JP3063757B1 - Nitride semiconductor device - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting device with improved light emission output and good electrostatic withstand voltage in order to enable an application range to be applied to various application products by using an active layer having a multiple quantum well structure. To provide. SOLUTION: On an n-side, at least three layers of an undoped nitride semiconductor lower layer 5a, an n-type impurity-doped nitride semiconductor intermediate layer 5b, and an undoped nitride semiconductor upper layer 5c are sequentially laminated on a substrate 1. The active layer 7 includes a first multilayer film layer 5, and the active layer 7 is made of In _a Ga _1-a N (0 ≦ a <
1) and a p-side formed by stacking third and fourth nitride semiconductor layers having different band gap energies and different or the same p-type impurity concentrations from each other. Multilayer clad layer 8 or p
A p-side single film clad layer 8 made of Al _b Ga ₁ -bN (0 ≦ b ≦ 1) containing a p _- type impurity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LE).
D), a nitride semiconductor used for a light emitting element such as a laser diode (LD), a solar cell, an optical sensor, a light receiving element, or an electronic device such as a transistor or a power device (for example, In _X Al _Y Ga _{1 -XYN).} , 0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1) Regarding the element.

[0002]

2. Description of the Related Art Nitride semiconductors have been put into practical use as materials for high-brightness blue LEDs and pure green LEDs in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources. These LED elements are basically
A buffer layer of GaN on a sapphire substrate;
N-side contact layer made of doped GaN and InGa of a single quantum well structure (SQW: Single-Quantum-Well)
Multiple quantum well structure with N or InGaN (M
QW: Multi-Quantum-Well) active layer and Mg-doped A
a p-side cladding layer of lGaN and Mg-doped GaN
And a p-side contact layer composed of a blue LED with an emission wavelength of 450 nm at 5 mA and an external quantum efficiency of 9.1% and 520 nm at 20 mA.
3mW and an external quantum efficiency of 6.3%, which are very excellent characteristics. The multiple quantum well structure has a structure composed of a plurality of minibands, and can efficiently emit light even with a small current. Therefore, improvement in device characteristics such as higher light emission output than a single quantum well structure is expected. You. Also, for example, as an LED element using an active layer having a multiple quantum well structure, JP-A-10-135514 discloses at least a barrier layer made of undoped GaN, an undoped InGaN in order to improve luminous efficiency and luminous intensity. There is disclosed a nitride semiconductor device having a light emitting layer having a multiple quantum well structure composed of a well layer made of, and a cladding layer having a wider band gap than a barrier layer of the light emitting layer.

[0003]

However, in order to use the above-mentioned conventional element as an LED element for a light source for lighting, an outdoor display exposed to direct sunlight, or the like, the light emission output is not sufficiently satisfactory. As described above, the active layer having the multiple quantum well structure can dramatically improve the light emission output, but it is difficult to sufficiently exhibit the expected possibility. Furthermore, a device made of a nitride semiconductor may deteriorate due to its structure even at a voltage of 100 V, which is much weaker than static electricity generated in a human body. For example, there is a risk of deterioration when taking out from a bag or the like that has been subjected to antistatic treatment, or when applying it to a product. In order to further enhance the reliability of the nitride semiconductor device, it is desired to eliminate such a risk of deterioration.

[0004] Therefore, an object of the present invention is to provide a multi-quantum well structure active layer that can be used in a wide range of application products, so that the light emitting output is further improved and the electrostatic breakdown voltage is improved. An object of the present invention is to provide a semiconductor light emitting device.

That is, the present invention provides the following (1) to (1)
The object of the present invention can be achieved by the configuration of 1). (1) In a nitride semiconductor device having an n-side nitride semiconductor layer, an active layer and a p-side nitride semiconductor layer formed on a substrate via a buffer layer, the n-side nitride semiconductor layer has a thickness of An n-side first layer in which at least three layers of a lower layer made of an undoped nitride semiconductor of 100 to 10000 °, an intermediate layer made of a nitride semiconductor doped with an n-type impurity, and an upper layer made of an undoped nitride semiconductor are sequentially stacked.
A nitride semiconductor device comprising a multilayer film layer. (2) The active layer is made of In _a Ga _1-a N (0 ≦ a <1).
The nitride semiconductor device according to the above (1), which has a multiple quantum well structure including a layer. (3) The nitride semiconductor device according to (1) or (2), wherein the thickness of the intermediate layer is 50 to 1000 Å, and the thickness of the upper layer is 25 to 1000 Å. (4) In between the n-side first multilayer film layer and the active layer, In
And an n-side second multilayer film layer in which a first nitride semiconductor layer containing: and a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer are stacked. The nitride semiconductor device according to any one of (1) to (3). (5) In the (1) to (4), the n-side nitride semiconductor layer has an n-side contact layer containing an n-type impurity on the substrate side of the n-side first multilayer film layer. The nitride semiconductor device according to any one of the above. (6) The nitride semiconductor device according to (5), wherein the n-side contact layer is formed on an undoped GaN layer. (7) In the nitride semiconductor device, the undoped GaN layer is Ga _d Al _{1 -dN} (0 <d ≦
The nitride semiconductor device according to (6), which is formed on the buffer layer according to (1). (8) the undoped GaN layer, the n-side contact layer,
And the total thickness of the n-side first multilayer film layer is 2 to 20 μm, (6) or (7). (9) The p-side nitride semiconductor layer is formed by stacking third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations from each other.
(1) to (4) including a side-side multilayer clad layer or a p-side multilayer-layer clad layer formed by laminating third and fourth nitride semiconductor layers having different band gap energies and the same p-type impurity concentration. The nitride semiconductor device according to any one of (8). (10) wherein the p-side nitride semiconductor layer comprises a p-side single layer cladding layer made of include p-type impurity _{Al b Ga 1-b N (} 0 ≦ b ≦ 1) (1) ~ (8) Any one of
6. A nitride semiconductor device according to any one of the above. (11) The nitride semiconductor device according to (9) or (10), wherein a p-side GaN contact layer containing Mg as a p-type impurity is formed on the p-side multilayer clad layer or the p-side single film clad layer.

That is, the present invention provides an n-side second layer having a specific layer configuration of an undoped lower layer, an n-type impurity-doped intermediate layer, and an undoped upper layer so as to sandwich an active layer having a multiple quantum well structure. A multi-layered film layer and a p-sided multi-layered cladding layer composed of third and fourth nitride semiconductor layers on the p-side or a p-layer composed of Al _b Ga _1-b N (0 ≦ b ≦ 1) containing p-type impurities.
By forming in combination with the side single-film cladding layer, it is possible to obtain a nitride semiconductor device having improved luminous efficiency, good luminous output, and good electrostatic withstand voltage. By thus combining a plurality of nitride semiconductor layers having a specific composition, a layer structure, and the like, the performance of the active layer having the multiple quantum well structure can be efficiently exhibited, and the electrostatic withstand voltage can be improved. Further, according to the present invention, by setting the film thickness of each layer constituting the n-side first multilayer film layer in a specific range, it is possible to improve the electrostatic discharge voltage as well as the excellent light emission output.

In the present invention, the term “undoped” refers to a layer formed without intentionally doping impurities, and is a layer in which impurities are mixed by diffusion of impurities from an adjacent layer or contamination from raw materials or equipment. Also, when the impurity is not intentionally doped, the undoped layer is used. Note that the impurity mixed by diffusion may have a gradient in the impurity concentration in the layer.

Also, a combination with an active layer having a multiple quantum well structure
In the combination, the other preferable nitride semiconductor layers are as follows.
It is described below. In the present invention, the n-side first multilayer film layer
First nitride semiconductor layer containing In between a semiconductor and an active layer
And a first nitride semiconductor having a composition different from that of the first nitride semiconductor layer.
The n-side second multilayer film layer in which the nitride semiconductor layers
And further improving the luminous efficiency and the forward voltage
(Hereinafter referred to as Vf) to improve luminous efficiency.
It is preferable because it can be performed. Further, in the present invention, the
The n-side including the n-type impurity is closer to the substrate than the n-side first multilayer film layer.
Having a contact layer improves the light emission output and increases Vf.
Preferred for lowering. Still further, in the present invention,
The n-side contact layer is formed on the undoped GaN layer.
Once formed, such an undoped GaN layer is crystalline
Because it is obtained as a good layer, it is a layer that forms the n-electrode
The crystallinity of the n-side contact layer is improved,
Other nitride semiconductor layers such as an active layer formed on the layer
Improves the crystallinity of the material, which is preferable for improving the light output.
No. Still further, in the present invention, the undoped GaN
The layer is a low temperature grown Ga _dAl_1-dN (0 <d ≦ 1)
Undoped G
The crystallinity of the aN layer is further improved, and the n-side contact layer, etc.
Has better crystallinity, which is favorable for improving light emission output.
More preferably, the p-side multilayer clad layer or the p-side single layer
Mg-doped p-side GaN contact layer on film cladding layer
Once formed, it becomes easier to obtain p-type characteristics,
P-side electrode on which a p-side GaN contact layer is formed
With good ohmic contact to improve light output
Preferred for Still further, in the present invention, undoped
GaN layer, n-side contact layer, and n-side first multilayer film layer
Total film thickness is 2 to 20 μm, preferably 3 to 10 μm
m, more preferably 4 to 9 μm, to improve electrostatic withstand voltage.
It is preferred in terms of. When the film thickness is in the above range, the electrostatic withstand voltage
Other element characteristics other than the above are also good. In addition, the combination of the above three layers
The total thickness of the three layers is within the preferable range of the thickness of each layer.
The total thickness is appropriately adjusted so as to be within the above range.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIG. 1 which is a schematic sectional view of a nitride semiconductor device showing a structure of a nitride semiconductor device according to an embodiment of the present invention. . FIG. 1 shows that a buffer layer 2 and an undoped G
an n-side first multilayer film 5 composed of three layers: an aN layer 3, an n-side contact layer 4 containing an n-type impurity, an undoped lower layer 5a, an n-type impurity-doped intermediate layer 5b, and an undoped upper layer 5c; N-side second multilayer film layer 6 composed of two nitride semiconductor layers, active layer 7 having a multiple quantum well structure, third and fourth
Has a structure in which a p-side multilayer clad layer 8 or a p-side single film clad layer 8 composed of a nitride semiconductor layer and a Mg-doped p-side GaN contact layer 9 are sequentially laminated. Further, an n-electrode 11 and a p-side GaN contact layer 9 are formed on the n-side contact layer 4.
A p-electrode 10 is formed thereon.

In the present invention, as the substrate 1, sapphire having a sapphire C-plane, R-plane or A-plane as a main surface, other insulating substrates such as spinel (MgA1 ₂ O ₄ ), SiC (6H , 4H, 3C), Si, Zn
A semiconductor substrate such as O, GaAs, or GaN can be used.

In the present invention, as the buffer layer 2,
Ga _d Al _1-d N (where d is in the range of 0 <d ≦ 1)
Preferably, a composition having a smaller proportion of Al has a remarkable improvement in crystallinity, more preferably a buffer layer 2 made of GaN. The thickness of the buffer layer 2 is 0.002 to 0.5 μm, preferably 0.005 to 0.2 μm, more preferably 0.01 to 0.2 μm.
Adjust to a range of 0.02 μm. When the thickness of the buffer layer 2 is in the above range, the crystal morphology of the nitride semiconductor becomes good, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 is improved. The growth temperature of the buffer layer 2 is 2
The temperature is adjusted to 00 to 900 ° C, preferably to 400 to 800 ° C. When the growth temperature is in the above range, a favorable polycrystal is formed, and this polycrystal is preferable because the crystallinity of the nitride semiconductor grown on the buffer layer 2 as a seed crystal can be improved. The buffer layer 2 grown at such a low temperature
May be omitted depending on the type of the substrate, the growth method, and the like.

Next, in the present invention, undoped GaN
The layer 3 is a layer grown without adding an n-type impurity during growth. Undoped GaN layer 3 on buffer layer 2
Is grown, the crystallinity of the undoped GaN layer 3 is improved, and the crystallinity of the n-side contact layer 4 and the like grown on the undoped GaN layer 3 is also improved. Undoped GaN
The thickness of the layer 3 is 0.01 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. The upper limit of the thickness of the undoped GaN layer 3 is not particularly limited, but is appropriately adjusted in consideration of production efficiency and the like. When the thickness is in this range, the layers subsequent to the n-side contact layer 4 can be grown with good crystallinity, which is preferable. Further, when the thickness of the undoped GaN layer 3 is within the above range, the total thickness of the n-side contact layer 4 and the n-side first multilayer film layer 5 is adjusted to the above range to improve the electrostatic breakdown voltage. Is preferred.

Next, in the present invention, the n-side contact layer 4 containing the n-type impurity has an n-type impurity of 3 × 10 ¹⁸ / cm 3.
³ or more, preferably at a concentration of 5 × 10 ¹⁸ / cm ³ or more. When the n-type impurity is heavily doped as described above and this layer is used as an n-side contact layer, Vf and the threshold value can be reduced. If the impurity concentration deviates from the above range, Vf
Tend to be less likely to decrease. Further, when the n-side contact layer 4 is formed on the undoped GaN layer 3 having a low n-type impurity concentration and good crystallinity, the n-side contact layer 4 has good crystallinity despite having a high concentration of n-type impurities. Can be formed. Although the upper limit of the n-type impurity concentration of the n-side contact layer 4 is not particularly limited, the limit at which the function as the contact layer can be maintained is preferably 5 × 10 ²¹ / cm ³ or less.

[0014] The composition of the n-side contact layer 4, an In _e Al _f
It can be composed of Ga _1-ef N (0 ≦ e, 0 ≦ f, e + f ≦ 1), and its composition is not particularly limited.
aN, less nitride semiconductor layer crystal defects and the f value of 0.2 or less of Al _f Ga _1-f N can be easily obtained. The thickness of the n-side contact layer 4 is not particularly limited, but is 0.1 to 20 μm, preferably 0.1 to 20 μm because it is a layer for forming an n-electrode.
It is 5 to 10 μm, more preferably 1 to 5 μm. When the film thickness is in the above range, the resistance can be reduced, and the Vf of the light emitting element can be reduced.
Can be reduced, which is preferable. Further, it is preferable that the film thickness of the n-side contact layer 4 be in the above range, because the combination with the undoped GaN layer 3 and the n-side first multilayer film layer 5 improves the electrostatic withstand voltage. Further, the n-side contact layer 4 can be omitted when the later-described n-side first multilayer film layer 5 is formed as a thick film.

Next, in the present invention, the n-side first multilayer film layer
5 is an undoped lower layer 5a, an n-type impurity
At least the doped intermediate layer 5b and the undoped upper layer 5c
Is also composed of three layers. The n-side first multilayer film layer
It may have another layer other than the lower layer 5a to the upper layer 5c.
No. The n-side first multilayer film layer 5 is in contact with the active layer.
May have another layer between the active layers. Below these
As the nitride semiconductor constituting the layers 5a to 5c, I
n_gAl_hGa _1-ghExpressed as N (0 ≦ g <1, 0 ≦ h <1)
Nitride semiconductors of various compositions can be used,
Preferably, a composition of GaN is used. Ma
Each layer of the first multilayer film 5 has the same composition but is different.
Is also good.

The thickness of the n-side first multilayer film layer 5 is not particularly limited, but is 175 to 12,000 angstroms, preferably 1,000 to 10,000 angstroms, and more preferably 2000 to 6000 angstroms. It is preferable that the film thickness of the first multilayer film layer 5 be in the above range in terms of optimizing Vf and improving electrostatic withstand voltage. Furthermore, it is preferable that the film thickness of the n-side first multilayer film layer 5 is in the above range, because the combination of the undoped GaN layer 3 and the n-side contact layer 4 improves the electrostatic breakdown voltage. Adjustment of the film thickness of the first multilayer film layer 5 having a film thickness in the above range is performed by appropriately adjusting the respective film thicknesses of the lower layer 5a, the intermediate layer 5b, and the upper layer 5c to obtain the total film thickness of the first multilayer film layer 5. Is preferably in the above range.

The lower layer 5a constituting the n-side first multilayer film layer 5,
Although the thickness of each of the intermediate layer 5b and the upper layer 5c is not particularly limited, the influence on various characteristics of the element performance varies depending on the position where the layers are stacked in the n-side first multilayer film layer 5, so that the element performance of each layer is greatly affected. Paying particular attention to the characteristics involved, fixing the film thickness of any two layers, changing the film thickness of the remaining one layer stepwise, measuring the film thickness in a good range of the characteristics, The range of the film thickness is specified by the adjustment. Each layer of the n-side first multilayer film layer 5 may not directly affect the electrostatic withstand voltage in some cases. However, by combining the respective layers to form the n-side first multilayer film layer 5, various elements as a whole are obtained. The characteristics are good, and the light emission output and electrostatic withstand voltage are particularly excellent. Such an effect can be said to be an unexpected effect that can be obtained only when an element formed by laminating each layer is actually manufactured.
The thickness of each layer is specifically shown below, and FIGS.
FIG. 4 shows a change in element characteristics due to a change in film thickness. However, the comparative conventional product is a conventional example shown in Example 1 described later. Po in the figure indicates the light emission output. Further, the film thickness shown on the horizontal axis in each figure is varied within a range not including zero.

The thickness of the undoped lower layer 5a is 100 to
10,000 angstroms, preferably 500-80
00 Å, more preferably 1000 to 50
00 angstroms. Undoped lower layer 5a
As shown in FIGS. 2A and 2B, as the film thickness is gradually increased, the electrostatic withstand voltage increases.
When Vf rises sharply in the vicinity of Angstrom, and when the film thickness is reduced, Vf decreases, but the electrostatic withstand voltage decreases greatly. When the film thickness is less than 100 Angstroms, the yield decreases as the electrostatic withstand voltage decreases. There is a tendency to increase. Further, since it is considered that the upper layer 5a improves the influence of the decrease in the crystallinity of the n-side contact layer 4 containing the n-type impurity, the upper layer 5a is grown to a thickness that improves the crystallinity. Is preferred.

The thickness of the intermediate layer 5b doped with n-type impurities is
50-1000 angstroms, preferably 100-
500 angstroms, more preferably 150-40
0 Angstrom. The intermediate layer 5b doped with the impurity is a layer having a sufficient carrier concentration and having a relatively large effect on the light emission output. If this layer is not formed, the light emission output tends to decrease significantly. Note that FIG.
In (a), the reason why the light emission output slightly decreases even when the film thickness is reduced to about 25 angstroms is considered so that the light emission output does not decrease even when the thickness of the intermediate layer 5b is 50 angstroms. This is because the thickness of the other layers was adjusted. Further, as shown in FIG. 3A, when the film thickness exceeds 1000 angstroms, the light emission output tends to greatly decrease to a level that makes it difficult to commercialize. On the other hand, looking only at the electrostatic resistance, FIG.
As shown in (1), when the film thickness of the intermediate layer 5b is large, the electrostatic withstand voltage is good, but when the film thickness is less than 50 angstroms, the electrostatic withstand voltage tends to be greatly reduced, which is not satisfactory as a commercial product.

The thickness of the undoped upper layer 5c is 25 to 1
000 angstroms, preferably 25-500 angstroms, more preferably 25-150 angstroms. The undoped upper layer 5c is formed in contact with or closest to the active layer in the first multilayer film and greatly contributes to prevention of leakage current.
If the thickness of c is less than 25 angstroms, the leak current tends to increase. Further, as shown in FIGS. 4A and 4B, when the thickness of the upper layer 5c exceeds 1000 angstroms, Vf tends to increase and the electrostatic breakdown voltage tends to decrease. .

As described above, the film thickness of each of the lower layer 5a to the upper layer 5c focuses on the element characteristics which are easily affected by the fluctuation of the film thickness of each layer as described above. When the upper layer 5c is combined with the upper layer 5c, various examinations are made so that all of the various element characteristics become almost uniformly good, and particularly, the light emission output and the electrostatic withstand voltage become good. By defining the film thickness, it is possible to obtain an electrostatic breakdown voltage capable of achieving good emission output and further improvement in product reliability. Further, the combination of the film thicknesses of the respective layers of the first multilayer film layer 5 may be determined by a change in the composition of the active layer depending on the type of the emission wavelength, an electrode, an LED, or the like.
Depending on various conditions such as the shape of the element, it is appropriately adjusted to obtain the best effect. The performance associated with the combination of the film thicknesses of the respective layers can achieve better emission output and better electrostatic withstand voltage than those of the related art by appropriately combining the film thicknesses in the above ranges.

The composition of each layer constituting the first multilayer film layer is In _g Al _h Ga _1-gh N (0 ≦ g <1, 0 ≦ h <
Any composition may be used as long as it is the composition represented by 1), and the composition of each layer may be the same or different. Preferably, the composition is such that the proportion of In and Al is small, and more preferably, a layer made of GaN.

The doping amount of the n-type impurity in the n-type impurity-doped intermediate layer 5b of the first multilayer film layer 5 is not particularly limited, but is not less than 3 × 10 ¹⁸ / cm ³ , preferably 5 × 10 ¹⁸ / cm ^3.
/ Cm ³ or more. The upper limit of the n-type impurity is not particularly limited, but is preferably 5 × 10 ²¹ / cm ³ or less as a limit that does not deteriorate crystallinity too much. It is preferable that the impurity concentration of the intermediate layer of the first multilayer film be in the above range in terms of improvement of light emission output and reduction of Vf.
As the n-type impurity, an element of Group IVB or VIB of the periodic table such as Si, Ge, Se, S, or O is selected.
i, Ge, and S are n-type impurities.

Further, at the interface of the first multilayer film layer 5, both layers function as both layers as long as the function of each layer and the element is not impaired.

Next, in the present invention, the n-side second multilayer film layer 6 includes a first nitride semiconductor layer containing In and a second nitride layer having a composition different from that of the first nitride semiconductor layer. It is composed of an n-side multilayer film layer in which a semiconductor layer is laminated. At least one of the first nitride semiconductor layer and the second nitride semiconductor layer preferably has a thickness of 10
The thickness is set to 0 angstrom or less, more preferably 70 angstrom or less, and further preferably 50 angstrom or less. By reducing the film thickness in this manner, the multilayer film layer has a superlattice structure, and the crystallinity of the multilayer film layer is improved, so that the output tends to be improved.

Even if the thickness of at least one of the first and second nitride semiconductors is less than 100 Å, the thin film layer becomes less than the elastic critical thickness and the crystal becomes better. Since the crystallinity of the first nitride semiconductor layer or the second nitride semiconductor layer is improved, and the crystallinity of the entire multilayer film layer is improved, the output of the device is improved.

If the thickness of each of the first and second nitride semiconductors is less than 100 angstroms, the thickness becomes less than the elastic critical thickness of the nitride semiconductor single layer. Alternatively, one of the second nitride semiconductors is 10
A nitride semiconductor having better crystallinity can be grown as compared with the case where the thickness is 0 Å or less. If both are set to 70 angstroms or less, the n-side second multilayer film layer 6 has a superlattice structure. When an active layer is grown on the multilayer film structure with good crystallinity, the n-side second multilayer film layer 6 has a superlattice structure. Acts like a buffer layer, and the active layer can be grown with higher crystallinity.

In the present invention, the n-side nitride semiconductor layer includes
When the n-side first multilayer film layer and the n-side second multilayer film layer are combined, the light emission output is improved and Vf is preferably reduced. Although the reason for this is not clear, it is considered that the crystallinity of the active layer grown on the n-side second multilayer film layer is improved.

The thickness of at least one of the first nitride semiconductor layer and the second nitride semiconductor layer of the n-side second multilayer film layer 6 is close to that of the first nitride semiconductor layer. Alternatively, even if the second nitride semiconductor layers are different from each other,
They may be the same. Preferably, at least one of the first nitride semiconductor layer and the second nitride semiconductor layer has a different thickness between adjacent first nitride semiconductor layers or second nitride semiconductor layers. Is preferred.
The difference in thickness between adjacent layers means that when a multilayer film layer in which a plurality of first nitride semiconductor layers and a plurality of second nitride semiconductor layers are stacked is formed, the second nitride semiconductor layer ( This means that the thickness of the first nitride semiconductor layer) and the thickness of the first nitride semiconductor layer (second nitride semiconductor layer) sandwiching the first nitride semiconductor layer are different from each other. For example, when the first nitride semiconductor layer is made of InGaN and the second nitride semiconductor layer is made of GaN, the thickness of the InGaN layer between the GaN layers gradually increases as approaching the active layer. Since the refractive index changes within the multilayer film layer by reducing or reducing the thickness, it is possible to form a layer whose refractive index gradually changes substantially. That is, the same effect as that of forming a nitride semiconductor layer having a substantially composition gradient can be obtained.
Therefore, for example, in an element requiring an optical waveguide such as a laser element, a waveguide is formed with this multilayer film layer,
The mode of the laser beam can be adjusted.

The composition of at least one group III element in the first or second nitride semiconductor layer is the same as the composition of the same group III element in the adjacent first or second nitride semiconductor layer. They may be different or the same. Preferably, the composition of at least one group III element of the first nitride semiconductor layer or the second nitride semiconductor layer is the same as that of the adjacent first nitride semiconductor layer or second nitride semiconductor layer. The compositions of the same group III elements are different from each other. This difference is that when a multilayer film layer in which a plurality of first nitride semiconductor layers or second nitride semiconductor layers are stacked is formed,
III of the second nitride semiconductor layer (first nitride semiconductor layer)
This means that the composition ratio of the group III element and the composition ratio of the group III element of the first nitride semiconductor layer (second nitride semiconductor layer) sandwiching the group element are different from each other.

For example, if the compositions of the same group III elements are different from each other, the first nitride semiconductor layer is made of InGaN, and the second nitride semiconductor layer is made of GaN.
By gradually increasing or decreasing the In composition of the InGaN layer between the layer and the GaN layer as approaching the active layer, the refractive index is changed inside the multilayer film layer, and the composition gradient is substantially increased. The nitride semiconductor layer thus formed can be formed. The refractive index tends to decrease as the In composition decreases.

For example, as shown in FIG. 1, the n-side second multilayer film layer 6 includes a first nitride semiconductor containing In in an n-side nitride semiconductor layer below the active layer 7. It has an n-side second multilayer film layer 6 in which a layer and a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer are stacked. In the n-side second multilayer film layer 6, at least one first nitride semiconductor layer and at least one second nitride semiconductor layer are formed, and a total of two or more layers, preferably three or more layers,
More preferably, at least two or more layers are laminated, and a total of four or more layers are desirably laminated.

The n-side second multilayer film layer 6 may be formed separately from the active layer, but is most preferably formed in contact with the active layer. When formed in contact with the active layer, the output tends to be more easily improved. When the n-side second multilayer film layer 6 is formed in contact with the active layer, the multilayer film layer in contact with the first layer (the well layer or the barrier layer) of the active layer may be the first nitride semiconductor layer or the first nitride semiconductor layer. The order of laminating the n-side second multilayer film layer 6 is not particularly limited. In FIG. 1, the n-side second multilayer film layer 6 is formed.
Is formed in contact with the active layer 7, but the n-side second
A layer made of another n-type nitride semiconductor may be provided between the multilayer film layer 6 and the active layer.

The first nitride semiconductor layer is a nitride containing In.
Semiconductor, preferably ternary mixed crystal In _kGa_1-kN (0 <k
<1), and more preferably In with a k value of 0.5 or less.
_kGa_1-kN, most preferably In with a k value of 0.2 or less._k
Ga_1-kN. On the other hand, the second nitride semiconductor layer
If the nitride semiconductor has a composition different from that of the nitride semiconductor layer
Good, although not particularly limited, the second nitride semiconductor having good crystallinity
In order to grow the conductor, the first nitride semiconductor
Binary mixed crystal with large band gap energy or 3
Original mixed crystal In_mGa_1-mGrow N (0 ≦ m <1, m <k)
And preferably GaN. The second nitride semiconductor
With GaN, a multilayer film layer with good crystallinity can be grown
Wear. Preferred combinations include the first nitride semiconductor
In the body _kGa_1-kN (0 <k <1) and the second nitride
Semiconductor In_mGa_1-mN (0 ≦ m <1, m <k), preferred
Or GaN. More preferred
A good combination is the k value of the first nitride semiconductor layer.
Is 0.5 or less In_kGa_{1 -k}N and the second nitride half
The conductor layer is a combination with GaN.

The first and second nitride semiconductor layers may both be undoped, both may be doped with n-type impurities, or one of them may be doped with impurities (modulation doping). In order to improve the crystallinity, it is most preferable that both are undoped, followed by modulation doping and then both doping. When both are doped with an n-type impurity, the n-type impurity concentration of the first nitride semiconductor layer and the n-type impurity concentration of the second nitride semiconductor layer may be different. In addition, the fact that one of the first nitride semiconductor layer and the second nitride semiconductor layer is doped with an n-type impurity is called modulation doping. Has a tendency to improve.

The n-type impurities include Si, Ge, S
A group IV or group VI element such as n or S is preferably selected, and more preferably, Si or Sn is used. When doping with an n-type impurity, the impurity concentration is adjusted to 5 × 10 ²¹ / cm ³ or less, preferably 1 × 10 ²⁰ / cm ³ or less. If it is more than 5 × 10 ²¹ / cm ^3, the crystallinity of the nitride semiconductor layer deteriorates, and the output tends to decrease. This is the same in the case of modulation doping.

In the present invention, the active layer 7 having a multiple quantum well structure is formed of a nitride semiconductor containing In and Ga, preferably, In _a Ga ₁ -aN (0 ≦ a <1), and n
It may be of either p-type or p-type, but undoped (doped with no impurities) is preferred because strong interband emission is obtained and the half-width of the emission wavelength is reduced. The active layer 7 may be doped with an n-type impurity and / or a p-type impurity. When the active layer 7 is doped with an n-type impurity, the inter-band emission intensity can be further increased as compared with the undoped one. When the active layer 7 is doped with a p-type impurity, the peak wavelength can be shifted to an energy side lower than the peak wavelength of the inter-band emission by about 0.5 eV, but the half width is widened. When the active layer is doped with both a p-type impurity and an n-type impurity,
The light emission intensity of the active layer doped with only the p-type impurity can be further increased. In particular, when forming an active layer doped with a p-type dopant, the conductivity type of the active layer is S
It is preferable that an n-type dopant such as i is also doped to make the whole n-type. In order to grow an active layer having good crystallinity, non-doping is most preferable.

The stacking order of the barrier layer and the well layer of the active layer 7 is as follows.
It does not matter even if the layers are stacked from the well layer and ends with the well layer, the layers from the well layer are ended with the barrier layer, the layers from the barrier layer are ended with the barrier layer, or the layers from the barrier layer are ended with the well layer. good. The thickness of the well layer is adjusted to 100 angstroms or less, preferably 70 angstroms or less, and more preferably 50 angstroms or less. Although the upper limit of the thickness of the well layer is not particularly limited, it is at least one atomic layer, preferably at least 10 Å. If the well layer is thicker than 100 angstroms, the output tends to be hardly improved. On the other hand, the thickness of the barrier layer is adjusted to 2000 angstroms or less, preferably 500 angstroms or less, and more preferably 300 angstroms or less. Although the upper limit of the thickness of the barrier layer is not particularly limited,
It is at least one atomic layer, preferably at least 10 angstroms. When the barrier layer is within the above range, the output can be easily improved, which is preferable. Further, the thickness of the entire active layer 7 is not particularly limited.
The total number of layers of the active layer 7 is adjusted by adjusting the number of layers and the order of the layers of the barrier layer and the well layer in consideration of a desired wavelength of the LED element and the like.

In the present invention, the p-side cladding layer 8
Third Nitride Semiconductor Layer with Large Band Gap Energy
And a bandgap energy more than that of the third nitride semiconductor layer.
And a fourth nitride semiconductor layer having low energy.
Different p-type impurity concentrations or the same
Or Al containing p-type impurities_bGa_1-bN (0 ≦ b ≦
It is a single layer consisting of 1). First, the p-side cladding layer 8
P-side multilayer cladding with multilayer structure (superlattice structure)
The case of a layer will be described below. p-side multilayer cladding
Third and fourth nitride semiconductors constituting the multilayer film of layer 17
The layer thickness should be less than 100 Å, more preferably
Or less than 70 Å, most preferably 10 Å
Adjusted to a film thickness of ~ 40 Å, the third nitride
Even if the semiconductor layer and the fourth nitride semiconductor layer have the same thickness,
It may be different. Each film thickness of the multilayer structure is within the above range
In some cases, the thickness becomes less than the elastic critical thickness of the nitride semiconductor.
Nitride semiconductor with better crystallinity than when grown by
Can be grown and the crystallinity of the nitride semiconductor layer improves.
Therefore, when a p-type impurity is added, the carrier concentration increases.
A p layer having a small resistivity can be obtained, and the Vf and threshold value of the element can be reduced.
It tends to decrease. Two layers of such thickness
Multiple layers are stacked as a pair to form a multilayer film layer. Soshi
Therefore, the adjustment of the total film thickness of the p-side multilayer clad layer 8 is performed by
The thickness of each of the third and fourth nitride semiconductor layers was adjusted and the number of laminations was adjusted.
This is done by adjusting. of the p-side multilayer clad layer 8
Although the total thickness is not particularly limited, it is 2,000 angstroms.
Or less, preferably less than 1000 Angstroms,
More preferably, it is 500 angstrom or less.
When the film thickness is in this range, the light emission output is high, and Vf decreases.
preferable. The third nitride semiconductor layer contains at least Al.
Nitride semiconductor, preferably Al _nGa_1-nN (0 <n ≦
Preferably, a fourth nitride semiconductor is grown.
Is preferably Al_pGa_1-pN (0 ≦ p <1, n> p),
In_rGa_1-rBinary mixed crystal such as N (0 ≦ r ≦ 1), ternary
It is desirable to grow a mixed crystal nitride semiconductor. p side
When the cladding layer 8 has a superlattice structure, the crystallinity is improved.
Therefore, the resistivity tends to decrease and Vf tends to decrease.

The case where the p-type impurity concentration of the third nitride semiconductor layer is different from that of the fourth nitride semiconductor layer in the p-type impurity concentration of the p-side multilayer clad layer 8 will be described below. The p-type impurity concentration of the third nitride semiconductor layer and the fourth nitride semiconductor layer of the p-side multilayer clad layer 8 are different, and the impurity concentration of one layer is high and the impurity concentration of the other layer is low. I do. Similarly to the n-side cladding layer 12, the p-type impurity concentration of the third nitride semiconductor layer having a larger bandgap energy is increased, and the p-type impurity concentration of the fourth nitride semiconductor layer having a smaller bandgap energy is increased. Is small, preferably undoped, the threshold voltage, V
f etc. can be reduced. The reverse is also possible.
That is, the p-type impurity concentration of the third nitride semiconductor layer having a large band gap energy may be reduced and the p-type impurity concentration of the fourth nitride semiconductor layer having a small band gap energy may be increased.

The preferable doping amount of the third nitride semiconductor layer is 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ , more preferably 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ²⁰ / cm 3. Adjust to the range of ³ . If it is less than 1 × 10 ¹⁸ / cm ³ , the difference from the fourth nitride semiconductor layer is similarly reduced, and similarly, a layer having a high carrier concentration tends to be hardly obtained.
If it is more than × 10 ²¹ / cm ³ , the crystallinity tends to deteriorate. On the other hand, the p-type impurity concentration of the fourth nitride semiconductor layer may be lower than that of the third nitride semiconductor layer, preferably 1/10 or more. Most preferably, an undoped layer is obtained, which has the highest mobility. However, since the layer is thin, there is a p-type impurity diffused from the third nitride semiconductor side, and its amount is 1 × 10 ²⁰ / cm 3. ³ or less is desirable. In addition, the third having a large band gap energy
The same applies to the case where the nitride semiconductor layer is doped with a small amount of p-type impurities and the fourth nitride semiconductor layer having a small band gap energy is doped with a large amount of p-type impurities. Examples of p-type impurities include Mg, Zn, Ca, Be, etc.
A group IIA or IIB element is selected, and preferably, Mg, Ca or the like is used as the p-type impurity.

Further, in the nitride semiconductor layer constituting the multilayer film, the layer in which impurities are doped at a high concentration has a higher impurity concentration near the center of the semiconductor layer and a higher impurity concentration near both ends in the thickness direction. Is small (preferably undoped) to reduce the resistivity.

When the third and fourth nitride semiconductor layers of the p-side multilayer cladding layer 8 have the same p-type impurity concentration, the third and fourth nitride semiconductor layers have the same p-type impurity concentration. The impurity concentration is adjusted within the range of the p-type impurity concentration of the third nitride semiconductor layer when the p-type impurity concentration is different. Thus, when the p-type impurity concentration is the same, the crystallinity tends to be slightly inferior to the case where the impurity concentration is different,
The p-type clad layer 8 having a high carrier concentration can be easily formed, which is preferable from the viewpoint of improving output.

Next, in the case where the p-side cladding layer 8 is a single layer containing p-type impurities and made of Al _b Ga ₁ -bN (0 ≦ b ≦ 1), The thickness is 2000
Angstrom or less, preferably 1000 angstrom or less, and more preferably 500 to 100 angstrom or less. When the film thickness is in the above range, the light emission output is improved, and Vf is preferably reduced. The composition of the p-side single film cladding layer 8 is Al _b Ga ₁ -bN (0 ≦ b ≦ 1). In addition, although the single-layer clad layer has slightly lower crystallinity than the p-side clad layer of the multilayer structure, it can be grown with good crystallinity in combination with the first multilayer layer 4. As a result, the threshold value and Vf can be reduced. Further, even when a single film is used in this manner, a decrease in element performance is reduced by combining with another layer configuration, and since the single film is used, the manufacturing process can be simplified, which is preferable in mass production. The concentration of the p-type impurity in the p-side single film cladding layer 8 is 1 × 10 ¹⁸ to 1 × 10 ²¹ / cm.
³ , preferably 5 × 10 ^{18 to} 5 × 10 ²⁰ / cm ³ , more preferably 5 × 10 ¹⁹ to 1 × 10 ²⁰ / cm ³ . When the impurity concentration is within the above range, a favorable p-type film can be formed, which is preferable.

Next, in the present invention, the Mg-doped p-side G
The aN contact layer 9 has a composition of a binary mixed crystal nitride semiconductor not containing In and Al. If In and Al are contained, ohmic contact with the p-electrode 10 cannot be obtained, and the luminous efficiency decreases. The thickness of the p-side contact layer 9 is 0.001 to 0.5 μm, preferably 0.01
To 0.3 μm, more preferably 0.05 to 0.2 μm. If the film thickness is less than 0.001 μm, p-type GaAl
An electrical short-circuit easily occurs with the N-clad layer, and it is difficult to function as a contact layer. In addition, since a binary mixed crystal GaN contact layer having a different composition is laminated on the ternary mixed crystal GaAlN cladding layer, if the thickness of the GaN contact layer is made larger than 0.5 μm, a misfit between the crystals may occur. Lattice defects tend to occur in the p-side GaN contact layer 9 and the crystallinity tends to decrease. Note that the smaller the thickness of the contact layer, the lower the Vf and the higher the light emission efficiency. When the p-type impurity of the p-type GaN contact layer 9 is Mg, p-type characteristics are easily obtained, and ohmic contact is easily obtained. The concentration of Mg is 1 × 10 ¹⁸ to 1
× 10 ²¹ / cm ³ , preferably 5 × 10 ^{19 to} 3 × 10 ²⁰ / c
m ³ , more preferably about 1 × 10 ²⁰ / cm ³ . Mg
When the concentration is within this range, a good p-type film is easily obtained.
f decreases, which is preferable.

The n-electrode 11 is formed on the n-side contact layer 4, and the p-electrode is formed on the Mg-doped p-side GaN contact layer 9. The material of the n-electrode and the p-electrode is not particularly limited. For example, the n-electrode may be W / Al,
Ni / Au or the like can be used as the p-electrode.

[0047]

EXAMPLES Examples which are embodiments of the present invention will be shown below, but the present invention is not limited to these. Embodiment 1 Embodiment 1 will be described with reference to FIG. The substrate 1 made of sapphire (C surface) was set in a MOVPE reaction vessel, and the temperature of the substrate was set to 10 while flowing hydrogen.
The temperature is raised to 50 ° C., and the substrate is cleaned.

(Buffer Layer 2) Subsequently, the temperature is set to 510 ° C.
The buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 150 angstroms using hydrogen as the carrier gas and ammonia and TMG (trimethylgallium) as the source gas.

(Undoped GaN layer 3) After growing the buffer layer 2, only TMG is stopped, and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C, TM
G, an undoped GaN layer 3 is grown to a thickness of 1.5 μm using ammonia gas.

(N-side contact layer 4) Subsequently, at 1050 ° C.
Similarly, TMG, ammonia gas and silane gas were used as the source gas and the impurity gas, and Si was 4.5 × 10 ¹⁸ / cm ^3.
The n-side contact layer 4 made of doped GaN is
It is grown to a thickness of 65 μm.

(N-side first multilayer film layer 5) Then, only the silane gas is stopped, and a lower layer 5a made of undoped GaN is grown at 1050 ° C. using TMG and ammonia gas to a thickness of 2000 angstroms. A silane gas was added at a temperature to grow an intermediate layer 5b made of GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si to a thickness of 300 Å, followed by stopping only the silane gas and undoping undoped GaN at the same temperature. Is grown to a thickness of 50 angstroms, and a total film thickness of 3 layers 2
A first multilayer film layer 5 of 350 Å is grown.

(N-side Second Multilayer Film Layer 6) Next, at the same temperature, a second nitride semiconductor layer made of undoped GaN is grown at 40 Å, and then the temperature is set to 800 ° C., and TMG, TMI The first nitride semiconductor layer made of undoped In _0.13 Ga _0.87 N using
Grow 0 Å. These operations are repeated so that ten layers are alternately stacked in the second + first order.
An n-side second multilayer film layer 6 composed of a multilayer film having a super lattice structure grown by angstrom is grown to a thickness of 640 angstrom.

(Active Layer 7) Next, a barrier layer made of undoped GaN is grown to a thickness of 200 angstroms. Then, the temperature is raised to 800 ° C., and undoped In _0.4 Ga _0.6 N using TMG, TMI and ammonia. A well layer having a thickness of 30 Å is grown. Then, five barrier layers and four well layers are alternately stacked in the order of barrier + well + barrier + well.
An active layer 7 having a multiple quantum well structure of 0 Å is grown.

(P-side multilayer clad layer 8)
TMG, TMA, ammonia, Cp ₂ Mg at 050 ° C
Using (cyclopentadienyl magnesium), is grown in a thickness of 1 × 10 ²⁰ / cm ³ doped with p-type Al _0.2 Ga consisting _0.8 N third nitride semiconductor layer 40 Å Mg, followed by temperature To 800 ° C., TMG,
Mg is 1 × 10 using TMI, ammonia and Cp ₂ Mg.
^A fourth nitride semiconductor layer made of In _0.03 Ga _0.97 N doped with ²⁰ / cm ³ is grown to a thickness of 25 Å. These operations are repeated, and five layers are alternately stacked in the third + fourth order. Finally, a p-layer made of a superlattice-structured multilayer film in which a third nitride semiconductor layer is grown to a thickness of 40 angstroms. The side multilayer clad layer 8 is grown to a thickness of 365 angstroms.

(P-side GaN contact layer 9)
At 50 ° C., TMG, ammonia, Cp ₂ Mg
g of p-type GaN doped with 1 × 10 ²⁰ / cm ³
The side contact layer 9 is grown to a thickness of 700 Å.

After the completion of the reaction, the temperature was lowered to room temperature, and the wafer was placed in a reaction vessel in a nitrogen atmosphere for 700 minutes.
Anneal at ℃ to further reduce the resistance of the p-type layer.

After annealing, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer 9, and etching is performed from the p-side contact layer side by an RIE (reactive ion etching) apparatus. Do
As shown in FIG. 1, the surface of the n-side contact layer 4 is exposed.

After the etching, almost the entire surface of the uppermost p-side contact layer is formed of a light-transmitting p-electrode 10 containing 200 Å of Ni and Au and a bonding Au on the p-electrode 10. The p pad electrode 11 is formed with a thickness of 0.5 μm. On the other hand, an n-electrode 12 containing W and Al was formed on the surface of the n-side contact layer 4 exposed by etching, to obtain an LED element.

This LED element emits pure green light of 520 nm at a forward current of 20 mA, and Vf is 3.5 V
In comparison with the conventional multiple quantum well structure LED element,
Vf decreased by about 1.0 V, and the output increased 2.0 times or more. Therefore, an LED having a characteristic substantially equal to that of a conventional LED element at 10 mA was obtained. Further, the obtained L
The electrostatic breakdown voltage of the ED was measured by gradually applying a voltage in the opposite direction from each electrode of the n-layer and the p-layer of the LED element.

The structure of the conventional LED element is GaN
A second buffer layer made of undoped GaN and an n layer made of Si-doped GaN on the first buffer layer made of
Side contact layer, an active layer having the same multiple quantum well structure as in Example 1, a single Mg-doped Al _0.1 Ga _0.9 N layer,
The p-side contact layer made of Mg-doped GaN is sequentially laminated.

[Embodiment 2] In the embodiment 1, the active layer 7
Was prepared in the same manner except that the following was changed. (Active Layer 7) Next, a barrier layer made of undoped GaN is grown to a thickness of 250 Å, and then the temperature is set to 800 ° C., and a well layer made of undoped In _0.3 Ga _0.7 N using TMG, TMI and ammonia. Is grown to a thickness of 30 Å. And barrier + well +
Barrier + well... + Barrier in the order of seven barrier layers and six well layers alternately stacked to grow an active layer 7 having a multiple quantum well structure with a total thickness of 1930 Å. The obtained LED element emits pure blue light of 470 nm at a forward current of 20 mA, and good results are obtained as in Example 1.

[Embodiment 3] In the embodiment 1, the active layer 7
Was prepared in the same manner except that the following was changed. (Active Layer 7) Next, a barrier layer made of undoped GaN is grown to a thickness of 250 Å, and then the temperature is set to 800 ° C., and a well layer made of undoped In _0.3 Ga _0.7 N using TMG, TMI and ammonia. Is grown to a thickness of 30 Å. And barrier + well +
Barrier + well... + Barrier in the order of six barrier layers and five well layers are alternately laminated to grow an active layer 7 having a multiple quantum well structure with a total film thickness of 1650 Å. The obtained LED element emits pure blue light of 470 nm at a forward current of 20 mA, and good results are obtained as in Example 1.

[Embodiment 4] In the embodiment 1, the active layer 7
Was prepared in the same manner except that the following was changed. (Active Layer 7) Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstroms, then the temperature is set to 800 ° C., and a well layer made of undoped In _0.35 Ga _0.65 N using TMG, TMI and ammonia. Is grown to a thickness of 30 Å. An active layer 7 having a multiple quantum well structure with a total thickness of 1930 angstroms is formed by alternately stacking seven barrier layers and six well layers in the order of barrier + well + barrier + well... + Barrier. Grow. The obtained LED element emits blue-green light of 500 nm at a forward current of 20 mA, and good results are obtained as in Example 1.

Fifth Embodiment In the first embodiment, the active layer 7
Was prepared in the same manner except that the following was changed. (Active Layer 7) Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstroms, then the temperature is set to 800 ° C., and a well layer made of undoped In _0.35 Ga _0.65 N using TMG, TMI and ammonia. Is grown to a thickness of 30 Å. Four barrier layers and three well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier to form an active layer 7 having a multiple quantum well structure with a total film thickness of 1090 Å. Grow. The obtained LED element emits blue-green light of 500 nm at a forward current of 20 mA, and good results are obtained as in Example 1.

[Embodiment 6] In Embodiment 1, the n-side second
An LED device was manufactured in the same manner except that the multilayer film layer 6 was not grown. Although the obtained LED element has slightly lower element characteristics and light emission output than the first embodiment, the electrostatic breakdown voltage is almost as good as that of the first embodiment.

[Embodiment 7] In the same manner as in the embodiment 1, except that the p-side multilayer cladding layer 8 is changed as follows.
An ED element was manufactured. (P-side single film clad layer 8) TMG at a temperature of 1050 ° C.
A p-side single film cladding layer 8 of p-type Al _0.16 Ga _0.84 N doped with Mg at 1 × 10 ²⁰ / cm ³ using TMA, ammonia, Cp ₂ Mg (cyclopentadienyl magnesium), and a 300 Å film Grow in thickness. Although the obtained LED element is grown as a single layer without using the clad layer as a superlattice, the performance such as the light emission output is slightly inferior to that of Example 1 due to the combination with other layer configurations. Good results are obtained with almost the same breakdown voltage. In addition, it is preferable to use a single layer because the manufacturing process can be simplified as compared with the case of forming a multilayer film layer.

[Embodiment 8] In Embodiment 1, the n-side first
An LED element was produced in the same manner except that the thickness of the multilayer film layer 5 was changed as follows. (N-side first multilayer film layer 5) Then, only the silane gas is stopped and 1
At 050 ° C., using TMG and ammonia gas, a lower layer 5a made of undoped GaN was grown to a thickness of 3000 Å, and then silane gas was added at the same temperature to dope 4.5 × 10 ¹⁸ / cm ^{3 of} Si. An intermediate layer 5b made of GaN is grown to a thickness of 300 angstroms, then only silane gas is stopped, and an upper layer 5c made of undoped GaN is grown at the same temperature to a thickness of 50 angstroms to form a total film consisting of three layers. A first multilayer film layer 5 having a thickness of 3350 angstroms is grown. L obtained
The ED element has substantially the same characteristics as those of the first embodiment, and good results can be obtained.

Ninth Embodiment In the eighth embodiment, the thickness of the n-side contact layer 4 is set to 4.165 μm, 5.165 μm.
m, 7.165 μm except for 3 kinds of LED
A device is manufactured. The obtained LED element has substantially the same characteristics as those of Example 1, and good results are obtained. In addition, when the film thickness is 4.165 μm or 5.165 μm, the element characteristics such as light emission output are maintained. The electrostatic withstand voltage is slightly better than that of the first embodiment.

[Embodiment 10] In Embodiment 1, the n-side second multilayer film layer 6 is made of a second nitride semiconductor layer made of undoped GaN and In doped with 5 × 10 ¹⁷ / cm ^{3 of} Si.
_An LED element is manufactured in the same manner except that a multilayer film including a first nitride semiconductor layer made of _0.13 Ga _0.87 N is used.
The obtained LED element shows almost the same characteristics as in Example 1.

[Embodiment 11] In Embodiment 1, the p-side
The cladding layer 8 is made of Mg¹⁹/ Cm^ThreeDope
Al_0.2Ga_0.8Third nitride semiconductor layer made of N
And undoped In _0.03Ga_0.97The fourth nitrogen consisting of N
Except that a multi-layer film composed of
An ED element is manufactured. The obtained LED element was obtained in Example 1.
Shows almost the same characteristics.

[Example 12] In Example 1, the p-side multilayer clad layer 8 was made of a third nitride semiconductor layer of undoped Al _0.2 Ga _0.8 N and Mg of 5 × 10 ¹⁹ / cm.
³ addition to doped with an In _{0.0 3} Ga _0.97 fourth nitride semiconductor layer made of N multilayer film made in the same manner LED
A device is manufactured. The obtained LED element shows almost the same characteristics as in Example 1.

[Embodiment 13] In the embodiment 8, the n-side first multilayer film 5 is composed of a lower layer 5a of undoped GaN having a thickness of 3000 Å and 4.5 × 10 ¹⁸ / cm 2.
cm ³ doped 300 Å thick Al _0.1
An LED element is manufactured in the same manner as above except that an intermediate layer 5b made of Ga _0.9 N and an upper layer 5c made of undoped GaN having a thickness of 50 Å are grown. The obtained LED element has substantially the same characteristics as in Example 8,
Good results are obtained.

[Embodiment 14] In the embodiment 8, the n-side first multilayer film layer 5 is composed of undoped Al _0.1 Ga _0.9 N lower layer 5a having a thickness of 3000 Å and 4.5.
An intermediate layer 5b made of Al _0.1 Ga _0.9 N having a thickness of 300 Å doped with × 10 ¹⁸ / cm ³ and an upper layer 5c made of 50 Å made of undoped Al _0.1 Ga _0.9 N are grown. LED in the same way
A device is manufactured. The obtained LED element has substantially the same characteristics as in Example 8, and good results are obtained.

[Embodiment 15] In Embodiment 8, the n-side first multilayer film layer 5 has a lower layer 5a of 3,000 angstroms made of undoped Al _0.1 Ga _0.9 N and 4.5.
An LED element is manufactured in the same manner except that an intermediate layer 5b made of GaN with a thickness of 300 Å doped with × 10 ¹⁸ / cm ³ and an upper layer 5c made of undoped GaN with a thickness of 50 Å are grown. . The obtained LED element has substantially the same characteristics as in Example 8,
Good results are obtained.

Example 16 The procedure of Example 8 was repeated, except that the n-side contact layer 4 was made of Al _0.05 Ga _0.95 N doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si and having a thickness of 4.165 μm. To produce an LED element. The obtained LED element shows substantially the same characteristics as in Example 8.

[Comparative Example 1] In Example 1, the n-side first
Lower layer 5 made of undoped GaN constituting multilayer film layer 5
An LED element was fabricated in the same manner except that a was not formed.
In the obtained LED element, the electrostatic withstand voltage was remarkably reduced as compared with Example 1, and the characteristics regarding the leak current and Vf were not sufficiently satisfactory.

[Comparative Example 2] In Example 1, the n-side first
An LED element was manufactured in the same manner except that the intermediate layer 5b made of Si-doped GaN constituting the multilayer film layer 5 was not formed. In the obtained LED element, the light emission output and the electrostatic breakdown voltage were greatly reduced as compared with Example 1, and other characteristics were not sufficiently satisfactory.

[Comparative Example 3] In Example 1, the n-side first
Upper layer 5 of undoped GaN constituting multilayer film layer 5
An LED element was fabricated in the same manner except that c was not formed.
In the obtained LED element, the leak current increased as compared with Example 1, and other characteristics were not satisfactory values.

[0079]

According to the present invention, a nitride semiconductor having an improved luminous output and a good electrostatic withstand voltage can be obtained by using an active layer having a multiple quantum well structure to expand the range of application to various applied products. A light-emitting element can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure of an LED element according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in device characteristics when the thickness of an undoped lower layer 5a of the present invention is changed.

FIG. 3 shows an n-type impurity-doped intermediate layer 5 according to the present invention.
6 is a graph showing a change in device characteristics when the film thickness b is changed.

FIG. 4 is a graph showing changes in device characteristics when the thickness of the undoped upper layer 5c of the present invention is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... Undoped GaN layer 4 ... N side contact layer 5 ... N side first multilayer film layer 5a ... Undoped lower layer 5b ... n Intermediate layer of type impurity doping 5c ... Undoped upper layer 6 ... n-side second multilayer film layer 7 ... active layer 8 ... p-side cladding layer 9 ... Mg-doped p-side GaN contact layer 10 ... p electrode 11 ... n electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-232629 (JP, A) JP-A-8-228025 (JP, A) JP-A-5-82834 (JP, A) JP-A-8-22834 51251 (JP, A) JP-A-4-68579 (JP, A) JP-A-10-135575 (JP, A) IEEE Journal of Selected Topics in Quantum Electronics Vol. 4 No. 3 p. 483-489 (1998, May 6) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 21/205 H01L 33/00 JICST file (JOIS)

Claims (11)

(57) [Claims] 1. A nitride semiconductor device having an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer formed on a substrate via a buffer layer, wherein the n-side nitride semiconductor layer comprises: An n in which at least three layers of a lower layer made of an undoped nitride semiconductor having a thickness of 100 to 10000 °, an intermediate layer made of a nitride semiconductor doped with an n-type impurity, and an upper layer made of an undoped nitride semiconductor are stacked in this order.
A nitride semiconductor device comprising a first side multilayer film layer. 2. The method according to claim 1, wherein the active layer is formed of In _a Ga ₁ -aN (0 ≦ a
<1> A multiple quantum well structure including a layer.
The nitride semiconductor device as described in the above. 3. The intermediate layer has a thickness of 50 to 1000 angstroms, and the upper layer has a thickness of 25 to 1000 angstroms.
3. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is angstrom. 4. A first nitride semiconductor layer containing In between the n-side first multilayer film layer and the active layer, and a second nitride semiconductor having a composition different from that of the first nitride semiconductor layer. The nitride semiconductor device according to any one of claims 1 to 3, further comprising an n-side second multilayer film layer on which an object semiconductor layer is laminated. 5. The semiconductor device according to claim 1, wherein the n-side nitride semiconductor layer has an n-side contact layer containing an n-type impurity on a substrate side of the n-side first multilayer film layer. 2. The nitride semiconductor device according to claim 1. 6. An undoped G-side contact layer.
6. The semiconductor device according to claim 5, wherein the semiconductor device is formed on the aN layer.
3. The nitride semiconductor device according to item 1. 7. The nitride semiconductor device, wherein the undoped GaN layer is grown at a low temperature by using Ga _d Al _{1 -dN} (0
7. A semiconductor device according to claim 6, wherein said buffer layer is formed on a buffer layer comprising <d ≦ 1).
The nitride semiconductor device as described in the above. 8. The total film thickness of the undoped GaN layer, the n-side contact layer, and the n-side first multilayer film layer is 2 to 20.
8. The nitride semiconductor device according to claim 6, wherein the thickness is μm. 9. 9. A p-side multi-layer clad layer formed by laminating third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations from each other. 9. A p-side multilayer clad layer formed by laminating third and fourth nitride semiconductor layers having different band gap energies and the same p-type impurity concentration from each other. 2. The nitride semiconductor device according to item 1. 10. The p-side nitride semiconductor layer according to claim 1, wherein the p-side nitride semiconductor layer includes a p-side single film clad layer containing p-type impurities and made of Al _b Ga ₁ -bN (0 ≦ b ≦ 1). Any one of them
Item 6. The nitride semiconductor device according to item 1. 11. A p-side layer containing Mg as a p-type impurity on the p-side multilayer clad layer or the p-side single film clad layer.
The nitride semiconductor device according to claim 9, wherein an aN contact layer is formed.