JP2023113378A - Light-emitting element - Google Patents

Abstract

An object of the present invention is to provide a light-emitting element capable of improving light extraction efficiency and reducing forward voltage.
A light emitting element is a semiconductor structure having a p-side semiconductor layer, an active layer, and an n-side semiconductor layer in order from bottom to top, wherein the n-side semiconductor layer is has a first portion and a second portion, the first surface being the lower surface of the p-side semiconductor layer located below the first portion, the second surface being the upper surface of the second portion, and the a semiconductor structure having a third surface which is a lower surface of the p-side semiconductor layer located below the second portion; a p-side electrode arranged on the first surface; and a p-side electrode arranged on the second surface. An n-side electrode and an insulating member disposed on the third surface are provided, and the maximum thickness of the first portion is thinner than the maximum thickness of the second portion.
[Selection drawing] Fig. 2

Description

The present invention relates to light emitting devices.

Patent Document 1 discloses that light extraction efficiency is improved by thinning a semiconductor structure in a light emitting device, but this may lead to an increase in forward voltage.

JP 2013-84878 A

An object of the present invention is to provide a light-emitting element capable of improving light extraction efficiency and reducing forward voltage.

According to one aspect of the present invention, a light-emitting element is a semiconductor structure having, in order from bottom to top, a p-side semiconductor layer, an active layer, and an n-side semiconductor layer, wherein, when viewed from above, The n-side semiconductor layer has a first portion and a second portion. a semiconductor structure having two surfaces and a third surface which is a lower surface of the p-side semiconductor layer located below the second portion; a p-side electrode disposed on the first surface; An n-side electrode arranged on the surface and an insulating member arranged on the third surface, wherein the maximum thickness of the first portion is thinner than the maximum thickness of the second portion.

ADVANTAGE OF THE INVENTION According to this invention, the light emitting element which can improve light extraction efficiency and can reduce a forward voltage can be provided.

1 is a schematic top view of a light emitting device according to one embodiment of the present invention; FIG. FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG. 1; 1 is a schematic top view of a semiconductor structure in a light emitting device according to one embodiment of the present invention; FIG. 4 is a graph showing measurement results of light output and forward voltage for samples A to E. FIG. 1 is a schematic top view of a light emitting device according to one embodiment of the present invention; FIG.

Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components are given the same reference numerals. Since each drawing schematically shows the embodiment, the scale, spacing, positional relationship, etc. of each member may be exaggerated, or illustration of a part of the member may be omitted. Also, as a cross-sectional view, an end view showing only a cut surface may be shown.

In the following description, constituent elements having substantially the same functions are denoted by common reference numerals, and their description may be omitted. Also, terms that indicate a particular direction or position (eg, "upper", "lower", and other terms that include those terms) may be used. However, these terms are only used for clarity of relative orientation or position in the referenced figures. If the relative direction or positional relationship of terms such as “upper” and “lower” in the referenced drawings is the same, then in drawings other than this disclosure, actual products, etc., the arrangement is not the same as that of the referenced drawings. may In this specification, "parallel" means not only cases where two straight lines, sides, surfaces, etc. do not intersect even if they are extended, but also cases where an angle formed by two straight lines, sides, surfaces, etc. intersects within a range of 10°. Also includes In the present specification, the positional relationship expressed as "upper" includes contacting and not contacting but positioned above.

As shown in FIGS. 1 and 2, the light emitting device 1 includes a semiconductor structure 20, a p-side electrode 31, an n-side electrode 32, and an insulating member 41. As shown in FIGS.

The semiconductor structure 20 has a first surface 20a as described below. A first direction Y and a second direction X are two directions that are parallel to the first surface 20a and orthogonal to each other. A direction perpendicular to the first direction Y and the second direction X is defined as a third direction Z. As shown in FIG. The semiconductor structure 20 has a p-side semiconductor layer 23, an active layer 22, and an n-side semiconductor layer 21 in order from bottom to top in the third direction Z. As shown in FIG.

The p-side semiconductor layer 23, the active layer 22, and the n-side semiconductor layer 21 are nitride semiconductor layers. The nitride semiconductor has a chemical formula of In _x Al _y Ga _1-x-y N (0≦x≦1, 0≦y≦1, x+y≦1) in which the composition ratios x and y are varied within respective ranges. Includes semiconductors of all compositions.

The p-side semiconductor layer 23 has a p-type layer containing p-type impurities. The n-side semiconductor layer 21 has an n-type layer containing n-type impurities. The p-side semiconductor layer 23 and the n-side semiconductor layer 21 may include undoped layers formed without intentionally doping n-type impurities or p-type impurities.

The active layer 22 can emit ultraviolet light. The peak wavelength of the light from the active layer 22 is, for example, 410 nm or less, specifically 210 nm or more and 410 nm or less. The active layer 22 can have, for example, a multiple quantum well structure including multiple well layers and multiple barrier layers.

As shown in FIG. 3, the shape of the semiconductor structure 20 when viewed from above is a quadrangle having two sides extending in the first direction Y and two sides extending in the second direction X. As shown in FIG. In a top view of the semiconductor structure 20, the n-side semiconductor layer 21 is positioned on the outermost surface. The n-side semiconductor layer 21 has a first portion 21-1 and a second portion 21-2 when viewed from above. In FIG. 3, the second portion 21-2 is represented by a dot pattern.

The second portion 21-2 has first extending portions 21c extending in the first direction Y and the second direction X along the four sides in the vicinity of the four sides of the semiconductor structure 20. As shown in FIG. Further, the second portion 21-2 has two second extending portions 21d extending so as to connect the central portions in the first direction X of the two first extending portions 21c extending in the second direction X. As shown in FIG. The two second extending portions 21d are arranged apart from each other. When viewed from above, the periphery of the first portion 21-1 is surrounded by the second portion 21-2. The area of the upper surface of the first portion 21-1 is larger than the area of the upper surface of the second portion 21-2.

As shown in FIG. 2, the semiconductor structure 20 has a first surface 20a, a second surface 20b, a third surface 20c and a fourth surface 20d. The first surface 20 a is the lower surface of the p-side semiconductor layer 23 located below the first portion 21 - 1 of the n-side semiconductor layer 21 . The lower surface of the p-side semiconductor layer 23 is the surface located on the opposite side of the surface of the p-side semiconductor layer 23 on the side of the active layer 22 . The second surface 20b is the upper surface of the second portion 21-2 of the n-side semiconductor layer 21. As shown in FIG. The third surface 20 c is the lower surface of the p-side semiconductor layer 23 located below the second portion 21 - 2 of the n-side semiconductor layer 21 . The fourth surface 20d is the upper surface of the first portion 21-1 of the n-side semiconductor layer 21. As shown in FIG. The upper surface of the first portion 21-1 and the upper surface of the second portion 21-2 of the n-side semiconductor layer 21 are surfaces located on the opposite side of the surface of the n-side semiconductor layer 21 on the active layer 22 side.

Light from the active layer 22 is extracted to the outside of the light emitting element 1 mainly through the fourth surface 20d. The fourth surface 20d is roughened and has a plurality of protrusions. Thereby, the light extraction efficiency from the light emitting element 1 can be improved. The surface roughness of the second surface 20b is smaller than the surface roughness of the fourth surface 20d.

The maximum thickness of the first portion 21 - 1 of the n-side semiconductor layer 21 is thinner than the maximum thickness of the second portion 21 - 2 of the n-side semiconductor layer 21 . The maximum thickness of the first portion 21-1 is between the fourth surface 20d of the n-side semiconductor layer 21 and the lower surface of the n-side semiconductor layer 21 located on the opposite side of the fourth surface 20d in the third direction Z. represents the maximum distance in the third direction Z; The maximum thickness of the second portion 21-2 is between the second surface 20b of the n-side semiconductor layer 21 and the lower surface of the n-side semiconductor layer 21 located on the opposite side of the second surface 20b in the third direction Z. represents the maximum distance in the third direction Z;

The p-side electrode 31 is arranged on the first surface 20 a and electrically connected to the p-side semiconductor layer 23 . The p-side electrode 31 is not arranged on the third surface 20c. The p-side electrode 31 preferably has high reflectivity with respect to light emitted from the active layer 22 . The p-side electrode 31 preferably has a reflectance of 60% or more, preferably 70% or more, for light emitted from the active layer 22, for example. Ag, Al, or the like, for example, can be used as the material of the p-side electrode 31 .

The n-side electrode 32 is arranged on the second surface 20 b and electrically connected to the n-side semiconductor layer 21 . The n-side electrode 32 is not arranged on the fourth surface 20d. At least one metal selected from the group consisting of Ti, Pt, and Au, for example, can be used as the material of the n-side electrode 32 .

The insulating member 41 is arranged on the third surface 20c. An n-side electrode 32 is arranged above the insulating member 41 . No n-side electrode 32 is arranged above the p-side electrode 31 . As a result, current concentration in the region immediately below the n-side electrode 32 is reduced, and the current tends to spread to regions where the insulating member 41 is not arranged. Silicon oxide or silicon nitride, for example, can be used as the material of the insulating member 41 .

On the lower surface of the p-side semiconductor layer 23, the area of the first surface 20a on which the p-side electrode 31 is arranged is larger than the area of the third surface 20c on which the insulating member 41 is arranged. In top view, the n-side electrode 32 is preferably arranged at a position not overlapping the p-side electrode 31 . As a result, unevenness in current density in the semiconductor structure 20 can be reduced.

It is preferable to cover the second surface 20 b , the fourth surface 20 d and the side surfaces of the semiconductor structure 20 and the n-side electrode 32 with the protective film 42 . The protective film 42 can protect the semiconductor structure 20 and the n-side electrode 32 from dust, moisture, and the like. Silicon oxide or silicon nitride, for example, can be used as the material of the protective film 42 .

In the light emitting device 1 of the embodiment, the substrate 11 can be provided on the opposite side of the fourth surface 20d, which is the main light extraction surface of the semiconductor structure 20. As shown in FIG. The substrate 11 is bonded to the p-side electrode 31 and the insulating member 41 via the bonding member 12 . A conductive member 33 can be arranged on the lower surface of the substrate 11 .

The substrate 11 is a support member that supports the semiconductor structure 20 and also functions as a current path between the conductive member 33 and the p-side electrode 31 . Therefore, the substrate 11 and the joining member 12 have conductivity. A silicon substrate, for example, can be used as the substrate 11 . Metals such as Ti, Pt, and Au, for example, can be used as the bonding member 12 . The bonding member 12 can have, for example, a laminated structure including a plurality of metal layers, and a laminated structure including metal layers of Ti, Pt, Au, Pt, and Ti in order from the semiconductor structure 20 side can be used. . As a material of the conductive member 33, for example, Au or the like can be used.

The light-emitting element 1 of the embodiment can be arranged on the wiring board such that the conductive member 33 faces the wiring board on which the wiring portion is arranged, and the fourth surface 20d and the n-side electrode 32 face upward from the wiring board. can. The conductive member 33 is electrically connected to the wiring portion arranged on the wiring board, for example, via solder or the like.

As shown in FIG. 1, the n-side electrode 32 can have a pad portion 32a and an extension portion 32b extending from the pad portion 32a. The extending portion 32b is arranged along the first extending portion 21c and the second extending portion 21d of the second portion 21-2 of the n-side semiconductor layer 21 on the second surface 20b, which is the upper surface of the second portion 21-2. ing. The pad portion 32a is located at the connecting portion between the first extending portion 21c and the second extending portion 21d of the second portion 21-2. At least part of the upper surface of the pad portion 32 a is exposed from the protective film 42 . The exposed portion of the upper surface of the pad portion 32a exposed from the protective film 42 is electrically connected to the wiring portion arranged on the wiring substrate by a conductive wire or the like. By applying an anode potential to the conductive member 33 and a cathode potential to the n-side electrode 32, the active layer 22 emits light. Light from the active layer 22 is extracted to the outside of the light emitting element 1 mainly through the fourth surface 20d.

According to the embodiment, by making the maximum thickness of the first portion 21-1 thinner than the maximum thickness of the second portion 21-2, light from the fourth surface 20d, which is the upper surface of the first portion 21-1, Extraction efficiency can be improved. In addition, by making the maximum thickness of the second portion 21-2 where the n-side electrode 32 is arranged larger than the maximum thickness of the first portion 21-1, the gap between the n-side electrode 32 and the p-side electrode 31 is reduced. The cross-sectional area of the current path is increased, the resistance of the current path is reduced, and the forward voltage can be reduced. In order to improve the light extraction efficiency and reduce the forward voltage, for example, the difference between the maximum thickness of the first portion 21-1 and the maximum thickness of the second portion 21-2 is 0.7 μm or more and 1.6 μm. The following are preferred. The thickness of the first portion 21-1 is preferably, for example, 0.6 μm or more and 1.5 μm or less. By setting the thickness of the first portion 21-1 to 0.6 μm or more, it is possible to prevent leakage current from occurring due to the first portion 21-1 being too thin. Further, by setting the thickness of the first portion 21-1 to 1.5 μm or less, the light extraction efficiency can be enhanced. The thickness of the second portion 21-2 can be, for example, 1.3 μm or more and 3.1 μm or less.

The n-side semiconductor layer 21 can be composed of a nitride semiconductor layer containing aluminum and gallium. Also, the n-side semiconductor layer 21 can have a first layer 21a and a second layer 21b positioned closer to the active layer 22 than the first layer 21a. The first layer 21a and the second layer 21b are, for example, AlGaN layers. When light with a relatively short wavelength with a peak wavelength of 410 nm or less is emitted from the active layer 22, using AlGaN for the n-side semiconductor layer 21 reduces the n-side semiconductor layer 21 by using GaN rather than using GaN for the n-side semiconductor layer 21. can reduce light absorption by

The aluminum composition ratio of the first layer 21a is preferably lower than that of the second layer 21b. By lowering the aluminum composition ratio of the first layer 21a, the resistance of the first layer 21a can be reduced. For example, the aluminum composition ratio of the first layer 21a is 1% or more and 3% or less, and the aluminum composition ratio of the second layer 21b is 3% or more and 5% or less. The difference between the aluminum composition ratio of the first layer 21a and the aluminum composition ratio of the second layer 21b is preferably 1% or more and 4% or less. For example, the aluminum composition ratio of the first layer 21a can be 3%, and the aluminum composition ratio of the second layer 21b can be 5%.

The second portion 21-2 has a first layer 21a and a second layer 21b. The second surface 20b of the second portion 21-2 is the upper surface of the first layer 21a. The first portion 21-1 has at least a second layer 21b. The first layer 21a is not arranged in the first portion 21-1. Alternatively, the thickness of the first layer 21a of the first portion 21-1 is thinner than the thickness of the first layer 21a of the second portion 21-2.

Since the aluminum composition ratio of the first layer 21a is lower than that of the second layer 21b, the light absorption rate of the first layer 21a is higher than that of the second layer 21b. By making the thickness of the first layer 21a of the first portion 21-1 thinner than the thickness of the first layer 21a of the second portion 21-2, or not arranging the first layer 21a on the first portion 21-1, , the light absorption in the first portion 21-1 can be reduced, and the light extraction efficiency from the fourth surface 20d can be improved.

As the aluminum composition ratio in the AlGaN layer increases, cracks are more likely to occur in the AlGaN layer. Also, as the thickness of the AlGaN layer increases, cracks are more likely to occur in the AlGaN layer.

According to the embodiment, as described above, in order to reduce the resistance of the second portion 21-2 where the n-side electrode 32 is arranged, the maximum thickness of the second portion 21-2 is set to the thickness of the first portion 21-1. Thicker than the maximum thickness. For this reason, not only the second layer 21b but also the first layer 21a, which has a lower aluminum composition ratio than the second layer 21b and is less susceptible to cracking, is arranged in the second portion 21-2. As a result, rather than making the second portion 21-2 thicker than the first portion 21-1 with only the second layer 21b, the resistance of the second portion 21-2 can be reduced while reducing the occurrence of cracks. Directional voltage can be reduced.

Next, with reference to FIG. 4, measurement results of light output and forward voltage for samples A to E will be described. In FIG. 4, the vertical axis on the left represents the optical output, and the vertical axis on the right represents the forward voltage. Both the light output and the forward voltage are relative values with the measured value of sample A being 1. The bar graph represents the measured light output and the black dots represent the measured forward voltage.

In sample A, the maximum thickness of the first portion 21-1 and the maximum thickness of the second portion 21-2 are the same. In samples B to E, the maximum thickness of the first portion 21-1 was made thinner than the maximum thickness of the second portion 21-2. That is, in sample A, the overall thickness of the n-side semiconductor layer 21 was made thinner than the maximum thickness of the second portion 21-2 in samples BE. In sample A, the total thickness of the n-side semiconductor layer 21 was set to 1.3 μm. In samples B to E, the maximum thickness of the first portion 21-1 was 1.3 μm, and the maximum thickness of the second portion 21-2 was 2.2 μm.

In sample B, the boundary between the first portion 21-1 and the second portion 21-2 is located at a position overlapping the p-side electrode 31 when viewed from above. In the directions (first direction Y and second direction X) parallel to the first surface 20a, the distance between the boundary between the first portion 21-1 and the second portion 21-2 and the outer edge 31a of the p-side electrode 31 is 10 μm. An outer edge 31 a of the p-side electrode 31 is located at the boundary between the p-side electrode 31 and the insulating member 41 on the lower surface of the p-side semiconductor layer 23 . That is, in sample B, a portion of the second portion 21-2 overlaps the p-side electrode 31 when viewed from above.

In sample C, the boundary between the first portion 21-1 and the second portion 21-2 is located at a position overlapping the outer edge 31a of the p-side electrode 31 when viewed from above.

In the sample D, the boundary between the first portion 21-1 and the second portion 21-2 is separated from the outer edge 31a of the p-side electrode 31 by 10 μm in the direction parallel to the first surface 20a. position. That is, in sample D, a portion of the first portion 21-1 overlaps the insulating member 41 when viewed from above.

FIG. 5 is a schematic top view of the light-emitting element 1 in sample E. FIG. In sample E as well, the extending portion 32b of the n-side electrode 32 extends along the first extending portion 21c and the second extending portion 21d of the second portion 21-2 to the second surface, which is the upper surface of the second portion 21-2. 20b. The pad portion 32a of the n-side electrode 32 is located at the connecting portion between the first extending portion 21c and the second extending portion 21d of the second portion 21-2.

In the sample E, when viewed from above, the boundary between the first portion 21-1 and the second portion 21-2 in the region A near the pad portion 32a of the n-side electrode 32 is the same as in the sample D, the first surface 20a 10 μm away from the outer edge 31a of the p-side electrode 31 in the direction parallel to . The boundary between the first portion 21-1 and the second portion 21-2 in the vicinity of the extending portion 32b of the n-side electrode 32 is located at a position overlapping the outer edge 31a of the p-side electrode 31 when viewed from above, as in the sample C. be. When viewed from above, the distance between the boundary between the first portion 21-1 and the second portion 21-2 in the vicinity area A of the pad portion 32a of the n-side electrode 32 and the outer edge 31a of the p-side electrode 31 is 1 distance. The distance between the boundary between the first portion 21-1 and the second portion 21-2 in the vicinity of the extended portion 32b of the n-side electrode 32 and the outer edge 31a of the p-side electrode 31 is defined as a second distance. In sample E, the first distance is greater than the second distance. In the sample E, only the region A near the pad portion 32a where the current is more likely to concentrate than the region near the extending portion 32b of the n-side electrode 32, and a part of the first portion 21-1 is the insulating member 41 in top view. is in a position overlapping with .

From the results shown in FIG. 4, samples B to E in which a thin portion (first portion 21-1) and a thick portion (second portion 21-2) are arranged in the n-side semiconductor layer 21 are A lower forward voltage can be obtained than sample A, which is made thinner overall.

In sample D, in which a part of the first portion 21-1 does not overlap the p-side electrode 31 but overlaps the insulating member 41 when viewed from above, an optical output equivalent to that of the sample A is ensured. Forward voltage can be reduced compared to sample A. From consideration of the measurement results of sample D, in order to improve the light extraction efficiency and reduce the forward voltage, the boundary between the first portion 21-1 and the second portion 21-2 is formed on the first surface 20a. It is preferably located outside the p-side electrode 31 in the parallel direction by 0.1 μm or more and 15 μm or less, preferably 0.5 μm or more and 15 μm or less from the outer edge 31 a of the p-side electrode 31 .

In addition, the sample E in which only the region A near the pad portion 32a and a part of the first portion 21-1 overlaps the insulating member 41 when viewed from above secures the same light output as the sample A, The forward voltage can be further reduced than in sample D. Considering the measurement results of sample E, the difference between the first distance and the second distance is preferably 0.1 μm or more and 15 μm or less, more preferably 0.5 μm or more and 15 μm or less.

The embodiments of the present invention have been described above with reference to specific examples. However, the invention is not limited to these specific examples. Based on the above-described embodiment of the present invention, all forms that can be implemented by those skilled in the art by appropriately designing and changing are also included in the scope of the present invention as long as they include the gist of the present invention. In addition, within the scope of the idea of the present invention, those skilled in the art can conceive of various modifications and modifications, and these modifications and modifications also belong to the scope of the present invention.

DESCRIPTION OF SYMBOLS 1... Light emitting element, 11... Substrate, 12... Joining member, 20... Semiconductor structure, 20a... 1st surface, 20b... 2nd surface, 20c... 3rd surface, 20d... 4th surface, 21... n-side semiconductor layer , 21-1 first portion 21-2 second portion 21a first layer 21b second layer 22 active layer 23 p-side semiconductor layer 31 p-side electrode 32 n Side electrode 32a Pad portion 32b Extension portion 33 Conductive member 41 Insulating member 42 Protective film

Claims (9)

A semiconductor structure having, in order from bottom to top, a p-side semiconductor layer, an active layer, and an n-side semiconductor layer, wherein the n-side semiconductor layer has a first portion and a second portion when viewed from above. a first surface that is a lower surface of the p-side semiconductor layer located below the first portion; a second surface that is an upper surface of the second portion; and a second surface that is located below the second portion. a semiconductor structure having a third surface that is the lower surface of the p-side semiconductor layer;
a p-side electrode arranged on the first surface;
an n-side electrode disposed on the second surface;
an insulating member disposed on the third surface;
with
The light emitting device, wherein the maximum thickness of the first portion is thinner than the maximum thickness of the second portion. A boundary between the first portion and the second portion is located outside the p-side electrode by 0.1 μm or more and 15 μm or less from the outer edge of the p-side electrode in a direction parallel to the first surface. Item 1. The light-emitting device according to item 1. The n-side electrode has a pad portion and an extension portion extending from the pad portion,
When viewed from above, the first distance between the boundary between the first portion and the second portion in the region near the pad portion and the outer edge of the p-side electrode is the first distance in the region near the extension portion. 2 . The light-emitting device according to claim 1 , wherein the second distance between a boundary between the second portion and the outer edge of the p-side electrode is greater than a second distance. 4. The light emitting device according to claim 3, wherein the difference between said first distance and said second distance is 0.1 [mu]m or more and 15 [mu]m or less. A boundary between the first portion and the second portion in the vicinity of the pad portion is 0.1 μm or more and 15 μm or less from the outer edge of the p-side electrode in a direction parallel to the first surface, and located far outside,
4. The light-emitting device according to claim 3, wherein a boundary between the first portion and the second portion in the vicinity of the extending portion is positioned so as to overlap the outer edge of the p-side electrode when viewed from above. 6. The thickness of the first portion is 0.6 μm or more and 1.5 μm or less, and the thickness of the second portion is 1.3 μm or more and 3.1 μm or less, according to any one of claims 1 to 5. light-emitting element. The n-side semiconductor layer has a first layer and a second layer which are nitride semiconductor layers containing aluminum and gallium, and the aluminum composition ratio of the first layer is higher than the aluminum composition ratio of the second layer. low,
The light emitting device according to any one of claims 1 to 6, wherein the thickness of the first layer of the first portion is thinner than the thickness of the first layer of the second portion. The n-side semiconductor layer has a first layer and a second layer which are nitride semiconductor layers containing aluminum and gallium, and the aluminum composition ratio of the first layer is higher than the aluminum composition ratio of the second layer. low,
The light emitting device according to any one of claims 1 to 6, wherein the first layer is not arranged in the first portion. 9. The light-emitting device according to claim 1, wherein the peak wavelength of light emitted from said active layer is 410 nm or less.

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