JP3663869B2 - Gallium nitride compound semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gallium nitride-based compound semiconductor element used for an optical device such as a light emitting diode.
[0002]
[Prior art]
Gallium nitride compound semiconductors such as GaN, AlGaN, and InGaN are attracting attention as semiconductor materials for visible light emitting devices such as green and blue and high-temperature operating electronic devices. Recently, high-luminance blue light-emitting diodes exceeding 2000 mcd are also available. It has been put into practical use.
[0003]
In the manufacture of optical devices using this gallium nitride compound semiconductor, sapphire is exclusively used as a substrate for crystal growth. In the case of using an insulating substrate such as sapphire, an electrode cannot be taken out from the substrate side unlike a light emitting element using a conductive semiconductor substrate such as GaAs or InP. The provided p-side and n-side electrodes are formed on one side of the substrate on which the semiconductor layers are stacked.
[0004]
In general, a gallium nitride-based compound semiconductor light-emitting device is formed by stacking an n-type layer and a p-type layer on a substrate surface by metal organic vapor phase epitaxy or molecular beam epitaxy, and then etching a part of the p-type layer. To expose the n-type layer, and an n-side electrode and a p-side electrode are bonded to the exposed surface of the n-type layer and the surface of the p-type layer, respectively.
[0005]
In such a semiconductor light emitting device, the lamination of the n-type layer and the p-type layer has a double hetero structure composed of an n-type cladding layer, an active layer, and a p-type cladding layer, thereby improving the light emission output. It is already widely known that this is possible. Also, a p-type cladding layer made of AlGaN doped with magnesium (Mg) as a p-type impurity, and a p-type GaN contact layer doped with Mg as a layer on which an electrode is to be formed is provided. Then, good ohmic properties with the electrode can be obtained, the forward voltage of the element can be reduced, and the light emission efficiency can be improved. A semiconductor light emitting device having such a structure is disclosed in, for example, Japanese Patent Laid-Open No. 6-268259.
[0006]
By the way, a p-type layer of a gallium nitride-based compound semiconductor generally has a higher electrical resistance than an n-type layer, so that current does not flow easily. For this reason, when a pad electrode for wire bonding is formed as a p-side electrode on the surface of the p-type layer by vapor deposition or the like, the current injected from the pad electrode does not spread in the layer direction of the p-type layer. There is a tendency that current flows only to the lower side of the formed region. Therefore, the light emission in the light emitting portion is limited to the region below the pad electrode, and the light traveling toward the p-type layer is blocked by the pad electrode, resulting in a reduction in light emission efficiency.
[0007]
On the other hand, as disclosed in, for example, Japanese Patent Application Laid-Open No. 6-314822, in order to easily inject current into the entire p-type layer as well as the pad electrode portion, a conductive material is formed on the upper surface of the p-type layer. It is effective to form a thin film and use it as an electrode. If the electrode made of a conductive thin film is made transparent and formed on almost the entire surface of the p-type layer, and the light-transmitting electrode is used, the upper surface of the p-type layer can be used as a light emission observation surface from the light emitting portion. . As the translucent electrode, Au and Ni, which can obtain ohmic contact with the p-type layer, are used.
[0008]
FIG. 4 is a diagram showing a cross-sectional structure of the above-described conventional gallium nitride-based compound semiconductor light emitting device, which is typical of what has been mainstream in recent years.
[0009]
In FIG. 4, a GaN buffer layer 12, an n-type GaN layer 13, an n-type AlGaN layer 14, an InGaN active layer 15, a p-type AlGaN layer 16 and a p-type GaN layer 17 are sequentially arranged on a sapphire substrate 11. It has a stacked double hetero structure. An n-side electrode 18 made of Ti and Al is formed on the upper surface of the n-type GaN layer 13, and a translucent p-side electrode 19 made of Au and Ni is formed almost on the upper surface of the p-type GaN layer 17. Is formed. Further, a p-side bonding electrode 20 is formed on the upper surface of the p-side electrode 19.
[0010]
[Problems to be solved by the invention]
As described above, Ni and Au are used as the p-side electrode 19. In general, the p-side electrode 19 is formed to have a thickness of 1 to 5 nm in the case of Ni and 5 to 20 nm in the case of Au. That is, a metal such as Ni or Au is formed as a very thin film to obtain translucency, but the transmissivity is 100% with respect to light emission from the InGaN active layer 15 which is a light emitting layer. Must not. For example, for light emission with a blue wavelength, the transmissivity is about 40% to 70%.
[0011]
On the other hand, if the p-side electrode 19 is formed extremely thin in order to increase the transmissivity, the adhesiveness and ohmic property with the p-type GaN layer 17 are deteriorated due to the thickness variation and the like, and a current is uniformly supplied to the p-type layer. There is a tendency to be unable to inject.
[0012]
For this reason, in the conventional gallium nitride-based compound semiconductor light emitting device, the average light emission characteristic is that the forward voltage Vf is about 3.6 V when the forward current If is 20 mA.
[0013]
On the other hand, for example, when a display panel is assembled by arranging a large number of light emitting diodes, the voltage drop is reduced for each of the light emitting diodes, so that the voltage applied to the entire display panel can be reduced. Therefore, the reduction of the forward voltage Vf is important from the viewpoint of power saving. Since the forward voltage is conventionally as large as about 3.6 V, it is effective to further reduce this value.
[0014]
The problem to be solved in the present invention is to reduce the forward voltage Vf in a gallium nitride compound semiconductor device by changing the material of the light-transmitting p-side electrode formed on the p-type gallium nitride compound semiconductor layer. The aim is to improve the transmissivity.
[0015]
[Means for Solving the Problems]
In the gallium nitride based semiconductor element of the present invention, the p-side electrode formed on the p-type gallium nitride based compound semiconductor layer has a layer made of Sb (antimony) or an alloy containing Sb (antimony). To do.
[0016]
By using Sb (antimony) or an alloy containing Sb (antimony) for the p-side electrode in contact with the p-type gallium nitride compound semiconductor layer, the ohmic property is improved, the interelectrode resistance is lowered, and the forward voltage Vf is reduced. Can be reduced. In addition, Sb (antimony) or an alloy containing Sb (antimony) has higher transmissivity than Ni (nickel) used in conventional semiconductor elements, so that the external quantum efficiency is improved in the light emitting element. When the brightness is equal to that of the conventional element, the thickness of the p-side electrode can be increased, bonding defects during assembly can be reduced, and the reliability of the element itself can be increased.
[0017]
Even when the gallium nitride based semiconductor element of the present invention is applied to a light receiving element, the forward voltage Vf can be reduced as in the case of the light emitting element.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 is a gallium nitride system comprising a p-type gallium nitride compound semiconductor layer, and a translucent p-side electrode formed on substantially the entire surface of the p-type gallium nitride compound semiconductor layer. In the compound semiconductor device, the p-side electrode has a layer made of an alloy containing Sb (antimony) or Sb (antimony) in contact with the p-type gallium nitride compound semiconductor layer, and reduces the forward voltage Vf. It has the effect of increasing the light transmittance.
[0019]
According to a second aspect of the present invention, the p-side electrode according to the first aspect has at least a two-layer structure in which Au (gold) is laminated on a layer of Sb (antimony) or an alloy containing Sb (antimony). Then, when it is taken out into the atmosphere with Sb exposed and Au for bonding is deposited again, the adhesion failure occurs, whereas the adhesion with the metal material in the next step can be increased. .
[0020]
Specific examples of embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a view showing a cross-sectional structure of a semiconductor light emitting device according to an embodiment of the present invention. The semiconductor light emitting device is a wafer in which a GaN buffer layer 2, an n-type GaN layer 3, an n-type AlGaN layer 4, an InGaN active layer 5, a p-type AlGaN layer 6, and a p-type GaN layer 7 are laminated in this order on the surface of the sapphire substrate 1. Then, a pattern having a predetermined shape is formed on the surface of the p-type GaN layer 7 and dry etching is performed from the p-type GaN layer 7 side to expose a part of the n-type GaN layer 3 where the n-side electrode is to be formed. An n-side electrode 8 is formed on the surface. The steps so far are the same as those of the conventional semiconductor light emitting device shown in FIG.
[0021]
In the semiconductor light emitting device of this embodiment, as the p-side electrode 9, an alloy Au—Sb containing Sb is vapor-deposited with a thickness of 100 mm on the entire surface of the p-type GaN layer 7. A p-side bonding electrode 10 is formed on the p-side electrode 9.
[0022]
By using the alloy Au—Sb containing Sb as the p-side electrode 9 in this way, the forward voltage Vf is reduced as compared with the conventional semiconductor light emitting device using Ni or Au as the p-side electrode. A light-emitting element having a high light rate was obtained.
[0023]
FIG. 2 is a diagram illustrating the gap between the p-electrode and the p-electrode in the semiconductor light-emitting device (A) of the present embodiment and the conventional semiconductor light-emitting device (B) in which 50 μm of Ni is deposited on the p-side electrode and 50 μm of Au is deposited thereon. It is a figure which shows the current-voltage characteristic. As shown in the figure, it can be seen that both the electrodes (A) and (B) obtain ohmic contact with the p-type GaN layer.
[0024]
Further, as is apparent from the characteristic diagram of FIG. 2, due to the relationship of R = V / I, the larger the slope of the straight line indicating the characteristic, the smaller the resistance, so the interelectrode resistance becomes smaller, and the p-type GaN layer and the better You can see that you are getting in touch.
[0025]
FIG. 3 is a diagram showing the transmissivity of the p-side electrode of the semiconductor light-emitting element (A) of this embodiment and the p-side electrode of the conventional semiconductor light-emitting element (B) by film thickness. The horizontal axis in the figure is the film thickness of the p-side electrode, and the vertical axis is the light transmittance of light having a wavelength of 450 nm. As shown in the figure, the p-side electrode of the semiconductor light emitting device (A) of this embodiment using the alloy Au—Sb has a light transmittance as compared with the p-side electrode of the conventional semiconductor light emitting device (B). The external quantum efficiency is improved by about 12%. When the brightness is equivalent to that of the conventional semiconductor light emitting device (B), the thickness of the p-side electrode in the semiconductor light emitting device (A) of the present embodiment is set to be larger than that of the p-side electrode of the conventional semiconductor light emitting device (B). The thickness can be increased by about 60 mm, bonding defects during assembly can be reduced, and the reliability of the element itself can be increased.
[0026]
【Example】
(Example 1)
In the cross-sectional structure of the semiconductor light emitting device shown in FIG. 1, the surface of the sapphire substrate 1 has a GaN buffer layer 2 of 200 mm, an n-type GaN layer 3 of 4 μm, an n-type AlGaN layer 4 of 0.1 μm, and an InGaN active layer 5 of 0. A wafer is prepared by sequentially stacking 05 μm, p-type AlGaN layer 6 with a thickness of 0.1 μm, and p-type GaN layer 7 with a thickness of 0.5 μm. Next, a pattern having a predetermined shape is formed on the surface of the p-type GaN layer 7 of this wafer, dry etching is performed from the p-type GaN layer 7 side, and one of the n-type GaN layer 3 on which the n-side electrode 8 is to be formed. Expose the part. Next, Ti is deposited on the exposed n-type GaN layer 3 as an n-side electrode 8 in order with a film thickness of 0.3 μm and Au in a thickness of 2 μm, and is patterned into a predetermined shape. Further, an alloy Au—Sb containing Sb is vapor-deposited on the almost entire surface of the p-type GaN layer 7 as the p-side electrode 9. After vapor deposition, the wafer is heat-treated in an inert gas atmosphere. Here, it is necessary to form the p-side bonding electrode 10 for bonding the Au wire to a part of the p-side electrode 9, but this may be performed before or after the heat treatment. Thus, the semiconductor light-emitting device obtained by cutting the electrode-formed wafer into a predetermined shape was assembled as an LED lamp.
[0027]
This LED achieved a forward voltage Vf of 3.2 v at a forward current If of 20 mA. Therefore, when a large number of LEDs having the forward voltage Vf are arranged to form a display panel, the power consumption of the entire circuit is greatly reduced, and at the same time, the LED alone is caused by the forward voltage Vf. Since heat generation is also suppressed, reliability is ensured and the service life is extended.
[0028]
In addition, the light emission output was 1.2 times that of an LED using a conventional semiconductor light emitting device in which 50 μm of Ni was vapor-deposited on the p-side electrode and 50 μm of Au was vapor-deposited thereon.
[0029]
(Example 2)
An LED lamp was assembled in the same manner as in Example 1 except that 50 p of Sb was vapor deposited on almost the entire surface of the p-type GaN layer 7 as the p-side electrode 9 and 50 g of Au was vapor deposited thereon. This LED achieved a forward voltage Vf of 3.2 v as in Example 1 at a forward current If of 20 mA. In addition, the light emission output was 1.2 times that of an LED using a conventional semiconductor light emitting element.
[0030]
(Example 3)
As a p-side electrode 9, an LED lamp was assembled in the same manner as in Example 1 except that 150% of the alloy Au-Sb containing Sb was deposited on almost the entire surface of the p-type GaN layer 7. This LED achieved a forward voltage Vf of 3.2 v as in Example 1 at a forward current If of 20 mA. Moreover, the light emission output was also equivalent to the LED using the conventional semiconductor light emitting element.
[0031]
【The invention's effect】
The gallium nitride compound semiconductor device of the present invention reduces the forward voltage Vf by using Sb (antimony) or an alloy containing Sb (antimony) for the p-side electrode in contact with the p-type gallium nitride compound semiconductor layer. Thus, the efficiency of the LED can be improved. In addition, Sb (antimony) or an alloy containing Sb (antimony) has higher transmissivity than Ni (nickel) used in conventional semiconductor elements, so that the external quantum efficiency is improved in the light emitting element. When the brightness is equivalent to that of a conventional light emitting device, the thickness of the p-side electrode can be increased, bonding defects during assembly can be reduced, and the reliability of the device itself can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross-sectional structure of a semiconductor light emitting device in an embodiment of the present invention. FIG. 2 is a diagram showing current-voltage characteristics of the semiconductor light emitting device of the present embodiment and a conventional semiconductor light emitting device. The figure which shows the transmissivity about the p side electrode of the semiconductor light emitting element of a form, and the p side electrode of the conventional semiconductor light emitting element [FIG. 4] The figure which shows the cross-section of the conventional gallium nitride type compound semiconductor light emitting element ]
1,11 Sapphire substrate 2,12 GaN buffer layer 3,13 n-type GaN layer 4,14 n-type AlGaN layer 5,15 InGaN active layer 6,16 p-type AlGaN layer 7,17 p-type GaN layer 8,18 n side Electrodes 9, 19 p-side electrode 10, 20 p-side bonding electrode

Claims (2)

In the gallium nitride compound semiconductor device having a p-type gallium nitride compound semiconductor layer, and a light-transmitting p-side electrode formed on substantially the entire surface of the p-type gallium nitride compound semiconductor layer , the p-side electrode Has a layer made of Sb (antimony) or an alloy containing Sb (antimony) in contact with the p-type gallium nitride compound semiconductor layer .   2. The gallium nitride compound semiconductor device according to claim 1, wherein the p-side electrode has at least a two-layer structure in which Au (gold) is laminated on a layer of Sb (antimony) or an alloy containing Sb (antimony).

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