WO2011065745A2

WO2011065745A2 - Light-emitting diode package

Info

Publication number: WO2011065745A2
Application number: PCT/KR2010/008353
Authority: WO
Inventors: 이종람; 손준호
Original assignee: 서울옵토디바이스주식회사; 포항공과대학교 산학협력단
Priority date: 2009-11-27
Filing date: 2010-11-24
Publication date: 2011-06-03
Also published as: WO2011065745A3

Abstract

Disclosed is a light-emitting diode package, comprising high-output and high-efficiency light-emitting diodes in which the efficiency droop phenomenon, which occurs in response to the injection of high current, is prevented to achieve improved light emission efficiency. The light-emitting diode package is configured such that the surface of a base on which the light-emitting diodes are to be attached is curved by means of a device or a specific structure, and the light-emitting diodes are die-bonded to the curved surface so as to enable the light-emitting diodes to be bent by the curvature of the curved surface. Here, stresses are applied to the light-emitting diodes, thus causing changes in a band structure of a quantum well layer. In the thus-produced light-emitting diode package, efficiency droop, which occurs in response to the injection of high current, is reduced to achieve the high output and high efficiency of the package.

Description

LED Package

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode package, and more particularly, to a light emitting diode package which improves luminous efficiency by suppressing a phenomenon of 'efficiency droop' generated during high current injection.

The light emitting diode package using GaN series light emitting diode (LED) has long life, small size, light weight, strong light directivity, low voltage driving, and it does not require preheating time and complicated driving circuit, and is resistant to shock and vibration. Many types of high-quality lighting systems can be implemented, and it is expected to replace incandescent lamps, fluorescent lamps, mercury lamps and existing white light sources within the next 10 years. In order for GaN-based LEDs to be used in white light sources to replace existing mercury or fluorescent lamps, the GaN-based LEDs must not only have excellent thermal stability but also be able to emit high power at low power consumption. Currently, horizontal GaN-based blue light emitting diodes have advantages in that they are relatively inexpensive and have a simple manufacturing process. However, sapphire used as a substrate is an insulator and has poor thermal conductivity, which is not suitable for a high output device having a high applied current and a large area. The disadvantage is that. A vertical light emitting diode is a device that overcomes the disadvantages of the horizontal light emitting diode and is easily applied to a large output high power light emitting diode. Such vertical light emitting diodes have several advantages compared to horizontal light emitting diodes. Vertical light emitting diodes do not require transparent electrodes, so there is no light absorption, and because thick electrodes can be used, the current spreading resistance is small, resulting in a relatively very uniform current spreading distribution, resulting in lower operating voltage and greater light output. In addition, the heat dissipation is possible through a metal substrate having good thermal conductivity, so that a relatively long life and high power operation are possible. In addition, the vertical type light emitting diode emits light in all areas, and thus has a relatively large light emitting area. Since the vertical light emitting diode can increase the maximum applied current by 3-4 or more compared to the horizontal light emitting diode, it can be used as a white light source for illumination. Currently, Nichia chemical in Japan, Lumileds and Cree in USA, Leading companies of GaN light emitting diodes, such as Germany's Osram and several related companies in Taiwan, are actively conducting R & D for the commercialization of high power vertical light emitting diodes.

In order to realize a high output high efficiency light emitting diode suitable for lighting, a large area of the light emitting diode device and high current injection are required. In general, the light emitting diode exhibits high quantum efficiency at a very low current, and rapidly increases as the injection current increases. A decreasing 'efficiency droop' phenomenon occurs. Therefore, in order for LEDs to effectively replace existing lighting products, the 'efficiency droop' phenomenon must be suppressed. So far, much research has been conducted on the phenomenon of 'efficiency droop', but there is still a lot of controversy and the exact cause has not been identified.

An object of the present invention is to solve the problems described above, to provide a light emitting diode package that improves the luminous efficiency by suppressing the 'efficiency droop' phenomenon generated during high current injection.

According to the present invention, there is provided a light emitting diode package comprising a base and a light emitting diode disposed on the base, a curved surface having a curvature is formed on the base, the light emitting diode is attached to the curved surface.

According to an embodiment of the present invention, the light emitting diode is a vertical light emitting diode including a support substrate and semiconductor layers on the support substrate, and the curved surface is preferably a convex curved surface. The semiconductor layers sequentially include a p-GaN layer, an active layer, and an n-GaN layer in a direction away from the support substrate, and a p-type reflective contact layer is interposed between the p-GaN layer and the support substrate. The vertical light emitting diode is attached so that the bottom surface of the support substrate faces the curved surface, and the bottom surface of the support substrate has a concave curved surface. It is preferable that the said support substrate is a metal substrate. The vertical light emitting diode is bent while being die bonded to the curved surface. The vertical light emitting diode is attached to the curved surface by Ag-based paste or Au-Sn alloy. The curvature is preferably 1 (m ^-1 ) to 100 (m ^-1 ). The curved surface is preferably spherical. A plurality of vertical light emitting diodes may be arranged on the base, and the plurality of vertical light emitting diodes may be attached to one curved surface on the base. Alternatively, a plurality of vertical light emitting diodes may be arranged on the base, and the plurality of vertical light emitting diodes may be attached to each of the plurality of curved surfaces formed on the base.

According to another exemplary embodiment of the present invention, the light emitting diode is a horizontal light emitting diode including a growth substrate and semiconductor layers formed on the growth substrate and having an n-type electrode and a p-type electrode thereon, and the curved surface is a concave curved surface. It is preferable. The growth substrate is a sapphire substrate, and the semiconductor layers sequentially include an n-GaN layer, an active layer, and a p-GaN layer in a direction away from the sapphire substrate. The horizontal light emitting diode is attached so that the bottom surface of the growth substrate faces the curved surface, and the growth substrate has a curved surface that is convex toward the base. The horizontal light emitting diode is bent while being die bonded to the curved surface. The horizontal light emitting diode is attached to the curved surface by Ag-based paste or Au-Sn alloy. The curvature is preferably 1 (m ^-1 ) to 100 (m ^-1 ). In addition, the curved surface is preferably a spherical surface. A plurality of horizontal light emitting diodes are arranged on the base, wherein the plurality of horizontal light emitting diodes may be attached to one curved surface on the base, alternatively, a plurality of horizontal light emitting diodes on the base. And a plurality of horizontal light emitting diodes may be attached to each of the plurality of curved surfaces on the base.

When die bonding the light emitting diode to the base upper surface having the curvature of the light emitting diode package, the light emitting diode is bent by the curvature of the upper surface of the base. At this time, the bending of the light emitting diode is applied to the light emitting diode so that the band structure of the quantum well layer is changed. The light emitting diode package manufactured as described above has a characteristic of high power and high efficiency since the 'efficiency droop' phenomenon generated during high current injection is reduced.

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

2 is a cross-sectional view showing a vertical light emitting diode applied to the light emitting diode package shown in FIG.

3 is a view showing a vertical light emitting diode fabricated to evaluate a change in optical characteristics of a vertical light emitting diode according to a change in curvature.

4 is a view showing optical and electrical characteristics change according to the curvature change of the vertical light emitting diode.

FIG. 5 is a diagram showing light output and normalized external quantum efficiency according to injection current of vertical light emitting diodes having different curvatures. FIG.

FIG. 6 is a diagram illustrating a band bending change of an InGaN / GaN quantum well according to a change in curvature. FIG.

7 is a cross-sectional view illustrating a light emitting diode package and a horizontal light emitting diode applied thereto according to another embodiment of the present invention.

FIG. 8 is a view showing a comparison of EL spectra of a horizontal light emitting diode on a flat top surface and a concave base top surface. FIG.

FIG. 9 is a diagram showing the band warpage change and the wave function of electrons and holes in an InGaN / GaN quantum well of a horizontal light emitting diode having a flat bottom surface and a concave bottom surface. FIG.

10 and 11 are views for explaining another modified form of the present invention.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art. It is provided for complete information.

As shown in FIG. 1, the light emitting diode package 100 according to the present embodiment includes a base 110 and a vertical light emitting diode 120 attached to the base 110 by a die bonding method. . The base 110 includes terminals electrically connected to the vertical light emitting diodes 120 on an upper surface thereof. In this case, the light emitting diode package 100 is formed such that the surface on which the light emitting diode 120 is attached in a die bonding manner, that is, the upper surface of the base 110 includes a convex curved surface 112 having a curvature. In the state attached to the curved surface 112 of the base 110, the bottom surface of the light emitting diode 120 is a concave curved surface. Ag-based paste or Au-Sn alloy may be used as a material (not shown) for die bonding the light emitting diodes 120 to the base 110.

Referring to FIG. 2, the light emitting diode 120 includes a support substrate 121 and a p-GaN layer 123, an active layer 125, and an n-GaN layer 127 in this order from the support substrate 121. do. The p-type reflective contact layer 122 may be interposed between the paper substrate 121 and the p-GaN layer 123. The substrate substrate 121 is preferably a metal substrate. The active layer 125 preferably includes an InGaN / GaN multiple quantum well (MQW) structure. Other layers may be further interposed between the layers mentioned above. The

layers

123, 125, and 127 are grown on a sapphire substrate (not shown), and the sapphire substrate is an n-GaN layer 127 or a buffer layer (not shown) after the growth of the

layers

123, 125, and 127. Shown).

Nitride-based light emitting diode epi wafers, especially InGaN / GaN light emitting diode epi wafers, grown on a typical c-plane sapphire substrate, have a compressive stress on the quantum well due to the difference in lattice constant and thermal expansion coefficient of the sapphire substrate and GaN. Since polarization occurs and spontaneous polarization also exists, the band structure of the quantum well bends, thereby decreasing the internal quantum efficiency, and as the current injection increases, the efficiency of the LED decreases. Therefore, by controlling the stress applied from the outside to reduce the bending of the quantum well of the light emitting diode can improve the internal quantum efficiency and suppress the 'efficiency droop' phenomenon.

Referring back to FIG. 1, since the metal support substrate 121 may be bent according to the curvature of the upper surface of the base 110 where the light emitting diodes 120 are attached, the degree of bending of the metal support substrate 121 may be adjusted. In addition, the stress applied to the light emitting diodes 120 may be controlled.

FIG. 3 shows a scanning electron micrograph and a rough image of a vertical light emitting diode fabricated in order to evaluate a characteristic change of the vertical light emitting diode according to a change in curvature. The vertical light emitting diodes had a convex curvature, which was confirmed by the two-dimensional surface profiler.

4 shows EL spectra and current-voltage curves of vertical light emitting diodes having different curvatures. It can be seen that as the curvature of the vertical light emitting diode increases, the center wavelength moves to a shorter wavelength, and the light output increases. When the curvature increases to some extent, almost no wavelength change occurs, and the light output of the vertical LED is also reduced. There was no difference in the current-voltage curve according to the curvature change, and since the same driving voltage was maintained, the change in curvature of the vertical light emitting diode mainly affected the optical characteristics.

FIG. 5 shows light output characteristics according to injection currents of vertical light emitting diodes having different curvatures and normalized wall-plug efficiency in each vertical light emitting diode. It can be seen that the light output increases as the injection current increases. The normalized efficiency shows that as the curvature increases, the 'efficiency droop' phenomenon that occurs as the injection current increases, and the light output also increases. However, the 'efficiency droop' phenomenon occurred less in the vertical type light emitting diode, which has the largest curvature, but the light output decreased slightly, so that the appropriate curvature is required to suppress the 'efficiency droop' phenomenon and to realize the high efficiency vertical light emitting diode. Able to know.

FIG. 6 illustrates a band change of an InGaN / GaN quantum well according to a change in curvature. In the light emitting diode epi wafer grown on a general c-plane sapphire substrate, the band is bent due to spontaneous polarization and piezoelectric polarization, and separation of electrons and hole wavelength functions occurs, thereby reducing internal quantum efficiency. When the curvature of the light emitting diode epi wafer changes, the stress is applied to alleviate the band warpage of the quantum well, so that the overlap of the wavelength function of the electron and the hole increases, thereby increasing the internal quantum efficiency and thus the light output. have.

When using the LED package of the embodiment as described above, the 'efficiency droop' phenomenon generated during high current injection is suppressed to implement a high output high efficiency vertical light emitting diode with improved luminous efficiency. As described above, the vertical light emission of the light emitting diode package to which the vertical light emitting diode is attached forms a convex structure having curvature and / or convex mechanism on one side of the base of the light emitting diode package, and uses a metal substrate as a supporting substrate on the surface having the curvature. When the diode is die bonded, the vertical light emitting diode is bent by the curvature of the bottom surface. In this case, stress is applied to the light emitting diode epitaxial wafer, thereby changing the band structure of the quantum well layer, thereby increasing the internal quantum efficiency.

7 is a cross-sectional view showing a light emitting diode package according to another embodiment of the present invention.

As mentioned in the description of the foregoing embodiment, the InGaN / GaN light emitting diode epiwafer grown on a general c-plane sapphire substrate has a piezoelectric effect due to compressive stress on the quantum well due to the difference in lattice constant and thermal expansion coefficient of the sapphire substrate and GaN. Since polarization occurs and spontaneous polarization also exists because the number of Ga atoms and N atoms are not the same, the band structure of the quantum well is bent, and the internal quantum efficiency decreases. As the current injection increases, the efficiency of the light emitting diode increases. A decreasing 'efficiency droop' phenomenon is seen. Therefore, by controlling the stress applied from the outside to reduce the bending of the quantum well of the light emitting diode epiwafer can improve the internal quantum efficiency and suppress the 'efficiency droop' phenomenon.

As shown in FIG. 7, in attaching the horizontal light emitting diode 220 including the sapphire substrate 221 to the upper surface of the base 210 by a die bonding method, the sapphire substrate 221 contacted with the base 110 is attached. If the thin film is formed by polishing, for example, when the upper surface of the base 210 to which the horizontal light emitting diode 220 is attached is formed into a concave curved surface having a curvature, the sapphire substrate 221 may be bent according to the curvature. In this way, by adjusting the curvature of the sapphire substrate 221 by adjusting the curvature of the top surface of the base 210, the stress applied to the horizontal light emitting diode 220 can be adjusted. It is preferable that the curved shape of the upper surface is a spherical shape. As a material for die bonding the light emitting diodes 220 to the base 110, an Ag-based paste or an Au—Sn alloy may be used.

As shown in FIG. 7, the horizontal light emitting diode 220 includes an sapphire substrate 221, an n-GaN layer 223, an active layer 225, and a p-GaN in a direction away from the sapphire substrate 221. Layers 227 in turn. A buffer layer 222 may be formed between the sapphire substrate 221 and the n-GaN layer 223 to mitigate lattice mismatch. A transparent electrode layer 228 such as, for example, indium tin oxide (ITO) may be formed on the p-GaN layer 227 for effective current dispersion. The horizontal light emitting diode 220, as is well known, has electrodes (preferably bonding pads) having different polarities when viewed from above, that is, the n-type electrode 229a and the p-type electrode 229b. As is well known, this structure is, as is well known, a portion of the p-GaN layer 225 and the active layer 225 etched to a depth that exposes the n-GaN 227, so that the p-GaN layer 223 Alternatively, the p-type electrode 229a may be formed on the transparent electrode layer 228 thereon, and the n-type electrode 229b may be formed on the n-GaN 227.

8 shows an EL spectrum of a horizontal light emitting diode according to the present embodiment, which includes a conventional horizontal light emitting diode having a flat bottom and a concave bottom having a curvature, more preferably, a substantially hemispherical concave bottom. have. In the case of a horizontal light emitting diode including a concave bottom surface having a curvature, the light output also increases along with the wavelength shift from the EL spectrum to the blue wavelength. This increase in light output is due to the increase in internal quantum efficiency because the light extraction efficiency is achieved in the same light emitting diode.

FIG. 9 shows a band change of an InGaN / GaN quantum well of a horizontal light emitting diode having a flat bottom surface and a horizontal light emitting diode including a concave bottom surface having a curvature. In the light emitting diode epi wafer grown on a general c-plane sapphire substrate, the band of the quantum well is bent by spontaneous polarization and piezoelectric polarization, so that the separation of electrons and hole wavelength functions occurs, thereby reducing the internal quantum efficiency. When the curvature of the light emitting diode epi wafer changes, stress is applied to alleviate the band warpage of the quantum wells, thereby increasing the overlap of the wavelength function of electrons and holes, thereby increasing the internal quantum efficiency and thus increasing the light output. have. The blue shift of the center wavelength of FIG. 9 is due to the effect of reducing band warpage due to the reduction of piezoelectric polarization and increasing the band gap.

10 and 11 are diagrams for describing modified embodiments of the present invention.

As shown in FIG. 10, a plurality of vertical light emitting diodes 320 may be arranged on the base 310. In this case, as shown in FIG. 10A, one convex curved surface 312 is formed on the base 310, and the plurality of vertical

light emitting diodes

320, 320, and 320 are formed on the curved surface 312. Alternatively, as shown in FIG. 10B, a plurality of

convex surfaces

312, 312, and 312 may be formed on the base 310, and the plurality of

curved surfaces

312, 312 and 312 may be formed. Each of the plurality of vertical

light emitting diodes

320, 320, and 320 may be die bonded to each other.

As illustrated in FIG. 11, a plurality of horizontal light emitting diodes 320 may be arranged on the base 410. In this case, as shown in FIG. 11A, one concave curved surface 412 is formed on the base 410, and the plurality of vertical

light emitting diodes

420, 420, and 420 are formed on the one concave curved surface 412. And alternatively, as shown in FIG. 11B, a plurality of concave

curved surfaces

412, 412, and 412 are formed on the base 410, and the plurality of concave

curved surfaces

412 and 412 are formed. Each of the plurality of horizontal

light emitting diodes

420, 420, and 420 may be die bonded to each other.

According to the embodiment described above, the 'efficiency droop' phenomenon generated during the high current injection is suppressed to realize a high output high efficiency horizontal light emitting diode having improved luminous efficiency. When the base light emitting diode is attached to the base concave curvature to form a structure or mechanism, and the curvature of the horizontal light emitting diode comprising a thin polished sapphire substrate on the curved surface, the horizontal light emitting diode is curvature of the bottom surface Bent by At this time, stress is applied to the light emitting diode epitaxial wafer, thereby changing the characteristics of the piezoelectric polarization of the quantum well layer. Therefore, the band structure of the quantum well layer is changed to increase the internal quantum efficiency and to suppress the 'efficiency droop' phenomenon. The horizontal light emitting diode package manufactured as described above can reduce the 'efficiency droop' phenomenon generated during high current injection, thereby obtaining a high output high efficiency horizontal compound semiconductor light emitting diode for lighting.

Claims

Base; And

A light emitting diode disposed on the base;

The curved surface is formed on the base,

The light emitting diode package, characterized in that attached to the curved surface.
The light emitting diode package of claim 1, wherein the light emitting diode is a vertical light emitting diode including a support substrate and semiconductor layers on the support substrate, and the curved surface is a convex curved surface.
The semiconductor device of claim 1 or 2, wherein the semiconductor layers include a p-GaN layer, an active layer, and an n-GaN layer in a direction away from the support substrate, and a p-type reflection between the p-GaN layer and the support substrate. A light emitting diode package, characterized in that a contact layer is interposed.
The light emitting diode package of claim 1 or 2, wherein the vertical light emitting diode is attached so that the bottom surface of the support substrate faces the curved surface, and the bottom surface of the support substrate has a concave curved surface.
The light emitting diode package of claim 1 or 2, wherein the support substrate is a metal substrate.
The light emitting diode package of claim 1 or 2, wherein the vertical light emitting diode is bent while being die bonded to the curved surface.
The light emitting diode package of claim 1 or 2, wherein the vertical light emitting diode is attached to the curved surface by Ag-based paste or Au-Sn alloy.
The light emitting diode package according to claim 1 or 2, wherein the curvature is 1 (m −1 ) to 100 (m −1 ).
The light emitting diode package of claim 1 or 2, wherein the curved surface is a spherical surface.
The light emitting diode package of claim 1 or 2, wherein a plurality of vertical light emitting diodes are arranged on the base, and the plurality of vertical light emitting diodes are attached to one curved surface on the base.
The light emitting diode package of claim 1 or 2, wherein a plurality of vertical light emitting diodes are arrayed on the base, and the plurality of vertical light emitting diodes are attached to each of a plurality of curved surfaces formed on the base.
The light emitting diode of claim 1, wherein the light emitting diode is a horizontal light emitting diode including a growth substrate and semiconductor layers formed on the growth substrate and having an n-type electrode and a p-type electrode thereon, and the curved surface is a concave curved surface. LED package.
The light emitting diode package of claim 12, wherein the growth substrate is a sapphire substrate, and the semiconductor layers sequentially include an n-GaN layer, an active layer, and a p-GaN layer in a direction away from the sapphire substrate.
The light emitting diode package of claim 12 or 13, wherein the horizontal light emitting diode is attached so that the bottom surface of the growth substrate faces the curved surface, and the growth substrate has a convex curved surface toward the base.
The light emitting diode package according to claim 12 or 13, wherein the horizontal light emitting diode is bent in a die-bonded state on the curved surface.
The light emitting diode package of claim 12 or 13, wherein the horizontal light emitting diode is attached to the curved surface by Ag-based paste or Au-Sn alloy.
The light emitting diode package according to claim 12 or 13, wherein the curvature is 1 (m −1 ) to 100 (m −1 ).
The light emitting diode package of claim 12 or 13, wherein the curved surface is a spherical surface.
The light emitting diode package of claim 12 or 13, wherein a plurality of horizontal light emitting diodes are arranged on the base, and the plurality of horizontal light emitting diodes are attached to one curved surface on the base.
The light emitting diode package of claim 12 or 13, wherein a plurality of horizontal light emitting diodes are arranged on the base, and the plurality of horizontal light emitting diodes are attached to each of the plurality of curved surfaces on the base.