JPH0786635A - Light emitting diode - Google Patents

Abstract

PURPOSE:To obtain a light emitting diode that delivers a high luminous efficiency, by forming on a light extract surface a large number of projections of inverted mesa structure. CONSTITUTION:When a driving current flows from the upper electrode 26 to the lower electrode 24 in a light emitting diode 10, light is emitted from the luminous layer 18 in the diode. Light that is directed to the opposite side to the substrate 12, is externally extracted through the upper face, or the light extract surface 28, of the light extract layer 22 parallel with the luminous layer 18. The light extract surface 28 has a large number of projections 30 formed thereon. These projections 30 are of reverse mesa structure, which reduces the percentage of light going from the luminous layer 18 to the opposite side to the substrate 12, being totally reflected. This increases the quantity of light externally extracted through the light extract surface 28, and thus improves the luminous efficacy of the light emitting diode 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode, and more particularly to a technique for improving luminous efficiency.

[0002]

2. Description of the Related Art In a light emitting diode, light generated from a light emitting layer formed on a substrate is usually extracted to the outside and used. However, the light generated from the light emitting layer is not always fully utilized,
High luminous efficiency is desired. Even the light traveling from the light emitting layer, which is relatively easy to extract to the outside, to the side opposite to the substrate is partially absorbed by the surface electrode during repeated total reflection, while the light traveling from the light emitting layer to the substrate side enters the light emitting diode. It is easy to be confined and is difficult to be effectively used because it is absorbed by the substrate and the lower electrode. For this reason, conventionally, only about 1/10 of the light generated from the light emitting layer is used.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light emitting diode having high luminous efficiency.

The inventors of the present invention have conducted various studies to achieve the above object, and as a result, on the light extraction surface through which the light generated from the light emitting layer is taken out, a large number of irregularities of a mesa structure or a large number of spherical shapes are formed. It has been found that the formation of the concave surface allows the light traveling from the light emitting layer to the side opposite to the substrate to be efficiently extracted. Further, it has been found that the light emitting efficiency of the light emitting diode can be suitably improved by forming a groove on the side surface of the substrate and reflecting the light traveling from the light emitting layer toward the substrate side by the inner wall surface of the groove. It was The present invention has been made based on such knowledge.

[0005]

[Means for Solving the Problems] That is, the gist of the first invention for achieving the above-mentioned object is to have a light emitting layer which emits light, and to emit light emitted from the light emitting layer. In the light emitting diode of the type in which the light is emitted to the outside through the extraction surface, a large number of convex portions having an inverted mesa structure are formed on the light extraction surface.

[0006]

According to this structure, the large number of convex portions formed on the light extraction surface have an inverted mesa structure, so that of the light traveling from the light emitting layer to the side opposite to the substrate. The proportion of total internal reflection is reduced, and the amount absorbed by the upper electrode is reduced. Therefore, the amount of light extracted from the light extraction surface to the outside is increased, so that the luminous efficiency of the light emitting diode is improved.

[0007]

A second aspect of the present invention for achieving the above object is to have a light emitting layer which emits light, and to emit light emitted from the light emitting layer. In the light emitting diode of the type in which the light is emitted to the outside through the extraction surface, a large number of spherical concave surfaces are formed on the light extraction surface.

[0008]

With this configuration, since a large number of spherical concave surfaces are formed on the light extraction surface, the proportion of the light reflected from the light emitting layer to the side opposite to the substrate is totally reflected. Less and less absorbed by the upper electrode. Therefore, a large amount of light is extracted from the light extraction surface to the outside, so that the luminous efficiency of the light emitting diode is improved.

[0009]

A third aspect of the invention for achieving the above object is to provide a substrate and a plurality of semiconductor layers including a light emitting layer laminated on the upper surface of the substrate. In the light emitting diode having, a concave groove is formed on a side surface of the substrate by removing a boundary portion between the substrate and the semiconductor layer, and an inner wall surface of the concave groove allows light traveling from the light emitting layer to the substrate side to a side. This is because a reflecting surface for reflecting the light is formed.

[0010]

According to this structure, a concave groove is formed on the side surface of the substrate by removing the boundary between the substrate and the semiconductor layer, and the inner wall surface of the concave groove separates the light emitting layer from the light emitting layer. Since the reflecting surface for reflecting the light traveling toward the substrate side to the side is formed, a part of the light traveling from the light emitting layer toward the substrate is reflected by the reflecting surface to the side of the substrate. Go to Such light is reflected by the stem or the like and contributes to the brightness of the light emitting diode, so that the light emitting efficiency of the light emitting diode is suitably enhanced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the structure of a light emitting diode 10 according to an embodiment of the present invention. In the figure, a light emitting diode 10 is an LED having an epitaxial structure,
A substrate 12 made of aAs (n-type gallium-arsenic compound semiconductor) single crystal having a thickness of about 350 μm, and a large number of pairs of n-Al sequentially laminated on the substrate 12 by crystal growth.
_0.2 GaAs / AlAs Bragg reflection layer 14, n-Al
Clad layer 1 made of _0.45 GaAs and having a thickness of about 2 μm
6, a light emitting layer 18 made of p-GaAs having a thickness of about 0.1 μm, a clad layer 20 made of p-Al _0.45 GaAs having a thickness of about 12 μm, and p-Al _0.1 Ga _0.9 A
The light extraction layer 22 is made of s and has a thickness of about 1.5 μm. A lower electrode 24 and an upper electrode 26 for supplying a current are provided on the bottom surface of the substrate 12 and the top surface of the light extraction layer 22.

In the light emitting diode 10 described above, when a drive current is passed from the upper electrode 26 to the lower electrode 24, light is emitted from the light emitting layer 18, and the light traveling toward the side opposite to the substrate 12 is parallel to the light emitting layer 18. The light is extracted from the upper surface of the light extraction layer 22, that is, the light extraction surface 28. This light extraction surface 28 has a surface shown in FIGS.
As shown in, a large number of convex portions 30 are formed. The convex portions 30 are provided at intervals of about 2 to 4 μm.

As shown in FIG. 2, the convex portions 30 have a rectangular shape in a plan view and are regularly arranged at regular intervals with rectangular concave holes 32 shown by diagonal lines. 3 shows the cross-sectional shape of the convex portion 30 in the reverse mesa direction, and FIG. 4 shows the cross-sectional shape of the convex portion 30 in the forward mesa direction. The reverse mesa direction is G
When the etching treatment is performed in the [1 1 0] direction of the aAs single crystal, a cross section perpendicular to the direction becomes an inverted mesa (inverted trapezoid) shape. The forward mesa direction is GaA.
When the etching process is performed on the s single crystal in the direction shown in Formula 1, a cross section perpendicular to the direction becomes a mesa (trapezoid) shape.

[0015]

[Equation 1]

The convex portion 30 provided on the light extraction surface 28 of the light emitting diode 10 is formed as follows.
First, a wafer on which the electrodes 24 and 26 are formed is prepared, the light extraction surface 28 is degreased and washed, and then patterning is performed by a normal photolithography technique using a lattice-shaped mask as shown in FIG. Next, the concave hole 32 is formed by etching using a phosphoric acid-based etchant. Then, when the resist is removed, the convex portion 30 is formed.

The light emitting diode 1 constructed as described above.
0, a large number of convex portions 30 formed on the light extraction surface 28
Has a reverse mesa structure, when light is radiated from the light emitting layer 18, the light which has been totally reflected in the related art is reversely tapered as shown by the alternate long and short dash line in FIG. Light is extracted from the side of the. For this reason, the proportion of the light traveling from the light emitting layer 18 to the side opposite to the substrate 12 is totally reflected, and the amount absorbed by the upper electrode 26 is reduced. Therefore, the amount of light extracted from the light extraction surface 28 to the outside increases, so that the light emission efficiency of the light emitting diode 10 is improved.

6 and 7 show a light extraction surface 28 according to another embodiment of the present invention. On the light extraction surface 28 of this embodiment, a large number of spherical concave surfaces 34 are arranged at intervals of about 5 μm, and rhomboid projections 36 having flat tops are formed between the spherical concave surfaces 34. GaAs single crystal [11
If the reverse mesa direction which is the [0] direction is an oblique direction as shown in FIG. 6, a reverse taper is also formed on the edge portion 38 of the diamond-shaped projection 36 parallel to the reverse mesa direction.

Also in this embodiment, a large number of spherical concave surfaces 34 and rhomboid projections 36 are formed by performing the same etching treatment as in the above-mentioned embodiments, but the resist mask 40 shown in FIG. 8 is used. That is, small holes 42 of about 2 μm are arranged in the resist mask 40 at intervals of about 5 μm, and etching is performed with the resist mask 40 formed as shown in FIG.

The light emitting diode 1 configured as described above
At 0, since a large number of spherical concave surfaces 34 are formed on the light extraction surface 28, when light is emitted from the light emitting layer 18, it is emitted from any light emitting point of the light emitting layer 18, as shown in FIG. Even the light is extracted to the outside through each spherical concave surface. For this reason, the proportion of the light traveling from the light emitting layer 18 to the side opposite to the substrate 12 is totally reflected, and the amount absorbed by the upper electrode 26 is reduced. Therefore, the amount of light extracted from the light extraction surface 28 to the outside increases, so that the light emission efficiency of the light emitting diode 10 is improved.

Further, in this embodiment, the diamond-shaped projection 36 has an inverted mesa structure in a cross section parallel to the reverse mesa direction, and the edge portion 38 has an inverse taper.
As shown in FIG. 3, since the light that has been totally reflected in the related art is extracted to the outside, the light emitting efficiency of the light emitting diode 10 is further enhanced.

FIG. 11 shows another resist mask 44 different from the above resist mask 40. In the present embodiment, since the small holes 42 are arranged in a staggered pattern, the spherical concave surfaces 34 are formed alternately on the light extraction surface 28, and triangular projections are formed between the spherical concave surfaces 34. It is formed in place of the diamond-shaped protrusion 36.

FIG. 12 shows a light emitting diode 5 according to another embodiment.
0 configuration is shown. In the figure, the light emitting diode 5
Reference numeral 0 denotes an LED having an epitaxial structure, which is n-Ga
A transparent substrate 52 made of As single crystal and having a thickness of about 250 μm, and 0.3 μm made of n-Al _x GaAs (x = 0.1 to 0.45) sequentially laminated on the substrate 52 by crystal growth. Buffer layer 54 with a thickness of approximately n-Al
Clad layer 5 made of _0.45 GaAs and having a thickness of about 2 μm
6, a light emitting layer 58 made of p-GaAs having a thickness of about 0.1 μm, a clad layer 60 made of p-Al _0.45 GaAs having a thickness of about 12 μm, and a cap layer 62 made of p-GaAs having a thickness of about 0.1 μm. Is equipped with.
A lower electrode 64 and an upper electrode 66 for supplying a current are provided on the bottom surface of the substrate 52 and the top surface of the cap layer 62.

A concave groove 70 is formed on the side surface of the substrate 52 by removing the boundary portion of the substrate 52 with the buffer layer 54, and the inner wall surface 72 of the concave groove 70 extends from the light emitting layer 58 to the substrate 52 side. A reflecting surface for reflecting light to the side is formed. The groove 70 is formed by the etching process described below.

First, the wafer on which the electrodes 24 and 26 have been formed is attached to an adhesive tape, and the chips are divided by a dicing machine to be arranged on the adhesive tape at substantially equal intervals. FIG. 13 shows the state of the chip. On the other hand, when etching is performed by immersing the chips, which are arranged on the adhesive tape at substantially equal intervals, in an etchant using NH ₄ OH and H ₂ O ₂ by immersing the chips in the selective etchant, the substrate 52 having a small Al mixed crystal ratio And cap layer 6
2 is partially removed to form a light emitting diode chip as shown in FIG. Here, the reason why the portion of the side surface of the substrate 52 adjacent to the buffer layer 54 is deeply etched is not clear, but the distribution of the flow rate of the etchant, the uneven distribution of lattice defects of the substrate 52, and the like are considered.

The light emitting diode 5 constructed as described above.
0, the side surface of the substrate 52 is provided with a groove 70 in which the boundary portion of the substrate 52 with the buffer layer 54 is removed.
Due to the inner wall surface 72 of the groove 70, the light emitting layer 58 is separated from the substrate 5
Since the reflecting surface for reflecting the light traveling toward the 2 side to the side is formed, a part of the light traveling from the light emitting layer 58 toward the substrate 52 side is reflected by the reflecting surface and is reflected by the substrate 52 side. Head towards. Since such light is reflected by the stem or the like and contributes to the brightness of the light emitting diode 50, the light emitting efficiency of the light emitting diode 50 is suitably enhanced.

Further, according to the present embodiment, since the side surface of the substrate 52, including the inside of the concave groove 70, has fine frosted glass-like irregularities formed by the etching process, the substrate which has been totally reflected in the prior art. There is an advantage that the light in 52 is extracted to the outside.

The line A in FIG. 14 shows an etching time for forming the groove 70 and a light output ratio of the light emitting diode 50 having the groove 70 having a depth formed by the etching time. It shows the relationship with the ratio (when the light output is 1 when it is not present). As is clear from this, as the groove 70 becomes deeper, the amount of light traveling from the light emitting layer 58 toward the substrate 52 side is reflected by the inner wall surface 72 of the groove 70 and increases toward the side, and thus the light is emitted. Efficiency is improved. It is also considered that the deeper the groove 70 is, the smaller the absorption in the substrate 52 is. Figure 1
The line B of 4 shows the case where the groove 70 is formed by performing the etching while being fixed to the Kovar stem.

Although one embodiment of the present invention has been described above with reference to the drawings, the present invention can be applied to other modes.

For example, in the embodiment described above, FIG.
The light extraction surface 68 of the light emitting diode 50 may be formed with a large number of convex portions 30 having an inverted mesa structure shown in FIG. 3 and a large number of spherical concave surfaces 34 shown in FIG. 7. By doing so, the amount of light extracted from the light emitted from the light emitting layer 58 toward the side opposite to the substrate 52 is increased, and the light emission efficiency is further enhanced.

In the embodiment of FIG. 1 described above, 1.
The 5 μm light extraction layer 22 does not need to be Al _0.1 Ga _0.9 As, and is not used because GaAs has absorption, but AlGaAs may be used.

The light extraction layer 22 is not always necessary, and a large number of convex portions 30 and spherical concave surfaces 34 may be formed directly on the surface of the Al _0.45 Ga _0.55 As clad layer 20. In this case, it is easier to use a layer having a smaller Al mixed crystal ratio than Al _0.45 Ga _0.55 As because selective etching can be performed.

In the embodiment of FIG. 2 described above, the convex portion 30 of the inverted mesa structure is rectangular in plan view, but it may be polygonal or circular.

In the embodiment of FIG. 6 described above, the spherical concave surface 34 is formed in a circular shape in plan view, but it may be a polygonal shape.

The above description is merely one embodiment of the present invention, and the present invention can be variously modified without departing from the gist thereof.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a light emitting diode according to an embodiment of the present invention.

FIG. 2 is a plan view showing an enlarged light extraction surface of the embodiment of FIG.

FIG. 3 is a view showing a cross-sectional shape in the reverse mesa direction on the light extraction surface of the embodiment of FIG.

FIG. 4 is a view showing a cross-sectional shape in the forward mesa direction on the light extraction surface of the embodiment of FIG.

5A and 5B are views for explaining the light extraction action in the convex portion of the inverted mesa structure of the embodiment of FIG.

FIG. 6 is a view corresponding to FIG. 2 in another embodiment of the present invention.

7 is a diagram corresponding to FIG. 3 in the embodiment of FIG.

8 is a diagram illustrating an etching mask used for forming a spherical concave surface in the embodiment of FIG.

9 is a view showing a state in which an etching mask is formed on the light extraction layer in the embodiment of FIG.

FIG. 10 is a diagram for explaining the light extraction action of the spherical concave surface in the embodiment of FIG.

FIG. 11 is a view corresponding to FIG. 8 showing an etching mask of another embodiment of the present invention.

FIG. 12 is a view corresponding to FIG. 1 in another embodiment of the present invention.

13 is a view showing a chip shape before forming a concave groove of the light emitting diode of the embodiment of FIG.

FIG. 14 is a diagram showing the relationship between the etching time of a groove and the light output ratio in the example of FIG.

[Explanation of symbols]

 10, 50: Light emitting diode 12, 52: Substrate 28, 68: Light extraction surface 30: Convex portion of inverted mesa structure 34: Spherical concave surface 70: Recessed groove 72: Inner wall surface (reflection surface)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Imaizumi 2-chome 38-302, Nakamachi, Ichinomiya, Aichi (72) Inventor Yoshiyuki Mizuno 2-194, Kosha, Meito-ku, Nagoya, Aichi (72) Invention Sone Gone Sone 18 Minamikamochi, Kagiya-cho, Tokai City, Aichi Prefecture Daido Special Kochita Dormitory

Claims (3)

[Claims] 1. A light emitting diode having a light emitting layer which emits light, wherein the light emitted from the light emitting layer is emitted to the outside through a light extraction surface, and a large number of convex portions having an inverted mesa structure are provided in the light emitting diode. A light-emitting diode formed on the extraction surface. 2. A light emitting diode of a type having a light emitting layer which emits light, wherein the light emitted from the light emitting layer is emitted to the outside through a light extraction surface, and a large number of spherical concave surfaces are formed on the light extraction surface. A light emitting diode characterized by the above. 3. A light emitting diode having a substrate and a plurality of semiconductor layers including a light emitting layer laminated on an upper surface of the substrate, wherein a recess formed in a side surface of the substrate by removing a boundary portion between the substrate and the semiconductor layer. A light emitting diode, wherein a groove is provided, and a reflection surface for laterally reflecting light traveling from the light emitting layer toward the substrate side is formed by an inner wall surface of the groove.