JP3767491B2 - Gallium nitride compound semiconductor light emitting device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an n-type gallium nitride compound semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1, hereinafter gallium nitride based) used in an electronic device such as a light emitting diode and a laser diode. The present invention relates to a gallium nitride-based compound semiconductor light-emitting element using a crystal of a compound semiconductor.
[0002]
[Prior art]
Laser diodes emitting blue and ultraviolet, and nitride semiconductors as materials for light emitting diodes (In _{X ′} Al _{Y ′} Ga _{1-X′-Y ′} N, 0 ≦ X ′, 0 ≦ Y ′, X ′ + Y ′ ≦ 1 Recently, blue light-emitting diodes having a light intensity of 1 cd with this material have just been put into practical use. As shown in FIG. 1, the blue light-emitting diode has a buffer layer 2 made of GaN, an n-type layer 3 made of GaN, an n-type clad layer 4 made of AlGaN, and an InGaN film on the surface of a substrate 1 made of sapphire. The p-type cladding layer 6 made of AlGaN and the p-type contact layer 7 made of GaN are sequentially stacked.
[0003]
Nitride semiconductor devices generally use vapor phase growth methods such as MOVPE (metal organic vapor phase epitaxy), MBE (molecular beam epitaxy), HDVPE (hydride vapor phase epitaxy), and a nitride semiconductor layer is formed on the substrate surface. It is obtained by laminating. A material such as sapphire, ZnO, SiC, GaAs, or MgO is used for the substrate. An n-type nitride semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1, among which n-type GaN and n-type AlGaN are particularly formed on the surface of the substrate via a buffer layer. A lot). In addition, when a substrate having a lattice constant close to that of a nitride semiconductor such as SiC or ZnO is used, an n-type nitride semiconductor may be grown directly on the substrate without forming a buffer layer. Basically, an n-type nitride semiconductor layer is first grown on the surface of a substrate, thereby producing a nitride semiconductor element such as a light emitting element or a light receiving element.
[0004]
For example, according to the MOVPE method, a nitride semiconductor uses an organometallic compound gas serving as a Ga source, an Al source, and an In source and an ammonia gas serving as an N source as a source gas. By bringing these source gases into contact with the heated substrate surface, the source gases are decomposed, and a nitride semiconductor is epitaxially grown on the substrate. As the buffer layer, GaN, AlN, GaAlN or the like is usually selected and grown at a temperature of 300 ° C. to 900 ° C. to a thickness of 10 Å to 0.1 μm. The n-type nitride semiconductor layer grown on the buffer layer is grown at a temperature of 900 ° C. or higher and usually a film thickness of 1 μm or more and 4 μm or less.
[0005]
[Problems to be solved by the invention]
Nitride semiconductors are known to be crystals that are very difficult to grow epitaxially because there is no substrate that perfectly matches the lattice. Therefore, conventionally, a substrate close to the lattice constant of the nitride semiconductor to be grown, such as a SiC substrate, has been used, or it has been forcibly epitaxially grown through a buffer layer that relaxes lattice mismatch.
[0006]
An example of a schematic cross-sectional view of an n-type nitride semiconductor crystal grown on the surface of a substrate that is not lattice matched is shown in FIG. This is quoted from Journal of Crystal Growth, {Jounal of Crystal Growth, 115, (1991) P628-633}, where n-type GaN is epitaxially grown on the surface of the sapphire substrate through a buffer layer made of AlN, and its cross section. Is measured by TEM (transmission electron microscopy), and the structure of the crystal is schematically shown from the TEM image. According to this figure, a buffer layer with no orientation is grown on the substrate in a columnar shape. When GaN is epitaxially grown on the buffer layer, a part of the buffer layer plays a role like a seed crystal. It is shown that a GaN layer with improved crystallinity is grown by gradually adjusting the orientation of GaN.
[0007]
However, it is difficult to grow GaN having no crystal defects completely, and many crystal defects as shown by broken lines in FIG. 2 extend from the interface between the buffer layer and the GaN layer until reaching the surface of the GaN layer. Although some of these defects stop inside the crystal, there are, for example, 10 ⁷ to 10 ⁹ / cm ^{2 on the} surface reaching the surface of the GaN layer. Similarly, the same phenomenon occurs in the crystal of the n-type layer 3 in the light emitting diode element of FIG.
[0008]
If there are a large number of crystal defects on the surface of the n-type nitride semiconductor layer grown on the surface of the substrate, the defects are inherited by all semiconductor layers, such as a cladding layer and an active layer, which grow on the surface of the n-type layer. There is the problem of adversely affecting the entire structure. An element having a large number of crystal defects has a drawback in that, for example, when the light emitting diode as described above is used, the element performance such as light emission output and lifetime is adversely affected.
[0009]
In growing an n-type nitride semiconductor layer on the surface of a substrate, it is very important to grow an n-type crystal with few crystal defects, and if this can be realized, a cladding layer grown on the n-type crystal. Since the crystal defects such as the active layer are reduced, the performance of any element made of a nitride semiconductor can be improved. Accordingly, the present invention has been made in view of such circumstances. When an n-type nitride semiconductor layer is grown on the surface of a substrate that is not completely lattice-matched by vapor phase growth methods such as MOVPE and MBE. Another object of the present invention is to provide a light emitting device using an n-type nitride semiconductor grown by reducing lattice defects in the n-type nitride semiconductor layer.
[0010]
[Means for Solving the Problems]
The present invention is a nitride semiconductor light emitting device comprising an n-type nitride semiconductor layer made of AlGaN or GaN between a substrate and an active layer, wherein the n-type nitride semiconductor layer has a thickness of 0.001 μm or more. Two or more buffer layers made of n-type In _a Ga _1-a N (0 < a ≦ 1) having a composition different from that of the n-type nitride semiconductor layer are 0.1 μm or less. A part of the nitride semiconductor layer is exposed to provide an electrode, and the buffer layer is provided closer to the active layer than the exposed portion.
[0012]
[Action]
When a second nitride semiconductor layer having a different composition is formed in the n-type nitride semiconductor layer, the second nitride semiconductor functions as a buffer layer, that is, a buffer layer, so that crystal defects can be alleviated by the buffer layer. (In this specification, the second nitride semiconductor layer is hereinafter referred to as a second buffer layer). More specifically, when an n-type nitride semiconductor layer is grown on a substrate, there is a large mismatch between the substrate and the nitride semiconductor, so that a crystal defect as shown by a broken line in FIG. 2 occurs in the crystal during the growth. . However, by interposing a second buffer layer having a composition different from that of the n-type nitride semiconductor layer to be grown as an intermediate layer, the continuous crystal defects of the n-type nitride semiconductor layer are different from each other in the composition. Temporarily stops at the buffer layer. Next, when an n-type nitride semiconductor is grown on the surface of the second buffer layer, the second buffer layer acts like a substrate with few mismatches, so that it grows on the second buffer layer. It is assumed that the crystallinity of the n-type nitride semiconductor to be improved is improved.
[0013]
The second buffer layer may be formed in one or more layers, and the film thickness per layer is adjusted to a range of 10 angstroms (0.001 μm) to 1 μm, more preferably 0.001 μm to 0.1 μm. Is desirable. When the thickness is smaller than 0.001 μm, it tends to be difficult to stop the crystal defects with the second buffer layer. Further, if it is thicker than 1 μm, new crystal defects tend to be generated from the second buffer layer. The second buffer layer can also be a multilayer film in which one layer is several tens of angstroms and two or more layers are stacked.
[0014]
The second buffer layer may be In _a Ga _1-a N (0 <a ≦ 1), Al _b Ga _1-b N (0 <b ≦ 1), or Al _b Ga _1-b N (0 A multilayer film in which thin films of ≦ b ≦ 1) are laminated is desirable. More preferably, In _a Ga _1-a N having an _a value of 0.5 or less or Al _b Ga _1-b N having a b value of 0.5 or less is grown. This is because, in a nitride semiconductor, the ternary mixed crystal as described above has better crystallinity than the quaternary mixed crystal semiconductor layer. Among them, in ternary mixed crystals of In _a Ga _1-a N and AlbGa _1-b N, a buffer layer having a value and a b value adjusted to the above ranges can be obtained with better crystallinity. The crystal defects of the second buffer layer are reduced, and the crystal defects of the n-type nitride semiconductor layer grown on the second buffer layer are reduced. Furthermore, if the second buffer layer is a multilayer film, crystal defects can be stopped very well. The most preferred combination is that the n-type nitride semiconductor layer is n-type GaN (GaN has the fewest lattice defects), and the second buffer layer is n-type In _a Ga _1-a N (0 <a ≦ 0.5). N _- type Al _b Ga _1-b N (0 <b ≦ 0.5), or a multilayer film in which thin films of Al _b Ga _1-b N (0 ≦ b ≦ 1) having different compositions are stacked (super Lattice).
[0015]
Furthermore, it is desirable to adjust the electron carrier concentration of the second buffer layer to be substantially the same as or larger than that of the previously formed n-type nitride semiconductor layer. 3 and 4 show an n-clad layer 4 ', an active layer 5', a p-clad layer 6 ', and a p-contact layer 7' stacked on the n-type nitride semiconductor layer 3 "obtained by the method of the present invention. Fig. 3 is a cross-sectional view showing the structure of the light emitting element as an actual light emitting element, in which the second buffer layer 33 is more active than the etched surface of the n-type layer for forming the negative electrode. 4 differs from FIG. 4 in that the second buffer layer 33 is formed on the substrate 1 ′ side from the etching surface, for example, to realize a light emitting device as shown in FIG. In other words, when an element in which the position of the second buffer layer 33 is closer to the active layer side than the etching surface where the negative electrode is to be formed is realized, the electron carrier concentration of the second buffer layer 33 Is smaller than the n-type layer 3 ′, the second buffer layer supplies n to p. When the electron carrier concentration of the second buffer layer 33 is higher than that of the n-type layer 3, the current is less likely to flow from the n-type layer to the p-layer. The electrons can easily spread uniformly in the second buffer layer 33, so that uniform light emission can be obtained, whereas the element as shown in Fig. 4 has a low electron carrier concentration in the second buffer layer 33. However, since the current flows through the n-type layer 3 ″ having a higher electron carrier concentration, there is almost no effect on the characteristics of the light emitting element. Conversely, when the electron carrier concentration of the second buffer layer 33 is large, the current Can easily flow toward the second buffer layer 33, and uniform light emission can be obtained. Therefore, the electron carrier concentration of the second buffer layer 33 is preferably adjusted to be substantially the same as or larger than that of the previously formed n-type nitride semiconductor layer.
[0016]
By growing the n-type nitride semiconductor layer thicker than 5 μm, crystal defects reaching the surface can be reduced. In FIG. 2, the fact that the broken line stops in the middle of the n-type layer indicates that the crystal defect stops halfway. When the crystal defects stopped in the middle were further studied, it was newly found that many n-type nitride semiconductor layers stop at about 4 μm from the substrate. Therefore, if the same material is continuously grown, it is possible to gradually stop the crystal defects during the growth, so that the crystal defects reaching the surface of the n layer by growing the n layer at 5 μm or more. Can be reduced. A more preferable thickness of the n-type nitride semiconductor layer is 7 μm or more.
[0017]
In the present invention, an n-type nitride semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) grown on a substrate has a Y value of 0 ≦ Y ≦ 0. Al _Y Ga ₁ -YN in the range of 5, more preferably 0.3 or less Al _Y Ga ₁ -YN, most preferably Y = 0 is grown. This is because the ternary mixed crystal nitride semiconductor has fewer crystal defects than the quaternary mixed crystal nitride semiconductor as described above. Furthermore, when using an n-type nitride semiconductor as an electronic device such as a light-emitting element or a light-receiving element, the n-type nitride semiconductor first grown on the substrate is AlGaN having a larger band gap than InGaN having a smaller band gap. This is because GaN is more advantageous in realizing various structures such as single hetero and double hetero. Among them, particularly AlGaN tends to have more crystal defects as Al is contained, and GaN tends to grow an n-type nitride semiconductor layer having the fewest crystal defects.
[0018]
A material such as sapphire, GaAs, Si, ZnO, or SiC can be used for the substrate, but sapphire is generally used. When sapphire is used as a substrate, it is preferable to grow a buffer layer on the substrate, but depending on the plane orientation of the sapphire substrate, it can be grown without the buffer layer. By preferably growing the buffer layer, a smooth and mirror-like n-type nitride semiconductor crystal capable of measuring lattice defects can be obtained. Further, to make the nitride semiconductor n-type can be realized in an undoped state or by doping a donor impurity such as Si, Ge, or C during crystal growth.
[0019]
【Example】
Hereinafter, the method of the present invention by the MOVPE method will be described in detail.
[Example 1]
(1) First, a well-washed sapphire substrate is placed on a susceptor in a reaction vessel. After evacuating the inside of the container, the substrate is heated for about 20 minutes at 1050 ° C. while flowing hydrogen gas into the container to remove the surface oxide, and the substrate is cleaned. Thereafter, the temperature of the susceptor is adjusted to 500 ° C., and at 500 ° C., TMG (trimethyl gallium gas) as a Ga source and ammonia gas as an N source are flowed to the surface of the substrate, and a buffer layer made of GaN is formed to a thickness of 0.02 μm Grow.
[0020]
(2) Next, after stopping the TMG gas and raising the temperature to 1050 ° C., the TMG gas and SiH ₄ gas are flowed to grow the Si-doped n-type GaN layer with a thickness of 2 μm.
[0021]
(3) Next, TMG gas and SiH ₄ gas are stopped and the temperature is set to 800 ° C. When the temperature reaches 800 ° C., the carrier gas is switched to nitrogen, TMG gas, TMI (trimethylindium), and SiH ₄ gas are allowed to flow, and a Si-doped n-type In0.1Ga0.9N layer having a thickness of 0.01 μm is formed as the second buffer layer. Grow in.
[0022]
(4) After the growth of the In0.1Ga0.9N layer, the temperature is raised again to 1050 ° C., the carrier gas is returned to hydrogen, TMG gas and SiH ₄ gas are flown, and the Si-doped n-type GaN layer is formed in a 2 μm film in the same manner. Grow with thickness. The carrier concentration of the second buffer layer and the carrier concentration of the n-type GaN layer were almost the same.
[0023]
After the growth, the substrate is taken out of the reaction vessel, the surface of the uppermost n-type GaN layer was measured by TEM, than the TEM images, it was measured number of crystal defects per unit area, approximately 1 × 10 ⁴ cells / cm ² .
[0024]
[Example 2] TMG, TMA (trimethylaluminum), and SiH ⁴ gas were used in the steps of the n-type nitride semiconductor layer of (2) and ( ⁴ ), and each of the Si-doped n-type Al0.3Ga0.7N layer was 2 μm. Example 2 is performed in the same manner as in Example 1 except that the second buffer layer is sandwiched between the first and second layers. As a result, when the same measurement was performed, the number of crystal defects reaching the surface of the Si-doped n-type Al0.3Ga0.7N layer was about 5 × 10 ⁵ / cm ² . The electron carrier concentration of the Si-doped n-type Al0.3Ga0.7N layer was almost the same as that of the second buffer layer.
[0025]
[Example 3] A Si-doped n-type GaN layer is grown to a thickness of 1 μm in the same manner as in the process of the n-type nitride semiconductor layer in (2). Next, in the same manner as the second buffer layer step (3), a Si-doped n-type In0.1Ga0.9N layer is grown as a second buffer layer to a thickness of 50 angstroms. Further, similarly to the step of the n-type nitride semiconductor layer of (4), a Si-doped n-type GaN layer is sequentially grown in a thickness of 1 μm.
[0026]
Further, after the Si-doped n-type In0.1Ga0.9N layer was grown once again at a thickness of 50 angstroms as the third buffer layer in the same manner as the step (3) on the Si-doped n-type GaN layer, Finally, a Si-doped GaN layer is grown to a thickness of 2 μm in the same manner as in step (4). That is, in Example 3, the surface of the sapphire substrate has a GaN buffer layer of 200 Å, an n-type GaN layer of 1 μm, a Si-doped n-type In0.1Ga0.9N second buffer layer of 50 Å, an n-type GaN layer of 1 μm, and a Si-doped n-type In0. A .1Ga0.9N third buffer layer 50 Å and an n-type GaN layer 2 μm were sequentially stacked.
[0027]
As a result, the number of crystal defects reaching the surface of the final Si-doped n-type GaN layer was about 1 × 10 ⁴ / cm ² . The second buffer layer, the third buffer layer, and the Si-doped n-type GaN layer have substantially the same electron carrier concentration.
[0028]
[Example 4] In the step of the second buffer layer in ( ₃ ), TMG, TMA (trimethylaluminum), SiH ₄ gas is used without changing the growth temperature, and the Si-doped n-type Al0.3Ga0.7N layer is changed to 0. The same procedure as in Example 1 is performed except that the second buffer layer is formed by growing to a thickness of 0.01 μm. As a result, when measured in the same manner, the number of crystal defects reaching the surface of the Si-doped n-type GaN layer was about 1 × 10 ⁴ / cm ² . The electron carrier concentration of the second buffer layer was almost the same as that of the Si-doped n-type GaN layer.
[0029]
[Example 5] In the second buffer layer step (3), TMG, TMA, and SiH ₄ gas are used without changing the growth temperature, and a Si-doped n-type Al0.02Ga0.98N layer is first formed to a thickness of 30 Å. Grow with thickness. Next, the TMA gas is stopped and a Si-doped n-type GaN layer is grown to a thickness of 30 angstroms. This operation is repeated five times to form a multilayer film in which five 30 Å Si-doped n-type Al 0.02 Ga 0.98 N layers and 30 Å n-type GaN layers are alternately stacked. The same procedure as in Example 1 is performed except that the second buffer layer is formed as described above. As a result, when the lattice defects were measured in the same manner, the number of crystal defects reaching the surface of the Si-doped n-type GaN layer was approximately 5 × 10 ³ / cm ² . Note that the electron carrier concentration of the multilayer film, which is the second buffer layer, was almost the same as that of the Si-doped n-type GaN layer.
[0030]
[Embodiment 6] In the same manner as in Embodiment 2, except that Si-doped n-type Al0.1GaGa0.9N is grown to a thickness of 0.01 μm as the second buffer layer, Si-doped n-type Al0.3Ga0 is used. A .7N layer was grown. As a result, the number of lattice defects that had reached the outermost n-type Al0.3Ga0.7N layer was approximately 1 × 10 ⁵ / cm 2. The electron carrier concentration in this example was also substantially the same.
[0031]
[Comparative Example 1] In Example 1, when the second buffer layer was not grown and a Si-doped n-type GaN layer was continuously grown to a thickness of 4 µm, a crystal reached the surface of the n-type GaN layer. The number of defects was approximately 1 × 10 ⁷ / cm ² .
[0032]
[Embodiment 7] An embodiment in which the structure of an actual light emitting element is used is shown. The following steps were added after the step (4) in Example 1.
(5) After growth of the Si-doped n-type GaN layer, TMA (trimethylaluminum) gas is newly added, and at 1050 ° C., an Si-doped n-type Al0.2Ga0.8N layer is formed to a thickness of 0.1 μm as an n-cladding layer. Grow.
[0033]
▲ 6 ▼ n clad layer was grown, TMG, stopped TMA, SiH4 gas, again by setting the temperature to 800 ° C., TMG, TMI, flowing DEZ (diethyl zinc) in addition to SiH ₄ gas, Si as an active layer Then, a Zn-doped In0.05Ga0.95N layer is grown to a thickness of 0.1 μm.
[0034]
(7) After growth of the active layer, TMG, TMI, SiH ₄ , DEZ gas is stopped and the temperature is raised to 1050 ° C., and then TMG, TMA, Cp 2 Mg (cyclopentadienyl magnesium) gas is flowed to form Mg doping as the p-clad layer A p-type Al0.1Ga0.9N layer is grown to a thickness of 0.1 μm.
[0035]
(8) After growing the p-type Al0.1Ga0.9N layer, the TMA gas is stopped, and an Mg-doped p-type GaN layer is grown to a thickness of 0.3 μm as a p-contact layer at 1050 ° C.
[0036]
(9) The element obtained as described above is etched to expose the n-type GaN layer grown next to the second buffer layer, and an electrode is formed on the p-contact layer and the exposed Si-doped n-type GaN layer. Formed. That is, a light emitting diode element having a structure as shown in FIG. 4 was obtained. Further, this element was attached to a lead frame and molded with resin. This light-emitting diode had a Vf of 3.6 V and an emission wavelength of 450 nm at 20 mA, a luminous intensity of 3.0 cd, and a light emission output of 3.5 mW.
[0037]
[Comparative Example 2] The same process as in Example 7 was performed on the Si-doped GaN layer grown in Comparative Example 1 to obtain a light-emitting diode element having a structure as shown in FIG. Vf was 3.6 V and the emission wavelength was 450 nm, but the luminous intensity was 1.0 cd and the emission output was only 1.2 mW.
[0038]
As described above, the light-emitting element of the present invention has an n-type layer with few crystal defects, so that crystal defects such as a clad layer and an active layer laminated thereon are reduced. In particular, since the thickness of the active layer is as thin as about 0.2 μm or less, it is very important to grow a crystal with few crystal defects. Therefore, by growing a crystal with few crystal defects, it is possible to realize a light-emitting diode element having a luminous intensity of 1 cd or more and an excellent light emission output.
[0039]
[Example 8]
{Circle around (1)} A buffer layer made of GaN is grown to a thickness of 0.02 μm on the surface of the sapphire substrate in the same manner as in step {circle around (1)} in Example 1.
[0040]
(2) Similar to the step (2) of Example 1, a Si-doped n-type GaN layer is grown on the buffer layer to a thickness of 10 μm.
[0041]
After the growth, the substrate was taken out of the reaction vessel, the surface of the n-type GaN layer was measured with TEM, and the number of crystal defects per unit area was measured from the TEM image, which was about 1 × 10 ⁵ pieces / cm ^2. It was.
[0042]
[Example 9] Crystal growth was performed in the same manner as in Example 5 except that the film thickness of the Si-doped n-type GaN layer was set to 5 µm, and the number of crystal defects on the surface of the n-type GaN layer was about 5 × 10 ^6. It was a piece.
[0043]
[Example 10] In the process (2) of Example 5, except that a Si-doped n-type Al0.3Ga0.7N layer was continuously grown to a thickness of 10 μm in the same manner as in (2) of Example 2. When crystal growth was performed in the same manner, the number of crystal defects on the surface of the n-type Al0.3Ga0.7N layer was about 3 × 10 ⁶ / cm ² .
[0044]
[Example 11] An n-clad layer, an active layer, a p-clad layer, and a p-contact layer are stacked on the Si-doped GaN layer obtained in Example 5 in the same manner as in Example 7, and light is emitted in the same manner. The characteristics of the diode were almost the same as those of Example 7.
[0045]
【The invention's effect】
As described above, the light-emitting element of the present invention has the n-type nitride semiconductor layer with few crystal defects on the substrate. Therefore, the present invention is very useful for a nitride semiconductor light emitting device that does not have a lattice-matching substrate, because it has laminated crystals with few crystal defects, and can be applied to an electronic device such as a light receiving device.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing one structure of a conventional light emitting diode element.
FIG. 2 is a schematic cross-sectional view showing a crystal structure when an n-type GaN layer is grown on the surface of a substrate via an AlN buffer layer.
FIG. 3 is a schematic cross-sectional view showing one structure of a light-emitting diode element having an n-type nitride semiconductor layer of the present invention.
FIG. 4 is a schematic cross-sectional view showing one structure of a light-emitting diode element having an n-type nitride semiconductor layer of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 1 '... Board | substrate 2, 2' ... Buffer layer 3, 3 ', 3 "... N-type nitride semiconductor layer 4, 4' ... N-type clad layer 5, 5 '... Active layer 6, 6 ′... P cladding layer 7, 7 ′... P contact layer 33... Second buffer layer (second nitride semiconductor layer)

Claims (5)

A nitride semiconductor light emitting device comprising an n-type nitride semiconductor layer made of AlGaN or GaN between a substrate and an active layer,
  In the n-type nitride semiconductor layer, n-type In having a composition different from that of the n-type nitride semiconductor layer is 0.001 μm or more and 0.1 μm or less. _a Ga _1-a N (0 < a Two or more buffer layers consisting of ≦ 1) are interposed,
  A portion of the n-type nitride semiconductor layer is exposed to provide an electrode;
  The nitride semiconductor light emitting element in which the buffer layer is provided on the active layer side with respect to the exposed portion. Between the substrate and the active layer, the first n-type nitride semiconductor layer, the first buffer layer, and the second n-type nitride having the same composition as the first n-type nitride semiconductor layer A semiconductor layer, a second buffer layer having the same composition as that of the first buffer layer, and a third n-type nitride semiconductor layer having the same composition as that of the second n-type nitride semiconductor layer. The nitride semiconductor light emitting device according to claim 1, wherein the nitride semiconductor light emitting device is laminated. The nitride semiconductor light emitting element according to claim 1, further comprising an n-type cladding layer between the active layer and the n-type nitride semiconductor layer. 4. The nitride semiconductor light emitting device according to claim 1, further comprising: an AlGaN p-type cladding layer on the active layer; and a GaN p-type contact layer thereon. 5. The nitride semiconductor light-emitting device according to any one of claims 1 to 4 wherein the n-type nitride semiconductor layer is characterized in that it consists of GaN.

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