JP7104519B2 - Nitride semiconductor light emitting device - Google Patents

Description

The present invention relates to a nitride semiconductor light emitting device.

In recent years, nitride semiconductor light emitting devices such as light emitting diodes and laser diodes that output ultraviolet light have been provided, and development of nitride semiconductor light emitting devices with improved light emission intensity is underway (see Patent Document 1). ..

Japanese Unexamined Patent Publication No. 2015-162631

The nitride semiconductor light emitting element described in Patent Document 1 includes a substrate, a first n-type nitride semiconductor layer arranged on the substrate, and an activity arranged on the first n-type nitride semiconductor layer. A second connection between the layer, the p-type nitride semiconductor layer arranged on the active layer, and the p-type nitride semiconductor layer arranged on the upper surface of the p-type nitride semiconductor layer is a tunnel junction. An n-type nitride semiconductor layer, a p-side electrode arranged on the second n-type nitride semiconductor layer and electrically connected to the p-type nitride semiconductor layer, and the first n-type nitride. It includes an n-side electrode that is electrically connected to the semiconductor layer.

By the way, in a nitride semiconductor light emitting device that emits deep ultraviolet rays having a central wavelength of, for example, 360 nm or less, a p-type AlGaN-based semiconductor material is used for the p-type nitride semiconductor layer. In such a nitride semiconductor light emitting device, it is preferable to thin the p-type nitride semiconductor layer formed of p-type AlGaN in order to increase the efficiency of injecting holes into the active layer.

According to the nitride semiconductor light emitting device described in Patent Document 1, the thickness from the p-type nitride semiconductor layer constituting the tunnel junction to the second n-type nitride semiconductor layer, that is, the distance from the active layer to the electrode is determined. It is considered preferable to shorten it.

On the other hand, while the nitride semiconductor light emitting device is energized, the metal atom used for the electrode easily transmits the rearrangement generated in the p-type AlGaN-based semiconductor to reach the active layer side, and as a result, the nitride There is a risk that the light emission output of the semiconductor light emitting device will be reduced and the life of the semiconductor light emitting device will be shortened. When the distance from the active layer to the electrode was short, the decrease in light emission output and the decrease in life due to the transmission of dislocations during energization were particularly remarkable.

Therefore, an object of the present invention is to provide a nitride semiconductor light emitting device having a long life with a small decrease in light emission output during energization.

The present invention has a first n-type clad layer formed of n-type AlGaN, a multiple quantum well layer located above the first n-type clad layer, and a multiple quantum well layer, for the purpose of solving the above problems. A p-type clad layer located above the multiple quantum well layer and formed by p-type AlGaN and a layer containing an n-type semiconductor in the p-type clad layer located above the p-type clad layer are tunneled. A nitride semiconductor light emitting device including a tunnel junction layer to be joined and an electrode layer formed above the tunnel junction layer, which is formed by n-type AlGaN between the tunnel junction layer and the electrode layer. The nitride semiconductor light emitting device further includes a second n-type clad layer, the nitride semiconductor light emitting device is a flip type, the multiple quantum well layer emits ultraviolet light, and the electrode layer is the second n-type clad layer. A reflective electrode portion that reflects light emitted from the multiple quantum well layer and a contact electrode portion that supplies an electric current to the second n-type clad layer are alternately provided on the second n-type clad. The layer has an absorption rate of ultraviolet light emitted by the multiple quantum well layer of 0.1% or less, the thickness of the tunnel junction layer is 10 nm or less, and the width of the reflective electrode portion is the second. Provided is a nitride semiconductor light emitting device having a thickness of 20 times or less the thickness of the n-type clad layer .

According to the present invention, it is possible to provide a nitride semiconductor light emitting device having a small decrease in light emission output and a long life.

FIG. 1 is a cross-sectional view schematically showing the configuration of a nitride semiconductor light emitting device according to the first embodiment of the present invention. FIG. 2 is a top view schematically showing the configuration of the first electrode layer. FIG. 3 is a partial cross-sectional view showing a second n-type clad layer and a first electrode layer extracted from the light emitting element shown in FIG. FIG. 4 is a graph schematically showing the relationship between the thickness of the pGaN layer and the transmittance of ultraviolet light. FIG. 5 is a diagram schematically showing the efficiency of extracting light from the light emitting element. FIG. 6 is a top view schematically showing a modified example of the configuration of the first electrode layer. FIG. 7 is a cross-sectional view schematically showing the configuration of the light emitting element according to the second embodiment of the present invention. FIG. 8 is a partial cross-sectional view showing a second n-type clad layer and a first electrode layer extracted from the light emitting element shown in FIG. 7.

[First Embodiment]
The first embodiment of the present invention will be described with reference to FIGS. 1 to 5. It should be noted that the embodiments described below are shown as suitable specific examples for carrying out the present invention, and there are some parts that specifically exemplify various technical matters that are technically preferable. , The technical scope of the present invention is not limited to this specific aspect. Further, the dimensional ratio of each component in each drawing does not necessarily match the dimensional ratio of the actual nitride semiconductor light emitting device. In the following description of the present invention, "upper" or "lower" indicates a relative positional relationship between one object and another object, and the one object is the object. Not only those directly above or below the other object, but also the one object indirectly above or below the other object via another third object. Including those placed in.

FIG. 1 is a cross-sectional view schematically showing the configuration of a nitride semiconductor light emitting device according to the first embodiment of the present invention. The nitride semiconductor light emitting device 1 (hereinafter, also simply referred to as “light emitting device 1”) is a light emitting diode (LED) that emits light having a wavelength in the ultraviolet region. In the present embodiment, in particular, the light emitting element 1 that emits deep ultraviolet light having a center wavelength of 200 nm to 360 nm will be described as an example.

As shown in FIG. 1, the light emitting element 1 includes a substrate 10, a buffer layer 20, a first n-type clad layer 30, an intermediate layer 40, an active layer 50 including a multiple quantum well layer, and an electron block layer. It includes 60, a p-type clad layer 70, a tunnel junction 80, a second n-type clad layer 90, a cathode electrode 200, and an anode electrode 100.

The semiconductor constituting the light emitting element 1 includes, for example, a binary system represented by Al _x Gay In _{1-xy N} (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A ternary or quaternary group III nitride semiconductor can be used. Further, some of these Group III elements may be replaced with boron (B), thallium (Tl), etc., and a part of N may be replaced with phosphorus (P), arsenic (As), antimony (Sb), etc. It may be replaced with bismuth (Bi) or the like.

The substrate 10 has translucency with respect to the deep ultraviolet light emitted by the light emitting element 1. The substrate 10 is, for example, a sapphire substrate containing sapphire (Al ₂ O ₃ ). As the substrate 10, in addition to the sapphire (Al ₂ O ₃ ) substrate, for example, an aluminum nitride (AlN) substrate or an aluminum gallium nitride (AlGaN) substrate may be used.

The buffer layer 20 is formed on the substrate 10. The buffer layer 20 includes an AlN layer 22 and an undoped u-Al _p Ga _1-p N layer 24 (0 ≦ p ≦ 1) formed on the AlN layer 22. Further, the substrate 10 and the buffer layer 20 form a base structure portion 2. The u-Al _p Ga _1-p N layer 24 does not necessarily have to be provided.

The first n-type clad layer 30 is formed on the base structure portion 2. The first n-type clad layer 30 is a layer formed of n-type AlGaN (hereinafter, also simply referred to as “n-type AlGaN”), and for example, silicon (Si) is doped as an n-type impurity. Al _q Ga _1-q N layer (0 ≦ q ≦ 1). As the n-type impurity, germanium (Ge), selenium (Se), tellurium (Te), carbon (C) and the like may be used. The first n-type clad layer 30 has a thickness of about 1 μm to 3 μm, and has a thickness of, for example, about 2 μm. The first n-type clad layer 30 may be a single layer or a multilayer structure.

The intermediate layer 40 is formed on the first n-type clad layer 30. The intermediate layer 40 is a layer containing at least silicon (Si), aluminum (Al) and nitrogen (N), and is, for example, an AlGaN layer doped with Si as an impurity.

The active layer 50 including the multiple quantum well layer is formed on the intermediate layer 40. The active layer 50 is a three-layer barrier including a barrier layer 52a on the intermediate layer 40 side of the multiple quantum well layer composed of Al _r Ga _1-r N and a barrier layer 52c on the electron block layer 60 side, which will be described later. Alternating three-layer well layers 54a, 54b, 54c (0≤r≤1, 0≤s≤1, r> s) including layers 52a, 52b, 52c and Al _s Ga _1-s N. It is a layer including a multiple quantum well layer laminated on. The active layer 50 is configured to have a band gap of 3.4 eV or more in order to output deep ultraviolet light having a wavelength of 360 nm or less. In the present embodiment, the active layer 50 is provided with three barrier layers 52 and three well layers 54, but the active layer 50 is not necessarily limited to three layers, and may be two layers or four or more layers.

The electron block layer 60 is formed on the active layer 50. The electron block layer 60 is formed of p-type AlGaN (hereinafter, also simply referred to as "p-type AlGaN"). The electron block layer 60 has a thickness of about 1 nm to 10 nm. The electron block layer 60 may include a layer formed of AlN. Further, the electron block layer 60 is not necessarily limited to the p-type semiconductor layer, and may be an undoped semiconductor layer.

The p-type clad layer 70 is formed on the electron block layer 60. That is, the p-type clad layer 70 is located above the multiple quantum well layer via the electron block layer 60. The p-type clad layer 70 is a layer formed of p-type AlGaN, and is, for example, an Alt Ga _{1-t N} layer (0 ≦ t ≦ 1) doped with magnesium (Mg) as a p-type impurity. .. As the p-type impurities, zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba) and the like may be used.

The tunnel junction 80 is formed on the p-type clad layer 70. The tunnel junction 80 is for tunnel-junctioning the p-type clad layer 70 and the second n-type clad layer 90 as an n-type semiconductor layer described later. That is, the tunnel junction 80 generates holes in the valence band of the p-type semiconductor by tunneling electrons in the valence band of the p-type semiconductor into the conductor of the n-type semiconductor.

The tunnel junction 80 includes a p-type layer 82 located on the p-type clad layer 70 side and an n-type layer 84 located on the second n-type clad layer 90 side. The p-type layer 82 is, for example, a pGaN layer formed of p-type GaN (hereinafter, also referred to as “pGaN”) in which impurities such as Mg are heavily doped. The semiconductor material forming the p-type layer 82 is not necessarily limited to pGaN, and may be, for example, p-type AlGaN, p-type InGaN, or p-type AlInGaN. When Al is contained in the p-type layer 82, the Al composition ratio is preferably 0.2 or less. When In is contained in the p-type layer 82, the In composition ratio is preferably 0.2 or less. In other words, the p-type layer 82 is a layer formed by p-type Al _a In _b Ga _1-ab N (0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.2).

The n-type layer 84 is an nGaN layer formed of n-type GaN doped with impurities such as Si. The semiconductor material forming the n-type layer 84 is not necessarily limited to nGaN, and may be, for example, n-type AlGaN, n-type InGaN, or n-type AlInGaN. When Al is contained in the n-type layer 84, the Al composition ratio is preferably 0.2 or less. When In is contained in the n-type layer 84, the In composition ratio is preferably 0.2 or less. In other words, the n-type layer 84 is a layer formed by n-type Al _c In _d Ga _1-c-d N (0 ≦ c ≦ 0.2, 0 ≦ d ≦ 0.2).

Further, both the p-type layer 82 of the pGaN layer and the n-type layer 84 of the nGaN layer have a property of absorbing a part of ultraviolet light. Details will be described later.

The thickness of the p-type layer 82 is preferably 10 nm or less, more preferably 5 nm or less. Further, similarly to the p-type layer 82, the thickness of the n-type layer 84 is preferably 10 nm or less, more preferably 5 nm or less. In other words, the thickness of the tunnel junction 80 is preferably 20 nm or less, more preferably 10 nm or less.

A second n-type clad layer 90 is formed on the tunnel junction 80. That is, the second n-type clad layer 90 is located above the p-type clad layer 70 via the tunnel junction 80. The second n-type clad layer 90 is a layer that conducts and diffuses the current flowing from the contact electrode portion 122, which will be described later, in the lateral direction. Here, the "horizontal direction" means a direction orthogonal to the thickness direction of the second n-type clad layer 90. Details will be described later.

The second n-type clad layer 90 is a layer containing an n-type semiconductor (hereinafter, also referred to as an “n-type semiconductor layer”). Specifically, the second n-type clad layer 90 is a layer formed of n-type AlGaN, for example, an Al u Ga 1-u N layer (for example, an Al _u Ga _1-u N layer doped with silicon (Si) as an n-type impurity. 0 ≦ u ≦ 1). Preferably, the composition of the n-type AlGaN constituting the second n-type clad layer 90 is substantially equal to the composition of the n-type AlGaN constituting the first n-type clad layer 30, that is, q = u. Further, the second n-type clad layer 90 absorbs a very small amount of ultraviolet light emitted from the active layer 50 as compared with the above-mentioned pGaN layer, and the amount of ultraviolet light emitted from the second n-type clad layer 90 is very small. The amount of absorption is 0.1% or less.

The cathode electrode 200 is formed on a part of the region of the first n-type clad layer 30. The cathode electrode 200 is formed of, for example, a multilayer film in which titanium (Ti) / aluminum (Al) / Ti / gold (Au) are sequentially laminated on the first n-type clad layer 30.

The anode electrode 100 is formed on the second n-type clad layer 90. The anode electrode 100 is formed of a second electrode layer 120 including a reflective electrode portion 124, a contact electrode portion 122, and a second multilayer film in which aluminum (Al) / Ti / gold (Au) are laminated in this order. Includes the electrode layer 140 of the above. The first electrode layer 120 is an example of the electrode layer. The second electrode layer 140 does not necessarily have to include an aluminum (Al) layer.

The reflecting electrode unit 124 reflects the ultraviolet light emitted from the multiple quantum well layer on the surface on the side of the second n-type clad layer 90. Preferably, the reflective electrode portion 124 is configured to include a material having a high reflectance to ultraviolet light. For example, the reflective electrode portion 124 is configured to contain a metal such as Al. The reflectance of Al with respect to ultraviolet light is about 90%.

The contact electrode portion 122 is an electrode portion that supplies an electric current to the second n-type clad layer 90. The contact electrode portion 122 is made of a material different from that of the reflective electrode portion 124. Preferably, the contact electrode portion 122 is formed of a material having a contact resistance with respect to the second n-type clad layer 90, which is smaller than the contact resistance of the reflective electrode portion 124 with respect to the second n-type clad layer 90. By doing so, in pursuit of increasing the reflectance of the anode electrode 100 to ultraviolet light, by selecting a material having a high reflectance to ultraviolet light for the reflecting electrode portion 124, the second n-type Even if the contact resistance to the clad layer 90 increases, it can be expected to suppress the difficulty of current flowing through the anode electrode 100. Specifically, the contact electrode portion 122 is configured to contain a metal such as Ti. The material of the contact electrode portion 122 is not limited to Ti, and may be Ni, palladium (Pd), or ITO (Indium Tin Oxide).

For convenience of explanation, three reflective electrode portions 124 and three contact electrode portions 122 are provided, but the number is not necessarily limited to three, and may be two or four or more. Further, the number of the reflective electrode portions 124 and the number of the contact electrode portions 122 may be different.

FIG. 2 is a top view schematically showing the configuration of the first electrode layer 120. The reflective electrode portion 124 and the contact electrode portion 122 are spatially separated from each other. Here, "spatially separated" means that the reflective electrode portion 124 and the contact electrode portion 122 are provided at different positions on the upper surface of the second n-type clad layer 90. In "spatial separation", not only the reflective electrode portion 124 and the contact electrode portion 122 are arranged side by side at a predetermined interval, but also the reflective electrode portion 124 and the contact electrode portion 122 are provided. It also includes configurations that are lined up without gaps. Specifically, as shown in FIGS. 1 and 2, the reflective electrode portion 124 and the contact electrode portion 122 are striped (striped) in the top view of the second n-type clad layer 90. Are arranged alternately in.

Preferably, the surface area of the upper surface of the reflective electrode portion 124 (hereinafter, also referred to as “area of the reflective electrode portion 124”) is also referred to as the surface area of the upper surface of the contact electrode portion 122 (hereinafter, also referred to as “area of the contact electrode portion 122”). ) That's all. By doing so, it is expected that more ultraviolet light emitted from the multiple quantum well layer will be reflected and the efficiency of extracting ultraviolet light will be improved.

On the other hand, since it is difficult for the current to diffuse directly under the reflecting electrode portion 124, the area of the reflecting electrode portion 124 is preferably a predetermined value or less in order to diffuse the current more efficiently. Based on the above, specifically, the area of the reflective electrode portion 124 is 50 to 90% of the area of the first electrode layer 120. The area of the first electrode layer 120 is the total value of the area of the reflective electrode portion 124 and the area of the contact electrode portion 122. Here, the “area” refers to the total area of the reflective electrode portion 124 or the contact electrode portion 122 constituting the first electrode layer 120.

(Uniformization of in-plane light emission)
FIG. 3 is a partial cross-sectional view showing the second n-type clad layer 90 and the first electrode layer 120 extracted from the light emitting element shown in FIG. 1, and is a conceptual diagram schematically showing the diffusion of electric current. Arrows in FIG. 3 indicate current flow. As shown in FIG. 3, since the reflective electrode portion 124 is configured to contain Al having a high contact resistance, it is difficult for a current to flow, whereas the contact electrode portion 122 contains Ti having a low contact resistance. Because it is configured, current easily flows. Therefore, the current flowing from the contact electrode portion 122 tends to flow not only in the vertical direction (thickness direction) but also in the horizontal direction (direction orthogonal to the thickness direction) when passing through the second n-type clad layer 90. .. As described above, the current flowing from the first electrode layer 120 diffuses laterally in the second n-type clad layer 90 and becomes uniform.

The length at which the current diffuses in the lateral direction (hereinafter, also referred to as “current diffusion length”) is about 1/2 times the width of the reflecting electrode portion 124 (see “W”), that is, 1/2 × W. be. In other words, the lateral current diffusion length is 1/2 of the distance between the contact electrode portions 122 located closest to each other. Further, preferably, the current diffusion length in the lateral direction is 10 times or less the thickness of the second n-type clad layer 90 (see “d”). That is, preferably, the width W of the reflective electrode portion 124 is 20 times or less the thickness of the second n-type clad layer 90 (that is, W ≦ 20 × d). More preferably, when the thickness d of the second n-type clad layer 90 is about 0.5 μm, the width W of the reflective electrode portion 124 is about 4.0 μm, and the width of the contact electrode portion 122 is about 2.0 μm. Is. Further, in this case, the ratio of the reflective electrode portion 124 to the area of the first electrode layer 120 is about 60%.

The current flowing from the first electrode layer 120 is laterally diffused and homogenized in the second n-type clad layer 90, so that the carriers are spatially and uniformly injected into the multiple quantum well layer of the active layer 50. As a result, the non-uniformity of the in-plane light emission is suppressed, and the in-plane light emission can be made uniform. Further, as a result of uniformly emitting light in the plane, the degree of deterioration of the light emitting element 1 is suppressed from being spatially biased in the light emitting element 1, so that it can be expected that the life of the light emitting element can be extended.

(Improvement of light extraction efficiency)
Next, the efficiency of extracting light from the light emitting element 1 will be described with reference to FIGS. 4 and 5. FIG. 4 is a graph schematically showing the relationship between the thickness of the pGaN layer and the transmittance of ultraviolet light. FIG. 5 is a diagram schematically showing the efficiency of extracting light from the light emitting element. Hereinafter, for convenience of explanation, a configuration in which the area of the reflective electrode portion 124 and the area of the contact electrode portion 122 are substantially equal in the flip type light emitting element 1 will be described as an example. Unless otherwise specified, both the thickness of the p-type layer 82 and the thickness of the n-type layer 84 will be described as 10 nm.

The horizontal axis of the graph shown in FIG. 4 indicates the thickness (nm) of the pGaN layer constituting the p-type layer 82, and the vertical axis indicates the transmittance (%) of the ultraviolet light incident on the pGaN layer passing through the pGaN layer. ) Is shown. Note that FIG. 4 shows, as an example, the transmittance (%) of ultraviolet light having a wavelength of 280 nm with respect to the pGaN layer.

The pGaN layer partially absorbs ultraviolet light. The ultraviolet light incident on the pGaN layer is transmitted through the pGaN layer with the rest not absorbed by the pGaN layer. As shown in FIG. 4, the transmittance P of ultraviolet light with respect to the pGaN layer is expressed by the following relational expression using the thickness t (nm) of the pGaN layer and the absorption coefficient α (nm ^-1 ).
P = exp (-α x t)
here,
α = 1.7x10 ^-2
The value of α is an example of a value for ultraviolet light having a wavelength of 280 nm. Also, exp is the base of the natural logarithm.

As shown in FIG. 4, for example, the transmittance of ultraviolet light having a wavelength of 280 nm with respect to the pGaN layer is about 50% (about 50% absorption) when the thickness of the pGaN layer is 40 nm, and the thickness of the pGaN layer is 10 nm. At that time, it is about 84% (about 16% absorption).

As shown in FIG. 5, the ultraviolet light emitted from the multiple quantum well layer of the active layer 50 is transmitted by about 50% each above and below the light emitting element 1 (up and down direction shown in FIG. 1). Of these, the upward ultraviolet light is partially absorbed by the p-type layer 82 (pGaN layer) constituting the tunnel junction 80 when passing through the tunnel junction 80. As described above, when the thickness of the p-type layer 82 is 10 nm, about 84% of ultraviolet light is transmitted. That is, 42% (50% x 84%) of the upward ultraviolet light emitted from the multiple quantum well layer passes through the tunnel junction 80.

The ultraviolet light transmitted through the tunnel junction 80 is reflected by the first electrode layer 120. Assuming that the area of the reflective electrode portion 124 is 50% of that of the first electrode layer 120 and the reflectance of the reflective electrode portion 124 is 90%, about 19% (42) of the ultraviolet light emitted from the multiple quantum well layer and directed upward. % X 50% x 90%) is reflected by the first electrode layer 120.

The ultraviolet light reflected by the first electrode layer 120 goes downward again and passes through the tunnel junction 80. As described above, since the transmittance of the ultraviolet light of the tunnel junction 80 is about 84%, 84% of the 19% ultraviolet light reflected by the first electrode layer 120, that is, 16% (19%). x84%) ultraviolet light is transmitted to the lower side. In other words, 16% of the ultraviolet light emitted from the multiple quantum well layer can be extracted.

<Modification example>
FIG. 6 is a top view schematically showing a modified example of the configuration of the first electrode layer 120. For example, as shown in FIGS. 6A and 6B, the circular contact electrode portions 122 are arranged in a dot shape in a top view, and then the reflective electrode portion 124 is placed around the contact electrode portion 122. May be placed in. Further, as shown in FIGS. 6 (a) and 6 (b), the contact electrode portion 122 may be arranged so as to have rotational symmetry (4-fold symmetry (FIG. 6 (a)), 6-fold symmetry ( FIG. 6 (b))). In FIGS. 6A and 6B, for convenience of explanation, the reflective electrode portion 124 is shown in white so that the reflective electrode portion 124 and the contact electrode portion 122 can be easily visually distinguished. The contact electrode portion 122 is shown in black.

As an example, in the arrangement having 6-fold symmetry shown in FIG. 6B, when the thickness d of the second n-type clad layer 90 is 1.0 μm, the diameter of the contact electrode portion 122 is 4. The distance between the centers of the contact electrode portion 122 can be set to about 0 μm, and the distance between the centers can be set to about 8.0 μm. In this case, the ratio of the reflective electrode portion 124 to the area of the first electrode layer 120 is about 77.3%. The cross-sectional shape of the contact electrode portion 122 is not limited to the circular shape described above, and may be an elliptical shape or a polygonal shape.

(Actions and effects of the first embodiment and modifications)
As described above, in the light emitting device 1 according to the first embodiment and the modified example of the present invention, the first n-type clad layer 30 formed of n-type AlGaN and the first n-type clad layer are formed. The multiple quantum well layer located above 30, the p-type clad layer 70 located above the multiple quantum well layer and formed by p-type AlGaN, and the p-type clad located on the p-type clad layer 70. A tunnel junction 80 in which a layer containing an n-type semiconductor is tunnel-bonded to the layer 70 and an Al composition ratio of AlGaN located on the tunnel junction 80 and forming the first n-type clad layer 30 are substantially equal to the Al composition ratio. A second n-type clad layer 90 made of AlGaN, a reflective electrode portion 124 located above the second n-type clad layer 90 and reflecting light emitted from the weight child well layer, and a reflective electrode portion. It includes a first electrode layer 120 that is spatially separated from the 124 and includes a reflective electrode portion 124 and a contact electrode portion 122 formed of a different material.

In this way, by inserting the second n-type clad layer 90 between the multiple quantum well and the first electrode layer 120, the distance between the multiple quantum well and the first electrode layer 120 is increased. Therefore, the diffusion of metal atoms in the first electrode layer 120 into the multiple quantum wells, which occurs during the use of the light emitting element, is suppressed, and as a result, the decrease in the light emitting output of the light emitting element 1 is reduced. At the same time, its life can be extended.

Further, since the Al composition of the second n-type clad layer 90 is substantially the same as the Al composition ratio of the first n-type clad layer 30, the crystallinity of the second n-type clad layer 90 is improved, and the metal Since the number of dislocations that serve as the diffusion path of atoms is reduced and the diffusion of metal atoms can be suppressed, the decrease in the emission output of the light emitting element 1 can be reduced and the life thereof can be extended.

Furthermore, by providing the reflective electrode portion 124 as described above, the light extraction efficiency of the light emitting element 1 can be improved, and the current can be diffused in the lateral direction in the second n-type clad layer 90. This makes it possible to emit light uniformly in the plane.

[Second Embodiment]
FIG. 7 is a cross-sectional view schematically showing a configuration of a light emitting element and a light emitting element according to a second embodiment of the present invention. The light emitting element 1 according to the second embodiment is different from the light emitting element 1 according to the first embodiment in that the second n-type clad layer includes a current diffusion layer. Hereinafter, the same components as those of the first embodiment will be described with the same reference numerals, duplicate description will be omitted, and points different from those of the first embodiment will be mainly described.

As shown in FIG. 7, the second n-type clad layer 90 includes a current diffusion layer 94 inside. The current diffusion layer 94 contains Si having an addition concentration smaller than the addition concentration of Si in the second n-type clad layer 90. The addition concentration of the current diffusion layer 94 is preferably about 10% of the addition concentration of Si in the second n-type clad layer 90, that is, about 1.0 × 10 ¹⁸ cm ^-3 . Therefore, the electric resistance of the current diffusion layer 94 is higher than the electric resistance of the second n-type clad layer 90.

FIG. 8 is a partial cross-sectional view showing the second n-type clad layer 90 and the first electrode layer 120 extracted from the light emitting element 1 shown in FIG. 7. The current diffusion layer 94 is a layer that promotes the diffusion of current in the lateral direction. As shown in FIG. 8, the current flowing from the contact electrode portion 122 is further diffused in the lateral direction in the current diffusion layer 94. Further, as described above, since the electric resistance of the current diffusion layer 94 is higher than the electric resistance of the second n-type clad layer 90, the diffused current is less likely to flow into the current diffusion layer 94. Therefore, the diffusion of the current in the second n-type clad layer 90 is further promoted.

(Actions and effects of the second embodiment)
As described above, even in the second embodiment of the present invention, the decrease in the light emitting output can be reduced, the life of the light emitting element can be extended, and the light extraction efficiency of the light emitting element 1 can be improved. At the same time, it is possible to emit light uniformly in the plane. Further, in addition to this, the light emitting element 1 according to the second embodiment of the present invention is further provided with the second current diffusion layer 94 having high resistance, so that the diffusion of current is further promoted. It is possible to emit light uniformly in the plane.

(Summary of Embodiment)
Next, the technical idea grasped from the above-described embodiment will be described with reference to the reference numerals and the like in the embodiment. However, the respective reference numerals and the like in the following description are not limited to the members and the like in which the components in the claims are specifically shown in the embodiment.

[1] A first n-type clad layer formed of n-type AlGaN, a multiple quantum well layer located above the first n-type clad layer, and a multiple quantum well layer located above the multiple quantum well layer. A p-type clad layer (70) formed of p-type AlGaN and a layer located above the p-type clad layer (70) and containing an n-type semiconductor are tunnel-bonded to the p-type clad layer (70). A nitride semiconductor light emitting device (1) including a tunnel junction layer (80) and an electrode layer formed above the tunnel junction layer (80), and between the tunnel junction layer and the electrode layer. A nitride semiconductor light emitting device (1) further comprising a second n-type clad layer (90) formed of n-type AlGaN.
[2] The Al composition ratio of AlGaN forming the second n-type clad layer (90) is substantially equal to the Al composition ratio of AlGaN forming the first n-type clad layer (30). ]. The nitride semiconductor light emitting device (1).
[3] The tunnel junction layer (90) is a p-type Al _a In _b Ga _1-ab N (0 ≦ a ≦ 0.2, 0 ≦ b) located on the p-type clad layer (70). The p-type layer (82) formed by ≦ 0.2) and the n-type Al _{c Ind} Ga _1-cd N (0 ≦ c ≦ 0.2) located on the p-type layer (82). The nitride semiconductor light emitting device (1) according to the above [1] or [2], which includes an n-type layer (84) formed by (0 ≦ d ≦ 0.2).
[4] The electrode layer includes a reflective electrode portion (124) that reflects light emitted from the multiple quantum well layer on the second n-type clad layer (90), and the second n-type clad. [1] to [3], wherein the layer (90) is provided with a contact electrode portion (122) for supplying an electric current, and the reflective electrode portion (124) and the contact electrode portion 122 are alternately arranged. The nitride semiconductor light emitting device (1) according to any one of the above.
[5] The nitride semiconductor light emitting device (1) according to the above [4], wherein the contact electrode portion (122) is arranged in a dot shape in a top view of the second n-type clad layer (90). ).
[6] The contact electrode portion (122) is based on the contact resistance of the reflective electrode portion (124) to the second n-type clad layer (90) with respect to the second n-type clad layer (90). The nitride semiconductor light emitting device (1) according to any one of the above [1] to [5], which also has a small contact resistance.
[7] The nitride semiconductor light emitting device (1) according to the above [6], wherein the reflective electrode portion (124) is configured to include aluminum (Al).
[8] The contact electrode portion (122) is configured to include any one of titanium (Ti), nickel (Ni) and palladium (Pd), according to the above [6] or [7]. Nitride semiconductor light emitting device (1).
[9] The nitride semiconductor light emitting device (1) according to any one of [1] to [8], wherein the surface area of the reflective electrode portion (124) is equal to or larger than the surface area of the contact electrode portion (122). ).
[10] The nitride semiconductor light emitting device (1) according to the above [9], wherein the cross-sectional area of the reflective electrode portion (124) is 50 to 90% of the cross-sectional area of the cross section of the electrode layer.
[11] The nitride semiconductor light emitting device (1) according to any one of [1] to [10], wherein the tunnel junction (80) has a thickness of 20 nm or less.
[12] The second n-type clad layer (90) includes a current diffusion layer (94) containing Si having an addition concentration smaller than the Si addition concentration of the n-type clad layer (90). The nitride semiconductor light emitting device (1) according to any one of the above [1] to [11].
[13] The nitride according to the above [12], wherein the addition concentration of Si in the current diffusion layer (94) is approximately 1/10 of the addition concentration of Si in the second n-type clad layer (90). Material semiconductor light emitting device (1).

1 ... Nitride semiconductor light emitting element (light emitting element)
2 ... Underlayer structure 10 ... Substrate 20 ... Buffer layer 22 ... AlN layer 24 ... u-Al _p Ga _1-p N layer 30 ... First n-type clad layer 40 ... Intermediate layer 50 ... Active layers 52, 52a, 52b , 52c ... Barrier layer 54, 54a, 54b, 54c ... Well layer 60 ... Electronic block layer 70 ... P-type clad layer 80 ... Tunnel junction 82 ... P-type layer 84 ... n-type layer 90 ... Second n-type clad layer 94 ... current diffusion layer 100 ... anode electrode 120 ... first electrode layer 122 ... contact electrode portion 124 ... reflective electrode portion 140 ... second electrode layer 200 ... cathode electrode P ... transmittance W ... width d of reflective electrode portion ... Thickness α of n-type clad layer of 2 ... Absorption coefficient

Claims (11)

The first n-type clad layer formed by n-type AlGaN and
The multiple quantum well layer located above the first n-type clad layer and
A p-type clad layer located above the multiple quantum well layer and formed by p-type AlGaN,
A tunnel junction layer located above the p-type clad layer and tunnel-junctioning a layer containing an n-type semiconductor to the p-type clad layer.
A nitride semiconductor light emitting device including an electrode layer formed above the tunnel junction layer.
A second n-type clad layer formed of n-type AlGaN is further included between the tunnel junction layer and the electrode layer.
The nitride semiconductor light emitting device is of a flip type and has a flip type.
The multiple quantum well layer emits ultraviolet light and emits ultraviolet light.
The electrode layer is a reflective electrode portion that reflects light emitted from the multiple quantum well layer on the second n-type clad layer, and a contact electrode portion that supplies a current to the second n-type clad layer. And alternately
The second n-type clad layer has an absorption rate of ultraviolet light emitted by the multiple quantum well layer of 0.1% or less .
The thickness of the tunnel junction layer is 10 nm or less, and the thickness is 10 nm or less.
A nitride semiconductor light emitting device in which the width of the reflective electrode portion is 20 times or less the thickness of the second n-type clad layer . The Al composition ratio of AlGaN forming the second n-type clad layer is substantially equal to the Al composition ratio of AlGaN forming the first n-type clad layer.
The nitride semiconductor light emitting device according to claim 1. The tunnel junction layer was formed by p-type Al _a In _b Ga _1-ab N (0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.2) located on the p-type clad layer. An n-type formed by a p-type layer and an n-type Al _c Ind Ga _{1-c-d N} (0 ≦ c ≦ 0.2, 0 ≦ d ≦ 0.2) located on the p-type layer. Including layers,
The nitride semiconductor light emitting device according to claim 1 or 2. The contact electrode portions are arranged in dots in the top view of the second n-type clad layer.
The nitride semiconductor light emitting device according to any one of claims 1 to 3 . The contact electrode portion has a contact resistance with respect to the second n-type clad layer, which is smaller than the contact resistance of the reflective electrode portion with respect to the second n-type clad layer.
The nitride semiconductor light emitting device according to any one of claims 1 to 4 . The reflective electrode portion is made of aluminum.
The nitride semiconductor light emitting device according to claim 5 . The contact electrode portion is configured to contain any one of titanium, nickel, and palladium.
The nitride semiconductor light emitting device according to claim 5 or 6 . The surface area of the reflective electrode portion is equal to or larger than the surface area of the contact electrode portion.
The nitride semiconductor light emitting device according to any one of claims 1 to 7 . The surface area of the reflective electrode portion is 50 to 90% of the cross-sectional area of the cross section of the electrode layer.
The nitride semiconductor light emitting device according to claim 8 . The second n-type clad layer includes a current diffusion layer containing Si having an addition concentration smaller than the addition concentration of Si in the second n-type clad layer.
The nitride semiconductor light emitting device according to any one of claims 1 to 9 . The addition concentration of Si in the current diffusion layer is approximately 1/10 of the addition concentration of Si in the second n-type clad layer.
The nitride semiconductor light emitting device according to claim 10 .

Images