KR102192428B1 - High efficiency light emitting diode - Google Patents

Abstract

According to an embodiment of the present invention, provided is a light emitting diode which can improve light emitting efficiency of the light emitting diode. The light emitting diode comprises a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, wherein the second conductivity type semiconductor layer includes: microscale first protrusions formed on a surface of the second conductivity type semiconductor; and nanoscale second protrusions formed on the microscale protrusions. The first protrusions have a height of 1 μm or more from a bottom surface, and the second protrusions have a height of 1 μm or less from the bottom surface, and have a shape inclined in one direction with respect to the bottom surface.

Description

High efficiency light emitting diode {HIGH EFFICIENCY LIGHT EMITTING DIODE}

The present invention relates to a high-efficiency light-emitting diode, and more particularly, to a light-emitting diode having improved light-emitting efficiency by increasing light extraction efficiency.

The III-V light emitting diode can emit light using the bandgap property of an inorganic material. For example, a Ⅲ-N-based light emitting diode can emit ultraviolet, blue, or green light by controlling the types of Group III elements such as Al, Ga, and In, and their composition ratio, and can emit Ⅲ-As, Ⅲ-P-based light emission. The diode may emit green light, red light, or infrared light by controlling the type of the group 3 element and the composition ratio of the group 3 element.

However, the material of the light-emitting diode generally has a high refractive index of 2.4 or more, and therefore, total internal reflection is easily generated due to the difference between the external environment and the refractive index of the light-emitting diode. In general, it is known that a loss of about 20% occurs in the substrate of the light emitting diode, and about 70% of the loss occurs in the semiconductor layers by the wave guide mode. Accordingly, less than about 10% of the light generated in the active layer may be emitted to the outside. In particular, since the Ⅲ-As and Ⅲ-P-based material layers have a considerably high refractive index, the red light emitting diode has lower luminous efficiency than the blue light emitting diode.

Therefore, a new structure for improving the light efficiency of the light emitting diode is required.

The problem to be solved by the present invention is to provide a light emitting diode capable of preventing light generated by the light emitting diode from being emitted to the outside and being lost inside the light emitting diode.

A light emitting diode according to an embodiment of the present invention includes: a first conductivity type semiconductor layer; Active layer; And a second conductivity-type semiconductor layer, wherein the second conductivity-type semiconductor layer comprises: microscale first protrusions formed on a surface of the second conductivity-type semiconductor; And nano-scale second protrusions formed on the micro-scale protrusions, wherein the first protrusions have a height of 1 μm or more from a bottom surface, and the second protrusions have a height of less than 1 μm from a bottom surface.

The second protrusions may have a shape inclined in one direction with respect to the bottom surface of the second protrusions.

The first protrusions may have a conical shape or a pyramid shape.

The width of the bottom surface of the first protrusions may be 10 μm or less, and the height of the first protrusions may be in the range of 1 μm to 2 μm.

The width of the bottom surface of the second protrusions may be in the range of 300 nm to 1600 nm, and the height of the second protrusions may be in the range of 200 nm to 900 nm.

Second protrusions may also be formed on a surface of the second conductivity type semiconductor layer between the first protrusions.

By combining the micro-scale first protrusions and the nano-scale second protrusions, light loss due to Fresnel reflection can be reduced and light loss due to total internal reflection can be reduced, thereby improving luminous efficiency of the light emitting diode.

1 is a schematic plan view illustrating a light emitting diode according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view taken along the cut line A-A' of FIG. 1.
3 is an enlarged cross-sectional view of a portion of FIG. 2 to describe first and second protrusions according to an exemplary embodiment of the present invention.
4A, 4B, and 4C are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode according to an exemplary embodiment.
5A, 5B, and 5C are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode according to another exemplary embodiment.
6 is a simulation graph showing light output of a light emitting diode according to various comparative examples.
7 is a simulation graph for explaining light transmittance according to the presence or absence of nanoscale protrusions.
8 is a simulation graph for explaining light output of a light emitting diode including a first protrusion and a second protrusion according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In addition, in the drawings, the same reference numerals denote the same elements, and the width, length, and thickness of the elements may be exaggerated and expressed for convenience.

1 is a schematic plan view for explaining a light emitting diode according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view taken along a cut line A-A' of FIG. 1, and FIG. 3 is an embodiment of the present invention. 2 is an enlarged cross-sectional view illustrating a portion of the first and second protrusions according to FIG.

1 and 2, the light emitting diode 10 includes a first conductivity type semiconductor layer 21, an active layer 23, and a second conductivity type semiconductor layer 25. The light emitting diode 10 may further include a support substrate and electrodes, although not shown.

The supporting substrate is not necessarily required. The support substrate may be disposed on the side of the first conductivity type semiconductor layer 21 or on the side of the second conductivity type semiconductor layer 25 to support the semiconductor layers.

The electrodes are electrically connected to the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 25 to supply power for driving the light emitting diode 10.

The first conductivity type semiconductor layer 21, the active layer 23, and the second conductivity type compound semiconductor layer 25 are III-V series compound semiconductors, such as (Al, Ga, In)(N, P, As) semiconductors. Can be formed as Each of the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 25 may be a single layer or multiple layers. For example, the first conductivity-type semiconductor layer 21 and/or the second conductivity-type semiconductor layer 25 may include a contact layer and a cladding layer, and may also include a superlattice layer.

Meanwhile, the active layer 25 may have a single quantum well structure or a multiple quantum well structure. The active layer 25 may generate blue, green, or red light depending on the composition ratio of the elements.

The first conductivity type and the second conductivity type are opposite to each other. In an embodiment, the first conductivity type may be n-type and the second conductivity type may be p-type. In another embodiment, the first conductivity type may be p-type and the second conductivity type may be n-type.

The second conductivity type semiconductor layer 25 includes micro-scale first protrusions 25a and nano-scale second protrusions 25b on the surface. The first protrusions 25a have a size greater than the wavelength of light generated by the active layer 23.

Referring to FIG. 3, the width W1 and the height H1 of the bottom surfaces of the first protrusions 25a are greater than the wavelength of light generated by the active layer 23. The width W1 of the bottom surface may be, for example, 1 μm or more. The first protrusions 25a form an inclined surface to induce scattering to mitigate the occurrence of total internal reflection. The width W1 may be, for example, 10 um or less, more specifically 5 um or less, further, 4 um or less. The first protrusions 25a may be a truncated cone such as a truncated cone or a triangular truncated cone, a square truncated cone, a pentagonal truncated cone, and a hexagonal truncated cone. For example, the side inclination angle of the first protrusions 25a may be about 70 degrees or less, and further, about 60 degrees or less. Meanwhile, the height H1 of the first protrusions 25a may be within the range of 0.6um to 2um, and further, within the range of 1um to 2um.

The width W2 of the bottom surfaces of the second protrusions 25b may be in the range of about 300 nm to 1600 nm, for example. Meanwhile, the height H2 of the second protrusions 25b may be smaller than the width W2 of the bottom surface, and may be in the range of 200 nm to 900 nm, for example. The second protrusions 25b may prevent light loss by reducing Fresnel reflection generated from the surface. The second protrusions 25b may be located on the upper surface of the first protrusions 25a, and further, may also be located on the surface of the second conductivity type semiconductor layer 25 between the first protrusions 25a. .

Furthermore, the second protrusions 25b may have a cone shape or an inclined cone or wedge shape. Here, the cone shape means that the second protrusions 25b have a mirror plane symmetric structure or a rotation symmetric structure. Accordingly, the inclination angle α1 of the second protrusions 25a represents the same value as α2. In contrast, the inclined cone or inclined wedge shape has a minimum inclination angle (α1) and a maximum inclination angle (α2) in a cross-sectional view as shown in FIG. 3, and a minimum inclination angle (α1) is a value smaller than the maximum inclination angle (α2) Has.

4A, 4B, and 4C are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode according to an exemplary embodiment.

Referring to FIG. 4A, a micro-scale mask pattern 27 is formed on the second conductivity type semiconductor layer 25. The mask pattern 27 may be formed using, for example, a photoresist. Before forming the mask pattern 27, the first conductivity type semiconductor layer 21, the active layer 23, and the second conductivity type semiconductor layer 25 may be grown on the growth substrate.

Referring to FIG. 4B, the second conductivity type semiconductor layer 25 is etched using the mask pattern 27 as an etching mask to form protrusions 25a. The protrusions 25a may be formed to correspond to the mask pattern 27, and as shown, may be formed in a shape of a horn. Depending on the shape of the mask pattern 27, protrusions 25a having a truncated cone shape or a truncated cone shape may be formed. The second conductivity type semiconductor layer 25 may be etched using a dry etching technique, and the mask pattern 27 may be removed after the etching is completed.

Referring to FIG. 4C, the exposed protrusions 25a and the surfaces of the second conductivity type semiconductor layer 25 are etched to form second protrusions 25b. The second protrusions 25b may be formed using, for example, a wet etching technique, and may be formed to have a cone shape or an inclined cone or wedge shape.

According to the present embodiment, the second protrusions 25b may be formed not only on the upper surface of the first protrusions 25a, but also in the region between the first protrusions 25a.

5A, 5B, and 5C are schematic cross-sectional views illustrating a method of manufacturing a light emitting diode according to another exemplary embodiment.

Referring to FIG. 5A, first, the surface of the second conductivity-type semiconductor layer 25 is etched to form nano-scale second protrusions 25b. The second protrusions 25b may be formed using a wet etching technique. The second protrusions 25b may be formed to have a cone shape or an inclined cone or wedge shape. Before forming the second protrusions 25b, the first conductivity type semiconductor layer 21, the active layer 23, and the second conductivity type semiconductor layer 25 may be grown on the growth substrate.

Referring to FIG. 5B, a micro-scale mask pattern 127 is formed on the surface of the second conductivity type semiconductor layer 25 on which the second protrusions 25b are formed. The mask pattern 27 may be formed using, for example, a photoresist.

Referring to FIG. 5C, the second conductivity type semiconductor layer 25 is etched using the mask pattern 127 as an etching mask to form protrusions 25a. The protrusions 25a may be formed to correspond to the mask pattern 27, and as shown, may be formed in a shape of a horn. Depending on the shape of the mask pattern 27, protrusions 25a having a truncated cone shape or a truncated cone shape may be formed. The second conductivity type semiconductor layer 25 may be etched using a dry etching technique, and the mask pattern 27 may be removed after the etching is completed.

Accordingly, as shown, the second conductivity type semiconductor layer 25 having the first protrusions 25a and the second protrusions 25b formed on the upper surfaces of the first protrusions 25a may be provided. .

6 is a simulation graph showing light output of a light emitting diode according to various comparative examples.

All of the comparative examples have a similar structure, except that Comparative Example 1 does not have any protrusions on the surface of the second conductivity-type semiconductor layer, and Comparative Example 2 has a cone shape inclined to the surface of the second conductivity-type semiconductor layer. 2 protrusions, and Comparative Example 3 has cone-shaped second protrusions on the surface of the second conductivity-type semiconductor layer. Meanwhile, all of the comparative examples do not include micro-scale first protrusions. Here, in Comparative Example 2, the width of the bottom surface is 540 nm and the height is 310 nm, the minimum inclination angle α1 is 30 degrees, and in Comparative Example 3, the width of the bottom surface is 358 nm and the height is 310 nm. The first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer are configured to emit light having a wavelength of 625 nm.

Referring to FIG. 6, it can be seen that Comparative Examples 2 and 3 in which the second protrusions are formed exhibit higher light output than Comparative Example 1 in which the second protrusions are not formed. In addition, Comparative Example 2 employing the inclined cone-shaped second protrusions exhibited slightly higher light output than Comparative Example 3 employing the normal cone shape.

According to FIG. 6, it is possible to improve light output by adopting the second protrusions, which is determined to increase light efficiency by reducing Fresnel reflection.

7 is a simulation graph for explaining light transmittance according to the presence or absence of nanoscale protrusions. Light transmittance according to the presence or absence of the cone-shaped second protrusions through roughening was simulated, and the second protrusions were simulated to have a height of 310 nm and a bottom width of 540 nm.

Referring to FIG. 7, light transmittance of the epi layer including the second conductivity type semiconductor layer having second protrusions formed thereon was higher than that of the epi layer without second protrusions in all wavelength ranges of visible light.

The epitaxial layer without forming the second protrusions exhibited a pattern in which the transmittance greatly changed according to the wavelength, and a graph fitting this was shown together with a solid line. For a wavelength of 625 nm, the second conductivity-type semiconductor layer with the second protrusions formed 86% of the light transmittance, whereas the second conductivity-type semiconductor layer without the second protrusions was about 55% as a fitting value. It shows the light transmittance of.

8 is a simulation graph for explaining light output of a light emitting diode including a first protrusion and a second protrusion according to an embodiment of the present invention.

Here, Comparative Example 1 and Comparative Example 2 are the same as Comparative Examples 1 and 2 described with reference to FIG. 6, and Example 1 is formed to have both first and second protrusions compared to Comparative Example 2. There is a difference. Further, the first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer are configured to emit light of a wavelength of 625 nm.

In Example 1, the first protrusions have a bottom surface of 4 μm width and a height of 1 μm, the second protrusions have a bottom surface of 540 nm width and a height of 310 nm, and the minimum inclination angle α1 is 30 degrees.

Referring to FIG. 8, Example 1 exhibits a relatively higher light output than Comparative Example 2. In particular, with respect to the light output in the upper surface direction, Example 1 exhibited significantly higher light output compared to Comparative Examples 1 and 2, and accordingly, the total light output was relatively high. For example, Comparative Example 2 exhibits a light output of about 143% compared to Comparative Example 1, whereas Example 1 shows a light output of about 227% compared to Comparative Example 1, showing that the light output significantly increases.

In the above, various embodiments and features of the present invention have been described, but the present invention is not limited to the embodiments and features described above, and may be variously modified within the scope not departing from the spirit of the present invention. have.

Claims (6)

A first conductivity type semiconductor layer;
Active layer; And
Including a second conductivity type semiconductor layer,
The second conductivity type semiconductor layer,
Micro-scale first protrusions formed on the surface of the second conductivity type semiconductor; And
Including nano-scale second protrusions formed on the micro-scale protrusions,
The first protrusions have a height of 1 μm or more from the bottom surface,
The second protrusions have a height of less than 1 um from the bottom surface,
All of the second protrusions are inclined in one direction with respect to the bottom surface of the second protrusions. The method according to claim 1,
The second protrusions have an inclined cone shape or an inclined wedge shape,
The second protrusions have a maximum inclination angle and a minimum inclination angle in a cross-sectional view,
Light-emitting diode with the minimum inclination angle of 30 degrees The method according to claim 1,
The first protrusions are light-emitting diodes having a truncated cone shape or a pyramid shape. The method according to claim 1,
The width of the bottom surfaces of the first protrusions is 10um or less,
A light emitting diode having a height of the first protrusions within a range of 1um to 2um. The method of claim 4,
The width of the bottom surface of the second protrusions is in the range of 300 nm to 1600 nm,
A light emitting diode having a height of the second protrusions in a range of 200 nm to 900 nm. The method according to claim 1,
A light emitting diode having second protrusions formed on a surface of the second conductivity-type semiconductor layer between the first protrusions.

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