JP3410166B2 - Red light emitting diode element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode device using a III-V compound semiconductor. 2. Description of the Related Art Hitherto, III-V compound semiconductor devices, for example, high-brightness light-emitting diodes (hereinafter referred to as LEDs) comprising a heterojunction on a gallium aluminum arsenide (GaAlAs) semiconductor substrate have been compared with homojunction structure LEDs. Since the carrier injection efficiency is high, high output and high-speed response can be obtained, and an LED having a single hetero junction structure or a double hetero junction structure is used. In particular, a high-brightness red LED using a double hetero junction structure is mounted on a high-mount stop lamp for a vehicle, an outdoor display device, and the like. A feature of these heterojunction structure LEDs is that a Ga _1-x Al _x As semiconductor substrate having a high mixed crystal ratio X of aluminum arsenide (AlAs) is used on the light extraction side. FIG. 3 is a cross-sectional view of a conventional LED element formed of a GaAlAs semiconductor substrate and will be described. p-type Ga
After a zinc (Zn) -doped Ga _0.20 Al _0.80 As layer of 100 μm is formed as a p-cladding layer 11 on an As substrate ((100) plane) 10 by a liquid phase epitaxial growth method or the like.
As the p-type active layer 12 Zn-doped Ga _{0. 65} Al
_{A 0.35} As layer is formed to have a thickness of 1 to 2 μm, and then the tellurium (Te) doped Ga _0.20 Al _0.80 A is formed as the n-type cladding layer 13.
An s layer is formed to a thickness of about 30 μm. Then, the light absorbing GaAs substrate 10 is removed using a GaAs substrate selective etchant to obtain a high brightness red LED element. [0004] The above-described high-brightness red LE
The AlAs mixed crystal ratio of the n-type cladding layer 13 on the front surface and the p-type cladding layer 11 on the rear surface of the D element is as high as 0.8. Ga _1-x Al _x As having a high AlAs mixed crystal ratio as described above
Since the layer is extremely oxidizable, the substrate surface in contact with the atmosphere,
There is a characteristic that an Al oxide layer is formed on the back surface and the growth of the Al oxide layer is remarkably promoted by adding water.
Then, the Al oxide layer becomes a light absorbing layer, and there is a problem in that the growth of the Al oxide layer causes deterioration of the light emission characteristics, thereby significantly shortening the element life. As a countermeasure against this oxidation, a natural oxide film called a native oxide film (NO film) using an etchant, or a SiO2 film formed by CVD or sputtering is used.
There is a method of forming _two films, a SiN film, and a SiON film as a protective film on the surface. However, such a protective film is not completely uniform, and the moisture resistance may be broken due to the occurrence of pinholes and the like. In order to completely cover the surface, the protective film 14 is formed so as to cover the periphery of the n-type electrode 6 as shown in FIG. Water easily penetrates from the interface between the electrode 6 and the protective film 14. For this reason, an Al oxide layer grows from the periphery of the n-type electrode 6, luminance degradation starts, and the Al oxide layer proceeds inside the LED element, which eventually causes a fatal result that the LED element is cracked and disconnected. This phenomenon was the same for LEDs sealed with epoxy resin or the like. The present invention has been made to solve the above problems, and prevents the formation of an Al oxide layer without deteriorating the light emission characteristics.
An object is to provide a high-quality LED element. According to the present invention, a GaAlAs epitaxial layer having an AlAs mixed crystal ratio of 0.6 or less is formed on a first surface layer and a first rear surface layer of a semiconductor substrate, and an electrode is formed. Forming a mesa-etched portion extending from the front surface of the semiconductor substrate to the back surface first layer, and then forming a protective film on the entire surface of the first surface layer excluding the electrodes and on the mesa-etched surface. According to the present invention, an epitaxial layer having an AlAs mixed crystal ratio of 0.6 or less is formed on the first surface layer and the first rear layer of the semiconductor substrate in contact with the atmosphere. Can be suppressed. In addition, since the protective film is attached to the high AlAs mixed crystal ratio portion exposed on the side surface after the division of the LED element, the formation of the Al oxide layer on the side surface can be prevented. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the LED element of the present invention. This LED element is formed on a p-type GaAs substrate (100 surface) (not shown) by Zn-doped G having an AlAs mixed crystal ratio of 0.6.
p-type contact layer 1 ungated, then Zn-doped Ga _0.2 Al _0.8 As layer 20μm growth of the AlAs mixed crystal ratio of 0.8 and p-type cladding layer 2 to 100μm grow a _{0. 4} Al _0.6 As layer, subsequently Ga _0.65 A which is the p-type active layer 3
A _0.35 As layer is grown to 1 μm, and a Te-doped Ga _0.2 Al _0.8 As layer as the n-type cladding layer 4 is grown to 20 μm.
An n-type contact layer 5 is formed by growing a Te-doped Ga _0.4 Al _0.6 As layer having an lAs mixed crystal ratio of 0.6 by 10 μm. Finally, the p-type GaAs substrate is removed with a GaAs substrate selective etchant. Then, the electrode 6 is formed on the n-type contact layer and the electrode 7 is formed on the p-type contact layer 1 by vapor deposition and heat treatment to form a gold alloy electrode. Finally, dicing or the like is performed to obtain an LED element. As described above, the n-type contact layer 5 having an AlAs mixed crystal ratio of 0.6 or less is used as the first surface layer of the semiconductor substrate.
Also, since the p-type contact layer 1 having the same AlAs mixed crystal ratio of 0.6 or less is formed as the backside first layer, generation and growth of the Al oxide layer can be prevented. Next, a sectional view of an embodiment in which a protective film is further formed in addition to the above will be described with reference to FIG. In FIG. 2, after the above-described electrodes 6 and 7 are formed, mesa etching is performed on a boundary portion of the LED element, and a protective film 9 is formed on a portion other than the electrode 6. As a manufacturing procedure, a photoresist (not shown) is attached to the entire surface except for a predetermined portion of the semiconductor substrate after the electrode 6 is formed, and a portion where the photoresist is not attached is etched by means such as wet etching.
A mesa etching portion 8 is formed. This mesa etching portion 8 becomes a boundary at the time of LED element division. The mesa etching portion 8 is formed from the front surface of the semiconductor substrate to p
The depth reaches the mold contact layer 1. Thereafter, a protective film 9 such as a SiO ₂ film or a SiN film is formed on the entire surface excluding the electrode 6, and the bottom of the mesa etching portion 8 is divided by means such as dicing to obtain an LED element. Here, the protective film 9 may be in contact with the electrode 6, or there may be a gap between the protective film 9 and the electrode 6 that allows for a mask alignment error. After the mesa etching is performed to reach the p-type contact layer 1 as the first layer on the back surface, the protective film 9 is formed.
High Al exposed on the side surface when the element is divided
The As mixed crystal ratio portion, that is, the side surfaces of the n-type clad layer 5 and the p-type clad layer 2 can be covered with the protective film 9, and the formation of the Al oxide film on the side surfaces can be prevented. Next, Table 1 shows the results of the life tests of the LED element of the present invention and the LED element of the conventional structure in comparison of the residual luminance ratio. [Table 1] Test A was conducted at a temperature of 85 ° C. and a relative humidity of 85%.
A high-temperature and high-humidity continuous energization test with a driving current of 5 mA, Test B is a high-temperature and high-humidity continuous energization test with a temperature of 65 ° C., a relative humidity of 95%, and a driving current of 10 mA. The luminance remaining ratio is a value in which the luminance at 0 hour before the test is 100% and the luminance after the test is expressed in%. The luminance residual ratio of the conventional product after 1000 hours has passed is not more than 20% in both the tests A and B, and the deterioration has progressed considerably. On the other hand, the product of the present invention has 90% or more even after 1000 hours has passed. The high level is maintained, which clearly shows the effect of preventing the formation of the Al oxide layer of the present invention. In this embodiment, Zn and Te are used as doping materials, but the present invention is not limited to the types of doping materials. According to the present invention, an Al oxide layer can be formed by forming an epitaxial layer having an AlAs mixed crystal ratio of 0.60 or less on the front surface first layer and the back surface first layer of the semiconductor substrate. By forming a protective film such as a SiO ₂ film or a SiN film on the mesa-etched portion, the Al oxide layer formed on the n-type cladding layer having a high AlAs mixed crystal ratio and the p-type cladding layer exposed on the side surface is prevented. can do. Thereby, the moisture resistance of the LED element is remarkably improved, and the life characteristics can be improved by reducing the influence of light absorption due to the formation of the Al oxide layer.

[Brief description of the drawings] FIG. 1 is a sectional view of an LED element according to an embodiment of the present invention. FIG. 2 is a process sectional view of an LED device according to another embodiment of the present invention. FIG. 3 is a process sectional view of a conventional LED element. [Explanation of symbols] 1 p-type contact layer 2 p-type cladding layer 3 p-type active layer 4 n-type cladding layer 5 n-type contact layer 8 Mesa etching part 9 Protective film 10 p-type GaAs substrate 11 p-type cladding layer 12 p-type active layer 13 n-type cladding layer 14 Protective film

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kenichi Koya               Matsushita Electronics Corp., 1-1 1-1 Sachicho, Takatsuki-shi, Osaka               Industry Co., Ltd.                (56) References JP-A-60-153186 (JP, A)                 JP-A-59-114885 (JP, A)                 JP-A-4-212480 (JP, A)                 JP-A-3-127873 (JP, A)                 JP-A-1-226181 (JP, A)                 JP-A-4-273174 (JP, A)

Claims (1)

(57) [Claim 1] A back contact layer and a front contact layer made of a III-V compound semiconductor are formed of a gallium aluminum arsenide epitaxial layer containing aluminum and having an aluminum arsenic mixed crystal ratio of 0.6 or less. Then, a heterojunction having a gallium aluminum arsenide epitaxial layer having an aluminum mixed crystal ratio exceeding 0.6 as a cladding layer is formed between the contact layers on both front and back surfaces, and a mesa etching surface reaching the back contact layer from the front contact layer is formed. A protective film is formed on the mesa-etched surface and the exposed surface of the surface contact layer, and the clad layer is in direct contact with the atmosphere.
A red light-emitting diode element characterized by being eliminated .