JPS5839080A - Light emitting diode - Google Patents

Abstract

PURPOSE:To obtain a light emitting diode which is largely increased in the light coupling amount to an optical fiber with high light power and emitting intensity by disposing a plurality of light emitting units which are not electrically independent on the same chip in high density at an interval longer than the relation that spherical lenses mounted thereon are contacted each other. CONSTITUTION:An N type AlGaAs layer 2, a P type GaAs light emitting layer 3, a P type AlGaAs layer 4 and an N type AlGaAs layer 5 are sequentially grown on an N type GaAs substrate. A P type region 7 is diffused with Zn from the surface after forming circular recesses 61-67. Spherical lenses 81-87 engaged with the recesses 61-67 are bonded fixedly via transparent epoxy resin 9. When a voltage is applied between a P-side electrode 10 and an N-side electrode 11 with the P side as positive, a current is concentrated under the recesses 61-67, thereby simultaneously emitting lights from the circular parts isolated in seven from the layer 3. The emitted lights are produced from the seven circular windows, and are emitted as luminous flux having good directivity via the spherical lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a light emitting diode that has high output power, high radiance, and can be coupled with a source fiber with high efficiency.

Various structures have been devised as high-radiance light-emitting diodes, but among them, a light-emitting diode (hereinafter abbreviated as LED) with a ball lens attached to the light-emitting part was developed by KEE, Transa. ctionone
on Electron Devices, vo
llE-24, A'7, P, P, 986-9
As detailed in 90.1977, it has excellent characteristics that enable highly efficient coupling with optical fibers close to the theoretical limit.

Figure 1 shows a conventional ball lens with which the present invention is based:
L]! This is a cross-sectional view showing the basic structure of tD.
) are N-type GaAs substrates, (2), (3), (4) and (5) I/'i were each grown sequentially on the main surface of the N-type EAAS substrate (1) by liquid phase growth. N type A1Ga
They are an As layer, a P-type GILAa light-emitting layer, a P-type AIGaAe layer, and an N-type AlGaAs layer. (6) is a circular recess formed by selective etching. The dotted area (7) in the figure is a P-shape area formed by diffusing in from the surface after forming the circular recess (6), and below the recess (6), the P-shape A
It has reached the lGaAs layer (4). (8) is a circular recess (
6) is a spherical lens fitted with a lens made of a material that is transparent to the emission wavelength. This ball lens (8) is made of an adhesive medium that is transparent to the emission wavelength, such as an epoxy resin (9).
It is fixed with adhesive. (10) and (11) are the P-side and N-side electrodes provided on the P shadow area (7) and the N-type GaAs substrate (1), respectively, and the P-side electrode (10) has a circular recess ( The upper part of 6) is removed in a circular shape. In this structure, P 4wJ electrode (1
0) and the N-side electrode (11), when a voltage is applied with the P side as the positive side, the flowing current is caused by the P-type AlGaAs layer (4) K The light is concentrated in the circular part that it reaches, and emits light in the circular part of the P-type GaAs light emitting layer (3) below it. This light emitting layer (3)
Because AlGaAs has a wider forbidden band width than GaAs, the light from AlGaAs is not absorbed and is emitted from the circular part where the Nt pole (xO) has been removed, and is emitted by the ball lens (8) fixed with adhesive. It is converted into a luminous flux with a narrow half-value angle and good directional characteristics.

Because the directivity of the emitted light beam improves, it becomes possible to couple with an optical fiber with high efficiency close to the theoretical limit.With this conventional structure, in order to achieve high efficiency coupling, it is necessary to use a ball lens (8). The diameter DL of the optical fiber to be coupled needs to be selected to be approximately the same as the core diameter Dr of the optical fiber to be coupled, and the emission diameter DE determined by the diameter of the circular recess (6) is determined by the increase in coupling efficiency by using a spherical lens. Since the ratio is proportional to DF/DE in principle, it is advantageous to make it smaller, but if it is too small, the operating current density will become high and the output will reach saturation before obtaining a sufficient amount of output light. , is usually designed to have a value of about 1/2 to 1/4 of the spherical lens diameter Dt.An optical fiber used for optical fiber communication usually has a core diameter DF of 150 μm.
For this type of optical 7-eyeper, the emission diameter DE is approximately 30 to 40 μm. However, due to recent advances in optical fiber manufacturing technology, the core diameter DF has increased to 20
It has become possible to obtain optical fibers with a large diameter of 0.07Im or more and low loss, and the application of an optical transmission system that transmits a large amount of light using such a large diameter optical 7-eyeper is now being considered. However, the IFiD of the conventional structure has the drawback that it cannot obtain a coupled light amount corresponding to the rate of increase in the core area of the optical fiber when used for such a large diameter optical fiber. In other words, even if the emission diameter DE and the spherical lens diameter Dt are simply increased in accordance with the optical fiber core diameter, in the conventional structure, the peripheral length of the light emission part increases only in proportion to the first power of the emission diameter. It will only decrease if Therefore, the current value at which the optical output saturates is also proportional to the first power of the emission diameter, and even if the core area of the optical fiber increases n2 times, the optical output is limited to saturation, and the connection to the optical fiber is limited to the saturation of the optical output. The amount of valley light is suppressed to about n times. Figure 2 shows the luminous diameter part μm and the luminous diameter 10
The graph shows a comparison of the optical characteristics of LEDs with a conventional structure of 0 μm, where A/ indicates the case where the emission diameter is 1100p, and B indicates the case where the emission diameter is 35 μm. Even though the area of the light emitting part is approximately 9 times larger, the LID has a light emitting diameter of 100 μm.
The current value at which the optical output of is saturated is Ll! with a luminous diameter of 35 μm.
It can be seen that the increase is only about three times that of iD.

The present invention attempts to eliminate the above-mentioned drawbacks of the conventional method by arranging a plurality of electrically non-independent light emitting parts on the same chip at a high density at a distance that is longer than the distance between the ball lenses attached thereon. That is. Hereinafter, the LED according to the present invention will be explained in detail using the drawings.

FIG. 3 shows an embodiment of an IFiD according to the present invention;
The same parts as in FIG. 1 are designated by the same symbols, and detailed explanation thereof will be omitted. In the figure, on an N-type GaA3 substrate (1), an N-type AlGaAs layer (2), a P'-type GaAs light emitting layer (3), a P-type AlGaAs layer (4), an N-type AlGaAs
As in FIG. 1, the layers (5) are grown sequentially.

Next, as shown in the figure, seven circular recesses (61
) to (67) are formed. The dotted area in the cross-sectional view (η is the P shadow area formed by diffusing Zn from the surface after forming the circular recesses (61) to (67); each recess (61)
~(67) reaches the P-type AlGaAs layer (4). (81) to (87) are the circular recesses (61) to (6
7), which are each fitted with a spherical lens, each of which is adhesively fixed with a transparent epoxy resin (9).

(10) and (11) are the P-side and N-side electrodes, respectively, as in FIG.
Seven circular parts for extracting light have been removed corresponding to 1) to (67). Also in this structure, when a voltage is applied between the P-side electrode (10) and the N-side electrode (11) with the P side being the positive side, the current flows through each of the circular recesses (61) to (
67) and the corresponding P-type GaAs light-emitting layer (3
) emits light simultaneously in seven separate circular parts.

Emitted light is extracted from the seven circular windows of the P-side electrode (10), and is emitted as a highly directional light beam by the ball lens above, as in the conventional structure. In this embodiment, the conventional structure 111! has seven light emitting parts and one light emitting part of the same diameter. ! Compared to D, although the effective area of the light emitting part is seven times larger, the peripheral length of the light emitting part is also seven times larger, and each light emitting part is spaced apart, so the series resistance and thermal resistance are approximately 1
/7.

Therefore, the current value that causes optical output saturation increases by about 7 times, and it is possible to obtain an output that is about 2 times higher than when the light emitting diameter is 3 times -1 with the conventional structure. Wear. Figure 4 shows this effect, and shows a conventional Lfi structure with a spherical lens of 300 μm in diameter and a light emission diameter of 100 μm.
The light output-current characteristics of D (A) and the LED (B) having the structure of this example having seven 100 μm diameter spherical lenses with each light emitting diameter of 35 μm are compared. As is clear from the figure, although the effective light emitting area of the structure of this example is more than 10% smaller than that of the conventional LFiD structure, the current value at which the optical output is saturated is more than twice as high. . −
There is no difference in the directivity of the emitted light because the ratio of the spherical lens diameter to the emission diameter is almost the same, and the effective diameter as a circular light source is the same for both, 300 μm, and the core diameter is 30 μm.
The upper limit value of the amount of light coupled to the optical fiber 01a due to optical output saturation was also more than twice that of the conventional structure in the IFiD with the structure of this example.

Above, the effects of the present invention have been explained with reference to an example in which seven light emitting sections are arranged in the highest density. However, the effects of the present invention depend on arranging the light emitting sections in a high density, and in the previous embodiment, the effect of the present invention is also If the spacing is greater than twice the diameter of the ball lens adhesively fixed thereon, there will be no significant difference in the amount of light coupled into the optical fiber compared to conventionally structured LEDs.

Another embodiment of the invention is shown in FIG. In the figure.

(6) and (8) show a circular concave portion (light emitting portion) and a ball lens. (a) and (Q) are examples in which a ball lens with the same diameter and a light emitting section are combined, while lb) and (d) are examples in which a ball lens with a different diameter and a light emitting section are combined. An infinite number of such embodiments can be considered depending on the number and arrangement of light emitting parts. In addition, although the embodiments shown in FIGS. 3 and 5 have the highest density arrangement, even if there is some spacing between the ball lenses, the effect of the invention will be somewhat reduced, but it will still be roughly the same as the conventional structure. It is clear from the above description that the amount of light coupled to the original fiber can be obtained.

Since the LED according to the present invention has both high output and high radiance, it is useful not only as a light source for large-diameter optical 7-eye cameras, but also as a light source for space transmission optical communications, light wave ranging devices, etc. It is.

As described above, the LFiD according to the present invention has the same diameter as the effective light source, and has the conventional structure T, I]lCD shown in Figure 9g1.
Compared to the Hikari 7 AINO, the series resistance and thermal resistance are lower, and the current value at which the optical output saturates is increased, so higher optical output and radiance can be obtained, and the amount of light coupled to the optical In addition, even when operated at the same operating current level, the junction temperature rise is low due to low thermal resistance.
In addition to providing a longer life than the conventional structure, this structure also has the effect of improving the linearity of the optical output-current characteristics over a wide range.

In the embodiment shown in FIG. 3, GaAs-AIG
Although the case of a double heterojunction type using aA8-based material has been described, the present invention is not limited to this, and may also be applied to the case of using other materials such as the nGaAs P-nP type, as well as the case of a single heterojunction type. It is clear that the same effect can be obtained even if it is applied to a nine-mouth joint type.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an LZD with a conventional structure, which is the basis of the present invention, Fig. -2 is a diagram showing the optical Kerr current of LKDs with a conventional structure and different emission diameters, and Fig. 3 is a cross-sectional view of an LZD according to the present invention. ! ! D
An example is shown in which (&) is a top view and (b) is a cross-sectional view. Figure 4 shows an LID of a conventional structure and an LID of an embodiment of the present invention having the same effective diameter and directional characteristics as a light source.
FIG. 5, which is a diagram showing the optical output-current characteristics of the lnD, is a top view showing another embodiment of the present invention. (1)-N-type GaA13 substrate, (2)-N-type AlGaA
s layer, (3), P-type GaAs light emitting layer, (4)-P-type AlGaAs layer, (5)--N-type AlGaAs layer,
(6) ---Circular recess (light emitting part'), (7) ---
P shadow area, (8)... Ball lens, (9)... Transparent resin, (1o)... P side electrode, (11)... N side electrode, (6]) to (67) ...Circular recess, (81) to (8
7)...Spherical lens agent Makoto Kuzuno - Fig. 1 Fig. 2 ・ Fuchu Tsun (mA) Fig. 3 Fig. 4 -/L (A) Fig. 5

Claims (3)

[Claims] (1) A plurality of electrically non-independent light emitting parts are provided on the same chip, and a spherical body made of a substance transparent to the emission wavelength is placed on each of the light emitting parts. A light emitting diode characterized by being adhesively fixed using an adhesive medium. (2) Each light-emitting part is arranged at a distance between adjacent other light-emitting parts that is not more than twice the diameter of the spherical forming body adhesively fixed thereon, and at least at a distance that the spherical forming bodies are in contact with each other. A light emitting diode according to claim 1, characterized in that: (3) Each of the plurality of light emitting parts has a recessed part, and a spherical forming body having a diameter larger than the diameter of the sphere inscribed in the recessed part is fitted and fixed with adhesive. The light emitting diode according to item 1 or 2.