KR20070068061A - Light emitting diode and fabricating method thereof - Google Patents

Abstract

A method for fabricating an LED is provided to increase a critical angle and reduce the light consumed in a p-type nitride semiconductor layer by forming a plurality of protrusions of a pyramid type on the p-type nitride semiconductor layer. An n-type nitride semiconductor layer(320), an active layer(330) and a p-type nitride semiconductor layer(340) are sequentially formed on a substrate(300). A plurality of protrusions(350) of pyramid type are formed on the p-type nitride semiconductor layer, separated from each other. A mesa-etch process is performed on a portion from the p-type nitride semiconductor layer to a part of the n-type nitride semiconductor layer. A transparent electrode(360) is formed on the p-type nitride semiconductor layer, surrounding the plurality of protrusions. A p-electrode(380) is formed on the transparent electrode, and an n-electrode(370) is formed on the n-type nitride semiconductor layer exposed by the mesa-etch process. The protrusion of pyramid type can be formed by an SEG(selective epitaxial growth) method or a surface pretreatment using anti-surfactant.

Description

Light emitting diode and manufacturing method thereof

1 is a cross-sectional view of a conventional nitride based light emitting diode.

2 is a view showing a state in which light generated in the active layer is totally reflected on the nitride-based semiconductor surface.

3A to 3E are sectional views showing an embodiment of a method of manufacturing a light emitting diode of the present invention.

4A to 4E illustrate a process of forming a pyramid-shaped protrusion on the substrate using a selective epitaxial growth method.

5 is a cross-sectional view showing a light emitting diode of the present invention.

Explanation of symbols on the main parts of the drawings

100, 300: substrate 110, 310: buffer layer

120, 320: n-type nitride semiconductor layer 130, 330: active layer

140 and 340 p-type nitride semiconductor layers 150 and 350 protrusions

160, 360: transparent electrode 170, 370: n-electrode

180, 380: p-electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode and a method of manufacturing the same. In particular, a plurality of pyramidal protrusions are formed on the p-type nitride semiconductor layer to be spaced apart from each other to increase the critical angle of the surface of the p-type nitride semiconductor layer and a method of manufacturing the same. It is about.

In general, a light emitting diode (LED) is a kind of semiconductor device that transmits and receives signals by converting electricity into light using characteristics of a compound semiconductor.

The light emitting diode generates energy with high efficiency at low voltage, so it is very energy-saving.In recent years, the luminance problem, which was the limitation of the light emitting diode, has been greatly improved, and the entire industry including a backlight unit, an electronic board, an indicator, a home appliance, and various automation devices It is used throughout.

In particular, the nitride-based light emitting diode has a wide energy band gap of the active layer, so that the emission spectrum is broadly formed from ultraviolet rays to infrared rays, and includes environmentally harmful substances such as arsenic (As) and mercury (Hg). Because it is not, it has a high response in terms of environmental friendliness.

In addition, researches are being conducted to obtain high brightness light emitting diodes in order to utilize them in various applications.How to obtain high brightness light emitting diodes improves the quality of the active layer to improve internal quantum efficiency and light generated from the active layer. There is a method of increasing the light extraction efficiency by helping to emit to the outside and gathering in the required direction.

At present, attempts have been made to improve both the internal quantum efficiency and the light extraction efficiency, but the device electrode design, the shape of the device itself, and the packaging method are improved compared to the method of improving the internal quantum efficiency by improving the quality of semiconductor materials. Attempts have been made to increase the light extraction efficiency.

The attempted methods up to now are mainly focused on improving the transmittance of the upper electrode or placing a reflector outside the device to collect light emitted from the side of the sapphire substrate or the device to the top.

Here, light extraction efficiency is determined by the ratio of electrons injected into the light emitting diode to photons emitted out of the light emitting diode, and the higher the extraction efficiency, the brighter the light emitting diode.

Since the light extraction efficiency of the light emitting diode is greatly influenced by the shape or surface shape of the chip, the structure of the chip, and the packaging type, great care must be taken when designing the light emitting diode.

In high power and high brightness light emitting diodes, the light extraction efficiency serves as an important parameter for determining the light emission efficiency. By the way, there is a limit in light extraction efficiency in the conventional manufacturing method of the nitride-based light emitting diode.

1 is a cross-sectional view of a conventional nitride based light emitting diode. As shown therein, the buffer layer 11, the n-type nitride semiconductor layer 12, the active layer 13, and the p-type nitride semiconductor layer 14 are sequentially stacked on the sapphire substrate 10.

Mesa etching is performed from the p-type nitride semiconductor layer 14 to a portion of the n-type nitride semiconductor layer 12 to expose a portion of the n-type nitride semiconductor layer 12,

An n-electrode 15 is formed on the exposed n-type nitride semiconductor layer 12, and a transparent electrode 16 is formed on the p-type nitride semiconductor layer 14, and on the transparent electrode. It has a structure in which the p-electrode 17 is formed.

In the method of manufacturing a nitride-based light emitting diode configured as described above, first, the buffer layer 11, the n-type nitride semiconductor layer 12, the active layer 13, and the p-type nitride semiconductor layer 14 are sequentially disposed on the sapphire substrate 10. After the formation, the mesa is etched from the p-type nitride semiconductor layer 14 to a portion of the n-type nitride semiconductor layer 12 by a reactive ion etching (RIE) method.

Thereafter, a transparent electrode 16 is formed on the p-type nitride semiconductor layer 14 to improve ohmic characteristics, and a p-electrode 17 is formed on the transparent electrode 16.

Next, the n-electrode 15 is formed on the n-type nitride semiconductor layer 12 exposed by the mesa etching.

Here, the light emitting diode is driven in the following manner. That is, when voltage is applied to the p-electrode 17 and the n-electrode 15, holes and electrons flow from the p-type nitride semiconductor layer 14 and the n-type nitride semiconductor layer 12 to the active layer 13. In the active layer 13, the electron-hole recombination occurs to emit light.

Light emitted from the active layer 13 proceeds up and down the active layer 13, and the light propagated upward is emitted through the transparent electrode 16 thinly formed on the p-type nitride semiconductor layer 14.

In addition, the light propagated down the active layer 13 escapes to the lower part of the substrate 10 and is absorbed by a solder used in packaging the light emitting diode, or is reflected from the substrate 10 and then proceeds upward again to the active layer 13. May be absorbed again through the transparent electrode 16 or may be pulled out through the transparent electrode 16.

In the conventional nitride-based light emitting diode, when the light emitted from the active layer exits to the outside, total reflection condition is generated by the difference in refractive index between the nitride-based semiconductor material and the outside, and light incident at an angle greater than or equal to the critical angle of the total reflection is emitted to the outside. It is not known and is reflected back into the device.

That is, as shown in FIG. 2, when the light generated in the active layer 30 reaches the surface of the nitride semiconductor material 40, the incident angle of incident light is determined by the external refractive index and the refractive index of the nitride semiconductor material. If (θ _C ) or more, the light does not escape to the outside, but is reflected inside the device, and the reflected light passes through various paths and the light is attenuated.

Here, the critical angle is determined by Snell's Law, which can be obtained by the following equation.

sinθ _C = N ₁ / N ₂

Where θ_CRepresents a critical angle, N_One Silver external refractive index, N₂Represents the internal refractive index of the device.

As described above, the conventional nitride-based light emitting diode has a problem in that light extraction efficiency is lowered by total reflection of the nitride-based light emitting diode when the light generated in the active layer reaches the surface of the nitride-based semiconductor material.

The present invention has been made to solve the above problems, by providing a plurality of pyramid-shaped protrusions formed on the p-type nitride semiconductor spaced apart from each other, to provide a light emitting diode and a method for manufacturing the light extraction efficiency of the device is improved The purpose is.

In an embodiment of the light emitting diode of the present invention, an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially formed on a substrate, and mesas are formed from the p-type nitride semiconductor layer to a part of the n-type nitride semiconductor layer. (Mesa) is etched;

A plurality of pyramid-shaped protrusions are formed on the p-type nitride semiconductor layer and the n-type nitride semiconductor layer exposed by the mesa etching to be spaced apart from each other, and the plurality of protrusions are wrapped around the p-type nitride semiconductor layer. An electrode is formed, a p-electrode is formed on the transparent electrode, and an n-electrode is formed on the exposed n-type nitride semiconductor layer.

Embodiments of the method of manufacturing a light emitting diode of the present invention, the step of sequentially stacking an n-type nitride semiconductor layer, an active layer, a p-type nitride semiconductor layer on the substrate, and a plurality of pyramidal shape on the p-type nitride semiconductor layer Forming protrusions spaced apart from each other, etching the mesa from the p-type nitride semiconductor layer to a portion of the n-type nitride semiconductor layer, and wrapping the plurality of protrusions on the p-type nitride semiconductor layer Forming an electrode, and forming a p-electrode on the transparent electrode, and forming an n-electrode on the n-type nitride semiconductor layer exposed by the mesa etching.

Hereinafter, the light emitting diode of the present invention and a manufacturing method thereof will be described in detail with reference to FIGS. 3 to 5. 3A to 3E are cross-sectional views showing an embodiment of a method of manufacturing a light emitting diode of the present invention.

As shown in the drawing, first, the buffer layer 110, the n-type nitride semiconductor layer 120, the active layer 130, and the p-type nitride semiconductor layer 140 are sequentially stacked on the substrate 100 (FIG. 3A).

Here, the substrate 100 is made of any one material selected from sapphire (Al ₂ O ₃ ), silicon carbide (SiC) and gallium nitride (GaN), in particular sapphire substrate is typically used.

This is because there is no commercial substrate in the lattice match that is identical to the crystal structure of the nitride semiconductor material grown on the substrate 100.

The buffer layer 110 is formed to mitigate a difference in lattice mismatch and thermal expansion coefficient between the substrate 100 and the n-type nitride semiconductor layer 120 formed on the substrate 100. Or an AlN layer is used.

The n-type nitride semiconductor layer 120 is n− having an Al _x In _y Ga _(1-xy) N composition formula, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1. It may be made of a doped semiconductor material, in particular GaN is widely used.

The active layer 130 has a quantum well structure, and Al _x In _y Ga _(1-xy) N composition formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1 A nitride semiconductor material).

The p-type nitride semiconductor layer 140, like the n-type nitride semiconductor layer 120, Al _x In _y Ga _(1-xy) N composition formula (where 0≤x≤1, 0≤y≤1, 0 ≦ x + y ≦ 1) and p-doped.

The buffer layer 110, the n-type nitride semiconductor layer 120, the active layer 130, and the p-type nitride semiconductor layer 140 may be formed by a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. Grow using a deposition process.

Next, a plurality of pyramid-shaped protrusions 150 are formed on the p-type nitride semiconductor layer 140 to be spaced apart from each other (FIG. 3B).

As a method of forming a plurality of pyramid-shaped protrusions 150 spaced apart from each other on the p-type nitride semiconductor layer 140, a method using selective epitaxial growth or a non-surfactant may be used. In addition, various methods may be used. Details thereof will be described later.

The plurality of pyramidal protrusions 150 formed on the p-type nitride semiconductor layer 140 are AlInGaN compound semiconductors including GaN, AlGaN, and InGaN, that is, Al _x In _y Ga _(1-xy) N composition formula (where , 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1).

The plurality of protrusions 150 may not be doped or may be doped with a p type. The protrusions 150 may have a height of 10 μm to 10 μm, a width of 20 μm to 20 μm, and an interval between 20 μm and 20 μm It is preferable to set it as.

Here, when the plurality of protrusions 150 are formed by selective epitaxial growth, if the SiN film is used as a mask, the remaining SiN film is removed using a HF-based solution.

Subsequently, Mesa etching is performed from the p-type nitride semiconductor layer 140 to a portion of the n-type nitride semiconductor layer 120 (FIG. 3C).

When the mesa is etched as described above, a plurality of protrusions formed on the p-type nitride semiconductor layer 140 are transferred to the surface of the n-type nitride semiconductor layer 120 exposed by mesa etching. In this case, the plurality of protrusions formed on the surface of the n-type nitride semiconductor layer 120 is made of the same material as the n-type nitride semiconductor layer 120.

Subsequently, the transparent electrode 160 is formed on the p-type nitride semiconductor layer 140 on which the plurality of protrusions 150 are formed (FIG. 3D).

The p-type nitride semiconductor layer 140 has a low impurity doping concentration and high contact resistance, thereby resulting in poor ohmic characteristics. Therefore, in order to improve such ohmic characteristics, the transparent electrode 160 is formed on the p-type nitride semiconductor layer 140.

As the transparent electrode 160, a transparent electrode layer composed of a double layer of Ni / Au is widely used, and the transparent electrode layer composed of a double layer of Ni / Au forms an ohmic contact while increasing a current injection area to form a forward voltage (V _f ). Lowers.

Meanwhile, instead of the Ni / Au bilayer having a low transmittance of about 60% to 70%, a transparent conducting oxide (TCO) layer known to have a transmittance of about 90% or more may be formed on the p-type nitride semiconductor layer 140. have.

In this case, before forming the TCO layer on the p-type nitride semiconductor layer 140, a short period superlattice (SPS) is formed to form a contact resistance with the p-type nitride semiconductor layer 140 Reduce.

That is, since there is a large work function difference between the TCO layer and the p-type nitride semiconductor layer 140, when the TCO layer is directly deposited on the p-type nitride semiconductor layer 140, a high ohmic contact is formed. Will not be.

Accordingly, before forming the TCO layer, a short period superlattice layer (SPS) is formed to reduce contact resistance with the p-type nitride semiconductor layer 140.

Herein, the short-period superlattice layer is formed by periodically laminating InGaN and GaN, and in order to lower contact resistance, the InGaN and GaN layer is doped with N + with a silicon concentration of 1 × 10 ¹⁸ / cm ³ or more, Preferably it is doped to an impurity concentration of 1 x 10 ¹⁸ / cm ³ to 1 x 10 ²⁰ / cm ³ .

In order to form the short-period superlattice layer, in addition to InGaN, it is also possible to form a laminated structure with GaN using another known compound semiconductor such as AlGaN or AsGaN.

Next, an n-electrode 170 is formed on the exposed n-type nitride semiconductor layer 120, and the p-electrode 180 is formed on the p-type nitride semiconductor layer 140 on the transparent electrode 160. To form (FIG. 3E).

When forming the n-electrode 170, as shown in FIG. 3e, after removing the plurality of protrusions in the region where the n-electrode 170 is formed, the n-electrode 170 may be formed. When the plurality of protrusions is very small, the n-electrode 170 may be formed without removing the protrusions.

4A to 4E illustrate a process of forming a pyramidal protrusion on the substrate by using the selective epitaxial growth method.

Selective Epitaxial Growth refers to a technique for growing a special 3D structure or reducing dislocation density by controlling the growth to occur preferentially in only a portion of the substrate through patterning.

As shown in FIG. 4, first, a plurality of masks 210 formed of SiN or SiO ₂ is spaced apart from each other on the substrate 200 (FIG. 4A).

Next, GaN crystal nuclei 220 are grown in a region where the mask 210 is not formed by vapor phase epitaxy (VPE) (FIG. 4B).

In this case, since GaN does not grow on the mask 210 made of SiN or SiO ₂ , GaN crystal nuclei 220 do not occur on the mask.

Subsequently, as the growth progresses, the isolated GaN crystal nuclei 220 gradually enlarge and combine with each other to form islands, and the islands are connected to each other to form a thin film 230 (FIG. 4C).

When the GaN thin film 230 grows to the height of the mask 210, the GaN thin film 230 grows higher than the mask 210, but because GaN does not grow on the mask 210, the GaN crystals are raised in the shape of a cone 235 (FIG. 4D). In the end, a pyramidal shape 240 is formed (FIG. 4E).

In the selective epitaxial growth method, the growth conditions of the GaN thin film can be individually controlled by controlling the growth conditions, and thus, GaN pyramid structures can be realized.

In addition, by forming a mask on the substrate it is possible to control the growth region and to control the position and density of the grown GaN pyramid structure.

In FIG. 4, a process of forming a pyramid-shaped protrusion on the substrate using the selective epitaxial growth method is illustrated. The protrusion may be formed using a non-surfactant.

Here, a method using an anti-surfactant is a method in which a non-surfactant is supplied to a reactor immediately before growth of a GaN thin film to pretreat the growth surface, and then the thin film to be grown shows a 3D growth pattern. .

In more detail, when a GaN compound semiconductor is grown by using a metal-organic chemical vapor deposition (MOCVD) method, first a GaN thin film is grown at a high temperature (900 to 1200 ° C.), and then a non-surfactant is added to the MOCVD device. Supply it.

In this case, it is preferable to use Si as the non-surfactant, and as a supply method, a compound containing Si such as tetraethylsilane (TESi) and silane (SiH ₄ ) is supplied in a gas state.

When the non-surfactant is applied to the surface of the GaN thin film, the non-surfactant is immobilized at the atomic level on the surface of the GaN thin film to increase the surface energy. Thus, the GaN compound semiconductor does not grow well in the region where the surface energy is increased.

This phenomenon is interpreted as inhibiting the two-dimensional growth of GaN-based crystals by the non-surfactant is immobilized on the surface of the GaN thin film by adsorption or chemical bonding to cover the surface of the GaN thin film.

That is, the non-surfactant acts as a mask in the selective epitaxial growth method described above, and the GaN-based compound semiconductor grows in a dot structure in a region where the non-surfactant is not immobilized.

Here, the shape of the dot structure may take various forms such as pyramid shape or dome shape, and the shape depends on crystal growth conditions, distribution density of non-surfactant, and the like.

5 is a cross-sectional view showing a light emitting diode of the present invention. As shown therein, the buffer layer 310, the n-type nitride semiconductor layer 320, the active layer 330, and the p-type nitride semiconductor layer 340 are sequentially formed on the substrate 300. Mesa is etched from the semiconductor 340 layer to a portion of the n-type nitride semiconductor layer 320,

A plurality of pyramidal protrusions 350 are formed on the p-type nitride semiconductor layer 340 and the n-type nitride semiconductor layer 320 exposed by the mesa etch to be spaced apart from each other, and the p-type nitride semiconductor layer A transparent electrode 360 is formed around the plurality of protrusions 350, and an n-electrode 370 is formed on the exposed n-type nitride semiconductor layer 320. It is configured to include a p-electrode 380 formed on the electrode 360.

In the light emitting diode of the present invention configured as described above, a plurality of pyramidal protrusions are formed on an upper portion of the p-type nitride semiconductor layer and an n-type nitride semiconductor layer exposed by mesa etching so that the light generated in the active layer is formed in the p-type and n-type nitride semiconductor layers. When reaching the surface of the type nitride semiconductor layer it is possible to reduce the phenomenon that is totally reflected inside the device to improve the light extraction efficiency.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and variations of the present invention without departing from the spirit or field of the invention provided by the claims below It will be readily apparent to one of ordinary skill in the art that it can be used.

As described above, according to the present invention, by forming a plurality of pyramidal-shaped protrusions on the p-type nitride semiconductor layer to increase the critical angle, when the light generated in the active layer is incident on the surface of the p-type nitride semiconductor layer, it is totally reflected inside. It is possible to reduce the light consumed in, thereby improving the light extraction efficiency.

In addition, by forming a plurality of pyramidal protrusions on the p-type nitride semiconductor layer and mesa etching, the plurality of protrusions are also formed on the n-type nitride semiconductor layer exposed by the mesa etching to form the n-type nitride semiconductor layer The total amount of light consumed can be reduced.

Claims (8)

Sequentially stacking an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on the substrate; Forming a plurality of pyramidal protrusions spaced apart from each other on the p-type nitride semiconductor layer; Mesa etching from the p-type nitride semiconductor layer to a portion of the n-type nitride semiconductor layer; Forming a transparent electrode surrounding the plurality of protrusions on the p-type nitride semiconductor layer; And Forming a p-electrode on the transparent electrode, and forming an n-electrode on the n-type nitride semiconductor layer exposed by the mesa etching process. The method of claim 1, The pyramidal shaped protrusions are formed by surface pretreatment using Selective Epitaxial Growth or Anti-Surfactant. The method of claim 2, Formation of the pyramidal protrusions by the selective epitaxial growth method, Forming a plurality of SiN masks spaced apart from each other on the p-type nitride semiconductor layer; Forming a pyramid-shaped protrusion in an area where the SiN mask is not formed; And The method of manufacturing a light emitting diode comprising the step of removing the SiN mask. The method of claim 1, The plurality of protrusions are made of p-type Al _x In _y Ga _(1-xy) N (0≤x≤1, 0≤y≤1, 0≤x + y≤1). Way. The method of claim 1, The height of the plurality of protrusions 10 ~ 10㎛, the width 20 ~ 20㎛, the distance between each other 20 ~ 20㎛ manufacturing method of the light emitting diode. The method of claim 1, Forming the transparent electrode, Forming an InGaN short-period superlattice layer on the p-type nitride semiconductor layer, and forming a TCO (Transparent Conducting Oxide) layer on the InGaN short-period superlattice layer manufacturing a light emitting diode Way. An n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially formed on the substrate; Mesa etching is performed from the p-type nitride semiconductor layer to a portion of the n-type nitride semiconductor layer; A plurality of pyramid-shaped protrusions are formed to be spaced apart from each other on the p-type nitride semiconductor layer and the n-type nitride semiconductor layer exposed by the mesa etching; A transparent electrode is formed on the p-type nitride semiconductor layer to surround the plurality of protrusions; A p-electrode is formed on the transparent electrode; The n-electrode is formed on the exposed n-type nitride semiconductor layer. The method of claim 7, wherein A plurality of protrusions formed on the p-type nitride semiconductor layer is p-type Al _x In _y Ga _(1-xy) N (0≤x≤1, 0≤y≤1, 0≤x + y≤1) And a plurality of protrusions formed on the n-type nitride semiconductor layer, n-type Al _x In _y Ga _(1-xy) N (0≤x≤1, 0≤y≤1, 0≤x + y≤1 Light emitting diodes).

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