JPH07153993A - Light-emitting diode - Google Patents

Abstract

PURPOSE:To obtain high light-emitting efficiency by forming an inwardly curved slope spreading from a second clad layer toward a substrate and exposing the periphery of an active layer to the slant face. CONSTITUTION:A second clad layer 18 is smaller in area than a substrate 12, and a slope 24 including the edge of a first clad layer 14 on the substrate 12 and the upper edge of the second clad layer 18 is inwardly curved. The slope exposes an end face 26 of an active layer 16 and the periphery including the end face 26 forms a prescribed angle theta to an end face 28 of the substrate 12. Thereby, current density becomes high so as to obtain higher light-emitting efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for increasing the luminous efficiency of a light emitting diode.

[0002]

2. Description of the Related Art A first clad layer, an active layer and a second clad layer are sequentially laminated on a substrate, and an operating current is passed between the substrate and the second clad layer to generate in the active layer. There is known a surface emitting light emitting diode (hereinafter referred to as an LED) that takes out the emitted light from the second cladding layer side. Generally, in the LED having such a structure, the light generated in the active layer is attenuated or reflected by the time it reaches the surface of the second clad layer which is the light extraction surface, or the light other than the surface of the second clad layer is attenuated. Is also emitted from the substrate side, is reflected by the bottom surface of the substrate, and travels toward the side surface.Because the incident angle on the side surface is relatively large, the light is reflected and absorbed inside. Only a part of the generated light is extracted from the 2 clad layer side, and high luminous efficiency cannot be obtained. Therefore, in order to increase the luminous efficiency, for example, when assembling an LED,
The LED is fixed in the concave surface facing the opening side, the light emitted from the end surface is reflected by the concave surface, and the light is extracted in the same direction as the light extracted from the second cladding layer side.

[0003]

However, even with the above-mentioned assembly, the improvement of the luminous efficiency is still insufficient. In the above assembly structure, only the light emitted from the end face of the LED can be taken out, and
In order to sufficiently increase the reflection efficiency on the tapered surface, high-precision processing is required, which results in a great increase in cost, so that the reflection efficiency is also low.

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

[0005]

In order to achieve such an object, the gist of the present invention is that a first clad layer, an active layer and a second clad layer are sequentially laminated on a substrate,
The light generated in the active layer when an operating current is passed between the substrate and the second cladding layer
A surface emitting light emitting diode extracted from the side of a clad layer, wherein a slope is formed toward the outer peripheral side from the second clad layer toward the substrate, and the peripheral edge of the active layer is exposed on the slope. is there.

[0006]

With this configuration, a slope is formed between the second clad layer and the substrate, the peripheral edge of the active layer is exposed on the slope, and the second clad layer is more than the substrate. Since the area is small, the inclined surface is directed in the same direction as the light extracted from the second cladding layer side, that is, in the light extraction direction. Therefore, a part of the light emitted from the end face side of the active layer is directly emitted in the light extraction direction. Further, since the slope is oriented in the light extraction direction, the active layer has a larger area than the second cladding layer, and the active layer is generated at a portion located outside the surface of the second cladding layer. The light traveling from the active layer to the second cladding layer side is extracted before reaching the surface of the second cladding layer. So this light is
It is extracted with almost no attenuation or reflection in the LED. Further, the light emitted from the active layer to the substrate side, reflected by the bottom surface of the substrate, and directed to the side surface has a small incident angle of reflected light because the side surface is an inclined surface and is extracted to the outside through the inclined surface. . Therefore, a relatively large amount of light emitted from the side surface of the LED is extracted, attenuation and reflection of the generated light are reduced, and the light traveling toward the substrate side is also efficiently extracted, so that high luminous efficiency is obtained. Further, as a result of the formation of the inclined surface as described above, the active layer has a smaller area than the substrate, so that the current density becomes higher than that in the case where the areas are made equal, and higher luminous efficiency is obtained. can get.

[0007]

1 is a diagram showing the structure of an LED (light emitting diode) 10 according to an embodiment of the present invention. This LED
10 is, for example, on a substrate 12 by MOCVD (Metal Organic Chemical Vapor Deposit).
ion) method and molecular beam epitaxy (MBE: Molecular Be
am Epitaxy) method or vapor phase epitaxy (VPE: Va
por phase epitaxy) method, etc.
4, the active layer 16 and the second cladding layer 18 are sequentially grown, and then the lower electrode 20 and the upper electrode 22 are vapor-deposited on the lower surface of the substrate 12 and the upper surface of the second cladding layer 18, respectively. .

The substrate 12 is a compound semiconductor made of n-Al _0.4 Ga _0.6 As single crystal having a thickness of, for example, about 350 μm, and the first cladding layer 14 has a thickness of, for example, about 4 μm. A compound semiconductor made of Al _0.4 Ga _0.6 As single crystal, the active layer 16 is made of p-GaAs single crystal having a thickness of, for example, about 1 μm,
The second cladding layer 18 is, for example, p-A having a thickness of about 4 μm.
It is a compound semiconductor composed of l _0.4 Ga _0.6 As single crystal. In addition, the lower electrodes 20 are Au− in order from the substrate 12 side.
A Ge alloy, Ni, and Au are laminated and formed, and the upper electrode 22 is formed of an Au—Zn alloy on the second cladding layer 18 side.
Au is laminated thereon. The lower electrode 20 and the upper electrode 22 are ohmic electrodes.

Although the LED 10 has a substantially prismatic shape as a whole, the area of the second cladding layer 18 side is smaller than that of the substrate 12 side, and the area of the substrate 12 on the first cladding layer 14 side is smaller. The side surface 24 connecting the end portion and the end portion of the upper surface of the second cladding layer 18 is a curved inclined surface as shown in the figure. That is, a slope is formed which extends from the second cladding layer 18 toward the base 12 toward the outer peripheral side. Therefore, the first clad layer 14, the active layer 16, and the second clad layer 18 are stacked so as to taper from the substrate 12 side to form a substantially truncated pyramid shape, and the peripheral edge including the end face 26 of the active layer 16 is , An inclined surface forming a predetermined angle θ (for example, about 60 °) with respect to the end surface 28 of the substrate 12. In the figure, the substrate 12, the layers 14, 16, 18 and the electrode 2 are shown.
Sizes such as 0, 22 are not necessarily shown in exact proportions.

In the LED 10 configured as above, an operating voltage is applied to the lower electrode 20 and the upper electrode 22, and an operating current is passed between the first cladding layer 14 and the second cladding layer 18, Light is generated in the active layer 16, and the light is extracted from the upper surface side of the second cladding layer 18.

Here, in this embodiment, the LED 10 is used.
Since the above-mentioned side surface 24 of the above is a slope, the end portion of the active layer 16 has a size (width a) obtained by multiplying its thickness by tan θ,
It is directed upward in the drawing, which is the light extraction direction. Therefore, a part of the light emitted from the end surface 26 of the active layer 16 is directly emitted in the light extraction direction. Further, the area of the upper surface of the second cladding layer 18 is smaller than the area of the upper surface of the active layer 16, and the light generated within the width b in the figure is not emitted to the second upper surface before reaching the upper surface of the second cladding layer 18.
It is taken out from the end face of the clad layer 18. Therefore, this light is extracted in the LED 10 with almost no attenuation or reflection. In addition, the active layer 16 is radiated to the substrate 12 side and reflected by the bottom surface of the substrate 12 to form the side surface 24.
Since the side surface 24 is a slope, the angle of incidence of the light traveling toward is small, and the light that was reflected and absorbed inside due to the too large angle of incidence is extracted to the outside through the slope. . Therefore, a relatively large amount of light emitted from the side surface 24 is extracted, attenuation and reflection of the generated light are reduced, and the light traveling toward the substrate 12 side is also efficiently extracted, so that high light emission efficiency is obtained. Furthermore,
Since the active layer 16 has an area smaller than that of the substrate 12, the current density becomes higher than that in the case where the areas are made equal, and higher luminous efficiency can be obtained.

The LED 10 is, for example, as shown in FIGS.
It is manufactured according to the step (h). In the step (a), the first clad layer 14, the active layer 16 and the second clad layer 1 are formed on the substrate 12 for manufacturing a large number of LEDs 10.
Epitaxial layer 8 is sequentially grown to form epitaxial layer 30. Note that, in FIG. 2, the boundaries between the layers of the epitaxial layer 30 are omitted. Next, in the step (b), the upper electrode 22 having a predetermined pattern is formed on the epitaxial layer 30 by photolithography, and in the step (c), a photoresist film 32 is formed thereon, and the upper electrode 22 is formed by photolithography. Patterning is performed for each of the individual elements 34 that will be the LEDs 10. At this time,
As shown in (c), the upper electrode 22 is covered with the photoresist film 32. Next, in the step (d), etching is performed from the upper surface side of the epitaxial layer 30 with an etching solution in which phosphoric acid and hydrogen peroxide solution are mixed, for example. This etching solution is preferably one that does not dissolve the photoresist film 32 but only the epitaxial layer 30 and the substrate 12. At this time, since the respective layers of the epitaxial layer 30 and the substrate 12 have substantially the same solubility, they are dissolved so that a concave portion 36 having a substantially circular arc centered on a point P on the surface thereof is formed, and the composition and concentration of the etching solution are increased. By appropriately setting the processing temperature and the processing time, the upper surface of the epitaxial layer 30 is made slightly smaller than the upper electrode 22. Next, in the step (e), the photoresist film 32 is removed, and in the step (f), each element 34 is separated by dicing. At this time, the upper electrode 22 protruding from the upper surface of the epitaxial layer 30 by the etching process described above.
The peripheral portion of is removed by water flow or ultrasonic waves. Then, in the step (g), the lower electrode 20 is formed, and
The LED 10 shown in is manufactured. This LED10
In the step (h), the lower electrode 20 is fixed to the bottom surface of the case 40 having the tapered inner wall surface 38 so as to be electrically connected to a lead (not shown), and the lead 42 is connected to the upper electrode 22. It is bonded and used by being enclosed in a resin mold in a step (not shown).

In the above manufacturing process, the recess 36 is formed.
Is much larger than the width of the cutting margin of the dicing, and the recess 36 is formed up to a part of the upper portion of the substrate 12. Therefore, the element 34 is separated by the dicing in the step (f). Then, the lower end face of the substrate 12 is perpendicular to the bottom face thereof, but the end faces of the epitaxial layer 30 and a part of the substrate 12 form a slightly curved slope. Therefore, part of the epitaxial layer 30 and the substrate 12 has a substantially truncated pyramid shape, that is, the side surface 24 connecting the substrate 12 and the upper surface of the second cladding layer 18 shown in FIG. Is easily obtained.

In this embodiment, since the dicing is performed after the recess 36 is formed, the cutter does not touch the active layer 16 during the dicing. Therefore, the active layer 16
Etc., there is no chipping due to dicing, and current leakage is less likely to occur. Also, the tapered inner wall surface 3
Since the LED 10 is fixed in the case 40 provided with 8, the light emitted from the side surface of the active layer 16 in the direction parallel to the surface of the second cladding layer 18 is also reflected by the inner wall surface 38 of the light. It is directed in the take-out direction, and higher luminous efficiency is obtained.

FIG. 3 is a graph showing the light output, that is, the luminous efficiency when the etching time is changed in the step (d) of the above-mentioned manufacturing process. In the above-mentioned process, for example, by performing the treatment for 40 to 50 minutes, the LED 10 having a light output about 1.8 times higher than that of the LED not subjected to the etching treatment is obtained. The optimum etching time varies depending on conditions such as the type and concentration of the etching solution and the processing time and the processing temperature. However, if it is too short, the area of the epitaxial layer 30 will not be sufficiently small and the current density will not increase. Moreover, since the inclined portion on the side surface is not formed, a high light output cannot be obtained.
Further, even if the etching process is performed for a longer time than necessary, the current density increases, but the active layer 16, that is, the light emitting area decreases, so that the light output above a certain value cannot be obtained.

FIG. 4 is a graph showing the relationship between the current density and the light output when the operating current of the LED 10 is 50 mA. In this graph, the relative light output is shown with the light output of an LED with a current density of about 54 mA / cm ² used conventionally being 1. As is clear from the figure, the relative light output increases as the current density increases. In the LED 10 of the present embodiment, as a result of the above-mentioned configuration, the current density is as high as about 128 mA / cm ² , and as described above, a light output about 1.8 times higher than that of the conventional one can be obtained. is there. In addition, since this figure is the measurement result by the LED 10 having the above-described structure, the light output includes the effect of the side surface 24 being inclined as described above, and does not necessarily indicate the current density and the relative light output. It does not represent a strict relationship.

FIG. 5 shows an LED 44 according to another manufacturing method.
Is an example of. In this embodiment, the side surface 46 that connects the substrate 12 and the upper surface of the second cladding layer 18 is a straight slope that does not curve. Also in such a structure, similarly to the above-described embodiment, the end face 26 of the active layer 16 is a slope, the light emitted from the end face 26 is directed in the light extraction direction, and the side surface 46 is a slope. The attenuation and reflection of the light generated on the end side of the active layer 16 is reduced, and the light emitted to the substrate 12 side and reflected on the bottom surface thereof is extracted from the slope surface. Since the area is smaller than that of the substrate 12 and the current density is high,
High luminous efficiency can be obtained. Further, in this embodiment, since the side surface 46 is not curved, when the area ratio between the upper surface of the second cladding layer 18 and the bottom surface of the substrate 12 is made equal, the width a becomes larger than that of the LED 10 described above, and High luminous efficiency can be obtained. This LED 44 is, for example,
In the step of FIG. 2 described above, an etching solution that gives such a profile is used, or instead of the etching process, a groove is processed with a diamond cutter having a wide tip and a tapered tip, and then It can be obtained by performing dicing similarly to the step (f).

Incidentally, the above-mentioned LED 10 and LED 44
In the above, the upper electrode 22 is directly formed on the second cladding layer 18.
However, for example, as shown in FIG. 6, a current blocking layer 48 having a conductivity type different from that of the second cladding layer 18 is provided on the second cladding layer 18, and an upper electrode 22 is formed thereon. , LED 50 or the like. In the above-described embodiment, the upper electrode 22 is formed, for example, as shown in FIG. 7, and the portion to which the lead 42 is bonded, that is, the central portion 52 of the upper electrode 22 is energized to generate light. The light cannot be extracted because it is blocked by the upper electrode 22. On the other hand, in the LED 50, the central portion 52 cannot be energized due to the presence of the current blocking layer 48, and thus cannot emit light. That is, only the part where the light is extracted without being shielded by the upper electrode 22 is made to emit light, so that the efficiency of extracting the generated light is further increased and a high light output is obtained. The current blocking layer 48
Is formed into an arbitrary shape by, for example, photolithography.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in still another mode.

For example, in the above embodiment, GaA
s / AlGaAs double heterostructure surface emitting LED 1
However, the composition ratio of Al and Ga is appropriately set, and GaP, InP, InGaAs
Double-heterostructure LED composed of P etc., or simply pn
The invention can likewise be applied to LEDs consisting of junctions.
Further, the substrate 12 may be made of another semiconductor such as GaAs.

Also, in the above-described embodiment, the substrate 12
Although an n-type semiconductor is used for the side and a p-type semiconductor is used for the side of the second cladding layer 18 so that an operating current flows from the upper electrode 22 to the lower electrode 20, the p-type and the n-type are reversed. The operating current may flow in the opposite direction.

For example, in the above-mentioned embodiment, the inclination angle θ of the end face 26 of the active layer 16 is set to about 60 °, but this angle θ can take a value in the range of 10 to 80 °. Is.

Further, in the above-mentioned embodiment, when the first cladding layer 14 is relatively thick (for example, about 50 μm), the first cladding layer 14 may be inclined.

Further, in the above-mentioned embodiment, the LED 1
Although 0, 44, and 50 are all formed in a substantially prismatic shape, and the epitaxial layer 30 (that is, the first cladding layer 14 to the second cladding layer 18) and a part of the substrate 12 are formed in a quadrangular pyramid shape, The entire shape of the LED 10 and the like may be, for example, a polygonal column shape, and the epitaxial layer 30 and a part of the substrate 12 may be a polygonal pyramid shape including a triangular pyramid or a truncated cone shape. In the present invention, the active layer 16 has a smaller area than the substrate 12, and the end face 2
If the peripheral edge including 6 is exposed on the slope, that effect can be obtained. The shape of the LED 10 and the like can be easily changed by, for example, forming the upper electrode 22 and the photoresist film 32 in a polygonal shape or a circular shape in the step of FIG. 2 and performing an etching process.

Although not illustrated one by one, the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a light emitting diode that is an embodiment of the present invention, which is obtained by the manufacturing method of FIG.

FIG. 2 is a diagram showing a method for manufacturing a light emitting diode according to an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between etching time and light output in the step of FIG.

FIG. 4 is a graph showing the relationship between the current density and the light output of the light emitting diode obtained in the process of FIG.

FIG. 5 is a diagram showing another embodiment of the present invention.

FIG. 6 is a diagram showing still another embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of electrodes of the light emitting diode of FIG. 1.

[Explanation of symbols]

 10: LED (light emitting diode) 12: Substrate 14: First clad layer 16: Active layer 18: Second clad layer 22: Upper electrode 24: Side surface 26: End surface (periphery) of active layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Goki Sone 18 Minamikamochi, Kagiya-cho, Tokai City, Aichi Prefecture (72) Inventor Yoshiyuki Mizuno 2-194 Kosha, Meito-ku, Nagoya City, Aichi Prefecture

Claims (1)

[Claims] 1. A first clad layer, an active layer and a second clad layer are sequentially laminated on a substrate, and an operating current is passed between the substrate and the second clad layer so that the active layer is formed in the active layer. A surface emitting light emitting diode for extracting generated light from a side of the second cladding layer, wherein a slope is formed toward an outer peripheral side from the second cladding layer toward the substrate, and the peripheral surface of the active layer is formed on the slope. A light-emitting diode characterized by being exposed.