WO2022219731A1

WO2022219731A1 - Nitride semiconductor uv light-emitting element and production method therefor

Info

Publication number: WO2022219731A1
Application number: PCT/JP2021/015380
Authority: WO
Inventors: 光平野; 陽祐長澤
Original assignee: 創光科学株式会社
Priority date: 2021-04-14
Filing date: 2021-04-14
Publication date: 2022-10-20
Also published as: TW202240932A; JPWO2022219731A1

Abstract

This nitride semiconductor UV light-emitting element comprises an n-type layer, an active layer, and a p-type layer which are each formed from an AlGaN semiconductor having a wurtzite structure. Each of the semiconductor layers is an epitaxially grown layer having a surface in which multi-stage terraces parallel to the (0001) plane are formed. The n-type layer has a layer region where an extension direction in which the AlN molar fraction is locally low is inclined with respect to the upper surface. A first average AlN molar fraction in the entire range in the depth direction of the n-type layer is more than (n-0.25)/12 but less than (n+0.25)/12. On the upper side of at least one specific depth of one or more depths which correspond to a depth d from the upper end of the n-type layer and in which a second average AlN molar fraction becomes equal to n/12, there is a region in which the AlN molar fraction is greater than n/12. On the lower side of the specific depth, there is a region in which the AlN molar fraction is less than n/12. In the layer region, an intermediate AlGaN region in which the AlN molar fraction is (n-0.5)/12 is formed.

Description

Nitride semiconductor ultraviolet light emitting device and manufacturing method thereof

The present invention relates to a nitride semiconductor ultraviolet light emitting device having a light emitting device structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are vertically laminated, and a manufacture thereof. Regarding the method.

In general, there are many nitride semiconductor light emitting devices in which a light emitting device structure composed of a plurality of nitride semiconductor layers is formed by epitaxial growth on a substrate such as sapphire. The nitride semiconductor layer is represented by the general formula Al _1-xy Ga _x In _y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).

A light-emitting element structure of a light-emitting diode has a double heterostructure in which an active layer made of a nitride semiconductor layer is sandwiched between two cladding layers of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. there is When the active layer is an AlGaN-based semiconductor, by adjusting the AlN mole fraction (also referred to as the Al composition ratio), the bandgap energy can be adjusted to the bandgap energy (approximately 3.4 eV and approximately 6.2 eV) that can be taken by GaN and AlN. ) can be adjusted within the lower and upper limits, respectively, and an ultraviolet light emitting device having an emission wavelength of about 200 nm to about 365 nm can be obtained. Specifically, by passing a forward current from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer, the recombination of carriers (electrons and holes) in the active layer causes the bandgap energy Luminescence occurs. In order to supply the forward current from the outside, a p-electrode is provided on the p-type nitride semiconductor layer, and an n-electrode is provided on the n-type nitride semiconductor layer.

When the active layer is an AlGaN-based semiconductor, the n-type nitride semiconductor layer and the p-type nitride semiconductor layer sandwiching the active layer are composed of an AlGaN-based semiconductor with a higher AlN mole fraction than the active layer. However, since it is difficult for a p-type nitride semiconductor layer with a high AlN mole fraction to form a good ohmic contact with a p-electrode, a p-type nitride semiconductor layer with a low AlN mole fraction is placed on the uppermost layer of the p-type nitride semiconductor layer. It is common practice to form a p-type contact layer capable of good ohmic contact with a p-electrode made of an AlGaN-based semiconductor (specifically, p-GaN). Since the p-type contact layer has a smaller AlN mole fraction than the AlGaN-based semiconductor forming the active layer, the ultraviolet rays emitted from the active layer toward the p-type nitride semiconductor layer are absorbed by the p-type contact layer. , cannot be effectively extracted to the outside of the device. For this reason, a general ultraviolet light emitting diode whose active layer is an AlGaN-based semiconductor employs an element structure as schematically shown in FIG. is effectively extracted to the outside of the device (see, for example,

Patent Documents

1 and 2 below).

As shown in FIG. 18, a general ultraviolet light emitting diode has a template 102 formed by depositing an AlGaN semiconductor layer 101 (for example, an AlN layer) on a substrate 100 such as a sapphire substrate. A semiconductor layer 103, an active layer 104, a p-type AlGaN-based semiconductor layer 105, and a p-type contact layer 106 are deposited in order, and a part of the active layer 104, the p-type AlGaN-based semiconductor layer 105, and the p-type contact layer 106 is , the n-type AlGaN-based semiconductor layer 103 is removed by etching until it is exposed, and the n-electrode 107 is formed on the exposed surface of the n-type AlGaN-based semiconductor layer 103, and the p-electrode 108 is formed on the surface of the p-type contact layer 106, respectively. be.

In addition, in order to increase the luminous efficiency (internal quantum efficiency) due to carrier recombination in the active layer, the active layer is made to have a multiple quantum well structure, and an electron blocking layer is provided on the active layer. .

On the other hand, in the clad layer composed of the n-type AlGaN-based semiconductor layer, compositional modulation occurs due to Ga segregation (segregation associated with mass transfer of Ga), and localized AlN moles extending in an oblique direction with respect to the clad layer surface It has been reported that a layered region with a low fraction is formed (see, for example, Patent Document 3 and

Non-Patent Documents

1 and 2 below). Since an AlGaN-based semiconductor layer with a locally low AlN mole fraction also has a locally small bandgap energy, in Patent Document 3, carriers in the cladding layer tend to be localized in the layered region, and the active layer It has been reported that a low-resistance current path can be provided by using a UV light emitting diode, and that the luminous efficiency of the ultraviolet light emitting diode can be improved.

International Publication No. 2014/178288 International Publication No. 2016/157518 International Publication No. 2019/159265 JP 2012-089754 A

An ultraviolet light emitting element composed of an AlGaN-based semiconductor is fabricated on a substrate such as a sapphire substrate, for example, by a well-known epitaxial growth method such as an organometallic compound vapor phase epitaxy (MOVPE) method. However, when producing UV light emitting devices, the characteristics of UV light emitting devices (emission wavelength, wall plug efficiency, forward bias, etc.) fluctuate under the influence of the drift of the crystal growth apparatus, so stable yields can be achieved. is not always easy to produce.

Drift in crystal growth equipment is caused by changes in the effective temperature of the crystal growth site due to deposits on trays, chamber walls, etc. For this reason, in order to suppress the drift, conventionally, the growth history is examined, and an experienced person slightly changes the set temperature or the composition of the raw material gas, or the growth schedule for a certain period is fixed, cleaning, etc. Although we have devised ways such as performing maintenance in the same way for a certain period of time, it is difficult to completely eliminate drift.

Therefore, the inventors of the present application have found a locally low AlN mole fraction formed by Ga segregation in the clad layer composed of an n-type AlGaN semiconductor layer and providing a low-resistance current path to the active layer. By growing the n-type AlGaN-based semiconductor layer so that "metastable AlGaN" having an AlGaN composition ratio of an integer ratio, which will be described later, predominantly exists in the layered region, characteristic fluctuations caused by drift of the crystal growth apparatus can be prevented. have been found to be able to stably produce a nitride semiconductor ultraviolet light-emitting device having desired light-emitting characteristics by suppressing the emission, and have proposed the use of metastable AlGaN in the layered region of the n-type AlGaN-based semiconductor layer ( See specifications of international applications such as PCT/JP2020/024827, PCT/JP2020/024828, PCT/JP2020/026558, and PCT/JP2020/031620).

<Characteristics of Metastable AlGaN>
For convenience of explanation, first, the characteristics of "metastable AlGaN" in which the AlGaN composition ratio is represented by a predetermined integer ratio will be explained.

If metastable AlGaN is not taken into account, a ternary mixed crystal such as AlGaN is a crystalline state in which Group 3 elements (Al and Ga) are randomly mixed, and can be approximated by a "random configuration". explained in a simple way. However, since the covalent bond radius of Al differs from the covalent bond radius of Ga, the higher the symmetry of the atomic arrangement of Al and Ga in the crystal structure, the more stable the structure generally.

AlGaN-based semiconductors with a wurtzite structure can have two types of arrangement: random arrangement without symmetry and stable symmetric arrangement. Here, at a certain ratio, a state appears in which the symmetrical arrangement is dominant. As will be described later, in "metastable AlGaN" in which the AlGaN composition ratio (the composition ratio of Al, Ga, and N) is represented by a predetermined integer ratio, a symmetric arrangement structure of Al and Ga appears.

In the symmetrical arrangement structure, even if the amount of Ga supplied to the crystal growth surface slightly increases or decreases, the high symmetry results in an energetically stable mixed crystal mole fraction, and the mass transfer of Ga is easy. Concentration can be prevented from getting out of control.

<Symmetric Arrangement Structure of Al and Ga in Metastable AlGaN>
Next, the symmetric arrangement structure of Al and Ga in "metastable AlGaN" will be described.

Fig. 1 shows a schematic diagram of one unit cell (two monolayers) in the c-axis direction of AlGaN. In FIG. 1, white circles indicate sites where Group 3 element atoms (Al, Ga) are located, and black circles indicate sites where Group 5 element atoms (N) are located. In the following description, a monoatomic layer is denoted as ML. In FIG. 1, one unit cell is denoted as 2ML.

The site planes of the group 3 elements (A3 plane, B3 plane) and the site planes of the group 5 elements (A5 plane, B5 plane) indicated by hexagons in FIG. 1 are both parallel to the (0001) plane. Each site on the A3 plane and the A5 plane (generically called the A plane) has six sites at each vertex of the hexagon and one site at the center of the hexagon. The same applies to the B3 plane and the B5 plane (generally called the B plane), but FIG. 1 shows only three sites that exist within the hexagon of the B plane. Each site on the A plane overlaps in the c-axis direction, and each site on the B plane overlaps in the c-axis direction. However, the atoms (N) at one site on the B5 plane are composed of atoms (Al, Ga) at three sites on the A3 plane located above the B5 plane and one site on the B3 plane located below the B5 plane. Site atoms (Al, Ga) form a 4-coordinate bond, and the atom (Al, Ga) at one site of the B3 plane is the atom (N) at one site of the B5 plane located above the B3 plane. and 4-coordinate bonds with atoms (N) at three sites on the A5 plane located below the B3 plane. Therefore, as shown in FIG. It does not overlap with each site in the c-axis direction.

FIG. 2 illustrates the positional relationship between each site on the A plane and each site on the B plane as a plan view of the A3 plane and the B3 plane viewed from the c-axis direction. The black circles and white circles in FIG. 2 distinguish whether the site surface is the A3 surface or the B3 surface. In both the A3 and B3 faces, each of the six vertices of a hexagon is shared by two other adjacent hexagons, and the central site is not shared with any other hexagon, so within one hexagon: There are substantially three atomic sites. Therefore, there are six sites for group 3 element atoms (Al, Ga) and six sites for group 5 element atoms (N) per unit cell (2ML). Therefore, there are the following five cases of AlGaN composition ratios represented by integer ratios excluding GaN and AlN.
₁ ) _Al1Ga5N6 _,
₂ ) _Al2Ga4N6 ₍ ₌ _Al1Ga2N3 ) _,
₃ ) _Al3Ga3N6 ₍ ₌ _Al1Ga1N2 ₎ ,
₄ ) _Al4Ga2N6 ₍ ₌ _Al2Ga1N3 ₎ ,
₅ ) _Al5Ga1N6 _.

Here, Al ₁ Ga ₂ N ₃ , Al ₁ Ga ₁ N ₂ and Al ₂ Ga ₁ N ₃ in 2) to 4) above are, as shown in FIG. Since it can have a symmetrical arrangement structure, the metastable AlGaN having the AlGaN composition ratios 2) to 4) is formed in the c-axis direction in units of 1 ML. FIG. 3 illustrates an arrangement structure of only one of the A3 plane and the B3 plane. In FIG. 3, Ga is indicated by a large black circle, and Al is indicated by a small black circle.

On the other hand, the Al ₁ Ga ₅ N ₆ of 1) above has one of the A3 plane and the B3 plane of the Al ₁ Ga ₂ N ₃ arrangement structure of 2) above, and the other of the GaN arrangement structure (the site of the group 3 element is It can take a 2ML unit symmetric arrangement structure with all Ga). Furthermore, the Al ₁ Ga ₅ N ₆ of 5) above has one of the A3 plane and the B3 plane of the Al ₂ Ga ₁ N ₃ arrangement structure of 4) above, and the other AlN arrangement structure (the site of the group 3 element is A symmetric arrangement structure of 2ML units with all Al) can be taken.

Furthermore, as four metastable AlGaNs with integer ratios of AlGaN composition ratios located between the above 1) and 2), 2) and 3), 3) and 4), and 4) and 5), the following 6 ) to 9) are assumed.
₆ ) _Al3Ga9N12 ₍ ₌ _Al1Ga3N4 ₎ ,
₇ ) _Al5Ga7N12 _,
₈ ) _Al7Ga5N12 _,
₉ ) _Al9Ga3N12 ₍ ₌ _Al3Ga1N4 ₎ .

Here, the Al ₁ Ga ₃ N ₄ of 6) above has one of the A3 plane and B3 plane having the Al ₁ Ga ₁ N ₂ arrangement structure of 3) above, and the other having the GaN arrangement structure (group 3 element site can take a symmetrical array structure of 2 ML units where all are Ga). Al ₅ Ga ₇ N ₁₂ of 7) above has the arrangement structure of Al ₁ Ga ₂ N ₃ of 2) above on one of the A3 plane and the B3 plane, and the arrangement structure of Al ₁ Ga ₁ N ₂ of 3) above on the other. A symmetric array structure of 2ML units can be taken. Al ₇ Ga ₅ N ₁₂ in 8) above has the arrangement structure of Al ₁ Ga ₁ N ₂ in 3) above on one of the A3 plane and the B3 plane, and the arrangement structure of Al ₂ Ga ₁ N ₃ in 4) on the other. A symmetric array structure of 2ML units can be taken. Al ₃ Ga ₁ N ₄ in 9) above has one of the A3 plane and B3 plane having the Al ₁ Ga ₁ N ₂ arrangement structure of 3) above, and the other having the AlN arrangement structure (all sites of group 3 elements are Al ) can have a 2ML unit symmetric array structure.

Therefore, Al ₁ Ga ₅ N ₆ , Al ₅ Ga ₁ N ₆ , Al ₃ Ga ₉ N ₁₂ (= Al ₁ Ga ₃ N ₄ ), Al ₅ Ga ₇ N ₁₂ , Al ₇ Ga ₅ N ₁₂ or Al ₉ Ga ₃ N ₁₂ (=Al ₃ Ga ₁ N ₄ ), as described above, when the 2 ML unit arrangement structure is different between the A3 plane and the B3 plane, , and the AlGaN composition ratios 1) and 5) to 9) above are formed in the c-axis direction in units of 2 ML.

However, even in each of the AlGaN composition ratios 1), 5) to 9), although not specifically exemplified, for example, by synthesizing different symmetrical arrangement structures in the same plane on the A3 plane and the B3 plane described above, , Al ₁ Ga ₂ N ₃ , Al ₁ Ga ₁ N ₂ , and Al ₂ Ga ₁ N ₃ in 2) to 4) above, each of the A3 plane and the B3 plane has the same symmetric arrangement structure of Al and Ga. considered to be obtained. In that case, each metastable AlGaN having the AlGaN composition ratios 1), 5) to 9) is formed in the c-axis direction in units of 1 ML in the same manner as the metastable AlGaN having the AlGaN composition ratios 2) to 4). can be

As described above, the metastable AlGaN shown in the above 1) to 9) has a symmetrical arrangement of Al and Ga atoms, and is energetically stable AlGaN. However, in order to grow AlGaN while maintaining a certain crystal quality, it is necessary to grow the crystal at a high temperature of 1000° C. or higher. However, Ga is assumed to move around at 1000° C. or higher even after the atoms reach sites on the crystal surface. On the other hand, unlike Ga, Al easily adsorbs to the surface, and although it is thought that Al moves somewhat after entering the site, it is strongly restricted. Therefore, even if it is metastable AlGaN, Al ₁ Ga ₅ N ₆ of the above 1) has a high composition ratio of Ga. It is considered that the disorder causes the atomic arrangement of Al and Ga to become nearly random, and the stability described above is lowered compared to other metastable AlGaN.

Here, the metastable AlGaN having the above AlGaN composition ratios 1) to 9) can be expressed as Al _n Ga _12-n N ₁₂ using an integer n (n=2 to 10), and Al _n Ga _12-n N The AlN mole fraction of ₁₂ is n/12 when expressed as a fraction, but when expressed as a percentage, a fraction occurs after the decimal point. Therefore, for convenience of explanation, 2/12 (= 1/6), 4/12 (= 1/3), 5/12, 7/12, 8/12 (= 2/3), The six AlN mole fractions of 10/12 (=5/6) are approximately 16.7%, 33.3%, 41.7%, 58.3%, 66.7%, 83. It is written as 3%.

<Issues when using metastable AlGaN in the layered region>
As described above, the inventors of the present application have proposed the use of metastable AlGaN in the layered region of the n-type AlGaN semiconductor layer in order to suppress the characteristic fluctuations caused by the drift of the crystal growth apparatus. describes the problems that can arise from the dominant formation of metastable AlGaN in the layered regions.

In general ultraviolet light emitting diodes that take out ultraviolet rays emitted from the active layer toward the n-type nitride semiconductor layer (n-type AlGaN semiconductor layer) side, the peak emission wavelength ( λp) and the absorption edge wavelength (λae) determined by the average AlN mole fraction of the absorption spectrum of the n-type AlGaN semiconductor layer, if the wavelength difference (λp−λae) is 10 nm or more, light emission from the active layer absorption in the n-type AlGaN semiconductor layer is suppressed.

The transmittance (ratio of incident light intensity I0 and transmitted light intensity I, I/I0) when light emitted from the active layer is transmitted through the n-type AlGaN semiconductor layer in the depth direction is the optical path length of n-type AlGaN. Attenuates exponentially with respect to the thickness of the system semiconductor layer. While the thickness of the n-type AlGaN-based semiconductor layer is as large as about 1 to 4 μm, the thickness of each layer in the depth direction of the layered region is as short as about 20 nm on average. Therefore, since the AlN mole fraction in the layered region is about 4% lower than the average AlN mole fraction in the n-type AlGaN semiconductor layer, the absorption edge wavelength in the layered region is the absorption of the entire n-type AlGaN semiconductor layer. Although it shifts slightly to longer wavelengths than the edge wavelength λae, the optical density of the layered region (the common logarithm of the reciprocal of the transmittance) is smaller than that of the entire n-type AlGaN semiconductor layer, so the wavelength is longer than the absorption edge wavelength λae. Absorption at the side becomes very limited.

In order for metastable AlGaN to be predominantly formed in the layered region, the average AlN mole fraction of the n-type AlGaN-based semiconductor layer should be about 4% higher than the AlN mole fraction of the metastable AlGaN. set. On the other hand, since the AlGaN composition ratio of metastable AlGaN is an integer ratio, the AlN mole fraction can take discrete values of about 8.33%. Therefore, the setting range of the average AlN mole fraction of the n-type AlGaN-based semiconductor layer is similarly a discrete range about 4% higher than the metastable AlGaN.

In the n-type AlGaN-based semiconductor layer in which metastable AlGaN is predominantly formed in the layered region, the absorption edge wavelength λae determined by the average AlN mole fraction of the n-type AlGaN-based semiconductor layer is different from the peak emission wavelength λp. If the wavelength difference (λp−λae) of 10 nm or more cannot be secured by using the above method, part of the emission spectrum (especially the part distributed on the short wavelength side) is absorbed in the n-type AlGaN semiconductor layer, and the external quantum efficiency decreases. lead to decline. Therefore, in order to avoid this decrease in external quantum efficiency, the discrete AlN mole fraction that can be taken by metastable AlGaN is increased by one step (approximately 8.33%) so that the wavelength difference (λp−λae) becomes Similarly, the average AlN mole fraction of the n-type AlGaN-based semiconductor layer must be increased stepwise so as to be 10 nm or more.

On the other hand, when the average AlN mole fraction of the n-type AlGaN-based semiconductor layer increases, the contact resistance between the n-electrode and the n-type AlGaN-based semiconductor layer and the bulk of the current flowing through the n-type AlGaN-based semiconductor layer increase. Due to the higher resistivity, the parasitic resistance of the current path between the n-electrode and the active layer becomes higher, reducing the wall plug efficiency. In particular, the contact resistance between the n-type AlGaN-based semiconductor layer and the n-electrode (for example, a Ti/Al/Ti/Au laminated structure: the bottom layer is Ti and the top layer is Au) is the AlN mol of the n-type AlGaN-based semiconductor layer. As the fraction increases, it tends to increase, especially when it exceeds 60%. . If the AlN mole fraction of the n-type AlGaN semiconductor layer is 60% or less, the contact resistance can be adjusted to 0.01 Ωcm ² or less by appropriately selecting the heat treatment temperature, and the forward voltage Vf is practically problematic. It becomes a level that does not exist (see Patent Document 4).

Therefore, if the wavelength difference (λp-λae) exceeds 10 nm in order to avoid a decrease in external quantum efficiency, the contact resistance and bulk resistivity will rather increase, resulting in a decrease in wall plug efficiency. Things can happen. Therefore, in order to avoid a decrease in the external quantum efficiency with respect to the target peak emission wavelength λp, if the average AlN mole fraction is set one step higher (about 8.33%), the wavelength difference (λp -λae) changes from less than 10 nm to more than 10 nm, and the wall plug efficiency decreases, the metastable AlGaN dominates in the layered region so that the wavelength difference does not significantly exceed 10 nm. It is preferable to set an average AlN mole fraction without forming . As a result, it is possible to prevent a decrease in external quantum efficiency and at the same time suppress a decrease in wall plug efficiency according to the target peak emission wavelength λp.

The present invention has been made in view of the above-mentioned problems, and aims to form metastable AlGaN locally in a layered region having a low AlN mole fraction in an n-type AlGaN semiconductor layer. By suppressing it, it is possible to prevent the deterioration of the luminous efficiency caused by the dominant formation of metastable AlGaN in the layered region.

In order to achieve the above objects, the present invention provides a nitride semiconductor comprising a light-emitting element structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are stacked vertically. An ultraviolet light emitting element,
The n-type layer is composed of an n-type AlGaN semiconductor,
the active layer disposed between the n-type layer and the p-type layer has a quantum well structure including one or more well layers made of an AlGaN-based semiconductor;
The p-type layer is composed of a p-type AlGaN semiconductor,
each of the semiconductor layers in the n-type layer, the active layer, and the p-type layer is an epitaxial growth layer having a surface on which a multi-stepped terrace parallel to the (0001) plane is formed;
wherein the n-type layer has a layered region with a locally low AlN mole fraction dispersed within the n-type layer;
Each extending direction of the layered region on a first plane perpendicular to the upper surface of the n-type layer has a portion that is inclined with respect to a line of intersection between the upper surface of the n-type layer and the first plane. death,
the integer n is 6 or 7,
A first average AlN mole fraction Xna1 over the entire depth direction of the n-type layer is
(n−0.25)/12<Xna1<(n+0.25)/12
is within the range of
A second average AlN mole fraction Xna2(d) at a depth d from the top of the n-type layer varies with the depth d such that within the n-type layer Xna2(d)=n /12, at least one specific depth has a region satisfying Xna2(d)<n/12 on the upper side of the specific depth, and a region satisfying Xna2(d)> on the lower side of the specific depth. There is a region of n/12,
A first feature of the present invention is that an intermediate AlGaN region having an AlN mole fraction of (n-0.5)/12 is formed in the layered region.

Further, in the nitride semiconductor ultraviolet light emitting device having the first characteristic, the third average AlN mole fraction Xna3 over the region from the upper end of the n-type layer to the specific depth is
(n−0.25)/12<Xna3<(n+0.25)/12
It is preferable to be within the range of

Further, in the nitride semiconductor ultraviolet light emitting device of the first characteristic, the second average AlN mole fraction Xna2(d) is, over the entire depth direction of the n-type layer,
(n−0.25)/12<Xna2(d)<(n+0.25)/12
It is preferable to be within the range of

In order to achieve the above objects, the present invention provides a nitride semiconductor comprising a light-emitting element structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are stacked vertically. A method for manufacturing an ultraviolet light emitting device,
The n-type layer of an n-type AlGaN semiconductor is epitaxially grown on a base portion including a sapphire substrate having a main surface inclined at a predetermined angle with respect to the (0001) plane. ) a first step of expressing a multi-stepped terrace parallel to the surface;
On the n-type layer, the active layer having a quantum well structure including one or more well layers made of an AlGaN-based semiconductor is epitaxially grown, and a multistep terrace parallel to the (0001) plane is formed on the surface of the well layer. A second step of expressing
a third step of forming the p-type layer of a p-type AlGaN semiconductor on the active layer by epitaxial growth;
In the first step,
the integer n is 6 or 7,
A first average AlN mole fraction Xna1 over the entire depth direction of the n-type layer is
(n−0.25)/12<Xna1<(n+0.25)/12
is within the range of
A second average AlN mole fraction Xna2(d) at a depth d from the top of the n-type layer varies with the depth d such that within the n-type layer Xna2(d)=n /12, at least one specific depth has a region satisfying Xna2(d)<n/12 above the specific depth, and a region satisfying Xna2(d)> below the specific depth. so that there is a region of n/12, and
A layered region with a locally low AlN mole fraction, which is uniformly dispersed in the n-type layer and is formed by extending obliquely upward,
so that an intermediate AlGaN region having an AlN mole fraction of (n−0.5)/12 is formed in the layered region,
A method for manufacturing a nitride semiconductor ultraviolet light emitting device is provided, the first feature of which is the formation of the n-type layer.

Further, in the method for manufacturing a nitride semiconductor ultraviolet light emitting device according to the first characteristic, in the first step, a third average AlN mole fraction Xna3 over a region from the upper end of the n-type layer to the specific depth but,
(n−0.25)/12<Xna3<(n+0.25)/12
It is preferable to form the n-type layer so as to be within the range of

Furthermore, in the method for manufacturing a nitride semiconductor ultraviolet light emitting device having the first characteristic, in the first step, the second average AlN mole fraction Xna2(d) is set in the depth direction of the n-type layer across the
(n−0.25)/12<Xna2(d)<(n+0.25)/12
It is preferable to form the n-type layer so as to be within the range of

The AlGaN-based semiconductor is represented by the general formula Al _1-x Ga _x N (0≦x≦1), and the bandgap energies that GaN and AlN can take are the lower and upper limits, respectively. A trace amount of impurities such as a group 3 element such as B or In or a group 5 element such as P may be contained within the range. A GaN-based semiconductor is basically a nitride semiconductor composed of Ga and N, but it may contain trace amounts of impurities such as group 3 elements such as Al, B or In or group 5 elements such as P. You can AlN-based semiconductors are nitride semiconductors basically composed of Al and N, but contain trace amounts of impurities such as group 3 elements such as Ga, B or In or group 5 elements such as P. You can Therefore, in the present application, the GaN-based semiconductor and the AlN-based semiconductor are each part of the AlGaN-based semiconductor.

Furthermore, n-type or p-type AlGaN semiconductors are AlGaN semiconductors doped with Si, Mg, or the like as donor or acceptor impurities. In the present application, an AlGaN-based semiconductor not specified as p-type or n-type means an undoped AlGaN-based semiconductor, but even an undoped AlGaN-based semiconductor does not include a small amount of donor or acceptor impurities that are unavoidably mixed. obtain. In addition, the first plane is not an exposed surface specifically formed in the manufacturing process of the n-type layer or a boundary surface with another semiconductor layer, but an imaginary plane extending vertically in parallel within the n-type layer. is a flat surface. Furthermore, in this specification, an AlGaN-based semiconductor layer, a GaN-based semiconductor layer, and an AlN-based semiconductor layer are semiconductor layers made of an AlGaN-based semiconductor, a GaN-based semiconductor, and an AlN-based semiconductor, respectively.

In the nitride semiconductor ultraviolet light emitting device of the first characteristic, the first average AlN mole fraction Xna1 is n/12, which is the discrete AlN mole fraction of metastable AlGaN where the integer n is 6 or 7. is controlled within a range of ±0.25/12 (±about 2.08%) around , a first metastable AlGaN region (Al _n Ga _12-n N ₁₂ ) having an AlN mole fraction of n/12 is stably formed. Furthermore, the second average AlN mole fraction Xna2(d) is also distributed in the vicinity of n/12. As a result, a second metastable AlGaN region (Al _n−1 Ga _{13 -n} N ₁₂ ) is not predominantly formed, instead an intermediate AlGaN region (Al _n-0.5 Ga _{12.5 −n} N ₁₂ ) are formed.

Therefore, in a nitride semiconductor ultraviolet light emitting device that utilizes metastable AlGaN in the n-type layer, when metastable AlGaN is predominantly formed in the layered region, the target peak emission wavelength λp is determined by the AlN mole fraction is within a certain wavelength range where it is difficult to simultaneously avoid a decrease in external quantum efficiency and a decrease in wall-plug efficiency due to the selection of discrete values of about 8.33%. wherein an intermediate AlGaN region is formed within the layered region and a first metastable AlGaN region is formed within the n-type body region to avoid a reduction in external quantum efficiency while at the same time reducing wall plug efficiency. can be suppressed.

Furthermore, according to the method for manufacturing a nitride semiconductor ultraviolet light emitting device having the first characteristic, the nitride semiconductor ultraviolet light emitting device having the first characteristic is manufactured, so metastable AlGaN is dominant in the layered region. A decrease in luminous efficiency due to the formation can be prevented.

Furthermore, in addition to the above first feature, the present invention provides that the second average AlN mole fraction Xna2(d) in a region from the upper end of the n-type layer to the specific depth,
Xna2(d)≤n/12
The present invention provides a nitride semiconductor ultraviolet light emitting device having a second feature that it is within the range of:

Furthermore, in addition to the above first feature, the present invention is characterized in that, in the first step, the second average AlN mole fraction Xna2(d) is from the upper end of the n-type layer to the specific depth. in the area
Xna2(d)≤n/12
There is provided a method for manufacturing a nitride semiconductor ultraviolet light emitting device, characterized in that the n-type layer is formed so as to fall within the range of:

According to the method for manufacturing the nitride semiconductor ultraviolet light emitting device of the second characteristic or the nitride semiconductor ultraviolet light emitting device nitride semiconductor ultraviolet light emitting device of the second characteristic, the contact resistance between the n-electrode and the n-type layer, and The bulk resistivity with respect to the current flowing through the upper layer portion of the n-type layer can be further suppressed, and the deterioration of the wall plug efficiency can be further suppressed while avoiding the deterioration of the external quantum efficiency.

Further, in the nitride semiconductor ultraviolet light emitting device having the second characteristic, in a region where the second average AlN mole fraction Xna2(d) is deeper than the specific depth of the n-type layer,
Xna2(d)≧n/12
It is preferable to be within the range of

Further, in the method for manufacturing a nitride semiconductor ultraviolet light emitting device having the second characteristic, in the first step, the second average AlN mole fraction Xna2(d) is the specific depth of the n-type layer. In a deeper realm,
Xna2(d)≧n/12
It is preferable to form the n-type layer so as to be within the range of

According to any of the above preferred embodiments, absorption of light emitted from the active layer can be further suppressed in a region deeper than the specific depth of the n-type layer, and a decrease in external quantum efficiency can be further suppressed.

Further, in the nitride semiconductor ultraviolet light emitting device having the first or second characteristic, the peak emission wavelength is set to a predetermined value within the range of 280 nm to 315 nm when the integer n is 7, and the integer n is 6, it is preferably set to a predetermined value within the range of 300 nm to 330 nm.

Furthermore, in the method for manufacturing a nitride semiconductor ultraviolet light emitting device having the above characteristics, in the second step,
When the integer n is 6, the peak emission wavelength of the nitride semiconductor ultraviolet light emitting element is within the range of 300 nm to 330 nm when the integer n is 6, so that the peak emission wavelength is a predetermined value within the range of 280 nm to 315 nm when the integer n is 7. It is preferable to form the active layer so as to have a predetermined value.

According to any of the above preferred embodiments, when the integer n is 7, for a particular peak emission wavelength set to a predetermined value within the range of 280 nm to 315 nm, when the integer n is 6: To prevent a decrease in luminous efficiency due to the dominant formation of metastable AlGaN in the layered region, respectively, for a specific peak emission wavelength set to a predetermined value within the range of 300 nm to 330 nm. can be done. The specific peak emission wavelength is within the specific wavelength range described above, and the formation of metastable AlGaN predominantly in the layered region reduces the emission efficiency (external quantum efficiency or wall plug efficiency). It is the peak emission wavelength at which degradation can occur.

Further, in the nitride semiconductor ultraviolet light emitting device according to the first or second characteristic, the active layer has a multiple quantum well structure including two or more well layers, and an AlGaN-based quantum well layer is disposed between the two well layers. A barrier layer composed of a semiconductor is preferably present.

Further, in the method for manufacturing a nitride semiconductor ultraviolet light emitting device having the first or second characteristic, in the second step, the well layer made of an AlGaN-based semiconductor and the barrier layer made of an AlGaN-based semiconductor are alternately formed. It is preferable to form the active layer having a multiple quantum well structure including two or more well layers by epitaxial growth.

According to any of the preferred embodiments described above, the active layer has a multiple quantum well structure, and an improvement in luminous efficiency can be expected compared to the case where there is only one well layer.

Further, the nitride semiconductor ultraviolet light emitting device according to the first or second characteristic further includes a base portion including a sapphire substrate, and the sapphire substrate has a main surface inclined at a predetermined angle with respect to the (0001) plane. and the light emitting element structure is formed above the main surface, and each semiconductor layer from the main surface of the sapphire substrate to the p-type layer is formed in a multi-step shape parallel to the (0001) plane It is preferably an epitaxially grown layer having a terraced surface.

According to the preferred embodiment, epitaxial growth can be performed using a sapphire substrate having an off-angle so that multi-stepped terraces appear on the surface of each layer from the main surface of the sapphire substrate to the surface of the active layer. It is possible to realize a nitride semiconductor ultraviolet light emitting device having the above characteristics.

According to the nitride semiconductor ultraviolet light-emitting device or the method for manufacturing the nitride semiconductor ultraviolet light-emitting device having the first or second feature, at a specific peak emission wavelength, AlN moles are locally present in the n-type AlGaN-based semiconductor layer. By deliberately suppressing the formation of metastable AlGaN in the layered region with a low index, it is possible to prevent a decrease in luminous efficiency caused by predominantly forming metastable AlGaN in the layered region. Furthermore, when setting the target peak emission wavelength within a predetermined wavelength range, the embodiment that utilizes metastable AlGaN in the layered region of the n-type layer and the embodiment that does not utilize the metastable AlGaN are adjusted to the target peak emission wavelength. By using them properly according to need, it is possible to increase the degree of freedom in setting the peak emission wavelength while preventing a decrease in luminous efficiency.

FIG. 2 is a diagram schematically showing the wurtzite crystal structure of AlGaN; FIG. 2 is a plan view showing the positional relationship between each site on the A plane and each site on the B plane viewed from the c-axis direction of the wurtzite crystal structure shown in FIG. 1 ; On the site plane (A3 plane, B3 plane) of the Group 3 element in each metastable AlGaN represented by Al ₁ Ga ₂ N ₃ , Al ₁ Ga ₁ N ₂ , and Al ₂ Ga ₁ N ₃ with an AlGaN composition ratio of an integer ratio Schematically shows the symmetric arrangement structure of Al and Ga in FIG. FIG. 2 is a cross-sectional view of essential parts schematically showing an example of the structure of the nitride semiconductor ultraviolet light emitting device according to the first embodiment; FIG. 5 is a cross-sectional view of a main part schematically showing an example of the lamination structure of the active layer of the nitride semiconductor ultraviolet light emitting device shown in FIG. 4; FIG. 6 is a diagram schematically showing a more detailed structure of the inclined area IA shown in FIG. 5; The emission wavelength of the quantum well structure composed of the AlGaN well layer and the AlGaN barrier layer, the film thickness of the well layer, and the AlN mole fraction of the barrier layer when the AlN mole fraction of the Ga-enriched well region 220a is 50%. A graph showing the relationship. Emission wavelength of quantum well structure composed of AlGaN well layer and AlGaN barrier layer, film thickness of well layer, and AlN mole fraction of barrier layer when Ga-enriched well region 220a has an AlN mole fraction of 41.7% A graph showing the relationship between Emission wavelength of a quantum well structure composed of an AlGaN well layer and an AlGaN barrier layer, the film thickness of the well layer, and the AlN mole fraction of the barrier layer when the AlN mole fraction of the Ga-enriched well region 220a is 33.3%. A graph showing the relationship between 4 is a graph showing the relationship between the emission wavelength of a quantum well structure composed of GaN well layers and AlGaN barrier layers, the film thickness of the well layers, and the AlN mole fraction of the barrier layers. FIG. 5 is a plan view schematically showing an example of the structure of the nitride semiconductor ultraviolet light emitting device shown in FIG. 4 when viewed from the upper side of FIG. 4; 7 is a graph showing an example of changes in second average AlN mole fraction Xna2(d) at depth d from the upper end of the n-type layer according to depth d; SEM image showing the main part of the cross section of the sample piece measured for the AlN mole fraction by the CL method. FIG. 14 is a diagram showing first and second CL spectra on six Y-coordinates on the measurement cross section of the sample piece shown in FIG. 13; HAADF-STEM images showing four measurement areas A to D where the AlN mole fraction in the layered region of the sample piece is measured by cross-sectional TEM-EDX line analysis. FIG. 2 is a cross-sectional view of a main part schematically showing an example of the structure of a nitride semiconductor ultraviolet light emitting device according to a second embodiment; FIG. 17 is a cross-sectional view of a main part schematically showing an example of a layered structure of a main part including an active layer of the nitride semiconductor ultraviolet light emitting device shown in FIG. 16; FIG. 2 is a cross-sectional view of a main part schematically showing an example of an element structure of a general ultraviolet light emitting diode;

A nitride semiconductor ultraviolet light emitting device (hereinafter simply referred to as "light emitting device") according to an embodiment of the present invention will be described based on the drawings. In the schematic diagrams of the drawings used in the following explanation, the contents of the invention are schematically shown with emphasis on the essential parts for easy understanding of the explanation, so the dimensional ratio of each part does not necessarily correspond to the actual element. They do not have the same dimensional ratio. In the following description of the present embodiment, it is assumed that the light-emitting element is a light-emitting diode.

[First embodiment]
<Element structure of light-emitting element>
As shown in FIG. 4, the light-emitting device 1 of the first embodiment includes a base portion 10 including a sapphire substrate 11, a plurality of AlGaN-based semiconductor layers 21 to 24, a p-electrode 26, and an n-electrode 27. and a structure 20 . The light emitting element 1 is mounted (flip-chip mounted) with the side of the light emitting element structure 20 (upper side in FIG. 4) facing a base for mounting (such as a submount). The direction is the base portion 10 side (lower side in FIG. 4). In this specification, for convenience of explanation, the direction perpendicular to the main surface 11a of the sapphire substrate 11 (or the upper surfaces of the underlying portion 10 and the AlGaN semiconductor layers 21 to 24) is referred to as the "vertical direction" (or the "vertical direction"). The direction from the base portion 10 to the light emitting element structure portion 20 is defined as the upward direction, and the opposite direction is defined as the downward direction. A plane parallel to the vertical direction is referred to as a "first plane". Further, a plane parallel to the main surface 11a of the sapphire substrate 11 (or the upper surfaces of the underlying portion 10 and the AlGaN-based semiconductor layers 21 to 24) is referred to as a "second plane", and a direction parallel to the second plane is referred to as a "second plane." lateral direction”.

The underlying portion 10 includes a sapphire substrate 11 and an AlN layer 12 directly formed on the principal surface 11 a of the sapphire substrate 11 . The sapphire substrate 11 has a main surface 11a inclined at an angle (off angle) within a certain range (for example, about 0.3° to 6°) with respect to the (0001) plane, and has a multistep shape on the main surface 11a. This is a slightly inclined substrate with exposed terraces.

The AlN layer 12 is composed of AlN crystal epitaxially grown from the main surface of the sapphire substrate 11 , and this AlN crystal has an epitaxial crystal orientation relationship with respect to the main surface 11 a of the sapphire substrate 11 . Specifically, for example, the AlN crystal is grown such that the C-axis direction (<0001> direction) of the sapphire substrate 11 and the C-axis direction of the AlN crystal are aligned. The AlN crystal forming the AlN layer 12 may be an AlN-based semiconductor layer that may contain a small amount of Ga or other impurities. In this embodiment, the film thickness of the AlN layer 12 is assumed to be approximately 2 μm to 3 μm. The structure of the base portion 10, the substrates to be used, and the like are not limited to those described above. For example, between the AlN layer 12 and the AlGaN-based semiconductor layer 21, an AlGaN-based semiconductor layer having an AlN mole fraction equal to or higher than the AlN mole fraction of the AlGaN-based semiconductor layer 21 may be provided.

The AlGaN-based semiconductor layers 21 to 24 of the light-emitting element structure 20 are composed of an n-type cladding layer 21 (n-type layer), an active layer 22, an electron block layer 23 (p-type layer), and a p-type layer in this order from the underlying portion 10 side. It has a structure in which the type contact layer 24 (p-type layer) is epitaxially grown in order and laminated.

In this embodiment, the AlN layer 12 of the base portion 10 epitaxially grown in order from the main surface 11a of the sapphire substrate 11, the n-type cladding layer 21 of the light emitting element structure portion 20, each semiconductor layer in the active layer 22, and the electron block. The layer 23 has a surface formed with multi-stepped terraces parallel to the (0001) plane derived from the main surface 11a of the sapphire substrate 11 by step-flow growth. As for the p-type contact layer 24 of the p-type layer, since it is formed by epitaxial growth on the electron blocking layer 23, a similar multi-stepped terrace can be formed, but a similar multi-stepped terrace is not necessarily formed. It does not have to have a surface.

In addition, as shown in FIG. 4, the active layer 22, the electron blocking layer 23, and the p-type contact layer 24 in the light-emitting element structure 20 are laminated on the second region R2 on the upper surface of the n-type cladding layer 21. The etched portion is removed by etching or the like and formed on the first region R1 on the upper surface of the n-type cladding layer 21 . The upper surface of the n-type cladding layer 21 is exposed in the second region R2 except for the first region R1. As schematically shown in FIG. 4, the upper surface of the n-type clad layer 21 may differ in height between the first region R1 and the second region R2. The upper surface is separately defined in the first region R1 and the second region R2.

In the n-type cladding layer 21 composed of an n-type AlGaN semiconductor, multi-stepped terraces parallel to the (0001) plane are formed on the growth surface in the epitaxial growth process, and Ga, which is easy to mass transfer, moves between adjacent terraces. By concentrating in the tilted regions tilted with respect to the connecting (0001) planes, Ga-enriched n-type regions with a lower AlN mole fraction than the terraced regions are formed. As the epitaxial growth progresses, the inclined region is formed by extending obliquely upward. As a result, the layered regions 21a having a low AlN mole fraction are locally dispersed uniformly in the n-type cladding layer 21. . Each extending direction of the layered region 21a on the first plane has a portion that is inclined with respect to the line of intersection between the upper surface of the n-type cladding layer 21 and the first plane.

In one embodiment, during the epitaxial growth of the n-type cladding layer 21, the formation of the Ga-enriched n-type region in the graded region, that is, mass transfer of Ga from the terrace region to the graded region causes In part, the density of Al can be relatively increased to form an Al-enriched n-type region in which the AlN mole fraction is higher than the average AlN mole fraction.

As described above in the background art section, the layered region 21a extends in an oblique direction with respect to the surface of the n-type cladding layer 21, and the bandgap energy is locally reduced, so that carriers are easily localized. and functions as a low-resistance current path. A region other than the layered region 21a in the n-type cladding layer 21 is called an n-type body region 21b.

In this embodiment, the first average AlN mole fraction Xna1 over the entire depth of the n-type cladding layer 21 is within the range represented by the following inequality (1). Incidentally, n in the following formula (1) is an integer of 6 or 7.
(n−0.25)/12<Xna1<(n+0.25)/12 (1)

Furthermore, in the present embodiment, the second average AlN mole fraction Xna2(d) at the depth d (nm) from the upper surface of the n-type cladding layer 21 changes according to the depth d, and Xna2( d) There are 1 or more depths d0 at which =0. In at least one specific depth dx of the depths d0, there exists a region where Xna2(d)<n/12 on the upper side across the specific depth dx, and Xna2(d)> on the lower side. There is a region of n/12.

As a typical example of the depth d0 and the specific depth dx, it is assumed that there is one depth d0 and d0=dx. Furthermore, in this typical example, Xna2(d)>n/12 at the start of the growth of the n-type cladding layer 21 as in the example shown in FIG. 12 described later, and Xna2(d )<n/12, where Xna2(d) decreases. Note that at least one depth d0 may be Xna2(d0)=0 in a continuous range of depths d instead of being Xna2(d0)=0 at one point. The same applies to the specific depth dx.

Furthermore, as one embodiment, the third average AlN mole fraction Xna3 over the region from the upper surface of the n-type cladding layer 21 to the specific depth dx is within the range represented by the following inequality (2) preferably in
(n−0.25)/12<Xna3<(n+0.25)/12 (2)
When there are a plurality of specific depths dx, it is preferable that the above relationship is satisfied for each of the specific depths dx.

Furthermore, as one embodiment, the second average AlN mole fraction Xna2(d) is within the range represented by the following inequality of formula (3) throughout the depth direction of the n-type cladding layer 21 is more preferable.
(n−0.25)/12<Xna2(d)<(n+0.25)/12 (3)

Furthermore, as one embodiment, Xna2(d) is preferably within the range represented by the following inequality (4) in the region from the upper surface of the n-type cladding layer 21 to the specific depth dx. Furthermore, in the above preferred embodiment in which Xna2(d) is within the range represented by formula (3), Xna2(d) is the following in a region from the upper surface of the n-type cladding layer 21 to a specific depth dx: It is more preferable to be within the range represented by the inequality of formula (5).
Xna2(d)≤n/12 (4)
(n−0.25)/12<Xna2(d)≦n/12 (5)

Furthermore, in the above preferred embodiment in which Xna2(d) is within the range represented by formula (4) or formula (5), Xna2(d) is expressed by the following formula (6) in a region deeper than the specific depth dx ), more preferably within the range represented by the inequality of formula (7).
n/12≤Xna2(d) (6)
n/12≦Xna2(d)<(n+0.25)/12 (7)

Also, the first average AlN mole fraction _Xna1 is the AlN mole fraction ( _n / ₁₂ ) is controlled within a range of ±0.25/12 (±about 2.08%) around the reference, the first metastable AlGaN region is uniform in the n-type body region 21b. is formed in In the region where the second average AlN mole fraction Xna2(d) is lower than the AlN mole fraction (n/12) of the first metastable AlGaN region, the Al-enriched n-type region of the n-type body region 21b A first metastable AlGaN region is formed therein.

In the layered region 21a, the AlN mole fraction is one step (approximately 8.33%) smaller than that of the first metastable AlGaN region, and the AlGaN composition ratio is Al _n−1 Ga _13-n N ₁₂ with an integer ratio. A second metastable AlGaN region can be formed with the mass transfer of Ga during the formation of the layered region 21a. However, within layered region 21a, the second metastable AlGaN region is not predominantly formed, but instead an intermediate AlGaN region in which the AlN mole fraction is intermediate between the first and second metastable AlGaN regions. (Al _n-0.5 Ga _12.5-n N ₁₂ ) is formed.

In this embodiment, the thickness of the n-type cladding layer 21 is assumed to be about 1 μm to 2 μm, which is the same as the thickness used in general nitride semiconductor ultraviolet light emitting devices. , 2 μm to 4 μm.

The active layer 22 includes two or more well layers 220 composed of AlGaN-based semiconductors (excluding AlN-based semiconductors) and one or more layers composed of AlGaN-based semiconductors (excluding GaN-based semiconductors) or AlN-based semiconductors. It has a multiple quantum well structure in which barrier layers 221 are alternately laminated. It is not always necessary to provide the barrier layer 221 between the bottom well layer 220 and the n-type cladding layer 21 . In addition, in this embodiment, the barrier layer 221 is not provided between the uppermost well layer 220 and the electron blocking layer 23. An AlGaN layer or an AlN layer may be provided.

The electron block layer 23 is composed of a p-type AlGaN semiconductor. The p-type contact layer 24 is composed of a p-type AlGaN semiconductor or a p-type GaN semiconductor. The p-type contact layer 24 is typically composed of p-GaN.

FIG. 5 schematically shows an example of a laminated structure (multiple quantum well structure) of well layers 220 and barrier layers 221 in the active layer 22 . FIG. 5 illustrates a case where the well layers 220 and the barrier layers 221 each include three layers. Three layers of a barrier layer 221 and a well layer 220 are laminated in this order on the n-type cladding layer 21, and the electron blocking layer 23 is positioned on the well layer 220 of the uppermost layer.

The structure in which the terraces T in the well layer 220, the barrier layer 221, and the electron blocking layer 23 shown in FIG. be. Between the laterally adjacent terraces T in each layer, as described above, an inclined area IA inclined with respect to the (0001) plane is formed. A region other than the inclined region IA, which is sandwiched between the terraces T, is referred to as a terrace region TA. In this embodiment, the depth of one terrace T (distance between adjacent inclined areas IA) is assumed to be several tens of nanometers to several hundreds of nanometers. Therefore, the (0001) plane appearing stepwise in the inclined area IA is distinguished from the terrace plane of the multi-stepped terrace T. FIG. FIG. 6 schematically shows, for example, a stepped structure (macrostep structure) appearing on the surface of the inclined region IA of one well layer 220. As shown in FIG.

As schematically shown in FIG. 5, when the well layer 220 is composed of an AlGaN-based semiconductor and the AlN mole fraction is not 0%, in each layer of the well layer 220, the mass of Ga from the terrace region TA to the inclined region IA is Due to the migration, a Ga-enriched well region 220a having an AlN mole fraction lower than the average AlN mole fraction Xwa in the well layer 220 is formed in the graded region IA. Further, in one embodiment, along with the formation of the Ga-enriched well region 220a within the graded area IA, i.e., due to mass transfer of Ga from the terrace area TA to the graded area IA, in a portion of the terrace area TA: The density of Al may be relatively increased to form an Al-enriched well region in which the AlN mole fraction is higher than the average AlN mole fraction Xwa.

Further, as a preferred embodiment, when the well layer 220 is composed of an AlGaN-based semiconductor and the AlN mole fraction is not 0%, the average AlN mole fraction Xwa of the well layer 220 is, for example, Ga-enriched When metastable AlGaN having an AlN mole fraction of Xw0 is formed in the well region 220a, it is preferably adjusted within a range of approximately Xw0+2% to Xw0+3%. According to this preferred embodiment, the AlN mole fraction difference between the inclined region IA and the terrace region TA in the well layer 220 is 4% or less, which can suppress the occurrence of double emission peaks due to the AlN mole fraction difference. Note that even if the average AlN mole fraction Xwa of the well layer 220 is outside the range of Xw0+2% to Xw0+3%, there are locally Ga-rich As long as the enriched well region 220a is formed, any amount within the range of Xw1+2% to Xw1+3%, where Xw1% is the AlN mole fraction in the Ga-enriched well region 220a corresponding to the target value of the peak emission wavelength. value.

In the present embodiment, when the barrier layer 221 is composed of an AlGaN-based semiconductor (excluding an AlN-based semiconductor), the barrier layer 221 also has an AlN mole fraction in the graded region IA equal to the average of the barrier layer 221. A Ga-enriched barrier region 221a having a lower AlN mole fraction Xba is formed. Furthermore, in one embodiment, an Al-enriched barrier region having a higher AlN mole fraction than the average AlN mole fraction Xba of the barrier layer 221 is formed in a part of the terrace region TA, similar to the well layer 220. It's okay to be there.

As a preferred embodiment, when forming a metastable AlGaN region with an AlN mole fraction Xb0 in the Ga-enriched barrier region 221a of the barrier layer 221, the average AlN mole fraction Xba of the barrier layer 221 is approximately , Xb0+2% to Xb0+8%. As a result, about 2% or more is ensured as the AlN mole fraction difference between the Ga-enriched barrier region 221a of the barrier layer 221 and the terrace region TA.

Furthermore, as a preferred embodiment, the AlN mole fraction of the terrace region TA of the barrier layer 221 is 1% or more higher than the AlN mole fraction of the Ga-enriched barrier region 221a within a range of approximately 51% to 90%, It is set to be higher, preferably 2% or more, more preferably 4% or more. In order to sufficiently secure the effect of localizing carriers in the Ga-enriched barrier region 221a, the AlN mole fraction difference between the Ga-enriched barrier region 221a and the terrace region TA in the barrier layer 221 is set to 4 to 5% or more. Although it is preferable to do so, the effect of carrier localization can be expected even with a concentration of about 1 to 2%.

In this embodiment, in the electron blocking layer 23 as well, the Ga-enriched EB region 23a having a lower AlN mole fraction than the average AlN mole fraction Xea of the electron blocking layer 23 is formed in the gradient region IA. Furthermore, in one embodiment, similarly to the well layer 220, an Al-enriched EB region having a higher AlN mole fraction than the average AlN mole fraction Xea of the electron blocking layer 23 is formed in a part of the terrace region TA. It's okay to be.

The AlN mole fraction of the terrace region TA of the electron blocking layer 23 is generally within the range of 69% to 90%, and is 20% or more, preferably 25% or more, more preferably 25% or more than the AlN mole fraction of the terrace region of the well layer 220. is set to be higher than 30%. Furthermore, the AlN mole fraction of the Ga-enriched EB region 23a of the electron blocking layer 23 is 20% or more, preferably 25% or more, more preferably 30%, more than the AlN mole fraction of the Ga-enriched well region 220a of the well layer 220. It is set to be higher than %.

As a preferred embodiment, when forming a metastable AlGaN region with an AlN mole fraction Xe0 in the Ga-enriched EB region 23a of the electron block layer 23, the average AlN mole fraction Xea of the electron block layer 23 is , Xe0+2% to Xe0+8%. Thereby, about 2% or more is ensured as the AlN mole fraction difference between the Ga-enriched EB region 23a of the electron block layer 23 and the terrace region TA.

In the laminated structure (macrostep structure) of the light emitting element structure portion 20 shown in FIG. In the active layer 22, in the Ga-enriched well region 220a having a locally low AlN mole fraction present in the graded region IA of the well layer 220, the AlN mole fraction locally present in the graded region IA of the barrier layer 221 In the Ga-enriched barrier region 221a with a low AlN mole fraction, carriers are easily localized. , carriers are more likely to be localized. Therefore, from the n-type cladding layer 21 side through the layered region 21a, from the electron blocking layer 23 side through the Ga-enriched EB region 23a, the Ga-enriched well region 220a of the well layer 220 is efficiently charged. , and the recombination of carriers (electrons and holes) in the well layer 220 can improve the luminous efficiency.

In this embodiment, the film thickness of the well layer 220, including the terrace region TA and the inclined region IA, is set within a range of, for example, 3ML to 14ML according to the target value of the peak emission wavelength λp of the light emitting element 1. there is Also, the film thickness of the barrier layer 221 is set within a range of 6 nm to 8 nm, for example, including the terrace area TA and the inclined area IA. Furthermore, the film thickness of the electron blocking layer 23 is set within a range of, for example, 15 nm to 30 nm (optimum value is about 20 nm), including the terrace area TA and the inclined area IA.

When the well layer 220 is composed of an AlGaN-based semiconductor and the AlN mole fraction is not 0%, the AlN mole fraction and film thickness of the well layer 220 (especially the Ga-enriched well region 220a in the graded region IA) are And the AlN mole fraction of the barrier layer and the electron blocking layer 23 adjacent to the well layer 220 (particularly the Ga-enriched barrier region 221a and the Ga-enriched EB region 23a in the graded region IA) is the peak emission of the light-emitting device 1. It is set according to the target value of the wavelength λp.

When the well layer 220 is composed of a GaN-based semiconductor and the AlN mole fraction is 0%, the barrier layers and the electron block layer 23 adjacent to the well layer 220 (in particular, the Ga-enriched barrier region 221a in the graded region IA) and the AlN molar fraction of the Ga-enriched EB region 23 a ) and the film thickness of the well layer 220 are set according to the target value of the peak emission wavelength λp of the light emitting device 1 .

7, 8 and 9 show the quantum well structure model in which the well layer 220 and the barrier layer 221 are made of AlGaN, and the film thickness of the well layer is varied within the range of 3ML to 14ML or 4ML to 14ML. It is a graph of the simulation result of the emission wavelength (corresponding to the peak emission wavelength) obtained by As a condition of the above simulation, it is assumed that the Ga-enriched well region 220a of the well layer 220 is dominated by metastable AlGaN having an AlGaN composition ratio of an integer ratio, and the Ga-enriched well region 220a of the well layer 220 is 50% (1/2), which is the AlN mole fraction of metastable AlGaN, in FIG. 7, and 41.7% (1/2), which is the AlN mole fraction of metastable AlGaN in FIG. 5/12), and in FIG. 9, 33.3% (1/3), which is the AlN mole fraction of metastable AlGaN, and in each of FIGS. The AlN mole fraction of the region 221a was set to 66.7% (2/3), 75% (3/4), and 83.3% (5/6). The simulation results shown in FIGS. 7 to 9 assume that the well layer 220 emits ultraviolet rays significantly in the inclined region IA. Therefore, it is important to satisfy the film thickness condition of the well layer 220 in the inclined region IA.

7 to 9, when the film thickness of the well layer 220 is within the range of 3 ML to 14 ML, the smaller the film thickness of the well layer 220, the greater the quantum confinement effect in the well layer 220 and the shorter the emission wavelength. Furthermore, it can be seen that as the AlN mole fraction of the barrier layer 221 increases, the degree of change in the emission wavelength with respect to the change in the film thickness of the well layer 220 increases. Further, from FIG. 7, when the AlN mole fraction of the Ga-enriched well region 220a is 50%, the emission wavelength is approximately 246 nm within the above ranges of the film thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221. It can be seen that it varies in the range of ~295 nm. From FIG. 8, when the AlN mole fraction of the Ga-enriched well region 220a is 41.7%, the emission wavelength is approximately 249 nm within the above ranges of the film thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221. It can be seen that it varies in the range of ~311 nm. From FIG. 9, when the AlN mole fraction of the Ga-enriched well region 220a is 33.3%, the emission wavelength is approximately 261 nm within the above ranges of the film thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221. It can be seen that it varies in the range of ~328 nm. Furthermore, if the barrier layer 221 is made of AlN (AlN mole fraction=100%), the emission wavelength can be further extended.

7 to 9, metastable AlGaN having an AlGaN composition ratio of Al ₁ Ga ₁ N ₂ , Al ₅ Ga ₇ N ₁₂ , or Al ₁ Ga ₂ N ₃ is present in the Ga-enriched well region 220 a of the well layer 220 . According to the AlN mole fraction of the metastable AlGaN formed, the film thickness of the well layer 220 is set within the range of 3 ML to 14 ML, and the AlN mole fraction of the Ga-enriched barrier region 221a of the barrier layer 221 is set to 66. It can be seen that the peak emission wavelength can be set within the range of 246 nm to 328 nm by adjusting each within the range of 7% to 100%.

FIG. 10 shows that the AlN mole fraction of the barrier layer is 66.7% (AlGaN) and 100% (AlN) for the quantum well structure model in which the well layer is GaN and the barrier layer is AlGaN or AlN. 2 is a graph of simulation results of emission wavelengths (corresponding to peak emission wavelengths) obtained by changing the film thickness of the well layer within the range of 4 ML to 10 ML. From FIG. 10, it can be seen that the emission wavelength varies within the range of approximately 270 nm to 325 nm. Therefore, even when the well layer is made of GaN (AlN mole fraction=0%), the film thickness of the well layer 220 is within the range of 4 ML to 10 ML, and the Ga-enriched barrier region 221a of the barrier layer 221 is It can be seen that by adjusting the AlN mole fraction within the range of 66.7% to 100%, the peak emission wavelength can be set within the range of 270 nm to 325 nm.

As a preferred embodiment of the present embodiment, the target value of the peak emission wavelength λp of the light emitting element 1 is set, for example, in the range of 280 nm to 315 nm when n = 7, and 300 nm to 330 nm when n = 6. It is assumed that each is set within the range of .

When n=7, the first average AlN mole fraction Xna1 is within the range shown by the above formula (1), that is, within the range of about 56.3% to about 60.4%. The absorption edge wavelength (λae) of the n-type cladding layer 21 determined by the average AlN molar fraction Xna1 of 1 is located within the range of about 263 nm to about 269 nm. Therefore, if the target value of the peak emission wavelength λp is within the above range of 280 nm to 315 nm, the wavelength difference (λp−λae) between the peak emission wavelength (λp) and the absorption edge wavelength (λae) is ensured to be 10 nm or more. , and light emission absorption in the n-type cladding layer 21 is sufficiently suppressed. Here, as a comparative example in the case of n=7, assuming that a second metastable AlGaN region having an AlN mole fraction of 50% is predominantly formed in the layered region 21a, the first average Since the typical AlN molar fraction Xna1 is a value of about 54.2%, the absorption edge wavelength (λae) is about 273 nm, and the target value of the peak emission wavelength λp is less than 283 nm. The wavelength difference becomes less than 10 nm, and emission absorption occurs in the n-type cladding layer 21, which may lead to a decrease in external quantum efficiency.

When n=6, the first average AlN mole fraction Xna1 is within the range shown by the above formula (1), that is, within the range of about 47.9% to about 52.1%. The absorption edge wavelength (λae) of the n-type cladding layer 21 determined by the average AlN molar fraction Xna1 of 1 is located within the range of about 276 nm to about 283 nm. Therefore, if the target value of the peak emission wavelength λp is within the above range of 300 nm to 330 nm, the wavelength difference (λp−λae) between the peak emission wavelength (λp) and the absorption edge wavelength (λae) is sufficiently 10 nm or more. is ensured, and light emission absorption in the n-type cladding layer 21 is sufficiently suppressed. Also, it is possible to lower the lower limit of the target value from 300 nm to about 293 nm. Here, as a comparative example in the case of n=6, assuming that a second metastable AlGaN region having an AlN mole fraction of about 41.7% is predominantly formed in the layered region 21a, the first Since the average AlN molar fraction Xna1 of 1 is around 45.8%, its absorption edge wavelength (λae) is about 286 nm, and the target value of the peak emission wavelength λp is less than 296 nm. Then, the wavelength difference becomes less than 10 nm, and emission absorption occurs in the n-type cladding layer 21, which may lead to a decrease in external quantum efficiency.

the AlN mole fraction (n/12) of the first metastable AlGaN region formed in the n-type body region 21b is about 58.3% for n=7 and 50% for n=6; The contact resistance between the n-type cladding layer 21 and the n-electrode 27 formed on its exposed surface is higher than when the AlN mole fraction is less than 50%, but higher than when the AlN mole fraction is 60%. is low, and a significant increase in contact resistance is suppressed.

Since the first average AlN mole fraction Xna1 is controlled within the range shown by the above formula (1), in the n-type body region 21b, when n=7, the AlN mole fraction is There may also be some regions above 60%. However, the n-electrode 27 is formed on the exposed surface of the n-type cladding layer 21 in the second region R2, and the contact area with the upper surface of the n-type cladding layer 21 is sufficiently large. In addition to the region with a mole fraction greater than 60%, it also includes a first metastable AlGaN region with an AlN mole fraction of about 58.3% and a layered region with an even smaller AlN mole fraction. The average contact resistance between the mold cladding layers 21 is kept low. In a preferred embodiment, when n=7, Xna2(d) is within the range represented by the above inequality (4) in the region from the upper surface of the n-type cladding layer 21 to the specific depth dx. , the average contact resistance between the n-electrode 27 and the n-type cladding layer 21 can be further reduced. Also, when n=6, the average contact resistance between the n-electrode 27 and the n-type cladding layer 21 is kept lower than when n=7.

Furthermore, in this embodiment, in order to suppress emission absorption in the n-type cladding layer 21, the first average AlN mole fraction Xna1 and the second average AlN mole fraction Xna2(d) are set to Since it is not set unnecessarily high, an unnecessary increase in bulk resistivity is also suppressed.

The p-electrode 26 is composed of a multilayer metal film such as Ni/Au, and is formed on the upper surface of the p-type contact layer 24 . The n-electrode 27 is composed of, for example, a multilayer metal film such as Ti/Al/Ti/Au, and is formed on a part of the exposed surface in the second region R2 of the n-type cladding layer 21 . The p-electrode 26 and the n-electrode 27 are not limited to the multilayer metal films described above, and the electrode structure such as the metals constituting each electrode, the number of layers, and the order of layers may be changed as appropriate. FIG. 11 shows an example of the shape of the p-electrode 26 and the n-electrode 27 viewed from above the light emitting element 1 . In FIG. 11, a line BL existing between the p-electrode 26 and the n-electrode 27 indicates a boundary line between the first region R1 and the second region R2, and includes the active layer 22, the electron blocking layer 23, and the p-type electrode. It coincides with the outer peripheral side wall surface of the contact layer 24 .

In the present embodiment, as shown in FIG. 11, the first region R1 and the p-electrode 26 have a comb shape as an example in plan view. The visual shape, arrangement, and the like are not limited to those illustrated in FIG. 11 .

When a forward bias is applied between the p-electrode 26 and the n-electrode 27, holes are supplied from the p-electrode 26 toward the active layer 22, and electrons are supplied from the n-electrode 27 toward the active layer 22. Holes and electrons each reach the active layer 22 and recombine to emit light. Further, this causes a forward current to flow between the p-electrode 26 and the n-electrode 27 .

<Method for manufacturing light-emitting element>
Next, an example of a method for manufacturing the light emitting device 1 illustrated in FIG. 4 will be described.

First, the AlN layer 12 included in the base portion 10 and the nitride semiconductor layers 21 to 24 included in the light emitting element structure portion 20 are epitaxially grown in order on the sapphire substrate 11 by the metal-organic compound vapor phase epitaxy (MOVPE) method. lamination. At this time, the n-type cladding layer 21 is doped with, for example, Si as a donor impurity, and the electron block layer 23 and the p-type contact layer 24 are doped with, for example, Mg as an acceptor impurity.

In this embodiment, at least the surfaces of the AlN layer 12, the n-type cladding layer 21, the active layer 22 (well layer 220 and barrier layer 221), and the electron block layer 23 are provided with multistep terraces parallel to the (0001) plane. In order to expose the sapphire substrate 11, the main surface 11a is inclined with respect to the (0001) plane at an angle (off angle) within a certain range (for example, about 0.3 ° to 6 °), A slightly inclined substrate is used in which a multi-stepped terrace is exposed on the main surface 11a.

As conditions for such epitaxial growth, in addition to the use of the slightly inclined (0001) sapphire substrate 11 described above, for example, a growth rate at which multi-stepped terraces are likely to appear (specifically, for example, growth temperature, raw material gas and carrier The growth rate is achieved by appropriately setting various conditions such as gas supply amount and flow rate. Since these conditions may vary depending on the type and structure of the film forming apparatus, several samples are actually produced in the film forming apparatus to specify these conditions.

As for the growth condition of the n-type cladding layer 21, the growth starting point of the layered region 21a is set in the stepped portion (inclined region) between the multi-stepped terraces formed on the upper surface of the AlN layer 12 immediately after the growth is started by the mass transfer of Ga. The growth temperature, the growth pressure, and the donor impurity concentration are set so that the layered region 21a can grow obliquely upward due to the segregation associated with the mass transfer of Ga, following the epitaxial growth of the n-type cladding layer 21. selected.

Specifically, the growth temperature is preferably 1050° C. or higher at which mass transfer of Ga easily occurs and 1150° C. or lower at which good n-type AlGaN can be prepared. Further, as a preferred embodiment, when forming the first metastable AlGaN region having an AlN mole fraction of n/12 in the n-type body region 21b, at a growth temperature exceeding 1170° C., the mass of Ga Due to excessive migration, the AlN mole fraction tends to fluctuate randomly even in metastable AlGaN, so it becomes difficult to stably form a metastable AlGaN region with an AlN mole fraction of 50% to 58.3%. there is a possibility. As for the growth pressure, 75 Torr or less is preferable as a favorable AlGaN growth condition, and 10 Torr or more is realistic and preferable as the control limit of the film forming apparatus. The donor impurity concentration is preferably about 1×10 ¹⁸ to 5×10 ¹⁸ cm ⁻³ . The above growth temperature, growth pressure, and the like are only examples, and optimal conditions may be appropriately specified according to the film forming apparatus to be used.

The supply amounts and flow rates of source gases (trimethylaluminum (TMA) gas, trimethylgallium (TMG) gas, and ammonia gas) and carrier gases used in the metal-organic compound vapor phase epitaxy are determined by the first is set as a target value of the average AlN mole fraction Xna1.

In the present embodiment, the second average AlN mole fraction Xna2(d) sandwiches the AlN mole fraction (n/12) of the first metastable AlGaN region as the depth d changes. is changing. The change in the AlN mole fraction Xna2(d) can be realized by positively modulating the supply amount and flow velocity of the raw material gas and carrier gas, or modulating the growth temperature. Furthermore, the natural change in substrate surface temperature that occurs as the n-type cladding layer 21 grows and becomes thicker may be utilized. In this case, the supply amounts and flow velocities of the raw material gas and the carrier gas are set according to the tendency of the substrate surface temperature change.

The donor impurity concentration does not necessarily have to be controlled uniformly in the vertical direction with respect to the thickness of the n-type cladding layer 21 . For example, the impurity concentration in the predetermined thin film thickness portion in the n-type cladding layer 21 is lower than the above set concentration, for example, less than 1×10 ¹⁸ cm ⁻³ , more preferably 1×10 ¹⁷ cm ⁻³ or less. It may be a controlled low impurity concentration layer. The thickness of the low impurity concentration layer is preferably greater than 0 nm and approximately 200 nm or less, more preferably approximately 10 nm or more and 100 nm or less, and further preferably approximately 20 nm or more and 50 nm or less. Also, the donor impurity concentration of the low impurity concentration layer may be lower than the set concentration, and may partially include an undoped layer (0 cm ⁻³ ). Furthermore, part or all of the low impurity concentration layer preferably exists in an upper layer region with a depth of 100 nm or less downward from the upper surface of the n-type cladding layer 21 .

After the n-type cladding layer 21 having the layered region 21a and the n-type main body region 21b is formed in the above manner, the entire upper surface of the n-type cladding layer 21 is subsequently subjected to metal organic chemical vapor phase epitaxy (MOVPE) or the like. The active layer 22 (well layer 220, barrier layer 221), electron block layer 23, p-type contact layer 24, etc. are formed by the known epitaxial growth method.

For example, the acceptor impurity concentration of the electron block layer 23 is preferably about 1.0×10 ¹⁶ to 1.0×10 ¹⁸ cm ⁻³ , and the acceptor impurity concentration of the p-type contact layer 24 is, for example, 1.0. About ×10 ¹⁸ to 1.0×10 ²⁰ cm ⁻³ is preferable. The acceptor impurity concentration does not necessarily have to be controlled uniformly in the vertical direction with respect to each film thickness of the electron blocking layer 23 and the p-type contact layer 24 .

In the formation of the active layer 22, in the same manner as the n-type cladding layer 21, the well layer 220 was grown under the growth conditions under which the above-described multi-stepped terraces are likely to appear, with the average AlN mole fraction Xwa of the well layer 220 as a target value. 220 is grown, and further, the barrier layer 221 is grown with the average AlN mole fraction Xba of the barrier layer 221 as a target value. The average AlN molar fractions Xwa and Xba of the well layer 220 and the barrier layer 221 are as described above, and redundant description is omitted.

In the formation of the electron blocking layer 23, in the same manner as for the n-type cladding layer 21, under the growth conditions where the above-described multi-stepped terraces are likely to appear, the average AlN mole fraction Xea of the electron blocking layer 23 is set as a target value. An electron blocking layer 23 is grown. The average AlN mole fraction Xea of the electron blocking layer 23 is as described above, and redundant description is omitted.

In this embodiment, the growth temperature of the active layer 22 (well layer 220, barrier layer 221), the electron blocking layer 23, and the p-type contact layer is set to T1 for the growth temperature of the n-type cladding layer 21, and T1 for the growth temperature of the active layer 22. When the temperature is T2, the growth temperature of the electron blocking layer 23 is T3, and the p-type contact layer growth temperature is T4, the following equations (8) and ( It is preferable that the relationship shown in 9) is satisfied.
T3≧T2 (8)
T3>T1>T4 (9)

The growth temperature T3 of the electron blocking layer 23 can be reduced, for example, by increasing the flow rate of the nitrogen source gas and decreasing the growth rate.

When the growth temperature T3 of the electron blocking layer 23 is raised from the growth temperature T2 of the active layer 22, the GaN is decomposed in the well layer 220 positioned therebelow during the transition process of the growth temperature. The characteristics of the light-emitting element 1 may deteriorate due to decomposition. Therefore, in order to suppress decomposition of the GaN, a film thinner than the barrier layer 221 (for example, 3 nm or less, preferably less than 3 nm) is placed between the uppermost well layer 220 and the electron blocking layer 23 to prevent the decomposition of the GaN. , 2 nm or less) with a higher AlN mole fraction than the barrier layer 221 and electron block layer 23 .

After forming the active layer 22 (well layer 220, barrier layer 221), the electron blocking layer 23, the p-type contact layer 24, etc. on the entire upper surface of the n-type cladding layer 21 in the manner described above, next, By a well-known etching method such as reactive ion etching, the second regions R2 of the nitride semiconductor layers 21 to 24 are selectively etched until the upper surface of the n-type cladding layer 21 is exposed. A portion of the second region R2 on the upper surface is exposed. Then, a p-electrode 26 is formed on the p-type contact layer 24 in the unetched first region R1 by a well-known film formation method such as an electron beam evaporation method, and an n electrode in the etched first region R2 is formed. An n-electrode 27 is formed on the mold cladding layer 21 . After forming one or both of the p-electrode 26 and the n-electrode 27, heat treatment may be performed by a known heat treatment method such as RTA (rapid thermal annealing).

As an example, the light emitting element 1 is flip-chip mounted on a base such as a submount, and then sealed with a predetermined resin (for example, a lens-shaped resin) such as silicone resin or amorphous fluorine resin. can be used in any situation.

The cross-sectional structure of the AlGaN-based semiconductor layers 21 to 24 of the light-emitting device 1 manufactured in the above manner is as follows. A sample piece having a vertical (or substantially vertical) cross section can be processed with a focused ion beam (FIB) and observed by an HAADF-STEM image of the sample piece. A HAADF-STEM image provides a contrast proportional to the atomic weight, and heavy elements are displayed brightly. Therefore, regions with a low AlN mole fraction are displayed relatively brightly. HAADF-STEM images are more suitable for observing differences in AlN mole fractions than normal STEM images (bright field images).

Furthermore, the composition analysis within specific semiconductor layers in the AlGaN-based semiconductor layers 21 to 24 is performed using the above sample piece by energy dispersive X-ray spectroscopy (cross-sectional TEM-EDX) or CL (cathode luminescence) method. can be done with Regarding the composition analysis by cross-sectional TEM-EDX and CL method, the specifications of other previous applications by the inventor of the present application (PCT/JP2020/024827, PCT/JP2020/024828, PCT/JP2020/026558, PCT/JP2020/031620, etc.) A detailed explanation is given inside.

<Results of composition analysis of n-type cladding layer>
Next, the second average AlN mole fraction Xna2(d) of the n-type cladding layer 21 was measured by Rutherford backscattering (RBS) spectroscopy. Results of measurement of the AlN mole fraction of the main body region 21b by the CL (cathode luminescence) method, and measurement of the AlN mole fraction of the layered region 21a in the n-type clad layer 21 by the cross-sectional TEM-EDX method. Each result will be explained.

A sample for composition analysis of the n-type cladding layer 21 is prepared, and a sample piece having a cross section perpendicular (or substantially perpendicular) to the upper surface of the n-type cladding layer 21 is processed with a focused ion beam (FIB) from the sample, A sample piece for measurement was produced.

The sample was prepared by forming the n-type cladding layer 21 and AlN molar ratio higher than that of the n-type cladding layer 21 on the underlayer 10 composed of the sapphire substrate 11 and the AlN layer 12 according to the manufacturing procedure of the n-type cladding layer 21 and the like. A fractional AlGaN layer, an AlGaN layer for protecting the surface of the sample, and a protective resin film were deposited in order. In preparing the samples, a sapphire substrate 11 having a main surface at an off-angle with respect to the (0001) plane was used, and an underlayer 10 in which a multi-stepped terrace was exposed on the surface of an AlN layer 12 was used. Furthermore, the dose of donor impurities (Si) was controlled so that the donor impurity concentration was approximately 3×10 ¹⁸ cm ⁻³ .

The first average AlN molar fraction Xna1, the second average AlN molar fraction Xna2(d) at the depth d (nm), and the third average The AlN molar fraction Xna3 satisfies the above formulas (1), (3), and (2) when n=7. Therefore, a first metastable AlGaN region having an AlN mole fraction of 7/12 (approximately 58.3%) is formed in the n-type body region 21b, and an AlN mole fraction is formed in the layered region 21a. A 6.5/12 (approximately 54.2%) intermediate AlGaN region is formed.

FIG. 12 shows measured values of the second average AlN mole fraction Xna2(d) by the RBS analysis method. The AlN mole fraction Xna2(d) varies within the range of about 57.8% to about 59.9% according to the change in depth d, satisfying the above formula (3). The first average AlN mole fraction Xna1 is calculated to be about 58.4% from Xna2(d) shown in FIG. They are slightly higher, but they are roughly the same. As will be described later, there is one specific depth dx, which is approximately 1061 nm. The third average AlN mole fraction Xna3 is calculated to be about 57.9% from Xna2(d) shown in FIG. Is pleased. When the second average AlN mole fraction Xna2(d) satisfies the formula (3), the first average AlN mole fraction Xna1 naturally satisfies the above formula (1), The average AlN mole fraction Xna3 of 3 naturally also satisfies equation (2).

As shown in FIG. 12, the second average AlN mole fraction Xna2(d) is constant at about 57.8% in the upper layer region with a depth d (nm) of 0 nm to about 750 nm, and As the depth d (nm) increases from about 750 nm to about 1900 nm, it gradually increases from about 57.8% to about 59.9%, and the first metastable It is equal to the AlN mole fraction (approximately 58.3%) of the AlGaN region. Therefore, in the example shown in FIG. 12, the specific depth dx is approximately 1061 nm. The second average AlN mole fraction Xna2(d) is the AlN mole fraction of the first metastable AlGaN region (about 58.3%) in the region where the depth d (nm) is 0 nm to about 1061 nm. is smaller than the AlN mole fraction (about 58.3%) of the first metastable AlGaN region in the region where the depth d (nm) is about 1061 nm to about 1900 nm, satisfying the formula (5). , satisfies equation (7). Therefore, the second average AlN mole fraction Xna2(d) shown in FIG. 12 is one of the typical examples satisfying the formulas (5) and (7). That is, d=approximately 1061 nm is the specific depth dx.

In the RBS analysis method, for example, a He ²⁺ ion beam (beam diameter: 2.2 mm) is vertically irradiated from the upper surface side of the n-type cladding layer 21 of the sample at an acceleration voltage of 2.3 MeV. Since the range is as large as 300 nm, the film thickness to be analyzed should be greater than 300 nm.

FIG. 13 is a scanning electron microscope (SEM) image showing the main part including the n-type cladding layer 21 on the cross section of the sample piece to be measured. The measurement range of the sample piece (the range of the incident point of the electron beam irradiated for measurement) is 6.5 mm in each of the X direction (horizontal direction parallel to the second plane) and Y direction (vertical direction orthogonal to the second plane). The incident points of the electron beams are set in a grid pattern of 121 mesh×41 mesh with 25 μm and 2.2 μm. The mesh spacing is about 52 nm in the X direction and about 55 nm in the Y direction.

The Y value (Y coordinate) written in the measurement range of the sample piece shown in FIG. 13 represents the number of meshes counted from the upper end of each measurement range, and the upper end is Y=0. In FIG. 13, Y=4 and Y=38 are located near the upper end and the lower end of the n-type cladding layer 21, respectively. Therefore, the thickness of the n-type cladding layer 21 is approximately 1.9 μm.

An electron beam with a beam diameter of 50 nm (diameter) was irradiated once to the grid-shaped electron beam incident point within the measurement range of the sample piece, and the CL spectrum at each incident point was measured.

FIG. 14 shows the 121 A first CL spectrum (solid line) and a second CL spectrum (dashed line) derived in the following manner are shown for the CL spectra. The six Y coordinates (Y=10 to 35) correspond to approximately 330 nm to approximately 1700 nm when converted to the depth d from the upper end of the n-type cladding layer 21 . The first and second CL spectra of six Y-coordinates are displayed on the same graph so as to be mutually identifiable with their respective origins shifted in the direction of the vertical axis. The vertical axis of FIG. 14 indicates the emission intensity (arbitrary unit), and the emission intensity of the two Y coordinates (Y = 10, 35) is 0.5 times (Y = 10) and 1.5 times (Y=35) to make it easier to see. The horizontal axis of FIG. 14 indicates the wavelength (nm).

Also, on FIG. 14, for reference, three CL wavelengths (about 253 nm, about 266 nm, about 279 nm) is shown by a dashed-dotted vertical line.

The first CL spectrum of each Y coordinate shown in FIG. 6 to 7 points or more of CL spectra shifted to the same wavelength on the wavelength side were extracted, and the extracted CL spectra were averaged for calculation. Therefore, the measurement area related to the first CL spectrum contains more layer regions 21a than other measurement areas of the same Y coordinate.

On the other hand, the second CL spectrum of each Y coordinate shown in FIG. 6 to 7 or more points of the CL spectrum shifted to the vicinity of the same wavelength on the shorter wavelength side were extracted, and the extracted CL spectrum was averaged for calculation. Therefore, the measurement region for the second CL spectrum includes more n-type body regions 21b (in particular, Al-enriched n-type regions) than other measurement regions with the same Y coordinate.

In the first CL spectrum of each Y coordinate shown in FIG. 14, the wavelength λ0 (Y) indicating the maximum signal intensity In0 (Y) exists within the range of about 268 nm to about 271 nm, and the intermediate CL wavelength (approximately 273 nm) corresponding to the AlN mole fraction ((n-0.5)/12) of the AlGaN region (Al _n-0.5 Ga _12.5-n N ₁₂ ), and when n=7 and the CL wavelength (approximately 266 nm) corresponding to the AlN mole fraction (n/12) of the first metastable AlGaN region (Al _n Ga _12-n N ₁₂ ). This is because the first CL spectrum includes the CL spectrum from the layered region 21a, the CL spectrum from the first metastable AlGaN region in the n-type body region 21b, and the Al-enriched n-type in the n-type body region 21b. This is because the CL spectrum from the region is included, and in particular the two previous CL spectra are primarily included, resulting in a composite spectrum of these.

Here, as described above, the Al-enriched n-type region in the n-type body region 21b is formed in the layered region 21a ( _Ga _- enriched _n -type region) is formed along with the formation of the Al A second intermediate AlGaN region (Al _n+0.5 Ga _11.5−n N ₁₂ ) may also be formed within the enriched n-type region. The second intermediate AlGaN region has an AlN mole fraction in the first metastable AlGaN region and a third subregion in which the AlN mole fraction is one step (about 8.33%) higher than that of the first metastable AlGaN region. It is located intermediate to the stable AlGaN region (Al _n+1 Ga _11-n N ₁₂ ). The CL wavelength corresponding to the AlN mole fraction ((n+0.5)/12) of the second intermediate AlGaN region when n=7 is approximately 259 nm.

Further, in the first CL spectrum of each Y coordinate, the signal intensity In11(Y) at the wavelength λs1 (about 266 nm) corresponding to the AlN mole fraction (about 58.3%) of the first metastable AlGaN region is the maximum signal. an n-type body region having an intensity of about 67% to about 96% of In0(Y) and formed predominantly by a first metastable AlGaN region within the measurement region for the first CL spectrum at each Y coordinate; 21b is included.

Further, in the first CL spectrum of each Y coordinate, the signal intensity In1m (Y) at the wavelength λsm (about 273 nm) corresponding to the AlN mole fraction (about 54.2%) in the middle AlGaN region is the maximum signal intensity In0 (Y ), and the middle AlGaN region (Al _n-0.5 Ga _12.5-n N ₁₂ ) is dominant in the measurement region for the first CL spectrum of each Y coordinate. It can be seen that the formed layered region 21a is included.

Regarding the above measurement results, if the signal intensity In1m(Y) is 70% or more of the maximum signal intensity In0(Y), the intermediate AlGaN region (Al _n-0.5 Ga _12.5-n N ₁₂ ) is predominantly formed. The case of n=6 is also conceivable. However, in order to ensure the measurement accuracy by the CL method, the Y coordinate of the first CL spectrum is the middle Limited to the Y coordinate in the region, the influence from the active layer 22 existing above the n-type cladding layer 21 and the underlayer 10 existing below the n-type cladding layer 21 (in one embodiment, the top layer preferably eliminates the influence from AlN12).

Further, in the first CL spectrum of each Y coordinate, the signal intensity In12 (Y) at the wavelength λs2 (about 279 nm) corresponding to the AlN mole fraction (50%) of the second metastable AlGaN region is the maximum signal intensity In0 ( Y) is about 13% to about 40%, and the second metastable AlGaN region exists, but is not predominantly formed, within the measurement region of the first CL spectrum of each Y coordinate. I understand.

Regarding the above measurement results, if the signal intensity In12(Y) is less than 50% of the maximum signal intensity In0(Y), it means that the second metastable AlGaN region is not dominantly formed in the layered region 21a. can be determined. The case of n=6 is also conceivable. However, in order to ensure measurement accuracy by the CL method, it is preferable to limit the Y coordinate of the first CL spectrum to the Y coordinate within the intermediate region.

In the second CL spectrum of each Y coordinate shown in FIG. 14, the wavelength λ1(Y) indicating the maximum signal intensity In1(Y) exists within the range of about 258 nm to about 261 nm, and each wavelength λ1(Y) The AlN mole fraction Xn1(d) at the corresponding depth d lies in the range of about 61.5% to about 63.5%, both of which are within the second average AlN mole fraction Xna2(d ). Therefore, it can be seen that an Al-enriched n-type region is formed in the n-type body region 21b with the mass transfer of Ga during the formation of the layered region 21a. In the vicinity of the upper end of the n-type cladding layer 21, the AlN mole fraction Xn1(d) is about 61.5%.

Further, in the second CL spectrum of each Y coordinate, the signal intensity In21(Y) at the wavelength λs1 (about 266 nm) corresponding to the AlN mole fraction (about 58.3%) of the first metastable AlGaN region is the maximum signal. an n-type body region having an intensity of about 55% to about 84% of In1(Y) and formed predominantly by a first metastable AlGaN region within the measurement region for the second CL spectrum at each Y coordinate; 21b is included.

Furthermore, in the first and second CL spectra of each Y coordinate, the signal intensity In21(Y) at the wavelength λs1 (about 266 nm) corresponding to the AlN mole fraction (about 58.3%) of the first metastable AlGaN region is , are the same, it can be seen that the first metastable AlGaN region is uniformly formed in the n-type body region 21b.

Further, in the second CL spectrum of each Y coordinate, the signal intensity In2m(Y) at the wavelength λsm (about 259 nm) corresponding to the AlN mole fraction (62.5%) of the second intermediate AlGaN region is the maximum signal intensity In2 (Y) is about 90% to about 100%, and a second intermediate AlGaN region (Al _n+0.5 Ga _11.5−n N ₁₂ ) is within the measurement region for the second CL spectrum of each Y coordinate. It can be seen that the Al-enriched n-type region within the predominantly formed n-type body region 21b is included.

Therefore, on the surface of the n-type cladding layer 21 (particularly, the exposed surface in the second region R2), the AlN molar fraction uniformly and predominantly formed in the n-type body region 21b is approximately 58.3%. Since the first metastable AlGaN region of and the layered region 21a with a lower AlN mole fraction are exposed, an Al-enriched n-type region with an AlN mole fraction slightly exceeding 60% is partially present. It can be seen that the contact resistance between the surface of the n-type cladding layer 21 and the n-electrode 27 is kept low even with this.

FIG. 15 is an HAADF-STEM image showing four measurement regions A to D where the AlN mole fraction in the layered region 21a of the sample piece is measured by cross-sectional TEM-EDX line analysis.

In the composition analysis (EDX measurement) by the cross-sectional TEM-EDX method, first, in the entire measurement area covering the four measurement areas A to D shown in FIG. direction) and lateral direction (parallel to the second plane), and the detection data (Al and Ga X-ray intensity corresponding to each composition) was obtained.

Next, in order to perform line analysis by EDX measurement on the layered regions 21a dispersed in the entire measurement region, the four measurement regions A to D (broken lines in FIG. 15) are set in the entire measurement region. ) was set. Each measurement area A to D is rectangular, and the inclination and size are set for each measurement area so that the extending direction of at least one layered area 21a in the measurement area is orthogonal to the scanning direction of line analysis. ing. The inclinations of the measurement areas A to D (the angles formed by the vertical direction of the entire measurement area and the vertical direction of each measurement area) are approximately equal to about 20°, but strictly speaking, they are not necessarily the same. Here, apart from the vertical and horizontal directions of the entire measurement area, in each measurement area A to D in FIG. 15, for convenience of explanation, the scanning direction of line analysis is the vertical direction, and the direction. The central vertical line shown in each measurement region indicates the scanning direction, and the x mark on the vertical line indicates the position in the vertical direction of the layered region 21a whose AlN mole fraction is to be measured. The positions of the X marks in the measurement regions A to D roughly correspond to Y coordinates 10, 21, 31, and 36 in the measurement range of the AlN mole fraction by the CL method shown in FIG.

In the EDX measurement, since the diameter of the electron beam probe to be irradiated is as small as about 2 nm, the spatial resolution is high. Detection data obtained from a plurality of probe locations aligned in the horizontal direction are accumulated to obtain detection data at each scanning position. Note that "horizontally aligned" means that the irradiation range of the electron beam probe overlaps with a horizontal line that intersects the vertical line and extends in the horizontal direction at each scanning position.

The AlN mole fractions in the layered regions 21a indicated by the crosses in the measurement regions A to D derived based on the cumulative detection data obtained in the manner described above are as follows. The AlN mole fraction of the intermediate AlGaN region (approximately 54.17 %) is subtracted to show the AlN mole fraction difference Δ.
Measurement area A (Y = about 10): 52.62% (Δ = -1.55%)
Measurement area B (Y = about 21): 54.52% (Δ = 0.35%)
Measurement area C (Y = about 31): 54.63% (Δ = 0.46%)
Measurement area D (Y = about 36): 54.05% (Δ = -0.12%)

From the measurement results of the AlN mole fraction in the layered region 21a in each of the measurement regions A to D, an intermediate AlGaN region having an AlN mole fraction of 6.5/12 (about 54.2%) was found in the layered region 21a. is predominantly formed. This agrees with the results derived from the first CL spectrum in FIG.

[Second embodiment]
In the light-emitting device 1 of the first embodiment, the p-type layer constituting the light-emitting device structure portion 20 was composed of two layers, the electron blocking layer 23 and the p-type contact layer 24, but in the light-emitting device 2 of the second embodiment, , the p-type layer has a p-type clad layer 25 composed of one or more p-type AlGaN semiconductors between the electron block layer 23 and the p-type contact layer 24 .

Therefore, in the second embodiment, as shown in FIG. 16, the AlGaN-based semiconductor layers 21 to 25 of the light emitting element structure 20 are composed of an n-type cladding layer 21 (n-type layer), an active layer 22, an electron blocking layer 23 (p-type layer), a p-type cladding layer 25 (p-type layer), and a p-type contact layer 24 (p-type layer) which are epitaxially grown in order and stacked.

The base portion 10 and the AlGaN-based semiconductor layers 21 to 24, the p-electrode 26, and the n-electrode 27 of the light-emitting element structural portion 20 in the light-emitting element 2 of the second embodiment are the light emission of any one of the first to third embodiments. Since they are the same as the AlGaN-based semiconductor layers 21 to 24, the p-electrode 26, and the n-electrode 27 of the base portion 10 and the light-emitting device structure portion 20 of the device 1, redundant description will be omitted.

The p-type cladding layer 25 is composed of the AlN layer 12 of the underlying portion 10 epitaxially grown in order from the main surface 11a of the sapphire substrate 11, the n-type cladding layer 21 of the light emitting element structure portion 20, and each semiconductor layer in the active layer 22. Like the electron blocking layer 23 , it has a surface on which multi-stepped terraces parallel to the (0001) plane derived from the main surface 11 a of the sapphire substrate 11 are formed.

FIG. 17 schematically shows an example of a laminated structure (multiple quantum well structure) of well layers 220 and barrier layers 221 in the active layer 22 . In FIG. 17, a p-type cladding layer 25 is formed on the electron blocking layer 23 having the laminated structure described with reference to FIG. 5 in the first embodiment.

Also in the p-type cladding layer 25, between the laterally adjacent terraces T, the inclined regions IA inclined with respect to the (0001) plane are formed as described above. A region other than the inclined region IA, which is sandwiched between the terraces T, is referred to as a terrace region TA. The thickness of the p-type cladding layer 25 is adjusted, for example, within the range of 20 nm to 200 nm including the terrace area TA and the inclined area IA.

As schematically shown in FIG. 17, in the p-type cladding layer 25, due to mass transfer of Ga from the terrace region TA to the gradient region IA, Ga enrichment with a lower AlN mole fraction in the gradient region IA than in the terrace region TA A p-type region 25a is formed.

The AlN mole fraction of the terrace region TA of the p-type cladding layer 25 is set within a range of 51% or more and less than the AlN mole fraction of the terrace region TA of the electron blocking layer 23 . Furthermore, the AlN mole fraction of the Ga-enriched p-type region 25 a of the p-type cladding layer 25 is set to be less than the AlN mole fraction of the Ga-enriched EB region 23 a of the electron blocking layer 23 .

Furthermore, the AlN mole fraction of the terrace region TA of the p-type cladding layer 25 is 1% or more, preferably 2% or more, more preferably 2% or more, more preferably than the AlN mole fraction of the Ga-enriched p-type region 25a within the above range. It is set to be higher than 4%. In order to sufficiently ensure the effect of localizing carriers in the Ga-enriched p-type region 25a, the AlN mole fraction difference between the Ga-enriched p-type region 25a of the p-type cladding layer 25 and the terrace region TA is 4-5. % or more is preferable, but the effect of localizing carriers can be expected even at about 1 to 2%.

Next, a method for growing the p-type cladding layer 25 will be briefly described. In the formation of the p-type cladding layer 25, the p-type cladding layer 25 is formed under the same growth conditions as those for the n-type cladding layer 21 and the electron blocking layer 23 described in the first embodiment under the growth conditions under which the above-described multi-stepped terraces are easily exposed. The p-type cladding layer 25 is grown with an average AlN mole fraction Xpa of 25 as a target value.

[Another embodiment]
Modifications of the first and second embodiments will be described below.

(1) In each of the above embodiments, the active layer 22 alternately comprises two or more well layers 220 made of an AlGaN-based semiconductor and one or more barrier layers 221 made of an AlGaN-based semiconductor or an AlN-based semiconductor. However, the active layer 22 has a single quantum well structure with only one well layer 220 and does not have a barrier layer 221 (quantum barrier layer). It may be configured. It is clear that the effect of the well layer 220 employed in each of the above-described embodiments can be similarly obtained for such a single quantum well structure.

(2) In each of the above embodiments, an n-type AlGaN semiconductor layer having a higher AlN mole fraction than the n-type cladding layer 21 (hereinafter referred to as "n-type lower (referred to as "stratum") may be provided. As a result, the average AlN mole fraction over the entire area in the depth direction where the n-type cladding layer 21 and the n-type underlayer are united may be higher than the range of the above formula (1).

Since the n-type underlayer provided below the n-type cladding layer 21 has a higher AlN mole fraction than the n-type cladding layer 21, light emitted from the active layer is not absorbed. In addition, even if the n-type underlayer has a higher AlN mole fraction than the n-type cladding layer 21, it does not come into contact with the n-electrode 27 and forms a current path between the n-electrode 27 and the active layer. Therefore, the parasitic resistance between the n-electrode 27 and the active layer is not increased, and the wall plug efficiency is not lowered. In other words, since the n-type underlayer does not substantially function as part of the light emitting element structure 20, it can be said that the provision of the n-type underlayer does not bring any particular advantage or conspicuous disadvantage.

(3) In each of the above-described embodiments, the first region R1 and the p-electrode 26 have, as an example, a comb shape in plan view, but the plan view shape is not limited to a comb shape. . Moreover, a planar view shape in which a plurality of first regions R1 are present and each of which is surrounded by one second region R2 may be used.

(4) In each of the above-described embodiments, the base portion 10 in which a multi-stepped terrace is exposed on the surface of the AlN layer 12 using the sapphire substrate 11 whose main surface has an off-angle with respect to the (0001) plane is used. , the magnitude of the off-angle and the direction in which the off-angle is provided (specifically, the direction in which the (0001) plane is tilted, such as the m-axis direction and the a-axis direction) are different from the surface of the AlN layer 12 It may be determined arbitrarily as long as a multi-stepped terrace is exposed at the end and a growth starting point of the layered region 21a is formed.

(5) In each of the above-described embodiments, the light emitting element 1 including the underlying portion 10 including the sapphire substrate 11 is illustrated as the light emitting element 1 as illustrated in FIG. A part or all of the layers included in the portion 10) may be removed by lift-off or the like. Furthermore, the substrate forming the underlying portion 10 is not limited to the sapphire substrate.

INDUSTRIAL APPLICABILITY The present invention is applicable to a nitride semiconductor ultraviolet light emitting device having a light emitting device structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are stacked vertically. .

Reference Signs List 1: nitride semiconductor ultraviolet light emitting device 10: base portion 11: sapphire substrate 11a: main surface of sapphire substrate 12: AlN layer 20: light emitting device structure portion 21: n-type clad layer (n-type layer)
21a: layered region (n-type layer)
21b: n-type body region (n-type layer)
22: Active layer 220: Well layer 220a: Ga-enriched well region 221: Barrier layer 221a: Ga-enriched barrier region 23: Electron blocking layer (p-type layer)
23a: Ga-enriched EB region 24: p-type contact layer (p-type layer)
25: p-type clad layer (p-type layer)
25a: Ga-enriched p-type region 26: p-electrode 27: n-electrode 100: substrate 101: AlGaN-based semiconductor layer 102: template 103: n-type AlGaN-based semiconductor layer 104: active layer 105: p-type AlGaN-based semiconductor layer 106: p-type contact layer 107: n-electrode 108: p-electrode BL: boundary line between first region and second region IA: inclined region R1: first region R2: second region T: terrace TA: terrace region

Claims

A nitride semiconductor ultraviolet light-emitting device comprising a light-emitting device structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are vertically stacked,
The n-type layer is composed of an n-type AlGaN semiconductor,
the active layer disposed between the n-type layer and the p-type layer has a quantum well structure including one or more well layers made of an AlGaN-based semiconductor;
The p-type layer is composed of a p-type AlGaN semiconductor,
each of the semiconductor layers in the n-type layer, the active layer, and the p-type layer is an epitaxial growth layer having a surface on which a multi-stepped terrace parallel to the (0001) plane is formed;
wherein the n-type layer has a layered region with a locally low AlN mole fraction dispersed within the n-type layer;
Each extending direction of the layered region on a first plane perpendicular to the upper surface of the n-type layer has a portion that is inclined with respect to a line of intersection between the upper surface of the n-type layer and the first plane. death,
the integer n is 6 or 7,
A first average AlN mole fraction Xna1 over the entire depth direction of the n-type layer is
(n−0.25)/12<Xna1<(n+0.25)/12
is within the range of
A second average AlN mole fraction Xna2(d) at a depth d from the top of the n-type layer varies with the depth d such that within the n-type layer Xna2(d)=n /12, at least one specific depth has a region satisfying Xna2(d)<n/12 above the specific depth, and a region satisfying Xna2(d)> below the specific depth. There is a region of n/12,
A nitride semiconductor ultraviolet light emitting device, wherein an intermediate AlGaN region having an AlN mole fraction of (n-0.5)/12 is formed in the layered region.
A third average AlN mole fraction Xna3 over a region from the upper end of the n-type layer to the specific depth is
(n−0.25)/12<Xna3<(n+0.25)/12
2. The nitride semiconductor ultraviolet light emitting device according to claim 1, wherein the range is:
The second average AlN mole fraction Xna2(d) is, over the entire depth direction of the n-type layer,
(n−0.25)/12<Xna2(d)<(n+0.25)/12
3. The nitride semiconductor ultraviolet light emitting device according to claim 1 or 2, wherein the range is:
In a region from the upper end of the n-type layer to the specific depth, the second average AlN mole fraction Xna2(d) is
Xna2(d)≤n/12
The nitride semiconductor ultraviolet light emitting device according to any one of claims 1 to 3, characterized in that it is within the range of:
In a region where the second average AlN mole fraction Xna2(d) is deeper than the specific depth of the n-type layer,
Xna2(d)≧n/12
5. The nitride semiconductor ultraviolet light emitting device according to claim 4, wherein the range is:
The nitride semiconductor ultraviolet light according to any one of claims 1 to 5, wherein the integer n is 7 and the peak emission wavelength is set to a predetermined value within the range of 280 nm to 315 nm. light-emitting element.
The nitride semiconductor ultraviolet light according to any one of claims 1 to 5, wherein the integer n is 6, and the peak emission wavelength is set to a predetermined value within the range of 300 nm to 330 nm. light-emitting element.
wherein the active layer has a multiple quantum well structure including two or more well layers;
8. The nitride semiconductor ultraviolet light emitting device according to claim 1, further comprising a barrier layer made of an AlGaN-based semiconductor between the two well layers.
further comprising a base portion including a sapphire substrate,
The sapphire substrate has a main surface inclined by a predetermined angle with respect to the (0001) plane, and the light emitting element structure is formed above the main surface,
Each of the semiconductor layers from the main surface of the sapphire substrate to the p-type layer is an epitaxial growth layer having a surface on which a multi-stepped terrace parallel to the (0001) plane is formed. 9. The nitride semiconductor light emitting device according to any one of 8.
A method for manufacturing a nitride semiconductor ultraviolet light-emitting device comprising a light-emitting device structure in which an n-type layer, an active layer, and a p-type layer made of an AlGaN-based semiconductor having a wurtzite structure are vertically stacked,
The n-type layer of an n-type AlGaN semiconductor is epitaxially grown on a base portion including a sapphire substrate having a main surface inclined at a predetermined angle with respect to the (0001) plane. ) a first step of expressing a multi-stepped terrace parallel to the surface;
On the n-type layer, the active layer having a quantum well structure including one or more well layers made of an AlGaN-based semiconductor is epitaxially grown, and a multistep terrace parallel to the (0001) plane is formed on the surface of the well layer. A second step of expressing
a third step of forming the p-type layer of a p-type AlGaN semiconductor on the active layer by epitaxial growth;
In the first step,
the integer n is 6 or 7,
A first average AlN mole fraction Xna1 over the entire depth direction of the n-type layer is
(n−0.25)/12<Xna1<(n+0.25)/12
is within the range of
A second average AlN mole fraction Xna2(d) at a depth d from the top of the n-type layer varies with the depth d such that within the n-type layer Xna2(d)=n /12, at least one specific depth has a region satisfying Xna2(d)<n/12 above the specific depth, and a region satisfying Xna2(d)> below the specific depth. so that there is a region of n/12, and
A layered region with a locally low AlN mole fraction, which is uniformly dispersed in the n-type layer and is formed by extending obliquely upward,
so that an intermediate AlGaN region having an AlN mole fraction of (n−0.5)/12 is formed in the layered region,
A method for manufacturing a nitride semiconductor ultraviolet light emitting device, comprising forming the n-type layer.
In the first step, the third average AlN mole fraction Xna3 over the region from the upper end of the n-type layer to the specific depth is
(n−0.25)/12<Xna3<(n+0.25)/12
11. The method of manufacturing a nitride semiconductor ultraviolet light emitting device according to claim 10, wherein said n-type layer is formed so as to be within the range of:
In the first step, the second average AlN mole fraction Xna2(d) in the entire depth direction of the n-type layer is
(n−0.25)/12<Xna2(d)<(n+0.25)/12
12. The method for manufacturing a nitride semiconductor ultraviolet light emitting device according to claim 10, wherein the n-type layer is formed so as to fall within a range of:
In the first step, the second average AlN mole fraction Xna2(d) in a region from the upper end of the n-type layer to the specific depth is
Xna2(d)≤n/12
13. The method for manufacturing a nitride semiconductor ultraviolet light emitting device according to claim 10, wherein said n-type layer is formed so as to fall within a range of:
In the first step, in a region where the second average AlN mole fraction Xna2(d) is deeper than the specific depth of the n-type layer,
Xna2(d)≧n/12
14. The method of manufacturing a nitride semiconductor ultraviolet light emitting device according to claim 13, wherein the n-type layer is formed so as to be within the range of:
The integer n is 7, and in the second step, the active layer is formed so that the peak emission wavelength of the nitride semiconductor ultraviolet light emitting element is a predetermined value within the range of 280 nm to 315 nm. A method for manufacturing a nitride semiconductor ultraviolet light emitting device according to any one of claims 10 to 14.
The integer n is 6, and in the second step, the active layer is formed so that the peak emission wavelength of the nitride semiconductor ultraviolet light emitting element is a predetermined value within the range of 300 nm to 330 nm. A method for manufacturing a nitride semiconductor ultraviolet light emitting device according to any one of claims 10 to 14.
In the second step, the well layers made of an AlGaN-based semiconductor and the barrier layers made of an AlGaN-based semiconductor are alternately laminated by epitaxial growth, and the active layer has a multiple quantum well structure including two or more of the well layers. The method for manufacturing a nitride semiconductor light-emitting device according to any one of claims 10 to 16, wherein a is formed.