JPH07106633A - Gallium nitride based compound semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To provide a gallium nitride based compound semiconductor light emitting element having an emission observing plane on the side of an electrode formed on the same side in which the ohmic characteristics are sustained by preventing deterioration of p-layer translucent ohmic electrode due to the migration of a pad electrode and the external quantum efficiency is prevented from lowering by sustaining the translucency of the translucent electrode. CONSTITUTION:The electrode of p-layer 3 comprises a first translucent ohmic electrode 11 formed substantially on the entire surface of the p-layer 3, and a second bonding electrode 12 (pad electrode) formed on the surface of the first electrode 11. The second electrode 12 is made of Au or an alloy thereof containing no Cr thus sustaining the translucency of the first electrode and the ohmic characteristics of the first electrode and the p-layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a gallium nitride compound semiconductor (In _X Al _Y Ga _1-XY N, 0≤X≤1, 0≤Y≤ used for a light emitting diode, a laser diode, etc.
The present invention relates to a gallium nitride-based compound semiconductor light-emitting device in which (1) is laminated, and particularly to a structure of an electrode of a gallium nitride-based compound semiconductor light-emitting device having a pn junction.

[0002]

2. Description of the Related Art A conventional gallium nitride-based compound semiconductor light emitting device includes an n-type gallium nitride-based compound semiconductor layer and a high-resistance i-type gallium nitride-based compound semiconductor layer doped with a p-type dopant on a substrate. So-called M in which and are stacked
An IS structure is known, but recently, a technique of changing a high resistance i-type to a p-type (Japanese Patent Laid-Open Nos. 2-257679, 3-218325, and 5-183).
No. 189, etc.) has been announced, and a pn junction type light emitting device has become feasible.

At present, a p-n junction type gallium nitride compound semiconductor light-emitting element is usually p-type because the manufacturing method of the p-type gallium nitride compound semiconductor (hereinafter referred to as p layer) is limited. The layer is the uppermost layer (that is, the layer at the end of lamination). Further, since sapphire having a light-transmitting property and an insulating property is used for the substrate of the light emitting element, the light emission observation surface side of the light emitting element is often the substrate side. However, in a pn junction type light emitting device in which the substrate side is the light emission observation surface side, when connecting the electrodes of the p layer and the n layer formed on the same surface side to the lead frame, one chip is divided into two lead frames. Since one chip must be mounted over the other, there is a disadvantage that the size of one chip becomes large. That is, the n-layer electrode is p
Since it is electrically short-circuited when it comes into contact with the layer, it is necessary to increase the width of each of the positive and negative electrodes on the chip, the width of the two lead frames, and the space between them, which naturally increases the chip size. Therefore, there are disadvantages that the number of chips that can be obtained from one wafer is small and the cost is high.

On the other hand, in the light emitting element having the electrode side as the light emission observation surface, one chip can be mounted on one lead frame, so that the chip size can be reduced. Moreover, since both the positive and negative electrodes can be taken out from the emission observation surface side, there is an advantage that it is advantageous in terms of production technology. On the other hand, the electrodes on the emission observation surface side hinder the emission, so that the substrate side can be removed. The external quantum efficiency is lower than that of the light emitting device used as the emission observation surface.

[0005]

In order to solve the problem of external quantum efficiency, we first proposed that the electrode formed on the p-layer of a light-emitting element having the p-layer side as an emission observation surface is made of a light-transmitting material made of metal. , And a pad electrode (second electrode) for bonding is formed on the entire surface electrode (first electrode). This technique has improved the problems of the conventional gallium nitride-based compound semiconductor light emitting device. However, there has been a problem that migration of the pad electrode due to the metal material occurs during energization, and the translucency of the translucent electrode is lost. In particular, since the light-transmissive electrode has a very thin film thickness to maintain the light-transmissive property, when migration of the pad electrode occurs, the influence thereof is great and the ohmic characteristic of the light-transmissive electrode is deteriorated. Briefly, a part of the metal material of the bad electrode diffuses into the translucent electrode during energization, so that the translucent electrode deteriorates and loses its translucency, and at the same time, the translucency with the p-type layer is lost. The ohmic contact with the conductive electrode deteriorates.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a gallium nitride-based compound semiconductor light-emitting device in which the electrode side formed on the same surface side has an emission observation surface. The purpose is to prevent the translucent electrode of the p layer from being deteriorated due to migration of the pad electrode, maintain the ohmic characteristics, and maintain the translucency of the translucent electrode so as not to reduce the external quantum efficiency.

[0007]

As a result of repeated experiments on the material of the pad electrode formed on the surface of the translucent electrode, by using Au which does not contain a specific element in the pad electrode, The inventors have found that the problem can be solved and have completed the present invention. That is, in the gallium nitride-based compound semiconductor light-emitting device of the present invention, an n-layer electrode and a p-layer electrode are formed on the same surface side, and the gallium nitride-based compound semiconductor light emission with the electrode side as the light emission observation surface side. In the element, the electrode of the p-layer includes a light-transmissive first electrode formed on almost the entire surface of the p-layer, and a second electrode for bonding formed on the surface of the first electrode, The second electrode is made of a simple substance of Au or an alloy containing Au but not Al or Cr. In the present application, the light-transmitting property means that light emitted from the gallium nitride-based compound semiconductor is transmitted, and does not necessarily mean colorless and transparent.

[0008]

In the light emitting device of the present invention, since the first electrode formed on the p layer is a full surface electrode formed on almost the entire surface of the p layer, the current is uniformly spread over the entire p layer, and the pn junction is formed. Uniform light emission can be obtained from the interface. Moreover, by making the first electrode transparent, the light emission is not obstructed by the electrode when the light emission is observed from the electrode side, so that the external quantum efficiency of the light emitting element is significantly improved. Further, in the light emitting device of the present invention, the second electrode is formed as a pad electrode for bonding on the first electrode. Since the second electrode contains Au, it has good adhesiveness to the first electrode and also has good adhesiveness to a ball made of a gold wire used in wire bonding. Further, Au is less likely to migrate to the first electrode during energization of the element, and is less likely to deteriorate the quality of the first electrode. However, Al in Au
Or, if an alloy containing Cr is used as the second electrode,
These metals cause migration in a relatively short time (for example, 500 hours) during energization to deteriorate the first electrode. Therefore, when the second electrode is made of Au or an alloy containing Au and not containing Al or Cr, it is possible to realize an electrode that has good adhesiveness to the first electrode and the ball and does not easily cause migration during energization.

[0009]

FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention. This device has a homo structure in which an n layer 2 and ap layer 3 are laminated in this order on a sapphire substrate 1. The ohmic electrode of the n-layer 2 is formed on the n-layer 2, and the translucent first electrode 11 for the ohmic is formed on the p-layer 3. , The first electrode 1
A second electrode 12 for bonding is formed on the first electrode 1.

To make the first electrode 11 transparent, A
It can be realized by forming an electrode material such as u, Pt, Al, Sn, Cr, Ti, and Ni to be very thin. Specifically, a thin film is formed directly by a technique such as vapor deposition or sputtering so that the electrode becomes transparent, or a thin film is formed and then annealing is performed to make the electrode transparent. can do. That is, the first electrode is the p-layer 3
And an electrode for obtaining ohmic contact with Al, and may contain Al or Cr, unlike the second electrode. A preferable first electrode 11 is a translucent electrode made of an alloy in which Ni and Au are sequentially stacked, and most preferably an alloy in which Ni and Au are sequentially stacked from the p-layer side. By configuring the first electrode 11 as described above, good ohmic contact with the p layer can be obtained. FIG. 2 is a diagram in which Ni and Au are vapor-deposited on the p-type GaN layer in order to have a film thickness of 0.1 μm, respectively, and then annealed to alloy the electrodes so that the electrodes are translucent and the current-voltage characteristics thereof are measured. . As shown in this figure, it can be seen that the first electrode 11 formed by sequentially stacking Ni and Au has very good ohmic contact.

The thickness of the first electrode 11 is 0.001 μm
It is preferably formed with a thickness of 1 μm. 0.001μ
If it is thinner than m, the electrode resistance tends to increase. On the other hand, if the thickness is thicker than 1 μm, the electrode becomes less transparent and is not practical. Although slightly different depending on the electrode material, the first electrode 11 is almost transparent, hardly interferes with light emission, and has a low contact resistance.
The range of 05 μm to 0.2 μm is particularly preferable.

Next, the light emitting device of the present invention comprises a first electrode 11
The second electrode 12 is formed as a pad electrode for bonding on the surface of the. The second electrode 12 is made of Au alone or an alloy containing Au and not Al or Cr.

In the light emitting device having the structure shown in FIG. 1, the first electrode 11 is a translucent electrode in which Ni and Au are laminated in order, and a second electrode for bonding is formed on the translucent electrode with various materials. After forming the electrode 12, wire bonding was performed on the n-layer electrode 4 and the second electrode 12 to cause light emission as a normal light emitting diode, and the state of the first electrode after continuous lighting for 500 hours was examined. The results are shown in Table 1. In Table 1, the electrode material shown on the column side shows the electrode material on the first electrode 11 side, and the electrode material shown on the row side shows the electrode material on the side in contact with the ball. That is, it is shown that the second electrode 12 in Table 1 is an electrode in which the electrode material shown in the column and the electrode material shown in the row are sequentially laminated.

In Table 1, the characteristics of the second electrode 12 are as follows:
After 500 hours of lighting, the first electrode material did not discolor at all and the translucency was maintained, and the ohmic characteristics of the p layer 3 and the first electrode 11 did not change.
The color of the first electrode around 2 is slightly discolored, but it is not such that the light emission is attenuated and the ohmic characteristics are not changed, and the transparency of the first electrode 11 is lost, and the ohmic characteristics are decreased. What was lost was evaluated as x. However, those in which the adhesiveness between the second electrode 12 and the ball was poor and wire bonding was difficult were indicated by − regardless of the presence or absence of discoloration of the first electrode 11.

[0015]

[Table 1]

As shown in Table 1, for example, when the first electrode is Ni-Au, the material of the bonding second electrode 12 formed on the first electrode is the same as that of the first electrode. If the same material as that of Au-Ni, that is, Au-Ni, is used, the first electrode 11 does not discolor at all and remains transparent. Also, Au alone can achieve the same effect as Au-Ni. On the other hand, Cr and Al easily cause migration with respect to the first electrode 11, and when these metals are contained in the second electrode 12, even if Au is contained, the first electrode 1
The characteristic of 1 is lost.

As another embodiment, the first electrode 11
Au-Ti (however, the ohmic characteristics of Au-Ti are
It was slightly inferior to Ni-Au. ), A number of second electrode materials were similarly formed, and the second electrode materials were evaluated. The results are not shown in the table, but when the second electrode material is Au alone, or when Au-Ti is used.
(The order of stacking Au-Ti does not matter.), ○ in the case of electrodes made of Ni, In, Pt, etc. containing Au, where Au, Al, Al, Cr are included. As in the case of 1, the evaluation was x.

Further, as another embodiment, the first electrode 1
1 was formed of Au-Al (however, the ohmic characteristics of Au-Al were slightly inferior to those of Ni-Au), and then a number of second electrode materials were formed in the same manner to form the second electrode. The material was evaluated. The results are also not shown in the table, but when the second electrode material is Au alone, ◯, Au
In the case of an electrode made of Ni, Ti, In, Pt, etc. containing, Δ is evaluated, but Au-Al is the same as Table 1 even though Au-Al is the same material, and the same is true when Au-Cr is included. It was x.

[0019]

As described above, the light emitting device of the present invention is a gallium nitride-based compound semiconductor light emitting device having the electrode side as a light emission observation surface, and the first electrode for ohmic contact is transparent. Of the second electrode material for bonding formed on the surface of the first electrode of Au alone or Au.
By using an alloy containing Al but not Al or Cr, the ohmic characteristics of the first electrode are not changed and the color is not changed, so that the reliability of the light emitting element is significantly improved. Further, in the present specification, a homo-structured pn
Although the junction type light emitting device has been described, it is needless to say that the present invention is not limited to the homostructure and is also applicable to a gallium nitride compound semiconductor light emitting device having a single hetero structure or a double hetero structure having a pn junction.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a current-voltage characteristic of a first electrode Ni-Au.

[Explanation of symbols]

 1 ... Sapphire substrate 2 ... n-type GaN layer 3 ... p-type GaN layer 4 ... n-type layer electrode 11 ... first electrode 12 ... Second electrode

Claims (4)

[Claims] 1. In a gallium nitride-based compound semiconductor light-emitting device in which an n-layer electrode and a p-layer electrode are formed on the same surface side, and the electrode side is the emission observation surface side, the p-layer electrode is , A translucent first electrode formed on substantially the entire surface of the p-layer, and a bonding second electrode formed on the surface of the first electrode, and the second electrode is made of Au.
A gallium nitride-based compound semiconductor light emitting device comprising a single substance or an alloy containing Au and not containing Al or Cr. 2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the first electrode and the second electrode are made of the same material. 3. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the first electrode is made of an alloy in which Ni and Au are laminated. 4. The second electrode comprises, in addition to Au, Ti,
2. An alloy containing at least one selected from the group consisting of Ni, In and Pt.
2. A gallium nitride-based compound semiconductor light emitting device according to.