KR100812736B1 - High brightness nitride semiconductor light emitting device - Google Patents

Abstract

The present invention relates to a high brightness nitride-based semiconductor light emitting device comprising: an n-type electrode, a light emitting structure in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially formed on the n-type electrode; The present invention provides a high brightness nitride-based semiconductor light emitting device including a p-type reflective electrode having a plurality of ODR layers formed on a surface of the p-type reflective electrode, the structure supporting layer formed on the surface of the p-type reflective electrode.

LED, reflection efficiency, ODR layer, brightness

Description

High Brightness Nitride Semiconductor Light Emitting Device {HIGH BRIGHTNESS NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE}

1 is a cross-sectional view showing the structure of a high brightness nitride-based semiconductor light emitting device according to a first embodiment of the present invention.

2 is a conceptual diagram illustrating Snell's law to which the present invention is applied.

3 is a conceptual diagram for showing the operation of the ODR layer according to the present invention.

4 is a cross-sectional view showing the structure of a high-brightness nitride-based semiconductor light emitting device according to a second embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

110: n-type electrode 120: n-type nitride semiconductor layer

130: active layer 140: p-type nitride semiconductor layer

150: p-type reflective electrode 160: ODR layer

The present invention relates to a nitride-based semiconductor light-emitting device, and more particularly to a high-brightness nitride-based semiconductor light-emitting device that can improve the luminous efficiency by minimizing the amount of light lost by the absorption of light by the reflective layer inside the light emitting device will be.

In general, nitride semiconductors are actively employed in optical devices for generating short wavelength light such as blue or green as materials having relatively high energy band gaps (for example, about 3.4 eV in GaN semiconductors). As the nitride semiconductor, a material having an Al _x In _y Ga _(1-xy) N composition formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1) is widely used.

The light emitting device made of such a nitride semiconductor has recently adopted a metal such as silver (Ag), which has been spotlighted as a reflective layer material in order to increase the brightness, and the light emitted to the opposite side from the front side is moved forward through the rear reflective layer. The light is reflected and reduced light due to the low transmittance of the previous p-type electrode to improve the light extraction efficiency.

However, the rear reflective layer is not able to reflect all the light emitted to the opposite side of the front surface, but reflects only a portion thereof and absorbs and dissipates the remaining portion. For example, a back reflective layer of silver with the best reflectance reflects about 80% to 85% of light while absorbing and extinguishing the remaining 15% to 20% of light.

Therefore, a nitride-based semiconductor light emitting device using a rear reflective layer is required to reduce the number of times of use of the reflective layer or to minimize the absorption of light absorbed by the reflective layer.

Accordingly, an object of the present invention is to form an omnidirectional reflective layer (hereinafter referred to as 'ODR') made of a vacuum on the surface of the p-type reflective electrode in contact with the light emitting structure to solve the above problems. To provide a high brightness nitride semiconductor light emitting device that can improve the light extraction efficiency by maximizing the reflection efficiency of the light directed to the p-type reflective electrode.

In order to achieve the above object, the present invention provides an n-type electrode, a light emitting structure in which an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer are sequentially formed on the n-type electrode, and is formed on the light emitting structure It provides a high brightness nitride-based semiconductor light emitting device comprising a p-type reflective electrode having a plurality of ODR layers formed on the surface in contact with the predetermined interval and a structure supporting layer formed on the p-type reflective electrode.

In addition, in the high brightness nitride-based semiconductor light emitting device of the present invention, the ODR layer is preferably made of a vacuum, in order to reduce the light extraction efficiency by increasing the difference between the refractive index and the medium constituting the p-type nitride semiconductor layer. That is, the reflection efficiency may be increased by total reflection of the light emitted from the light emitting structure.

In addition, the high brightness nitride-based semiconductor light emitting device of the present invention, it is preferable to further include a protective film formed to cover the side surface and the upper surface of the light emitting structure, and to expose a portion of the upper surface of the p-type reflective electrode.

In addition, in the high brightness nitride-based semiconductor light emitting device of the present invention, it is preferable to further include a plating seed layer covering the outer side of the protective film and positioned between the p-type reflective electrode and the structure support layer.

In the high brightness nitride-based semiconductor light emitting device of the present invention, the metal seed layer is preferably formed of a double layer in which an adhesive layer and a reflective layer are sequentially stacked. In this case, the adhesive layer is made of one metal selected from the group consisting of Cr, Ni, Ti, and alloys of one or more thereof mixed with, and the reflective layer is made of Ag, Al, Pt and alloys of one or more thereof mixed with each other. It is preferred to consist of one metal selected.

Another object of the present invention is to provide an n-type nitride semiconductor layer formed on a substrate, an active layer formed in a predetermined region on the n-type nitride semiconductor layer, a p-type nitride semiconductor layer formed on the active layer, A p-type reflective electrode formed on the p-type nitride semiconductor layer, the p-type reflective electrode having a plurality of ODR layers spaced apart from each other by a predetermined interval, and an n-type electrode formed on the n-type nitride semiconductor layer on which the active layer is not formed; A high brightness nitride-based semiconductor light emitting device is provided.

In addition, in the high brightness nitride-based semiconductor light emitting device of the present invention, the ODR layer is preferably made of a vacuum, in order to reduce the light extraction efficiency by increasing the difference between the refractive index and the medium constituting the p-type nitride semiconductor layer.

In addition, in the high brightness nitride-based semiconductor light emitting device of the present invention, it is preferable to further include a transparent electrode layer at the interface between the p-type nitride semiconductor layer and the p-type reflective electrode to equalize the flow of current.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like parts throughout the specification.

Now, a high brightness nitride-based semiconductor light emitting device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Example  One

First, a high brightness nitride-based semiconductor light emitting device according to a first embodiment of the present invention will be described in detail with reference to FIG. 1.

1 is a cross-sectional view showing the structure of a high-brightness nitride-based semiconductor light emitting device according to a first embodiment of the present invention.

Referring to FIG. 1, an n-type bonding pad (not shown) for electrically connecting to an external device is formed at the bottom of the high brightness nitride-based semiconductor light emitting device according to the present invention.

An n-type electrode 110 is formed on the n-type bonding pad. In this case, the n-type electrode 110 is preferably made of a metal in ohmic contact.

An n-type nitride semiconductor layer 120 is formed on the n-type electrode 110. More specifically, the n-type nitride semiconductor layer 120 may be formed of an n-type impurity doped GaN layer or a GaN / AlGaN layer. Can be.

The active layer 130 and the p-type nitride semiconductor layer 140 are sequentially stacked on the n-type gallium nitride layer 120 to form a light emitting structure. At this time, the active layer 130 of the light emitting structure may be formed of a multi-quantum well structure (Multi-Quantum Well) consisting of InGaN / GaN layer, the p-type nitride semiconductor layer 140 is the n-type nitride semiconductor layer ( Like 120), the p-type impurity may be formed of a GaN layer or a GaN / AlGaN layer.

The p-type reflective electrode 150 is formed on the p-type nitride semiconductor layer 140 of the light emitting structure. The p-type reflective electrode 150 is preferably made of a metal having a high reflectance such as silver (Ag) so as to simultaneously serve as an electrode and a reflective role.

However, the p-type reflective electrode 150 is not able to reflect all the light emitted to the surface opposite to the front surface, that is, the p-type reflective electrode 150, but reflects only a portion thereof and absorbs the remaining portion to extinguish it. Let's do it. For example, when the reflectance is made of silver with the best reflectance, about 80% to 85% of light is reflected while the remaining 15% to 20% of light is absorbed and extinguished.

Therefore, the present invention includes a plurality of ODR layers 160 formed on the surface of the p-type reflective electrode 150 in contact with the light emitting structure, that is, the p-type nitride semiconductor layer 140. As such, the reason why the ODR layer 160 is formed to be spaced apart from each other is because the p-type reflective electrode 150 must be electrically connected to the p-type nitride semiconductor layer 140.

Next, the ODR layer according to the present invention will be described in more detail with reference to FIGS. 2 and 3.

First of all, refraction refers to the phenomenon that when light enters another transparent material, it does not go straight but goes straight again after bending. In addition, the degree of bending when refracting is referred to as the refractive index, the refractive index determined based on the vacuum is called the absolute refractive index, which is often referred to as the refractive index.

For example, if the speed of light in vacuum is C and the speed of light in the medium is V, the refractive index is expressed by Equation 1 below.

Refractive index n = C / V

a: Numerical value for wavelength 598 nm light (yellow light such as sodium).

b: STP (standard condition, 0 ℃, 1 atmosphere)

Therefore, the refractive index always appears greater than 1 as shown in Table 1 above.

Larger refractive index means dense medium and slower light. The opposite is called minor media, which is always a relative term.

In addition, the refraction in a medium has a certain rule between the angle of incidence and the angle of refraction, which is called Snell's law.

2 is a conceptual diagram illustrating Snell's law to which the present invention is applied.

Referring to FIG. 2, when light is emitted from a dense medium n1 having a large refractive index to a small medium n2 having a small refractive index, the light incident at a predetermined angle is Snell's law at a horizontal interface. Because it cannot meet, it is not refracted and reflected. This phenomenon is called total reflection. In addition, this boundary angle is referred to as a critical angle, wherein the larger the difference in refractive index between the two media, the smaller the critical angle, and thus the total reflection of incident light also increases.

In other words, in order to prevent the light from being absorbed by the p-type reflective electrode 150, that is, to increase the total reflection amount of light, the critical angles at the interface of different media should be reduced.

Therefore, in the present invention, as shown in FIG. 3, the p-type nitride semiconductor layer 140 is smaller than the p-type nitride semiconductor layer 140 made of GaN having a refractive index of 2.4 on the surface of the p-type reflective electrode 150 in contact with the p-type nitride semiconductor layer 140. An ODR layer 160 is formed of a medium having a refractive index.

In particular, in the ODR layer 160 according to the present invention, as shown in Table 2, the larger the difference in refractive index with GaN constituting the p-type nitride semiconductor layer 150 is, the smaller the critical angle and the lower the light extraction rate, so the GaN having a refractive index of 2.4 It is preferable that a vacuum is formed with the largest difference in refractive index.

As described above, in the high luminance nitride-based semiconductor light emitting device according to the present invention, as shown in FIG. 1, some of all the light emitted toward the p-type reflective electrode 150 is the p-type reflective electrode 150. By reflecting (see arrow (A)) and the remaining part through the ODR layer 160 (see arrow (B)), so that a portion of the light that has been absorbed and extinguished through the conventional p-type reflective electrode 150 is also lost. The reflection efficiency can be improved by reflecting.

Although not shown, the high-brightness nitride-based semiconductor light emitting device according to the first embodiment of the present invention has a surface adjacent to the top and side surfaces of the light emitting structure except for a portion of the p-type electrode 150 bonded to an external circuit. It is preferable that a protective film is formed to prevent an electrical short between the elements.

In addition, a plating seed layer is preferably formed on the outermost surface of the passivation layer and the p-type electrode 150. When the structural support layer, which will be described later, is formed through electrolytic plating or electroless plating, plating is performed during a plating process. It acts as a nucleus, and consists of a single layer using metals such as Au, Cu, Ta, and Ni. On the other hand, this is not limited to this, it may be composed of a double layer in which the adhesive layer and the reflective layer are sequentially stacked.

In this case, the adhesive layer constituting the plating seed layer is made of a metal selected from the group consisting of oxides and metals having excellent adhesion, that is, Cr, Ni, Ti and alloys of one or more of these protective layers 160 and There is an advantage that can further improve the adhesion of the. In addition, the reflective layer is made of a metal having a high reflectance, that is, one metal selected from the group consisting of Ag, Al, Pt, and an alloy of one or more thereof, and thus, light emitted from the light emitting structure is transmitted through the reflective layer. It is possible to reflect the light to the light emitting surface, there is an advantage that can further improve the light extraction efficiency.

In addition, the structural support layer (not shown) formed on the plating seed layer by the plating seed layer serves as a support layer for supporting the formed final high brightness nitride semiconductor light emitting device.

Example  2

Next, the high brightness nitride-based semiconductor light emitting device according to the second embodiment of the present invention will be described in detail with reference to FIG. 4.

As shown in FIG. 4, the high-brightness nitride semiconductor light emitting device according to the second embodiment includes a buffer layer (not shown), an n-type nitride semiconductor layer 210, an active layer 220, and p on a substrate 200. The type nitride semiconductor layer 230 is sequentially stacked.

The substrate 200 is preferably formed using a transparent material including sapphire. In addition to sapphire, the substrate 110 may be formed of zinc oxide (ZnO), gallium nitride (GaN), silicon carbide (SiC), and aluminum nitride (AlN).

The buffer layer (not shown) is formed of GaN and may be omitted.

The n-type or p-type nitride semiconductor layers 210 and 230 are formed of GaN layers or GaN / AlGaN layers doped with each conductive type impurity, and the active layer 220 is composed of a multi-well structure composed of InGaN / GaN layers. Quantum Well).

A portion of the active layer 220 and the p-type nitride semiconductor layer 230 are removed by mesa etching to expose a portion of the n-type nitride semiconductor layer 210 formed on the bottom surface.

The p-type reflective electrode 250 is formed on the p-type nitride semiconductor layer 230. In this case, the p-type reflective electrode 250 is preferably made of a metal having a high reflectance, for example, silver (Ag) so as to simultaneously serve as an electrode and a reflection role.

In particular, the high-brightness nitride semiconductor light emitting device according to the second embodiment of the present invention is a flip-chip light emitting device, and since light is emitted toward the substrate 200, the p-type reflective electrode 250 may be disposed on the front surface. In order to improve the light extraction efficiency by reflecting all the light emitted to the p-type reflective electrode 250 to the opposite surface, that is, toward the substrate 200.

However, the p-type reflective electrode 250 is not able to reflect all the light emitted therefrom, but reflects only a portion thereof and absorbs and dissipates the remaining portion.

Therefore, the high brightness nitride semiconductor light emitting device according to the second embodiment of the present invention includes a plurality of ODR layers 260 formed to be spaced apart from the surface of the p-type reflective electrode 250 in contact with the p-type nitride semiconductor layer 230 by a predetermined interval. ). As such, the reason why the ODR layer 260 is formed to be spaced apart from each other is because the p-type reflective electrode 250 must be electrically connected to the p-type nitride semiconductor layer 230.

Although not shown, the present invention may further include a transparent electrode layer for equalizing the flow of current at an interface between the p-type nitride semiconductor layer 230 and the p-type reflective electrode 250.

An n-type electrode 240 serving as a pole is formed in a predetermined portion on the n-type nitride semiconductor layer 210 exposed by the mesa etching. Herein, the n-type electrode 240 is made of Cr / Au or the like.

That is, the first embodiment illustrates vertically structured light emitting diodes, and the second embodiment illustrates flip chip light emitting diodes. The same operation and effect as in the first embodiment can be obtained.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

As described above, the present invention provides a plurality of ODR layers made of a medium having a large refractive index difference with the p-type nitride semiconductor layer on a surface of the p-type reflective electrode in contact with the p-type nitride semiconductor layer, at a predetermined interval apart from the p-type nitride electrode. It is possible to improve the light extraction efficiency by securing the light that is absorbed or scattered by the p-type reflective electrode and extinguished by maximally reflecting the light emitted toward the type reflective electrode.

Accordingly, the present invention can provide a nitride semiconductor light emitting device that implements high brightness.

Claims (10)

n-type electrode; A light emitting structure in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially formed on the n-type electrode; A p-type reflective electrode formed on the light emitting structure, the p-type reflective electrode having a plurality of ODR layers spaced apart from each other at predetermined intervals on a surface of the light emitting structure; And And a structure support layer formed on the p-type reflective electrode. The method of claim 1, The high brightness nitride-based semiconductor light emitting device, characterized in that the ODR layer is made of a vacuum. The method of claim 1, A high brightness nitride-based semiconductor light emitting device further comprising a passivation layer covering the side surface and the upper surface of the light emitting structure, the upper portion of the p-type reflective electrode is exposed. The method of claim 3, And a plating seed layer covering an outer side of the passivation layer and positioned between the p-type reflective electrode and the structure support layer. The method of claim 4, wherein The plating seed layer is a high brightness nitride-based semiconductor light emitting device, characterized in that consisting of a double layer in which the adhesive layer and the reflective layer are sequentially stacked. The method of claim 5, The adhesive layer is Cr, Ni, Ti and high brightness nitride-based semiconductor light emitting device, characterized in that made of one metal selected from the group consisting of one or more of these alloys. The method of claim 5, The reflective layer is a high brightness nitride-based semiconductor light emitting device, characterized in that made of one metal selected from the group consisting of Ag, Al, Pt, and alloys of one or more thereof. An n-type nitride semiconductor layer formed on the substrate; An active layer formed in a predetermined region on the n-type nitride semiconductor layer; A p-type nitride semiconductor layer formed on the active layer; A p-type reflective electrode formed on the p-type nitride semiconductor layer, the p-type reflective electrode having a plurality of ODR layers formed on the surface in contact with the p-type nitride semiconductor layer at predetermined intervals; And And an n-type electrode formed on the n-type nitride semiconductor layer on which the active layer is not formed. The method of claim 8, The high brightness nitride-based semiconductor light emitting device, characterized in that the ODR layer is made of a vacuum. The method of claim 8, And a transparent electrode layer at an interface between the p-type nitride semiconductor layer and the p-type reflective electrode.

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