KR20140036404A - Light emitting diode and its manufacturing method - Google Patents

Abstract

A light emitting diode is disclosed. The light emitting diode comprises: a transparent substrate having a first surface and a second surface; a gallium nitride-based semiconductor laminated structure disposed on the first surface of the transparent substrate and comprising a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer; and a refractive index adjusting layer formed on the second surface of the transparent substrate and having a pattern on a lower surface. The present invention can improve the light extraction efficiency by reducing the loss of light generated from the lower surface of the transparent substrate depending on the refractive index adjustment layer.

Description

LIGHT EMITTING DIODE AND ITS MANUFACTURING METHOD}

The present invention relates to a light emitting diode and a method of manufacturing the same.

In general, a light emitting diode is a semiconductor light emitting device that converts current directly into light by using a principle of emitting light when electrons in the n region meet and recombine with holes in the p region when a voltage is applied to the pn junction of the semiconductor. It has high energy conversion efficiency, long life, good light directivity, low voltage driving, no preheating time, no complicated driving circuit, and strong resistance to shock and vibration. It is attracting attention as the next generation light source to replace the light source.

The improvement of the efficiency of the light emitting diode is made in two directions. The first is to increase the internal quantum efficiency determined by the crystalline and epilayer structure, and the second is to generate the emitted light to the outside of the light emitting diode as much as possible. So as to improve the light extraction efficiency. Among these, light extraction efficiency is easy to heat In order to minimize the internal light loss due to the development of emission structure or total reflection at the interface between layers, in order to minimize the internal light loss due to the total reflection at the interface between layers, total reflection of the interface between layers by patterning Methods of reducing the properties are known.

In general, the light emitting diode includes a semiconductor stacked structure formed on a sapphire substrate, and the semiconductor stacked structure includes a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer in a direction away from the sapphire substrate. In such a light emitting diode, when light generated in the active layer passes through the first conductive semiconductor layer and the sapphire substrate and is emitted to the front side of the light emitting diode, a part of the light is totally reflected at the interface between the transparent substrate and the first conductive semiconductor layer. As a result, the light emitting diodes cannot be discharged to the outside of the light emitting diodes.

On the other hand, in the related art, a light emitting diode has been proposed in which an uneven pattern is formed on an upper surface of a transparent substrate, that is, an interface between the first conductive semiconductor layer and the transparent substrate to reduce total reflection at the interface.

Conventional light emitting diodes reduce the total reflection characteristics on the transparent substrate to prevent light loss, but the light extraction efficiency is limited by the light emitted to the lower portion of the transparent substrate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting diode which can prevent light from being emitted and lost through a second surface opposite to a first surface of a transparent substrate on which a semiconductor laminate structure is formed.

A light emitting diode according to embodiments of the present invention comprises: a transparent substrate having a first surface and a second surface; A gallium nitride based semiconductor laminate comprising a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer, formed on the first surface of the transparent substrate; It is formed on the second surface of the transparent substrate, and includes a refractive index control layer having a pattern on the lower surface.

By adopting the refractive index control layer to reduce the total reflection in the lower portion of the transparent substrate and to scatter the light by the pattern can improve the light extraction efficiency of the light emitting diode.

In one embodiment, the pattern may include a plurality of pyramid structures.

In one embodiment, the refractive index control layer comprises a rock salt metal oxide layer, the metal oxide layer is formed on the second surface of the sapphire substrate by deposition to form the pyramid structures.

In one embodiment, the metal oxide layer may include an MgO-based, NiO-based, CaO-based or ZnO-based metal oxide.

In one embodiment, the metal oxide layer may include a MgO-based metal oxide represented by the formula of Mg _x M _1-x O (x≤1, M is a metal). In one embodiment, M may include at least one of Be, Ca, Sr, Ba.

In one embodiment, the MgO-based metal oxide includes impurities doped to the surface, the impurities are B, In, Zn, Tl, Al, Sn, Ga, Te, Si, C, Ge, N, P, As, Sb, Bi, S, Se, Br, I, Ti and oxides thereof.

In one embodiment, the metal oxide layer may have a thickness of 5000 ~ 4㎛. More preferably, the metal oxide layer has a thickness of less than 2 μm. In this case, the thickness of the metal oxide layer and the thickness of the pattern may be substantially the same.

In one embodiment of the present invention, the light emitting diode further comprises a reflective film formed on the refractive index control layer to cover the pattern, the reflective film is formed of a reflective material having a reflectivity of 90% or more for the wavelength of 420 ~ 450nm .

In one embodiment, the refractive index control layer may have a median refractive index between the refractive index and the air refractive index of the gallium nitride-based semiconductor. The transparent substrate may be a sapphire substrate, and the refractive index adjusting layer may have a refractive index smaller than that of the sapphire substrate.

In the method of manufacturing a light emitting diode according to embodiments of the present invention, a transparent substrate having a first surface and a second surface facing each other is prepared, and a gallium nitride based semiconductor laminate structure is formed on the first surface of the sapphire substrate, Forming a refractive index control layer on the second surface of the sapphire substrate, characterized in that the refractive index control layer has a pattern on the lower surface.

In this case, the refractive index adjusting layer may be formed by depositing a metal oxide having a rock salt structure on the second surface of the transparent substrate with an electron beam or an ion beam assist, and the pattern is formed by a deposition process. The metal oxide may include an MgO-based, NiO-based, CaO-based, or ZnO-based metal oxide. In addition, the metal oxide is MgO-based metal oxide represented by the formula of Mg _x M _{1 -x} O (x≤1, M is a metal), M may include at least one of Be, Ca, Sr, Ba. . B, In, Zn, Tl, Al, Sn, Ga, Te, Si, C, Ge, N, P, As, Sb, Bi, S, Se, Br, I, Ti and oxides thereof Dopants selected from the containing group may be doped. The second surface of the sapphire substrate may be surface treated using oxygen plasma, nitrogen plasma, or UVO prior to deposition with the electron-beam or ion-beam assist.

In one embodiment, the shape and size of the pyramid structure can be adjusted by controlling the temperature at which the metal oxide layer is deposited.

The transparent substrate may be a sapphire substrate.

According to embodiments of the present invention, the total reflection may be reduced even on the lower surface of the sapphire substrate in contact with air. By forming a pyramid structure so that a flat surface does not exist on the lower surface side of the sapphire substrate, it is possible to maximize the effect of reducing the total reflection characteristics.

A horizontal light emitting diode according to an embodiment of the present invention, to which an MgO layer including a plurality of pyramid structures is applied as a refractive index adjusting layer, has a substantially same thickness as compared to a conventional light emitting diode including a sapphire substrate having a flat bottom surface. , Light output increased by approximately 13%.

1 is a cross-sectional view showing a light emitting diode according to an embodiment of the present invention;
2 to 6 are cross-sectional views illustrating a method of manufacturing a light emitting diode according to an embodiment of the present invention.
FIG. 7 is a scanning electron microscope (SEM) photograph showing pyramidal pattern structures according to a thickness of an MgO layer formed as a refractive index adjusting layer in a light emitting diode according to an embodiment of the present invention.
8 is a diagram showing a high-resolution transmission electron microscope (TEM) photograph showing the pyramid pattern structure of the MgO layer and a schematic diagram of the pyramidal crystal structure of MgO,
9 is a graph illustrating normalized light output of a gallium nitride-based horizontal light emitting diode to which an MgO layer having a pyramid pattern structure is applied according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples for allowing a person skilled in the art to sufficiently convey the idea of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, and the like of the components may be exaggerated for convenience.

1 is a cross-sectional view illustrating a light emitting diode according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a light emitting diode according to an embodiment of the present invention includes a transparent substrate 1, a semiconductor laminate structure 2, and a refractive index control layer 3. In addition, the light emitting diode includes a transparent electrode layer 4, a first electrode pad 5, and a second electrode pad 6.

The transparent substrate 1 includes an upper surface (or a first surface) and a lower surface (ie, a second surface) opposite thereto. The transparent substrate 1 is not particularly limited as long as it is a substrate that transmits light generated by the active layer 24, and may be, for example, a sapphire substrate. Hereinafter, the transparent substrate 1 will be described as a sapphire substrate.

A semiconductor laminate structure 2 is formed on an upper surface of the sapphire substrate 1, and a refractive index adjusting layer 3 described in detail below is formed on a lower surface of the sapphire substrate 1. Although not shown, the sapphire substrate 1 may be a PSS (Patterned Sapphire Substrate) having a predetermined concave-convex pattern formed on an upper surface thereof, that is, an interface with the semiconductor laminate structure 2.

The semiconductor laminate 2 may be formed using the sapphire substrate 1 as a growth substrate, and may include a first conductive semiconductor layer 22, an active layer 24, and a second conductive semiconductor layer ( 26). The active layer 24 is interposed between the first conductive semiconductor layer 22 and the first conductive semiconductor layer 26. The first conductive semiconductor layer 22 is a layer formed adjacent to the sapphire substrate 1 and may be an n-type semiconductor layer. In addition, the second conductivity-type semiconductor layer 26 is a layer relatively far from the sapphire substrate 1 and may be a p-type semiconductor layer. Conversely, the first conductive semiconductor layer 22 may be a p-type semiconductor layer and the second conductive semiconductor layer 26 may be an n-type semiconductor layer.

The first conductive semiconductor layer 22, the active layer 24, and the second conductive semiconductor layer 26 may be formed of a gallium nitride-based compound semiconductor material, that is, (Al, In, Ga) N. The active layer 24 has a composition element and composition ratio determined so as to emit light of a required wavelength such as ultraviolet light or blue light. The first conductive semiconductor layer 22 and / or the second conductive semiconductor layer 26 may be formed as a single layer, as shown, but may be formed in a multilayer structure. In addition, the active layer 24 may be formed of a single quantum well or multiple quantum well structures. Although not shown, a buffer layer for mitigating lattice mismatch may be interposed between the sapphire substrate 1 and the first conductivity-type semiconductor layer 22.

The light emitting diode according to the present exemplary embodiment is a horizontal light emitting diode having both the first electrode pad 5 and the second electrode pad 6 thereon, and exposes the upper portion of the first conductive semiconductor layer 22 to expose it. In order to form the first electrode pad 5 in the formed region, the semiconductor laminate structure 2 has a structure in which some regions of the second conductive semiconductor layer 26 and the active layer 24 are removed. The first electrode pad 5 is formed in the upper exposed region of the first conductive semiconductor layer 22, and the second electrode pad 6 is formed on the second conductive semiconductor layer 26.

As illustrated, the transparent electrode layer 4 may be formed on the second conductive semiconductor layer 26, and the second electrode pad 6 may be formed on the transparent electrode layer 4. The transparent electrode layer 4 is formed of, for example, ITO or Ni / Au, and has a specific resistance lower than that of the second conductive semiconductor layer 26 to distribute current.

In the present embodiment, the refractive index control layer 3 is an MgO layer formed by vapor deposition on the lower surface of the sapphire substrate 1, and the refractive index of the gallium nitride-based semiconductor together with the sapphire substrate having a refractive index of n = 1.77 (n = It has a refractive index of 2.5) and an intermediate value (n = 1.74) of the refractive index of air (n = 1), and serves as a refractive index adjusting layer that can reduce total reflection by adjusting the refractive index. At this time, the refractive index control layer (hereinafter referred to as "MgO refractive index control layer") has a refractive index smaller than the refractive index of the sapphire substrate, that is, the refractive index having a relatively small difference with the refractive index of the air, further reducing the total reflection Can be. In addition, the MgO refractive index control layer 3 includes a pattern for reducing total reflection on the side of the lower surface in contact with air and emitting light, which includes a plurality of pyramid structures 32.

As described above, the MgO refractive index adjusting layer 3 functions to adjust the refractive index together with the sapphire substrate 1 so that the light generated in the active layer 24 and passed through the first conductive semiconductor layer 22 is transferred to the sapphire substrate ( 1) and the critical angle emitted to the outside through the MgO refractive index control layer 3 is increased. In addition, a pyramid pattern structure is formed on the surface of the MgO refractive index control layer 3 without an additional process during MgO deposition, so that light incident on the MgO refractive index control layer 3 is more scattered by the pyramid pattern structure. Light may be reflected back into the device and emitted to the outside.

At this time, the MgO refractive index adjusting layer 3 and the thickness of the pyramid pattern thereof may be determined within 5000 m to 4 m.

Referring to Figures 2 to 6 will be described a light emitting diode manufacturing method according to an embodiment of the present invention.

First, referring to FIG. 2, for example, by using MOCVD or MBE technology, a sapphire first conductive semiconductor layer 22, an active layer 24, and a second conductive type gallium nitride based on the upper surface of the substrate 1 may be used. The semiconductor layer 26 is formed in order. As for the thickness of the sapphire substrate 1, 100 micrometers-400 micrometers are preferable, and 150 micrometers or less are the most preferable. A process of reducing the thickness of the sapphire substrate 1 to 150 μm or less through a lapping process may be used. The lapping process may take place after the formation of the semiconductor laminate, in particular immediately before the deposition process of the MgO layer to be described below.

Next, referring to FIG. 3, a partial region 222 of the first conductive semiconductor layer 22 is patterned by removing a portion of the second conductive semiconductor layer 26 and the active layer 24 by using a photo and etching technique. ).

Next, referring to FIG. 4, for example, ITO or Ni / Au is deposited on the upper surface of the second conductive semiconductor layer 26 to form the transparent electrode layer 4, and the upper surface of the transparent electrode layer 4 and the first conductive layer. The second electrode pad 6 and the first electrode pad 5 are formed in each of the exposed regions 222 of the type semiconductor layer 22.

In this case, the transparent electrode layer 4 is formed immediately after the formation process of the first conductive semiconductor layer 22, the active layer 24 and the second conductive semiconductor layer 26 described in FIG. Some regions may be formed together with the second conductivity-type semiconductor layer 26 and the active layer 24 by etching and photolithography to expose the upper portion of the semiconductor layer 22.

Next, referring to FIG. 5, MgO is deposited on the lower surface of the sapphire substrate 1 to a predetermined thickness to form an MgO refractive index control layer 3 having a refractive index control function together with the sapphire substrate 1. Prior to MgO deposition, it is preferable to first perform a surface treatment for enhancing affinity with the MgO layer on the target surface of the sapphire substrate 1, i.e., the bottom surface, and such surface treatment may be oxygen plasma treatment, nitrogen plasma treatment or UVO ( Ultra Violet Ozone) treatment and the like can be used.

In addition, the MgO refractive index control layer 3 is a pyramid pattern having a plurality of pyramid structures 32 by the MgO crystal structure only by a deposition process, in particular, an e-beam deposition process, without any additional process. Is formed. At this time, the structure and shape of the pyramid pattern change depending on the MgO deposition thickness, and thus, by controlling the deposition thickness, it is possible to obtain a pyramid pattern having an intended structure.

The MgO refractive index control layer 3 may be formed of an MgO-based oxide, and the MgO-based oxide may be a ternary or more poly-based oxide obtained by adding one or more elements to MgO.

As the MgO-based ternary compound, for example, Mg _x Be _1-x O (x ≦ ₁ ), Mg _x Ca _1-x O (x ≦ ₁ ), Mg _x Sr _1-x O (x ≦ ₁ ), Mg _x There may be Ba _1-x O (x ≦ ₁ ).

In addition, as the MgO-based multicomponent compound, two or more elements among Be, Ca, Sr, and Ba elements may form a compound with Mg.

In addition, the MgO-based oxide may include doped impurities on the surface, and the impurities used may include B, In, Zn, Tl, Al, Sn, Ga, Te, Si, C, Ge, N, P, There may be oxides of As, Sb, Bi, S, Se, Br, I, Ti or their metals.

The MgO-based metal oxide is a rock salt metal oxide in which the above-described pyramidal structures 32 are spontaneously formed by electron-beam deposition. In addition to the MgO-based metal oxide, the MgO-based metal oxide may form a pattern of pyramidal structures by electron-beam deposition. Oxide materials of the rock salt structure may be NiO, CaO, ZnO or a metal oxide containing the same. The metal oxides as described above may be deposited on a sapphire substrate or another substrate to form a pattern having a plurality of pyramid structures, and thus may be used as a refractive index control layer of the light emitting diode according to the present invention.

 Although the process of forming the refractive index adjusting layer 3 is preferably performed after the process shown in FIG. 3, it may be performed at any point before and after the various processes described above.

Next, referring to FIG. 6, as an additional process, Ag is deposited on the back surface of the light emitting diode 1, that is, the lower surface of the MgO refractive index adjusting layer 3 to cover the pattern of the refractive index adjusting layer 3. (7) is formed. Instead of Ag, another reflective material, such as Al, may be formed on the bottom surface of the MgO refractive index control layer 3. In addition to Ag, Al, or a metal material including the same, other reflective materials may be applied to the reflective film 7, and the reflective material is preferably a material having a reflectivity of 90% or more with respect to a wavelength of 420 to 450 nm.

FIG. 7 is a scanning electron microscope (SEM) image showing pyramid pattern structures according to a thickness of an MgO layer formed as a refractive index adjusting layer in a light emitting diode according to an embodiment of the present invention. Referring to FIG. 7, it can be seen that the surfaces of the MgO layers deposited with thicknesses of 0.7 μm, 2 μm, and 4 μm have different and successfully formed pyramidal structures on the surface of the MgO layer according to the respective thicknesses.

FIG. 8 is a diagram showing a high-resolution transmission electron microscope (TEM) image showing the pyramid pattern structure of the MgO layer and a schematic diagram of the pyramidal crystal structure of MgO. Referring to FIG. 8, the MgO pyramid structure ends in the (200) plane. , (111) growth direction. This is because the (200) plane has lower surface energy than the (111) plane in the MgO layer having a rock salt structure, so that the pyramid pattern is spontaneously formed in order to lower the energy of the thin film during the deposition process. can do.

FIG. 9 is a graph illustrating normalized light output of a gallium nitride-based horizontal light emitting diode to which an MgO layer having a pyramid pattern structure is applied according to an embodiment of the present invention.

Referring to FIG. 9, normalized light output of a gallium nitride-based horizontal light emitting diode to which an MgO layer having a pyramid pattern is applied and a light emitting diode having a conventional sapphire substrate are compared. In the case of the light emitting diode to which the MgO layer is applied, the light output was measured after different thicknesses of 0, 0.2, 0.7, 2, and 4 μm of MgO layers were deposited on the lower surface of the sapphire substrate. In the absence of the MgO layer as a thickness of 0, the light output increased to 12.9% at 0.2㎛ thickness and 10.1% at 0.7㎛ thickness, -1% at 2㎛ thickness, and -0.2% at 4㎛ thickness. Rather, the light output was found to decrease.

That is, it was confirmed that the light efficiency of the light emitting diode changes depending on the thickness of the MgO layer, and the light efficiency increases only within a certain thickness range of the MgO layer.

10 is a scanning electron microscope (SEM) pictures showing that the shape and size of the pyramid pattern formed according to the temperature of the MgO layer formation in one embodiment of the present invention and the RMS roughness of the MgO pyramid structure generated at this time This is a graph showing.

Referring to FIG. 10, when a MgO layer having a pyramid pattern is deposited using an electron-beam or ion-beam assist, the deposition state temperature is different. At this time, the temperature was deposited at room temperature (RT), 200 ° C. and 300 ° C., respectively, and the shape and size of the MgO pyramid pattern generated according to the deposition temperature may be different. The MgO pyramid structure at 300 ° C. hardly forms a pyramid model, and it was confirmed that the pyramid structure at 200 ° C. also slightly collapsed. In addition, as a result of measuring the surface roughness (RMD roughness) it was confirmed that the reduction from 9.7nm (room temperature) to 6.2nm (300 ℃). That is, when MgO forms a pyramid structure, it is well formed at a temperature of 200 ° C. or less, and it is confirmed that the surface roughness, that is, the size of the structure can be adjusted according to the temperature.

The pyramid structure formed on the MgO layer can be fabricated using general optical lithography patterning without using electron beam lithography patterning, which is expensive and difficult to apply to large area wafer processes. In addition, since it requires no additional patterning process, it is very effective in terms of large area application and manufacturing cost.

1: Sapphire Substrate 2: Semiconductor Laminated Structure
3: refractive index control layer 22: first conductive semiconductor layer
24: active layer 26: second conductive semiconductor layer
32: pyramid structure

Claims (20)

A transparent substrate having a first side and a second side;
A gallium nitride based semiconductor laminate including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and formed on a first surface of the transparent substrate; And
A light emitting diode is formed on the second surface of the transparent substrate, the light emitting diode comprising a refractive index control layer having a pattern on the lower surface. The light emitting diode of claim 1, wherein the pattern includes a plurality of pyramid structures. The method of claim 2, wherein the refractive index control layer comprises a rock salt metal oxide layer, the metal oxide layer is formed on the second surface of the transparent substrate by deposition to form the pyramid structures Light emitting diode. The light emitting diode of claim 3, wherein the metal oxide layer comprises MgO-based, NiO-based, CaO-based, or ZnO-based metal oxides. The light emitting diode of claim 3, wherein the metal oxide layer comprises MgO-based metal oxide represented by the formula of Mg _x M _1-x O (x≤1, M is a metal). The light emitting diode of claim 5, wherein M comprises at least one of Be, Ca, Sr, and Ba. The method according to claim 5, wherein the MgO-based metal oxide comprises impurities doped on the surface, the impurities are B, In, Zn, Tl, Al, Sn, Ga, Te, Si, C, Ge, N, P, As , Sb, Bi, S, Se, Br, I, Ti and light emitting diodes selected from the group consisting of oxides thereof. The light emitting diode of claim 5, wherein the metal oxide layer has a thickness of 5000 kPa to 4 µm. The light emitting diode of claim 8, wherein the metal oxide layer has a thickness of less than 2 μm. The light emitting diode of claim 1, further comprising a reflective film formed on the refractive index control layer to cover the pattern, wherein the reflective film is formed of a reflective material having a reflectivity of 90% or more with respect to a wavelength of 420 to 450 nm. The light emitting diode of claim 1, wherein the refractive index adjusting layer has a median refractive index between the refractive index of the gallium nitride-based semiconductor and the air refractive index. The light emitting diode according to any one of claims 1 to 11, wherein the transparent substrate is a sapphire substrate, and the refractive index adjusting layer has a refractive index smaller than that of the sapphire substrate. Preparing a transparent substrate having a first side and a second side,
Forming a gallium nitride based semiconductor laminate on the first surface of the transparent substrate,
Forming a refractive index control layer on the second surface of the transparent substrate,
The refractive index control layer is a light emitting diode manufacturing method characterized in that it has a pattern on the lower surface. The method of claim 13, wherein a metal oxide having a rock salt structure is deposited on the second surface of the transparent substrate by electron-beam or ion-beam assist to form a refractive index control layer having the pattern. The method of claim 14, wherein the metal oxide comprises MgO-based, NiO-based, CaO-based, or ZnO-based metal oxides. The method according to claim 14, wherein the metal oxide is MgO-based metal oxide represented by the formula of Mg _x M _{1 - x} O (x≤1, M is a metal), wherein M is at least one of Be, Ca, Sr, Ba Light emitting diode manufacturing method comprising a. The method according to claim 16, B, In, Zn, Tl, Al, Sn, Ga, Te, Si, C, Ge, N, P, As, Sb, Bi, S, Se, Br, I, Ti And doping the impurities selected from the group comprising oxides thereof. The method of claim 14, wherein the second surface of the transparent substrate is subjected to surface treatment using oxygen plasma, nitrogen plasma, or UVO before the electron-beam deposition. The method of claim 15, wherein the shape and size of the pattern is controlled by adjusting the temperature of depositing the metal oxide layer. The light emitting diode manufacturing method according to any one of claims 13 to 19, wherein the transparent substrate is a sapphire substrate.

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