JPS6229183A - Light emitting diode - Google Patents

Abstract

PURPOSE:To increase the optical takeout rate as large as possible to enhance externally the light emitting efficiency and reduce loss in heating or the like caused by internal absorption, together with facilitating wiring work, by installing a metal film wiring stretchingly along an inclined side which composes forward-mesa structure on the electrode part mounted on the upper surface of the optical takeout part. CONSTITUTION:A P-Ga0.7Al0.3As layer 31 and N-Ga0.6Al0.4As layer 32 are made to grow on a P-type GaAs substrate 30 by liquid-phase epitaxial method. After this growth, with fixed patterns mesa-etched, an optical takeout part 35 is formed in a mesa structure in which both right and left sides are formed into forward-mesa faces 33 and both sided of the cross-section perpendicular to them are formed in reverse-mesa faces 34. After the etching, a crystal surface is covered with a phosphor-added glass film 36 to form a window part for mounting N electrodes 37 on the central surface of the optical takeout part using hydrofluoric acid-system etchant. When a chip formed this way is assembled into a stem 41 and coated 42 with epoxy resin to be dome-shaped, electrode wiring can be obtained with high reliability and without disconnection or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection type electroluminescent diode, and particularly to a mesa structure light emitting diode with improved light extraction efficiency.

[Prior Art] In general, light-emitting diodes for dot display elements or light-emitting diodes for numeric display elements are mainly so-called hybrid light-emitting diodes that are a combination of planar monolithic type or pelletized type using inter-fold spaces. .

Figure 6 shows the cross-sectional structure of an example of a diffused planar monolithic light emitting diode, where 1 is the substrate, 2 is the epitaxial layer, 3 is the zinc diffusion layer, 4 is the 5fN4 film, 5 is the aluminum clear electrode, and 6 is the n It is an electrode. Light is emitted to the outside from the PN junction surface in a vertical direction through a window portion surrounded by aluminum electrodes 5.

However, most of the light cannot escape to the outside due to the presence of the 513N4 film 4 or the aluminum electrode 5.
It then reflects and travels in the direction indicated by the dotted arrow. Most of this light is not only not extracted outside as luminescence, but also
It was absorbed into the element and caused the element to generate heat, resulting in a shortened lifespan and defects.

FIG. 7 shows a schematic diagram of a light emitting diode that is pelletized using the spaces between the folds, and for convenience of explanation, it is assumed that light is emitted from one point.

7 is an n-electrode, 8 is a substrate, 9 is an open surface, and 10 is a light emitting part. According to this, light within the shaded area 11 having an incident angle less than the critical angle can be extracted to the outside.

However, since light with an incident angle greater than the critical angle is totally reflected on the crystal surface and cannot be extracted to the outside, it is consumed within the crystal in the form of heat generation, etc., as in the case of Figure 6, and as a result, This method has the disadvantage that the external recognition efficiency is reduced.

Furthermore, in order to make this pelletized light emitting diode shown in FIG. 7, a plurality of light emitting diodes are combined to form a numeric display element and are called a hybrid type light emitting diode. ) must be wired with gold wires on a common substrate, making it difficult to attach the 1C electrodes and causing problems such as unstable characteristics.

Therefore, conventionally, in order to improve the light extraction efficiency and solve problems such as wiring, it has been considered to form the light emitting diode into a mesa structure by mesa etching instead of between the folds. That is,
As shown in FIG. 8, the cross-sectional shape of the light extraction portion 12 has a regular mesa structure on both the front, rear, left and right sides. According to this, the light emitted from the virtual light emitting point located at the bottom of the light extraction portion on the substrate 13 is uniformly emitted around the surface of the plate 14.
When the angle formed with 15 becomes a critical angle of 00 or more, total reflection occurs, so that the light in the three diagonally shaded areas 16 surrounded by the critical angle Oc can be extracted to the outside of the element.

Therefore, while it is possible to achieve a much higher light extraction rate than that of a planar monolithic light emitting diode, it is possible to achieve a much higher light extraction rate than a hybrid type light emitting diode. Since a light extraction part can be formed and these can be connected with metal film wiring,
Wiring work problems are solved.

[Problems to be Solved by the Invention] However, in the conventional mesa structure light emitting diode mentioned in 1., for example, GaP has a refractive index of about 2.9 Te, so the critical angle is θ=s+n (n2/ n+)～
It is small at 202°. Here, nl is the refractive index of GaP, and n2 is the refractive index of air (~1).

Further, in the case of GaAS, if the refractive index is approximately 3.36, the critical angle θ is −17.3°, and this value becomes even smaller, so that most of the light is totally reflected. Therefore, even with a mesa structure, a highly efficient light emitting diode could not be obtained.

``Object of the Invention'' The object of the present invention is to eliminate the drawbacks of the prior art described above, improve the light extraction rate as much as possible to increase the external luminous efficiency, reduce losses such as heat generation due to internal absorption, and It is an object of the present invention to provide a light emitting diode whose wiring work is easy.

[Summary of the Invention] As shown in FIG. 1A to FIG. 1B corresponding to the embodiment, the cross-sectional shape of the light extraction portion 35 from the injection/emission region has an inverted mesa structure on one side by mesa etching. The other side, which is perpendicular to this one side, has a mesa structure. Then, the electrode part 37 provided on the upper surface of the light extraction part 35 is
A metal film wiring 38 is extended along the inclined side surface 33 forming the structure.

As a result, even if light enters the upper surface 29 of the light extraction portion 35 or the inclined side surface (inverted mesa surface) 34 constituting the inverted merry structure at a critical angle or more) 1 and is totally reflected, the reflected light will not reach the substrate 30. Instead of directly hitting the interface of the reverse mesa surface 34 or the upper surface 2
9, and if it hits at a critical angle or less, the reflected light will go out to the outside of the crystal without being absorbed inside the crystal.

Further, since the gold B film wiring 38 is routed along the inclined side surface (forward mesa surface) 33 forming the forward mesa structure rather than the reverse mesa surface 34, no step breaks occur in the metal film.

[Example] An example of the present invention will be described below based on FIGS. 1A to 5.

First, we will explain the principle. Since compound semiconductors having a zincblende crystal structure such as I[-Vl, IV group, etc., have polarity in the <111> direction, (111) Δ plane and (11
1) The t and i etching speeds are different for the eight surfaces. From this, if a pattern is created in the <011> direction or <01> direction on a (100) plane crystal substrate and etched with a selective etching solution, it will produce a pattern as shown in Fig. 3 or 4. Mesa etching grooves 20 and 21, which are so-called forward mesa type or reverse mesa type, are formed, and an element having a cross-sectional shape of a forward mesa structure or a reverse mesa structure is completed.

At this time, since the inclined side surface 22 of the mesa becomes a (111) plane, it forms an angle αL! with the element surface 23, which is a (100) plane! The angle will be approximately 55°.

FIG. 5 shows a cross-sectional structure of the light emitting diode having the above-mentioned inverted mesa structure. The light △ emitted from the central virtual light emitting point goes straight and is emitted to the outside, whereas the light B that impinges obliquely on the upper surface 24 at an angle greater than the critical angle is totally reflected and is emitted from the inclined side surface. It hits the reverse mesa surface 25. If the angle at this time is less than the critical angle, the light is extracted outside the crystal as luminescence.

In addition, the light C that goes directly from the central light emitting point to the reverse mesa surface is
Since the angle is greater than the critical angle with respect to the perpendicular to the inverted mesa surface 25, it is totally reflected and hits the upper surface 24 of the crystal. If the angle of this light is less than the critical angle, it is emitted to the outside through the crystal.

Here, we will fold it inversely with the (100) surface which will be the upper surface (
111) As mentioned above, the angle formed with
It can be seen that the luminous efficiency is significantly improved compared to the conventional mesa structure or planar structure.

Next, a specific explanation will be given along with FIGS. 1A to 2.

As shown in Figure 1Δ and Figure 1B, P type Ga 8s
P-Gao, 782°, AS layer 31 on 73 plate 3o
, n-Ga6. (, t&0.t4As layer 32 is grown by liquid phase 1 bitaxial method. After growth, it is mesa-etched into a predetermined pattern, and the left and right side surfaces in FIG. 1A become normal mesa surfaces 33, and the 1 B A light extraction portion 35 having a mesa structure is formed in which both sides of the cross section as viewed from the arrow −1B are reverse mesa surfaces 34. In this case, the pattern of the light extraction portion is such that the reverse mesa surface is longer than the forward mesa surface. When formed, the light extraction rate is further improved.

After etching, the crystal surface is covered with a PSG (phosphorus-added glass) film 36, and an n-electrode 37 is placed in the center of the light extraction part surface.
A window section for providing a window is formed using a hydrofluoric acid etchant. After that, ZrAU-Ge/Ni/^ from the lower part of the forward mesa structure reaches the window on the upper surface along the forward mesa surface 33.
A gold m IFJ wiring 38 of U is vapor-deposited on the PSGI 36''-, and an n-electrode 37 is formed at one end of this wiring, and a wiring pad 39 larger than the wiring width is formed at the other end. Metal film wiring 38
1. It is deposited to a uniform thickness along the gentle mesa surface. Problems such as breakage of the viru membrane do not occur. on the other hand,
Similarly, an Au-Zn/Ni/Au electrode 40 is deposited on the entire surface of the back surface to serve as a P electrode.

As shown in FIG. 2, the chip thus formed is assembled into a stem 41 and coated with epoxy resin to form a dome shape, and the stem foot 43 is directly fused to the wiring pad 39 to form a light emitting diode. do. The connection between the stem leg 43 and the chip is not made by metal wire.
(i) Highly reliable electrode wiring is possible without any disconnections. Also, since the light extraction part has an inverted mesa structure and the charge/emission surface is shaped into a dome, the light extraction rate is improved. It is possible to further improve the luminous efficiency and obtain high luminous efficiency.

In the above embodiment, GaA was used as the abrasive material for the light emitting diode.
Although aP has been described above, any material may be used as long as an inverted mesa structure can be obtained by etching.

In addition, the epitaxial growth method is a liquid phase growth method, and lζ is not limited to the liquid phase growth method, but may also be a growth method using a vapor phase growth method, a metal organic film deposition method (MOCVD), or a diffusion growth method. P formed using the growth method of
t) Applicable when etching a -N junction layer to form a mesa structure.

[Effects of the Invention] In summary, the present invention exhibits the following excellent effects.

(1) By making use of the total reflection caused by the refractive index of the crystal and providing an inverted mesa structure on one side that makes it easier to extract light to the outside, it is different from conventional structures that have a normal mesa structure or planar monolithic structure around the entire circumference. In contrast, it is possible to increase the light extraction rate and improve the luminous efficiency as much as possible. Furthermore, since the amount of light absorbed into the crystal is reduced, losses such as heat generation are reduced, and the life of the element can be improved.

(2) The wiring on the element surface is formed by vapor deposition of a metal film instead of using metal wires, and is extended along the sloped side surface of the forward-mena structure, ensuring reliability without disconnections or breaks. High electrode wiring can be performed. In particular, the same
When a plurality of light emitting diodes are formed on a substrate and used as a numeral display element, it is sufficient to connect these light emitting diodes with gold i-film wiring, making the wiring work extremely easy.

[Brief explanation of the drawing]

FIG. 1A is a cross-sectional diagram showing an embodiment of the light emitting diode of the present invention, FIG. 1B is a cross-sectional diagram taken along line 18-IB in FIG. 1A,
Figure 2 shows the light emitting diode shown in Figure 1A attached to the stem.
Figure 3 is a cross-sectional view of a forward mesa structure obtained by mesa etching, Figure 4 is a cross-sectional view of an inverted mesa structure obtained by mesa etching, and Figure 5 is a light emitting diode with an inverted mesa structure. 6 is a cross-sectional view showing an example of a conventional planar monolithic light emitting diode, FIG. 7 is a cross-sectional view showing an example of a conventional hybrid light emitting diode, and FIG. There is a sectional view showing the state of light emission from a light emitting diode with a regular mesa structure. In the figure, 2 are the upper surface, 30 is the substrate, 33 is the forward mesa surface (slanted side surface), 34 is the reverse mesa surface, 35 is the light extraction part, 37 is the electrode part, and 38 is the full-reflection film wiring.

Claims (1)

[Claims] A light extraction part is formed on the substrate by mesa etching, with a cross-sectional shape on one side having an inverted mesa structure and a cross-sectional shape on the other side perpendicular to the one side having a forward mesa structure, and an electrode provided on the top surface of the light extraction part. 1. A light emitting diode characterized in that a metal film wiring is extended along a sloped side surface forming a mesa structure in a portion thereof.