KR101088476B1 - Light emitting diode and method for fabricating the same - Google Patents

Abstract

Provided are a light emitting diode and a method of manufacturing the same. The light emitting diode is disposed on a first type semiconductor layer disposed on a substrate, an active layer disposed on the first type semiconductor layer, a second type semiconductor layer disposed on the active layer, and the second type semiconductor layer. An anti-reflection photonic crystal layer having an anti-reflection film having a thickness of Equation 1 and a plurality of holes periodically arranged to form a photonic band gap in the anti-reflection film.

 &Quot; (1) "

d = (2n + 1) λ / 4n _c

In Equation 1, d represents the thickness of the antireflective photonic crystal layer, λ represents the wavelength of light generated in the active layer, n represents an integer, and n _c represents the refractive index of the antireflective photonic crystal layer. Indicates.

Light Emitting Diode, Antireflective Photonic Crystal Layer, Fresnel Reflection, Total Reflection

Description

Light emitting diode and method for manufacturing same

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

A light emitting diode (LED) is a device using a phenomenon of emitting light when a forward current flows through a PN junction diode of a compound semiconductor, and is mainly used as a light source of a display device.

Such a light emitting diode does not require a filament such as a light bulb, exhibits excellent characteristics such as being resistant to vibration, having a long lifetime, and having a fast reaction speed.

However, although the light emitting diode has such an advantage, light generated from the light emitting diode device due to Fresnel reflection due to the difference in refractive index between the semiconductor layer and the air layer in contact with the semiconductor layer and total reflection generated between different media is It can be trapped inside without getting out. Accordingly, problems such as deterioration of luminous efficiency may occur.

The technical problem to be solved by the present invention is to provide a light emitting diode and a method for manufacturing the same that can improve the luminous efficiency of the device.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above technical problem, an aspect of the present invention provides a light emitting diode. The light emitting diode is disposed on a first type semiconductor layer disposed on a substrate, an active layer disposed on the first type semiconductor layer, a second type semiconductor layer disposed on the active layer, and the second type semiconductor layer. An anti-reflection photonic crystal layer having an anti-reflection film having a thickness of Equation 1 and a plurality of holes periodically arranged to form a photonic band gap in the anti-reflection film.

 &Quot; (1) "

d = (2n + 1) λ / 4n _c

In Equation 1, d represents the thickness of the antireflective photonic crystal layer, λ represents the wavelength of light generated in the active layer, n represents an integer, and n _c represents the refractive index of the antireflective photonic crystal layer. Indicates.

The anti-reflection film may be formed of a material having a refractive index smaller than that of the second type semiconductor layer. For example, the anti-reflection film may be formed of Si _x O _y , ITO, MgO, Si _x N _y, or ZnO. It may be any one selected.

The light emitting diodes may have a period equal to a period of light emitted to form a photonic band gap in the antireflective photonic crystal layer, and may have an interval of about half the wavelength of the emitted light. The holes may have a rectangular arrangement or a hexagonal arrangement, and the light emitting diode may further include an inorganic layer or an organic layer disposed on the second type semiconductor layer in the holes.

Another aspect of the present invention provides a light emitting diode manufacturing method for achieving the above technical problem. The light emitting diode manufacturing method includes forming a first type semiconductor layer on a substrate, forming an active layer on the first type semiconductor layer, forming a second type semiconductor layer on the active layer, and Forming an antireflective photonic crystal layer having an antireflection film having a thickness of Equation 1 and a plurality of holes periodically arranged in the antireflection film to form a photonic bandgap on the second semiconductor layer; .

The anti-reflection photonic crystal layer may include forming an anti-reflection film on the second type semiconductor layer, and patterning the anti-reflection film into a photonic crystal structure to form a plurality of holes in the anti-reflection film.

As described above, by providing the antireflection photonic crystal layer satisfying Equation 1, total reflection and Fresnel reflection generated at the interface between the second semiconductor layer and the air can be prevented, so that the luminous efficiency in the vertical direction In addition to the improvement of the luminous efficiency, the luminous efficiency in the horizontal direction can be increased.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

1 is a cross-sectional view showing the structure of a light emitting diode according to an embodiment of the present invention, Figures 2a and 2b are schematic diagrams showing the structure of an antireflective photonic crystal layer according to an embodiment of the present invention.

1, 2A, and 2B, a nucleation layer (not shown) is formed on the substrate 10, and a first type semiconductor is formed on the substrate 10 based on the nucleation layer. Form layer 22. The substrate 10 may be an Al ₂ O ₃ (sapphire), SiC, ZnO, Si, GaAs, LiAl ₂ O ₃ , InP, BN, AlN or GaN substrate. Preferably, the substrate 10 may be an Al ₂ O ₃ substrate.

The first type semiconductor layer 22 may be a nitride-based semiconductor layer into which first type impurities, that is, n-type impurities, are implanted. As an example, the first type semiconductor layer 22 may be Si, a GaN layer into which n-type impurities of N, B, or P are implanted, an Al _x Ga _(1-x) N (0 ≦ _x ≦ 1) layer, or Al _x Ga _y In _z N (0 ≦ x, y, _z ≦ 1, x + y + z = 1) layer.

An active layer 24 is formed on the first semiconductor layer 22. The active layer 24 may have a quantum dot structure or a multi quantum well structure. When the active layer 24 has a multi-quantum well structure, the active layer 24 may have a multiple structure of an InGaN layer as a well layer and a GaN layer as a barrier layer.

The second type semiconductor layer 26 is formed on the active layer 24. The second type semiconductor layer 26 may be a nitride based semiconductor layer into which a second type impurity, that is, a p type impurity is implanted. As an example, the second type semiconductor layer 26 may include a GaN layer implanted with p-type impurities such as Mg or N, P, As, Zn, Li, Na, K, or Cu, and Al _x Ga _(1-x). N (0 ≦ x ≦ 1) layer or Al _x Ga _y In _z N (0 ≦ x, y, _z ≦ 1, x + y + z = 1) layer.

The current spreading layer 28 may be formed on the second semiconductor layer 26. The current spreading layer 28 may be a transparent conductive film, for example, an indium tin oxide (ITO) film, a ZnO film, or an MgO film. However, the current spreading layer 28 may be omitted.

The first type semiconductor layer 22, the active layer 24, the second type semiconductor layer 26, and the current spreading layer 28 may be formed using a metal organic chemical vapor deposition (MOCVD) technique or a molecular beam (MBE). Epitaxy) can be used to form.

The anti-reflection film 30a having the thickness of Equation 1 on the current spreading layer 28 and the plurality of holes 30b periodically arranged to form a photonic band gap in the anti-reflection film 30a are formed. An antireflection photonic crystal layer 30 is formed. In this case, in order to form a photonic band gap in the anti-reflective photonic crystal layer 30, the holes 30b have the same period (a) as the period of light emitted and the interval of about half wavelength of the light emitted. may have (w).

&Quot; (1) "

d = (2n + 1) λ / 4n _c

In Equation 1, d represents the thickness of the antireflective photonic crystal layer, λ represents the wavelength of light generated in the active layer, n represents an integer, and n _c represents the antireflective photonic crystal layer. Refractive index is shown.

In general, when light reaches the interface between two media having different refractive indices, that is, the interface between the type 2 semiconductor layer 26 and the air, some of the light penetrates the interface and is emitted to the outside, but some of the other It is reflected from the surface of the type 2 semiconductor layer 26 to return back to the opposite direction, that is, to the active layer 24.

The reflection occurring at the interface between two media having different refractive indices is called Fresnel reflection. When such Fresnel reflection proceeds, the light emitting diode may be degraded by a plurality of scattered light.

However, when the antireflective photonic crystal layer 30 satisfying the thickness of Equation 1 is formed on the second type semiconductor layer 26 as in an embodiment of the present invention, the air and the antireflective photonic crystal layer Since the light generated at the first interface between the 30 and the second interface between the antireflective photonic crystal layer 30 and the second type semiconductor layer 26 may have a phase difference of 180 °. The light generated at the first interface and the light generated at the second interface may cause mutual interference. Therefore, unnecessary scattered light disappears, and the intensity of light in a specific wavelength band can be increased.

In addition, in addition to the Fresnel reflection as described above, a general light emitting diode may be accompanied by total reflection to trap the emitted light in the device. In this case, the light extraction efficiency of the device is lowered, the luminous efficiency can be very low.

However, as shown in the embodiment of the present invention, the holes 30b having the same period as the period of the emitted light on the second type semiconductor layer 26 and having a half wavelength interval of the emitted light are formed. When the antireflective photonic crystal layer 30 is provided, the refractive index is periodically changed by the holes 30b periodically disposed in the antireflective photonic crystal layer 30, so that light may be scattered. A photonic band gap may be formed in the region where the holes 30b are formed by scattering.

In this case, the antireflection photonic crystal layer 30 may have a property of emitting light in a specific direction. That is, light emitted from the active layer 24 may not enter or pass through the holes 30b, and light may pass through an area between the holes 30b, that is, the antireflective photonic crystal layer 30.

Therefore, the emitted light is moved in the horizontal direction in the holes 30b area and reaches the anti-reflective photonic crystal layer 30, so that light can be emitted in the vertical direction, so that light is extracted in the horizontal and vertical directions. Efficiency can be maximized.

The anti-reflection photonic crystal layer 30 forms an anti-reflection film 30a on the second type semiconductor layer 26, and patterns the anti-reflection film 30a into a photonic crystal structure to form holes in the anti-reflection film 30a. 30b). The patterning may be formed using a lithography method using a nanoimprint method or a mask pattern. The anti-reflection film 30a may be patterned such that the holes 30b may be arranged in a rectangular array (FIG. 2A) or a hexagonal array (FIG. 2B).

In this case, the holes 30b may be filled with air, but the inorganic or organic materials may be filled to change the medium in various ways and control the light propagation direction.

The anti-reflection film 30a may be formed of a material having a refractive index smaller than that of the second type semiconductor layer 26. In this case, the second type semiconductor layer 26 may be formed of a material having a refractive index of 2.3 to 2.5. Can be used. As an example, the anti-reflection film 30a may use at least one selected from the group consisting of Si _x O _y , ITO, MgO, Si _x N _y or ZnO.

The antireflective photonic crystal layer 30, the current spreading layer 28, the second type semiconductor layer 26, and the active layer 24 are mesa-etched sequentially to expose a portion of the upper surface of the first type semiconductor layer 22. Can be. Accordingly, the metal electrode 32 may be disposed on the exposed upper surface of the first type semiconductor layer 22. The metal electrode 32 may contain Al and / or Ag. Specifically, the metal electrode 32 may be Ti / Al or NiO / Au.

In one embodiment of the present invention, the light emitting diodes are formed in a horizontal structure, but the light emitting diodes may be formed in a vertical structure without performing the mesa etching.

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

Experimental Example

An n-type AlGaInN layer formed by forming a gallium nitride nucleation layer at a temperature of 500 ° C. on a sapphire substrate with a thickness of 300 GPa and then doped with Si as a first type semiconductor layer by MOCVD on the gallium nitride nucleation layer. Was formed to a thickness of 2 μm. Subsequently, an 8 nm GaN layer and a 2 nm InGaN layer are stacked on the n-type AlGaInN layer to form an active layer having a multi-quantum well structure, and a p-type AlGaInN layer doped with Mg as a second type semiconductor layer is formed on the active layer. It was formed to a thickness of 0.2 μm.

Subsequently, an SiO ₂ layer was formed as an antireflection film on the p-type AlGaInN layer, and the SiO ₂ layer was patterned in a rectangular array to form holes in the antireflection film to form an antireflection photonic crystal layer. Four LEDs thus prepared are prepared, and the thickness, width, and period of each of the anti-reflective photonic crystal layers provided in the LEDs are (a) 74 nm (λ / 4 n _c ), 139 nm, and 312 nm (b), respectively. It was set to _{151nm (2λ / 4n c),} 156nm and 312nm, (c) 235nm (3λ / 4n c), 179nm and 312nm, (d) 302nm (4λ / 4n c), 298nm and 312nm.

In addition, in order to determine the luminous efficiency of the light emitting diode according to the presence or absence of the anti-reflective photonic crystal layer, the light emitting diode (e) and holes without the anti-reflective photonic crystal layer are not provided and only the anti-reflection film is provided. A light emitting diode (f) was prepared separately. In this case, the thickness of the anti-reflection film was set to 235 nm (3λ / 4n _c ).

Table 1 below is an optical microscope image showing the change in luminous efficiency according to the presence or absence of the antireflective photonic crystal layer and the thickness change of the antireflective photonic crystal layer according to an embodiment of the present invention. At this time, the image according to Table 1 are images of the light reflected in the device, the light emitted through the actual device may be the light transmitted through the device.

Thickness of Antireflective Photonic Crystal Layer (nm) (a) 74 nm (b) 151 nm (c) 235 nm (d) 302nm (e) 0nm (f) 235 nm Wavelength of light

Referring to Table 1, light emitting diodes (e) having no antireflective photonic crystal layer, light emitting diodes (f) having only an antireflective film, and light emitting diodes having an antireflective photonic crystal layer but not satisfying Equation 1 above The intensity of the light emitted from (a, b, c) is very low, or light close to blue is identified, such that the light emitting diodes are light in the wavelength range except the blue, that is, near the red light On the other hand, the light emitting diode (c) having an antireflective photonic crystal layer satisfying Equation 1 has a very high light intensity, and light close to red is confirmed by Equation 1 above. When the antireflective photonic crystal layer having the satisfactory value is provided, it can be predicted that light of a wavelength band close to blue can be secured.

Through these results, it can be confirmed that the thickness of the antireflection photonic crystal layer is provided with the presence or absence of an important factor.

<Manufacture example 1>

An n-type AlGaInN layer formed by forming a gallium nitride nucleation layer at a temperature of 500 ° C. on a sapphire substrate with a thickness of 300 GPa and then doped with Si as a first type semiconductor layer by MOCVD on the gallium nitride nucleation layer. Was formed to a thickness of 2 μm. Subsequently, an 8 nm GaN layer and a 2 nm InGaN layer are stacked on the n-type AlGaInN layer to form an active layer having a multi-quantum well structure, and a p-type AlGaInN layer doped with Mg as a second type semiconductor layer is formed on the active layer. It was formed to a thickness of 0.2 μm.

Subsequently, an SiO ₂ layer is formed on the p-type AlGaInN layer as an anti-reflection film at a thickness of 235 nm (3λ / 4n _c ), and the SiO ₂ layer is patterned in a rectangular array to have a width w in the SiO ₂ layer. A plurality of holes of 179 nm and period a of 312 nm were formed.

The SiO ₂ layer, the ITO layer, the p-type AlGaInN layer, and the GaN / InGaN layer were sequentially patterned to expose a portion of the n-type AlGaInN layer, and Ti / Al was formed on the n-type AlGaInN layer as a metal electrode.

Comparative Example 1

As in Preparation Example 1, a light emitting diode having no antireflection photonic crystal layer was prepared.

Comparative Example 2

A light emitting diode was manufactured in the same manner as in Preparation Example 1, except that the anti-reflective photonic crystal layer was not formed and a SiO ₂ layer having a thickness of 235 nm was formed on the second semiconductor layer as an anti-reflection film.

3A and 3B are graphs showing the intensity of light emitted in the vertical direction and the horizontal direction of the light emitting diode according to Preparation Example 1, respectively.

3A and 3B, the intensity of light emitted in the vertical direction and the horizontal direction from the light emitting diode (Preparation Example 1) having an antireflective photonic crystal layer in a wavelength range of 465 nm is determined. It can be seen from (Comparative Example 1) that the light extraction efficiency is increased by about 2.5 times as compared with the intensity of light emitted in the vertical and horizontal directions.

From this result, it can be confirmed that the antireflection photonic crystal layer is due to the improvement of the luminous efficiency, and it can be confirmed that not only the luminous efficiency in the vertical direction but also the luminous efficiency in the horizontal direction can be increased.

4A to 4C are full wave simulation results for confirming light flow of light emitting diodes according to Comparative Example 1, Comparative Example 2, and Preparation Example 1, respectively. The simulation was performed using a Finite Difference Time Domain (FDTD) calculation tool applying Genetic Algorithm (Ga).

Through the simulation results of the light emitting diodes as described above, the intensity of light in the vertical and horizontal directions emitted from the inside of the light emitting diodes to the outside can be confirmed. Herein, the closer the light emitted to the outside is to the blue, the lower the intensity of the light is. The closer to the red, the higher the intensity of the light is, and when the light becomes white, the intensity of the light may be the maximum. have.

4A to 4C, a light emitting diode having an antireflective photonic crystal layer (FIG. 4C, Preparation Example 1) according to an embodiment of the present invention is compared with a light emitting diode having no antireflective photonic crystal layer (FIG. 4A). It can be seen that the area of light emitted in the vertical direction is greatly increased compared to Example 1) and the light emitting diode having only the anti-reflection film (FIG. 4B, Comparative Example 2).

In addition, the light emitting diode (preparation example 1) having the antireflective photonic crystal layer has light emitted in the horizontal and vertical directions compared to the light emitting diodes (comparative example 1 and comparative example 2) which do not have the antireflective photonic crystal layer. It can be seen that the red and white areas are increased.

This is because the antireflective photonic crystal layer has a plurality of holes to prevent the total reflection by vertically converting the light trapped in the side, and at the same time to form the thickness of the antireflective photonic crystal layer to suppress the Fresnel reflection It is feed.

FIG. 5 is a graph quantitatively illustrating light extraction efficiency of light emitting diodes according to Comparative Example 1, Comparative Example 2, and Preparation Example 1. FIG.

Referring to FIG. 5, a light emitting diode (preparation example 1) having an antireflective photonic crystal layer according to Preparation Example 1 includes a light emitting diode having a nonreflective photonic crystal layer (Comparative Example 1) and a light emitting diode having an antireflection film ( It can be seen that the amount of light emitted to the outside is significantly increased compared to Comparative Example 2).

This result is also consistent with the image described with reference to FIGS. 4A to 4C.

Therefore, it can be seen from the above result that the light propagation direction can be adjusted by providing an antireflection photonic crystal layer formed by patterning an antireflection film having a predetermined thickness.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

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

2A and 2B are schematic diagrams showing the structure of an antireflective photonic crystal layer according to an embodiment of the present invention.

3A and 3B are graphs showing the intensity of light emitted in the vertical direction and the horizontal direction of the light emitting diode according to Preparation Example 1, respectively.

4A to 4C are full wave simulation results for confirming light flow of light emitting diodes according to Comparative Example 1, Comparative Example 2, and Preparation Example 1, respectively.

FIG. 5 is a graph quantitatively illustrating light extraction efficiency of light emitting diodes according to Comparative Example 1, Comparative Example 2, and Preparation Example 1. FIG.

Claims (8)

A first type semiconductor layer disposed on the substrate; An active layer disposed on the first type semiconductor layer; A second type semiconductor layer disposed on the active layer; And An antireflection photonic crystal layer disposed on the second type semiconductor layer and having an antireflection film having a thickness of Equation 1 and a plurality of holes periodically arranged to form a photonic band gap in the antireflection film; Light Emitting Diode  &Quot; (1) &quot; d = (2n + 1) λ / 4n _c In Equation 1, d represents the thickness of the antireflective photonic crystal layer, λ represents the wavelength of light generated in the active layer, n represents an integer, and n _c represents the refractive index of the antireflective photonic crystal layer. Indicates. The method of claim 1, The anti-reflection film is a light emitting diode using a material having a refractive index smaller than the refractive index of the second type semiconductor layer. The method of claim 1, The antireflection film is any one selected from the group consisting of Si _x O _y , ITO, MgO, Si _x N _y or ZnO. The method of claim 1, The holes have a period equal to a period of light emitted to form a photonic band gap in the antireflective photonic crystal layer, and the light emitting diode has a half wavelength interval of the emitted light. The method of claim 1, The holes have a rectangular array or a hexagonal array of light emitting diodes. The method of claim 1, A light emitting diode further comprising an inorganic layer or an organic layer disposed on the second type semiconductor layer in the holes. Forming a first type semiconductor layer on the substrate; Forming an active layer on the first type semiconductor layer; Forming a second type semiconductor layer on the active layer; And Forming an anti-reflection photonic crystal layer having an anti-reflection film having a thickness of Equation 1 on the second type semiconductor layer and a plurality of holes periodically arranged in the anti-reflection film to form a photonic bandgap; Light emitting diode manufacturing method comprising:  &Quot; (1) &quot; d = (2n + 1) λ / 4n _c In Equation 1, d represents the thickness of the antireflective photonic crystal layer, λ represents the wavelength of light generated in the active layer, n represents an integer, and n _c represents the refractive index of the antireflective photonic crystal layer. Indicates. The method of claim 7, wherein Forming an anti-reflection film on the second type semiconductor layer; And Patterning the anti-reflection film into a photonic crystal structure to form a plurality of holes in the anti-reflection film.

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