JP2002016282A - Nitride semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor element which can prevent deterioration of sealing material and maintain high luminance of a light-emitting diode. SOLUTION: In this nitride semiconductor element, an N-type nitride semiconductor layer, an active layer and a P-type nitride semiconductor layer are laminated on a substrate, and a trench is formed which penetrates the active layer from the uppermost surface of the P-type nitride semiconductor layer. In the trench, a first insulating layer, in contact with the inner wall surface of the trench, and a second insulating layer, in contact with the first insulating layer are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor device used for a light emitting diode or the like, and more particularly, to a nitride semiconductor device capable of preventing deterioration of a sealing material and maintaining high brightness of the light emitting diode.

[0002]

2. Description of the Related Art Since a nitride semiconductor has a wide band gap and is a direct transition type, it is used as a material for a light emitting element having a short wavelength, for example, a light emitting diode (LED). In particular, high-luminance blue light emission L using a nitride semiconductor device
EDs have been put to practical use as various light sources such as LED displays, traffic lights, and image scanner light sources.

[0003] The LED is basically composed of a semiconductor element, an electrode and a sealing material. The semiconductor element is a p-type and an n-type having at least a semiconductor junction formed on a substrate.
Type semiconductor, p electrode and n in contact with each semiconductor
It is composed of electrodes.

As a specific example of a semiconductor device, a nitride semiconductor device is exemplified. As shown in FIG. 5, a lattice constant mismatch between a nitride semiconductor and a substrate 501 such as sapphire or spinel which is a light-transmitting insulating substrate. Buffer layer (not shown) for alleviating the resistance, and S for obtaining ohmic contact with n electrode 508
n-type contact layer 50 made of GaN doped with i
2. GaN and In which generate light by carrier coupling
Active layer (light emitting layer) 503 made of GaN, AlGaN doped with Mg to confine carriers in the active layer
A nitride semiconductor in which a p-type cladding layer 504 made of InGaN doped with Mg and a p-type contact layer 505 made of GaN doped with Mg for obtaining ohmic contact with the p-electrode 507 are sequentially stacked; An n-electrode 508 formed in a desired shape on an exposed surface of the n-type nitride semiconductor formed by etching the nitride semiconductor;
Electrode 50 covering almost the entire surface of the p-type nitride semiconductor layer
6, a p-electrode 507 formed in a desired shape on
An insulating layer 509 is formed for the purpose of protecting the nitride semiconductor and each electrode from the outside and preventing a short circuit.
The nitride semiconductor element is mounted on a lead electrode, electrically connected, and sealed with a sealing material such as a translucent epoxy resin to obtain an LED. When such an LED is energized, light emitted from the active layer in the nitride semiconductor device is emitted from the uppermost surface of the p-type nitride semiconductor layer and the end surface of the active layer.

[0005]

However, with the recent increase in the output of LEDs, problems that have not been encountered in the past have occurred. One of the problems is that the epoxy resin as a sealing material is deteriorated by light emitted from the nitride semiconductor element.

Epoxy resins are generally used as encapsulants because of their good adhesion to nitride semiconductors, excellent mechanical strength, chemical stability, and low cost. It is the most frequently used material and has excellent weather resistance against weak light and heat from the outside such as sunlight. However, in the case of an LED using a nitride semiconductor element capable of emitting blue light, since the energy is higher than that of other colors, the epoxy resin is deteriorated and colored to a black-brown color, and light from the nitride semiconductor element is emitted. Absorbs. For this reason, there is a problem in that the emission intensity of the LED is reduced by long-time use, even though the nitride semiconductor element is not deteriorated.

Accordingly, it is an object of the present invention to provide a nitride semiconductor device which suppresses deterioration of an epoxy resin sealing a nitride semiconductor device and maintains high brightness of an LED.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, among the epoxy resins sealing the nitride semiconductor element, the deterioration is particularly severe. Is near the end face of the active layer. It has been found that the above problem can be solved by improving the shape of the nitride semiconductor device, and the present invention has been completed.

That is, a nitride semiconductor device of the present invention is a nitride semiconductor device in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate. A groove having a depth penetrating the active layer from the uppermost surface of the p-type nitride semiconductor layer, and a first insulating layer in contact with the inner wall surface inside the groove and a first insulating layer in contact with the first insulating layer A second insulating layer is formed.

Further, the first insulating layer and the second insulating layer are made of materials having different refractive indexes.

Further, the second insulating layer is made of a material having a higher refractive index than that of the first insulating layer.

It is preferable that the groove is formed along the vicinity of the outer periphery of the uppermost surface of the p-type nitride semiconductor layer of the nitride semiconductor device. With such a configuration, light propagating in parallel in the active layer can be efficiently diffused.

The first insulating layer may be made of SiO 2
Can be suitably used.

Further, a polyimide resin can be suitably used for the second insulating layer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A light emitting diode according to the present invention is a nitride semiconductor device in which an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer are laminated on a substrate. A nitride semiconductor device having a main emission wavelength of 500 nm or less. Hereinafter, a nitride semiconductor according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a front view of a nitride semiconductor device according to an embodiment of the present invention, and FIG. 1 is a cross-sectional view taken along the line AA 'of FIG. As shown in FIG. 1, the nitride semiconductor device according to the embodiment of the present invention has a buffer layer (not shown) for reducing mismatch of lattice constant with a nitride semiconductor layer on a substrate 101 such as sapphire or spinel. An n-type contact layer 102 made of GaN doped with Si for obtaining ohmic contact with the n-electrode 108; an active layer (light emitting layer) 103 made of GaN and InGaN for generating light by carrier coupling; Mg for confinement
-Doped AlGaN and Mg-doped In
A p-type cladding layer 104 of GaN, a p-electrode 107 and a p-type contact layer 105 of GaN doped with Mg for obtaining ohmic contact with the entire surface electrode 106 are sequentially stacked.

The buffer layer is made of GaN crystal-grown at a low temperature, and preferably has a thickness of 10 to 500 °. The n-type contact layer 102 is composed of GaN doped with Si, and has a thickness of preferably 1 to 20 μm, more preferably 2 to 6 μm. On the n-type contact layer 102, an n-type cladding layer made of, for example, AlGaN doped with Si may be formed with a thickness of 100 to 500 °. The active layer 103 may be made of InGaN having a thickness of 25 to 300 °, or GaN having a thickness of 50 °
A single or multiple quantum well layer may be formed by forming 1 to 10 layers of InGaN having a thickness of 30 ° and finally forming GaN having a thickness of 50 °.

The p-type cladding layer 104 is made of Mg-doped AlGaN and Mg-doped InGaN, and preferably has a thickness of 100 ° to 0.2 μm.
The mold contact layer 105 is made of GaN doped with Mg, and preferably has a thickness of 0.05 to 0.2 μm.

After that, the nitride semiconductor is etched. In the embodiment of the present invention, as shown in FIG. 1, the active layer 103 is formed from the uppermost surface of the p-type nitride semiconductor layer (p-type contact layer) 105. A penetrating groove 112 is formed, and a first insulating layer 109 in contact with the inner wall is formed inside the groove.
And a second insulating layer 111 in contact with the first insulating layer.

The depth of the groove may be such that it extends from the uppermost surface of the p-type nitride semiconductor layer through the active layer. When the p-electrode and the n-electrode are formed on the same side using an insulating substrate as in the present embodiment, the depth of the groove is set to the n-type nitride semiconductor layer in order to secure a current path. It is preferable that If the depth is too deep, the current path becomes narrow and the current becomes difficult to flow, and if the groove reaches the substrate, the current does not flow, which is not preferable. In another embodiment, a conductive material such as GaN is used as the substrate.
In the case of a nitride semiconductor device in which an n-electrode formed on the conductive GaN substrate side and a p-electrode formed on the p-type nitride semiconductor layer side face each other, a p-type nitride semiconductor is used. The groove formed from the uppermost surface of the layer is conductive GaN
Even if it reaches the substrate, it does not hinder the flow of current, and in such a case, the depth of the groove does not matter at all even up to the substrate.

Further, the groove of the present embodiment can be formed by etching. The groove may be formed at the same time as the etching when exposing the n-electrode formation surface, or may be further formed by etching after exposing the n-electrode formation surface. The former does not increase the number of processes,
The groove can be formed only by changing the mask, and the latter has a problem that the number of etching steps is increased twice, but a groove having an arbitrary depth can be formed.

In the groove of the present embodiment, an insulating layer is formed inside the groove. This makes it possible to keep the end face of the active layer (light emitting layer) away from the epoxy resin. In other words, the outer wall of the insulating layer and the groove (the portion between the end surface of the nitride semiconductor and the groove) is formed between the end surface of the active layer where the epoxy resin is most likely to deteriorate and the epoxy resin. Become. Since no p-electrode is formed on the outer wall of the groove, no current is supplied and the active layer is a nitride semiconductor that does not emit light. Therefore, there is no problem even if the outer wall of the groove is close to the epoxy resin.

A first insulating layer in contact with the inner wall and a second insulating layer in contact with the first insulating layer are formed inside the groove, and the two insulating layers have different refractive indexes. Materials are used. Here, FIG. 3 is an enlarged view of the periphery of the active layer end face of the nitride semiconductor device of the present embodiment. If the second insulating layer is made of a material having a higher refractive index than the first insulating layer, the light emitted from the active layer will reach the epoxy resin as indicated by the arrow in the drawing, It is mainly diffused when passing through the interface between the second insulating layer and another member. Broadly speaking, the first insulating layer and the second
Between the second insulating layer inside the groove and the first insulating layer in contact with the outer wall of the groove, the first insulating layer and the second insulating layer in contact with the outer wall of the outer wall of the groove. It is widely diffused at each of the interfaces with the layer. As described above, the first insulating layer having a small refractive index is formed in contact with the surface of the nitride semiconductor inside the groove, and the second insulating layer having a large refractive index is formed thereon. Light from the end face can be more efficiently diffused.

The position of the groove formed as described above is preferably formed along the vicinity of the outer periphery of the uppermost surface of the nitride semiconductor p-type nitride semiconductor layer as shown in FIG. The active layer between the outer wall of the groove and the side of the nitride semiconductor,
Since no current is supplied and no light is emitted, it is preferable to form a groove along the vicinity of the side wall of the nitride semiconductor in order to increase the light emitting area. Further, the width of the groove can be arbitrarily set depending on the etching accuracy, but is preferably narrow in order to increase the light emitting area. If the width is too large, the light emitting area becomes narrow, which is not preferable.

As a material of the first insulating layer, SiO 2 is used.
Further, as a material of the second insulating layer, a polyimide resin can be suitably used. Although SiO2 and polyimide resin have different properties such as refractive index, both are colorless and transparent materials similar to epoxy resin. However, as compared with the epoxy resin, the LED is hardly deteriorated by light having a short wavelength from the nitride semiconductor element inside the LED, so that it is difficult to lower the light emission intensity of the LED even when used for a long time.

Further, the nitride semiconductor device of the present invention has an LE
D, etc., for example, can be mounted on a bullet-shaped LED as shown in FIG. 4, but is not limited to this form, and a nitride semiconductor element is sealed with a sealing material such as an epoxy resin. If so, the outer shape can be arbitrarily selected, and it goes without saying that the present invention can be used for various LEDs such as a surface mount type. Further, the present invention can also be applied to a case where a sealing material contains a fluorescent substance which emits fluorescence when excited by light from a nitride semiconductor element, and even in such a case, the effect of suppressing luminance degradation of an LED. Can expect enough.

[0027]

[Embodiment] As a nitride semiconductor, a nitride semiconductor having the following configuration is used. Each semiconductor layer is
It is formed on a substrate by a metal organic vapor deposition method (MOCVD method). As shown in FIG. 1, G on a sapphire substrate
a buffer layer (not shown) made of aN and having a thickness of about 100 °, and a film thickness of about 4 μm made of GaN doped with Si
N-type contact layer / cladding layer, GaN and InGa
N-type active layer (light-emitting layer) having a multi-quantum well structure having a thickness of about 1600 °, p-type cladding layer having a thickness of about 400 ° made of AlGaN doped with Mg and InGaN doped with Mg, and doped with Mg. P-type contact layers made of GaN and having a thickness of about 3000 ° are stacked in this order.

A positive electrode and a negative electrode are formed on the nitride semiconductor. First, in order to form an n-electrode in an n-type contact layer, an end of the nitride semiconductor is removed by etching.
The etching is performed from the p-type contact layer side, and is set to about 1 μm to a depth where the n-type contact layer is exposed. At this time, a groove having a depth of about 1 μm from the surface of the p-type nitride semiconductor layer as shown in FIG. 1 is formed by using a mask capable of forming a groove along the periphery of the uppermost surface of the p-type contact layer. Is obtained.

Gold is formed by sputtering as an electrode which is in contact with the p-type contact layer (uppermost surface) of the nitride semiconductor obtained above and covers the entire surface. Gold is applied as a p-electrode on the whole surface electrode, and tungsten / tungsten is applied as an n-electrode on the n-type contact layer exposed by etching.
Aluminum is formed respectively. Thereafter, an SiO2 layer is formed on the entire surface by an evaporation method.

Then, the surfaces of the p-electrode and the n-electrode are exposed by dry etching using a resist mask. The resist mask is removed to expose the SiO2 layer on the nitride semiconductor. Next, a polyimide resin layer is formed on the entire surface, and the p-electrode and the n-electrode are exposed by wet etching to obtain the nitride semiconductor device of the present invention.

Comparative Example For comparison, a nitride semiconductor device was obtained in the same manner as in the example except that no groove was formed when forming the n-type contact layer.

FIG. 6 shows the emission intensity profiles around the end faces of the nitride semiconductor devices obtained in the above Examples and Comparative Examples.
Shown in FIG. 6 shows the relative luminous intensity, where the horizontal axis represents the distance from the end face of the nitride semiconductor element and the luminous intensity of the uppermost surface of the p-type nitride semiconductor layer where no groove is formed is the reference luminous intensity (100%). This is the profile on the vertical axis. The nitride semiconductor element without a groove obtained in the comparative example has an active layer end face (distance = 0 μm) as shown by a broken line in FIG.
m) is extremely strong, which is about 2.
The value is five times as large. On the other hand, in the nitride semiconductor device having the groove obtained in the example, as shown by the solid line in FIG. 6, the emission intensity around the end face of the active layer has three peaks derived from the groove. Is about 1.5 times the reference light emission intensity. As described above, it can be seen that the light having a high emission intensity from the end face of the active layer is diffused by forming the groove, and is not concentrated at one point of the epoxy resin. By diffusing strong light without concentrating it at one point, deterioration of the epoxy resin can be suppressed.

The nitride semiconductors obtained in the above Examples and Comparative Examples are mounted on lead electrodes using a die bonding device. Each electrode of the nitride semiconductor and the lead electrode are wire-bonded using a gold wire to establish electrical continuity. Next, an LED is obtained by sealing with an epoxy resin. FIG. 7 shows the result of measuring the emission intensity by supplying a current to the LED. L obtained in the comparative example
It can be seen that the intensity of the ED starts to deteriorate after about 1000 hours, and after about 10000 hours, the emission intensity is reduced to about 60% of the initial intensity.

[0034]

As described above, according to the present invention,
A groove having a depth penetrating the active layer from the outermost surface is formed near the outer periphery of the uppermost surface of the nitride semiconductor device, and two insulating layers having different refractive indices are formed in the groove, so that the end surface of the active layer is formed. The concentrated light can be diffused. Therefore, the deterioration of the epoxy resin around the end face of the active layer due to the light traveling parallel to the active layer can be suppressed, and the deterioration of the light emitting diode can also be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a nitride semiconductor device of the present invention.

FIG. 2 is a front view showing the configuration of the nitride semiconductor device of the present invention.

FIG. 3 is an enlarged view showing the periphery of an active layer end face of the nitride semiconductor of the present invention.

FIG. 4 is a diagram showing an example of an LED using the nitride semiconductor device of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional nitride semiconductor device.

FIG. 6 is a graph showing emission intensity profiles of nitride semiconductor devices according to an example of the present invention and a comparative example.

FIG. 7 is a graph showing a change over time in light emission luminance of an LED using the nitride semiconductor device of the example of the present invention and the comparative example.

[Explanation of symbols]

 101, 501: substrate 102, 502: n-type contact layer 103, 503: active layer (light-emitting layer) 104, 504: p-type cladding layer 105, 505: p-type contact layer 106 , 506... Overall electrode 107, 507... P-electrode 108, 508... N-electrode 109, 509... First insulating layer 111. ..Epoxy resin 421 Lead electrode 422 Nitride semiconductor element 423 Wire

Claims (6)

[Claims] 1. A nitride semiconductor device in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate, wherein the nitride semiconductor device is a p-type nitride semiconductor layer. A groove having a depth penetrating the active layer from an uppermost surface is formed, wherein the groove has a first insulating layer in contact with an inner wall surface and a second insulating layer in contact with the first insulating layer. A nitride semiconductor device, characterized in that: 2. The nitride semiconductor device according to claim 1, wherein the first insulating layer and the second insulating layer are made of materials having different refractive indexes. 3. The nitride semiconductor device according to claim 2, wherein said second insulating layer is made of a material having a higher refractive index than said first insulating layer. 4. The nitride semiconductor device according to claim 1, wherein the groove is formed along the vicinity of the outer periphery of the uppermost surface of the p-type nitride semiconductor layer of the nitride semiconductor device. 5. The nitride semiconductor device according to claim 1, wherein said first insulating layer is made of SiO 2. 6. The nitride semiconductor device according to claim 1, wherein said second insulating layer is made of a polyimide resin.