KR20080081676A - Light emitting diode having patterned substrate and the method of fabricating the same - Google Patents

Abstract

A light emitting diode having a patterned substrate and a manufacturing method thereof are provided to improve light emission efficiency of the light emitting diode by optimizing a trade-off condition between crystal properties of a first conductive semiconductor layer and a chemical semiconductor layer and light reflection efficiency on a patterned substrate. A light emitting diode includes a substrate(21), a first conductive type semiconductor layer(31), an active layer(35), and a second conductive type semiconductor layer(37). The substrate is patterned to have protruded patterns and a recessed region. The first conductive type semiconductor layer is formed on the substrate. The active layer is formed on the first conductive type semiconductor layer. The second conductive type semiconductor layer is formed on the active layer. A distance between the recessed region and the active layer lies between 2 and 4 mum.

Description

LIGHT EMITTING DIODE HAVING PATTERNED SUBSTRATE AND THE METHOD OF FABRICATING THE SAME}

1 to 3 are cross-sectional views illustrating a method of manufacturing a light emitting diode according to an embodiment of the present invention.

4 and 5 are graphs showing the light extraction effect by the light emitting diode according to an embodiment of the present invention.

The present invention relates to a light emitting diode having a patterned substrate and a method of manufacturing the same.

Gallium nitride (GaN) series light emitting diodes have been applied and developed for about 10 years. GaN-based LEDs have changed the LED technology considerably and are currently used in a variety of applications, including color LED displays, LED traffic signals and white LEDs.

Recently, high-efficiency white LEDs are expected to replace fluorescent lamps. In particular, the efficiency of white LEDs has reached a level similar to that of conventional fluorescent lamps. However, there is a possibility that the LED efficiency is further improved, and thus continuous efficiency improvement is further required.

Two major approaches are being attempted to improve LED efficiency. The first is to increase the internal quantum efficiency, which is determined by the crystal quality and epilayer structure, and the second is to increase the light extraction efficiency.

Internal quantum efficiency is currently 70-80%, so there is not much room for improvement, but light extraction efficiency has much room for improvement. Improving light extraction efficiency has been a major challenge to eliminate the internal light loss by adopting a heat dissipation structure and a roughened surface.

On the other hand, the rough surface is adopted to prevent total reflection due to the difference in refractive index of the GaN series LED and its surroundings, such as the substrate and the atmosphere. Since the GaN-based semiconductor material has a high refractive index of about 2.4, the critical angle is relatively large. Light incident on the surface at an angle below the critical angle is totally reflected and returned back to the interior of the LED, which is reflected back and emitted outward, but some of it is absorbed by the LED or electrodes and lost to heat. The roughened surface prevents light incident on the surface from returning to the inside of the LED by total reflection to emit light to the outside.

Meanwhile, a technology that adopts a patterned sapphire substrate to improve light extraction efficiency is entitled "InGaN-Based Near-Ultravilolet and Blue-Light-Emitting Diodes with High External Quantum Efficiency Using a Patterned Sapphire Substrate and a Mesh Electrode". Published December 15, 2002 in the Japanese Journal of Applied Physics, Vol. 41, 2002, pp. L1431-L143.

According to the above paper, by forming convex hexagons by etching the sapphire substrate, it is possible to reduce the total loss of light is reflected between the LED and the substrate to improve the light extraction efficiency.

However, the light extraction efficiency of the light emitting diode has not yet reached a satisfactory level, and continuous efforts for improving the light extraction efficiency are required.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a light emitting diode having a patterned substrate capable of further improving light extraction efficiency and a method of manufacturing the same.

According to an aspect of the present invention for achieving this technical problem, a substrate patterned to have protruding patterns and recessed regions, a first conductive semiconductor layer formed on the substrate, and the first conductive semiconductor layer A light emitting diode comprising an active layer formed thereon and a second conductive semiconductor layer formed on the active layer, wherein the distance between the recessed region of the substrate and the active layer is 2 to 4 μm.

The light emitting diode may further include at least one of a buffer layer and an undoped layer between the substrate and the first conductive semiconductor layer. Preferably, the protruding patterns of the substrate may have a hemispherical shape.

According to another aspect of the invention, the method comprising the steps of preparing a patterned substrate having protruding patterns and recessed regions, forming a first conductivity type semiconductor layer on the substrate, and the first conductivity type semiconductor layer And forming a second conductive semiconductor layer on the active layer, wherein the distance between the recessed region of the substrate and the active layer is 2 to 4 μm. .

Preferably, the light emitting diode manufacturing method may further include forming at least one of a buffer layer and an undoped layer between the substrate and the first conductive semiconductor layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 to 3 are cross-sectional views illustrating a method of manufacturing a light emitting diode by forming a nitride semiconductor layer on a patterned substrate according to an embodiment of the present invention. Here, the nitride semiconductor layer is described as being formed using the MOCVD technique. However, the present invention is not limited to the MOCVD technique, and other techniques such as MBE may be used.

Referring to FIG. 1, first, a patterned substrate 21 is prepared. The substrate 21 may be a sapphire substrate, but is not limited thereto, and may be another substrate such as SiC. The patterned substrate 21 has protruding patterns 21a and recessed regions. The protruding patterns 21a may be mesh-shaped patterns, but more preferably island patterns. In addition, recessed regions are formed with generally flat bottom surfaces, as shown.

Referring to FIG. 2, a first conductivity type semiconductor layer is formed on the patterned substrate 21. Here, the N-type semiconductor layer is formed of the first conductive semiconductor layer. The N-type semiconductor layer may be formed by doping silicon (Si) on a GaN-based semiconductor layer, that is, (Al, In, Ga) GaN. The first conductive semiconductor layer 31 is first grown on the flat bottom surface of the substrate 21 to fill the recessed regions of the substrate 21 and to cover the tops of the island patterns 21a.

Subsequently, the first conductivity type semiconductor layer 31 is continuously grown to form a thickness of 2 to 4 μm from the bottom of the patterned substrate 21.

In this case, the thickness d of the first conductivity-type semiconductor layer 31 becomes an important factor in determining the light extraction efficiency of the light emitting diode.

The thickness of the first conductivity-type semiconductor layer 31 formed on the patterned substrate 21 is determined by the crystal quality and patterned substrate 21 of the active layer 35 and the second conductivity-type semiconductor layer 37. The reflection effect by the trade off.

When the thickness of the first conductivity type semiconductor layer 31 is thin, light generated in the active layer 35 and traveling toward the substrate 21 may be effectively reflected by the patterned substrate 21. However, when the thickness of the first conductivity-type semiconductor layer 31 is too thin, the crystallinity of the first conductivity-type semiconductor layer 31 falls off and thus the active layer 35 and the second conductivity-type semiconductor layer 37 which are grown later. There is a risk of dropping the crystallinity.

On the other hand, when the thickness of the first conductivity-type semiconductor layer 31 is sufficiently thick, the crystalline of the first conductivity-type semiconductor layer 31 is excellent, the active layer 35 and the second conductivity-type semiconductor layer ( The crystallinity of 37) can be made excellent. However, when the thickness of the first conductivity type semiconductor layer 31 is too thick, the role of the patterned substrate 21 with respect to the light generated in the active layer 35 and traveling toward the substrate 21 may be reduced.

Therefore, it is important to set the thickness to have a suitable light reflection effect by the patterned substrate 21 while maintaining the crystallinity of the first conductivity type semiconductor layer 31 to some extent. Experimental results show that the first conductivity type semiconductor layer 31 interposed between the recessed region of the patterned substrate 21 and the active layer 35 shows the maximum light extraction efficiency when the thickness is 2 to 4 μm. Confirmed.

When the first conductive semiconductor layer 31 is formed, the active layer 35 is formed on the first conductive semiconductor layer 31.

The active layer 35 is a region where electrons and holes are recombined, and includes, for example, InGaN / GaN. The emission wavelength emitted from the light emitting diode is determined by the type of material constituting the active layer 35. The active layer 35 may be a multilayer film in which a quantum well layer and a barrier layer are repeatedly formed. A quantum well layer and the barrier layer may be a semiconductor layer 2-to 4 won the compounds represented by the general formula _{Al x In y Ga 1 -x- y} N (0≤x, y, x + y≤1).

The second conductive semiconductor layer 37 is formed on the active layer 35. For example, the second conductivity-type semiconductor layer 37 may be doped with zinc (Zn) or magnesium (Mg) in GaN to form a P-type semiconductor layer.

Referring to FIG. 3, one region of the first conductive semiconductor layer 31 is exposed by patterning the second conductive semiconductor layer 37 and the active layer 35. In addition, a first electrode pad 41 is formed on the exposed first conductive semiconductor layer 31, and a transparent electrode layer 43 and a second electrode pad ( The light emitting diode is completed by forming 45).

4 and 5 are graphs showing the light extraction effect by the light emitting diode according to an embodiment of the present invention. FIG. 4 is a graph of light extraction efficiency simulation results and FIG. 5 is a graph of light flux measurement results.

N-GaN (n = 2.4) is used as the first conductivity type semiconductor layer, P-GaN (n = 2.4) is used as the second conductivity type semiconductor layer for simulation and measurement, and the diameter of the protrusion pattern 21a is A sapphire substrate (n = 1.76) having a thickness of 3.5 µm, a distance between the protruding patterns of 1.5 µm, and a thickness of 100 µm was used, and the thickness of the first conductive semiconductor layer was changed on the substrate.

The simulation result shown in FIG. 4 shows the maximum light extraction efficiency when the thickness of the first conductive semiconductor layer interposed between the substrate and the active layer is 2 μm to 4 μm. In the light flux measurement result shown in FIG. 5, the light plus was observed in the range of about 2.5 μm to 4 μm.

These simulation and measurement results result in the formation of the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer on the patterned substrate with the protruding patterns and recessed regions. The first conductivity type semiconductor layer interposed between the active layers has a thickness of 2 μm to 4 μm, which is optimal between the crystalline of the first conductivity type semiconductor layer and the compound semiconductor layer grown thereon and the light reflection efficiency by the patterned substrate. You will see it as a trade off condition.

The present invention is not limited to the embodiments described above, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

For example, in an embodiment of the present invention, the first conductive semiconductor layer is an N-type semiconductor layer and the second conductive semiconductor layer is a P-type semiconductor layer, but the first conductive semiconductor layer is a P-type. Modifications in which the semiconductor layer is used and the second conductivity-type semiconductor layer is used as the N-type semiconductor layer are possible.

In addition, in the present invention, the shape of the protruding pattern formed on the substrate is hemisphere, but the triangle, the quadrangle, the square, the tetragon, the trapezium, and the strip Various modifications are possible in the form of.

In addition, although the height of the protruding patterns and the distance between the protruding patterns are not specified, the result of the deformation thereof may be predicted to some extent.

Further, in an embodiment of the present invention, the first conductive semiconductor layer is formed on the substrate, but at least one of the buffer layer and the undoped layer may be interposed between the substrate and the first conductive semiconductor layer. The buffer layer or undoped layer is used to mitigate the lattice mismatch between the semiconductor layers to be formed thereon and the substrate. The buffer layer or undoped layer may be formed of nitride such as AlN, GaN or the like.

According to the present invention, when the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer are formed on a patterned substrate having protruding patterns and recessed regions, the recessed region and the active layer of the patterned substrate are formed. A light emitting diode having improved light extraction efficiency can be manufactured by suggesting an optimal trade-off condition between the crystalline of the interposed first conductive semiconductor layer and the compound semiconductor layer grown thereon and the light reflection efficiency by the patterned substrate. have.

Claims (5)

A substrate patterned with protruding patterns and recessed regions, A first conductivity type semiconductor layer formed on the substrate; An active layer formed on the first conductivity type semiconductor layer, A second conductive semiconductor layer formed on the active layer, The distance between the recessed region of the substrate and the active layer is 2 to 4 ㎛. The method according to claim 1, And at least one of a buffer layer and an undoped layer between the substrate and the first conductive semiconductor layer. The method according to claim 1, The protruding patterns of the substrate have a hemispherical shape. Preparing a patterned substrate with protruding patterns and recessed regions; Forming a first conductivity type semiconductor layer on the substrate; Forming an active layer on the first conductivity type semiconductor layer; Forming a second conductivity type semiconductor layer on the active layer, The distance between the recessed region of the substrate and the active layer is 2 to 4 ㎛. The method according to claim 4, And forming at least one of a buffer layer and an undoped layer between the substrate and the first conductive semiconductor layer.

Images