JP2001028458A - Light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting device of 3-5 nitride compound semiconductor, capable of emitting light of a desired color rendering property by a method, where well layers which emit different colored lights are laminated, and lights emitted from the well layers are mixed together. SOLUTION: A light emitting device 100 is equipped with an active layer 106, which is provided with at least a first well layer 108 formed of In- containing nitride compound semiconductor and at least a second well layer 109, which emits light of main wavelength peak longer than the main wavelength peak which the first well layer emits. With this setup, for instance, when the first well layer emits blue light and the second well layer emits yellow light which is the complementary colored light of blue light, and these colored lights are mixed together, by which a light emitting device which serves as a white light source can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III-V nitride compound semiconductor (in general, In _x Al _Y Ga _{1 -XYN} (0 <X, 0 ≦
Y, X + Y ≦ 1)).
In particular, the present invention relates to a light-emitting element that emits light having a desired color rendering property by stacking well layers that emit different colors and mixing colors of the emitted light.

[0002]

2. Description of the Related Art Hitherto, with the development of light-emitting elements that emit red, green, and blue (so-called RGB) light with extremely high luminance, high-luminance type light-emitting elements have been mass-produced. In particular, in a light-emitting element using a nitride semiconductor, the emission color can be adjusted from the ultraviolet region to the red region by changing the mixed crystal ratio.

[0003] On the other hand, by utilizing the excellent characteristics of the light emitting element such as high luminance, low power consumption, miniaturization and high reliability, it can be used in the technical fields such as a light source of a vehicle-mounted meter, a liquid crystal backlight light source and various illuminations. , Its use is expanding rapidly.

In the field of application of such light emitting devices,
In particular, white is a color that is comfortable and pleasant to human eyes,
Especially high demand. Until now, to achieve white light,
A plurality of light-emitting elements having different emission colors such as red, green and blue, or blue and yellow are arranged on the same stem, and a desired white light is obtained by mixing the emission colors, or a light emission that emits blue light. White light has been obtained using the element and a fluorescent substance that emits fluorescent light in yellow which is complementary to the element.

[0005]

However, when white light is obtained by arranging a plurality of light-emitting elements on the same stem, the color mixing property (how the light looks uniform as one color when mixed) is improved. It is necessary to bring a plurality of light-emitting elements closer to each other for improvement, but there is a limit to this. In addition, when semiconductor materials of different systems are used, various problems occur, such as different temperature characteristics and different driving voltages. Similarly, when white light is obtained using a phosphor, it is necessary to attach the phosphor to the light emitting element, which complicates the process. In addition, when white light is obtained by combining blue light emission from a light emitting element and fluorescent light emission excited by the light emission, the emission efficiency is theoretically lower than when white light is obtained by a plurality of light emitting elements.

Therefore, in order to replace various conventional light sources with solid-state light-emitting elements, the light-emitting elements having the above-described structure are not sufficient, and it is necessary to provide a light-emitting element capable of emitting white light with high efficiency and high luminance. It has been demanded. An object of the present invention is to provide a light-emitting element that can emit a white or other light-emitting color with high efficiency and high luminance by using one light-emitting element in order to solve the above problem.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to:
It is an object of the present invention to provide a light emitting element for obtaining white light, which has a well layer made of a nitride compound semiconductor containing at least two In compositions different from each other.

A second object of the present invention is to provide a light emitting device having an improved luminous efficiency by making the first well layer larger and smaller than the second well layer.

[0009] A third object of the present invention is to form an A layer on each well layer.
It is another object of the present invention to provide a light emitting device with a reduced forward voltage and improved luminous efficiency by forming a first barrier layer containing l and a second barrier layer not containing Al thereon.

The light emitting device according to claim 1 of the present invention has
At least one first well layer made of a nitride compound semiconductor containing n and a nitride compound semiconductor containing In emitting light having a main peak wavelength longer than the main peak wavelength of light emitted from the first well layer An active layer having a multiple quantum well structure including at least one second well layer is sandwiched between an n-type semiconductor and a p-type semiconductor.

The main peak wavelength emitted by the first well layer and the second peak wavelength
When the main peak wavelengths emitted by the well layers are set to have a complementary color relationship with each other, white light is obtained by mixing these two lights.

According to a second aspect of the present invention, in the light emitting device, the second well layer is disposed between the first well layer and the p-type semiconductor.

In general, it is extremely difficult to form a nitride semiconductor containing In. The longer the emission wavelength by increasing the In composition ratio of the well layer, the worse the crystallinity becomes and the lower the light emission efficiency becomes. This tendency is observed when the composition ratio of In is 0.05
The above is remarkable. In particular, in the multiple quantum well structure of a nitride semiconductor, the diffusion length of holes is short. Where p
Since the recombination efficiency of electrons and holes is high on the p-type semiconductor layer side, by disposing a second well layer having relatively low crystallinity due to containing a large amount of In on the p-type semiconductor layer side,
That is, by arranging the second well layer between the first well layer and the p-type semiconductor, the luminous efficiency of the second well layer can be improved.

In the light emitting device according to the third aspect of the present invention, the luminous intensity ratio of the light emitted from the first and second well layers is controlled by adjusting the ratio of the number of stacked first and second well layers. ,
Desired color rendering (effect of light source on appearance of color of object)
Characterized by providing a light source having:

Conventional light sources such as incandescent lamps and fluorescent lamps have been developed as light sources having various color rendering properties depending on their uses. For example, there are many fluorescent lamps that illuminate in different colors. It has been desired that the color rendering of the light emitting device according to the present invention, which can replace the conventional light source, can be finely adjusted relatively easily.

That is, in the present invention, the luminous intensity ratio of light emitted from each well layer can be controlled relatively easily by adjusting the ratio of the number of stacked first and second well layers. As another method, for example, the luminous intensity ratio of light emitted from each well layer can be controlled by controlling the thickness of the well layer. However, when the active layer has a quantum well structure, the luminous intensity can be increased to some extent by reducing the thickness of the well layer, but light moves to the short wavelength side due to the quantum size effect. Similarly, if the thickness of the well layer is increased, the luminous intensity can be reduced to some extent, but light moves to the longer wavelength side. In any case, there is a problem that it is extremely difficult to obtain a desired emission wavelength.

In the light emitting device according to a fourth aspect of the present invention, the active layer further includes a plurality of barrier layers sandwiching the first and second well layers, and the first and second barrier layers are adjusted in thickness. By controlling the luminous intensity ratio of light emitted from the two well layers, a light source having desired color rendering properties is provided.

By controlling not only the ratio of the number of stacked layers of the first and second well layers but also the thickness of the barrier layer, the luminous intensity ratio of the light emitted from each well layer is controlled, and the desired color rendering properties are similarly obtained. A light source can be provided.

A light emitting device according to a fifth aspect of the present invention is characterized in that the first well layer is stacked more than the second well layer.

In particular, when the second well layer is stacked at a position closer to the p-type semiconductor than the first well layer, light emitted from the first well layer is absorbed by the second well layer, and the luminous intensity is reduced. I do. Therefore, by laminating the first well layers more than the second well layers, white light having desired color rendering properties can be obtained relatively easily.

According to a sixth aspect of the present invention, there is provided a light emitting device, wherein the spectral half width of light emitted from the first well layer is narrower than the spectral half width of light emitted from the second well layer.

In the case of a light emitting device having a first well layer whose main peak wavelength is in the blue region and a second well layer whose main peak wavelength is in the yellow region, the light emitted by this light emitting device is in the green and red regions. Has no or almost no wavelength component, and thus the color rendering properties may not be good. Therefore, the emission spectrum of light emitted from the second well layer is changed to the first
It is preferable to make it wider than that of the well layer. As a result, it is possible to improve the average color rendering index Ra of light emitted by the light emitting element without impairing the luminous efficiency, that is, to form a light emitting element capable of emitting white light with high luminance and high color rendering. Can be. As will be apparent to those skilled in the art, the spectral half width can be controlled by, for example, adjusting the crystallinity of the well layer or adding an impurity.

In a light emitting device according to a seventh aspect of the present invention, the first well layer is stacked in a range of 2 to 10 layers, and the second well layer is stacked in a range of 1 to 3 layers. It is characterized by that.

In the light emitting device according to the eighth aspect of the present invention, the main peak wavelength of light emitted from the first well layer is 450 to 50.
0 nm, the main peak wavelength of light emitted from the second well layer is 56 nm.
It is characterized by having a thickness of 0 to 670 nm.

The light emitting device according to the ninth aspect of the present invention is characterized in that the second well layer has a greater degree of unevenness than the first well layer.

In general, the luminous efficiency of a well layer having a multiple quantum well structure is higher as the interface with the barrier layer is flatter and the crystallinity is better. However, like the light emitting device of the present invention,
In an active layer having a multiple quantum well structure including well layers that emit different emission peak wavelengths, it is considered that some interaction occurs because the well layers are adjacent to each other across the barrier layer. That is, when the present inventor makes the degree of irregularity of the second well layer for long-wavelength emission larger than that of the first well layer for short-wavelength emission, the short-wavelength light emitted from the first well layer will It was confirmed that it became difficult to be absorbed. Also,
Under this condition, by optimizing the degree of unevenness of the second well layer, as will be described later, the luminous efficiency of long-wavelength light emission from the second well layer can be increased, and light emission as a light emitting element Efficiency can be increased.

An example of a method for comparing the degree of unevenness of the first and second well layers will be described. First, the light emitting element is cut in a direction perpendicular to the layer thickness direction, and the unevenness of the interface between the well layer and the barrier layer in this cross section is compared with a scanning electron microscope or the like. In some cases, the difference in the degree of roughness or roughness between the two can be clearly confirmed only by checking with a microscope. When the difference is not clear, the comparison may be made based on the degree R occupied by the concave region described later,
For at least one of the upper surface and the lower surface of the well layer, GIXR (Grazing Incidence X-Ray Reflection:
The roughness may be compared to determine the magnitude of the unevenness by thin film analysis by oblique incidence X-ray reflectance analysis. When the first and second well layers have a plurality of well layers, it is only necessary that at least one second well layer has a greater degree of unevenness than at least one first well layer. It is desirable that all of the second well layers have a greater degree of unevenness than all of the first well layers. However, as described above, since the crystallinity of the well layer and its growth form mainly depend on the In content,
Even if there are a plurality of first and second well layers, the irregularities thereof are substantially the same.

It is preferable to form the second well layer so that the unevenness of the second well layer is larger than that of the first well layer from the viewpoint of the crystallinity of the second well layer. That is, when the degree of unevenness of the second well layer is larger than that of the first well layer (including the case where only the second well layer has unevenness).
When the degree of unevenness of the first well layer is larger than that of the second well layer, the crystallinity of the second well layer is extremely poor. It becomes difficult to form a second well layer having a uniform thickness over the entire or partial region of the wafer, and there may be a region where crystals of the second well layer do not grow. On the other hand, when the degree of unevenness of the second well layer is larger than that of the first well layer, the second well layer is formed relatively constant. Therefore, it is considered that making the degree of unevenness of the second well layer larger than that of the first well layer contributes to improvement of the characteristics of the light emitting element. Further, in such a case, the first and second well layers both have good crystallinity and have a constant film thickness. As a result, the luminous intensity ratio of light from each well layer is stabilized, and problems such as uneven brightness and color shift between the obtained light emitting elements are greatly improved.

As will be apparent to those skilled in the art, the degree of unevenness of the first and second well layers can be changed by controlling film forming conditions such as a film forming speed and a film forming temperature. it can. By changing the film formation conditions other than those described above, the degree of unevenness of each well layer may be changed.

As described above, when the degree of unevenness of the second well layer is larger than that of the first well layer, the luminous efficiency of the light emitting element is improved. The exact relationship between each of the degree of unevenness of the first and second well layers and the luminous efficiency is not clear. However, it is considered that the first well layer that emits light having a shorter main peak wavelength and the second well layer that emits light having a longer main peak wavelength have different contributions to the luminous efficiency due to the degree of unevenness. That is, the In content in the well layer included in the active layer of the multiple quantum well, the number of layers, the arrangement relationship of the first and second well layers, and the like are closely related to the degree of unevenness of the well layer, and the device characteristics It seems to have affected. Since there is a difference in the contribution to the luminous efficiency depending on the degree of the unevenness, a difference also occurs in the optimal degree of the unevenness of the first and second well layers. Furthermore, the second
By making the degree of the unevenness of the well layer larger than that of the first well layer, the characteristics of the light emitting element can be improved. That is, the first and second well layers have the same degree of unevenness, or the first well layer has the same degree of unevenness as the second well layer.
The characteristics of the light-emitting element when the degree of unevenness of the second well layer is larger than that of the first well layer are not good as compared with the case of the well layer. This indicates that the improvement in the characteristics of the light emitting element mainly depends on the magnitude relation of the degree of the unevenness of each well layer rather than the degree of the unevenness of each well layer. In addition, when the degree of unevenness of the second well layer is larger than that of the first well layer, the light intensity ratio of light from each well layer is constant, so that a light source having desired color rendering properties can be easily obtained. . This is thought to be mainly due to the above-mentioned good crystallinity. In addition, regarding light emission from the first well layer, not only the light extraction efficiency is improved due to the unevenness of the second well layer, but also the luminous intensity of the light itself tends to be improved. However, there is such a tendency. As described above, the unevenness of each light emitting layer and the magnitude relation thereof increase the light emitting efficiency of the entire device by a synergistic effect, and light emission from the first well layer can be efficiently obtained, with the result that a desired color rendering property is obtained. Can be provided.

In the light emitting device according to the tenth and eleventh aspects of the present invention, the second well layer includes a partially thin concave portion having a thickness equal to or less than half of the average thickness, and the region of the concave portion is entirely formed. 10% or more of the above.

Here, an example of a method of measuring the degree of the occupied area of the concave area with respect to the whole will be described with reference to FIG. First, the light emitting element is cut in a direction perpendicular to the layer thickness direction, and the cross section of the well layer is observed with a scanning electron microscope or the like. The well layer includes a partially thin concave portion having a thickness equal to or less than half of the average film thickness, and a total range S of the concave portion is measured in a specific range (length L). Then, the degree R occupied by the concave region in the specific range is obtained by the equation R = S / L. Here, the area to be measured (length L) is at least 1 μm.
m is enough, but if it is about 10 μm or more,
Further, the degree R occupied by the concave region can be measured with good reproducibility, which is preferable. Further, the average thickness is sufficient if the average thickness of the well layer in the measurement range L is sufficient, and this may be used as the average thickness of the well layer in the entire device. Furthermore, since the degree R of the entire concave region is generally considered to be uniform in the entire light emitting element, it can be measured at an arbitrary cut surface.

The light emitting device according to the tenth and eleventh aspects of the present invention is characterized by having a second well layer that satisfies R ≧ 0.1. When the second well layer is formed such that the value of the degree R occupied by the concave region is less than 0.1, that is, when the second well layer has a relatively flat shape, the first well layer Not only is the luminous intensity relatively lower than that from the second well layer, but also the luminous efficiency of the entire light emitting element is reduced.

When a plurality of second well layers are stacked, the luminous efficiency of the first well layer is improved even if only one of the second well layers satisfies the above-mentioned conditional expression R ≧ 0.1. It is further desirable that all the second well layers satisfy the same condition.

If the degree R occupied by the concave region of the second well layer is larger than 0.5, the flatness of the p-type semiconductor layer grown on the second well layer is impaired. Decrease the luminous efficiency of the device. Therefore, when the light emitting element is formed with the upper limit of the degree R occupied by the concave region of the second well layer being 0.5, light emission from the first well layer is efficiently taken out, and the light emitting characteristics of the entire light emitting element are also well maintained. .

In the light emitting device according to the twelfth to fourteenth aspects of the present invention, the second well layer having a larger degree of unevenness than the first well layer or the first well layer satisfying R ≧ 0.1 is used. And a p-type semiconductor.

As described above, the luminous efficiency is improved by disposing the second well layer having a high In mixed crystal ratio and relatively poor crystallinity on the p-type semiconductor side having a high electron-hole recombination probability. Can be preferred.

Further, the degree of unevenness of the first well layer is equal to the second well layer.
When the thickness is substantially equal to the well layer or is larger than the second well layer, it is difficult to uniformly form the well layer on the wafer, and the emission wavelength varies between light emitting elements. If the variation in the emission wavelength is large, it is difficult to reliably produce a light source having a desired color rendering property. Therefore,
From this point as well, it is preferable that the second well layer having a larger degree of unevenness is arranged between the first well layer and the p-type semiconductor.

The light emitting device according to the present invention is characterized in that the first well layer is stacked more than the second well layer.

In particular, when the second well layer is stacked closer to the p-type semiconductor than the first well layer, light emitted from the first well layer is absorbed by the second well layer, and the luminous intensity is reduced. I do. Therefore, by laminating the first well layers more than the second well layers, white light having desired color rendering properties can be obtained relatively easily. Further, since the number of the second well layers having relatively poor crystallinity is small, it is preferable to form a p-type semiconductor to be subsequently stacked thereon.

The light-emitting device according to claim 18 of the present invention
On each of the first and second well layers, a first barrier layer made of a nitride compound semiconductor containing Al and a second barrier layer made of a nitride compound semiconductor containing substantially no Al are provided. Features.

[0042]

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more clearly understood from the following detailed description and the accompanying drawings, which are merely illustrative and do not limit the scope of the invention.

(Embodiment 1) At least two colors of light emitted from a well layer composed of at least two nitride compound semiconductors having different In contents are mixed to obtain light such as white light. Things. In particular, by providing a well layer that emits light at a longer wavelength on the p-type layer side than a well layer that emits light at a shorter wavelength, high luminous efficiency is achieved.
A light source having a desired color rendering property can be provided.

A well layer made of a nitride semiconductor containing In emits light having a short wavelength almost in proportion to its band gap energy depending on the In content. However, as the amount of In contained in the nitride semiconductor increases, its crystallinity tends to deteriorate, and the luminous efficiency tends to decrease.
That is, the second well layer has lower luminous efficiency than the first well layer. In addition, since the well layer having a multiple quantum well structure of a nitride semiconductor has a short hole diffusion length, a well layer provided near a p-layer semiconductor is better than a well layer provided near an n-layer semiconductor. The electron-hole recombination probability is high.

Therefore, according to the first embodiment of the present invention,
The second well layer having relatively low crystallinity due to the higher In content is disposed closer to the p-type semiconductor layer than the first well layer having relatively low crystallinity due to the lower In content. . That is, the second well layer is disposed between the first well layer and the p-type semiconductor layer. Thus, a light-emitting element having higher luminance and excellent luminous efficiency characteristics can be formed.

(Embodiment 1) A light emitting device according to Embodiment 1 of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing a light emitting device 100 of the present invention. The light emitting device 100 includes a GaN buffer layer 102 and an undoped Ga on a sapphire substrate 101.
N layer 103, n-type contact layer / cladding layer 104 made of Si-doped GaN, superlattice layer 105, active layer 106 having a multiple quantum well structure, Mg-doped AlGaN
A p-type cladding layer 110 made of and a p-type contact layer 111 made of Mg-doped GaN are sequentially formed.
The active layer 106 is composed of a barrier layer 107 and a first well layer 108 and a second well layer 109 made of InGaN, and a second well layer 108 on the p-type contact layer 111 side.
The well layer 109 contains a larger amount of In than the well layer 108 on the n-type contact layer 104 side. By forming the p-side and n-side electrodes 113 and 114 on the n-type and p-type contact layers 103 and 111, the light emitting element 100 capable of emitting mixed color light can be formed. Next, a method for forming a light emitting device according to the present invention will be described in detail.

A light emitting element is formed by forming a nitride semiconductor film by the MOCVD method. First, the cleaned substrate 101 made of 2-inch sapphire (C surface) is set in a reaction vessel of a MOCVD apparatus. While evacuating the reaction vessel,
After flowing H 2 to sufficiently replace the inside of the container with H 2, the substrate temperature is increased to 1050 ° C., and the substrate 101 is cleaned. As the semiconductor substrate 101, in addition to C-plane sapphire, sapphire having an R-plane or an A-plane as a main surface, an insulating substrate such as spinel (MgAl2O4), SiC (6
H, 4H, and 3C), Si, ZnO, GaAs, and GaN.

Next, the film formation temperature was lowered to 510 ° C.
(Trimethylgallium), NH3 as a source gas, and H2 as a carrier gas, a GaN layer having a thickness of about 150 ° is formed on the sapphire substrate 101, and the buffer layer 102 is formed.
To form The buffer layer 102 is made of GaN and A
Materials such as 1N and GaAlN can be used.

Subsequently, the flow of the raw material gas is stopped once, and the temperature of the substrate is increased to 1050 ° C. while flowing the carrier gas. After the film formation temperature was stabilized, TMG and NH3 were flowed as a source gas, and H2 was flowed as a carrier gas.
Is stacked on the buffer layer 102.

Then, while maintaining the film formation temperature at 1050 ° C., TMG and NH 3 as source gases, H 2 as a carrier gas, and SiH 4 as an impurity gas were flowed.
An n-type contact layer 104, which is a GaN layer having a Si impurity concentration of 1018 / cm3, is formed on the undoped GaN layer 103 with a thickness of 2.25 μm.

Further, in order to improve the crystallinity of the active layer 106 and uniformly emit light over the entire surface, the n-type contact layer 1
It is preferable to form the superlattice layer 105 on the substrate 04. By controlling the supply of the impurity gas SiH4 while maintaining the film formation temperature at 1050 ° C., the thickness is about 75 ° C.
Undoped GaN layer and Si-doped G
An aN layer is formed. With this as one cycle, the superlattice layer 105 having a total film thickness of 2500 ° is formed on the n-type contact layer 104 by repeating 25 cycles. Note that the Si-doped GaN layers constituting the superlattice layer 105 have different impurity concentrations (Si), and are so-called modulation-doped.

Next, the configuration of the active layer 106 having a multiple quantum well structure will be described in detail. Active layer 10 having multiple quantum well structure
6 is a barrier layer 107 made of GaN having a thickness of about 250 °.
And a first well layer 1 made of InGaN having a thickness of about 30 °
08 for three cycles, and then a similar thickness of about 2
It is formed by forming a barrier layer 107 made of 50 ° GaN and a second well layer 109 made of InGaN with a thickness of about 30 °. The first well layer 108 near the n-type cladding layer 105 emits blue light, and the second well layer 109 near the p-type cladding layer 110 emits yellow light. The active layer 1
It is desirable that both ends of 06 be GaN.

Further, the active layer 106 having a multiple quantum well structure
A specific method of forming will be described. By flowing TMG and NH 3 as source gases and H 2 as a carrier gas at a film forming temperature of 1050 ° C. by MOCVD, a GaN barrier layer 107 having a thickness of about 250 ° is formed on the superlattice layer 105.

Subsequently, the flow of the raw material gas was stopped once, the film formation temperature was adjusted to 800 ° C., and TM gas was again used as the raw material gas.
By flowing G, TMI (trimethylindium), NH3, and N2 as a carrier gas, an In0.5Ga0.5N film having a thickness of about 30 DEG is formed.

Thereafter, the film formation temperature was set to 1050 ° C., and TMG and NH 3 were used as source gases, and H 2 was used as a carrier gas.
GaN barrier layer 1 having a thickness of about 250 °
07 is formed on the first well layer 108. This is repeated as one cycle to repeat lamination for three cycles.

Subsequently, the inflow of the source gas was stopped once, the film formation temperature was adjusted to 800 ° C., and TM was again used as the source gas.
By flowing G, TMI (trimethylindium), NH3, and N2 as a carrier gas, a second well layer 109 is formed by forming In0.8Ga0.2N to a thickness of about 30 DEG. The second well layer 109 is formed so as to contain more In than the first well layer 108 by increasing the flow rate ratio of TMI (trimethyl indium) as compared with the case where the first well layer 108 is formed. ing.

The well layer 108, which is a light emitting layer, is non-doped or acceptor impurity such as Mg or Zn.
It may contain a donor impurity such as Si. Moreover,
A donor impurity and an acceptor impurity can be simultaneously contained.

After forming the active layer 106, a p-type cladding layer 110 having a superlattice structure is formed. M about 40mm thick
g-doped AlGaN layer and Mg-doped I about 25 ° thick
An nGaN layer is formed. The p-type cladding layer 110 is formed by repeating this process as one cycle and forming five cycles. Specifically, the film formation temperature is set to 1 by the MOCVD method.
050 ° C., TMG, TMA (trimethylaluminum) and NH ₃ as source gases, and C as an impurity gas.
By flowing p ₂ Mg (cyclopentadienyl magnesium) and H 2 as a carrier gas, an AlGaN layer having a thickness of about 40 ° is formed. Next, once the inflow of the source gas is stopped, the film formation temperature is adjusted to 850 ° C., and then TMG, TMI, and NH ₃ as the source gas, Cp ₂ Mg as the impurity gas, and N ₂ as the carrier gas flow again. To form an InGaN layer having a thickness of about 25 °. This is repeated five times to form a p-type cladding layer 110 having a superlattice structure having a thickness of about 325 °. In addition,
The p-type cladding layer 110 may have a superlattice structure as described above, or may have a single-layer structure such as AlGaN or AlBGaN.

Then, the film formation temperature was set to 1050 ° C., TMG and NH ₃ as source gases, H ₂ as a carrier gas, and Cp ₂ Mg as an impurity gas were flowed, and 1 × 1
The p-type contact layer 111, which is a GaN layer having a Mg impurity concentration of 020 / cm 3, is formed with a thickness of 2.25 μm.
It is formed on the mold cladding layer 110. p-type cladding layer 11
After the formation of 0, the temperature is lowered to room temperature, and the wafer is annealed at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

After the annealing treatment, the wafer is taken out of the reaction container, a mask having a desired shape is formed on the surface of the uppermost p-type contact layer 111, and the mask is formed from the p-type contact layer 111 side by an RIE (reactive ion etching) apparatus. An etching process is performed to expose the p-type and n-type semiconductor surfaces.

After the etching process, the sputtering device is used to cover almost the entire surface of the p-type contact layer 111 with a film thickness of 200 Å.
P-type electrode 112 containing Ni and Au, and p-type electrode 112
A p-type pad electrode 113 made of Au for bonding and having a thickness of 0.5 μm is formed thereon. On the other hand, on the n-type contact layer 104 exposed by the etching process,
An n-type electrode 114 containing W and Al is formed. Finally,
In order to protect the surface of the p-type electrode 112, an insulating layer (not shown) made of SiO2 is formed as a protective film. After the scribe line is drawn on the nitride semiconductor wafer thus formed, it is divided by an external force, and 350
A μm square LED chip is completed.

As described above, the light emitting device of the present invention generally has an active layer having a multiple quantum well structure, and this active layer
The first well layer 108 made of a nitride semiconductor containing n
It has a well layer 109. At this time, the second well layer 109
Emits a main peak wavelength longer than the main peak wavelength emitted from the first well layer 108. The well layer according to the present invention may be a nitride semiconductor containing In, for example, In _x Al _Y Ga _{1 -XYN} (0 <X, 0 ≦ Y, X + Y ≦
1), preferably a ternary mixed crystal of In _x Ga ₁ -xN
(0 <X <1). Because InGaAl
This is because, compared to other nitride semiconductors such as N, InGaN is formed as a well layer having relatively good crystallinity even if it has a concave region or unevenness on the film formation surface. The active layer having a multiple quantum well structure of the present invention further includes a barrier layer 1 made of the first well layer 108, the second well layer 109, or a nitride semiconductor having a larger band gap than other well layers.
07, and are formed by laminating the well layers 108 and 109 and the barrier layer 107 interposed therebetween. Barrier layer 1
07 is not particularly limited, but GaN, InGaN, A
It is formed of a material such as lGaN so as to be thicker than the well layers 108 and 109, for example, to have a thickness of about several hundreds of mm. The thicknesses of the first well layer 108 and the second well layer 109 are not particularly limited, but are preferably, for example, 100 ° or less, more preferably 7 °.
The thickness is adjusted to 0 ° or less, most preferably 50 ° or less. If the thickness is more than 100 °, the thickness of the well layer exceeds the elastic strain limit, and minute cracks or crystal defects are likely to enter the well layer.

The p-type semiconductor and the n-type semiconductor are not particularly limited. For example, p-type and n-type semiconductors made of a nitride semiconductor can be used. The material composition of the nitride semiconductor of the present invention is In _x Al _Y G
a _1-XY N (0 <X, 0 ≦ Y, X + Y ≦ 1), and as described above, have p-type conductivity or n-type conductivity.
P-type or n-type impurities are doped.

The lead frame of the light emitting diode lamp is made of silver-plated iron-containing copper. One of the lead frames is a mount lead having a cup for disposing the LED chip, and the other has an inner lead electrically connected to one electrode of the LED chip via a wire. After the LED chip is die-bonded on the mount leads using epoxy resin,
One of a 35 μm-diameter gold wire is ball-bonded to the p-electrode and the n-electrode of the chip, and the other is stitch-bonded to the tip of the lead frame. Thus, L
Each electrode of the ED chip is electrically connected to the inner lead and the mount lead.

When a forward current of 20 mA (Vf = 3.5 V) was passed through the light emitting diode lamp thus obtained, the coordinates on the CIE chromaticity diagram were (X, Y) =, as shown in FIG. White light having an emission spectrum represented by (0.333, 0.314) and having a color temperature of about 6000K is obtained. At this time, the first and second well layers 10
From about 8,470 nm and about 575 nm, respectively
Emission having a wavelength of Also, the second well layer 1
The emission spectrum of 09 has a wider half-width than that of the emission spectrum of the first well layer 108 and has excellent color rendering properties. Note that the light emitting element according to the present invention is not limited to two well layers emitting different emission spectra, and more well layers can be provided. Thereby, the spectrum width of the entire light emitting element can be widened.

In order to demonstrate the effect of the present invention, a comparative experiment was performed. That is, the first and second well layers 108, 1
A light-emitting diode lamp was formed in the same manner except that the light-emitting diode lamp was formed by changing the stacking order of No. 09. The brightness of the light-emitting diode lamp was darker, and the emission color appeared bluish. This is because the second light emitting layer 109 having a high In content
It is considered that the luminous intensity of the first well layer 108 decreased because the crystallinity of the first well layer 108 deteriorated by being dragged by the second well layer 109 having poorer crystallinity.

(Example 2) Next, a first well layer 208 for emitting blue light was added to make a total of four layers.
The light emitting element 200 was formed in the same manner as described above. The light-emitting color of the light-emitting element 200 obtained in this manner was higher in color temperature and bluish than that of the light-emitting element 100 of Example 1. Similarly, by adding two first well layers that emit blue light, a total of 5
Except for the layer, the light-emitting element thus formed looked more bluish in the same manner as in Example 1. The light emitting device 100 according to the first embodiment (three first well layers 108 and one second well layer 109) and the light emitting device 200 according to the second embodiment
(Four first well layers 208 and one second well layer 209)
FIG. 3 shows the coordinates on the chromaticity diagram of the emission spectrum emitted from. That is, the first well layer 108 and the second well layer 10
By adjusting the ratio of the number of layers of 9, the mixed color light having the desired CIE chromaticity diagram coordinates and color temperature can be obtained.

Example 3 A light emitting device 100 was formed in the same manner as in Example 1 except that the thickness of the barrier layer 107 sandwiching the first well layer 108 was changed from about 250 ° to about 300 °, respectively. When a forward current was applied to the light emitting element 100 thus obtained, the intensity of light emitted from the second well layer 109 was almost the same, but the intensity of light emitted from the first well layer 108 increased.

Example 4 A light emitting device 100 is formed in the same manner as in Example 1 except that the thickness of the barrier layers 107 sandwiching the second well layer 109 is changed from about 250 ° to about 200 °, respectively. When a forward current is applied to the light emitting element 100 thus obtained, the light emission intensity emitted from the first well layer 108 is substantially the same, while the light emission intensity emitted from the second well layer 109 is reduced. According to Examples 3 and 4, the barrier layer 1
By controlling the thickness of 07, the luminous intensity ratio of each emission color can be controlled to easily obtain a light source having a desired color rendering property.

(Example 5) A light emitting element is formed in the same manner as in Example 1 except that the half value width of the emission spectrum of the second well layer 109 is wider than that of the second well layer 109 of Example 1. . Specifically, in the first embodiment, the film formation temperature adjusted to 800 ° C. is increased to 810 ° C., and the TMI gas used in the first embodiment is made to flow more to form the second well layer 109. In general, when the deposition temperature is increased, the main wavelength peak wavelength shifts to the shorter wavelength side, and when the In material gas is increased, the main peak wavelength shifts to the shorter wavelength side. Further, in any case, the second well layer 109 thus formed is formed.
Has a broader emission spectrum distribution. That is, the half width of the emission spectrum is widened. As described above, by increasing the TMI flow rate so as to complement the fact that the main peak wavelength of the second well layer 109 has shifted to the shorter wavelength side by setting the film formation temperature from 800 ° C. to 810 ° C., the main peak wavelength is reduced. Without changing, it is possible to widen only the half width of the emission spectrum. FIG. 4 shows the emission spectrum distribution of Example 1 of the present invention, and FIG. 5 shows the emission spectrum distribution of Example 5.

By increasing the film forming temperature, increasing the thickness of the active layer, or adding impurities, the half width of the emission spectrum can be increased. They can be combined.

(Embodiment 2) In Embodiment 2 of the present invention, in the light emitting device of Embodiment 1, the unevenness of the second well layer is made larger than that of the second well layer, or By setting the degree occupied by the concave region having a thickness equal to or less than half of the average thickness of the second well layer to 10% or more, highly efficient light emission having desired color rendering properties is enabled.

An example of a method for evaluating the degree of unevenness of the well layer of the light emitting device formed in Embodiment 1 will be described.

First, the light emitting device 100 formed in Example 1
The cross section of the well layers 108 and 109 cut in a direction perpendicular to the layer thickness direction is observed by a scanning electron microscope or the like. As shown in FIG. 6, the target well layer 107 or 108 includes a partially thin concave portion D having a thickness equal to or less than half of the average thickness. The total sum S of the lengths of the concave portions D is measured for a specific range (length L). Then, the degree R occupied by the concave region in the specific range (the degree of unevenness of the well layer) R is obtained by the equation R = S / L. here,
It is sufficient if the area (length L) to be measured is at least about 1 μm, but if it is at least about 10 μm, the degree R of the unevenness can be measured with better reproducibility, which is preferable. Further, the average thickness is sufficient if the average thickness of the well layer in the measurement range L is sufficient, and this may be used as the average thickness of the well layer in the entire device. Furthermore, since the degree R of the unevenness of the well layer is generally considered to be uniform in the entire light emitting element, it can be measured on an arbitrary cut surface.

Here, when the degree R of the unevenness of the second well layer 108 of the light emitting device formed in Example 1 was actually measured, it was 0.15.

(Example 6) When forming the second well layer 108, the film formation rate was slightly increased from that in Example 1, and the degree R of the unevenness became 0.2. That is, a light-emitting device similar to that of Example 1 was obtained except that the degree R of unevenness was 0.2. According to the obtained light emitting device 100, the ratio of the luminous intensity of the blue light emitted by the first well layer 108 to the luminous intensity of the yellow light emitted by the second well layer 109 was slightly larger than that in the first embodiment. . The luminous efficiencies of the obtained light-emitting elements 100 were almost the same.

(Embodiment 7) First well layer emitting blue light
The light emission was performed in the same manner as in Example 1 except that the film formation temperature of Example 108 was changed.
An element is formed. Generally formed at higher deposition temperature
Then, the degree of unevenness of the well layer tends to increase. No.
After setting the deposition temperature of one well layer 108 to 830 ° C.
Again, TMG, TMI and N
H_ThreeAnd nitrogen gas as carrier gas
At a film speed of 2 ° / sec and a thickness of about 30 ° _0.5Ga_0.5N
Is formed. This is repeated three times and the content of In is small.
A first well layer 108 is formed.

At this time, the first well layer 108 has irregularities on both sides similarly to the second well layer 109, and the ratio R of the concave region is 0.1. Further, at this time, the light emitting element 100 has the same good luminous efficiency as that of the first embodiment. In addition, a variation in the luminous intensity ratio between the blue light and the yellow light between the elements is small, and as a result, a white light source having desired color rendering with good reproducibility can be provided.

(Embodiment 8) As shown in FIG.
In this embodiment, the light emitting element 300 is formed in the same manner as in Example 7, except that the first well layer 308 made of In _0.5 Ga _0.5 N has three layers, and the total number of layers is five in total by adding two layers.
At this time, the unevenness of the second well layer 309 is
Greater than. This light emitting element 300 is the first light emitting element of the second embodiment.
The well layer 207 looks more bluish than that of the four layers. The luminous efficiency of the light emitting element 300 of the eighth embodiment is higher than that of the second embodiment.
9, the intensity of light emission from the first well layer 3 is increased.
Light emission from 08 is greatly improved. In addition, since the intensity ratio of the light emitted from the first and second well layers is more stable than that of Example 7, it is possible to obtain a white light emitting device having desired color rendering with good reproducibility.

(Embodiment 9) Contrary to Embodiment 8, a light emitting device similar to that of Embodiment 8 was manufactured by making the irregularities of the first well layer 308 larger than that of the second well layer 309. Form. That is, a light emitting element having a light emitting layer including the first well layer 308 having a ratio R of 0.2 of the recessed region and the second well layer 309 having a ratio R of 0.4 of the recessed region. Form 300.

The luminous efficiency of the light emitting device 300 is greatly reduced as compared with the eighth embodiment, and also lower than that of the light emitting device 100 of the first embodiment. In addition, the first and second
The luminous intensity ratio of the light from the well layers 308 and 309 greatly varies from one light emitting element to another, making it difficult to obtain white light having desired color rendering with good reproducibility.

(Embodiment 10) In the same manner as in the eighth embodiment, the first well layer 308 in which the value of the ratio R of the recessed region is 0.05, and the value of the ratio R in the recessed region is 0.08. A light emitting element having an active layer 306 including a certain second well layer 309 is formed. At this time, when the thickness of each of the five first well layers 308 is measured, the value of R is about 0.05 in each case, and the values are almost equal between the first well layers 308. At this time, in the cross section of the light emitting element 300, it is easy to observe that the first well layer 308 is clearly smaller in unevenness than the second well layer 309, so that it is not always necessary to accurately measure the value of R. .

The obtained light emitting device 300 shows good light emission as in Example 8, and the luminous efficiency is slightly inferior, but acceptable, and the color rendering of the obtained mixed color light is satisfactory. . Therefore, the magnitude relationship between the concavities and convexities between the well layers is larger than the magnitude of the concavities and convexities in the first and second well layers.
It is understood that the characteristics of the light emitting device are greatly affected.

(Embodiment 3) In Embodiment 3 of the present invention, in the light emitting device of Embodiment 1, Al _z Ga _{1 -z} N (0 <) is formed on the first and second well layers. By forming a first barrier layer made of z <1) and a second barrier layer made of GaN, an object is to lower the forward voltage Vf and increase luminous efficiency.

(Embodiment 11) A description will be given with reference to FIG.

A light emitting device 400 according to another embodiment of the present invention is formed by using the same apparatus as in the first embodiment. The light-emitting element 400 generally includes an active layer 401, and an n-type semiconductor layer 402 and a p-type semiconductor layer 403 sandwiching the active layer 401.

The n-type semiconductor layer 402 is formed on the sapphire substrate 4
11. GaN buffer layer 412, undoped GaN layer 413a and Si-doped GaN layer 413b
N-type contact layer 4 formed by alternately repeating five layers
13. An n-type cladding layer 414 made of Si-doped InGaN is sequentially laminated. Note that an n-type electrode 436 is formed on the uppermost Si-doped GaN layer 413b of the n-type contact layer 413.

The p-type semiconductor layer 403 is made of Mg-doped In.
A first p-type cladding layer 431 made of GaN, a second p-type cladding layer 432 made of Mg-doped AlGaN,
The p-type contact layer 433 made of Mg-doped GaN is sequentially laminated. Also, the p contact layer 433
A p-type electrode 434 is formed on the substrate.

The active layer 401 has an n-type contact layer 414
Well layer 416 made of InGaN close to p-type and second well layer 420 made of InGaN close to p-type contact layer
Having a multiple quantum well structure. Second well layer 420
Has a larger In composition than the first well layer 416.
Particularly, in the third embodiment, AlG is formed on the first well layer 416.
A first barrier layer 417 made of aN and a second barrier layer 418 made of GaN are formed. Similarly, the second well layer 420
First barrier layer 421 made of AlGaN and GaN
A second barrier layer 422 is formed. First barrier layer 41
The layers 7 and 421 mainly function as barrier layers for stopping electrons, and the second barrier layers 418 and 422 mainly function as base layers for well layers formed thereon. By forming a plurality of barrier layers having different compositions on the well layer, the crystallinity is improved and Vf is reduced. Such first and second barrier layers are also effective in a light emitting device having an active layer having a single quantum well structure or a light emitting device having a multiple quantum well structure containing substantially the same amount of In. A light-emitting element having high crystallinity, low Vf, and capable of high-output light emission can be provided. However, since it is difficult to form a nitride-containing compound semiconductor containing In that emits light at a longer wavelength side than yellow with a main peak wavelength with good crystallinity, for example, the first well layer 416 that can emit blue light and the yellow light are The first and second barrier layers have a remarkable effect in forming a white light emitting element in combination with the second well layer 420 capable of emitting light. It should be noted that the first barrier layer having an Al composition ratio of 0.3 or more is more effective from the viewpoint of crystallinity. Here, the Al composition ratio is set to 0.5.

The active layer 401 includes a first well layer 416,
The first barrier layer 417 and the second barrier layer 418 are formed by repeating four cycles, and the second barrier layer 420, the first barrier layer 421, and the second barrier layer 422 are stacked thereon. . The first and second well layers 416 and 420 are made of InG
Light having a desired wavelength can be emitted by controlling the In composition ratio of aN. For example, the respective In composition ratios may be controlled such that the first well layer 416 emits blue light having a main peak wavelength of about 480 nm and the second well layer 420 emits yellow light having a main peak wavelength of about 580 nm. . The first and second well layers 416, 420 are about 30 °
And the first and second barrier layers 417, 421,
And 418, 422 have a thickness of about 300 °.

Hereinafter, a method for forming the light emitting element 400 will be described in detail.

A light emitting element 400 is formed by forming a nitride semiconductor film by the MOCVD method. First, a substrate 411 made of cleaned 2-inch sapphire (C-plane) is subjected to MOCVD.
Set in the reaction vessel of the device. After evacuating the reaction vessel and flowing H 2 to sufficiently replace the inside of the vessel with H 2, the substrate temperature is raised to 1050 ° C. to clean the substrate 411. As the semiconductor substrate 411, in addition to C-plane sapphire, sapphire having an R-plane or an A-plane as a main surface, an insulating substrate such as spinel (MgAl ₂ O ₄ ), SiC
(Including 6H, 4H, 3C), Si, ZnO, GaAs
Materials such as s and GaN can be used.

Next, the film formation temperature was lowered to 510 ° C.
A buffer layer 412 is formed by supplying (trimethylgallium), NH ₃ as a source gas and H ₂ as a carrier gas, and forming a GaN layer having a thickness of about 150 ° on the sapphire substrate 411. The buffer layer 412 is made of Al, in addition to GaN.
Materials such as N and GaAlN can be used.

Subsequently, the flow of the raw material gas is temporarily stopped, and
Increase substrate temperature to 1050 ° C while flowing rear gas
You. After the deposition temperature has stabilized, TMG and
And NH _Three, H as a carrier gas_TwoAnd undoped
The GaN layer 413a is stacked on the buffer layer 412. So
While maintaining the film forming temperature at 1050 ° C., the raw material gas
As TMG and NH_Three, H as a carrier gas_Two, Not
SiH as pure gas_FourAnd Si doped G
An aN layer 413b is formed on the undoped GaN layer 413a.
Film. Undoped GaN layer 413a and Si dopant
GaN layers 413b are alternately laminated in five layers to a thickness of about 4 μm.
A contact layer 413 is formed.

Subsequently, the flow of the raw material gas is stopped, and the film forming temperature is lowered to 800 ° C. After the temperature is stabilized, TMG, TMI, NH ₃ as a source gas, H ₂ as a carrier gas, SiH ₄ as an impurity gas are flowed, and InG doped with Si is used.
The cladding layer 414 made of aN is made of Si-doped n-type Ga
It is formed on the N layer 413b.

Next, an active layer 401 having a multiple quantum well structure is formed on the Si-doped InGaN layer 414. MO
Using a CVD method, the film formation temperature was set to 1050 ° C., TMG and NH ₃ as source gases, H ₂ as a carrier gas,
And a film is formed while flowing SiH ₄ gas as an impurity gas, and about 200 ° C. is formed on the n-type InGaN cladding layer 414.
A thick n-type GaN layer 415 is formed.

Next, once the inflow of the source gas is stopped and the film forming temperature is changed to 750 ° C., TM
G, TMI, NH ₃ , N ₂ as a carrier gas,
A first well layer 416 made of InGaN having a thickness of about 30 ° is formed.

Thereafter, the film formation temperature is set to 800 ° C., film formation is performed while flowing TMG, TMA and NH ₃ as source gases and H ₂ as a carrier gas, and a first barrier layer 417 having a thickness of about 30 ° is formed. .

Subsequently, the source gas is stopped, only the carrier gas is flowed, and the film forming temperature is raised to 1000 ° C. Then, while flowing TMG and NH ₃ as source gases and H ₂ as a carrier gas, a _second layer of GaN having a thickness of about 300 ° was formed.
A barrier layer 418 is formed.

Similarly, the first well layer 416, the first barrier layer 417, and the second barrier layer 418 are sequentially formed by repeating four layers each.

Subsequently, a second well layer 420 is formed in the same manner. However, while the first well layer 416 is formed with four layers, the second well layer 420 is formed with only one layer. In addition, the second well layer 420 has 580 n
It has the same layer configuration as the first well layer 416, except that the In composition ratio is controlled so as to emit light having a main peak wavelength of m.

After forming the active layer 401, a p-type first cladding layer 431 made of InGaN is formed. The p-type first cladding layer 431 is made of Mg-doped p-type InGaN and has a thickness of about 200 °. Using the MOCVD method, the deposition temperature was set at 1050 ° C.
MG, TMI and NH ₃ , Cp2 as impurity gas
The p-type first cladding layer 431 made of InGaN is formed by flowing Mg and H ₂ as a carrier gas.

After forming the p-type first cladding layer 431,
A p-type second cladding layer 432 made of AlGaN is formed. The p-type first cladding layer 432 is made of Mg-doped p-type AlGaN and has a thickness of about 200 °. The film formation temperature was maintained at 1050 ° C., and TMG, TM
A, NH ₃ , Cp ₂ Mg as an impurity gas, and H ₂ as a carrier gas flow to form a p-type first cladding layer made of AlGaN.

Then, the film formation temperature was kept at 1050 ° C., TMG and NH ₃ as source gases, H ₂ as carrier gas, and Cp ₂ Mg as impurity gas were passed.
The p-type contact layer 433 made of GaN has a thickness of about 3000
Is formed on the second p-type cladding layer 432 with a thickness of After forming the p-type contact layer 433, the temperature is lowered to room temperature, and the wafer is annealed at 700 ° C. in a nitrogen atmosphere.
The resistance of the p-type layer is further reduced.

After the annealing treatment, the wafer is taken out of the reaction vessel, a mask having a desired shape is formed on the surface of the uppermost second p-type contact layer 433, and the p-type contact layer 433 side is formed by an RIE (reactive ion etching) apparatus. To expose the p-type and n-type semiconductor surfaces.

After the etching process, a film thickness of 20 is formed on almost the entire surface of the second p-type contact layer 433 by a sputtering apparatus.
A p-type electrode 434 containing 0% Ni and Au, and a p-type electrode 4
A p-type pad electrode 435 made of Au for bonding and having a thickness of 0.5 μm is formed on. On the other hand, the n-type contact layer 413a exposed by the etching process
An n-type electrode 436 containing W and Al is formed thereon. Finally, to protect the surface of the p-type electrode 435, SiO2
An insulating layer (not shown) is formed as a protective film.
After the scribe line is drawn on the nitride semiconductor wafer thus formed, it is divided by an external force to complete an LED chip of 350 μm square as a light emitting element.

The lead frame of the light emitting diode lamp is formed of silver-plated iron-containing copper. The lead frame has, at one end, a mount lead having a cup, and at the other end, an inner lead electrically connected via a wire to one electrode of an LED chip disposed on the mount lead. . After the LED chip is die-bonded onto the mount leads using epoxy resin, the LED chip is
One of the wires is ball-bonded to each electrode of the ED chip, and the other of the wires is stitch-bonded to the tip of the lead frame. Thereby, each electrode of the LED chip is electrically connected to the inner lead and the mount lead.

When a forward current of 20 mA was passed through the light-emitting device thus obtained, the forward voltage of the conventional light-emitting device was 3.5 V, but dropped to 3.0 V. Even bright white light can be obtained.

[0110]

The present invention is embodied in the form described above and has the following effects.

Since the active layer of the light emitting device according to the present invention includes the first and second well layers emitting different emission wavelengths, a single light emitting device enables highly efficient and high luminance mixed light color such as white light. Can emit light. Further, by controlling the ratio of the number of stacked layers of the first and second well layers and / or the thickness of the barrier layer, the color rendering properties can be further improved.

Further, the degree of the unevenness of the second well layer may be made larger than that of the first well layer, and / or the degree of occupation by the recessed region having a thickness equal to or less than half the average thickness of the second well layer. By setting it to 10% or more, highly efficient light emission having desired color rendering properties can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a light emitting device of Example 1 according to Embodiment 1 of the present invention.

FIG. 2 is a schematic cross-sectional view of a light emitting device of Example 2 according to Embodiment 1.

FIG. 3 shows coordinates on a chromaticity diagram of light emitted by the light emitting elements formed in Example 1 and Example 2.

FIG. 4 shows an emission spectrum diagram of the light emitting device of Example 1 according to Embodiment 1.

FIG. 5 shows an emission spectrum diagram of the light emitting device of Example 5 according to Embodiment 1.

FIG. 6 is a schematic cross-sectional view illustrating unevenness of a well layer according to a second embodiment of the present invention.

FIG. 7 shows a schematic cross-sectional view of a light emitting device of Example 8 according to Embodiment 2.

FIG. 8 is a schematic sectional view of a light emitting device of Example 11 according to Embodiment 3 of the present invention.

[Explanation of symbols]

 100, 200, 300 ... light emitting elements 101, 201, 301 ... sapphire substrate 102, 202, 302 ... buffer layers 103, 203, 303 ... undoped layers 104, 204, 304 ... n-type Contact layers 105, 205, 305 n-type superlattice layers 106, 206, 306 active layers 107, 207, 307 barrier layers 108, 208, 308 first well layers 109, 209 , 309 second well layer 110, 210, 310 ... p-type cladding layer 111, 211, 311 ... p-type contact layer 112, 212, 312 ... p-type translucent electrode 113, 213 , 313... P-type pedestal electrodes 114, 214, 314... N-type electrodes 401... Active layer 402... N-type semiconductor layers 403. 11 ... substrate 412 ... buffer layer 413 ... n-type contact layer 414 ... n-type cladding layer 416 ... first well layer 420 ... second well layer 417, 421 ... first 1 barrier layer 418, 422 ... second barrier layer 431 ... p-type first cladding layer 432 ... p-type second cladding layer 433 ... p-type contact layer 434 ... p-type translucent Electrode 435: p-type pedestal electrode

Claims (18)

[Claims] At least one first well layer made of a nitride compound semiconductor containing In and containing In which emits light having a main peak wavelength longer than the main peak wavelength of light emitted from the first well layer. A light emitting device comprising: an active layer having a multiple quantum well structure, comprising at least one second well layer made of a nitride compound semiconductor, sandwiched between an n-type semiconductor and a p-type semiconductor. 2. The light emitting device according to claim 1, wherein the second well layer is disposed between the first well layer and the p-type semiconductor. 3. A light source having a desired color rendering property by controlling a luminous intensity ratio of light emitted from the first and second well layers by adjusting a stacking number ratio of the first and second well layers. The light emitting device according to claim 1, wherein the light emitting device is provided. 4. The active layer further includes a plurality of barrier layers sandwiching the first and second well layers, and the thickness of the barrier layers is adjusted so that light emitted from the first and second well layers is reduced. The light emitting device according to claim 1, wherein a light source having a desired color rendering property is provided by controlling a light intensity ratio. 5. The light emitting device according to claim 1, wherein the first well layer is stacked more than the second well layer. 6. The light emitting device according to claim 1, wherein the half-width of the light emitted from the first well layer is narrower than the half-width of the light emitted from the second well layer. 7. The method according to claim 5, wherein the first well layer is stacked in a range of 2 to 10 layers, and the second well layer is stacked in a range of 1 to 3 layers. The light-emitting element according to any one of the preceding claims. 8. The method according to claim 1, wherein the main peak wavelength of the light emitted from the first well layer is 450 to 500 nm, and the main peak wavelength of the light emitted from the second well layer is 560 to 670 nm. The light-emitting element according to any one of the preceding claims. 9. The light emitting device according to claim 1, wherein the degree of unevenness of the second well layer is larger than that of the first well layer. 10. The method according to claim 1, wherein the second well layer includes a partially thin recess having a thickness of less than half the average thickness thereof, and the area of the recess occupies at least 10% of the whole. 2. The light emitting device according to 1. 11. The method according to claim 1, wherein the second well layer includes a partially thin recess having a thickness of less than half the average thickness thereof, and the region of the recess occupies at least 10% of the whole. 10. The light emitting device according to item 9. 12. The light emitting device according to claim 9, wherein the second well layer is disposed between the first well layer and the p-type semiconductor. 13. The light emitting device according to claim 10, wherein the second well layer is disposed between the first well layer and the p-type semiconductor. 14. The light emitting device according to claim 11, wherein the second well layer is disposed between the first well layer and the p-type semiconductor. 15. The light emitting device according to claim 12, wherein the first well layer is stacked more than the second well layer. 16. The light emitting device according to claim 13, wherein the first well layer is stacked more than the second well layer. 17. The light emitting device according to claim 14, wherein the first well layer is stacked more than the second well layer. 18. A first barrier layer made of a nitride compound semiconductor containing Al and a second barrier made of a nitride compound semiconductor containing substantially no Al on each of the first and second well layers. The light emitting device according to claim 1, further comprising a layer.