Semiconductor light emitting device with an aluminum containing layer formed thereon

According to one embodiment, a semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, a well layer, a barrier layer, an Al-containing layer, and an intermediate layer. The p-type semiconductor layer is provided on a side of [0001] direction of the n-type semiconductor layer. The well layer, the barrier layer, the Al-containing layer and the intermediate layer are disposed between the n-type semiconductor layer and the p-type semiconductor layer subsequently. The Al-containing layer has a larger band gap energy than the barrier layer, a smaller lattice constant than the n-type semiconductor layer, and a composition of Alx1Ga1-x1-y1Iny1N. The intermediate layer has a larger band gap energy than the well layer, and has a first portion and a second portion provided between the first portion and the p-type semiconductor layer. A band gap energy of the first portion is smaller than that of the second portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-155591, filed on Jul. 8, 2010; the entire contents of which are incorporated herein by reference.

FIELD

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

BACKGROUND

A need for improvement of luminous efficiency in semiconductor light emitting devices such as Laser Diodes (LD), Light Emitting Diodes (LED) and the like is desired.

For example, various configurations have been proposed to suppress electron overflow in active layers in order to improve luminous efficiency. However, there is still room for further improvement of luminous efficiency.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, a first well layer, a first barrier layer, an Al-containing layer, and an intermediate layer. The n-type semiconductor layer includes a nitride semiconductor. The p-type semiconductor layer is provided on a side of [0001] direction of the n-type semiconductor layer and includes a nitride semiconductor. The first well layer is provided between the n-type semiconductor layer and the p-type semiconductor layer. The first well layer has a band gap energy smaller than a band gap energy of the n-type semiconductor layer and smaller than a band gap energy of the p-type semiconductor layer, and includes a nitride semiconductor. The first barrier layer is provided between the first well layer and the n-type semiconductor layer, and is in contact with the first well layer. The first barrier layer has a band gap energy larger than the band gap energy of the first well layer, and includes a nitride semiconductor. The Al-containing layer is provided between the first well layer and the p-type semiconductor layer, and is in contact with the first well layer. The Al-containing layer has a band gap energy larger than the band gap energy of the first barrier layer, has a lattice constant smaller than a lattice constant of the n-type semiconductor layer, and has a composition of Alx1Ga1-x1-y1Iny1N (where 0<x1<1 and 0≦y1<1). The intermediate layer is provided between the Al-containing layer and the p-type semiconductor layer, is in contact with the Al-containing layer, has a band gap energy larger than the band gap energy of the first well layer, and includes a nitride semiconductor. The intermediate layer has a first portion and a second portion provided between the first portion and the p-type semiconductor layer. A band gap energy of the first portion is smaller than a band gap energy of the second portion.

An embodiment of the invention will now be described with reference to the drawings.

Drawings are schematic or simplified illustrations and that relationships between thicknesses and widths of parts and proportions in size between parts may differ from actual parts. Also, even where identical parts are depicted, mutual dimensions and proportions may be illustrated differently depending on the drawing.

Drawings and specification of this application, the same numerals are applied to constituents that have already appeared in the drawings and been described, and repetitious detailed descriptions of such constituents are omitted as appropriate.

FIG. 1is a schematic cross-sectional view illustrating a configuration of a semiconductor light emitting device according to an embodiment.

As illustrated inFIG. 1, a semiconductor light emitting device110according to the embodiment includes an n-type semiconductor layer10, a p-type semiconductor layer20, a first well layer31a, a first barrier layer32a, an Al-containing layer40, and an intermediate layer50.

The n-type semiconductor layer10includes a nitride semiconductor.

The p-type semiconductor layer20is provided in a side of [0001] direction of the n-type semiconductor layer10. The p-type semiconductor layer20includes a nitride semiconductor.

The first well layer31ais provided between the n-type semiconductor layer10and the p-type semiconductor layer20. The first well layer31ahas a band gap energy smaller than a band gap energy of the n-type semiconductor layer10and smaller than a band gap energy of the p-type semiconductor layer20. The first well layer31aincludes a nitride semiconductor.

The first barrier layer32ais provided between the first well layer31aand the n-type semiconductor layer10and is in contact with the first well layer31a. The first barrier layer32ahas a band gap energy larger than the band gap energy of the first well layer31a. The first well layer31aincludes a nitride semiconductor.

The Al-containing layer40is provided between the first well layer31aand the p-type semiconductor layer20and is in contact with the first well layer31a. The Al-containing layer40has a band gap energy larger than the band gap energy of the first barrier layer32a. The Al-containing layer40has a lattice constant that is smaller than a lattice constant of the n-type semiconductor layer10. A composition of the Al-containing layer40is Alx1Ga1-x1-y1Iny1N (where 0<x1<1 and 0≦y1<1).

The intermediate layer50is provided between the Al-containing layer40and the p-type semiconductor layer20and is in contact with the Al-containing layer40. The intermediate layer50has a band gap energy larger than the band gap energy of the first well layer31a. The intermediate layer50includes nitride semiconductor.

A band gap energy of a portion on the n-type semiconductor layer10side of the intermediate layer50is smaller than a band gap energy of a portion on the p-type semiconductor layer20side of the intermediate layer50.

The band gap energy of the intermediate layer50is smaller than or equal to the band gap energy of the p-type semiconductor layer20. In other words, the band gap energy of the portion (the first portion) on the n-type semiconductor layer10side of the intermediate layer50is smaller than or equal to the band gap energy of the p-type semiconductor layer20.

Undoped InGaN, for example, is used for the intermediate layer50. In the intermediate layer50, by setting an In composition ratio of the portion on the Al-containing layer40side to be higher than that of the portion on the p-type semiconductor layer20side, the band gap energy of the portion on the n-type semiconductor layer10side of the intermediate layer50is set smaller than the band gap energy of the portion on the p-type semiconductor layer20side of the intermediate layer50.

For example, the band gap energy of the intermediate layer50increases with movement from the n-type semiconductor layer10side to the p-type semiconductor layer20side.

In this embodiment, the semiconductor light emitting device110further includes a second well layer31b, a second barrier layer32b, a third well layer31c, and a third barrier layer32c.

The second well layer31bis provided between the first barrier layer32aand the n-type semiconductor layer10and is in contact with the first barrier layer32a. The second well layer31bhas a band gap energy smaller than the band gap energy of the first barrier layer32a, smaller than the band gap energy of the Al-containing layer40, and smaller than the band gap energy of the intermediate layer50. The second well layer31bincludes a nitride semiconductor.

The second barrier layer32bis provided between the second well layer31band the n-type semiconductor layer10and is in contact with the second well layer31b. The second barrier layer32bhas a band gap energy larger than the band gap energy of the second well layer31band smaller than the band gap energy of the Al-containing layer40. The second barrier layer32bincludes a nitride semiconductor.

The third well layer31cis provided between the second barrier layer32band the n-type semiconductor layer10and is in contact with the second barrier layer32b. The third well layer31chas a band gap energy smaller than the band gap energy of the second barrier layer32b, smaller than the band gap energy of the Al-containing layer40, and smaller than the band gap energy of the intermediate layer50. The third well layer31cincludes a nitride semiconductor.

The third barrier layer32cis provided between the third well layer31cand the n-type semiconductor layer10and is in contact with the third well layer31c. The third barrier layer32chas a band gap energy larger than the band gap energy of the third well layer31cand smaller than the band gap energy of the Al-containing layer40. The third barrier layer32cincludes a nitride semiconductor.

In this example, a Multi Quantum Well structure provided with three of the well layers31is used. However, the embodiment is not limited thereto, and the number of the well layers31in the Multi Quantum Well structure can be set as desired. In the embodiment, a Single Quantum Well structure having one of the well layers31may be used.

When providing a plurality of the well layers31, the number of the well layers31is defined as well layer number N (where N is an integer greater than or equal to 2). A first of the well layers31is disposed on the side closest to the p-type semiconductor layer20among the plurality of the well layers31. An Nth of the well layers31is disposed on the side closest to the n-type semiconductor layer10among the plurality of the well layers31. The first well layer31ato the Nth well layer are collectively referred to as the well layers31. Each of the plurality of the well layers31correspond with the first well layer31a, the second well layer31b, the third well layer31c, and the like.

The barrier layers32are provided on the n-type semiconductor layer10side of each of the plurality of the well layers31. In other words, an Nth barrier layer is provided on the n-type semiconductor layer10side of the Nth well layer. The first barrier layer32ato the Nth barrier layer are collectively referred to as the barrier layers32. Each of the plurality of the barrier layers32correspond with the first barrier layer32a, the second barrier layer32b, the third barrier layer32c, and the like.

The Nth well layer is provided between an (N−1)th barrier layer and the n-type semiconductor layer10and is in contact with the (N−1)th barrier layer. The Nth well layer has a band gap energy smaller than the band gap energy of the (N−1)th barrier layer, smaller than the band gap energy of the Al-containing layer40, and smaller than the band gap energy of the intermediate layer50. The Nth well layer includes a nitride semiconductor.

The Nth barrier layer is provided between the Nth well layer and the n-type semiconductor layer10and is in contact with the Nth well layer. The Nth barrier layer has a band gap energy larger than the band gap energy of the Nth well layer and smaller than the band gap energy of the Al-containing layer40. The Nth barrier layer includes a nitride semiconductor.

The band gap energy of the Al-containing layer40is larger than the band gap energy of the Nth barrier layer. The band gap energy of the intermediate layer50is larger than the band gap energy of the Nth well layer.

InwGa1-wN (where 0<w≦1) is used, for example, for the well layers31(i.e., the first well layer31aetc.). An In composition ratio of the well layers31(well layer In composition ratio w) is, for example, not less than 0.01 and not more than 0.5. The well layer In composition ratio w is, for example, 0.07. In0.07Ga0.93N is used, for example, for the well layers31.

Alb2Inb1Ga1-b1-b2N (where 0≦b1<1, 0≦b2<1 and 0≦b1+b2≦1) is used, for example, for the barrier layers32(i.e., the first barrier layer32aetc.). An In composition ratio of the barrier layers32(barrier layer In composition ratio b1) is, for example, not less than 0.005 and is not more than the well layer In composition ratio w. The barrier layer In composition ratio b1 is, for example, 0.01. A barrier layer Al composition ratio b2 is, for example, 0. In0.01Ga0.99N is used, for example, for the barrier layers32.

Thereby the band gap energy of the barrier layer32becomes larger than the band gap energy of the well layers31.

However, the embodiment is not limited thereto, and compositions of the well layers31and the barrier layer32may be varied as desired as long as the band gap energy of the well layers31is smaller than the band gap energy of the barrier layer32.

A thickness of the well layers31is, for example, not less than 1 nanometer (nm) and not more than 10 nm. If the thickness of the well layers31is less than 1 nm, the characteristics of confining carriers in the well layers31will be reduced and a high luminous efficiency will not be obtained. If the thickness of the well layers31exceeds 10 nm, the crystal will degrade significantly. A thickness of the well layers31is, for example, 3 nm.

A thickness of the barrier layers32is, for example, 3 nm or more. If the thickness of the barrier layer32is less than 3 nm, the characteristics of confining carriers in the well layers31will be reduced and a high luminous efficiency will not be obtained. A thickness of the barrier layers32is, for example, 10 nm.

The wavelength (for example, a dominant wavelength) of the light emitted from the well layers31(i.e., the first well layer31aetc.) is not less than 330 nm and not more than 580 nm. Conditions of the material used for the well layers31are set appropriately so that such light will be emitted.

Here, as illustrated inFIG. 1, a direction from the n-type semiconductor layer10toward the p-type semiconductor layer20is defined as the +Z-axis direction. The p-type semiconductor layer20is disposed in the +Z-axis direction of the n-type semiconductor layer10.

A plane on a side of the +Z-axis direction of the n-type semiconductor layer10is, for example, a (0001) plane. The first barrier layer32ais provided on a side of this (0001) plane, the first well layer31ais provided on the side of the +Z-axis direction of the first barrier layer32a, the Al-containing layer40is provided on a side of the +Z-axis direction of the first well layer31a, the intermediate layer50is provided on a side of the +Z-axis direction of the Al-containing layer40, and the p-type semiconductor layer20is provided on a side of the +Z-axis direction of the intermediate layer50.

However, the plane of the side of the +Z-axis direction of the n-type semiconductor layer10need not be an exact (0001) plane, and may be a plane inclined from the exact (0001) plane at an offset angle. This offset angle is, for example, not less than 0 degrees and not more than 3 degrees. The state where the p-type semiconductor layer20is provided on the side of the [0001] direction of the n-type semiconductor layer10includes such cases where the face in the +Z-axis direction of the n-type semiconductor layer10is inclined from the (0001) plane.

As illustrated inFIG. 1, the crystal of the n-type semiconductor layer10is grown on a buffer layer6provided on a major surface of a substrate5that is, for example, a c-plane sapphire substrate. Moreover, crystals of the first barrier layer32a, the first well layer31a, the Al-containing layer40, the intermediate layer50, and the p-type semiconductor layer20are subsequently grown on the n-type semiconductor layer10. In the semiconductor light emitting device110, the substrate5and the buffer layer6are provided, but after the growing of the crystals described above, the substrate5and the buffer layer6may be removed.

In this example, the n-type semiconductor layer10has an n-side contact layer11provided on the substrate5side and an n-side cladding layer12provided on the first barrier layer32aside. A portion of the n-side contact layer11is exposed, and an n-side electrode70is provided so as to be electrically connected to the n-side contact layer11.

The p-type semiconductor layer20has a p-side cladding layer21provided on the intermediate layer50side and a p-side contact layer22provided on the side of the p-side cladding layer21opposite the intermediate layer50. A p-side electrode80is provided so as to be electrically connected to the p-side contact layer22.

Thereby, the semiconductor light emitting device110includes a stacked structural body10s. The stacked structural body10sincludes the n-type semiconductor layer10, the p-type semiconductor layer20, and the light emitting part (for example, the first barrier layer32a, the first well layer31a, the Al-containing layer40, and the intermediate layer50) provided between the n-type semiconductor layer10and the p-type semiconductor layer20. The stacked structural body10shas a first major surface10aof the p-type semiconductor layer20side, and a second major surface10bof the n-type semiconductor layer10side.

In this example, the p-type semiconductor layer20and the light emitting part are selectively removed, and a portion10pof the n-type semiconductor layer10(a portion of the n-side contact layer11) is exposed to the first major surface10aof the stacked structural body10s. The n-side electrode70is provided on the exposed portion10pof the n-type semiconductor layer10.

However, the embodiment is not limited thereto, and, for example, the n-side electrode70may be provided on the second major surface10bside of the n-type semiconductor layer10.

GaN doped with a high concentration of Si is used, for example, for the n-side contact layer11. The concentration of Si in the n-side cladding layer12is lower than in the n-side contact layer11. GaN doped with Si or AlGaN doped with Si is used, for example, for the n-side cladding layer12.

GaN doped with a high concentration of Mg is used, for example, for the p-side contact layer22. The concentration of Mg in the p-side cladding layer21is lower than in the p-side contact layer22. GaN doped with Mg or AlGaN doped with Mg is used, for example, for the p-side cladding layer21.

The n-side cladding layer12and the p-side cladding layer21can be designed so as to have a waveguide function with regards to the light emitted from the well layers31. In other words, the semiconductor light emitting device110can be made into a Laser Diode (LD). Additionally, the semiconductor light emitting device110may be an LED.

Hereinafter, a case in which the semiconductor light emitting device110is an LD will be described.

FIGS. 2A and 2Bare schematic diagrams illustrating the configuration of a semiconductor light emitting device according to the embodiment.

Specifically,FIG. 2Ais a schematic cross-sectional view illustrating the configuration of the semiconductor light emitting device110andFIG. 2Bis a graph showing the In composition ratio of the semiconductor light emitting device110. The horizontal axis inFIG. 2Brepresents position in the +Z-axis direction and the vertical axis represents In composition ratio CIn.

As illustrated inFIGS. 2A and 2B, the In composition ratio (the barrier layer In composition ratio b1) of the barrier layers32(the first to the third barrier layers32ato32c) is 0.01. The In composition ratio (the well layer In composition ratio w) of the well layers31(the first to the third well layers31ato31c) is 0.07.

In this example, Al0.05Ga0.95N is used for the Al-containing layer40. In other words, the In composition ratio of the Al-containing layer40is substantially 0.

InGaN is used for the intermediate layer50, and the In composition ratio of a portion of the intermediate layer50on the n-type semiconductor layer10side (first portion55) is 0.03, and the In composition ratio of a portion of the intermediate layer50on the p-type semiconductor layer20side (second portion56) is 0.01.

Thus, the In composition ratio of the first portion55of the intermediate layer50is higher than 0 and lower than the In composition ratio of the well layers31(i.e. the first well layer31a).

Moreover, in this example, the In composition ratio of the intermediate layer50decreases continuously from the portion on the n-type semiconductor layer10side (the first portion55) toward the portion on the p-type semiconductor layer20side (the second portion56). Thus, the In composition ratio of the intermediate layer50is inclined.

As discussed hereinafter, the state of variation of the In composition ratio of the intermediate layer50may be set as desired. The In composition ratio of the intermediate layer50may decrease continuously in a linear manner or in a curved manner or stepwise along the direction (with movement in the +Z-axis direction) from the Al-containing layer40toward the p-type semiconductor layer20.

Thus, in the intermediate layer50, by setting the In composition ratio of the first portion55on the n-type semiconductor layer10side to be higher than the In composition ratio of the second portion56on the p-type semiconductor layer20side, a band gap energy of the first portion55is set to be smaller than a band gap energy of the second portion56.

Thus, the intermediate layer50includes the first portion55and the second portion56provided between the first portion55and the p-type semiconductor layer20. The band gap energy of the first portion55is smaller than the band gap energy of the second portion56.

As illustrated inFIG. 2A, in this example, a p-side barrier layer32pis provided between the intermediate layer50and the p-type semiconductor layer20. InGaN is used for the p-side barrier layer32p, and the In composition ratio of the p-side barrier layer32pis set to 0.01. In other words, the same material used for the first to the third barrier layers32ato32cis used for the p-side barrier layer32p.

FIGS. 3A to 3Dare schematic diagrams illustrating band gap energies in semiconductor light emitting devices.

Specifically,FIG. 3Acorresponds to the semiconductor light emitting device110according to the embodiment, andFIGS. 3B to 3Dcorrespond to semiconductor light emitting devices119ato119cof the first to the third reference examples. In these drawings, the horizontal axis represents position in the +Z-axis direction, and the vertical axis represents a band gap energy Eb. Energy of a conduction band Bc and energy of a valence band By are shown schematically in these drawings.

As illustrated inFIG. 3A, in the semiconductor light emitting device110according to this embodiment, the band gap energies of the first to the third well layers31ato31care smaller than the band gap energies of the first to the third barrier layers32ato32c.

The band gap energy of the Al-containing layer40in contact with the first well layer31a, which is the closest to the p-type semiconductor layer20among the well layers31, is set to be larger than the band gap energy of the first to the third barrier layers32ato32c.

The band gap energy of the first portion55on the n-type semiconductor layer10side of the intermediate layer50is smaller than the band gap energy of the second portion56on the p-type semiconductor layer20side of the intermediate layer50.

In this example, the band gap energy of the p-side barrier layer32pis the same as the band gap energy of the first to the third barrier layers32ato32c.

In this example, the band gap energy of the intermediate layer50increases continuously in a linear manner along the +Z-axis direction.

However, as previously described, the state of variation of the In composition ratio of the intermediate layer50may be set as desired, and the band gap energy of the intermediate layer50may increase continuously in a curved manner along the +Z-axis direction. The band gap energy of the intermediate layer50may also increase stepwise along the +Z-axis direction.

The band gap energy of the first portion55of the intermediate layer50(the portion on the n-type semiconductor layer10side) is smaller than the band gap energy of the first to the third barrier layers32ato32c. Furthermore, the band gap energy of the first portion55is smaller than the band gap energy of the p-type semiconductor layer20(omitted inFIG. 3A).

The band gap energy of the second portion56of the intermediate layer50(the portion on the p-type semiconductor layer20side) is smaller than or equal to the band gap energy of the p-type semiconductor layer20(omitted inFIG. 3A).

As illustrated inFIG. 3B, in the semiconductor light emitting device119aof the first reference example, the Al-containing layer40and the intermediate layer50are not provided. In other words, the p-side barrier layer32pis provided in contact with the first well layer31a.

As illustrated inFIG. 3C, in the semiconductor light emitting device119bof the second reference example, an intermediate barrier layer32qis provided in contact with a face of the p-type semiconductor layer20side of the first well layer31a, and a reverse inclined layer59ris provided in contact with a face of the p-type semiconductor layer20side of the intermediate barrier layer32q. A band gap energy of a portion on the n-type semiconductor layer10side of the reverse inclined layer59ris larger than a band gap energy of a portion on the p-type semiconductor layer20side of the reverse inclined layer59r. In other words, an incline direction of the band gap energy of the reverse inclined layer59ris the opposite of a direction of an incline direction of the band gap energy of the intermediate layer50of the semiconductor light emitting device110. Moreover, the p-side barrier layer32pis provided on the p-type semiconductor layer20side of the reverse inclined layer59r.

As illustrated inFIG. 3D, in the semiconductor light emitting device119cof the third reference example, the intermediate barrier layer32qis provided in contact with a face of the p-type semiconductor layer20side of the first well layer31a. The Al-containing layer40is provided in contact with a face of the p-type semiconductor layer20side of the intermediate barrier layer32q. The intermediate layer50is provided in contact with a face of the p-type semiconductor layer20side of the Al-containing layer40. Furthermore, the p-side barrier layer32pis provided in contact with a face of the p-type semiconductor layer20side of the intermediate layer50. In other words, the configuration of the semiconductor light emitting device119cof the third reference example corresponds with the configuration in which the intermediate barrier layer32qis provided between the Al-containing layer40and the first well layer31ain the semiconductor light emitting device110according to this embodiment.

Hereinafter, results of simulations of the characteristics of the semiconductor light emitting devices110and119ato119cthat have the configurations will be described.

FIGS. 4A to 4Care schematic diagrams illustrating the configuration and characteristics of the semiconductor light emitting device according to the embodiment.

FIG. 4Ais a schematic cross-sectional view illustrating the configuration of the semiconductor light emitting device110.FIG. 4Bis a schematic diagram illustrating the simulation results of the band gap energy.FIG. 4Cis a schematic diagram illustrating the simulation results of an electron wave function WF1and a hole wave function WF2. In the hole wave function WF2, a light hole wave function and a heavy hole wave function were simulated, but since both were substantially consistent, the simulation results are represented by a single line. The horizontal axis inFIGS. 4B and 4Crepresent a position ZD along the +Z-axis direction.

As illustrated inFIG. 4A, in this simulation, a thickness of the third barrier layer32cwas 40 nm, and thicknesses of the first barrier layer32aand the second barrier layer32bwere 10 nm. The thicknesses of the first to the third well layers31ato31cwere 3 nm. A thickness of the Al-containing layer40was 3 nm. A thickness of the intermediate layer50was 20 nm. A thickness of the p-side barrier layer32pwas 17 nm.

In0.07Ga0.93N was used for the first to the third well layers31ato31c. In0.01Ga0.99N was used for the first to the third barrier layers32ato32cand the p-side barrier layer32p. Al0.05Ga0.95N was used for the Al-containing layer40. InGaN was used for the intermediate layer50, In0.03Ga0.97N was used for the portion (the first portion55) on the n-type semiconductor layer10side, and In0.01Ga0.99N was used for the portion (the second portion56) on the p-type semiconductor layer20side. The In composition ratio of the intermediate layer50was made to vary in a linear manner.

As illustrated inFIG. 4B, in the simulation results, a high barrier to electrons and holes is formed in a vicinity of an interface between the first well layer31aand the Al-containing layer40.

As illustrated inFIG. 4C, in the electron wave function WF1on the p-type semiconductor layer20side, a tail portion201is small. Electrons are efficiently confined in the interface between the first well layer31aand the Al-containing layer40. In other words, in the semiconductor light emitting device110, the electrons in the first well layer31aare more localized.

Four peaks are shown in the hole wave function WF2. Specifically, three peaks that respectively correspond to the first to the third well layers31ato31c, and a fourth peak that corresponds to a portion in the vicinity of the interface between the Al-containing layer40and the intermediate layer50are shown. The appearance of this fourth peak corresponds to holes being efficiently injected into the vicinity of the interface between the Al-containing layer40and the intermediate layer50. In other words, in the semiconductor light emitting device110, injection efficiency of holes into the Multiple Quantum Wells (MQW including the first to the third well layers31ato31c) is high.

FIGS. 5A to 5Care schematic diagrams illustrating the configuration and characteristics of the semiconductor light emitting device of the first reference example.

As illustrated inFIG. 5A, in the semiconductor light emitting device119a, the Al-containing layer40and the intermediate layer50were not provided, and the thickness of the p-side barrier layer32pwas 40 nm. The material of the p-side barrier layer32pwas set to be the same as in the semiconductor light emitting device110. The thicknesses and materials of the first to the third well layers31ato31cand the first to the third barrier layers32ato32cwere set to be the same as in the semiconductor light emitting device110.

As illustrated inFIG. 5B, in the simulation results, a barrier to the first well layer31ahas smaller energy on the p-side barrier layer32pside.

As illustrated inFIG. 5C, in the electron wave function WF1on the p-type semiconductor layer20side, a tail portion209ais large. In other words, in the semiconductor light emitting device119a, the electrons in the first well layer31aare not sufficiently confined in the first well layer31a.

FIGS. 6A to 6Care schematic diagrams illustrating the configuration and characteristics of the semiconductor light emitting device of the second reference example.

As illustrated inFIG. 6A, in the semiconductor light emitting device119b, a thickness of the intermediate barrier layer32qwas 3 nm, the thickness of the reverse inclined layer59rwas 20 nm, and the thickness of the p-side barrier layer32pwas 17 nm. The reverse inclined layer59rand the intermediate barrier layer32qcan be considered as a single layer. In this case, it is considered that, in a portion of the first well layer31aside of that single layer where the thickness is 3 nm, the band gap energy is constant, and in a remaining portion where the thickness is 20 nm, the band gap energy decreases along the +Z-axis direction.

InGaN was used for the reverse inclined layer59r, and the In composition ratio of a portion on the n-type semiconductor layer10side of the reverse inclined layer59rwas set to be lower than the In composition ratio of a portion on the p-type semiconductor layer20side of the reverse inclined layer59r. Compositions of the intermediate barrier layer32qand the p-side barrier layer32pwere the same as of the first to the third barrier layers32ato32c.

The thicknesses and materials of the first to the third well layers31ato31cand the first to the third barrier layers32ato32cwere set to be the same as in the semiconductor light emitting device110.

Thus, the configuration of the semiconductor light emitting device119bcorresponds to the configuration in which the intermediate barrier layer32qhaving the same composition as the other barrier layers32is disposed in lieu of the Al-containing layer40of the semiconductor light emitting device110, and a reverse inclined layer59rhaving an In composition ratio of a reversed direction is disposed in lieu of the intermediate layer50of the semiconductor light emitting device110.

As illustrated inFIG. 6B, a barrier at an interface between the first well layer31aand the intermediate barrier layer32qis small. Thus, in the semiconductor light emitting device119b, the intermediate barrier layer32q, the reverse inclined layer59r, and the p-side barrier layer32pare provided on the p-type semiconductor layer20side of the first well layer31a, but it is considered that the characteristics of confining the electrons is less than or equal to that of the semiconductor light emitting device119a.

As illustrated inFIG. 6C, even in the semiconductor light emitting device119b, a tail portion209bof the electron wave function WF1on the p-type semiconductor layer20side is large. In other words, the electrons in the first well layer31aare not sufficiently confined in the first well layer31a.

Four peaks are shown in the hole wave function WF2. The hole wave function WF2on the p-type semiconductor layer20side is located substantially in a center portion in a thickness direction of the reverse inclined layer59r, and the holes exist in a position distant from the first well layer31a. As a result, in the semiconductor light emitting device119b, it is considered that injection efficiency of the holes into the MQW is low.

FIGS. 7A to 7Care schematic diagrams illustrating the configuration and characteristics of the semiconductor light emitting device of the third reference example.

As illustrated inFIG. 7A, in the semiconductor light emitting device119c, the thickness of the intermediate barrier layer32qwas 15 nm and the thickness of the p-side barrier layer32pwas 12 nm. Material used for the p-side barrier layer32pwas the same as that used for the first to the third barrier layers32ato32c. Material used for the intermediate barrier layer32qwas In0.011Ga0.989N.

The thicknesses and materials of the first to the third well layers31ato31c, the first to the third barrier layers32ato32c, the Al-containing layer40, and the intermediate layer50were set to be the same as in the semiconductor light emitting device110.

As illustrated inFIG. 7B, in the semiconductor light emitting device119c, a barrier based on the Al-containing layer40exists at a position distant from the first well layer31a. This is due to the intermediate barrier layer32qbeing provided between the Al-containing layer40and the first well layer31a. In the semiconductor light emitting device119c, it is considered that the characteristics of confining the electrons is less than or equal to that of the semiconductor light emitting device119a.

As illustrated inFIG. 7C, even in the semiconductor light emitting device119c, a tail portion209bof the electron wave function WF1on the p-type semiconductor layer20side is large. In other words, the electrons in the first well layer31aare not sufficiently confined in the first well layer31a.

Four peaks are shown in the hole wave function WF2. The hole wave function WF2on the p-type semiconductor layer20side is located in a vicinity of the interface between the Al-containing layer40and the intermediate layer50, and the holes exist in a position distant from the first well layer31a. As a result, in the semiconductor light emitting device119c, it is considered that injection efficiency of the holes into the MQW is low.

FIGS. 8A and 8Bare graphs illustrating the characteristics of semiconductor light emitting devices.

Specifically, these graphs show the characteristics of the semiconductor light emitting device110and the semiconductor light emitting devices119ato119c. Current density Jc is shown on the horizontal axis of these graphs. Internal quantum efficiency IQE is shown on the vertical axis ofFIG. 8A. InFIG. 8A, characteristics of regions where the current density is low are omitted. Gain Gn is shown on the vertical axis ofFIG. 8B.

As illustrated inFIG. 8A, in the semiconductor light emitting device110according to this embodiment, compared to the semiconductor light emitting devices119ato119cof the first to the third reference examples, a high internal quantum efficiency IQE is obtained.

As illustrated inFIG. 8B, in the semiconductor light emitting device110according to this embodiment, compared to the semiconductor light emitting devices119ato119cof the first to the third reference examples, a high gain Gn is obtained.

FIGS. 9A and 9Bare graphs illustrating the characteristics of semiconductor light emitting devices.

Specifically, these graphs show the characteristics of the carrier concentration (hole concentration and electron concentration) of the semiconductor light emitting device110and the semiconductor light emitting devices119ato119c. Current density Jc is shown on the horizontal axis of these graphs. Hole concentration Ch is shown on the vertical axis ofFIG. 9A. Electron concentration Ce is shown on the vertical axis ofFIG. 9B.

As illustrated inFIGS. 9A and 9B, in the semiconductor light emitting devices119a,119b, and119cof the first, second, and third reference examples, compared to the electron concentration Ce, the hole concentration Ch is considerably high.

In the semiconductor light emitting device110according to this embodiment, the hole concentration Ch is substantially concurrent with the electron concentration Ce. Thus, in the semiconductor light emitting device110, the balance of the carrier density is good.

As described above, in the semiconductor light emitting device110, balance between the hole concentration Ch and the electron concentration Ce can be improved more than in the semiconductor light emitting devices119a,119b, and119cof the first, second, and third reference examples, and this is thought to be factor leading to high luminous efficiency.

FIG. 10is a graph illustrating the characteristics of semiconductor light emitting devices.

This graph shows operating voltages of the semiconductor light emitting device110and the semiconductor light emitting devices119ato119c. Current density JC is shown on the horizontal axis and operating voltage Vf is shown on the vertical axis.

As illustrated inFIG. 10, in the semiconductor light emitting device110and the semiconductor light emitting devices119ato119c, operating voltages Vf are substantially constant.

Thus, in the semiconductor light emitting device110, an internal quantum efficiency IQE and gain Gn that are higher than with the semiconductor light emitting devices119ato119ccan be realized while having an operating voltage Vf equivalent to that of the semiconductor light emitting devices119ato119cof the first to the third reference examples.

In the semiconductor light emitting device110according to this embodiment, high luminous efficiency is realized by appropriately setting the incline direction (increase/decrease) of the band gap energy of the intermediate layer50.

Hereinafter, simulation results regarding the characteristics when the incline direction of the band gap energy is varied in a configuration in which the Al-containing layer40is not provided will be described as a case where the impact of the incline direction of the band gap energy on luminous efficiency is clearer.

FIGS. 11A to 11Care schematic diagrams illustrating a configuration of a semiconductor light emitting device of a fourth reference example.

FIG. 11Ais a schematic cross-sectional view illustrating the configuration of the semiconductor light emitting device119dof the fourth reference example.FIG. 11Bis a schematic diagram illustrating band gap energy.FIG. 11Cshows an In composition ratio.

As illustrated inFIG. 11A, in the semiconductor light emitting device119d, the Al-containing layer40is not provided, and the intermediate layer50is provided in contact with a face of the p-type semiconductor layer20side of the first well layer31a. As illustrated inFIG. 11C, an In composition ratio of the intermediate layer50decreases in the +Z-axis direction. As illustrated inFIG. 11B, the band gap energy of the intermediate layer50increases in the +Z-axis direction.

FIGS. 12A to 12Care schematic diagrams illustrating a configuration of a semiconductor light emitting device of a fifth reference example.

As illustrated inFIG. 12A, in the semiconductor light emitting device119eof the fifth reference example, the Al-containing layer40is not provided, and the reverse inclined layer59ris provided in contact with a face of the p-type semiconductor layer20side of the first well layer31a. As illustrated inFIG. 12C, an In composition ratio of the reverse inclined layer59rincreases in the +Z-axis direction. As illustrated inFIG. 12B, the band gap energy of the reverse inclined layer59rdecreases in the +Z-axis direction.

FIG. 13is a graph illustrating the characteristics of the semiconductor light emitting devices of the fourth and fifth reference examples.

In this graph, current density JC is shown on the horizontal axis, and internal quantum efficiency IQE1of the first well layer31ais shown on the vertical axis. The internal quantum efficiency IQE in the previously describedFIG. 8Acorresponds to a general internal quantum efficiency including the first to the third well layers31ato31c. On the other hand, the internal quantum efficiency IQE1inFIG. 13is an internal quantum efficiency of only the first well layer31a.

As illustrated inFIG. 13, in the semiconductor light emitting devices119dand119ein which the incline directions of the band gap energies are mutually reversed, the internal quantum efficiencies IQE mutually differ.

Thus, the incline direction of the band gap energy affects luminous efficiency. Therefore, in order to obtain high luminous efficiency, it is necessary to appropriately set the incline direction of the band gap energy.

As described with respect toFIG. 4, in the semiconductor light emitting device110according to this embodiment, the Al-containing layer40is provided in contact with the face of the p-type semiconductor layer20side of the first well layer31a; and the intermediate layer50, having a band gap energy that increases along the +Z-axis direction, is provided in contact with the face of the p-type semiconductor layer20side of the Al-containing layer40. Therefore, a higher barrier to the electrons is formed in the vicinity of the interface between the first well layer31aand the Al-containing layer40. Moreover, the tail portion201of the electron wave function WF1of the p-type semiconductor layer20is contracted, and electron overflow from the first well layer31ais efficiently suppressed. Also, the hole wave function WF2is formed in the portion in the vicinity of the interface between the Al-containing layer40and the intermediate layer50, specifically, in a portion in the vicinity of the first well layer31a, and the holes are efficiently confined in the portion in the vicinity of the first well layer31a. Thereby, injection efficiency of the holes into the MQW can be improved.

Through this configuration, electron overflow in the first well layer31acan be suppressed and the injection efficiency of the holes into the MQW can be improved. Therefore, when the plurality of the well layers31is provided in the semiconductor light emitting device110, luminous efficiency of the plurality of the well layers31can be improved.

In the semiconductor light emitting device110according to this embodiment, the piezoelectric effect is beneficially utilized and the suppression of electron overflow and the improvement of injection efficiency of the holes is realized due to the appropriate setting of the band gap energies of the Al-containing layer40and the intermediate layer50and of the lattice constant of the Al-containing layer40.

For example, when using GaN for the n-type semiconductor layer10, if, for example, InGaN is used for the well layers31and the barrier layer32, compressive stress will be generated in the well layers31and the barrier layer32due to the lattice constant of InGaN being larger than GaN.

Moreover, if AlGaN is used for the Al-containing layer40, tensile stress will be generated in the Al-containing layer40due to the lattice constant of AlGaN being smaller than GaN.

Generally, the lattice constant of the well layers31is set to be larger than the lattice constant of the n-type semiconductor layer10. Therefore, if the lattice constant of the Al-containing layer40is set to be smaller than the lattice constant of the n-type semiconductor layer10, it will result in the lattice constant of the Al-containing layer40being set to be smaller than the lattice constant of the well layers31(i.e., the first well layer31aetc.).

Thereby, stress in mutually differing directions is generated in the mutually adjacent first well layer31aand the Al-containing layer40. Specifically, compressive stress is generated in the first well layer31aand tensile stress is generated in the Al-containing layer40.

As a result, orientation of an electric field generated by the piezo effect at the interface between the first well layer31aand the Al-containing layer40is reversed. This electric field acts in a direction of confining electrons in the first well layer31a, and results in the effective suppression of electron overflow from the first well layer31a. Moreover, holes are made to exist in the vicinity of the first well layer31aand the injection efficiency of the holes into the MQW can be improved.

In the semiconductor light emitting device110according to this embodiment, the n-type semiconductor layer10, the first barrier layer32a, the first well layer31a, the Al-containing layer40, the intermediate layer50, and the p-type semiconductor layer20are subsequently disposed along the [0001] direction of the n-type semiconductor layer10(the +Z-axis direction), and the lattice constant of the Al-containing layer40is set to be smaller than the n-type semiconductor layer10, specifically, smaller than the first well layer31a. Therefore, the characteristics described above are obtained.

Moreover, by causing the band gap energy of the intermediate layer50to increase along the +Z-axis direction, appropriate energy barriers to the electrons and the holes can be formed and the injection efficiency of the holes can be improved while suppressing electron overflow.

In a semiconductor light emitting device using a group III nitride semiconductor, a high bias is applied for injecting holes into an active layer. As a result, electrons may overflow from the active layer, an ineffective current of the p-type semiconductor layer20may increase, and luminous efficiency may decrease. Through this embodiment, electron overflow can be suppressed, the injection efficiency of holes can be improved, and luminous efficiency can be improved.

While various configurations have been proposed wherein a barrier layer for preventing electron overflow is provided on the p-type semiconductor layer side of the active layer or in the p-type semiconductor layer, the configuration of this embodiment is not known.

For example, there is a configuration wherein an n-side intermediate layer is disposed on an n-type semiconductor layer side of an active layer, a p-side intermediate layer is disposed on a p-type semiconductor layer side of the active layer, and Al compositions and In compositions of the n-side intermediate layer and the p-side intermediate layer vary along a thickness direction. However, optimum conditions regarding the relationship between the crystal orientation of the semiconductor layers and the incline direction of the Al composition and the In composition are not known.

For example, the incline direction of the In composition ratio of the reverse inclined layer59rof the semiconductor light emitting device119bof the second reference example is opposed to the incline direction of the In composition ratio of the intermediate layer50of the semiconductor light emitting device110according to this embodiment. Moreover, as illustrated inFIGS. 8A and 8B, the characteristics of the semiconductor light emitting device119bof the second reference example are lower than the characteristics of the semiconductor light emitting device110according to this embodiment.

Thus, in the semiconductor light emitting device110according to this embodiment, by appropriately designating the incline of the band gap energy (in other words, the incline of the In composition ratio) of the intermediate layer50by association with the [0001] direction of the n-type semiconductor layer10, a high luminous efficiency is gained.

As previously described with respect toFIG. 13, there is a relationship between the incline direction of the In composition ratio of the composition inclined layer having an inclined composition and, for example, the injection efficiency of carriers into the first well layer31a. Therefore, if the incline direction of the In composition ratio is inappropriate, the luminous efficiency cannot be sufficiently improved.

Therefore, in the semiconductor light emitting device110, the incline direction of the band gap energy of the intermediate layer50(in other words, the incline direction of the In composition ratio of the intermediate layer50) is determined by association with the direction of the crystal orientation of the n-type semiconductor layer10.

FIG. 14is a graph illustrating the characteristics of semiconductor light emitting devices.

This graph shows the simulations results of the characteristics of the semiconductor light emitting devices according to the embodiment when the thickness of the intermediate layer50is changed. Here, as illustrated inFIG. 4, a total of the thicknesses of the intermediate layer50and the p-side barrier layer32pare constant at 37 nm. In other words, a total of the thicknesses of the Al-containing layer40, the intermediate layer50, and the p-side barrier layer32pare constant at 40 nm.

A semiconductor light emitting device111ais defined where the thickness of the intermediate layer50is 5 nm (the thickness of the p-side barrier layer32pis 32 nm). A semiconductor light emitting device111bis defined where the thickness of the intermediate layer50is 10 nm (the thickness of the p-side barrier layer32pis 27 nm). A semiconductor light emitting device111cis defined where the thickness of the intermediate layer50is 37 nm (the thickness of the p-side barrier layer32pis 0 nm). The semiconductor light emitting device110is defined where the thickness of the intermediate layer50is 20 nm (the thickness of the p-side barrier layer32pis 17 nm).

In the semiconductor light emitting devices110and111ato111c, the In composition ratio of the ends of the intermediate layer50were 0.03 and 0.01, respectively, and the In composition ratio varied in a linear manner along the +Z-axis direction. In other words, the incline of the change of the In composition ratio varied with the thickness of the intermediate layer50.

Characteristics of a semiconductor light emitting device119fof the sixth reference example are also shown inFIG. 14. In the semiconductor light emitting device119f, the Al-containing layer40is provided in contact with the first well layer31a, but the intermediate layer50is not provided (the thickness of the intermediate layer50is the equivalent of 0 nm). Also, the p-side barrier layer32p, having a thickness of 37 nm, is provided in contact with the Al-containing layer40.

InFIG. 14, operating voltage Vf is shown on the horizontal axis, and electron current density Jep in the p-side electrode80is shown on the vertical axis. The electron current density Jep is equivalent to a degree of electron overflow. When the electron current density Jep is small, the overflow of the electrons is small.

As illustrated inFIG. 14, in the semiconductor light emitting device119fin which the intermediate layer50is not provided, the electron current density Jep is extremely high and electron overflow is great.

On the other hand, in the semiconductor light emitting devices110and111ato111c, the electron current density Jep is small, and electron overflow is suppressed.

The thickness of the intermediate layer50is preferably 5 nm or more. Thereby, electron overflow can be suppressed. The thickness of the intermediate layer50is more preferably 10 nm or more. Thereby, electron overflow can be further suppressed, and a state can be realized in which there is substantially no electron overflow.

The thickness of the intermediate layer50is preferably 100 nm or less. If the thickness of the intermediate layer50exceeds 100 nm, for example, the driving voltage Vf will rise and it will not be possible to obtain the desired specification.

Preferably, the intermediate layer50is substantially free of Al. Particularly, because the first portion55on the first well layer31aside of the intermediate layer50does not contain Al, the band gap energy of the first portion55can be sufficiently reduced, thus clearly differentiating the band gap energies of the interface between the intermediate layer50and an Al inclined layer40. Additionally, because the first portion55does not contain Al, the band gap energy of the first portion55can be sufficiently reduced, thus clearly facilitating the forming of the incline of the band gap energy in the intermediate layer50.

As described above, AlGaInN is used, for example, for the Al-containing layer40.

An Al composition ratio of the Al-containing layer40(Al-containing layer Al composition ratio x1) is not less than 0.001 and not more than 0.3. If the Al-containing layer Al composition ratio x1 is less than 0.001, the band gap energy of the Al-containing layer40will not be sufficiently larger than the band gap energy of the barrier layers32and the efficiency improvements described above will be difficult to obtain. If the Al-containing layer Al composition ratio x1 exceeds 0.3, the barriers to the holes will also increase, which may cause to inhibit the injection efficiency of the holes into the MQW. Additionally, crystallinity may deteriorate, resulting in a reduction in efficiency. The Al-containing layer40need not include In, and an In composition ratio may be set to 0.

A thickness of the Al-containing layer40is not less than 1 nm and not more than 50 nm. If the thickness of the Al-containing layer40is less than 1 nm, the efficiency improvements described above will be difficult to obtain. If the thickness of the Al-containing layer40exceeds 50 nm, the Al-containing layer40will become highly resistive and the operating voltage will increase. Additionally, crystallinity may deteriorate, resulting in a reduction in efficiency.

In the example described above, the band gap energy, or in other words, the In composition ratio of the intermediate layer50varied in a linear manner but the embodiment is not limited thereto. The band gap energy and the In composition ratio of the intermediate layer50may, for example, vary in a curved manner.

FIGS. 15A to 15Dare schematic diagrams illustrating configurations of semiconductor light emitting devices according to the embodiment.

Specifically,FIGS. 15A and 15Billustrate a band gap energy and an In composition ratio of another semiconductor light emitting device112aaccording to the embodiment.FIGS. 15C and 15Dillustrate a band gap energy and an In composition ratio, respectively, of still another semiconductor light emitting device112baccording to the embodiment.

As illustrated inFIGS. 15A and 15B, in the semiconductor light emitting device112a, the band gap energy and the In composition ratio of the intermediate layer50have four steps and vary in a stepwise manner.

As illustrated inFIGS. 15C and 15D, in the semiconductor light emitting device112bthe band gap energy and the In composition ratio of the intermediate layer50have three steps and vary in a stepwise manner.

Thus, the band gap energy and the In composition ratio of the intermediate layer50may vary in a stepwise manner. A difference in the In composition ratios and the band gap energies at each step need not be uniform, and that the manner in which the band gap energy and the In composition ratio varies may be selected as desired.

Thus, the intermediate layer50can include a plurality of sublayers which have mutually differing band gap energies and In composition ratios. The number of the plurality of sublayers may be determined as desired.

The Al-containing layer40may have a stacked structure.

FIGS. 16A to 16Dare schematic diagrams illustrating configurations of other semiconductor light emitting devices according to the embodiment.

FIG. 16Ais a schematic cross-sectional view illustrating a configuration of another semiconductor light emitting device113aaccording to the embodiment andFIG. 16Billustrates a band gap energy of the semiconductor light emitting device113a.FIG. 16Cis a schematic cross-sectional view illustrating a configuration of still another semiconductor light emitting device113baccording to the embodiment andFIG. 16Dillustrates a band gap energy of the semiconductor light emitting device113b.

As illustrated inFIGS. 16A to 16D, in the semiconductor light emitting device113aand the semiconductor light emitting device113b, the Al-containing layer40includes a first layer41and a second layer42. The first layer41is in contact with the first well layer31a. The second layer42is in contact with the first layer41and the second layer42is between the first layer41and the intermediate layer50. The second layer42has a band gap energy that differs from a band gap energy of the first layer41.

Specifically, in the semiconductor light emitting device113a, the band gap energy of the second layer42is larger than the band gap energy of the first layer41. In the semiconductor light emitting device113b, the band gap energy of the second layer42is smaller than the band gap energy of the first layer41.

Thus, the Al-containing layer40displays the same characteristics as described above even when having a stacked structure in which the plurality of layers have mutually differing band gap energies. Specifically, electron overload is suppressed and injection efficiency of holes is improved.

For example, because an Al composition ratio of the first layer41and an Al composition ratio of the second layer42are different, the band gap energy of the first layer41and the band gap energy of the second layer42are different.

By changing the Al composition ratios of the first layer41and the second layer42, lattice constants of the first layer41and the second layer42change. If a crystal having a large lattice constant (the well layer and the second portion56on the p-type semiconductor layer20side of the intermediate layer50) is grown in contact with a crystal having a small lattice constant (the Al-containing layer40), defects and dislocations will easily occur at an interface therebetween. Here, by providing the Al-containing layer40with the first layer41and the second layer42, a layer having a lattice constant between the crystal having the large lattice constant and the crystal having the small lattice constant can be provided. Thus, the occurrence of defects and dislocations can be suppressed and luminous efficiency can be improved more.

As illustrated inFIG. 4, in the semiconductor light emitting device110according to this embodiment, the characteristics of suppressing electron overflow and improving the injection efficiency of the holes is based on appropriately controlling the state (states of the barrier, the electron wave function WF1, and the hole wave function WF2) of the first well layer31a, which is the closest to the p-type semiconductor layer20among the well layers31, by providing the Al-containing layer40and the intermediate layer50. In other words, while the state of the first well layer31a, which is the closest to the p-type semiconductor layer20among the well layers31, is greatly affected by the Al-containing layer40and the intermediate layer50, the other well layers31(i.e. second well layer31band third well layer31c) are not greatly affected. Therefore, the characteristics of suppressing electron overflow and improving the injection efficiency of the holes obtained by providing the Al-containing layer40and the intermediate layer50are also displayed in a configuration in which one of the well layers31is provided (Single Quantum Well structure).

As described above, according to the embodiment, a semiconductor light emitting device having improved luminous efficiency can be provided.

Note that in this specification, the term, “nitride semiconductor” includes semiconductors of all compositions wherein composition ratios of x, y, and z in the formula BxInyAlzGa1-x-y-zN fall within the respective ranges of 0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z≦1. Furthermore, in the formula described above, “nitride semiconductor” shall also be understood to include semiconductors further including group V elements other than N (nitrogen), semiconductors further including various elements added to control various physical properties such as conductivity type and the like, and semiconductors further including various elements that are included unintentionally.

An embodiment of the invention with reference to examples was described above. However, the invention is not limited to these examples. For example, the scope of the invention includes all cases in which, for example, a person skilled in the art could make use of publicly known information to appropriately select constituents such as the n-type semiconductor layer, p-type semiconductor layer, well layers, barrier layers, Al-containing layer, intermediate layer, electrodes and the like included in the semiconductor light emitting device provided that the obtained effects are similar.

Additionally, combinations of constituents from two or more of the examples are also included in the scope of the invention, provided they are technically possible and do not depart from the spirit of the invention.

Beside such cases, all semiconductor light emitting devices based on the embodiments of the invention described above that are obtainable through appropriate design modifications by a person skilled in the art shall be understood to fall within the scope of the invention, provided such semiconductor light emitting devices do not depart from the spirit of the invention.

Furthermore, regarding the scope of the spirit of the invention, it is understood that a variety of variations and modifications could be conceived by a person skilled in the art and that these variations and modifications all fall within the scope of the invention as well.