JP6917953B2 - Nitride semiconductor light emitting device - Google Patents

Description

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

In recent years, nitride semiconductor light emitting devices such as light emitting diodes and laser diodes that output blue light have been put into practical use, and development of nitride semiconductor light emitting devices with improved light emitting output is underway (see Patent Document 1). ).

Japanese Patent No. 5521068

The nitride semiconductor light emitting element described in Patent Document 1 is a group III nitride semiconductor light emitting element having an active layer between an n-type clad layer and a p-type clad layer, and the active layer is the n-type clad. _{Three or more Al Xs} , including a first barrier layer in contact with the layers, a second barrier layer in contact with the p-type clad layer, and one or more intermediate barrier layers located between the first and second barrier layers. It _{has a multiple quantum well structure including a barrier layer made of Ga 1-X} N (0 ≦ X <1) and two or more well layers made of a group III nitride semiconductor sandwiched between the barrier layers. Then, the Al composition ratio X of the barrier layer gradually increases toward the first barrier layer and the second barrier layer with reference to the intermediate barrier layer having the _{smallest Al composition ratio X min among the intermediate barrier layers.} , Al composition ratio _{X 1} of the first barrier layer, the Al composition ratio _{X 2} of the second barrier layer, and the _{X min} is one that satisfies the following relational expression.
Note X ₂ + 0.01 ≤ X ₁
X _min +0.03 ≤ X ₂

However, in the nitride semiconductor light emitting device described in Patent Document 1, the composition ratio of Al at the interface between the n-type clad layer and the first barrier layer changes rapidly. Therefore, a state in which the band structure becomes deep in a V shape (hereinafter, also referred to as “notch”) occurs at the interface, and electrons are easily trapped in this notch and the flow of electrons is easily blocked. Further, at such an interface, an electric field is generated by the piezo effect, which tends to obstruct the flow of electrons. Due to such factors, the nitride semiconductor light emitting device described in Patent Document 1 may have a decrease in light emission output.

Therefore, the present invention suppresses the notch of the band structure that may occur at the interface between the n-type clad layer and the barrier layer on the n-type clad layer side of the multiple quantum well layer, and reduces the electric field generated by the piezo effect to emit light. and an object thereof is to provide a nitride semiconductor light emitting element capable of improving the output.

The present invention is located on the side of the n-type clad layer formed of n-type AlGaN having the first Al composition ratio and the multiple quantum well layer closest to the n-type clad layer for the purpose of solving the above problems. The first Al composition is located between the barrier layer formed of AlGaN having a second Al composition ratio larger than the first Al composition ratio, the n-type clad layer and the barrier layer. A nitride semiconductor light emitting element including an inclined layer having a third Al composition ratio between the ratio and the second Al composition ratio, wherein the third Al composition ratio of the inclined layer is X _Al. When (%) is set and the depth of the nitride semiconductor light emitting element is D (nm), the third Al composition ratio X _Al (%) of the inclined layer is the n-type clad from the barrier layer. With the direction toward the layer as positive, the gradient increases from the first Al composition ratio to the second Al composition ratio so as to satisfy the following relational expression.
X _Al (%) =-(1.0 ± 0.1) x D (nm) + X ₀ ,
X ₀ is a coefficient having a predetermined value, to provide a nitride semiconductor light emitting element.

According to the present invention, the notch of the band structure that may occur at the interface between the n-type clad layer and the barrier layer on the n-type clad layer side of the multiple quantum well layer is suppressed, and the electric field generated at this interface is reduced. , it is possible to provide a nitride semiconductor light emitting element capable of improving the emission output.

FIG. 1 is a cross-sectional view schematically showing a configuration of a nitride semiconductor light emitting device according to an embodiment of the present invention. FIG. 2 is a graph schematically showing the Al composition ratio of the light emitting device of the present invention in comparison with the Al composition ratio of the conventional light emitting device. 3A and 3B are diagrams showing wavelengths and emission outputs of light emitting elements according to Examples and Comparative Examples, FIG. 3A is a diagram showing each result in a table, and FIG. 3B is a graph showing each result. It is a figure.

[Embodiment]
Embodiments of the present invention will be described with reference to FIGS. 1 to 3. 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 technically preferable technical matters. , 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.

FIG. 1 is a cross-sectional view schematically showing a configuration of a nitride semiconductor light emitting device according to an 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 250 nm to 350 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, an n-type clad layer 30, an inclined layer 40, a light emitting layer 50 including a multiple quantum well layer, an electron block layer 60, and the like. It is composed of a p-type clad layer 70, a p-type contact layer 80, an n-side electrode 90, and a p-side electrode 92.

The semiconductor constituting the light-emitting element 1, for _example, 2-way system represented by _{Al x Ga y In 1-x} -y 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 is a substrate having transparency to the deep ultraviolet light emitted by the light emitting element 1. The substrate 10 is, for example, a sapphire (Al ₂ O ₃ ) substrate. 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 n-type clad layer 30 is formed on the base structure portion 2. The n-type clad layer 30 is a layer formed of n-type AlGaN (hereinafter, also simply referred to as “n-type AlGaN”), and is, for example, Al _q Ga doped with silicon (Si) as an n-type impurity. _{It is a 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 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 n-type clad layer 30 may be a single layer or a multi-layer structure.

The inclined layer 40 is formed on the n-type clad layer 30. The inclined layer 40 is a layer formed of n-type AlGaN, and is, for example, an Al _z Ga _1-z N layer (0 ≦ z ≦ 1) doped with silicon (Si) as an n-type impurity. The inclined layer 40 has a thickness of about 1 to 100 nm, and has a thickness of, for example, about 25 nm. The inclined layer 40 is a layer that plays a role of controlling the interface between the n-type clad layer 30 and the barrier layer 52a on the n-type clad layer 30 side of the multiple quantum well layer described later. Specifically, the inclined layer 40 has a role of suppressing a sudden change in the Al composition ratio (hereinafter, also simply referred to as “Al composition ratio”) between the n-type clad layer 30 and the barrier layer 52a. To bear. The inclined layer 40 is an example of a nitride semiconductor laminated structure.

The light emitting layer 50 including the multiple quantum well layer is formed on the inclined layer 40. The light emitting layer 50 _{includes three barrier layers 52a, 52b, 52c and Al s} Ga ₁ including a barrier layer 52a on the n-type clad layer 30 side of the multiple quantum well layer composed of _{Al r} Ga _{1-r N.} Multiple quantum well layers in which three well layers 54a, 54b, 54c (0 ≦ r ≦ 1, 0 ≦ s ≦ 1, r> s, see FIG. 2) composed of _{−s N are alternately laminated.} Is. The light emitting 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 350 nm or less.

The Al composition ratio of the light emitting element 1 will be described with reference to FIG. FIG. 2 is a graph schematically showing the Al composition ratio of the light emitting element 1 in comparison with the Al composition ratio of the conventional light emitting element. The symbol A in FIG. 2 indicates the Al composition ratio of the light emitting element 1 according to the present invention, and the symbol B in FIG. 2 indicates the Al composition ratio of the conventional light emitting element. As another expression, "AlN mole fraction" (%) can be used for the Al composition ratio.

The Al composition ratio of the n-type clad layer 30 (hereinafter, also referred to as “first Al composition ratio”) is about 40% to 60%, preferably about 50% to 60%, more preferably 54.6. It is about%. Further, the Al composition ratio of the barrier layer 52a (hereinafter, also referred to as “second Al composition ratio”) is larger than the first Al composition ratio, for example, 70% or more, preferably 80% or more. .. The same applies to the barrier layers 52b and 52c, but the description thereof will be omitted here.

The Al composition ratio of the inclined layer 40 suppresses the notch of the band structure that may occur at the interface between the n-type clad layer 30 and at least the barrier layer 52a, and reduces the electric field generated by the piezo effect. It increases at a predetermined rate of increase from the ratio toward the second Al composition ratio. In other words, the Al composition ratio of the inclined layer 40 (hereinafter, also referred to as “third Al composition ratio”) is the first Al composition ratio (for example, about 55%) toward the depth direction of the light emitting element 1. ) To the second Al composition ratio (about 80%).

Specifically, the Al composition ratio of the inclined layer 40 increases substantially linearly between the first Al composition ratio (about 55%) and the second Al composition ratio (about 80%). There is. That is, the third Al composition ratio of the inclined layer 40 increases at a constant rate of increase from the first Al composition ratio (about 55%) to the second Al composition ratio (about 80%). The details of the rate of increase will be described later.

In order to suppress the notch of the band structure and the sudden increase in the Al composition ratio that generates the electric field generated by the piezo effect, the increase rate is preferably set to a predetermined value (lower limit value) or more. When the rate of increase is made smaller than a predetermined value (lower limit value), the film thickness of the inclined layer 40 becomes thicker than 100 nm or more, the electric resistance becomes large, and it is necessary to prevent the forward voltage from becoming large.

More preferably, the Al composition ratio of the inclined layer 40 is between 55.3 mm and 83.1 mm when the upper surface of the p-clad layer 70 is 0 mm from the n-type clad layer 30 side toward the barrier layer 52a side. It has increased from 54.6% to 82.0%. That is, the Al composition ratio of the inclined layer 40 changes at an increase rate of about 28% with respect to about 28 nm. In other words, when the depth of the light emitting element 1 (the direction from the p-type clad layer 70 side to the n-type clad layer 30 side is positive) is D (nm), the Al composition ratio is X _Al (%). ) Satisfies the following relational expression.
X _Al (%) =-(1.0 ± 0.1) x D (nm) + X ₀
X ₀ is a coefficient having a predetermined value.

The Al composition ratio of the inclined layer 40 is not limited to one that linearly increases from the first Al composition ratio to the second Al composition ratio. For example, the second Al composition ratio from the first Al composition ratio. The Al composition ratio may be increased stepwise over a plurality of times at a predetermined depth. Further, the Al composition ratio of the inclined layer 40 may be increased by curvilinearly increasing from the first Al composition ratio to the second Al composition ratio. "Curveally inclined" means, for example, changing from the n-type clad layer 30 side toward the barrier layer 52 side so as to increase in a parabolic shape convex upward or downward. In other words, the Al composition ratio of the inclined layer 40 may change at an increasing rate that fluctuates from the n-type clad layer 30 side to the barrier layer 52 side.

The electron block layer 60 is formed on the light emitting layer 50. The electron block layer 60 is a layer 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, or may be formed of AlN that does not contain GaN. 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. p-type cladding layer 70 is a layer formed by p-type AlGaN, for example, a p-type _{Al t Ga 1-t} N cladding layer of magnesium as an impurity (Mg) is doped (0 ≦ t ≦ 1) be. As the p-type impurity, zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba) and the like may be used. The p-type clad layer 70 has a thickness of about 300 nm to 700 nm, and has a thickness of, for example, about 400 nm to 600 nm.

The p-type contact layer 80 is formed on the p-type clad layer 70. The p-type contact layer 80 is, for example, a p-type GaN layer doped with impurities such as Mg at a high concentration.

The n-side electrode 90 is formed on a part of the n-type clad layer 30. The n-side electrode 90 is formed of, for example, a multilayer film in which titanium (Ti) / aluminum (Al) / Ti / gold (Au) are sequentially laminated on the n-type clad layer 30.

The p-side electrode 92 is formed on the p-type contact layer 80. The p-side electrode 92 is formed of, for example, a nickel (Ni) / gold (Au) multilayer film that is sequentially laminated on the p-type contact layer 80.

Next, a method of manufacturing the light emitting element 1 will be described. The buffer layer 20 is formed on the substrate 10. Specifically, on the substrate 10, the AlN layer 22, the _{u-Al 1-p Ga p} N layer 24 of undoped to high temperature growth. Next, the n-type clad layer 30 is grown at a high temperature on the buffer layer 20. Next, the inclined layer 40 is grown at a high temperature on the n-type clad layer 30 while gradually increasing the supply amount of Al. Specifically, the inclined layer 40 is grown at a high temperature by adjusting the supply amount of Al so that the composition ratio of Al increases by about 1.0 ± 0.1% per unit depth (nm). The supply amount of Al may be adjusted by using a known technique such as adjusting the ratio of ammonia gas to the metal material. Alternatively, the relative supply amount of Al may be adjusted by adjusting the growth temperature of the inclined layer 40 while keeping the supply amount of the raw material of AlGaN constant. The "supply amount" means, for example, the relative ratio of Al to the raw material to be supplied.

Next, the light emitting layer 50, the electron block layer 60, and the p-type clad layer 70 are grown at high temperatures in this order on the inclined layer 40. The n-type clad layer 30, the inclined layer 40, the light emitting layer 50, the electron block layer 60, and the p-type clad layer 70 are formed by a metal organic chemical vapor deposition (MOCVD) method and a molecular beam epitaxy method (Molecular). It can be formed by using a well-known epitaxial growth method such as Beam Epitaxy (MBE) and Halide Vapor Phase Epitaxy (NVPE).

Next, a mask is formed on the p-type clad layer 70, and the inclined layer 40, the light emitting layer 50, the electron block layer 60, and the p-type clad layer 70 in the exposed region where the mask is not formed are removed. The inclined layer 40, the light emitting layer 50, the electron block layer 60, and the p-type clad layer 70 can be removed by, for example, plasma etching. The n-side electrode 90 is formed on the exposed surface 30a (see FIG. 1) of the n-type clad layer 30, and the p-side electrode 92 is formed on the p-type contact layer 80 from which the mask has been removed. The n-side electrode 90 and the p-side electrode 92 can be formed by a well-known method such as an electron beam deposition method or a sputtering method. As a result, the light emitting element 1 shown in FIG. 1 is formed.

Next, an example according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing the emission wavelength and emission output of the light emitting element 1 according to Examples 1 to 5 and Comparative Examples 1 and 2, and FIG. 3A is a diagram showing each result in a table. (B) is a diagram showing each result in a graph. The light-emitting element 1 according to the first to fifth embodiments includes a gradient layer 40 described above predicate. That is, the Al composition ratio of the light emitting device 1 according to Examples 1 to 5 gradually increases from the n-type clad layer 30 side toward the n-type clad layer 30 side barrier layer 52a side of the multiple quantum well layer. Further, the light emitting elements according to Comparative Examples 1 and 2 do not include the above-mentioned inclined layer 40. That is, the Al composition ratio of the light emitting elements according to Comparative Examples 1 and 2 changes sharply between the first Al composition ratio of the n-type clad layer 30 and the second Al composition ratio of the barrier layer 52a. ..

3 (a) and 3 (b) show the light emitting output (arbitrary unit, compared with our company) of the light emitting element 1 according to Examples 1 to 5 and Comparative Examples 1 and 2. The emission wavelength (nm) is the wavelength at which the emission output is measured. The light emission output can be measured by various known methods, but in this embodiment, as an example, a current is passed between the n-side electrode 90 and the p-side electrode 92 described above to be under the light-emitting element 1. It was measured by a photodetector installed on the side. The emission wavelength is specified depending on the growth temperature of the inclined layer 40 and the light emitting layer 50.

As shown in FIG. 3A, in Example 1, an emission output of 1.24 was obtained at an emission wavelength of 280.7 nm. In Example 2, an emission output of 1.28 was obtained at an emission wavelength of 283.3 nm. In Example 3, an emission output of 1.23 was obtained at an emission wavelength of 283.1 nm. In Example 4, an emission output of 1.25 was obtained at an emission wavelength of 281.7 nm. In Example 5, an emission output of 1.20 was obtained at an emission wavelength of 283.0 nm.

On the other hand, in Comparative Example 1, an emission output of 0.74 was obtained at an emission wavelength of 279.8 nm. In Comparative Example 2, an emission output of 0.86 was obtained at an emission wavelength of 283.8 nm.

Summarizing the above, in Comparative Examples 1 and 2, the light emission output was less than 1.0, whereas in Examples 1 to 5, the light emission output was 1.2 or more. In addition, the light emission output of Examples 1 to 5 was 1.6 times or more the light emission output of Comparative Example 1 and 1.4 times or more the light emission output of Comparative Example 2. As described above, it has been clarified that the light emitting output of the light emitting element 1 is increased by the present invention.

(Actions and effects of embodiments)
As described above, in the light emitting device 1 according to the embodiment of the present invention, the Al composition ratio is n between the n-type clad layer 30 and the barrier layer 52a on the n-type clad layer 30 side of the multiple quantum well layer. An inclined layer 40 that gradually increases from the type clad layer 30 side toward the n-type clad layer 30 side barrier layer 52a side of the multiple quantum well layer is provided. This makes it possible to increase the emission output of the deep ultraviolet light of the light emitting element 1. By providing the inclined layer 40 having such an Al composition ratio between the n-type clad layer 30 and the barrier layer 52a on the n-type clad layer 30 side of the multiple quantum well layer, the band generated in the conventional light emitting device can be formed. It is considered that the notch was suppressed and the electric field generated by the piezo effect could be reduced.

(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] The n-type clad layer (30) formed of n-type AlGaN having a first Al composition ratio and the first Al located on the n-type clad layer (30) side of the multiple quantum well layer. Between the barrier layer (52a, 52b, 52c) formed of AlGaN having a second Al composition ratio larger than the composition ratio, the n-type clad layer (30) and the barrier layer (52a, 52b, 52c). A nitride semiconductor light emitting device (1) including an inclined layer (40) having a third Al composition ratio between the first Al composition ratio and the second Al composition ratio. When the third Al composition ratio of the inclined layer is X _Al (%) and the depth of the nitride semiconductor light emitting device is D (nm), the third Al composition of the inclined layer (40). Al composition ratio satisfies the following relational expression, where the direction from the barrier layer to the n-type clad layer is positive.
X _Al (%) =-(1.0 ± 0.1) x D (nm) + X ₀ ,
X ₀ is Ru coefficient der having a predetermined value, the nitride semiconductor light emitting device (1).
[2] The third Al composition ratio of the inclined layer (40) increases in an inclined manner from the first Al composition ratio toward the second Al composition ratio, as described in the above [1]. Nitride semiconductor light emitting device (1).
[3] The third Al composition ratio of the inclined layer (40) increases substantially linearly from the first Al composition ratio toward the second Al composition ratio. ]. The nitride semiconductor light emitting device (1).
[4] The nitride according to any one of [1] to [3], wherein the first Al composition ratio of the n-type clad layer (30) is a value between 50% and 60%. Material semiconductor light emitting device (1).
[5] The nitride semiconductor according to any one of [1] to [4], wherein the second Al composition ratio of the barrier layer (52a, 52b, 52c) is a value of 80% or more. Light emitting element (1). [6] The n-type clad layer (30) formed of n-type AlGaN having a first Al composition ratio and the first Al located on the n-type clad layer (30) side of the multiple quantum well layer. The first Al composition ratio and the second Al composition ratio are located between the barrier layer (52a, 52b, 52c) formed of AlGaN having a second Al composition ratio larger than the composition ratio. It has a third Al composition ratio takes a value between, the third Al composition ratio of the gradient layer and X _{Al (%),} the depth of the nitride semiconductor light emitting device D (nm) In the case of, the third Al composition ratio X _Al (%) of the inclined layer satisfies the following relational expression, where the direction from the barrier layer to the n-type clad layer is positive.
X _Al (%) =-(1.0 ± 0.1) x D (nm) + X ₀ ,
X ₀ is Ru coefficient der having a predetermined value, the nitride semiconductor laminated structure.

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 ... n-type clad layer 30a ... Exposed surface 40 ... Inclined layer 50 ... Light emitting layers 52, 52a, 52b, 52c ... Barrier layers 54, 54a, 54b, 54c ... Well layer 60 ... Electronic block layer 70 ... p-type clad layer 80 ... p-type contact layer 90 ... n-side electrode 92 ... p-side electrode

Claims (4)

An n-type clad layer formed of an n-type AlGaN having a first Al composition ratio and
A barrier layer formed of AlGaN located closest to the n-type clad layer of the multiple quantum well layer and having a second Al composition ratio larger than that of the first Al composition ratio.
An inclined layer located between the n-type clad layer and the barrier layer and having a third Al composition ratio between the first Al composition ratio and the second Al composition ratio .
Nitride semiconductor light emitting device containing
When the third Al composition ratio of the inclined layer is X _Al (%) and the depth of the nitride semiconductor light emitting device is D (nm), the third Al composition ratio X of the inclined layer. _Al (%) is inclined from the first Al composition ratio to the second Al composition ratio so as to satisfy the following relational expression, with the direction from the barrier layer toward the n-type clad layer as positive. Increase ,
X _Al (%) =-(1.0 ± 0.1) x D (nm) + X ₀ ,
X ₀ is a coefficient having a predetermined value,
Nitride semiconductor light emitting device. The third Al composition ratio of the inclined layer increases substantially linearly from the first Al composition ratio toward the second Al composition ratio.
The nitride semiconductor light emitting device according to claim 1. The first Al composition ratio of the n-type clad layer is a value between 50% and 60%.
The nitride semiconductor light emitting device according to claim 1 or 2. The second Al composition ratio of the barrier layer is a value of 80% or more.
The nitride semiconductor light emitting device according to any one of claims 1 to 3 .

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