JP2015053531A - Semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting device having high light emission efficiency.SOLUTION: A semiconductor light-emitting device comprises: an n-type semiconductor layer including a nitride semiconductor; a p-type semiconductor layer including a nitride semiconductor; and a light-emitting layer provided between the n-type semiconductor layer and the p-type semiconductor layer. The light-emitting layer includes a plurality of barrier layers and a plurality of well layers, which are alternately laminated. A p-side barrier layer nearest to the p-type semiconductor layer among the plurality of barrier layers comprises: a plurality of first layers containing group III elements; and a plurality of second layers which include the group III elements laminated with the first layer, and in which In composition ratio in the group III elements in the second layer is higher than that in the group III elements in the first layer.

Description

  Embodiments described herein relate generally to a semiconductor light emitting device.

  Nitride III-V compound semiconductors such as gallium nitride (GaN) take advantage of the feature of wide band gap, and high-intensity light emitting diodes (LEDs), laser diodes (LDs), etc. Has been applied.

These light-emitting elements each include an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting layer that is provided therebetween and includes a quantum well layer and a barrier layer.
In such a semiconductor light emitting device, it is desired to realize high luminous efficiency.

JP 2007-116147 A

  The present invention provides a semiconductor light emitting device with high luminous efficiency.

  The semiconductor light emitting device according to the embodiment includes an n-type semiconductor layer including a nitride semiconductor, a p-type semiconductor layer including a nitride semiconductor, and light emission provided between the n-type semiconductor layer and the p-type semiconductor layer. A layer. The light emitting layer includes a plurality of barrier layers and a plurality of well layers that are alternately stacked. The p-side barrier layer closest to the p-type semiconductor layer among the plurality of barrier layers is a first layer containing a group III element and a second layer laminated with the first layer and containing a group III element. A second layer in which the In composition ratio in the group III element of the second layer is higher than the In composition ratio in the group III element of the first layer. A plurality of the first layers are provided, a plurality of the second layers are provided, and the plurality of first layers and the plurality of second layers are alternately arranged. One of the plurality of first layers contacts one of the plurality of well layers, and another one of the plurality of first layers contacts another one of the plurality of well layers. Each of the plurality of first layers has a thickness of 1 nanometer or less.

(A)-(b) is typical sectional drawing which illustrates the structure of a part of semiconductor light-emitting device based on embodiment. 1 is a schematic cross-sectional view illustrating the configuration of a semiconductor light emitting element according to an embodiment. It is a figure which illustrates In composition ratio of the semiconductor light-emitting device concerning an embodiment. It is a figure which illustrates In composition ratio of the semiconductor light-emitting device concerning an embodiment. It is a figure which illustrates In composition ratio of the semiconductor light emitting element of a reference example. (A)-(d) is a figure which illustrates the energy band and carrier concentration distribution which concern on embodiment. (A)-(d) is a figure which illustrates the energy band and carrier concentration distribution of the semiconductor light-emitting device which concern on embodiment. (A)-(d) is a figure which illustrates the energy band figure and carrier concentration distribution of the semiconductor light-emitting device of a reference example. It is a figure which illustrates the characteristic of a semiconductor light emitting element. (A)-(b) is a figure which illustrates In composition ratio of other semiconductor light emitting elements concerning an embodiment. (A)-(b) is a figure which illustrates In composition ratio of other semiconductor light emitting elements concerning an embodiment. It is a figure which illustrates In composition ratio of the other semiconductor light-emitting device concerning an embodiment. It is a figure which illustrates the characteristic of a semiconductor light emitting element. It is a figure which illustrates the characteristic of a semiconductor light emitting element.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio coefficient of the size between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratio coefficient may be represented differently depending on the drawing.
Further, in the present specification and each drawing, the same reference numerals are given to the same elements as those described above with reference to the previous drawings, and detailed description thereof will be omitted as appropriate.

(Embodiment)
FIG. 1A to FIG. 1B are schematic cross-sectional views illustrating the configuration of a part of the semiconductor light emitting element according to the embodiment.
FIG. 1A is a schematic cross-sectional view of a semiconductor light emitting device, and FIG. 1B is a schematic cross-sectional view of a barrier layer.
FIG. 2 is a schematic cross-sectional view illustrating the configuration of the semiconductor light emitting element according to the embodiment.
As shown in FIG. 2, the semiconductor light emitting device 110 according to this embodiment is provided between the n-type semiconductor layer 20, the p-type semiconductor layer 50, and the n-type semiconductor layer 20 and the p-type semiconductor layer 50. A light emitting layer 40. In the semiconductor light emitting device 110, the stacked body 30 may be provided between the light emitting layer 40 and the n-type semiconductor layer 20.

The n-type semiconductor layer 20 and the p-type semiconductor layer 50 include a nitride semiconductor.
The light emitting layer 40 is an active layer, for example. The stacked body 30 is, for example, a superlattice layer.

  In the semiconductor light emitting device 110, for example, the buffer layer 11 is provided on the main surface (for example, c-plane) of the substrate 10 made of sapphire, for example, an undoped GaN foundation layer 21 and an n-type GaN contact layer 22. And are provided. The n-type GaN contact layer 22 is included in the n-type semiconductor layer 20. The GaN foundation layer 21 may be included in the n-type semiconductor layer 20 for convenience.

  A stacked body 30 is provided on the n-type GaN contact layer 22. In the stacked body 30, for example, the first crystal layers 31 and the second crystal layers 32 are alternately stacked.

  A light emitting layer 40 (active layer) is provided on the stacked body 30. The light emitting layer 40 has, for example, a multiple quantum well (MQW) structure. That is, the light emitting layer 40 includes a structure in which a plurality of barrier layers 41 and a plurality of well layers 42 are alternately and repeatedly stacked. Detailed configurations of the barrier layer 41 and the well layer 42 will be described later.

  On the light emitting layer 40, a p-type AlGaN layer 51, a p-type Mg-doped GaN layer 52, and a p-type GaN contact layer 53 are provided in this order. Note that the p-type AlGaN layer 51 functions as an electron overflow suppression layer. The p-type AlGaN layer 51, the Mg-doped GaN layer 52, and the p-type GaN contact layer 53 are included in the p-type semiconductor layer 50. A transparent electrode 60 is provided on the p-type GaN contact layer 53.

Then, a part of the n-type GaN contact layer 22 which is the n-type semiconductor layer 20, the stacked body 30, the light emitting layer 40 and the p-type semiconductor layer 50 corresponding to the part are removed, and the n-type GaN contact layer 22 is The n-side electrode 70 is provided. For the n-side electrode 70, for example, a laminated structure of Ti / Pt / Au is used. On the other hand, a p-side electrode 80 is provided on the transparent electrode 60.
As described above, the semiconductor light emitting device 110 of this specific example according to the present embodiment is a light emitting diode (LED).

The semiconductor light emitting device 110 can be manufactured as follows, for example.
First, a substrate 10 of, for example, c-plane sapphire subjected to organic cleaning and acid cleaning is introduced into a reaction furnace of a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus and heated to about 1100 ° C. on the susceptor of the reaction furnace. Thereby, the oxide film on the surface of the substrate 10 is removed.

  Next, the buffer layer 11 is grown on the main surface (c-plane) of the substrate 10 to a thickness of 30 nm. Further, an undoped GaN foundation layer 21 is grown on the buffer layer 11 to a thickness of 3 micrometers (μm). Further, an n-type GaN contact layer 22 made of Si-doped GaN is grown on the GaN foundation layer 21 to a thickness of 2 μm.

Next, on the n-type GaN contact layer 22, the first crystal layer 31 that is In _x Ga _1-x N and the second crystal layer 32 that is In _y Ga _1-y N are alternately cycled 30 times. The stacked body 30 is formed by stacking.

Next, the barrier layers 41 and the well layers 42 are alternately stacked on the stacked body 30.
Further, an AlGaN layer having an Al composition ratio of 0.003 and a thickness of 5 nm is grown on the uppermost barrier layer 41. Thereafter, an Al composition ratio of 0.1 and an Mg composition having a thickness of 10 nm is grown. A doped AlGaN layer 51, an Mg-doped p-type GaN layer 52 having a thickness of 80 nm (Mg concentration is 2 × 10 ¹⁹ / cm ³ ), and a high-concentration Mg-doped GaN layer 53 having a thickness of about 10 nm (Mg concentration is 1 × 10 ²¹ / cm ³ ) are laminated. Thereafter, the substrate 10 on which the crystal has grown is taken out of the reactor of the MOCVD apparatus.

  Next, a part of the multilayer structure is exposed by dry etching partway through the n-type GaN contact layer 22, and a Ti / Pt / Au n-side electrode 70 is formed thereon. Further, a transparent electrode 60 made of ITO (Indium Tin Oxide) is formed on the surface of the high-concentration Mg-doped GaN layer 53, and a p-side electrode 80 made of Ni / Au having a diameter of 80 μm, for example, is formed on a part thereof. Thereby, the semiconductor light emitting device 110 is manufactured.

  In the above description, an example using the MOCVD (metal organic vapor phase) method as the film forming method has been described. However, other methods such as a molecular beam epitaxy (MBE) method and a halide vapor phase growth (HVPE) method are also applicable. Is possible.

Next, the multiple quantum well structure of the light emitting layer 40 will be described.
As shown in FIGS. 1A and 1B, the multiple quantum well structure of the light emitting layer 40 includes a plurality of barrier layers 41 (1) to 41 (n) and a plurality of well layers 42 (1) to 42. (N). Note that “n” included in the code is an integer of 2 or more corresponding to the layer number.
In this specification, the plurality of barrier layers 41 (1) to 41 (n) are collectively referred to as the barrier layer 41, and the plurality of well layers 42 (1) to 42 (n) are not distinguished. Are collectively referred to as the well layer 42.

  The plurality of barrier layers 41 include a first barrier layer 41 (1), a second barrier layer 41 (2),..., (N−1) from the n-type semiconductor layer 20 toward the p-type semiconductor layer 50. ) Th barrier layer 41 (n-1) and nth barrier layer 41 (n). Of the plurality of barrier layers 41, the first barrier layer 41 (1) closest to the n-type semiconductor layer 20 is also referred to as an n-side barrier layer, and the n-th barrier layer 41 (closest to the p-type semiconductor layer 50 ( n) is also referred to as a p-side barrier layer.

  The plurality of well layers 42 include a first well layer 42 (1), a second well layer 42 (2),..., (N−1) from the n-type semiconductor layer 20 toward the p-type semiconductor layer 50. ) Th well layer 42 (n-2) and nth well layer 42 (n). Of the plurality of well layers 42, the first well layer 42 (1) closest to the n-type semiconductor layer 20 is also referred to as an n-side well layer, and the n-th well layer 42 (closest to the p-type semiconductor layer 50 ( n) is also referred to as a p-side well layer.

The barrier layer 41 and the well layer 42 include a nitride semiconductor. The barrier layer 41 and the well layer 42 may contain a trace amount of Al or the like.
For the well layer 42, for example, a nitride semiconductor containing In is used. The band gap energy of the barrier layer 41 is larger than the band gap energy of the well layer 42.

The well layer 42 _{includes In w Ga 1-w N (} 0 <w <1). The thickness of the well layer 42 is a thickness t _w (nanometer). The thickness _{t w} of the well layer 42 is, for example, 3 nanometers (nm) or more 6nm or less.

In the semiconductor light emitting device 110, at least the nth barrier layer 41 (n) is provided with a first layer LL (n) and a second layer HL (n).
Note that the first layer LL (n) is also referred to as the first layer LL when collectively referred to regardless of the layer number. In addition, when the second layer HL (n) is generically referred to regardless of the layer number, it is also referred to as a second layer HL.

The first layer LL includes a group III element. The first layer LL includes, for example, In _b1 Ga _1-b1 N (0 ≦ b1). The second layer HL has a higher In composition ratio in the group III element than the In composition ratio in the group III element of the first layer LL. The second layer HL (n) includes, for example, In _b2 Ga _1-b2 N (b1 <b2).
The band gap energy of the second layer HL is smaller than the band gap energy of the first layer LL.

  In one barrier layer 41, a plurality of first layers LL are provided, and one or more second layers HL are provided. A second layer HL is provided between the plurality of first layers LL.

  In the semiconductor light emitting device 110, the In composition ratio averaged in the thickness direction of the nth barrier layer 41 (n) that is the p-side barrier layer is the first barrier layer 41 (1) that is the n-side barrier layer. ) Higher than the In composition ratio averaged in the thickness direction.

Here, the In composition ratio averaged in the thickness direction of the barrier layer 41 is referred to as an average In composition ratio.
That is, the first layer LL includes In _b1 Ga _1-b1 N (0 ≦ b1), has a thickness t _LL (nanometer), and the second layer HL includes In _b2 Ga _1-b2 N (b1 When it includes <b2) and has a thickness t _HL (nanometer), the average In composition ratio of the barrier layer 41 is defined as (b1 × t _LL + b2 × t _HL ) / (t _LL + t _HL ).

The first layer LL and the second layer HL may be provided on each of the plurality of barrier layers 41. When the first layer LL and the second layer HL are provided in the plurality of barrier layers 41, the In composition ratio b2 of the second layer HL may be different in each of the plurality of barrier layers 41.
In this case, the average In composition ratio of each of the plurality of barrier layers 41 is decreased stepwise from the barrier layer 41 close to the p-type semiconductor layer 50 to the barrier layer 41 close to the n-type semiconductor layer 50.

For example, the nth barrier layer 41 (n) which is a p-side barrier layer and the first barrier layer 41 (1) which is an n-side barrier layer are mth ( When there is a barrier layer 41 (m) where 1 <m <n), the average In composition ratio of the mth barrier layer 41 (m) is greater than the average In composition ratio of the nth barrier layer 41 (n). And the average In composition ratio of the first barrier layer 41 (1) is set higher.
As a specific example, the barrier layer 41 closer to the p-type semiconductor layer 50 has a larger In composition ratio b2, and the barrier layer 41 closer to the n-type semiconductor layer 20 has a smaller In composition ratio b2.

  In addition, the average In composition ratio of each of the plurality of barrier layers 41 need not be different from each other in all the barrier layers 41. For example, when a plurality of sets are configured with a plurality of adjacent barrier layers 41 as one set, the average In composition ratios of the same set of barrier layers 41 are equal, and the p-type semiconductor layer 50 to the n-type semiconductor layer 20 for each set. The average In composition ratio may be decreased step by step.

  For example, a set of the first barrier layer 41 (1) and the second barrier layer 41 (2), and the third barrier layer 41 (3) and the fourth barrier layer 41 (4) A set of the (n-3) th barrier layer 41 (n-3) and the (n-2) th barrier layer 41 (n-2), the (n-1) th barrier In the set of the layer 41 (n-1) and the nth barrier layer 41 (n), the average In composition ratio of the plurality of barrier layers 41 belonging to the same set is the same, and the average In composition ratio for each set May be configured to decrease from the p-type semiconductor layer 50 to the n-type semiconductor layer 20.

  When the plurality of barrier layers 41 are divided into a set on the p-type semiconductor layer 50 side (a set on the p-side) and a set on the n-type semiconductor layer 20 side (a set on the n-side), The one or more barrier layers 41 in the set have a composition ratio b21 (b21> 0), and the one or more barrier layers 41 in the n-side set have a composition ratio b22 (b22 <b21). But you can.

  By adopting such a configuration of the multiple quantum well structure of the light emitting layer 40, the quantum potential for the holes of the barrier layer 41 with respect to the well layer 42 is lowered. For this reason, hole injection in the multiple quantum well is made efficient and carrier dispersion is achieved, thereby increasing the external quantum efficiency of the LED.

Next, specific examples of the barrier layer 41 and the well layer 42 of the semiconductor light emitting device 110 according to the embodiment will be described.
In the semiconductor light emitting device 110 according to the present embodiment, the thickness t _b of the barrier layer 41 is as thin as 10 nm or less. Preferably, the thickness t _b is 3 nm or more and 8 nm or less. Thereby, holes injected from the p-type semiconductor layer 50 are efficiently supplied to the light emitting layer 40, and the light emission efficiency of the semiconductor light emitting element 110 is increased. In addition, the operating voltage of the semiconductor light emitting device 110 is reduced to a practically required level.

In the semiconductor light emitting device 110 according to this embodiment, the thickness t _LL of the first layer LL of the barrier layer 41 is preferably less than 3 nm, and more preferably about 1 nm. Thereby, the quantum potential for the hole of the barrier layer 41 with respect to the well layer 42 is lowered.

In the semiconductor light emitting device 110 according to this embodiment, the thickness t _HL of the second layer HL of the barrier layer 41 is desirably 2 nm or less. If the second layer HL is thicker than this, the crystallinity of the barrier layer 41 tends to deteriorate.

  In the semiconductor light emitting device 110 according to this embodiment, the In composition ratio b1 of the first layer LL of the barrier layer 41 is 0.02 or less, and is most preferably 0.00. If the In composition ratio is increased more than this, the crystallinity tends to deteriorate.

  In the semiconductor light emitting device 110 according to the present embodiment, the In composition ratio b2 of the second layer HL (n) of the nth barrier layer 41 (n) that is the p-side barrier layer is 0.04 or more and 0.13. It is desirable to set it as below, and it is more preferable to set it as 0.08 or more. Thereby, the reduction of the quantum potential of the barrier layer 41 with respect to the well layer 42 for holes becomes more effective.

  By configuring the barrier layer 41 having the first layer LL and the second layer HL as described above in the multiple quantum well layer, the hole injection efficiency in the quantum well layer is improved, and high light emission efficiency is realized. The

3 to 5 are diagrams illustrating examples of the In composition ratio profile of the light emitting layer.
3 to 5, the horizontal axis represents the position of the light emitting layer (position in the thickness direction), and the vertical axis represents the In composition ratio. 3 and 4 show examples of the semiconductor light emitting device according to the embodiment, and FIG. 5 shows an example of the semiconductor light emitting device according to the reference example.
The examples shown in FIGS. 3 to 5 each show an In composition ratio profile in a multiple quantum well structure in which eight barrier layers 41 and eight well layers 42 are alternately stacked.
Here, the In composition ratio profile shown in FIG. 3 is 110P, the In composition ratio profile shown in FIG. 4 is 120P, and the In composition ratio profile shown in FIG. 5 is 190P.

In the In composition ratio profile 110 </ b> P shown in FIG. 3, the average In composition ratio gradually decreases for each set of two barrier layers 41.
In the In composition ratio profile 110P, the In composition ratios of the well layers 42 (1) to 42 (8) are the same. The In composition ratio w of the well layers 42 (1) to 42 (8) is, for example, w = 0.13.

  In the barrier layer 41, the eighth barrier layer 41 (8), the seventh barrier layer 41 (7), the sixth barrier layer 41 (6), and the fifth barrier layer 41 (5) , Three first layers LL and two second layers HL are provided. Note that the In composition ratios of these first layers LL are the same. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.

Among the plurality of barrier layers 41, the In composition ratio of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7) is The same.
The In composition ratio b2 (8) of the second layers HL (8) and HL (7) is, for example, not less than 0.04 and not more than 0.13. As an example, the In composition ratio b2 (8) is b2 (8) = 0.06. The In composition ratio b2 (8) may be, for example, ½ or less of the In composition ratio w of the eighth well layer 42 (8) which is the p-side well layer.

Among the plurality of barrier layers 41, the In composition ratio of the second layer HL (6) of the sixth barrier layer 41 (6) and the second layer HL (5) of the fifth barrier layer 41 (5) is Although it is the same, it is lower than the In composition ratio of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7). The In composition ratio b2 (6) of the second layers HL (6) and HL (7) is, for example, b2 = 0.03.
With such a configuration, in the In composition ratio profile 110P, the set of the eighth barrier layer 41 (8) and the seventh barrier layer 41 (7), the sixth barrier layer 41 (6), and the In the fifth set of barrier layers 41 (5), the average In composition ratio gradually decreases.

In the In composition ratio profile 120P shown in FIG. 4, the first barrier layer 41 (1) that is the n-side barrier layer, the second to eighth barrier layers 41 (2) to 41 (n), and , The average In composition ratio is different.
In the In composition ratio profile 120P, the In composition ratio w of the well layers 42 (1) to 42 (8) is the same (for example, w = 0.13).

  In the barrier layer 41, three first layers LL and two second layers HL are provided in the second barrier layer 41 (2) to the eighth barrier layer 41 (8), respectively. The In composition ratio b1 of these first layers LL (2) to LL (8) is the same (for example, b1 = 0.00), and these second layers HL (2) to HL (8). The In composition ratio b2 is higher than the In composition ratio b1 and is the same (for example, b2 = 0.06).

  In the In composition ratio profile 190P shown in FIG. 5, the second layer HL is not provided in any barrier layer 41. That is, the In composition ratio of all the barrier layers 41 is constant.

FIG. 6A to FIG. 8D are diagrams illustrating energy band diagrams and carrier concentration distributions.
FIG. 6 shows an example of the semiconductor light emitting device 110 having the In composition ratio profile 110P shown in FIG. FIG. 7 shows an example of the semiconductor light emitting device 120 having the In composition ratio profile 120P shown in FIG. FIG. 8 shows an example of the semiconductor light emitting device 190 having the In composition ratio profile 190P shown in FIG.
In each figure, the horizontal axis represents the position (position in the thickness direction), (a) is the energy band diagram of the conductor, (b) is the energy band diagram of the valence band, and (c) is the electron concentration. , (D) show the hole concentration. Moreover, in any figure, the thick line represented to (a) and (b) has illustrated the quantum potential.

  As shown in FIGS. 8A to 8D, in the semiconductor light emitting device 190 according to the reference example, since the quantum barrier of the barrier layer 41 with respect to the well layer 42 is high, holes injected from the p-type semiconductor layer 50 are present. It is biased toward the well layer 42 close to the p-type semiconductor layer 50.

  In nitride semiconductors, the mobility of p-type carriers (holes) is low, so that the efficiency of injection of holes generated in the p-type semiconductor layer 50 of the LED into the multiple quantum well is poor. For this reason, holes are injected only into a part of the well layer 42 on the p-type semiconductor layer 50 side among the plurality of well layers 42. Therefore, the carrier density is locally increased, the Auger recombination probability is increased, and the external quantum efficiency of the LED particularly at the time of high current injection is lowered.

  As shown in the conduction band shown in FIG. 6A and the energy band diagram of the valence band shown in FIG. 6B, according to the configuration of the semiconductor light emitting device 110, compared to the semiconductor light emitting device 190 according to the reference example. Thus, the quantum barrier of the barrier layer 41 with respect to the well layer 42 is lowered. As a result, as shown in FIG. 6D, the hole injection efficiency is dramatically improved, and the light emission efficiency is dramatically increased as compared with the semiconductor light emitting device 190.

  In the conductor shown in FIG. 7A and the energy band diagram of the valence band shown in FIG. 7B, the well layer 42 is better than the energy band diagram shown in FIG. 6A and FIG. 6B. However, the quantum barrier of the barrier layer 41 with respect to the well layer 42 is lower than that of the semiconductor light emitting device 190 according to the reference example shown in FIGS. Yes. As a result, the light emitting efficiency of the semiconductor light emitting device 120 is higher than that of the semiconductor light emitting device 190 according to the reference example.

  Further, as shown in FIGS. 6A to 6D and FIGS. 7A to 7D, the closer to the n-type semiconductor layer 20, the lower the average In composition ratio of the barrier layer 41, thereby reducing the n-type. The crystallinity of the multiple quantum well structure of the light emitting layer 40 grown on the semiconductor layer 20 is improved.

Hereinafter, the examination results that led to finding the above conditions will be described.
In this examination, the semiconductor light emitting device is configured by changing the configuration of the light emitting layer 40 (the thickness of the barrier layer 41 and the modulation of the In composition ratio, the thickness of the well layer 42 and the modulation of the In composition ratio), The internal quantum efficiency in each case is compared.

(First embodiment)
The semiconductor light emitting device 111 according to the first example has an In composition ratio profile 110P shown in FIG.
The number of barrier layers 41 and well layers 42 is eight periods. Here, out of the eight-period well layers 42, the barrier layer closest to the n-type semiconductor layer 20 is defined as the first barrier layer 41 (1), and then the second-layer toward the p-type semiconductor layer 50 side. These are referred to as a barrier layer 41 (2), a third barrier layer 41 (3),..., An eighth barrier layer 41 (8).

  The In composition ratio b1 of the first layer LL (8) of the eighth barrier layer 41 (8) and the first layer LL (7) of the seventh barrier layer 41 (7) is b1 = 0.00, The In composition ratio b2 (8) of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7) is expressed as b2 (8). = 0.06.

  Next, the In composition ratio b1 of the first layer LL (6) of the sixth barrier layer 41 (6) and the first layer LL (5) of the fifth barrier layer 41 (5) is set to b1 = 0. 00, the In composition ratio b2 (6) of the second layer HL (6) of the sixth barrier layer 41 (6) and the second layer HL (5) of the fifth barrier layer 41 (5) is b2 (6) = 0.03.

  Finally, the In composition ratio of the first layers LL (4) to LL (1) of the fourth barrier layer 41 (4) to the first barrier layer 41 (1) and the second layer HL (4) The In composition ratio of .about.HL (1) is 0.00.

Further, in any of the first barrier layer 41 (1) to the eighth barrier layer 41 (8), the thickness t _LL of the first layers LL (1) to LL (8) is 1 nm, the second The thickness t _HL of the layers HL (1) to HL (8) was 1 nm, and these layers were alternately stacked for 2.5 periods so that the second layer HL would be on both sides of the barrier layer 41. Each thickness _{t b} of the first barrier layer 41 (1) to the eighth barrier layer 41 (8) is 5 nm.

(Second embodiment)
The semiconductor light emitting device 121 according to the second example has an In composition ratio profile 120P shown in FIG.

  In the semiconductor light emitting device 121, the In composition ratio of the first layers LL (2) to LL (8) for the second barrier layer 41 (2) to the eighth barrier layer 41 (8) is set to b1 = 0. 00, and the In composition ratio of the second layers HL (2) to HL (8) is b2 = 0.03. The In composition ratio of the first layer LL (1) of the first barrier layer 41 (1) and the In composition ratio of the second layer HL (2) are both 0.00. Except for these, the semiconductor light emitting device 111 is the same as that of the first embodiment.

(Reference example)
The semiconductor light emitting device 191 of the reference example has an In composition ratio profile 190P shown in FIG.

  That is, in the semiconductor light emitting device 191, all of the first barrier layer 41 (1) to the eighth barrier layer 41 (8) are GaN single layers.

In all of the In composition ratio w is 0.13 of the well layer 42 of the semiconductor light emitting elements 111, 121 and 191, and constant within the layer (i.e. _In 0.13 _{Ga 0.87} N), the thickness _{t w} is 3nm is there.
The semiconductor light emitting elements 111, 121, and 191 are blue LEDs that emit light at a dominant wavelength of 450 nm.

FIG. 9 is a diagram illustrating characteristics of the semiconductor light emitting device.
In FIG. 9, the horizontal axis represents current I (ampere: A), and the vertical axis represents internal quantum efficiency QE_AV. FIG. 9 illustrates the relationship of current I-internal quantum efficiency QE_AV for the semiconductor light emitting devices 111, 121, and 191. In FIG. 9, the internal quantum efficiency on the vertical axis is displayed as a relative value where the peak top value of the internal quantum efficiency of the semiconductor light emitting device 191 according to the reference example is “1”.

  As shown in FIG. 9, the internal quantum efficiency QE_AV of the semiconductor light emitting device 111 according to the first example is the highest, and then the internal quantum efficiency QE_AV of the semiconductor light emitting device 121 according to the second example is high. In both the semiconductor light emitting devices 111 and 121, the internal quantum efficiency QE_AV is higher than that of the semiconductor light emitting device 191 according to the reference example. For example, the internal quantum efficiency QE_AV when the current I is 0.2 A is 0.84 for the semiconductor light emitting device 111, 0.80 for the semiconductor light emitting device 121, and 0.76 for the semiconductor light emitting device 191. .

  In the semiconductor light emitting device 191, when four or more second layers HL are provided on the barrier layer on the n-type semiconductor layer side from the p-side barrier layer, the effect of improving the hole injection efficiency is small.

In the embodiment, the efficiency of hole injection is improved by providing the second layer HL in the p-side barrier layer 41 (n). At this time, as can be seen from FIG. 6D, the fourth barrier layer 41 (5) is provided on the n-type semiconductor layer 20 side from the eighth barrier layer 41 (8) which is the p-side barrier layer. )) By the time, holes have been injected efficiently. However, holes are not injected into the barrier layer on the n-type semiconductor layer 20 side more efficiently than that. For this reason, it is preferable not to put In in the barrier layers 41 that are about four or more from the p-side barrier layer 41 (n). Thereby, the average In composition ratio in the whole light emitting layer 40 can be kept low, and the lattice mismatch between the light emitting layer 40 and the n-type semiconductor layer 20 does not become excessively large. As a result, the deterioration of the crystal quality when the second layer HL containing In is provided in the barrier layer 41 is suppressed. From the viewpoint of crystal quality, it is desirable to reduce the In composition ratio of the n-type barrier layer 41 (1) (preferably to 0).
In this way, the first layer LL and the second layer HL are provided in the p-side barrier layer 41 (n) and not provided in the n-side barrier layer 41 (1) (the average In of the p-side barrier layer 41 (n) The internal quantum efficiency QE_AV is improved by the configuration in which the composition ratio is higher than the average In composition ratio of the n-side barrier layer 41 (1).

FIG. 10A to FIG. 12 are diagrams illustrating In composition ratio profiles of other semiconductor light emitting devices according to the embodiment.
10A to 12, the horizontal axis represents the position of the light emitting layer (position in the thickness direction), and the vertical axis represents the In composition ratio.
In each of the examples shown in FIGS. 10A to 12, the In composition ratio profile in a multiple quantum well structure in which eight barrier layers 41 and eight well layers 42 are alternately stacked is shown.

Here, the In composition ratio profile shown in FIG. 10A is 112P, the In composition ratio profile shown in FIG. 10B is 113P, the In composition ratio profile shown in FIG. 11A is 114P, and FIG. The In composition ratio profile shown in (b) is 115P, and the In composition ratio profile shown in FIG. 12 is 116P.
In each of the In composition ratio profiles 112P, 113P, 114P, 115P and 116P, the In composition ratio w of the well layer 42 is constant. As an example, the In composition ratio w is w = 0.13.

  In the In composition ratio profile 112P shown in FIG. 10A, the eighth barrier layer 41 (8) to the fifth barrier layer 41 (5) have two first layers LL and one second layer, respectively. A layer HL is provided. These first layers LL have the same In composition ratio. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.

Among the plurality of barrier layers 41, the In composition ratio of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7) is The same. The In composition ratio b2 (8) of the second layers HL (8) and HL (7) is, for example, b2 (8) = 0.06.
Among the plurality of barrier layers 41, the In composition ratio of the second layer HL (6) of the sixth barrier layer 41 (6) and the second layer HL (5) of the fifth barrier layer 41 (5) is The In composition ratio b2 (8) of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7) is the same. Lower than. The In composition ratio b2 (6) of the second layers HL (6) and HL (5) is, for example, b2 = 0.03.
With such a configuration, in the In composition ratio profile 112P, the set of the eighth barrier layer 41 (8) and the seventh barrier layer 41 (7), the sixth barrier layer 41 (6), and the In the fifth set of barrier layers 41 (5), the average In composition ratio gradually decreases.

  In the In composition ratio profile 113P illustrated in FIG. 10B, the first layer LL and the second layer HL are provided in the eighth barrier layer 41 (8) to the sixth barrier layer 41 (6). ing. The eighth barrier layer 41 (8) and the seventh barrier layer 41 (7) are each provided with four first layers LL and three second layers HL. The sixth barrier layer 41 (6) is provided with three first layers LL and two second layers HL. That is, the numbers of the first layer LL and the second layer HL are different between the p-side barrier layer and the m-th barrier layer 41 (m).

The In composition ratios of the first layers LL (8) to LL (6) provided in the eighth barrier layer 41 (8) to the sixth barrier layer 41 (6) are the same. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.
The In composition ratio of the second layer HL (8) of the eighth barrier layer 41 (8) and the second layer HL (7) of the seventh barrier layer 41 (7) are the same. The In composition ratio b2 (8) of the second layers HL (8) and HL (7) is, for example, b2 = 0.06.
The In composition ratio b2 (6) of the sixth second layer HL (6) is such that the second layer HL (8) of the eighth barrier layer 41 (8) and the seventh barrier layer 41 (7). Lower than the In composition ratio b2 (8) of the second layer HL (7). The In composition ratio b2 (6) of the second layer HL (6) is, for example, b2 = 0.03.

The thicknesses t _b8 and t _b7 of the eighth barrier layer 41 (8) and the seventh barrier layer 41 (7) are thicker than the thickness t _{b6 of the} sixth barrier layer 41 (6). It may be done.

  In the In composition ratio profile 114P shown in FIG. 11A, the eighth barrier layer 41 (8) to the fifth barrier layer 41 (5) have two first layers LL and one second layer, respectively. A layer HL is provided. The respective In composition ratios of the first layer LL and the second layer HL are the same as the In composition ratio profile 110P shown in FIG.

The In composition ratio of the first layer LL is the same. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.
The In composition ratio b2 (8) of the second layer HL (8) of the barrier layer 41 (8) and the second layer HL (7) of the barrier layer 41 (7) is, for example, b2 = 0.06.
The In composition ratio b2 (6) of the second layer HL (6) of the barrier layer 41 (6) and the second layer HL (5) of the barrier layer 41 (5) is, for example, b2 = 0.03.

In the In composition ratio profile 114P, as compared to the In composition ratio profile 110P, eighth well layer 42 thickness _{t w8} (8) is the nearest p-side well layer p-type semiconductor layer 50, n-type semiconductor The thickness of the first well layer 42 (1) that is the n-side well layer closest to the layer 20 is larger than the thickness _{tw 1} .

  In the In composition ratio profile 115P shown in FIG. 11B, the eighth barrier layer 41 (8) to the fifth barrier layer 41 (5) have three first layers LL and two second layers, respectively. A layer HL is provided. These first layers LL have the same In composition ratio. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.

In the In composition ratio profile 115P, the set of the eighth barrier layer 41 (8) and the seventh barrier layer 41 (7), the sixth barrier layer 41 (6), and the fifth barrier layer 41 In the group (5), the average In composition ratio gradually decreases.
However, in the In composition ratio profile 115P, in each barrier layer 41 of the eighth barrier layer 41 (8) to the fifth barrier layer 41 (5), there is a difference in the In composition ratio of the plurality of second layers HL. Is provided.

  The In composition ratio of the plurality of second layers HL provided in the respective barrier layers 41 of the eighth barrier layer 41 (8) to the fifth barrier layer 41 (5) is that of the p-type semiconductor layer 50. The height increases from the side toward the n-type semiconductor layer 20 side.

  For example, the second barrier layer 41 (8) is provided with two second layers HL (8) a and HL (8) b. In the two second layers HL (8) a and HL (8) b, the In composition ratio b2 (8) b of the second layer HL (8) b provided on the p-type semiconductor layer 50 side is the n-type semiconductor. The In composition ratio b2 (8) a of the second layer HL (8) a provided on the layer 20 side is higher.

  Similarly, the second barrier layer 41 (7) is provided with two second layers HL (7) a and HL (7) b. In the two second layers HL (7) a and HL (7) b, the In composition ratio b2 (8) b of the second layer HL (7) b provided on the p-type semiconductor layer 50 side is the n-type semiconductor. The In composition ratio b2 (8) a of the second layer HL (7) a provided on the layer 20 side is higher.

  The sixth barrier layer 41 (6) is provided with two second layers HL (6) a and HL (6) b. In the two second layers HL (6) a and HL (6) b, the In composition ratio b2 (6) b of the second layer HL (6) b provided on the p-type semiconductor layer 50 side is the n-type semiconductor. The In composition ratio b2 (6) a of the second layer HL (6) a provided on the layer 20 side is higher.

  Similarly, two second layers HL (5) a and HL (5) b are provided in the fifth barrier layer 41 (5). In the two second layers HL (5) a and HL (5) b, the In composition ratio b2 (6) b of the second layer HL (5) b provided on the p-type semiconductor layer 50 side is the n-type semiconductor. The In composition ratio b2 (6) a of the second layer HL (5) a provided on the layer 20 side is higher.

Of the plurality of second layers HL of the barrier layers 41 (8) and 41 (7), the In composition ratio b2 (8) b on the higher In composition ratio side is, for example, b2 (8) b = 0.06. .
Of the plurality of second layers HL of the barrier layers 41 (8) and 41 (7), the In composition ratio b2 (8) a on the lower In composition ratio is, for example, b2 (8) a = 0.04. .

Of the plurality of second layers HL of the barrier layers 41 (6) and 41 (5), the In composition ratio b2 (6) b on the higher In composition ratio side is, for example, b2 (6) b = 0.03. .
Of the plurality of second layers HL of the barrier layers 41 (6) and 41 (5), the In composition ratio b2 (6) a on the lower In composition ratio is, for example, b2 (6) a = 0.01. .

  In the In composition ratio profile 116P shown in FIG. 12, the first barrier layer 41 (8) to the fifth barrier layer 41 (5) have three first layers LL and two second layers HL, respectively. Is provided. These first layers LL have the same In composition ratio. The In composition ratio b1 of the first layer LL is, for example, b1 = 0.00.

In the In composition ratio profile 116P, the eighth barrier layer 41 (8), the seventh barrier layer 41 (7), the sixth barrier layer 41 (6), and the fifth barrier layer 41 (5). In this order, the average In composition ratio gradually decreases.
The In composition ratio b2 (8) of the plurality of second layers HL (8) of the barrier layer 41 (8) is, for example, b2 (8) = 0.06.
The In composition ratio b2 (7) of the plurality of second layers HL (7) of the barrier layer 41 (7) is, for example, b2 (7) = 0.05.
The In composition ratio b2 (6) of the plurality of second layers HL (6) of the barrier layer 41 (6) is, for example, b2 (6) = 0.04.
The In composition ratio b2 (5) of the plurality of second layers HL (5) of the barrier layer 41 (5) is, for example, b2 (5) = 0.03.

Hereinafter, with respect to the present embodiment, an example of characteristics when the configuration of the multiple quantum well structure is changed will be described. In this example, the configuration of the second layer HL is changed.
13 and 14 are diagrams illustrating characteristics of the semiconductor light emitting device.
13 and 14, the horizontal axis represents current I (A) and the vertical axis represents internal quantum efficiency IQE.
FIG. 13 shows the internal quantum efficiency QE11 according to the first configuration and the internal quantum efficiency QE12 according to the second configuration. The internal quantum efficiency QE0 is the internal quantum efficiency when 190P is used as the In composition ratio profile according to the reference example.

  The first configuration and the second configuration have a multiple quantum well structure in which eight barrier layers 41 and eight well layers 42 are alternately stacked, and the eighth barrier layer 41 (8) to the second one. Each of the barrier layers 41 (2) is provided with two first layers LL and one second layer HL.

Among these, in the first configuration (internal quantum efficiency QE11), the In composition ratio b2 of the second layer HL is the same as the In composition ratio w of the well layer 42 (for example, b2 = w = 0.13).
In the second configuration (internal quantum efficiency QE12), the In composition ratio b2 of the second layer HL is lower than the In composition ratio w of the well layer 42 (for example, w = 0.13, b2 = 0.08). ).

  FIG. 14 shows the internal quantum efficiency QE21 according to the third configuration and the internal quantum efficiency QE22 according to the fourth configuration. The internal quantum efficiency QE0 is the internal quantum efficiency when 190P is used as the In composition ratio profile according to the reference example, as in FIG.

  The third configuration and the fourth configuration are multi-quantum well structures in which eight barrier layers 41 and eight well layers 42 are alternately stacked, and the eighth barrier layer 41 (8) to the second one. The barrier layer 41 (2) is provided with three first layers LL and two second layers HL, respectively.

In the third configuration (internal quantum efficiency QE21), the In composition ratio b2 of the second layer HL is the same as the In composition ratio w of the well layer 42 (for example, b2 = w = 0.13).
In the fourth configuration (internal quantum efficiency QE22), the In composition ratio b2 of the second layer HL is lower than the In composition ratio w of the well layer 42 (for example, w = 0.13, b2 = 0.08).

  As shown in FIG. 13, the internal quantum efficiency QE11 according to the first configuration and the internal quantum efficiency QE12 according to the second configuration are both higher than the internal quantum efficiency QE0 according to the reference example. Also, the internal quantum efficiency QE11 is higher than the internal quantum efficiency QE12. When one barrier layer 41 is provided with one second layer HL, the quantum efficiency increases when the In composition ratio of the second layer HL is high.

  As shown in FIG. 14, the internal quantum efficiency QE21 according to the third configuration and the internal quantum efficiency QE22 according to the fourth configuration are both higher than the internal quantum efficiency QE0 according to the reference example. The internal quantum efficiency QE21 is substantially equal to the internal quantum efficiency QE22. When two barrier layers 41 are provided with two second layers HL, good internal quantum efficiency can be obtained regardless of the In composition ratio of the second layer HL.

  From the results shown in FIGS. 13 and 14, by providing two second layers HL in one barrier layer 41, good internal quantum can be achieved even if the In composition ratio per one second layer HL is lowered. It can be seen that efficiency can be obtained.

  In the embodiments and examples described above, the composition ratio of In in the group III elements of the first layer LL and the second layer HL has been described. However, composition ratios other than In are applicable.

  According to the embodiment, a semiconductor light emitting device with high luminous efficiency is provided.

In this specification, “nitride semiconductor” means B _α In _β Al _γ Ga _1-α-β-γ N (0 ≦ α ≦ 1, 0 ≦ β ≦ 1, 0 ≦ γ ≦ 1, α + β + γ ≦ 1) Semiconductors having all composition ratios in which the composition ratios α, β, and γ are changed within the respective ranges are included. Furthermore, in the above chemical formula, those that further include a group V element other than N (nitrogen), and those that further include any of various dopants added to control the conductivity type, etc. Shall be included.

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, the shape, size, material, and arrangement relationship of the specific configuration of each element of the n-type semiconductor layer, p-type semiconductor layer, active layer, well layer, barrier layer, electrode, substrate, and buffer layer included in the semiconductor light emitting device Even if the person skilled in the art has made various changes with respect to the above, etc., as long as the person skilled in the art can implement the present invention in the same manner by selecting appropriately from the well-known range and obtain the same effect, Included in the range.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

 DESCRIPTION OF SYMBOLS 10 ... Substrate, 11 ... Buffer layer, 20 ... N-type semiconductor layer, 21 ... Underlayer, 22 ... Contact layer, 30 ... Laminate, 31 ... First crystal layer, 32 ... Second crystal layer, 40 ... Light emitting layer, 41 ... barrier layer, 42 ... well layer, 50 ... p-type semiconductor layer, 51 ... p-type AlGaN layer, 52 ... Mg-doped GaN layer, 53 ... contact layer, 60 ... transparent electrode, 70 ... n-side electrode, 80 ... p Side electrode, 110, 111, 121, 190, 191 ... semiconductor light emitting device, LL ... first layer, HL ... second layer

Claims (7)

An n-type semiconductor layer including a nitride semiconductor;
A p-type semiconductor layer including a nitride semiconductor;
A light emitting layer provided between the n-type semiconductor layer and the p-type semiconductor layer;
With
The light emitting layer includes a plurality of barrier layers and a plurality of well layers stacked alternately,
The p-side barrier layer closest to the p-type semiconductor layer among the plurality of barrier layers is
A first layer containing a group III element;
A second layer stacked with the first layer and containing a group III element, wherein the In composition ratio in the group III element of the second layer is higher than the In composition ratio in the group III element of the first layer The second layer,
Including
A plurality of the first layers are provided,
A plurality of the second layers are provided,
The plurality of first layers and the plurality of second layers are alternately arranged,
One of the plurality of first layers is in contact with one of the plurality of well layers;
Another one of the plurality of first layers is in contact with another one of the plurality of well layers;
Each of the plurality of first layers has a thickness of 1 nanometer or less.   The semiconductor light emitting element according to claim 1, wherein the second layer has a thickness of 2 nanometers or less. The plurality of barrier layers include an intermediate barrier layer between the p-side barrier layer and the n-side barrier layer,
The intermediate barrier layer is
A third layer containing a group III element;
A fourth layer laminated with the third layer and containing a group III element, wherein the In composition ratio in the group III element of the fourth layer is higher than the In composition ratio in the group III element of the third layer A fourth layer,
3. The semiconductor light emitting device according to claim 1, wherein an average In composition ratio of the intermediate barrier layer is lower than the average In composition ratio of the p-side barrier layer and higher than the average In composition ratio of the n-side barrier layer. element. The In composition ratio of the first layer is 0.02 or less,
4. The semiconductor light emitting element according to claim 1, wherein the In composition ratio of the second layer is 0.13 or less.   The In composition ratio of the second layer is ½ or less of an In composition ratio of a p-side well layer closest to the p-type semiconductor layer among the plurality of well layers. The semiconductor light emitting element as described in one.   The thickness of the p-side well layer closest to the p-type semiconductor layer among the plurality of well layers is thicker than the thickness of the n-side well layer closest to the n-type semiconductor layer among the plurality of well layers. The semiconductor light-emitting device according to claim 1. Each of the plurality of barrier layers has a thickness of 10 nanometers or less;
7. The semiconductor light emitting element according to claim 1, wherein each of the plurality of well layers has a thickness of 3 nanometers or more and 6 nanometers or less.

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