KR101138976B1 - Light emitting diode - Google Patents

Abstract

Here, a high efficiency light emitting diode is disclosed. The disclosed high efficiency light emitting diodes include a semiconductor substrate including a support substrate, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, and a reflective layer disposed between the support substrate and the semiconductor laminate structure, The reflective layer includes an insulating DBR and an energizing DBR in other regions in the width direction.

Description

[0001] LIGHT EMITTING DIODE [0002]

The present invention relates to a light emitting diode technology, and more particularly, to a technology suitable for a light emitting diode structure in which a growth substrate is removed and a semiconductor laminate structure is mounted on a support substrate, and in particular, a semiconductor laminate structure is mounted on a support substrate. It relates to the improvement of the reflective layer of light emitting diodes.

In general, nitrides of group III elements, such as gallium nitride (GaN) and aluminum nitride (AlN), have excellent thermal stability and have a direct transition type energy band structure. It is attracting much attention as a substance. In particular, blue and green light emitting devices using indium gallium nitride (InGaN) have been used in various applications such as large-scale color flat panel display devices, traffic lights, indoor lighting, high density light sources, high resolution output systems, and optical communications.

Such a nitride semiconductor layer of Group III elements is difficult to fabricate homogeneous substrates capable of growing them, and therefore, such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), etc., on heterogeneous substrates having a similar crystal structure. Is grown through the process. As a hetero substrate, a sapphire substrate having a hexagonal structure is mainly used. However, sapphire is an electrically insulator, thus limiting the light emitting diode structure. Accordingly, recently, epitaxial layers, such as nitride semiconductor layers, are grown on dissimilar substrates such as sapphire, bonding supporting substrates to the epitaxial layers, and then separating the dissimilar substrates using a laser lift-off technique. Techniques for producing highly efficient light emitting diodes of structure have been developed (see, eg, US Pat. No. 6,744,071).

Such a vertical light emitting diode forms an n-type GaN layer, an active layer, and a p-type GaN layer in order on a growth substrate, forms a p-electrode and a reflective metal layer on the p-type GaN layer, and bonds a support substrate thereon. Thereafter, the sapphire substrate is removed, and the n-electrode or n-electrode pad is formed on the exposed n-type semiconductor layer. A support substrate is generally used as a conductive substrate and thus has a vertical structure in which n-electrodes and p-electrodes are disposed to face each other.

However, since the n-electrode or n-electrode pad is located on the n-type GaN layer which is the light emitting surface, the light generated in the active layer is absorbed or reflected by the n-electrode, thereby reducing the light extraction efficiency. In addition, Ag, which is mainly used as a reflective layer while making ohmic contact with a p-type GaN layer, is easily agglomerated due to a thermal process, and migration of Ag atoms during driving of a light emitting diode is likely to cause current leakage. It is difficult to form a stable ohmic metal reflective layer. Moreover, Ag is a metal material and has a limit in improving reflectance.

Distributed Bragg Reflector (DBR) is a layer of high and low refractive index layers that are repeatedly stacked, and the optical thickness of these layers is adjusted to maximize reflectance for light of a specific wavelength. It is known. For this reason, several attempts have been made to apply the DBR to the reflective layer of a vertical light emitting diode. However, since the general DBR has insulation properties, there are many difficulties in its application due to the structural characteristics of the vertical light emitting diodes to be disposed between the conductive semiconductor layer and the electrode structure or the support substrate. In the past, attempts have been made to solve the above problem by using conductive metal vias penetrating through the DBR, but this causes a problem of lowering the reflection efficiency of the reflective layer.

Accordingly, the present invention is to solve the problems of the prior art, to provide a high-efficiency light emitting diode that is further provided with a conduction DBR in the width direction in the reflective layer including the insulating DBR, improving both reflection characteristics and electrical characteristics.

According to an aspect of the present invention, a high-efficiency light emitting diode includes a semiconductor laminate including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and a reflective layer disposed between the support substrate and the semiconductor laminate. The reflective layer includes an insulating DBR and an energizing DBR in other regions in the width direction.

Preferably, the insulating DBR and the energizing DBR are disposed adjacent to each other in the width direction.

According to an embodiment, the energizing DBR and the insulating DBR may be independently formed by a grid pattern including a grid network and a plurality of grid eyes defined by the grid screen.

According to an embodiment, the reflective layer may include a plurality of energizing DBRs in other regions in the width direction, and at least one of the plurality of energizing DBRs may be configured to reflect light having a wavelength different from that of the other energizing DBRs. .

According to another exemplary embodiment, the reflective layer may include a plurality of insulating DBRs in different regions in a width direction, and at least one of the plurality of insulating DBRs may be configured to reflect light having a wavelength different from that of the other insulating DBRs.

According to one embodiment, the reflective layer is attached to the support substrate by a conductive adhesive layer, the energizing DBR may be electrically connected to the electrode pad on the side of the support substrate by the conductive adhesive layer.

 In example embodiments, the reflective layer may further include a metal layer interposed between the conductive DBR and the conductive adhesive layer.

According to one embodiment, the support substrate may be a sapphire substrate, the energizing DBR preferably comprises an ITO layer. More preferably, the energizing DBR may be formed by repeatedly stacking ITO layers having different refractive indices.

The insulating DBR may be a single structure DBR structure such that the reflectance is high for a specific wavelength. According to an alternative embodiment, the insulating DBR comprises a first insulating DBR portion suitable for reflecting light of a first wavelength and a second insulating DBR portion suitable for reflecting light of a second wavelength, wherein the first insulating DBR portion And the second insulating DBR portion may be disposed perpendicular to each other. According to yet another alternative embodiment, the insulating DBR comprises a plurality of pairs of a first material layer having a first optical thickness and a second material layer having a second optical thickness, and a third material layer having a third optical thickness. And a plurality of pairs of fourth material layers having a fourth optical thickness, wherein the refractive index of the first material layer is different from the refractive index of the second material layer, and the refractive index of the third material layer is the fourth material layer. Is different from the refractive index. According to the embodiments described above, the insulating DBR may have a reflectivity of 90% or more for light of the first wavelength in the blue wavelength region, light of the second wavelength in the green wavelength region, and light of the third wavelength in the red wavelength region. have.

According to the present invention, a light emitting diode, particularly a light emitting diode having a vertical structure, can improve light extraction efficiency by using a reflecting layer including a DBR having a high reflectance for a specific wavelength, and conduction DBR and insulating DBR in the width direction can be improved. By a structure including a, it is possible to implement a simple conduction structure between the semiconductor stacked structure region above the reflective layer and the electrode region below the reflective layer without lowering the light extraction efficiency. The reflective layer has a metal layer below the energizing DBR, in particular, the ITO DBR, so that the problem of deterioration of current spreading performance caused by the energizing DBR using ITO can be solved. In addition, by using an insulating DBR including a plurality of insulating DBR portions arranged vertically and suitable for reflecting light of different wavelengths, it is possible to realize high reflectance with respect to a radio wave field of a plurality of wavelength regions, and moreover, a visible light region. When applying a light emitting diode to a white light emitting diode package it can greatly contribute to increase the light efficiency.

1 is an enlarged cross-sectional view of a portion of a high efficiency light emitting diode according to an embodiment of the present invention;
2 and 3 are diagrams for explaining a DBR pattern applicable to the reflective layer of the high efficiency light emitting diode shown in FIG.
4 and 5 are cross-sectional views showing embodiments of an insulating DBR applicable to the present invention, and sectional views illustrating an insulating DBR formed by vertically stacking a plurality of insulating DBR portions.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to ensure that the spirit of the present invention to those skilled in the art will fully convey. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience.

1 is an enlarged cross-sectional view of a portion of a high-efficiency light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, the light emitting diode includes a support substrate 10, a semiconductor laminate structure 30 disposed on the support substrate 10, and between the semiconductor laminate structure 30 and the support substrate 10. It includes a reflective layer 20 disposed. As described below, the reflective layer 20 includes an insulating DBR 22 and a conducting DBR 24, and below the conducting DBR 24, a metal layer 26 having a lower surface resistance than the conducting DBR 24. It can be formed in a certain pattern.

The support substrate 10 is distinguished from a growth substrate for growing the compound semiconductor layers, and is a secondary substrate attached to the compound semiconductor layers that have been grown. The support substrate 10 may be a sapphire substrate, but is not limited thereto, and may be another kind of insulating or conductive substrate. Particularly, when the sapphire substrate is used as the growth substrate, since it has the same coefficient of thermal expansion as the growth substrate, it is preferable to warp the wafer when bonding the support substrate and removing the growth substrate.

The semiconductor stacked structure 30 is disposed on the support substrate 10 and includes a p-type compound semiconductor layer 31, an active layer 32, and an n-type compound semiconductor layer 33. The p-type compound semiconductor layer 31 is positioned closer to the support substrate 10 side than the n-type compound semiconductor layer 33. The semiconductor laminate 30 may be located on a portion of the support substrate 10 and disposed on the entire region.

The p-type compound semiconductor layer 31, the active layer 32, and the n-type compound semiconductor layer 33 may be formed of a III-N series compound semiconductor, such as (Al, Ga, In) N semiconductor. The n-type compound semiconductor layer 33 and the p-type compound semiconductor layer 31 may be a single layer or multiple layers, respectively. For example, the n-type compound semiconductor layer 33 and / or the p-type compound semiconductor layer 31 may include a contact layer and a cladding layer, and may also include a superlattice layer. In addition, the active layer 32 may have a single quantum well structure or a multiple quantum well structure. An n-type compound semiconductor layer 33 having a relatively low resistance is positioned opposite the support substrate 10, thereby providing a roughing surface or a texturing surface on the upper surface of the n-type compound semiconductor layer 33. It is easy to form, and the rough surface or the corrugated surface improves the extraction efficiency of the light generated in the active layer 32. One side of the support substrate 10, for example, a p-type electrode pad (not shown) may be formed on a bottom surface of the support substrate 10 or a portion of the upper surface of the support substrate 10 on which the semiconductor stack structure 30 is not formed. Can be formed. The n-type electrode pad is generally formed on the upper surface of the n-type compound semiconductor layer 33, but if an appropriate insulating structure is adopted, the n-type electrode pad may be positioned on one side of the support substrate 10.

As mentioned above, the reflective layer 20 includes an insulating DBR 22 and an energizing DBR 24 positioned in different regions in the width direction, and the insulating DBR 22 and the energizing DBR 24 are semiconductor stacked. The p-type compound semiconductor layer 31 positioned below the structure 30 is in contact with the substrate 30. The insulating DBR 22 and the conducting DBR 24 may be disposed adjacent to each other in the width direction. For this purpose, the insulating DBR 22 or the conducting DBR 24 is formed by depositing the semiconductor stack 30 on the semiconductor stack 30. A portion of the insulation DBR 22 or the conduction DBR 24 formed as described above may be removed by etching, and the insulation DBR 22 or the conduction DBR 24 may be formed by vapor deposition in the removed position. have.

The insulating DBR 22 may be formed by alternately stacking at least two high refractive index layers and a low refractive index layer selected from, for example, Si _x O _y N _z , Ti _x O _y , Ta _x O _y, and Nb _x O _y . have. By controlling the optical thicknesses of the high refractive index layer and the low refractive index layer which are alternately stacked, the reflectance of light of a specific wavelength may be maximized. In this case, although the insulating DBR 22 may have the same structure as a whole and have the same reflection characteristic with respect to a specific wavelength, alternatively, the insulating DBR 22 may be divided into a plurality and separately formed, and among the plurality of insulating DBRs 22. It may be contemplated to vary the reflected wavelength of at least one insulating DBR 22 from the reflected wavelength of the other insulating DBR 22. In this case, the reflective characteristic of the insulating DBR 22 may be adjusted by thickness or reflectance.

In addition, the energizing DBR 24 may be formed by alternately stacking ITO layers having different refractive indices. At this time, by adjusting the optical thickness of the ITO layer having different refractive index, it is possible to maximize the reflectance for light of a specific wavelength. In this case, although the energizing DBR 24 may have the same structure as a whole and have the same reflection characteristic with respect to a specific wavelength, alternatively, the energizing DBR 24 may be divided into a plurality and separately formed, and the plurality of energizing DBRs 24 may be formed. It may be considered to adjust the reflection wavelength of one energizing DBR 24 differently from the reflection wavelength of the other energizing DBR 24. For example, if light having a wavelength of 455 nm is generated in the active layer, it basically includes an energization DBR having a 455 nm reflection wavelength, but may further provide an energization DBR having a 450 nm reflection wavelength or a 460 nm reflection wavelength.

For example, a lattice pattern as shown in FIGS. 2 and 3 may be used to divide the conductive DBR 24 or the insulating DBR 22 into a plurality of regions in one reflective layer 20.

Referring to FIG. 2, the energizing DBR 24 is formed in the shape of a grid screen, and the grid shape forms a plurality of grid eyes. The plurality of insulating DBRs 22 are formed to occupy a plurality of gratings, whereby the plurality of insulating DBRs 22 are independent of each other in different regions. In contrast, referring to FIG. 3, the insulating DBR 22 is formed in the shape of a grid, and the grid forms a plurality of grid eyes. The plurality of energizing DBRs 24 are formed to occupy a plurality of grid eyes, whereby the plurality of energizing DBRs 24 are independent of each other in different regions.

Adjusting the thickness of the energizing DBR 24 relative to the total reflecting layer 20 and / or the width of the individual DBR 24 relative to the width of the total reflecting layer 20, or the layers constituting the energizing DBR 24, In particular, by adjusting the refractive index and / or thickness of the ITO layers having different refractive indices, it is possible to adjust the reflection characteristics of the reflective layer 20 to be optimal.

Meanwhile, the reflective layer 20 further includes a metal layer 26 interposed between the energizing DBR 24 and the conductive adhesive layer. The metal layer 26 is formed in a linear pattern corresponding to the conduction pattern to reduce surface resistance, improve the bad current spreading performance of the conduction DBR 24 made of ITO layers, and the p-type compound semiconductor layer 31. The ohmic contact effect can be provided to the over-current DBR 24. As the material of the metal layer 26, Ag, Ni, Cu, Ti, Cr, or an alloy thereof having good electrical properties may be used, and other metal materials may be used.

The support substrate 10 is attached to the conductive adhesive layer 21 on the reflective layer 20 formed under the semiconductor laminate structure 30. The adhesive layer 21 is generally referred to as a bonding metal, and may be formed of, for example, Au-Sn, and adheres the support substrate 10 to the semiconductor laminate structure 30 by eutectic bonding.

The above-mentioned insulating DBR preferably includes a single DBR formed by repeatedly stacking one high refractive index layer and one low refractive index layer in the vertical direction when reflecting light of a specific wavelength. However, when the light emitting diode as described above is applied to a light emitting diode package that emits white light, the structure of the insulating DBR including two or more stacked insulating DBR portions may contribute to further improving the light efficiency. . Hereinafter, another embodiment of the insulation DBR applicable to the above-described light emitting diode as a structure in which two or more insulation DBR portions suitable for reflecting light of two or more different wavelengths are stacked will be described.

Referring to FIG. 4, the insulation DBR 22 of the present embodiment includes a first insulation DBR portion 222 and a second insulation DBR portion 224.

The first insulating DBR portion 222 is formed by repeating a plurality of pairs of the first material layer 222a and the second material layer 222b, and the second insulating DBR portion 224 is the third material layer 224a. ) And a plurality of pairs of the fourth material layer 224b are formed repeatedly. The plurality of pairs of the first material layer 222a and the second material layer 222b have a relatively high reflectance for light in a red wavelength region, for example, light of 550 nm or 630 nm, compared to light in a blue wavelength region. The second insulating DBR unit 224 may have a relatively high reflectance of light in a blue wavelength region, for example, light of 460 nm, compared to light in a red or green wavelength region. At this time, the optical thicknesses of the material layers 222a and 222b in the first insulating DBR portion 222 are thicker than the optical thicknesses of the material layers 224a and 224b in the second insulating DBR portion 224. It is not limited and vice versa.

The first material layer 222a may have the same material as the third material layer 224a, that is, the same refractive index, and the second material layer 222b may have the same material as the fourth material layer 224b, That is, it may have the same refractive index. For example, the first material layer 222a and the third material layer 224a may be formed of TiO ₂ (n: about 2.5), and the second material layer 222b and the fourth material layer 224b may be formed. SiO ₂ (n: about 1.5).

On the other hand, the optical thickness (refractive index ㅧ thickness) of the first material layer 222a has a substantially integer relationship with the optical thickness of the second material layer 222b, and preferably, their optical thicknesses are substantially the same. Can be. In addition, the optical thickness of the third material layer 224a has a substantially integer relationship with the optical thickness of the fourth material layer 224b, and preferably, their optical thicknesses may be substantially the same.

In addition, the optical thickness of the first material layer 222a is thicker than the optical thickness of the third material layer 224a, and the optical thickness of the second material layer 222b is equal to that of the fourth material layer 224b. Thicker than optical thickness. The optical thicknesses of the first to fourth material layers 40a, 40b, 50a, and 50b may be controlled by adjusting the refractive index and / or the actual thickness of each material layer.

According to the present embodiment, a structure in which a first insulating DBR portion 222 having a relatively high reflectance with respect to long wavelength visible light and a second insulating DBR portion 224 having a relatively high reflectance with respect to short wavelength visible light are stacked on each other. An insulating DBR 22 of is provided. The insulation DBR 22 can increase the reflectance of light over most of the visible light region by the combination of the first insulation DBR portion 222 and the second insulation DBR portion 224.

Although the single DBR described above with reference to FIGS. 1 to 3 has a high reflectance for light in a specific wavelength range but a relatively low reflectance for light in a different wavelength range, the light efficiency of the light emitting diode package emitting white light is high. There is a limit to improvement. However, according to the present embodiment, since the insulating DBR 22 can have high reflectance not only for light in the blue wavelength region but also light in the green wavelength region and light in the red wavelength region, it is possible to improve the light efficiency of the LED package. Can be.

Further, by arranging the first insulating DBR portion 222 closer to the semiconductor laminate structure than the second insulating DBR portion 224, the optical loss in the insulating DBR 22 is reduced compared to the case where the first insulating DBR portion 222 is arranged in reverse. Can be reduced.

In the present embodiment, two reflectors of the first insulating DBR portion 222 and the second insulating DBR portion 224 are described, but a larger number of DBRs may be used. In this case, it is preferable that DBRs having a relatively high reflectance with respect to a long wavelength are located relatively close to the semiconductor stacked structure.

In addition, in the present embodiment, the thicknesses of the first material layers 222a in the first insulating DBR portion 222 may be different from each other, and the thicknesses of the second material layers 222b may be different from each other. have. In addition, the thicknesses of the first material layers 222a in the second insulating DBR portion 224 may be different from each other, and the thicknesses of the second material layers 224b may be different from each other.

In the present embodiment, the material layers 40a, 40b, 50a, and 50b have been described as being formed of SiO ₂ or TiO ₂ , but are not limited thereto, and other material layers such as Si ₃ N ₄ , a compound, and the like. It may be formed of a semiconductor or the like. However, the difference in refractive index between the first material layer 222a and the second material layer 222b and the difference in refractive index between the third material layer 224a and the fourth material layer 224b may be greater than 0.5, respectively. Do.

In addition, the number of pairs of the first material layer and the second material layer in the first insulating DBR portion 222 and the number of pairs of the third material layer and the fourth material layer in the second insulating DBR portion 224 The more the reflectance increases, the total number of these pairs can be 20 or more.

5 is a cross-sectional view for explaining the insulating DBR 22 according to another embodiment of the present invention. In the insulating DBR 22 according to the present embodiment, a plurality of pairs of the first material layer 222a and the second material layer 222b and a plurality of pairs of the third material layer 224a and the fourth material layer 224b. Are mixed with each other. That is, at least one pair of the third material layer 224a and the fourth material layer 224b is positioned between the plurality of pairs of the first material layer 222a and the second material layer 222b and further includes a first At least one pair of material layer 222a and second material layer 222b is positioned between the plurality of pairs of third material layer 224a and fourth material layer 224b. Here, the optical thicknesses of the first to fourth material layers 222a, 222b, 224a, and 224b are controlled to have a high reflectance for light over a wide range of visible light region.

10: substrate 20: reflective layer
22: insulated DBR 24: energized DBR
26 metal layer 30 semiconductor laminate structure
31: p-type compound semiconductor layer (conductive semiconductor layer)
32: active layer
33: n-type compound semiconductor layer (conductive semiconductor layer)
222: first insulation DBR portion 224: second insulation DBR portion

Claims (13)

Support substrate;
A semiconductor stacked structure comprising a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer; And
A reflective layer disposed between the support substrate and the semiconductor laminate structure,
The reflective layer includes an insulating DBR and an energizing DBR in different areas of the reflective layer. The light emitting diode of claim 1, wherein the insulating DBR and the energizing DBR are disposed adjacent to each other. The light emitting diode of claim 2, wherein the energizing DBR and the insulating DBR are independently formed by a grid pattern including a grid and a plurality of grids defined by the grid. The light emitting diode of claim 1, wherein the energizing DBR includes a plurality of energizing DBRs, wherein at least one energizing DBR of the plurality of energizing DBRs is configured to reflect light having a wavelength different from that of other electrifying DBRs. . The light emitting diode of claim 1, wherein the insulation DBR includes a plurality of insulation DBRs, and at least one insulation DBR of the plurality of insulation DBRs is configured to reflect light having a wavelength different from that of another insulation DBR. . The light emitting diode of claim 1, wherein the reflective layer is attached to the support substrate by a conductive adhesive layer, and the energizing DBR is electrically connected to an electrode pad on the side of the support substrate by the conductive adhesive layer. The light emitting diode of claim 6, wherein the reflective layer further comprises a metal layer interposed between the energizing DBR and the conductive adhesive layer. The light emitting diode of claim 6, wherein the support substrate is a sapphire substrate. The light emitting diode according to any one of claims 1 to 8, wherein the energizing DBR comprises an ITO layer. The light emitting diode of claim 9, wherein the energizing DBR is formed by repeatedly stacking ITO layers having different refractive indices.  The method of claim 1, wherein the insulating DBR comprises a first insulating DBR portion for reflecting light of a first wavelength, and a second insulating DBR portion for reflecting light of a second wavelength, wherein the first insulating DBR portion and the second The light emitting diodes of claim 1, wherein the insulating DBR portions are disposed perpendicular to each other. The method according to claim 1, wherein the insulating DBR,
A plurality of pairs of a first material layer having a first optical thickness and a second material layer having a second optical thickness; And
A plurality of pairs of a third material layer having a third optical thickness and a fourth material layer having a fourth optical thickness,
The refractive index of the first material layer is different from the refractive index of the second material layer, and the refractive index of the third material layer is different from the refractive index of the fourth material layer. The method of claim 1, wherein the insulating DBR has a reflectance of 90% or more to light of the first wavelength in the blue wavelength region, light of the second wavelength in the green wavelength region and light of the third wavelength in the red wavelength region. Light emitting diode.

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