JP6729644B2 - Nitride semiconductor light emitting device - Google Patents

Description

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

In recent years, a light emitting device (nitride semiconductor light emitting device) configured by using a nitride semiconductor has been widely used. In this nitride semiconductor light emitting device, for example, an n-type nitride semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer are stacked in this order on a substrate and emit light of a predetermined wavelength. In semiconductor light emitting devices, it is generally expected that light emitting efficiency can be improved by forming a light emitting layer in a quantum well structure. Even in a nitride semiconductor light emitting device, a structure including a light emitting layer having a quantum well structure aims to further improve light emitting efficiency. Various studies have been made.

For example, Patent Document 1 discloses a nitride semiconductor light emitting device that includes an intermediate barrier layer having a relatively wide bandgap in the active region as compared with other barrier layers, which improves the light emission efficiency. It is said that the above-mentioned light emitting diode can be provided.

Further, the nitride semiconductor has a higher dislocation density than other compound semiconductors such as GaAs. The nitride semiconductor light emitting device tends to reduce the degree of output reduction at high temperature by reducing the dislocation density.
Therefore, a technique for forming a nitride semiconductor having a low dislocation density is being developed, and a certain result has been obtained.

JP, 2008-311658, A

However, the present inventor has found that the nitride semiconductor light emitting device has a problem that a forward voltage for obtaining a predetermined current becomes higher as a nitride semiconductor having a low dislocation density can grow. This is considered to be due to the influence of the piezoelectric field. That is, it is considered that as the number of dislocations decreases, the influence of the piezo electric field increases, and the uniformity of carrier distribution in the light emitting layer deteriorates, which reduces the recombination probability of electrons and holes.

Therefore, an object of the present invention is to provide a nitride semiconductor light emitting device that can lower the forward voltage and improve the light emission efficiency.

In order to achieve the above object, a nitride semiconductor light emitting device according to an aspect of the present invention,
A nitride semiconductor light emitting device including a light emitting layer having a multiple quantum well structure between an n-side layer and a p-side layer,
The light emitting layer includes, in order from the n-side layer side, an n-side first barrier layer, an n-side first well layer that is a well layer having the shortest distance from the n-side layer, and the n-side first barrier layer. The n-side first intermediate barrier layer having a smaller bandgap, the n-side second well layer which is the second shortest well layer from the n-side layer, and the bandgap of the n-side first intermediate barrier layer It is characterized by including a large intermediate barrier layer and a well layer.

According to the nitride semiconductor light emitting device configured as described above, the forward voltage can be lowered and the light emission efficiency can be improved.

FIG. 3 is a cross-sectional view showing the configuration of the nitride semiconductor light emitting element of Embodiment 1 according to the present invention. 3 is a cross-sectional view showing a structure of a light emitting layer of the nitride semiconductor light emitting device according to Embodiment 1. FIG. 3 is a diagram schematically showing a band structure of a light emitting layer of the nitride semiconductor light emitting device according to Embodiment 1. FIG. 5 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting element according to Embodiment 2. FIG. 5 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 2. FIG. FIG. 6 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting device according to a third embodiment. FIG. 5 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 3. FIG. 7 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 4. FIG. 6 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 4. FIG. 9 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting element according to Embodiment 5. FIG. 9 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 5. FIG. 9 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 6. FIG. 9 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 6. FIG. 9 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting element according to Embodiment 7. FIG. 9 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 7. FIG. 9 is a cross-sectional view showing a structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 8. FIG. 9 is a diagram schematically showing a band structure of a light emitting layer of a nitride semiconductor light emitting device according to Embodiment 8. 5 is a graph showing evaluation results of slope efficiency (light output (au)/current (mA)) of the nitride semiconductor light emitting devices of Examples 1 and 2 according to the present invention. 5 is a graph showing evaluation results of forward voltage Vf of the nitride semiconductor light emitting devices of Examples 1 and 2 according to the present invention.

Hereinafter, a nitride semiconductor light emitting device according to an embodiment of the present invention will be described with reference to the drawings.

Embodiment 1.
As shown in FIG. 1, the nitride semiconductor light emitting device 10 of the first embodiment includes a substrate 1, an n-side layer (n-side semiconductor layer) 2, a light emitting layer 3 and a p-side layer (p) provided on the substrate 1. Side semiconductor layer) 4. The substrate 1 may be removed after forming the n-side layer 2, the light emitting layer 3, and the p-side layer 4, for example. The n-side layer 2 includes an n-type contact layer, and the p-side layer 4 includes a p-type contact layer.

Further, in the nitride semiconductor light emitting device 10, a full surface electrode 6 (first p electrode) formed on substantially the entire upper surface of the p-side layer 4 is provided, and a pad electrode 7 (second p electrode) is formed on a part of the whole surface electrode 6. Is provided. The whole surface electrode 6 is in contact with the p-type contact layer which is a part of the p-side layer 4. Further, part of the p-side layer 4 and the light emitting layer 3 and part of the n-side layer 2 are removed to expose the n-type contact layer, and the n-electrode 8 is provided on the exposed surface. n-side layer 2, the light-emitting layer 3 and the p-side layer 4 is, for _example, is represented by _{In x Al y Ga 1-x} -y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) Formed of a nitride semiconductor.

(Emitting Layer of Embodiment 1)
In the nitride semiconductor light emitting device 10, as shown in FIG. 2A, the light emitting layer 3 includes the n-side first barrier layer 3bn and the n-side which is the well layer closest to the n-side layer 2 in order from the n-side layer 2 side. The first well layer 3wn, the n-side first intermediate barrier layer 3mn having a smaller bandgap than the n-side first barrier layer 3bn, and the well layer 3w2 (n-side) which is the second shortest distance from the n-side layer. Second well layer), an intermediate barrier layer 3m2 having a bandgap larger than that of the n-side first intermediate barrier layer 3mn, a well layer 3w3, and a p-side first barrier layer 3bp.
FIG. 2B shows an example of an energy band structure (hereinafter, simply referred to as a band structure) related to the light emitting layer 3 configured as above. Note that FIG. 2B is a diagram schematically showing the magnitude relationship of band gaps. The same applies to the figures showing the band structure thereafter.
Here, in the present embodiment, the well layer located between the n-side first barrier layer 3bn and the n-side first intermediate barrier layer 3mn is referred to as an n-side first well layer 3wn to distinguish it from other well layers. There is.

In the nitride semiconductor light emitting device 10 configured as described above, the band gap of the n-side first intermediate barrier layer 3mn is made smaller than the band gap of the n-side first barrier layer 3bn, so that the well layer 3w2 and the well The amount of electrons injected into the layer 3w3 can be increased. Thereby, recombination of electrons and holes in the well layers (well layer 3w2 and well layer 3w3) on both sides of the intermediate barrier layer 3m2 can be increased. Therefore, the forward voltage can be reduced and the luminous efficiency can be improved.

That is, in the light emitting layer having the multiple quantum well structure, electrons injected into the well layer tend to be large in the n-side well layer and small in the central well layer, while holes are small in the n-side well layer. Tends to become. Since the injection of electrons into the well layer in the central portion is small, recombination with holes in the well layer is reduced and the forward voltage is increased. Such a tendency becomes more remarkable as the dislocation density decreases.
On the other hand, in the first embodiment, the band gap of the n-side first intermediate barrier layer 3mn is made smaller than the band gap of the n-side first barrier layer 3bn so that the n-side layer 2 moves to the well layer in the central portion. It makes it easy for electrons to flow in. As a result, the forward voltage can be reduced.

Moreover, in the nitride semiconductor light emitting device 10, the light emission efficiency can be improved. The luminous efficiency is indicated by, for example, the slope efficiency (optical output (au)/current (mA)) defined by the optical output with respect to the current value. The reason why the luminous efficiency is improved is considered to be as follows. First, since holes in the light-emitting layer tend to decrease toward the n-side, it is difficult to increase the emission efficiency of the well layer close to the n-side layer 2, for example, the n-side first well layer 3wn. Therefore, the band gap of the n-side first intermediate barrier layer 3mn is lowered to reduce the electrons in the n-side first well layer 3wn and relatively increase the electrons in the other well layers. Therefore, it is considered that the luminous efficiency in the other well layers can be relatively improved and the luminous efficiency of the nitride semiconductor light emitting element 10 can be improved.

Further, in the nitride semiconductor light emitting device 10, the band gap of the n-side first barrier layer 3bn and the band gap of the intermediate barrier layer 3m2 are made larger than the band gap of the n-side first intermediate barrier layer 3mn. Thereby, electrons and holes can be confined in the light emitting layer 3, and the electrons and holes can be efficiently recombined in the well layer.
That is, when the bandgap of the n-side first barrier layer 3bn and the bandgap of the intermediate barrier layer 3m2 are made small like the n-side first intermediate barrier layer 3mn, the barrier for confining electrons and holes in the light emitting layer 3 becomes small. Become. In this case, the confinement of electrons and holes in the light emitting layer 3 is weakened, and the recombination probability of electrons and holes in the light emitting layer 3 is reduced. With such a structure, it is difficult to improve the luminous efficiency in a low current region such as 20 mA or less.

As described above, in the nitride semiconductor light emitting device 10, the band gap of the n-side first intermediate barrier layer 3mn is smaller than that of the n-side first barrier layer 3bn and the intermediate barrier layer 3m2. This makes it possible to realize the nitride semiconductor light emitting device 10 in which the forward voltage can be lowered and the light emission efficiency can be increased.

In the nitride semiconductor light emitting device 10, for example, the n-side first barrier layer 3bn is formed of a nitride semiconductor represented by In _b1 Ga _1-b1 N (0≦b1<1), and the n-side first intermediate barrier layer is formed. 3 mn can be formed using a nitride semiconductor represented by In _m1 Ga _1-m1 N (0<m1<1). In this case, the In composition b1 of the n-side first barrier layer 3bn is made smaller than the In composition m1 of the n-side first intermediate barrier layer 3mn. As a result, the bandgap of the n-side first barrier layer 3bn becomes larger than the bandgap of the n-side first intermediate barrier layer 3mn. The n-side first barrier layer 3bn is made of, for example, GaN, and the n-side first intermediate barrier layer 3mn is made of, for example, InGaN. Further, the n-side first well layer 3wn, the well layer 3w2, and the well layer 3w3 have In _w Ga _1-w N (0<w<1 where In composition w is larger than In composition m1 of the n-side first intermediate barrier layer 3mn. ) Is formed of a nitride semiconductor. The n-side first well layer 3wn, the well layer 3w2, and the well layer 3w3 can be formed of, for example, a nitride semiconductor having the same band gap. In the present specification, a ternary nitride semiconductor containing In, Ga, and N may be simply referred to as InGaN.

When the n-side first barrier layer 3bn is In _b1 Ga _1-b1 N and the n-side first intermediate barrier layer 3mn is In _m1 Ga _1-m1 N, the In composition b1 of the n-side first barrier layer 3bn is It is preferable to set 0≦b1<0.1, and the In composition m1 of the n-side first intermediate barrier layer 3mn is 0<m1<0.2 and b1<m1. Since the crystallinity tends to deteriorate as the In composition ratio increases, it is preferable to set it within such a range in consideration of it. At this time, the In composition w of the n-side first well layer 3wn, the well layer 3w2, and the well layer 3w3 is, for example, 0.05≦w≦0.5. The In composition w of the well layer is set so that its band gap is smaller than that of any barrier layer.

Further, in the nitride semiconductor light emitting device 10, the p-side first barrier layer 3bp can be formed of, for example, a nitride semiconductor having the same band gap as the n-side first barrier layer 3bn. When the p-side first barrier layer 3bp is formed of, for example, a nitride semiconductor represented by In _bf Ga _1-bf N (0≦bf<1), the In composition bf is set to In of the n-side first barrier layer 3bn. It is set to be the same as the composition b1. The In composition bf of the p-side first barrier layer 3bp is preferably set in the range of 0≦bf<0.1 similarly to the In composition b1 of the n-side first barrier layer 3bn.

In the nitride semiconductor light emitting device 10, the intermediate barrier layer 3m2 can be formed of, for example, a nitride semiconductor having the same bandgap as the n-side first barrier layer 3bn and the p-side first barrier layer 3bp. The intermediate barrier layer 3m2 can be formed of a nitride semiconductor represented by In _m2 Ga _1-m2 N (0≦m2<1). At this time, the In composition m2 of the intermediate barrier layer 3m2 can be selected from the same range as the In composition b1 of the n-side first barrier layer 3bn and the In composition bf of the p-side first barrier layer 3bp, for example, substantially Same as.

In the nitride semiconductor light emitting device 10, the n-side first barrier layer 3bn and the n-side first intermediate barrier layer 3mn preferably contain an n-type impurity. This makes it possible to increase the number of electrons injected into the n-side first well layer 3wn and the well layers located closer to the p-side layer 4 than the first well layer 3wn and lower the forward voltage. In this case, it is preferable to make the n-type impurity concentration of the n-side first intermediate barrier layer 3mn lower than that of the n-side first barrier layer 3bn. As a result, it is possible to suppress a decrease in holes due to the addition of the n-type impurity, and thus a decrease in light output can be suppressed. Regarding the specific n-type impurity concentration of each layer, the size relation between the n-side first barrier layer 3bn and the n-side first intermediate barrier layer 3mn is maintained, and the n-side first barrier layer 3bn is 1×10 ¹⁸ / cm ³ less than 1 × ¹⁰ 20 / cm ³ can be cited above, n-side first intermediate barrier layer 3mn can be mentioned below 1 × ¹⁰ 17 / greater than cm ³ 1 × ¹⁰ 19 / cm ^3. For example, Si is used as the n-type impurity.

Next, the nitride semiconductor light emitting devices of Embodiments 2 to 8 will be described.
The nitride semiconductor light emitting elements of Embodiments 2 to 8 are configured similarly to the nitride semiconductor light emitting element of Embodiment 1 except that the configuration of the light emitting layer 3 is different from that of the nitride semiconductor light emitting element of Embodiment 1. It Also, unless otherwise stated, similar configurations can be used for layers having the same name. Hereinafter, the structure of the light emitting layer in the nitride semiconductor light emitting devices of Embodiments 2 to 8 will be described.

Embodiment 2.
As shown in FIG. 3A, the light emitting layer 3 of the nitride semiconductor light emitting device of the second embodiment further includes an n-side layer 2 between the well layer 3w3 and the p-side first barrier layer 3bp in the light-emitting layer 3 of the first embodiment. This is a structure in which a p-side first intermediate barrier layer 3mp and a p-side first well layer 3wp are added from the side. The band gap of the p-side first intermediate barrier layer 3mp is smaller than that of the p-side first barrier layer 3bp.
FIG. 3B shows an example of a band structure according to the light emitting layer 3 of the second embodiment configured as described above.
Here, in the second embodiment, the well layer located between the p-side first barrier layer 3bp and the p-side first intermediate barrier layer 3mp is referred to as a p-side first well layer 3wp, and is separated from other well layers. Different.

In this way, by making the band gap of the p-side first intermediate barrier layer 3mp smaller than that of the p-side first barrier layer 3bp, the well layer 3w3 located far from the p-side layer and the well layer closer to the n-side layer are located. The amount of holes flowing into the hole can be increased.
As a result, the droop phenomenon can be suppressed, and a decrease in luminous efficiency in a high current region of, for example, 40 mA or more can be suppressed.

In the light emitting layer 3 of the second embodiment, for example, the p-side first intermediate barrier layer 3mp is formed of a nitride semiconductor represented by In _m3 Ga _1-m3 N (0≦m3<1), and the p-side first barrier is formed. The layer 3bp is formed of a nitride semiconductor represented by In _bf Ga _1-bf N (0≦bf<1). In this case, the In composition m3 of the p-side first intermediate barrier layer 3mp is set to be larger than the In composition bf of the p-side first barrier layer 3bp. Further, it is preferable that the n-side first intermediate barrier layer 3mn and the p-side first intermediate barrier layer 3mp have a smaller bandgap than the n-side first barrier layer 3bn and the p-side first barrier layer 3bp.
The In composition bf of the p-side first barrier layer 3bp is set in the range of 0≦bf<0.1, and the In composition m3 of the p-side first intermediate barrier layer 3mp is 0<m3<0.2 and bf. <m3 is preferable. Thereby, the confinement of electrons in the light emitting layer 3 and the relaxation of the concentration of holes in the p-side first well layer 3p1 can be more efficiently performed. At this time, the In composition w of the n-side first well layer 3wn, the well layer 3w2, and the well layer 3w3 is, for example, 0.05≦w≦0.5. The In composition w of the well layer is set so that its band gap is smaller than that of any barrier layer.

The n-side first barrier layer 3bn and the p-side first barrier layer 3bp can be formed of, for example, a nitride semiconductor having an equal band gap.
For example, the n-side first barrier layer 3bn is formed of a nitride semiconductor represented by In _b1 Ga _1-b1 N (0≦b1<1), and the p-side first barrier layer 3bp is formed of In _bf Ga _1-bf N 2. In the case of forming the nitride semiconductor represented by (0≦bf<1), the In composition b1 of the n-side first barrier layer 3bn and the In composition bf of the p-side first barrier layer 3bp are made equal. In this case, the In composition b1 and the In composition bf are both set to 0, and the n-side first barrier layer 3bn and the p-side first barrier layer 3bp can be formed of GaN, respectively. As described above, the n-side first barrier layer 3bn and the p-side first barrier layer 3bp having large band gaps are advantageous for carrier confinement in the light emitting layer 3.

The n-side first intermediate barrier layer 3mn and the p-side second intermediate barrier layer 3mp can be formed of, for example, a nitride semiconductor having an equal bandgap. For example, when the n-side first intermediate barrier layer 3mn is formed of a nitride semiconductor represented by In _m1 Ga _1-m1 N (0<m1<1), the p-side first intermediate barrier layer 3mp is formed into the n-side first intermediate barrier layer 3mp. The intermediate barrier layer 3mn is formed of a nitride semiconductor represented by In _m3 Ga _1-m3 N (0<m3<1) having the same In composition m3 as the In composition m1.

Each of the p-side first barrier layer 3bp and the p-side first intermediate barrier layer 3mp is preferably an undoped layer or a layer having an n-type impurity concentration smaller than the n-side first intermediate barrier layer 3mn.
Accordingly, it is possible to suppress the decrease of holes in the well layer near the p-side layer 4 (the p-side first well layer 3wp), and it is possible to effectively emit light from the well layer near the p-side layer 4 having high light emission efficiency. Note that the undoped layer refers to a layer formed without intentionally doping n-type impurities and p-type impurities. In addition, the undoped layer can be referred to as a layer whose impurity concentration is less than or equal to the detection limit of analysis by secondary ion mass spectrometry (SIMS) or the like. The well layers included in the light emitting layer 3 are also typically all undoped layers.

Embodiment 3.
As shown in FIG. 4A, the light emitting layer 3 of the nitride semiconductor light emitting device of the third embodiment further includes the n-side layer 2 between the well layer 3w3 and the p-side first barrier layer 3bp in the light-emitting layer 3 of the first embodiment. This is a structure in which an intermediate barrier layer 3m3, a well layer 3w4, an intermediate barrier layer 3m4, a well layer 3w5, a p-side first intermediate barrier layer 3mp, and a p-side first well layer 3wp are added from the side.
In other words, the light emitting layer 3 of the nitride semiconductor light emitting device according to the third embodiment has the well layer 3w3 and the p-side first intermediate barrier layer 3mp in the light emitting layer 3 according to the second embodiment, and further from the n-side layer 2 side. This is a structure in which an intermediate barrier layer 3m3, a well layer 3w4, an intermediate barrier layer 3m4, and a well layer 3w5 are added.
FIG. 4B shows an example of a band structure relating to the light emitting layer 3 of Embodiment 3 configured as described above.

The well layer 3w3 (intermediate well layer) is a well layer having the third shortest distance from the n-side layer 2. The intermediate barrier layer 3m3 (second intermediate barrier layer) has a larger bandgap than the n-side first intermediate barrier layer 3mn. As a result, the amount of holes flowing out to the n-side layer 2 without recombination with electrons is reduced as compared with the case where the band gap of the intermediate barrier layer 3m3 is made low as in the n-side first intermediate barrier layer 3mn. Can be made. Therefore, the luminous efficiency in a low current region of 20 mA or less can be improved.
Here, the intermediate barrier layer 3m3 and the intermediate barrier layer 3m4 can be formed of a nitride semiconductor having the same bandgap as the intermediate barrier layer 3m2. For example, the intermediate barrier layer 3m3 and the intermediate barrier layer 3m4 is, In composition m4 and m5 is set to the same as the In composition m2 of the intermediate barrier layer _{3m2 In m4 Ga 1-m4 N} (0 ≦ m4 <1) and _In m5 Ga It can be formed of a nitride semiconductor represented by _1-m5N (0≦m5<1). The intermediate barrier layers 3m2, 3m3, 3m4 may have the same bandgap as the n-side first barrier layer 3bn and the p-side first barrier layer 3bp. For example, the intermediate barrier layers 3m2, 3m3, 3m4 are made of GaN.

Here, the intermediate barrier layer 3m2 may include an n-type impurity. When the intermediate barrier layer 3m2 is doped with an n-type impurity, the concentration of electrons in the well layer in the vicinity thereof can be increased, but the concentration of holes is decreased. Therefore, it is preferable that the n-type impurity concentration of the intermediate barrier layer 3m2 is lower than that of the n-side first barrier layer 3bn, like the n-side first intermediate barrier layer 3mn. As for the specific value of the n-type impurity concentration, the same range as that of the n-side first intermediate barrier layer 3mn can be selected.
Further, it is preferable to dope the intermediate barrier layer at a portion where the electron concentration tends to be low with n-type impurities and to make the other intermediate barrier layers undoped. As a result, the forward voltage can be reduced while suppressing the decrease in light output. Specifically, among the well layers and the intermediate barrier layers sandwiched between the well layers (including the n-side first intermediate barrier layer 3mn and the p-side first intermediate barrier layer 3mp), 1 or more in the order close to the n-side layer 2. It is preferable that the layer of n is an n-type impurity-containing layer and at least one layer closest to the p-side layer 4 is an undoped layer. Specifically, the number of intermediate barrier layers containing n-type impurities is preferably less than 80% of the total number of intermediate barrier layers. With the structure satisfying such a range, the forward voltage can be lowered and the light output can be made equal to or higher than that in the case where all the intermediate barrier layers are undoped. For example, in the case of having five intermediate barrier layers as shown in FIG. 4A, the range of n-type impurity doping is from the n-side first intermediate barrier layer 3mn to the maximum intermediate barrier layer 3m3, and the p-side layer The layer near 4 may be undoped.

The well layers 3w4 and 3w5 may be formed of the n-side first well layer 3wn, the well layer 3w2, the well layer 3w3, and the p-side first well layer 3wp by using a nitride semiconductor having the same band gap. it can. For example, it is formed of a nitride semiconductor represented by In _w Ga _1-w N (0≦w<1) having an In composition _w larger than the In composition m1 of the n-side first intermediate barrier layer 3mn.

Embodiment 4.
As shown in FIG. 5A, the light emitting layer 3 of the nitride semiconductor light emitting device of Embodiment 4 has a structure in which the n-side first barrier layer 3bn in the light emitting layer 3 of Embodiment 1 is used as a composition gradient layer.
Specifically, the n-side first barrier layer 3bn of the fourth embodiment is configured so that the band gap becomes smaller from the n-side layer 2 toward the n-side first well layer 3wn. For example, when the layer in contact with the first barrier layer 3bn of the n-side layer 2 is an n-type contact layer made of GaN and the n-side first well layer 3wn is InGaN, the In composition gradually increases from the n-type contact layer side. Is increased to substantially equalize the In composition of the n-side first well layer 3wn at the interface with the n-side first well layer 3wn.
FIG. 5B shows an example of a band structure according to the light emitting layer 3 of Embodiment 4 configured as described above.
As described above, in the light emitting layer 3 of the nitride semiconductor light emitting device 10, the n-side first barrier layer 3bn may be a composition gradient layer. Also in the light emitting layer 3 of the nitride semiconductor light emitting device of the second or third embodiment, the n-side first barrier layer 3bn can be a composition gradient layer. In this case, the magnitude relationship of the band gap with the n-side first intermediate barrier layer 3mn is compared with, for example, the maximum band gap in the composition gradient layer. It may be compared with the average bandgap of the compositionally graded layer, and further with the minimum bandgap of the compositionally graded layer. In Examples 1 and 2 described later, each layer including the n-side first barrier layer 3bn was a single composition layer instead of a composition gradient layer.

Embodiment 5.
As shown in FIG. 6A, the light emitting layer 3 of the nitride semiconductor light emitting device of the fifth embodiment has a composition gradient layer between the first barrier layer 3bn and the n-side first well layer 3wn in the light emitting layer 3 of the first embodiment. This is a structure in which the insertion layer 3i1 is added.
The insertion layer 3i1 is configured such that the band gap becomes smaller from the first barrier layer 3bn side toward the n-side first well layer 3wn. For example, the composition of the portion in contact with the first barrier layer 3bn is the same as that of the first barrier layer 3bn, the composition is gradually changed as the distance from the first barrier layer 3bn, and the composition is in contact with the n-side first well layer 3wn. The part has substantially the same composition as the n-side first intermediate barrier layer 3mn.
FIG. 5B shows an example of a band structure according to the light emitting layer 3 of the fifth embodiment configured as described above.
Thus, the barrier layer and the well layer may not be in contact with each other, and the insertion layer 3i1 may be provided.

Embodiment 6.
The light emitting layer 3 of the nitride semiconductor light emitting device of the sixth embodiment is inserted between the n-side first barrier layer 3bn and the n-side first well layer 3wn in the light emitting layer 3 of the first embodiment, as shown in FIG. 7A. It is similar to the light emitting layer 3 of the fifth embodiment in that it includes the layer 3i1. However, the composition of the insertion layer 3i1 is constant without changing in the thickness direction, and the bandgap of the insertion layer 3i1 is between the bandgap of the n-side first barrier layer 3bn and the bandgap of the n-side first well layer 3wn. It is set to a value.
For example, when the n-side first barrier layer 3bn is made of GaN and the n-side first well layer 3wn is made of InGaN, the insertion layer 3i1 is made of InGaN smaller than the In composition of the n-side first well layer 3wn.
FIG. 7B shows an example of a band structure according to the light emitting layer 3 of Embodiment 6 configured as described above.
As described above, the insertion layer 3i1 is not limited to the composition gradient layer, and may be provided with a composition and a film thickness such that the effect of the barrier layer such as the n-side first barrier layer 3bn is obtained.

Embodiment 7.
As shown in FIG. 8A, the light emitting layer 3 of the nitride semiconductor light emitting device of Embodiment 7 includes an insertion layer 3i1 between the n-side first barrier layer 3bn and the n-side first well layer 3wn, and further includes an n-side first layer. It differs from the light emitting layer 3 of the first embodiment in that an insertion layer 3i2 is included between the one well layer 3wn and the n-side first intermediate barrier layer 3mn. The band gap of the insertion layer 3i1 and the band gap of the insertion layer 3i2 are set to be smaller than the band gap of the n-side first intermediate barrier layer 3m1 and larger than the band gap of the n-side first well layer 3wn. The band gap of the insertion layer 3i1 and the band gap of the insertion layer 3i2 are preferably set to be the same, but may be different.
FIG. 8B shows an example of a band structure according to the light emitting layer 3 of Embodiment 7 configured as described above.
In this way, it is possible to provide a plurality of insertion layers 3i1 and 3i2.

Embodiment 8.
As shown in FIG. 9A, the light emitting layer 3 of the nitride semiconductor light emitting device of Embodiment 8 includes an insertion layer 3i1 between the first barrier layer 3bn and the n-side first well layer 3wn, and further includes the n-side first well. It differs from the light emitting layer 3 of Embodiment 1 in that an insertion layer 3i2 is included between the layer 3wn and the n-side first intermediate barrier layer 3mn. This point is similar to the light emitting layer 3 of Embodiment 7, but the light emitting layer 3 of Embodiment 8 is different from the light emitting layer 3 of Embodiment 7 in that the insertion layer 3i1 and the insertion layer 3i2 are compositionally graded layers. Are different.

Specifically, the insertion layer 3i1 is configured such that the band gap becomes smaller from the n-side first barrier layer 3bn toward the n-side first well layer 3wn. Further, the insertion layer 3i2 is configured such that the band gap increases from the n-side first well layer 3wn toward the n-side first intermediate barrier layer 3mn.
FIG. 9B shows an example of a band structure relating to the light emitting layer 3 of Embodiment 8 configured as described above.

The insertion layer described in Embodiments 5 to 8 is a layer formed for various purposes so that the functions of the well layer and the barrier layer are not substantially impaired. For convenience of drawing, the drawing is drawn to have a thickness similar to that of the well layer and the barrier layer, but actually, it is an extremely thin layer of, for example, about 1 nm or less.
The position where the insertion layer is formed is variously selected according to the purpose and may be formed between the intermediate barrier layer and the well layer or between the p-side barrier layer and the well layer.

Although the nitride semiconductor light emitting devices of Embodiments 1 to 8 according to the present invention have been described above, the dislocation density of the nitride semiconductor light emitting device 10 according to Embodiments 1 to ⁸ is less than 1×10 ⁸ /cm ^2. Is preferred. Furthermore, the dislocation density is preferably 5×10 ⁷ /cm ² or less. As a result, the function and effect described in each embodiment can be remarkably obtained. Normally, there is no great change in the dislocation density from the n-side layer 2 to the p-side layer 4, so the dislocation density may be evaluated at any position. It is considered that the dislocation density of the light emitting layer 3 is preferably less than 1×10 ⁸ /cm ² in order to reduce the degree of output reduction at high temperature. Therefore, it is preferable to evaluate the light emitting layer 3 or the vicinity thereof. .. Note that such a layer having a low dislocation density can be obtained, for example, by forming a crystalline AlN buffer layer instead of a polycrystal on the surface of a sapphire substrate and growing it.
Here, the dislocation density of the light emitting layer 3 is determined by a transmission electron microscope (TEM) or cathodoluminescence (CL) in which a crystal is irradiated with an electron beam to excite carriers in the crystal to disperse light emission generated upon recombination. Can be evaluated using the method.

Examples will be described below.
The nitride semiconductor light emitting device shown in Table 1 was produced as Example 1, the nitride semiconductor light emitting device shown in Table 2 was produced as Example 2, and the nitride semiconductor light emitting device shown in Table 3 as Comparative Example 1 thereof. Was produced. In each case, these semiconductor layers were grown on a sapphire substrate, and the chip size was 650 μm×650 μm. Further, in each case, the dislocation density measured by the CL method after singulation was about 5×10 ⁷ /cm ² .

(Table 1)

(Table 2)

(Table 3)

For the nitride semiconductor light emitting devices of Examples 1 and 2 and the nitride semiconductor light emitting device of Comparative Example 1 manufactured as described above, the slope efficiency (light output (au)/ The current (mA)) and the forward voltage Vf were evaluated. 10 and 11 show the evaluation results of the slope efficiency (light output (au)/current (mA)) and forward voltage Vf, respectively. In each case, the horizontal axis represents If (forward current).
As a result, it was confirmed that each of the nitride semiconductor light emitting devices of Examples 1 and 2 can have a lower forward voltage and higher slope efficiency than the nitride semiconductor light emitting device of Comparative Example 1.

1 substrate 2 n-side layer (n-side semiconductor layer)
3 Light emitting layer 3bn n-side first barrier layer 3wn n-side first well layer 3mn n-side first intermediate barrier layer 3w2, 3w3, 3w4, 3w5 well layer 3m2, 3m3 intermediate barrier layer 3bp p-side first barrier layer 3wp p-side First well layer 3mp p-side first intermediate barrier layer 4 p-side layer (p-side semiconductor layer)
6 Full surface electrode 7 p electrode 10 Nitride semiconductor light emitting device

Claims (5)

A nitride semiconductor light emitting device including a light emitting layer having a multiple quantum well structure between an n-side layer and a p-side layer,
The light emitting layer, in order from the n-side layer side,
An n-side first barrier layer made of GaN ,
An n-side first well layer which is a well layer having the shortest distance from the n-side layer,
An n-side first intermediate barrier layer made of In _m1 Ga _1-m1 N (where 0<m1<0.2) ,
An n-side second well layer that is the second shortest well layer from the n-side layer,
An n-side second intermediate barrier layer made of GaN ,
An n-side third well layer which is the third shortest well layer from the n-side layer,
An n-side third intermediate barrier layer made of GaN;
An n-side fourth well layer that is a well layer that is the fourth shortest distance from the n-side layer,
An n-side fourth intermediate barrier layer made of GaN,
A p-side second well layer which is the second shortest well layer from the p-side layer,
A p-side first intermediate barrier layer made of In _m3 Ga _1-m3 N (where 0<m3<0.2) ,
A p-side first well layer Ru shortest well layer der distance from the p-side layer,
Look including a p-side first barrier layer made of GaN,
The nitride semiconductor light emitting device, wherein the dislocation density in the light emitting layer or in the vicinity thereof is less than 1×10 ⁸ /cm ² . The n-side first barrier layer and the n-side first intermediate barrier layer include n-type impurities, and the n-type impurity concentration of the n-side first barrier layer is the n-type impurity of the n-side first intermediate barrier layer. The nitride semiconductor light emitting device according to claim 1, wherein the concentration is higher than the concentration. The p-side first barrier layer and the p-side first intermediate barrier layer is a nitride semiconductor according to claim 1 or 2 undoped layer or n-type impurity concentration of the first intermediate barrier layer is smaller than layer the n-side Light emitting element. The nitride semiconductor light emitting device according to any one of the n-side first In composition ratio of the composition ratio of In of the intermediate barrier layer and the p-side first intermediate barrier layer is substantially equal to Claim 1-3. The light emitting layer has a plurality of well layers and a plurality of intermediate barrier layers sandwiched between the well layers and the well layers,
The plurality of intermediate barrier layers include the n-side first intermediate barrier layer, the n-side second intermediate barrier layer, and the p-side first intermediate barrier layer,
Of the plurality of intermediate barrier layers, at least one layer is a layer containing n-type impurities, at least one layer closest to the p-side layer is an undoped layer, and the number of layers containing n-type impurities is the nitride semiconductor light emitting device according to any one of claims 1 to 4, which is less than 80% of the total number of the middle barrier layer.

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