.26 with respect to the standard sample.
Since it was 7.53 times that of the sample of Comparative Example 1,
Of the photoluminescence intensity of this example, the contribution to the peak intensity from the outermost InGaN well layer functioning as the light emitting layer in the LED structure is subtracted from the underlayer.
It was calculated to be 1.68 times that of the standard sample and 5.60 times that of the sample of Comparative Example 1.

Example 3 A sample was prepared in the same manner as in Example 2 except that InGaN other than the well layer was replaced by AlGaN without lattice relaxation. The AlN mixed crystal ratio in the GaAlN layer is 15% and has a lattice mismatch of −0.3% with respect to GaN in the a-axis direction. When the photoluminescence was evaluated in the same manner as in Example 1, the peak intensity was 0.96 times that of the standard sample and 3.20 times that of the sample of Comparative Example 1.

Example 4 A sample was prepared in the same manner as in Example 1 except that the thickness of GaN doped with Si for the intermediate layer was 50 nm instead of 100 nm. When photoluminescence was evaluated in the same manner as in Example 1, the peak intensity was 1.08 times that of the standard sample, and 3.60 with respect to the sample of Comparative Example 1.
It was double.

Example 5 An epiwafer for an LED is obtained by making a structure in which a p-type layer is further laminated on the sample described in this example. Further, an LED can be formed by further forming electrodes according to a conventional method. The LED thus obtained is an LED that emits light from a single quantum well with improved characteristics.

[0027]

Industrial Applicability The 3-5 group compound semiconductor of the present invention has high crystallinity and high quality, and a light emitting device using the same has high luminous efficiency and great industrial value.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a Group 3-5 compound semiconductor of the present invention.

FIG. 2 is a diagram showing a light emitting element of the present invention manufactured in Example 1.

[Explanation of symbols]

1. .. substrate 2. .. Buffer layer 3. .. GaN layer 4. .. InGaN layer 5. .. Middle class 6. .. Well layer 7. .. AlGaN barrier layer 8. .. Si-doped n-GaN layer 9. .. Non-doped GaN layer 10. .. Si-doped n-GaN layer

Continued front page    (72) Inventor Yoshinobu Ono             6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.             In the company (72) Inventor Seiya Shimizu             6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.             In the company F-term (reference) 5F041 AA03 AA04 AA40 CA04 CA05                       CA40 CA46

Claims (6)

[Claims] 1. An interface between two layers having a lattice mismatch, an intermediate layer having a film thickness of 25 nm or more, and a general formula In _x Ga _y Al _z N (where x + y + z =
1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1) and a single quantum well layer in this order. 2. The 3-5 group compound semiconductor according to claim 1, wherein the quantum well layer has a film thickness of 5 Å or more and 90 Å or less. 3. The interface according to claim 1, wherein the lattice mismatch is partially relaxed or not relaxed at the interface between the two layers having the lattice mismatch.
Group 5 compound semiconductors. 4. The two layers having a lattice mismatch have a laminated structure of a layer having a lattice match with GaN and a layer having a lattice mismatch with GaN. The compound semiconductor of Group 3-5 according to item 3. 5. The two layers having a lattice mismatch are laminated structures of a layer lattice-matched to GaN and a layer having a lattice constant larger than that of GaN. 3-5 group compound semiconductor. 6. A light emitting device comprising the Group 3-5 compound semiconductor according to claim 1.