JPH05145119A - Light emitting diode - Google Patents

Abstract

PURPOSE:To make it possible to enhance outer quantum efficiency through a relative reduction in void light emitting under an electrode, and what is more, emit short wavelength light with higher efficiency. CONSTITUTION:An electrode 16, which is installed on the surface 30 of a light emitting diode (semiconductor chip), is provided with a substantially semi- circular-shaped pad portion 18. It is further provided with primary branches 19a to 19d extending linearly from the pad portion 18 and secondary branches 20a, 20b, and 20c extending linearly from each of the primary branches 19a to 19d, and third branches extending linearly from each of the secondary branches 20a, 20b and 20c, at the least.

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 used for display or the like.

[0002]

2. Description of the Related Art Recently, as a light emitting diode (LED) which emits yellow or green light, a material using AlGaInP based material in addition to GaAsP or GaP based material is being developed.

A conventional AlGaInP-based LED is manufactured as follows. First, as shown in FIG. 6, n-type Ga
On the surface 100 of the As substrate 90, an n-type AlGaInP clad layer 91, an undoped AlGaInP light emitting layer 92, a p-type AlGaI.
An nP clad layer 93, a p-type AlGaAs current diffusion layer 94, a p-type GaAs contact layer 95, and a p-side electrode 96 are laminated on the entire surface. Next, as shown in FIG. 7, the electrode 96 and the p-type GaAs layer 95 are partially removed and patterned. That is, the electrode 96 is composed of a circular pad portion 98 for wire bonding and branches 99a, 99b, 99c and 99d linearly extending from the pad portion 98 in all directions. By providing a plurality of branches in this way, the current is diffused in the chip as uniformly as possible. Then, the n-side electrode 97 is formed on the back surface of the substrate 90. Light emitted from the light emitting layer 92 is absorbed by the substrate 90 and the electrode 96,
Area 100 of the chip surface 100 from which the electrode 96 has been removed
The light is emitted from the a and the side surface 101 to the outside of the chip.

In this LED, the light emitting layer 92 has two clad layers 9 having a band gap larger than that of the layer 92.
It has a double hetero structure sandwiched by 1,93. Here, in order to effectively confine electrons and holes in the light emitting layer 92 by the cladding layers 91 and 93, the cladding layer 9
The composition of _{1,93 (AlyGa 1- y) 0.} 5 In 0. Certain Al ratio y is necessary to increase the 0.7 to 1 in ₅ P. However,
When the Al mixed crystal ratio y is increased in this way, it becomes difficult to p-type or n-type doping into the layer, and the cladding layer 91,
It becomes difficult to reduce the specific resistance of 93. Therefore, in this LED, the current diffusion layer 94 is provided to prevent the current from concentrating immediately below the electrode 96, thereby increasing the amount of light emission in the region 100a not covered by the electrode 96.

[0005]

However, the function of the current spreading layer 94 is not sufficient, and as a result, the electrode 9
The amount of ineffective light emission immediately below 6 is larger than that in the region 100a not covered with the electrode 96. For this reason,
The conventional LED described above has a problem that external quantum efficiency is low.

The emission wavelength is 590 nm (yellow) to 550 nm.
Since it is nm (green), there is a problem that light absorption occurs in the AlGaAs current diffusion layer 94. This is because Al x Ga _1- x As has an absorption edge of 574 nm and does not transmit light having a wavelength shorter than this even if the mixed crystal ratio x = 1 that provides the widest band gap is set. AlAs (corresponding to x = 1) is easily corroded in air and is not suitable for use as a surface layer.

Therefore, an object of the present invention is to provide a light emitting diode which can relatively reduce the ineffective light emission right under the electrode to improve the external quantum efficiency, and at the same time, can omit the current diffusion layer and efficiently emit light of a short wavelength. To provide.

[0008]

In order to achieve the above object, the present invention has an electrode on the surface of a semiconductor chip, and emits light to the outside of the chip from a region of the chip surface not covered by the electrode. In the light emitting diode, the electrode has a substantially circular pad portion, a primary branch linearly extending from the pad portion, and a linear branch linearly branching from the primary branch. It is characterized in that it has at least a secondary branch and a tertiary branch linearly branched from the secondary branch.

Further, it is desirable that the line widths of the branches of the respective orders become thinner as the order increases.

Further, it is desirable that the length of each branch is shortened at a constant rate as the order increases.

Further, it is desirable that the angle between the branches of each order is 0 ° or 90 °.

[0012]

In order to compensate for the large current diffusion resistance, it is sufficient that the electrode is located at a distance not far from any part of the light emitting layer. However, if the area of the electrode is simply increased, it becomes difficult to emit light to the outside of the chip. If the electrode width is narrowed in order to avoid this point, then the wiring resistance at the electrode increases. The present invention is to harmonize such contradictory conditions as much as possible.

According to the present invention, the electrode provided on the surface of the chip has the primary branch extending from the pad portion, the secondary branch extending from the primary branch, and further the secondary branch. Two
Because it has a third branch that extends from the next branch
(It may have higher-order branches), and the chip surface is in a dendritic state covered by the branches of each order.
As a result, the current is spread to every corner of the chip, and the current spreading resistance is substantially reduced. Therefore, the light emission in the region not covered with the electrode is relatively larger than the ineffective light emission right under the electrode. Therefore, the light is easily emitted to the outside of the chip, and the external quantum efficiency is improved. Further, since the current can be sufficiently diffused in the chip by the shape of the electrode, it is not necessary to provide an AlGaAs current diffusion layer in an AlGaInP LED having a wavelength shorter than yellow.
Therefore, even if the light having a short wavelength is absorbed, it has a preferable characteristic. The shape of this electrode is AlGaInP system LE.
Not only D, but also general AlGaAs series, GaP series, ZnSe
It is applied to LED, GaN, and SiC LEDs. As a result, the characteristics of various LEDs can be improved.

When the line widths of the branches of each order become narrower as the order increases, the area of the chip surface directly below the electrodes does not increase so much, and the current spreading resistance is effectively reduced. .. Therefore, the external quantum efficiency is further improved. Moreover, since the line width of the low-order branch is relatively wide, the wiring resistance hardly increases. Further, when the line width of each branch described above is made thinner at a constant rate as the order increases, the pattern design of the electrode becomes easier.

If the length of each branch is shortened at a constant rate as the order increases, the chip surface is efficiently covered with each branch. That is, almost all of the surface of the chip is covered in a dendritic manner, with the higher-order branches hardly overlapping each other. Moreover, since the length of each branch is shortened at a constant rate as the order increases, the pattern design of the electrode becomes easy.

When the angle between the branches of each order is 0 ° or 90 °, similarly, the branch surface of each order effectively covers the chip surface. That is, substantially the entire surface of the chip is covered in a dendritic manner without the higher-order branches overlapping each other. Moreover, the pattern design of the electrode becomes easy.

[0017]

The light emitting diode of the present invention will be described in detail below with reference to examples.

1 and 2 show the AlGaInP system L of the first embodiment.
The chip surface and the chip cross section of the ED are shown respectively.
As shown in FIG. 1, electrodes 16 are provided on the chip surface 30. The electrode 16 is provided with a circular pad portion 18 having a predetermined size for wide bonding in the center. From the pad portion 18, the first-order branch 19a is formed linearly in a diagonal direction.
19b, 19c and 19d extend. The first branch 19a,
19b, 19c and 19d have the same line width and the same length. The secondary branches 20a, 20b, 2 in three directions from the tips of the primary branches 19a, 19b, 19c, 19d, respectively.
0c is branched and extends. The angle formed by the primary branch and the secondary branch is 0 ° or 90 °. By design, each of the first-order branches 19a, 19b, 19c, 19
There is a secondary branch (not shown) that overlaps d. The secondary branches 20a, 20b, 20c have the same line width and the same length as each other, and both the line width and the length are ½ of those of the primary branch. Also, each secondary branch 20a, 2
Third-order branches 21a, 21b, and 21c linearly extend in three directions from the ends of 0b and 20c, respectively. Second
The angle between the next branch and the third branch is 0 ° or 90
It has become °. In addition, the third branch 21a, 21b, 21
c has the same line width as each other, and both the line width and the length of the secondary branch are ½. In addition,
The third from the middle of each first-order branch 19a, 19b, 19c
The next branch is branched, but this is the branch of each primary 19
This is because there is the tip of the secondary branch (not shown) that overlaps a, 19b, and 19c. Furthermore, each third branch 21
Fourth-order branches 22a, 22b, 22c are branched and extended linearly in three directions from the tips of a, 21b, 21c, respectively.
The angle formed by the third-order branch and the fourth-order branch is 0 ° or 90 °. Also, the fourth-order branches 22a, 22b,
The line widths 22c have the same line width and the same length, and the line widths and lengths of the third branch lines 21a, 21b, 21c are both 1/2.

As described above, the number of branches of this electrode 16 is the same in every branch, and the relationship between the lower-order branch and the higher-order branch is 1 / length at the four tips of the'X 'shape. It is a regular and similar self-similar shape that is a combination of 2'X's, that is, a fractal shape. Therefore, the pattern can be designed easily. Further, substantially the entire surface 30 of the chip can be covered in a dendritic manner without the high-order branches overlapping each other. Further, since the wiring width of the low-order branch is relatively wide, the wiring resistance can be suppressed low. This is because a lower branch has a larger current flow. However, if the wiring resistance is sufficiently small even if the wiring width is thin, it is not necessary to increase the wiring width.

As shown in FIG. 2, the electrode 16 is made of Al
It is provided on the surface 30 of the GaInP-based chip. This chip is manufactured as follows. First, MOCVD (metalorganic chemical vapor deposition) on the back surface of the n-type GaAs substrate 10.
Thus, the n-type AlGaInP clad layer 11, the undoped light emitting layer 12, the p-type AlGaInP clad layer 13, and the p-type AlGa
An As contact layer 14, a p-type GaAs contact layer 15, and an electrode 16 are sequentially formed on the entire surface. Next, by photolithography, the electrode 16 and the contact layers 14 and 15 are partially removed and patterned so that the electrode 16 has the shape shown in FIG. After that, the electrode 17 is also formed on the back surface side of the substrate 10. Unlike the prior art, the p-type AlGaAs contact layer 14 is only under the electrode 16 and does not function as a current diffusion layer.

As described above, this AlGaInP-based LED
Since the chip surface 30 is covered with the electrodes 16 in a dendritic manner, the current can be diffused to every corner of the chip without providing a current diffusion layer, and the current diffusion resistance can be substantially reduced. Therefore, the light emission in the region 30a not covered by the electrode 16 can be relatively increased as compared with the ineffective light emission right under the electrode 16. Therefore, it becomes easier to emit light to the outside of the chip, and the external quantum efficiency can be improved. In addition, since the current diffusion layer is not provided, it is possible to prevent absorption of light of short wavelength. When the characteristics were actually measured, the emission wavelength was 570
The external quantum efficiency was 1.5% in nm (yellowish green).

The position of the pad portion 18 is determined by the chip surface 3
It is not limited to the center of 0, but may be in the peripheral portion.

Further, the pattern shape of the electrode 16 may be formed by so-called mask vapor deposition (vapor deposition using a metal mask having an opening having the same shape as the electrode 14) instead of etching.

The material of the LED is not limited to AlGaInP, but AlGaAs, GaAsP, GaP, Al
III-V group compound semiconductors such as GaN and GaInAsP,
It may be a II-VI group compound semiconductor such as ZnCdSSe or ZnCdSeTe, or a chalcopyrite semiconductor such as CuAlSSe or CuGaSSe.

The substrate material is not limited to GaAs, but may be GaP, InP, sapphire, or the like, and may be opaque or transparent with respect to the emission wavelength.
The conductivity type of the substrate may be n-type or p-type.

Further, in this embodiment, the electrode 16 having a branch is provided on the side of the chip surface 30, but when a substrate transparent to the emission wavelength is used, the electrode 17 on the back side of the substrate is also provided with a branch. Thereby, the light emission efficiency can be further improved.

The junction at the interface of the light emitting layer 12 is not limited to the double hetero junction, but a single hetero junction,
It may be homozygous.

Further, each of the semiconductor layers 11, ...
It was formed by D method (metalorganic chemical vapor deposition method), but MBE method
(Molecular beam epitaxy method), VPE method (vapor phase growth method), LPE
It may be formed by a method (liquid phase growth method) or the like. The pn junction may be formed during crystal growth or may be formed by diffusing a dopant after crystal growth.

FIGS. 3 and 4 show the AlGaAs LE of the second embodiment.
The chip surface and the chip cross section of D are respectively shown. As shown in FIG. 3, the electrode 45 provided on the chip surface 60
Is a substantially circular pad portion 48, primary branches 49a and 49b linearly extending from the pad portion 48, secondary branches 50a and 50b, and tertiary branches 51a and 51b. The fourth branch 52a, 52b, the fifth branch 53a, 53b, and the sixth branch 54a, 54b are included. Each branch above is'H '
The shape is a fractal shape in which four tips of the shape are repeatedly combined with'H 'having a length of ½. In this example, each branch is formed by a line parallel to the four sides of a square chip, so that pattern design can be performed easily.

As shown in FIG. 4, the electrode 45 is made of Al
It is provided on the surface 60 of the GaAs-based chip. When manufacturing this chip, first, the n-type A is formed on the n-type GaAs substrate 40.
lGaAs layer 41, p-type AlGaAs light-emitting layer 42, p-type AlGaA
An s layer 43 and a p-type GaAs contact layer 44 are formed, and subsequently, an electrode 45 is formed on the entire surface of the substrate and an electrode 46 is formed on the entire surface of the substrate. Then, the contact layer 44 and the electrode 45 are partially etched and patterned to have the shape shown in FIG.

This AlGaAs LED has a chip surface 6
Since 0 is covered with the electrode 45 in a dendritic manner, the external quantum efficiency can be improved as in the first embodiment.
In addition, since the current diffusion layer is not provided, it is possible to prevent absorption of light of short wavelength.

FIG. 5 shows the AlGaInP system L of the third embodiment.
The chip surface of ED is shown. The electrode 75 provided on the chip surface 70 includes a pad portion 78 having a substantially circular shape, primary branches 79a and 79b, and secondary branches 80a, 80b and 80.
c, 80d, 80e and third-order branches 81a, 81b, 81c, 81d, 81e, which are branched from the respective second-order branches 80a, ..., 80e.
81f, 81g, 81h, 81i, and third-order branches 81a, ...
Fourth branch 82a, 82b, 82c, 8 branched from 81i
Has 2d. That is, the first-order branches 79a, 7a are formed on the straight line AB passing through the pad portion 78 and parallel to the chip side surface 71.
9b is provided, and the first branch 79a, 79b is perpendicular to the second branch 79a.
Five branches 80a, ..., 80e are provided. Further, the third branch 81a, perpendicular to each second branch 80a, ..., 80e,
..., eight 81i are provided. The third branch is not actually formed in the pad portion 78 or the portion overlapping the first branch 79a, 79b. Furthermore, the third
The fourth branch 82a, perpendicular to the next branch 81a, ..., 81i
..., 82d is provided. The branches on each side have a thicker portion on the side of the pad portion 78 through which a large amount of current flows. Although this example is not a fractal in a narrow sense because the number of branches is different depending on the degree of branching, the design concept is fractal.

The internal structure of the AlGaInP LED chip is the same as that of the first embodiment, and the description thereof is omitted. In this AlGaInP-based LED, the chip surface 70 is covered with the electrodes 75 in a dendritic manner, so that the external quantum efficiency can be improved as in the first and second embodiments. Further, since the current diffusion layer is not provided, it is possible to prevent absorption of light of short wavelength.

[0034]

As is apparent from the above, in the light emitting diode of the present invention, the electrode provided on the surface of the chip has a pad portion having a substantially circular shape, and a linear portion extending linearly from the pad portion. At least a branch, a secondary branch that is branched from the first branch and extends linearly, and a third branch that is branched from the second branch and linearly extends. Since it has, the surface of the chip can be covered with each branch in a dendritic manner, and the current spreading resistance can be substantially reduced. Therefore, the light emission in the region not covered with the electrode can be made relatively larger than the ineffective light emission right under the electrode, and the external quantum efficiency can be improved. Moreover, the current diffusion layer can be omitted, and as a result, even light with a short wavelength can be efficiently emitted.

When the line width of each branch is thinned at a constant rate as the order increases, the current spreading resistance is effectively reduced without increasing the area directly below the electrodes on the chip surface. The external quantum efficiency can be further improved. Moreover, an increase in wiring resistance can be suppressed, and the electrode pattern can be easily designed.

If the lengths of the branches of each order are shortened at a constant rate as the order increases, it is possible to prevent the branches of higher orders from overlapping with each other, and substantially the entire surface of the chip. Can be covered in a dendritic manner. Moreover, the electrode pattern can be easily designed.

Further, when the angle between the branches of each order is 0 ° or 90 °, it is possible to avoid that the branches of higher orders overlap each other, and substantially the entire surface of the chip is covered. Can be covered in a dendritic manner. Moreover, the electrode pattern can be easily designed.

[Brief description of drawings]

FIG. 1 is an AlGaInP system LE according to a first embodiment of the present invention.
It is a figure which shows the surface electrode pattern of D.

FIG. 2 is a view showing a chip cross section of the LED.

FIG. 3 is an AlGaAs LED according to a second embodiment of the present invention.
It is a figure which shows the surface electrode pattern of.

FIG. 4 is a view showing a chip cross section of the LED.

FIG. 5: AlGaInP system LE of the third embodiment of the present invention
It is a figure which shows the surface electrode pattern of D.

FIG. 6 is a view showing a chip cross section of a conventional AlGaIn LED.

FIG. 7 is a diagram showing a surface electrode pattern of the conventional AlGaInP-based LED.

[Explanation of symbols]

10, 40 n-type GaAs substrate 11 n-type AlGaInP clad layer 12 Andove light emitting layer 13 p-type AlGaInP clad layer 14 p-type AlGaAs contact layer 15 p-type GaAs contact layer 16, 17, 45, 46, 75 electrode 18, 48, 78 Pad portion 19a, ..., 19b, 49a, 49b, 79a, 79b First branch 20a, 20b, 20c, 50a, 50b, 80a, ..., 80e Second branch 21a, 21b, 21c, 51a, 51b, 81a, ..., 81i Third branch 22a, 22b, 22c, 52a, 52b, 82a, ..., 82d Fourth branch 30, 60, 70 Chip surface 31, 61, 71 Chip side surface 41 n Type AlGaAs layer 42 p type AlGaAs light emitting layer 43 p type AlGaAs layer 44 p type GaAs contact layer 53a, 53b 5th branch 54a, 54b 6th branch

Front page continued (72) Inventor Tadashi Takeoka 22-22 Nagaike-cho, Nagano-cho, Abeno-ku, Osaka-shi, Osaka Prefecture (72) Instructor Osamu Yamamoto 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture

Claims (4)

[Claims] 1. A light emitting diode having an electrode on the surface of a semiconductor chip and emitting light to the outside of the chip from a region of the chip surface which is not covered with the electrode, wherein the electrode has a substantially circular pad portion. A linear branch extending linearly from the pad portion, a secondary branch linearly branching from the primary branch, and a secondary branch further extending from the primary branch. A light-emitting diode having at least a third-order branch that branches and extends linearly. 2. The light emitting diode according to claim 1, wherein the line width of the branches of each order becomes narrower as the order increases. 3. The light emitting diode according to claim 1, wherein the length of each branch is shortened at a constant rate as the order increases. 4. The light emitting diode according to claim 1, wherein an angle between the branches of each order is 0 ° or 90 °.