KR101138948B1 - High efficiency light emitting diode - Google Patents

Abstract

A high efficiency light emitting diode is disclosed. The light emitting diode includes a semiconductor laminate structure located on a support substrate. The semiconductor laminated structure includes a p-type compound semiconductor layer, an active layer and an n-type compound semiconductor layer, and the p-type compound semiconductor layer is located closer to the supporting substrate side than the n-type compound semiconductor layer. On the other hand, the opening exposes the n-type compound semiconductor layer through the p-type compound semiconductor layer and the active layer. In addition, the p-electrode is positioned between the p-type compound semiconductor layer and the support substrate to make ohmic contact with the p-type compound semiconductor layer, and a portion of the p-electrode is exposed to the outside of the semiconductor stacked structure. Meanwhile, an n-electrode is positioned between the p-electrode and the support substrate and contacts the n-type compound semiconductor layer through the opening. In addition, a high reflection insulating layer is positioned between the p-electrode and the n-electrode to insulate the p-electrode from the n-electrode and reflect light from the active layer toward the support substrate. By disposing the n-electrode and the p-electrode on the opposite side of the n-type compound semiconductor layer with respect to the active layer, it is possible to prevent light loss caused by the electrode or the electrode pad, thereby providing a high efficiency light emitting diode which can improve the light extraction efficiency. Can be.

Description

High Efficiency Light Emitting Diodes {HIGH EFFICIENCY LIGHT EMITTING DIODE}

The present invention relates to a light emitting diode, and more particularly, to a gallium nitride-based high efficiency light emitting diode having a growth substrate removed by applying a substrate separation process.

In general, nitrides of group III elements, such as gallium nitride (GaN) and aluminum nitride (AlN), have excellent thermal stability and have a direct transition type energy band structure. It is attracting much attention as a substance. In particular, blue and green light emitting devices using indium gallium nitride (InGaN) have been used in various applications such as large-scale color flat panel display devices, traffic lights, indoor lighting, high density light sources, high resolution output systems, and optical communications.

Such a nitride semiconductor layer of Group III elements is difficult to fabricate homogeneous substrates capable of growing them, and therefore, such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), etc., on heterogeneous substrates having a similar crystal structure. Is grown through the process. As a hetero substrate, a sapphire substrate having a hexagonal structure is mainly used. However, sapphire is an electrically insulator, thus limiting the light emitting diode structure. Accordingly, recently, epitaxial layers, such as nitride semiconductor layers, are grown on dissimilar substrates such as sapphire, bonding supporting substrates to the epitaxial layers, and then separating the dissimilar substrates using a laser lift-off technique. Techniques for producing high efficiency light emitting diodes of construction have been developed (see, eg, US Pat. No. 6,744,071).

Such a vertical light emitting diode has an n-type GaN layer, an active layer, and a p-type GaN layer sequentially formed on a growth substrate, a p-electrode and a reflective metal layer formed on the p-type GaN layer, and a support substrate is bonded thereon. Thereafter, the sapphire substrate is removed and manufactured by forming an n-electrode or an n-electrode pad on the exposed n-type semiconductor layer. A support substrate is generally used as a conductive substrate and thus has a vertical structure in which n-electrodes and p-electrodes are disposed to face each other.

However, since the n-electrode or n-electrode pad is located on the n-type GaN layer which is the light emitting surface, the light generated in the active layer is absorbed or reflected by the n-electrode, thereby reducing the light extraction efficiency. In addition, Ag, which is mainly used as a reflective layer while making ohmic contact with a p-type GaN layer, is easily agglomerated by a thermal process, and migration of Ag atoms during driving of a light emitting diode is easy to cause current leakage. It is difficult to form a stable ohmic metal reflective layer. Moreover, Ag is a metal material and has a limit in improving reflectance.

United States Patent Application Publication No. US6,744,071

The problem to be solved by the present invention is to provide a high-efficiency light emitting diode having a new structure that can prevent the light generated in the active layer is absorbed or reflected by the electrode or electrode pad.

Another object of the present invention is to provide a high-efficiency light emitting diode having improved reflectance of light propagating toward a support substrate while forming a p-omic contact.

The light emitting diode according to the embodiments of the present invention, the support substrate; A semiconductor stacked structure on the support substrate, the semiconductor stacked structure comprising a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer, wherein the p-type compound semiconductor layer is located closer to the support substrate than the n-type compound semiconductor layer; An opening exposing the n-type compound semiconductor layer through the p-type compound semiconductor layer and the active layer; A p-electrode disposed between the p-type compound semiconductor layer and the support substrate and being in ohmic contact with the p-type compound semiconductor layer, and partially exposed to the outside of the semiconductor laminate structure; An n-electrode disposed between the p-electrode and the support substrate and contacting the n-type compound semiconductor layer through the opening; And a high reflection insulating layer positioned between the p-electrode and the n-electrode to insulate the p-electrode from the n-electrode and to reflect light from the active layer toward the support substrate.

By disposing the n-electrode and the p-electrode on the opposite side of the n-type compound semiconductor layer with respect to the active layer, it is possible to prevent light loss caused by the electrode or the electrode pad, thereby providing a high efficiency light emitting diode which can improve the light extraction efficiency. Can be.

The high reflection insulating layer may cover the sidewall of the opening to insulate the n-electrode, the p-type compound semiconductor layer and the active layer, and may reflect light incident on the high reflection insulating layer. Therefore, light loss may be reduced by shortening an optical path traveling inside the light emitting diode.

The high reflection insulating layer may be a distributed Bragg reflector (DBR). The high reflection insulating layer may include at least one element selected from Si, Ti, Ta, Nb, In, and Sn. Specifically, the high reflection insulating layer may be formed by alternately stacking at least two layers selected from Si _x O _y N _z , Ti _x O _y , Ta _x O _y and Nb _x O _y .

The p-electrode may have a plurality of openings exposing the p-type compound semiconductor layer, and the high reflection insulating layer may fill the plurality of openings. The high reflection insulating layer filling the plurality of openings reflects light incident directly on the high reflection insulating layer without passing through the p-electrode. Therefore, the reflectance can be further improved by reducing the light loss caused by the p-electrode. The p-electrode may preferably be a reflective metal, a transparent metal or a transparent conductive oxide film.

Further, a p-electrode pad may be formed on the exposed p-electrode. In addition, a portion of the n-electrode may be exposed to the outside of the semiconductor laminate, and an n-electrode pad may be located on the exposed n-electrode. Thus, there is provided a light emitting diode having an n-electrode pad and a p-electrode pad on the same side of the support substrate.

Meanwhile, a bonding metal may be located between the n-electrode and the support substrate. The bonding metal couples the semiconductor laminate to the support substrate.

According to the present invention, it is possible to provide a high-efficiency light emitting diode that can prevent light generated in the active layer from being absorbed or reflected by an electrode or an electrode pad to improve light extraction efficiency. In addition, by adopting a high reflection insulating layer together with the p-electrode, it is possible to provide a high-efficiency light emitting diode having improved reflectance of light traveling toward the side of the supporting substrate as compared to a light emitting diode employing a conventional metal reflective layer. Furthermore, the highly reflective insulating layer can be formed with a distributed Bragg reflector, so that the reflectance can be optimized according to the wavelength of light generated in the active layer.

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

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to ensure that the spirit of the present invention to those skilled in the art will fully convey. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience.

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

Referring to FIG. 1, the light emitting diode includes a support substrate 51, a semiconductor stack 30, an opening 30a, a p-electrode 31, a high reflection insulating layer 35, and an n-electrode 37. Include. The light emitting diode may also include a p-electrode pad 37, an n-electrode pad 39 and a bonding metal 41.

The support substrate 51 is separated from the growth substrate for growing the compound semiconductor layers, and is a secondary substrate attached to the compound semiconductor layers that have already been grown. The support substrate 51 may be a sapphire substrate, but is not limited thereto, and may be another kind of insulating or conductive substrate. In particular, when the sapphire substrate is used as the growth substrate, since it has the same thermal expansion coefficient as that of the growth substrate, it is preferable because the warping of the wafer can be prevented when bonding the support substrate and removing the growth substrate.

The semiconductor stacked structure 30 is disposed on the support substrate 51 and includes a p-type compound semiconductor layer 27, an active layer 25, and an n-type compound semiconductor layer 23. Here, the p-type compound semiconductor layer 27 is located closer to the support substrate 51 side than the n-type compound semiconductor layer 23, similar to a general vertical light emitting diode. The semiconductor laminate 30 may be located on a portion of the support substrate 51.

The n-type compound semiconductor layer 23, the active layer 25, and the p-type compound semiconductor layer 27 may be formed of a III-N series compound semiconductor, such as (Al, Ga, In) N semiconductor. The n-type compound semiconductor layer 23 and the p-type compound semiconductor layer 27 may be a single layer or multiple layers, respectively. For example, the n-type compound semiconductor layer 23 and / or the p-type compound semiconductor layer 27 may include a contact layer and a cladding layer, and may also include a superlattice layer. In addition, the active layer 25 may have a single quantum well structure or a multiple quantum well structure. Since the n-type compound semiconductor layer 23 having a relatively small resistance is located on the opposite side of the support substrate 51, it is easy to form a roughened surface R on the upper surface of the n-type compound semiconductor layer 23, which is rough. The true surface R improves the extraction efficiency of light generated in the active layer 25.

The opening (s) 30a expose the n-type compound semiconductor layer 23 through the p-type compound semiconductor layer 27 and the active layer 25. The opening 30a may be formed as a hole, a groove, or a trench, and a plurality of openings 30a may be formed. For example, the opening 30a may be formed as a hole, and a plurality of holes may be arranged in a matrix form.

The p-electrode 31 is positioned between the p-type compound semiconductor layer 27 and the support substrate 51 and makes ohmic contact with the p-type compound semiconductor layer 27. The p-electrode 31 may be formed in a predetermined pattern to have a plurality of openings exposing the p-type compound semiconductor layer 27. Although the p-electrodes 31 are shown as being separated from each other in the drawing, the p-electrodes are connected to each other and may be formed in a mesh shape, for example. In addition, the p-electrode 31 may be formed of a transparent metal such as Ni / Au, for example, a transparent conductive oxide film such as ITO, ZnO, or a reflective metal. A portion of the p-electrode 31 is exposed to the outside of the semiconductor stacked structure 30.

Meanwhile, the n-electrode 35 is positioned between the p-electrode 31 and the support substrate 51 and contacts the n-type compound semiconductor layer 23 through the opening 30a. The n-electrode 35 may ohmic contact the n-type compound semiconductor layer 23. A portion of the n-electrode 35 may be exposed to the outside of the semiconductor stacked structure 30.

On the other hand, the high reflection insulating layer 33 insulates the n-electrode 35 from the p-electrode 31. The high reflection insulating layer 33 is formed of an insulating layer having a higher reflectance than Al or Ag, and may include, for example, at least one element selected from Si, Ti, Ta, Nb, In, and Sn. In addition, the high reflection insulating layer 33 may be formed by alternately stacking at least two layers selected from Si _x O _y N _z , Ti _x O _y , Ta _x O _y and Nb _x O _y , and distributed Bragg It may be a reflector DBR. The distributed Bragg reflector can maximize the reflectance of light of a specific wavelength by controlling the optical thicknesses of the alternating high and low refractive index layers. Accordingly, by forming a distributed Bragg reflector with optimized reflectance according to the wavelength of light generated in the active layer 25, it is possible to form a high reflection insulating layer 33 having a high reflectance for, for example, ultraviolet rays, visible rays or infrared rays.

The high reflection insulating layer 33 may fill the openings formed in the p-electrode 31, and thus, a portion of the high reflection insulating layer 33 may directly contact the p-type compound semiconductor layer 27. The high reflection insulating layer 33 may also cover the sidewall of the opening 30a. Therefore, the sidewalls of the p-type compound semiconductor layer 27 and the sidewalls of the active layer 25 exposed to the opening 30a are connected to the n-electrode 35 in contact with the n-type compound semiconductor layer 23 through the opening 30a. Short circuit can be prevented. In addition, the high reflection insulating layer 33 may reflect the light traveling in the semiconductor laminate 30, thus reducing the optical path by shortening the optical path inside the semiconductor laminate 30. . In particular, in order to improve light extraction by the high reflection insulating layer 33 in the opening 30a, the width of the opening 30a may be formed to become narrower toward the n-type compound semiconductor layer 23.

Meanwhile, the p-electrode pad 37 and the n-electrode pad 39 may be positioned on the p-electrode 31 and the n-electrode 35 exposed to the outside of the semiconductor stack 30. Accordingly, a light emitting diode in which the p-electrode pad 37 and the n-electrode pad 39 are formed on the same side of the support substrate 51 may be provided.

The bonding metal 41 may be located between the support substrate 51 and the n-electrode 35. The bonding metal 41 may be formed of Au-Sn, and the support substrate 51 is adhered to the semiconductor laminate structure 30 by eutectic bonding.

According to the present embodiment, a high-efficiency light emitting diode having high light extraction efficiency by adopting a high reflection insulating layer 33 which is superior in process stability and high reflectivity compared to Al or Ag and improves the reflectance of light traveling to the support substrate 51 side Can be provided. Further, by arranging the n-electrode and / or the n-electrode pad formed on the light extraction surface of the n-type compound semiconductor layer 23 under the n-type compound semiconductor layer 23, the light once generated is absorbed or reflected again. Can be prevented from being lost, thereby improving the light efficiency.

Hereinafter, the manufacturing method of the high efficiency light emitting diode according to the present invention will be briefly described.

First, epitaxial layers including the n-type compound semiconductor layer 23, the active layer 25 and the p-type compound semiconductor layer 27 are grown on a growth substrate (not shown) such as sapphire. Subsequently, the p-type compound semiconductor layer 27 and the active layer 25 are etched to form an opening 30a exposing the n-type compound semiconductor layer 23. Thereafter, the p-electrode 31 is formed on the p-type compound semiconductor layer 23. The p-electrode 31 may have a plurality of openings exposing the p-type compound semiconductor layer 23 like a mesh. A high reflection insulating layer 33 is formed on the p-electrode 31. The high reflection insulating layer 33 may cover the p-electrode 31 and fill the plurality of openings formed in the p-electrode 31. In addition, the high reflection insulating layer 33 may cover the side wall in the opening 30a. The bottom surface of the opening 30a, that is, the high reflection insulating layer 33 formed on the n-type compound semiconductor layer 23 is removed.

Subsequently, an n-electrode 35 is formed on the high reflection insulating layer 33. The n-electrode is electrically connected to the n-type compound semiconductor layer 23 through the opening 30a.

Then, a metal layer for bonding is formed on the n-electrode 35, a metal layer for bonding is also formed on the support substrate 51, and these metal layers are bonded to each other. Accordingly, the bonding metal 41 is formed by the metal layers for bonding, and the support substrate 51 is bonded to the compound semiconductor layers 23, 25, and 27.

Thereafter, the growth substrate is removed using a laser lift-off technique or the like to expose the n-type compound semiconductor layer 23. After that, a part of the compound semiconductor layers 23, 25, and 27 are removed to expose a part of the p-electrode 31, and also to expose the n-electrode 35.

The n-electrode pad 37 and the p-electrode pad 39 are formed on the exposed p-electrode 31 and the n-electrode 35, respectively, and divided into individual LED chips to complete the light emitting diode.

23: n-type compound semiconductor layer, 25: active layer,
27: p-type compound semiconductor layer, 30: semiconductor laminate structure,
30a: opening, 31: p-electrode,
33: high reflection insulating layer, 35: n-electrode,
37: p-electrode pad, 39: n-electrode pad,
41: bonding metal, 51: support substrate

Claims (10)

Support substrate;
A semiconductor stacked structure on the support substrate, the semiconductor stacked structure comprising a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer, wherein the p-type compound semiconductor layer is located closer to the support substrate than the n-type compound semiconductor layer;
A plurality of openings exposing the n-type compound semiconductor layer through the p-type compound semiconductor layer and the active layer;
A plurality of openings disposed between the p-type compound semiconductor layer and the support substrate and being in ohmic contact with the p-type compound semiconductor layer and exposing the p-type compound semiconductor layer, and partially exposed to the outside of the semiconductor laminate structure P-electrode;
An n-electrode disposed between the p-electrode and the support substrate and contacting the n-type compound semiconductor layer through a plurality of openings exposing the n-type semiconductor layer;
A light located between the p-electrode and the n-electrode to insulate the p-electrode from the n-electrode, to fill a plurality of openings exposing the p-type compound semiconductor layer, and to be directed toward the support substrate in the active layer; A light emitting diode comprising an insulating layer for reflecting. The method according to claim 1,
The insulating layer covers sidewalls of a plurality of openings exposing the n-type compound semiconductor layer to insulate the n-electrode, the p-type compound semiconductor layer and the active layer, and to reflect light incident to the insulating layer. . The method according to claim 1,
Wherein said insulating layer is a distributed Bragg reflector. The method according to claim 1,
The insulating layer is a light emitting diode formed by alternately stacking at least two layers selected from Si _x O _y N _z , Ti _x O _y , Ta _x O _y and Nb _x O _y . The method according to claim 1,
The insulating layer includes at least one element selected from Si, Ti, Ta, Nb, In and Sn. delete The method according to claim 1,
And a p-electrode pad on the exposed p-electrode. The method of claim 7,
further comprising n-electrode pads,
A portion of the n-electrode is exposed outside the semiconductor laminate,
And the n-electrode pad is located on the exposed n-electrode. The method according to claim 1,
And a bonding metal positioned between the n-electrode and the support substrate. The method according to claim 1,
The p-electrode is a transparent conductive oxide film.

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