JP3063756B1 - Nitride semiconductor device - Google Patents

Abstract

The present invention provides a nitride semiconductor light-emitting device having a multi-quantum well structure active layer, capable of expanding the range of application to various applied products, further improving light emission output, and improving electrostatic withstand voltage. It is. SOLUTION: At least two kinds of nitride semiconductor layers having the same composition, in which at least n-type impurities are doped at different concentrations and different in band gap energy or n-type impurities are doped at different concentrations, are laminated. N-side first multilayer film layer 5 and In _a Ga _1-a
Active layer 7 having a multiple quantum well structure composed of N (0 ≦ a <1)
And a p-side multilayer clad layer 8 formed by laminating third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations, or Al _b Ga ₁ containing p-type impurities. _-b p consisting of N (0 ≦ b ≦ 1)
Side single-film clad layer 8.

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. For example,
As an LED device using an active layer having a multiple quantum well structure,
Japanese Patent Application Laid-Open No. Hei 10-135514 discloses that at least undoped Ga is used in order to improve luminous efficiency and luminous intensity.
A nitride semiconductor device having a light emitting layer having a multiple quantum well structure including a barrier layer made of N, a well layer made of undoped InGaN, and a cladding layer having a band gap wider than the barrier layer of the light emitting layer is disclosed.

[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. Therefore, an object of the present invention is to provide a nitride semiconductor light emitting device that further improves the light emission output and expands the range of application to various applied products using an active layer having a multiple quantum well structure, and that improves the electrostatic breakdown voltage. To provide.

[0004]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (12). (1) In a nitride semiconductor device having an active layer between an n-side nitride semiconductor layer and a p-side nitride semiconductor layer, the active layer is an In _a Ga _1-a N (0 ≦ a <1) layer. Wherein the n-side nitride semiconductor layer has the same composition as the n-side contact layer containing the n-type impurity, the nitride semiconductor layer doped with the n-type impurity, and the nitride semiconductor layer. And at least two types of nitride semiconductor layers including an undoped nitride semiconductor layer not doped with an n-type impurity are laminated, and an n-side multilayer film layer formed on the n-side contact layer is formed. A nitride semiconductor device, comprising: (2) The nitride semiconductor device according to (1), wherein the nitride semiconductor layer doped with the n-type impurity and the undoped nitride semiconductor layer not doped with the n-type impurity are each a GaN layer. (3) The nitride semiconductor device according to (1) or (2), wherein the n-side contact layer is formed on an undoped GaN layer. (4) The p-side nitride semiconductor layer is formed by stacking third and fourth nitride semiconductor layers having different band gap energies and different or the same p-type impurity concentrations.
(1)-characterized by including a side multilayer clad layer
The nitride semiconductor device according to any one of (3). (5) The p-side multilayer clad layer has a superlattice structure,
The third nitride semiconductor layer is formed of Al _n Ga _1-n N (0 <n ≦
1), wherein the fourth nitride semiconductor layer is formed of Al _p Ga
_1-p N (0 ≦ p <1, p <n) or In _r Ga _1-r N (0
≦ r ≦ 1) (4). (6) In the nitride semiconductor device, the undoped GaN layer is Ga _d Al _{1 -dN} (0 <d ≦
A) a p-side G layer formed on the buffer layer of 1) and containing Mg as a p-type impurity on the p-side multilayer clad layer;
The nitride semiconductor device according to (4), wherein the aN contact layer is formed. (7) In a nitride semiconductor device having an active layer between an n-side nitride semiconductor layer and a p-side nitride semiconductor layer, the active layer is an In _a Ga _1-a N (0 ≦ a <1) layer. An n-side multilayer film formed by laminating at least two types of nitride semiconductor layers having the same composition in which the n-type nitride semiconductor layers are doped with different concentrations from each other. A nitride semiconductor device comprising a layer. (8) The nitride semiconductor device according to (7), wherein each of the two types of nitride semiconductor layers having the same composition and doped with different concentrations of the n-type impurity is a GaN layer. (9) The nitride semiconductor device according to (7) or (8), wherein the n-side contact layer is formed on an undoped GaN layer. (10) The p-side nitride semiconductor layer is a p-side multilayer clad layer formed by laminating third and fourth nitride semiconductor layers having different band gap energies and different or identical p-type impurity concentrations. (7)-characterized by including
The nitride semiconductor device according to any one of (9). (11) The p-side multilayer clad layer has a superlattice structure, and the third nitride semiconductor layer is formed of Al _n Ga _1-n N (0 <
n ≦ 1), and the fourth nitride semiconductor layer is made of Al _p
Ga _1-p N (0 ≦ p <1, p <n) or In _r Ga _1-r N
The nitride semiconductor device according to (10), wherein (0 ≦ r ≦ 1). (12) In the nitride semiconductor device, the undoped GaN layer is Ga _d Al _1-d N (0 <d ≦
A) a p-side G layer formed on the buffer layer of 1) and containing Mg as a p-type impurity on the p-side multilayer clad layer;
The nitride semiconductor device according to (10), wherein the aN contact layer is formed.

That is, the present invention provides an n-side first multilayer film layer comprising two or more types of nitride semiconductor layers having different n-type impurity concentrations on the n-side so as to sandwich a light emitting layer having a multiple quantum well structure.
On the p-side, a p-side multilayer clad layer composed of third and fourth nitride semiconductor layers or a p-type impurity-containing Al _b Ga _1-b N (0
≦ b ≦ 1), it is possible to obtain a nitride semiconductor device having improved luminous efficiency, improved luminous output, and further improved electrostatic withstand voltage by forming in combination with the p-side single film clad layer of ≦ b ≦ 1). . By combining a plurality of nitride semiconductor layers having a specific composition, structure, and the like, the performance of the active layer having the multiple quantum well structure can be efficiently exhibited. Other preferred nitride semiconductor layers in combination with an active layer having a multiple quantum well structure are described below.

In the present invention, the n-side first multilayer film layer may be
A first nitride semiconductor layer containing In between the active layer,
A second nitride semiconductor having a composition different from that of the first nitride semiconductor layer;
An n-side second multilayer film layer on which a nitride semiconductor layer is laminated
Then, the luminous efficiency is further improved, and Vf is reduced.
Luminous efficiency can be improved, which is preferable. In addition,
, An n-type first multilayer film
When an n-side contact layer containing impurities is provided, light emission output is reduced.
It is preferable for improving and decreasing Vf. Moreover,
In the present invention, the n-side contact layer is undoped.
When formed on a GaN layer, such undoped G
Since the aN layer is obtained as a layer having good crystallinity, the n electrode is
The n-side contact layer to be formed has good crystallinity.
Such as an active layer formed on the n-side contact layer.
The crystallinity of the other nitride semiconductor layers also improves, improving the light emission output.
It is preferable to make it higher. Still further, in the present invention,
The undoped GaN layer is made of Ga grown at a low temperature. _dAl_1-d
N (0 <d ≦ 1) formed on a buffer layer
Then, the crystallinity of the undoped GaN layer is further improved,
The crystallinity of the n-side contact layer and the like also becomes better, and light emission
It is preferable in improving the force.
Mg-doped p-side G on the pad layer or p-side single film clad layer
Forming an aN contact layer makes it easier to obtain p-type characteristics
And the p-side GaN contact layer is
Has good ohmic contact with the p-electrode formed at
It is preferable for improving light output. Still further, the present invention
The undoped GaN layer, the n-side contact layer,
And the total film thickness of the n-side first multilayer film layer is 2 to 20 μm,
Preferably 3 to 10 μm, more preferably 4 to 9 μm
This is preferable from the viewpoint of improving the electrostatic withstand voltage. The above range
If the film thickness is too small, the device characteristics other than the electrostatic withstand voltage are good.
You. The total film thickness of the three layers is preferably a preferable film thickness of each layer.
Within the thickness range, the total thickness of the three layers is within the above range.
Is adjusted appropriately.

[0007]

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 layer 3, n-side contact layer 4 containing n-type impurity, n-side first multilayer film 5 containing n-type impurity, n-side second multilayer film layer 6 composed of first and second nitride semiconductor layers, multiple An active layer 7 having a quantum well structure, a p-side multilayer clad layer 8 made of third and fourth nitride semiconductor layers, or a p-side single film clad layer 8,
It has a structure in which Mg-doped p-side GaN contact layers 9 are sequentially stacked. Further, an n-electrode 1 is formed on the n-side contact layer 4.
1. A p-electrode 10 is formed on the p-side GaN contact layer 9.

In the present invention, the substrate 1 may be sapphire having a sapphire C-plane, an R-plane or an A-plane as a main surface, an insulating substrate such as spinel (MgA1 ₂ O ₄ ), or 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)
The composition is preferably a nitride semiconductor, and the composition having a smaller proportion of Al is more remarkably improved in crystallinity, and 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 film thickness is in the above range, 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 crystallinity of the contact layer becomes too poor is preferably 5 × 10 ²¹ / cm ³ or less.

[0012] 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 value can be reduced and the forward voltage of the light emitting element can be reduced, which is preferable. Further, the n-side contact layer 4
Is preferably in the range described above in that the combination with the undoped GaN layer 3 and the n-side first multilayer film layer 5 improves the electrostatic withstand voltage. Also, the n-side contact layer 4
When forming an n-side first multilayer film layer 5 described later in a thick film,
Can be omitted.

Next, in the present invention, the n-side first multilayer film layer 5 is doped with different concentrations of n-type impurities or different in band gap energy or doped with different concentrations of n-type impurities. It is composed of a multilayer film in which at least two types of nitride semiconductor layers having the same composition are laminated. The thickness of the n-side first multilayer film 5 is 2 μm or less, preferably 1.5 μm or less, and more preferably 0.9 μm or less. The lower limit is not particularly limited, but is, for example, 0.05 μm or more. When the film thickness is in this range, it is preferable to improve the light emission output. Furthermore,
It is preferable that the film thickness of the n-side first multilayer film layer 5 be 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. The fact that the nitride semiconductor layers constituting the multilayer film have different impurity concentrations from each other is referred to as modulation doping. In this case, it is preferable that one of the layers has no impurity doped, that is, undoped.

First, the case where the n-side first multilayer film layer 5 is a multilayer film formed by laminating at least two types of nitride semiconductor layers having different band gap energies will be described below. The thickness of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy constituting the multilayer film layer of the n-side first multilayer film layer 5 are 100 Å or less, more preferably 70 Å or less. Most preferably 10-4
Adjust to a thickness of 0 Å. When the thickness is larger than 100 angstroms, the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy have a film thickness equal to or more than the elastic strain limit,
There is a tendency for minute cracks or crystal defects to easily enter the film. The lower limit of the film thickness of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy is not particularly limited, and may be at least one atomic layer, and is most preferably at least 10 Å as described above. .

When the n-side first multilayer film 5 has a thin multilayer film structure as described above, the thickness of each nitride semiconductor layer constituting the multilayer film layer is set to be equal to or less than the elastic critical thickness. Thus, a nitride semiconductor having very few crystal defects can be grown. In addition, the undoped GaN
Crystal defects generated through the layer 3 and the n-side contact layer 4 can be stopped to some extent, and the crystallinity of the n-side second multilayer film layer 6 grown on the multilayer film layer can be improved. There is also an effect similar to HEMT.

It is desirable to grow a nitride semiconductor containing at least Al, preferably Al _g Ga _{1 -g} N (0 <g ≦ 1), for the nitride semiconductor layer having a large band gap energy. On the other hand, the nitride semiconductor having a small band gap energy may be any nitride semiconductor having a band gap energy smaller than that of a nitride semiconductor having a large band gap energy, but is preferably Al _h Ga ₁ -hN ( 0 ≦ h <1, g> h), In _j Ga _1-j
Binary mixed crystal and ternary mixed crystal nitride semiconductors such as N (0 ≦ j <1) can be easily grown, and those having good crystallinity can be easily obtained. Among them, particularly preferably, the nitride semiconductor having a large band gap energy is Al _g Ga _{1 -g} N (0 <g <1) containing substantially no In, and the nitride semiconductor having a small band gap energy is substantially Al. _Inj Ga _{1 -jN} (0 ≦ j <1) containing no Al, and especially for the purpose of obtaining a multilayer film having excellent crystallinity, an Al mixed crystal ratio (g value) of 0.
3 or less of Al _g Ga _1-g N (0 <g ≦ 0.3);
Is most preferred.

When the n-side first multilayer film layer 5 forms a cladding layer as an optical confinement layer and a carrier confinement layer, it is necessary to grow a nitride semiconductor having a larger band gap energy than the well layer of the active layer. There is. The nitride semiconductor layer having a large band gap energy is a nitride semiconductor having a high Al mixed crystal ratio. Conventionally, Al
When a nitride semiconductor having a high mixed crystal ratio is grown as a thick film, cracks are easily formed, and crystal growth is very difficult. However, when the n-side first multilayer film layer 5 is a multilayer film layer as in the present invention, even if a single layer constituting the multilayer film layer is a layer having a somewhat higher Al alloy crystal ratio, the thickness is not more than the elastic critical thickness. It is hard to crack because it is grown. for that reason,
Since a layer having a high Al mixed crystal ratio can be grown with good crystallinity, the light confinement and carrier confinement effects can be enhanced, and the threshold voltage can be reduced in a laser device and Vf (forward voltage) can be reduced in an LED device.

Further, it is preferable that the n-type first nitride film layer 5 has a different n-type impurity concentration between the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy. This is what is called modulation doping. If the n-type impurity concentration of one layer is low, preferably in a state where the impurity is not doped (undoped), and the other is heavily doped, the threshold voltage, Vf, etc. are reduced. be able to. This is because the presence of a layer with a low impurity concentration in the multilayer film layer increases the mobility of the layer, and the presence of a layer with a high impurity concentration at the same time allows the multilayer film to remain at a high carrier concentration. This is because a layer can be formed. That is, since a layer having a low impurity concentration and a high mobility and a layer having a high impurity concentration and a high carrier concentration are present at the same time, a layer having a high carrier concentration and a high mobility becomes a cladding layer. , Vf decrease.

Nitride having a large band gap energy
When the semiconductor layer is heavily doped with n-type impurities,
Suitable for nitride semiconductor layer with large gap energy
The doping amount is 1 × 10¹⁷/cm^Three~ 1 × 10²⁰/ C
m^Three, More preferably 1 × 10 ¹⁸/cm^Three~ 5 × 10¹⁹/ C
m^ThreeAdjust to the range. 1 × 10¹⁷/cm^ThreeLess than
And nitride semiconductor layer with small band gap energy
And a layer with a high carrier concentration is obtained.
1 × 10²⁰/cm^ThreeMore than
The leakage current of the element itself tends to increase.
You. On the other hand, a nitride half having a small band gap energy
The n-type impurity concentration of the conductor layer is lower than the bandgap energy.
Less is required than the large nitride semiconductor layer, preferably
Is preferably 1/10 or less. Most preferably
When doped, the layer with the highest mobility is obtained.
Nitriding with large band gap energy due to thin thickness
N-type impurities diffuse from the semiconductor
Is 1 × 10¹⁹/cm^ThreeThe following is desirable. As an n-type impurity
Is group IVB of the periodic table such as Si, Ge, Se, S, O, VI
A group B element is selected, and preferably Si, Ge, and S are n-type
Pure. The effect is that the bandgap energy
Doping a large nitride semiconductor layer with n-type impurities
Nitride semiconductor layer with small band gap energy
The same applies to the case where a large amount of n-type impurities are doped. Less than
Above, when the impurity is preferably modulated and doped into the multilayer film layer
As mentioned above, nitrogen with large band gap energy
Nitride with small band gap energy
The impurity concentration of the target semiconductor layer can be made equal.

Further, in the nitride semiconductor layer constituting the multilayer film of the n-side first multilayer film layer, the layer in which the impurity is highly doped has an impurity concentration near the center of the semiconductor layer in the thickness direction. It is desirable that the concentration is large and the impurity concentration near both ends is low (preferably undoped). Specifically, for example, when a multilayer film layer is formed of AlGaN doped with Si as an n-type impurity and an undoped GaN layer, electrons are emitted to the conduction band as donors because AlGaN is doped with Si. Then, the electrons fall into the conduction band of GaN having a low potential. Since the GaN crystal is not doped with a donor impurity, carriers are not scattered by the impurity. Therefore, the electrons are easily converted to GaN
It can move through the crystal, increasing the substantial electron mobility. This is similar to the effect of a two-dimensional electron gas, in which the electron mobility in the lateral direction is substantially increased and the resistivity is reduced. Furthermore, Al with a large band gap energy
The effect is further enhanced when the central region of GaN is heavily doped with n-type impurities. That is, some of the electrons moving in GaN are scattered more or less by n-type impurity ions (in this case, Si) contained in AlGaN. But Al
If the both ends are undoped in the thickness direction of the GaN layer, it becomes difficult to receive the scattering of Si, so that the mobility of the undoped GaN layer is further improved.

Next, the case where the n-side first multilayer film layer 5 is formed by laminating nitride semiconductor layers having the same composition and n-type impurities are doped at different concentrations between the nitride semiconductor layers will be described. . First, the nitride semiconductor constituting the n-side first multilayer film layer 5 is not particularly limited and may have the same composition, but preferably GaN. n-side first
When the multilayer film layer 5 is composed of GaN, it is preferable that the GaN is a binary mixed crystal rather than a ternary mixed crystal because the GaN can grow with good crystallinity and the nitride semiconductor to be grown thereafter has good crystallinity. Such an n-side first multilayer film layer 5 of the same composition, for example, GaN is composed of a first GaN layer containing an n-type impurity and a first G layer.
Second GaN having a concentration different from the n-type impurity concentration of the aN layer
It is preferable that a layer, preferably one of them, has a multilayer film structure composed of at least two or more kinds of nitride semiconductors, each of which is an undoped GaN layer. With such a modulation-doped multilayer structure, the same effect as in the case where the n-side first multilayer film layer 5 is composed of at least two types of layers which are different in band gap energy and are modulation-doped is obtained. can get. The concentration of the n-side impurity is 1 × 10 ¹⁷ to 1 ×
10 ²¹ / cm ³ , preferably 1 × 10 ¹⁸ to 1 × 10 ¹⁹ / cm ³
cm ³ , more preferably 3 × 10 ^{18 to} 7 × 10 ¹⁸ / cm ³
It is. In this case, the total thickness of the n-side first multilayer film layer 5 is not particularly limited, but is 1000 to 4000 angstroms, preferably 2000 to 3000 angstroms. Each film thickness of the multilayer film is 500 Å or less, preferably 200 Å or less, more preferably 100 Å or less. The lower limit of the film thickness is not particularly limited, but may be 1 atomic layer or more, but 10 Å or more. Is preferred. With the above film thickness, it is possible to grow with good crystallinity,
It is preferable for improving the light emission output.

Further, the n-side first multilayer film layer 5 composed of two or more layers having different band gap energies or the same composition and further different impurity concentrations as described above can also serve as the n-side contact layer. In this case, the n-side first
The thickness of the multilayer film layer 5 is 0.5 to 4 μm, preferably 1 to 4 μm.
It is 3 μm, more preferably 2 to 2.8 μm. In this case, the film thickness of the n-side first multilayer film layer 5 is at least 2
It is adjusted by the number of kinds or more of nitride semiconductor layers. In this case, each film thickness of the n-side first multilayer film layer 5 may be a multilayer film layer of the thin film layers in the above range, or the n-side first multilayer film layer 5 in the case where the overall film thickness also serves as the n-side contact layer. 1 multilayer film layer 5
If the thickness is within the above range, each film thickness exceeds the above range.
The adjustment may be made by using more than three kinds of nitride semiconductors.

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. A first nitride semiconductor layer or a second nitride semiconductor layer having a thickness of 100 angstroms or less; Preferably, both the first nitride semiconductor layer and the second nitride semiconductor layer are 100 Å or less,
More preferably, it is 70 Å or less, most preferably 50 Å 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. Here, the n-side first multilayer film layer and the n-side first multilayer film layer
When combined with the second side multilayer film layer, the light emission output is improved and the forward voltage (Vf) is reduced, which is preferable. 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 first nitride semiconductor layer is made of In _k Ga _{1 -kN}
(0 <k <1), and the second nitride semiconductor layer is made of In _m G
a _1-m N (0 ≦ m <1, m <k), and most preferably GaN.

Further, at least one of the first nitride semiconductor layer and the second nitride semiconductor layer has a thickness close to that of the first nitride semiconductor layer or the second nitride semiconductor layer. May be different from each other or the same. Also. The difference in thickness between adjacent layers means that when a multilayer film layer in which a plurality of first nitride semiconductor layers or second nitride semiconductor layers are stacked is formed, the second nitride semiconductor layer ( This means that the thicknesses of the first nitride semiconductor layers (second nitride semiconductor layers) sandwiching the first nitride semiconductor layers) are different from each other.

Further, the first nitride semiconductor layer,
Alternatively, the composition of at least one group III element in the second nitride semiconductor layer is different from each other in the composition of the same group III element in the adjacent first nitride semiconductor layer or second nitride semiconductor layer. Is preferred. This means that the second nitride semiconductor layer (first nitride semiconductor layer) is formed when a multilayer film layer in which a plurality of first nitride semiconductor layers or second nitride semiconductor layers are stacked is formed. This means that the interposed first nitride semiconductor layer (second nitride semiconductor layer) has a different group III element composition ratio.

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.

Preferably, the first nitride semiconductor layer and the second nitride semiconductor layer of the n-side second multilayer film layer 6 are undoped. Undoped refers to a state in which impurities are not intentionally doped. For example, in the present invention, impurities mixed by diffusion from an adjacent nitride semiconductor layer are also referred to as undoped. Note that impurities mixed by diffusion often have a gradient in impurity concentration in the layer.

One of the first nitride semiconductor layer and the second nitride semiconductor layer may be doped with an n-type impurity. This is called modulation doping, and the modulation doping tends to improve the output. As the n-type impurity, a group IV or group VI element such as Si, Ge, Sn, or S is preferably selected, and more preferably, Si or Sn is used.

Further, both the first nitride semiconductor layer and the second nitride semiconductor layer may be doped with an n-type impurity. When doping with an n-type impurity, the impurity concentration is 5
It is adjusted to not more than × 10 ²¹ / cm ³ , preferably not more than 1 × 10 ²⁰ / cm ³ . 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.

As shown in FIG. 1, a first nitride semiconductor layer containing In and a composition different from that of the first nitride semiconductor layer are formed in an n-side nitride semiconductor layer below the active layer 7. And an n-side second multilayer film layer 6 in which a second nitride semiconductor layer having the following structure is laminated. 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, and more preferably at least two layers are formed.
It is desirable to laminate at least four layers and to laminate at least four layers in total.
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
The multilayer film layer 6 is formed in contact with the active layer 7, but has a layer made of another n-type nitride semiconductor between the n-side second multilayer film layer 6 and the active layer. Is also good. This n-side second
By setting the thickness of at least one of the first nitride semiconductor layer and the second nitride semiconductor layer constituting the multilayer film layer to 100 Å or less, preferably 70 Å or less, more preferably 50 Å or less, The crystal becomes better when the layer has an elastic critical thickness or less, and the crystallinity of the first or second nitride semiconductor layer laminated thereon is improved, and the crystallinity of the entire multilayer film is improved. The output of the device is improved.

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
Gallium nitride nitride semiconductors are grown.
Then, a multilayer film layer with good crystallinity can be grown as a whole. Obedience
The most preferable combination is the first nitride half.
The conductor layer has an k value of 0.5 or less._kGa_1-kN
The second nitride semiconductor layer is a combination with GaN.

The thickness of the first and second nitride semiconductor layers is 100 Å or less, preferably 70 Å or less, more preferably 50 Å or less. By setting the thickness of the single nitride semiconductor layer to 100 angstrom or less, the thickness becomes less than the elastic critical thickness of the nitride semiconductor single layer, and a nitride semiconductor having good crystallinity as compared with the case of growing a thick film is grown. it can. In addition, by making both of them 70 angstrom or less, n
When the side second multilayer film layer 6 has a superlattice (multilayer film) structure, and an active layer is grown on this multilayer film structure having good crystallinity,
The n-side second multilayer film layer 6 acts like a buffer layer,
The active layer can be grown with good crystallinity.

Further, the thickness of at least one of the first and second nitride semiconductor layers may be different from each other between the adjacent first and second nitride semiconductor layers. preferable. 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 is gradually increased as approaching the active layer. Since the refractive index changes within the multilayer film layer by reducing or reducing the thickness, a layer in which the refractive index gradually changes can be formed. 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.

Further, the composition of at least one group III element of the first or second nitride semiconductor layer may be changed to the composition of the same group III element of the adjacent first or second nitride semiconductor layer. May be different from each other or the same. For example, if the compositions of the same group III elements are different from each other,
When the first nitride semiconductor layer is made of InGaN and the second nitride semiconductor layer is made of GaN, the In composition of the InGaN layer between the GaN layers is gradually increased as approaching the active layer, Also, by reducing the thickness, the nitride semiconductor layer having a substantially composition gradient can be formed by changing the refractive index inside the multilayer film layer as in the above-described embodiment. The refractive index tends to decrease as the In composition decreases.

The first and second nitride semiconductor layers may both be undoped, both may be doped with an n-type impurity, or one of them may be doped with an impurity. In order to improve the crystallinity, undoping is most preferable, 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 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 within this range, the light emission output is high and the forward voltage
(Vf) is preferred. The third nitride semiconductor layer is less
Nitride semiconductor containing at least Al, preferably Al _nG
a_1-nIt is desirable to grow N (0 <n ≦ 1),
The fourth nitride semiconductor is preferably Al_pGa_1-pN (0 ≦
p <1, n> p), In_rGa_1-rN (0 ≦ r ≦ 1)
For growing a binary mixed crystal or ternary mixed crystal nitride semiconductor
Is desirable. The p-side cladding layer 8 has a superlattice structure
, Crystallinity is improved, resistivity is reduced, and Vf is reduced.
Tend.

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 1 9~3 × 10 20} /
cm 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 5 μm.

(N-side first multilayer film layer 5) Then, only silane gas is stopped, and an undoped GaN layer is grown at 1050 ° C. using TMG and ammonia gas to a thickness of 75 Å, and subsequently at the same temperature. Add silane gas and add Si
Is grown to a thickness of 25 Å with a 4.5 × 10 ¹⁸ / cm ³ doped GaN layer. In this way, 7
A pair consisting of an A layer made of an undoped GaN layer of 5 Å and a B layer made of 25 Å having a Si-doped GaN layer is grown. And 25 pairs
The n-side first multilayer film layer 5 composed of a multilayer film having a superlattice structure is grown to a thickness of 2500 angstroms by stacking the layers.

(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 electrostatic withstand voltage is 1.3 times or more the conventional value, which is good.

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 Example 1, it has a good light emission output as compared with the conventional LED element.

[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 superlattice as the cladding layer, almost the same good results as in Example 1 are obtained, although the performance is slightly inferior to that of Example 1 due to the combination with other layer configurations. can get. 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
LED is changed in the same manner except that the multilayer film 5 is changed as follows.
An element was manufactured. (N-side first multilayer film layer 5) A composed of an undoped GaN layer
A layer is grown to a thickness of 100 angstroms, and a pair of an A layer and a B layer is formed by growing a B layer made of Al _0.1 Ga _0.9 N doped with 1 × 10 ¹⁸ / cm ^{3 of} Si to a thickness of 25 angstroms. Are stacked to have a thickness of 2500 Å, and the n-side first multilayer film layer 5 is grown. The obtained LED element has substantially the same characteristics as in Example 1, and good results are obtained.

Example 9 An LED was manufactured in the same manner as in Example 1 except that the n-side contact layer 4 was changed as follows.
An element was manufactured. (N-side contact layer 4) At 1050 ° C., the raw material gas
G, ammonia gas, using silane gas as impurity gas,
An n-side contact layer 4 made of GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si is grown to a thickness of 6 μm. The obtained LED element has substantially the same characteristics as in Example 1,
Good results are obtained.

[Embodiment 10] In Embodiment 1, the thickness of the n-side contact layer 4 was set to 4.25 μm, 5.25 μm,
Three kinds of LED elements are manufactured in the same manner except that the thickness is set to 7.25 μm. The obtained LED element has almost the same characteristics as those of Example 1 and good results are obtained. In addition, when the film thickness is 4.25 μm and 5.25 μm, the electrostatic breakdown voltage and the like are slightly different from those of Example 1. It is better than 1.

[Embodiment 11] 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 is doped with Si at 5 × 10 ¹⁷ / cm ^3.
_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.

Example 12 In Example 1, the p-side multilayer clad layer 8 was made of a third nitride semiconductor layer made of Al _0.2 Ga _0.8 N doped with Mg at 5 × 10 ¹⁹ / cm ³ ,
Addition to a multilayer film comprising a fourth semiconductor layer of undoped In _{0. 03} Ga _0.97 N in the same manner LED
A device is manufactured. The obtained LED element shows almost the same characteristics as in Example 1.

[Example 13] 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.

[0073]

According to the nitride semiconductor device of the present invention, by combining an active layer having a multiple quantum well structure with the above-mentioned specific layer structure, the possibility of an active layer having a multiple quantum well structure can be improved. It is possible to enhance the light emission output and the electrostatic breakdown voltage.

[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.

[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 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-5-82834 (JP, A) JP-A-8-51251 (JP, A) JP-A-4- 68579 (JP, A) JP-A-10-135575 (JP, A) IEEE Journal of Selected Topics in Quantum Electronics 4 [3] p. 483-489 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00 JICST file (JOIS)

Claims (12)

(57) [Claims] 1. A nitride semiconductor device having an active layer between an n-side nitride semiconductor layer and a p-side nitride semiconductor layer, wherein the active layer is In _a Ga ₁ -aN (0 ≦ a <1). A multi-quantum well structure having an n-side contact layer containing an n-type impurity; a nitride semiconductor layer doped with an n-type impurity; At least two types of nitride semiconductor layers including an undoped nitride semiconductor layer having the same composition and not doped with an n-type impurity are laminated,
A nitride semiconductor device comprising an n-side multilayer film layer formed on a side contact layer. 2. The nitride semiconductor according to claim 1, wherein each of the nitride semiconductor layer doped with the n-type impurity and the undoped nitride semiconductor layer not doped with the n-type impurity is a GaN layer. element. 3. An undoped G-side contact layer,
3. The nitride semiconductor device according to claim 1, which is formed on the aN layer. 4. A p-side multi-layered cladding comprising the third and fourth nitride semiconductor layers, wherein the p-side nitride semiconductor layers have different band gap energies and different or different p-type impurity concentrations. The nitride semiconductor device according to claim 1, further comprising a layer. 5. The p-side multilayer clad layer has a superlattice structure, and the third nitride semiconductor layer is Al _n Ga ₁ -nN.
(0 <n ≦ 1), and the fourth nitride semiconductor layer is formed of Al _p Ga _1-p N (0 ≦ p <1, p <n) or In _r Ga
5. The nitride semiconductor device according to claim 4, comprising _1-rN (0 ≦ r ≦ 1). 6. The nitride semiconductor device, wherein the undoped GaN layer is grown at a low temperature by using Ga _d Al _{1 -dN} (0
5. The nitride semiconductor device according to claim 4, wherein a p-side GaN contact layer containing Mg as a p-type impurity is formed on the buffer layer made of <d ≦ 1) and on the p-side multilayer clad layer. . 7. A nitride semiconductor device having an active layer between an n-side nitride semiconductor layer and a p-side nitride semiconductor layer, wherein the active layer is In _a Ga _1-a N (0 ≦ a <1). A multi-quantum well structure having a plurality of layers, wherein the n-side nitride semiconductor layer has the same composition in which n-type impurities are doped at different concentrations.
A nitride semiconductor device comprising an n-side multilayer film layer in which various kinds of nitride semiconductor layers are stacked. 8. The nitride semiconductor device according to claim 7, wherein the two types of nitride semiconductor layers having the same composition and in which the n-type impurities are doped at different concentrations are GaN layers. 9. An undoped G-side contact layer,
9. The nitride semiconductor device according to claim 7, wherein the nitride semiconductor device is formed on the aN layer. 10. A p-side multilayer film clad comprising a third and a fourth nitride semiconductor layers, wherein the p-side nitride semiconductor layers have different band gap energies and different or different p-type impurity concentrations. The nitride semiconductor device according to any one of claims 7 to 9, further comprising a layer. 11. The p-side multilayer clad layer has a superlattice structure, and the third nitride semiconductor layer is formed of Al _n Ga _1-n N.
(0 <n ≦ 1), and the fourth nitride semiconductor layer is formed of Al _p Ga _1-p N (0 ≦ p <1, p <n) or In _r Ga
11. The nitride semiconductor device according to claim 10, comprising _1-rN (0 ≦ r ≦ 1). 12. In the nitride semiconductor device, the undoped GaN layer is grown at a low temperature by using Ga _d Al _{1 -dN.}
The nitride according to claim 10, wherein a p-side GaN contact layer formed on a buffer layer made of (0 <d ≦ 1) and containing Mg as a p-type impurity is formed on the p-side multilayer clad layer. Semiconductor element.