JP4501234B2 - Nitride semiconductor device - Google Patents

Description

[0001]
BACKGROUND 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 luminance of the light emitting diode.
[0002]
[Prior art]
A nitride semiconductor has a wide band gap and is a direct transition type, so that 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-emitting LEDs using nitride semiconductor elements have been put into practical use as various light sources such as LED displays, traffic signal lights, and image scanner light sources.
[0003]
An LED is basically composed of a semiconductor element, an electrode, and a sealing material. The semiconductor element includes a p-type and an n-type semiconductor having at least a semiconductor junction formed on a substrate, and a p-electrode and an n-electrode in contact with each semiconductor.
[0004]
When a nitride semiconductor element is given as a specific example of the semiconductor element, the mismatch of the lattice constant with the nitride semiconductor is relaxed on a substrate 501 such as sapphire or spinel which is a light-transmitting insulating substrate as shown in FIG. Buffer layer (not shown), n-type contact layer 502 made of Si-doped GaN for obtaining ohmic contact with n-electrode 508, active layer (light-emitting layer) made of GaN and InGaN that generates light by carrier coupling 503, p-type cladding layer 504 made of Mg-doped AlGaN and Mg-doped InGaN for confining carriers in the active layer, and p-electrode 507 made of Mg-doped GaN for making ohmic contact with the p-electrode 507 Nitride semiconductor in which type contact layer 505 is sequentially laminated and formed by etching this nitride semiconductor An n-electrode 508 formed in a desired shape on the exposed surface of the deposited n-type nitride semiconductor, and a p-electrode formed in a desired shape on the entire surface electrode 506 covering almost the entire surface of the p-type nitride semiconductor layer 507, and an insulating layer 509 formed for the purpose of protecting the nitride semiconductor and each electrode from the outside and preventing a short circuit. This nitride semiconductor element is mounted on a lead electrode, electrically connected, and sealed with a sealing material such as a light-transmitting epoxy resin to form an LED. When such an LED is energized, light emitted from the active layer in the nitride semiconductor element is emitted from the surface of the uppermost p-type nitride semiconductor layer and the end face of the active layer.
[0005]
[Problems to be solved by the invention]
However, with the recent increase in output of LEDs, problems that have not existed before 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.
[0006]
Epoxy resins are currently most commonly used as sealing materials because they have good adhesion to nitride semiconductors, excellent mechanical strength, are chemically stable, and are inexpensive. This material is excellent in weather resistance against weak light and heat from 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 other colors, the epoxy resin deteriorates and becomes a black-brown color, and light from the nitride semiconductor element Will be absorbed. For this reason, there is a problem that the light emission intensity of the LED is lowered due to long-term use, even though the nitride semiconductor element is not deteriorated.
[0007]
Accordingly, an object of the present invention is to provide a nitride semiconductor device that suppresses deterioration of the epoxy resin sealing the nitride semiconductor device and maintains high brightness of the LED.
[0008]
[Means for Solving the Problems]
As a result of intensive investigations to achieve the above object, the inventors of the present invention have a particularly severe deterioration in the vicinity of the active layer end face among the epoxy-based resins sealing the nitride semiconductor element. It has been found that the above problems can be solved by improving the shape of the physical semiconductor element, and the present invention has been completed.
[0009]
That is, the 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,
In the nitride semiconductor device, a groove having a depth penetrating the active layer from the uppermost surface of the p-type nitride semiconductor layer is formed, and a first insulating layer in contact with the inner wall surface is formed in the groove, And a second insulating layer in contact with the insulating layer.
[0010]
The first insulating layer and the second insulating layer are made of materials having different refractive indexes.
[0011]
Furthermore, the second insulating layer is made of a material having a refractive index higher than that of the first insulating layer.
[0012]
The groove is preferably formed along the vicinity of the outer periphery of the uppermost surface of the p-type nitride semiconductor layer of the nitride semiconductor element. With this configuration, it is possible to efficiently diffuse light propagating in parallel through the active layer.
[0013]
Moreover, SiO2 can be suitably used as the first insulating layer.
[0014]
Moreover, a polyimide resin can be suitably used as the second insulating layer.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The light-emitting diode 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, and particularly has a main emission wavelength emitted from the active layer. It is a nitride semiconductor device having a thickness of 500 nm or less. A nitride semiconductor according to an embodiment of the present invention will be described below with reference to the drawings.
[0016]
FIG. 2 is a front view of the nitride semiconductor device according to the embodiment of the present invention, and FIG. 1 is a cross-sectional view taken along the plane 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) that relaxes the lattice constant mismatch with the nitride semiconductor layer on the substrate 101 such as sapphire or spinel. In order to obtain ohmic contact with the n electrode 108, an n-type contact layer 102 made of Si-doped GaN, an active layer (light-emitting layer) 103 made of GaN and InGaN that generates light by carrier coupling, and carriers as active layers P-type cladding layer 104 made of Mg-doped AlGaN for confinement and Mg-doped InGaN, p-type contact layer made of Mg-doped GaN for obtaining ohmic contact with the p-electrode 107 and the entire surface electrode 106 105 are sequentially stacked.
[0017]
The buffer layer is GaN crystal-grown at a low temperature, and the film thickness is preferably 10 to 500 mm. The n-type contact layer 102 is composed of GaN doped with Si, and the film thickness is preferably 1 to 20 μm, more preferably 2 to 6 μm. On the n-type contact layer 102, for example, an n-type cladding layer made of AlGaN doped with Si may be formed to a thickness of 100 to 500 mm. The active layer 103 may be composed of InGaN with a thickness of 25 to 300 mm, or 1 to 10 layers of GaN with a thickness of 50 mm and InGaN with a thickness of 30 mm are formed, and finally GaN with a thickness of 50 mm is formed. It may be configured as a single or multiple quantum well layer.
[0018]
The p-type cladding layer 104 is made of AlGaN doped with Mg and InGaN doped with Mg, and the film thickness is preferably 100 to 0.2 μm. The p-type contact layer 105 is made of GaN doped with Mg, The film thickness is preferably 0.05 to 0.2 μm.
[0019]
Thereafter, the nitride semiconductor is etched. In the embodiment of the present invention, as shown in FIG. 1, a groove penetrating the active layer 103 from the uppermost surface of the p-type nitride semiconductor layer (p-type contact layer) 105 is formed. 112 is formed, and a first insulating layer 109 in contact with the inner wall and a second insulating layer 111 in contact with the first insulating layer are formed in the groove.
[0020]
The depth of the groove may be formed so as to penetrate the active layer from the uppermost surface of the p-type nitride semiconductor 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 it is too deep, the current path becomes narrow and it becomes difficult for the current to flow, and if the groove reaches the substrate, the current does not flow, which is not preferable.
As another form, an n-electrode formed on the conductive GaN substrate side using a conductive material such as GaN as a substrate, and a p-electrode formed on the p-type nitride semiconductor layer side face each other. In the case of the nitride semiconductor device of the form, even if the groove formed from the uppermost surface of the p-type nitride semiconductor layer reaches the conductive GaN substrate, it does not hinder the flow of current. In such a case, the depth of the groove may be up to the substrate.
[0021]
Further, the groove in this embodiment can be formed by etching. It may be formed at the same time as etching when exposing the n-electrode forming surface, or a groove may be formed by etching after exposing the n-electrode forming surface. The former can form a groove by simply changing the mask without increasing the number of steps, and the latter can form a groove of any depth, although there is a problem that the number of etching steps increases twice.
[0022]
In the groove of this embodiment, an insulating layer is formed inside the groove. As a result, the end face of the active layer (light emitting layer) and the epoxy resin can be kept away. That is, the insulating layer and the outer wall of the groove (the portion between the end surface of the nitride semiconductor and the groove) are formed between the active layer end face 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 trench, no current is supplied and the active layer does not emit light. Therefore, there is no problem even if the outer wall of the groove is close to the epoxy resin.
[0023]
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 are made of materials having different refractive indexes. It is done. Here, FIG. 3 shows an enlarged view around the active layer end face of the nitride semiconductor device of the present embodiment. When the second insulating layer is a material having a refractive index higher than that of the first insulating layer, the light emitted from the active layer reaches the epoxy resin as indicated by an arrow in the figure, It is diffused mainly when passing through the interface between the second insulating layer and another member. Broadly speaking, (1) the interface between the first insulating layer and the second insulating layer in contact with the inner side wall in the groove, and (2) the first in contact with the second insulating layer in the groove and the outer wall of the groove. (3) It diffuses widely at each interface of the interface between the first insulating layer and the second insulating layer in contact with the outer wall of the outer wall of the groove. 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, thereby forming the active layer. Light from the end face can be diffused more efficiently.
[0024]
Further, 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 p-type nitride semiconductor layer of the nitride semiconductor as shown in FIG. Since the active layer between the outer wall of the groove and the side surface of the nitride semiconductor does not emit current and does not emit light, it is preferable to form the 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 a narrower width is preferable in order to increase a light emitting area. If it is too wide, the light emitting area becomes narrow, which is not preferable.
[0025]
SiO2 can be suitably used as the material for the first insulating layer, and polyimide resin can be suitably used as the material for the second insulating layer. Although SiO 2 and polyimide resin are different in properties such as refractive index, both are colorless and transparent materials similar to epoxy resin. However, since it is less likely to deteriorate with respect to light having a short wavelength from the nitride semiconductor element inside the LED as compared with the epoxy resin, it is difficult to reduce the light emission intensity of the LED even if it is used for a long time.
[0026]
Further, the nitride semiconductor device of the present invention can be used for an LED or the like, for example, can be mounted on a bullet-type LED as shown in FIG. 4, but is not limited to this form and is sealed with an epoxy resin or the like. Since the outer shape can be arbitrarily selected as long as the nitride semiconductor element is sealed with a material, it goes without saying that it can be used for various types of LEDs such as a surface mount type. Further, the present invention can also be applied to a case where the sealing material contains a fluorescent material that emits fluorescence when excited by light from the nitride semiconductor element. Can be expected enough.
[0027]
【Example】
[Example]
A nitride semiconductor having the following configuration is used as the nitride semiconductor. Each semiconductor layer is formed on the substrate by a metal organic vapor deposition method (MOCVD method). As shown in FIG. 1, a buffer layer (not shown) made of GaN with a thickness of about 100 mm, an n-type contact / cladding layer with a thickness of about 4 μm made of Si-doped GaN, GaN, and An active layer (light emitting layer) having a multi-quantum well structure made of InGaN having a thickness of about 1600 mm, a p-type cladding layer having a thickness of about 400 mm made of AlGaN doped with Mg and InGaN doped with Mg, and doped with Mg A p-type contact layer made of GaN and having a thickness of about 3000 mm is stacked in this order.
[0028]
A positive electrode and a negative electrode are formed on the nitride semiconductor. First, the end portion of the nitride semiconductor is removed by etching in order to form the n-electrode in the n-type contact layer. Etching is performed from the p-type contact layer side, and is about 1 μm to the depth at which the n-type contact layer is exposed. At this time, by using a mask capable of forming a groove along the vicinity of the uppermost surface of the p-type contact layer, a groove having a depth of about 1 μm from the surface of the p-type nitride semiconductor layer as shown in FIG. The nitride semiconductor which has is obtained.
[0029]
Gold is deposited by sputtering as an electrode that contacts the p-type contact layer (uppermost surface) of the nitride semiconductor obtained above and covers the entire surface. Gold is formed as a p-electrode on the entire surface electrode, and tungsten / aluminum is formed as an n-electrode on the n-type contact layer exposed by etching. Thereafter, a SiO2 layer is formed on the entire surface by vapor deposition.
[0030]
Next, 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, thereby obtaining the nitride semiconductor device of the present invention.
[0031]
[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 the n-type contact layer was formed.
[0032]
FIG. 6 shows the emission intensity profile around the end face of the nitride semiconductor device obtained in the above-described examples and comparative examples. FIG. 6 shows the relative light emission intensity with the distance from the end face of the nitride semiconductor element as the horizontal axis and the light emission intensity of the uppermost surface of the p-type nitride semiconductor layer without grooves formed as the reference light emission intensity (100%). The profile is plotted on the vertical axis. As shown by the broken line in FIG. 6, the nitride semiconductor element without grooves formed in the comparative example has an extremely strong emission intensity at the end face of the active layer (distance = 0 μm), and has a reference emission intensity. The value is about 2.5 times. On the other hand, the nitride semiconductor device having the groove obtained in the example has three peaks derived from the groove, as shown by the solid line in FIG. Even the one having the strongest emission intensity is about 1.5 times the reference emission intensity. Thus, it can be seen that light having strong emission intensity from the end face of the active layer is diffused by forming a groove and does not concentrate on one point of the epoxy resin. By diffusing strong light without concentrating it on one point, deterioration of the epoxy resin can be suppressed.
[0033]
The nitride semiconductors obtained in the above examples and comparative examples are mounted on the lead electrode using a die bonding apparatus. 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 supplying the current to the LED and measuring the emission intensity. The LED obtained in the comparative example began to deteriorate in intensity from about 1000 hours, and the emission intensity decreased to about 60% of the initial intensity after about 10,000 hours. Recognize.
[0034]
【The invention's effect】
As described above, according to the present invention, a groove having a depth penetrating the active layer from the outermost surface is formed along the vicinity of the outermost surface of the nitride semiconductor element, and two grooves having different refractive indexes are formed in the groove. By forming the insulating layer, the light concentrated on the end face of the active layer can be diffused. Therefore, deterioration of the epoxy resin around the end face of the active layer due to light traveling in parallel with the active layer can be suppressed, so that 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 the active layer end face of the nitride semiconductor of the present invention.
FIG. 4 is a view 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 diagram showing a profile of light emission intensity of nitride semiconductor devices according to examples and comparative examples of the present invention.
FIG. 7 is a view showing a change with time of light emission luminance of an LED using nitride semiconductor elements of examples and comparative examples of the present invention.
[Explanation of symbols]
101, 501 ... substrate 102, 502 ... n-type contact layer 103, 503 ... active layer (light emitting layer)
104, 504 ... p-type cladding layers 105, 505 ... p-type contact layers 106, 506 ... full surface electrodes 107, 507 ... p electrodes 108, 508 ... n electrodes 109, 509 ... 1st insulating layer 111 ... 2nd insulating layer 112 ... groove | channel 410 ... epoxy resin 421 ... lead electrode 422 ... nitride semiconductor element 423 ... wire

Claims (3)

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,
In the nitride semiconductor element, a groove having a depth penetrating the active layer from the uppermost surface of the p-type nitride semiconductor layer is formed along the outer periphery of the uppermost surface of the p-type nitride semiconductor layer,
The groove includes a first insulating layer in contact with the inner wall surface in its interior, said second insulating layer and is formed in contact with the first insulating layer,
The nitride semiconductor element, wherein the second insulating layer is made of a material having a refractive index higher than that of the first insulating layer . The first insulating layer, a nitride semiconductor device according to claim 1, wherein comprised of SiO _2. The second insulating layer, according to claim 1 or claim 2 nitride semiconductor device according made of polyimide resin.

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