JPH06334215A - Surface emitting light emitting diode - Google Patents

Abstract

(57) [Summary] [Object] To provide a chip-shaped surface-emitting light-emitting diode capable of obtaining high luminous efficiency. [Structure] Of the light traveling upward from the active layer 16 located directly below the ohmic electrode 24, light in the angle range smaller than 78.7 ° with respect to the thickness direction of the chip is conventionally shielded by the ohmic electrode 24. However, according to the surface-emitting light-emitting diode 10, 6 of the angular range is
Light in the angle range of 3.04 ° or more shown in A is the low refractive index layer 2
The light is emitted from the chip side surface 30 to the outside by being reflected by the boundary surface 25 with 0 and then by the reflecting surface 32, and thus contributes to the brightness. Therefore, the luminous efficiency is higher than that of the conventional light emitting diode. Will be higher.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Light emitting diodes are widely used in optical communication and displays. Such a light emitting diode is generally formed on a semiconductor substrate by liquid phase epitaxy (LPE).
axy) method or other epitaxial growth method is used to form the pn junction. Usually, one kind of such a light emitting diode is provided with a light extraction surface having an electrode partially provided, an active layer which is provided in parallel with the light extraction surface and which generates light, and an active layer provided below the active layer. The active layer is provided with a reflection means for reflecting the light emitted downward from the active layer toward the light extraction surface, for example, a BR layer formed on the bottom surface of the chip or on the semiconductor substrate. There is known a chip-shaped surface emitting light emitting diode that emits the emitted light from the light extraction surface. According to the surface emitting light emitting diode of this type, the light emitted downward from the active layer is reflected toward the light extraction surface side by the reflecting means, so that the light emitting efficiency is relatively improved.

[0003]

The electrode provided on the light extraction surface of the conventional surface emitting light emitting diode is necessary for supplying a current for generating light to the active layer. Since it is made of a metal that does not transmit light, such as aluminum and gold, the light extraction area is reduced, and sufficient luminous efficiency cannot be obtained yet. Since the current density of the active layer in the portion of the active layer located immediately below the electrode is high, the electrode prevents the light having relatively high brightness generated from that portion from being extracted from the light extraction surface.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a chip-shaped surface-emitting light emitting diode which can obtain high luminous efficiency.

[0005]

The inventors of the present invention have made various studies in view of the above circumstances, and as a result, have found that the distance between the active layer and the light extraction surface is lower than that of the layer positioned above the active layer. It has been found that by providing a low-refractive index layer having a refractive index, light that was conventionally blocked by an electrode can be guided to the outside. The present invention has been made based on such findings.

That is, the gist of the present invention is to
An electrode is provided on a part of the light extraction surface, an active layer is provided in parallel with the light extraction surface to generate light, and an active layer is provided below the active layer and extends downward from the active layer. A chip-shaped surface-emitting light-emitting diode, comprising: a reflection means for reflecting the emitted light, wherein the light emitted from the active layer is emitted from the light extraction surface. This is because a low refractive index layer having a relatively lower refractive index than the layer positioned on the light extraction surface side of the active layer is provided between the layer and the surface.

[0007]

With this configuration, the light emitted from the active layer toward the light extraction surface side is formed at the interface between the layer located on the light extraction surface side of the active layer and the low refractive index layer. Of these, light having an inclination angle of a predetermined value or more with respect to the thickness direction of the chip is totally reflected. Therefore, of the light emitted from the portion of the active layer located immediately below the electrode and originally obstructed by the electrode, the light having an inclination angle larger than the above-mentioned predetermined value is totally reflected by the boundary surface to the outside from the side surface of the chip. Taken out. Further, of the light generated from the active layer other than the portion immediately below the electrode, the light having an inclination angle with respect to the thickness direction larger than a predetermined value is also extracted to the outside from the side surface of the chip in the same manner as described above.

Since the distance between the electrode and the active layer is small, the light emitted upward from the active layer directly below the electrode is relatively largely blocked by the electrode. Of the light emitted upward, Light larger than a predetermined angle with respect to the thickness direction of the chip is totally reflected at the boundary surface between the layer located on the light extraction surface side of the active layer and the low refractive index layer, and is extracted to the outside from the side surface of the chip. , High luminous efficiency can be obtained. In addition, since the light generated from the active layer other than the portion immediately below the electrode is extracted to the outside from the light extraction surface and the side surface of the chip,
The existence of the boundary surface does not affect the extraction of light generated from the active layer other than the portion immediately below the electrode.

[0008]

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 a chip-shaped surface-emitting light emitting diode 1 having a double hetero structure according to an embodiment of the present invention.
It is a figure for demonstrating the laminated constitution of 0. In the figure,
The light emitting diode 10 includes a cladding layer 14, an active layer 16, a cladding layer 18, and a low refractive index layer 2 on a substrate 12.
0, the cap layer 22, and the ohmic electrode 24 are sequentially stacked.

The substrate 12 is an n-Al _0.1 Ga _0.9 As compound semiconductor having a thickness of about 200 μm, and the cladding layer 14 is an n-Al _0.45 Ga having a thickness of about 4 μm.
_0.55 As compound semiconductor, active layer 16 is a p-GaAs compound semiconductor having a thickness of about 0.1 μm, cladding layer 1
8 is p-Al _0.45 Ga _0.55 having a thickness of about 12 μm.
As compound semiconductor, the low refractive index layer 20 is a p-Al _0.6 Ga _0.4 As compound semiconductor having a thickness of about 0.1 μm,
The cap layer 22 is a p-G layer having a thickness of about 0.1 μm.
Each of these layers is, for example, metal organic chemical vapor deposition (MOCVD).
cal Vapor Deposition) method and molecular beam epitaxy (MBE; M
olecular beam epitaxy method or vapor phase epitaxy (V
By PE (Vapor Phase Epitaxy) method or the like, it is formed by sequentially growing in a single crystal state on the substrate 12 in a common chamber. The ohmic electrode 24 has an area smaller than the light extraction surface 26, for example, 120 μm on the light extraction surface 26 on the cap layer 22 by using a well-known photolithography technique.
It is a p-type Au-Zn electrode provided in the central portion at φ.

The low refractive index layer 20 is made of p-Al _x Ga.
By setting the mixed crystal ratio x of the _1-x As compound semiconductor to 0.6, the refractive index n ₂₀ is set to 3.20, which is lower than the refractive index n ₁₈ = 3.29 of the adjacent clad layer 18. ing. The refractive index n ₂₀ of the low refractive index layer 20 is made smaller as the mixed crystal ratio x is increased, but on the contrary, since the resistance value is increased, the mixed crystal ratio x is set to 0.6 in this embodiment. -ing Therefore, in order to reduce the total reflection angle, the mixed crystal ratio x of the low refractive index layer 20 is further increased from 0.6 to lower its refractive index n ₂₀ , or the Al mixed crystal ratio of the cladding layer 18 is lowered. Then, n ₁₈ may be increased.

By thus making the refractive index n ₂₀ of the low refractive index layer 20 relatively lower than that of the cladding layer 18, at the interface 25 between the low refractive index layer 20 and the cladding layer 18, With the light having an emission wavelength of 880 nm of the active layer 16, the light toward the upper light extraction surface 26 is totally reflected in the angle range with respect to the thickness direction (vertical direction in FIG. 1) of 63.04 ° or more.

In the surface-emitting light-emitting diode 10 constructed as above, the ohmic electrode 24 to the substrate 1
When a drive current is applied to the ohmic electrode 28 provided on the bottom surface of the second electrode 2, light having a wavelength of 880 nm is generated from the active layer 16. Of the light traveling from the active layer 16 toward the light extraction surface 26 side that is not located immediately below the ohmic electrode 24, the light in the angle range of 63.04 ° or less with respect to the thickness direction of the chip passes through the low refractive index layer 20. , Is radiated from the light extraction surface 26 to the outside, while being 6 in the thickness direction of the chip.
The light in the angle range of 3.04 ° or more is totally reflected by the boundary surface 25 between the cladding layer 18 and the low refractive index layer 20, but emitted from the chip side surface 30 to the outside. Further, since the light that goes downward from the portion of the active layer 16 that is not located directly below the ohmic electrode 24 is reflected upward by the reflecting surface 32,
It is taken out in the same manner as above. In any case, the light emitted upward and downward from the active layer 16 in the portion not directly below the ohmic electrode 24 is emitted to the outside from the light extraction surface 26 or the chip side surface 30 and contributes to the brightness.

On the other hand, the light emitted from the active layer 16 located immediately below the ohmic electrode 24 is assumed to have an effective distance of 12 μm between the active layer 16 and the ohmic electrode 24, and as shown in FIG. Light emitted from the active layer 16 on the center line of the active layer 16 will be described below.
The light in the angle range of 8.7 ° or less and the light in the angle range of 8.2 ° or less with respect to the thickness direction of the chip of the light traveling downward from the active layer 16 are emitted to the outside by the ohmic electrode 24. Was blocked, which was one of the reasons why the luminous efficiency was not obtained. However, in this embodiment, the light in the angle range of 63.04 ° or more out of the light traveling upward from the active layer 16 located directly below the ohmic electrode 24 is totally reflected by the boundary surface 25, and then the above-mentioned reflection is performed. The light is emitted from the side surface 30 of the chip by being reflected by the surface 32 and contributes to the brightness, so that the light emission efficiency is increased at a predetermined rate as compared with the conventional light emitting diode. In addition,
Active layer 1 located directly under the ohmic electrode 24
Of the light traveling downward from 6, the light of 8.2 ° to 63.04 ° with respect to the thickness direction of the chip is reflected by the reflecting surface 32 and then passes through the boundary surface 25 to reach the light extraction surface 26. However, the light of 63.04 ° or more is totally reflected by the boundary surface 25 and reaches the chip side surface 30.

As described above, in the related art, since the distance between the ohmic electrode 24 and the active layer 16 is small, of the light emitted upward from the active layer 16 in a portion located immediately below the ohmic electrode 24, the chip of the light is emitted. 78.7 in the thickness direction
Light in a large angle range of less than or equal to ° was blocked by the ohmic electrode 24 and could not contribute to the brightness. However, according to the surface-emitting light emitting diode 10 of the present embodiment, the thickness of the chip among the light emitted to the upper side is The light in the relatively large angle range of 63.04 ° to 78.7 ° with respect to the direction, that is, the light in the angle range shown in FIG. 2A is totally reflected by the boundary surface 25 with the low refractive index layer 20. Since the light is taken out from the side surface 30 of the chip, the luminous efficiency can be improved. Since the density of the current passing through the active layer 16 in the portion directly below the ohmic electrode 24 is high, the effect is remarkable.

Further, according to the present embodiment, the light emitted upward from the portion of the active layer 16 located immediately below the ohmic electrode 24 is refracted at the boundary surface 25 and is extracted to the outside by the ohmic electrode 24. Since the angle range in which is blocked is reduced,
There is an advantage that the luminous efficiency can be improved.

FIG. 3 is a view corresponding to FIG. 1 showing another embodiment of the present invention. In the figure, an n-type light wave interference type light reflection layer 40 is provided between the cladding layer 14 and the substrate 12. The light wave interference type light reflection layer 40 is formed of, for example, a pair of AlAs layers and Al layers each having a thickness of several tens of μm.
It is configured by laminating dozens to dozens of pairs of _0.2 Ga _0.8 As layers, has a relatively wide reflection band with a center wavelength of about 880 to 900 nm according to the principle of Bragg reflection, and has 880 nm from the active layer 16. And a light having a longer wavelength than that can be reflected.

Also in this embodiment, as shown in FIG.
Of the light traveling upward from the active layer 16 located immediately below the ohmic electrode 24, light in the angle range of 63.04 ° or more is totally reflected by the boundary surface 25, and then reflected by the reflective surface 32. Then, the light is radiated to the outside from the chip side surface 30 and contributes to the brightness. Therefore, light in a relatively large angle range of 63.04 ° to 78.7 °, that is, the angle range shown in A of FIG. Light is totally reflected by the boundary surface 25 and is extracted to the outside from the chip side surface 30, so that the luminous efficiency is improved.

In the embodiment shown in FIGS. 1 and 3, the active layer 1 in that portion is located immediately below the ohmic electrode 24.
6 has a structure in which the current density is high.
In order to relatively increase the current density in the portion not directly underneath, even in the structure in which the conductivity of that portion is increased by doping impurities such as Zn into the portion other than directly under the ohmic electrode 24 You can enjoy tentative effects.

Further, in the above-described embodiment, the ohmic electrode 24 is directly provided on the light extraction surface 26, but
It is a p-type compound semiconductor layer configured in the same manner as the light wave interference type light reflection layer 40 for the purpose of reflecting the light generated from the active layer 16 toward the ohmic electrode 24 side downward. It may be indirectly provided on the light extraction surface 26 via a layer having the same area as the ohmic electrode 24.

Also, n in the embodiment of FIGS. 1 and 3 described above is used.
And p may be inverted. In the low refractive index layer 20 in such a case, the refractive index n ₂₀ can be lowered to about 2.97.

Further, although the surface emitting light emitting diode 10 of the above-mentioned embodiment has a GaAs / AlGaAs double hetero structure, it is a light emitting diode made of another compound semiconductor such as GaP, InP, InGaAsP, or a single hetero structure, or It may be a light emitting diode having a homo structure.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a laminated structure of a surface-emitting light emitting diode that is an embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of the surface emitting light emitting diode of FIG.

FIG. 3 is a view corresponding to FIG. 1 of another embodiment of the present invention.

FIG. 4 is a diagram illustrating an operation of the surface emitting light emitting diode of FIG.

[Explanation of symbols]

 10: surface emitting light emitting diode 16: active layer 20: low refractive index layer 24: ohmic electrode 26: light extraction surface 32: reflecting surface (reflecting means) 40: light wave interference type light reflecting layer (reflecting means)

Claims (1)

[Claims] 1. A light extraction surface having an electrode partially provided thereon, an active layer provided in parallel with the light extraction surface to generate light, and an active layer provided below the active layer from the active layer. In a chip-shaped surface-emitting light-emitting diode, which is provided with a reflection means for reflecting light emitted toward the lower side, and is adapted to emit light generated from the active layer from the light extraction surface, A surface emitting light emitting diode comprising a low refractive index layer having a relatively lower refractive index than a layer located above the active layer between the active layer and the light extraction surface.