JP2697572B2 - Gallium nitride based compound semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gallium nitride compound semiconductor (InXAlYGa1-X-YN, 0≤X≤1, 0≤Y≤) used for a light emitting diode, a laser diode or the like.
The present invention relates to a gallium nitride-based compound semiconductor light-emitting device in which 1) is laminated, and in particular, has a p-type gallium nitride-based compound semiconductor layer on the outermost surface, and uses the p-type gallium nitride-based compound semiconductor layer side as a light emission observation surface. The present invention relates to a structure of an electrode of a light emitting element.

[0002]

2. Description of the Related Art A conventional gallium nitride-based compound semiconductor light emitting device comprises 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
Although those having an IS structure are known, recently, a technique of converting a high-resistance i-type into a p-type (JP-A-2-257679, JP-A-3-218325, and JP-A-5-183)
No. 189) has been announced, and a pn junction type light emitting device has become feasible.

At present, pn junction type gallium nitride-based compound semiconductor light emitting devices are generally limited to p-type gallium nitride-based compound semiconductors (hereinafter referred to as p-layers) because of their limited manufacturing methods. 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-emitting observation surface side of the light-emitting element is often the substrate side. However, the pn junction type light emitting element having the substrate side as 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 connected to two lead frames. Therefore, there is a disadvantage that the size of one chip increases. That is, the electrode of the n-layer is p
When a contact is made with the layer, an electrical short circuit occurs, and the chip size naturally increases due to the necessity of increasing the distance between each of the positive and negative electrodes on the chip and the width of the two lead frames. Therefore, there is a disadvantage that the number of chips that can be obtained from one wafer is reduced, and the cost is increased.

On the other hand, in a light emitting device having a gallium nitride-based compound semiconductor layer side as a light emission observation surface, one chip can be mounted on one lead frame, so that the chip size can be reduced. In addition, since both positive and negative electrodes can be taken out from the emission observation surface side, there is an advantage that it is advantageous from the viewpoint of production technology. There is a disadvantage that the external quantum efficiency is lower than that of the light emitting element used as the light emission observation surface.

[0005]

SUMMARY OF THE INVENTION In order to provide a light emitting device having a high external quantum efficiency and excellent production technology, first, the p layer of a light emitting device having a light emitting observation surface on the p layer side. A technique was proposed in which the electrode formed on the substrate was a light-transmitting whole surface electrode.

According to the above technology, the problem of the conventional gallium nitride-based compound semiconductor light emitting device has been improved. However, when an electrode for bonding (bonding pad) is further formed on the entire surface electrode formed on the p layer,
At the time of wire bonding, there is a problem that the wire is pulled by the wire and the bonding electrode and the transparent full-surface electrode are easily peeled off, or the whole-surface electrode is easily peeled off from the p-layer.

Accordingly, the present invention has been made in view of such circumstances, and it is an object of the present invention to reduce the external quantum efficiency of a gallium nitride-based compound semiconductor light emitting device having a p-layer as a light emission observation surface side. Another object of the present invention is to provide a light emitting element having excellent reliability by eliminating peeling of a p-layer electrode and a bonding electrode mainly during wire bonding.

[0008]

As shown in FIGS. 1, 2 and 3, a gallium nitride based compound semiconductor light emitting device according to the present invention comprises at least an n-type gallium nitride based semiconductor light emitting device on an insulating substrate (1). A compound semiconductor layer (2) and a p-type gallium nitride-based compound semiconductor layer (3) are sequentially stacked, and a gallium nitride-based compound having the p-type gallium nitride-based compound semiconductor layer (3) side as a light emission observation surface In the semiconductor light emitting device, a light-transmitting first electrode (11) is formed on substantially the entire surface of the p-type gallium nitride-based compound semiconductor layer (3), and the first electrode (11) is formed on the first electrode (11). Has a window (13) penetrating a part of the first electrode (11), and the window (13) is further electrically connected to the first electrode (11). A second electrode (12) for bonding is formed. And which, furthermore the second electrode (12) is characterized in that it is bonded to the first electrode (11) p-type gallium nitride-based compound semiconductor layer stronger than (3). That is, the ohmic electrode and the bonding electrode are separately formed on the p layer, and the adhesive force per unit area of the bonding electrode is made larger than the adhesive force per unit area of the ohmic electrode. It is the solution to the problem. In the present application, translucency means that light emitted by a gallium nitride-based compound semiconductor is transmitted, and does not necessarily mean colorless and transparent.

[0009]

In the light emitting device of the present invention, the first electrode formed on the p-type layer is a light-transmitting thin-film electrode. Since light emission is not hindered by the opaque electrode, external quantum efficiency is improved. In addition, the harmful effects of using the first electrode as a thin film, that is, the easiness of peeling of the first electrode and the second electrode and the easiness of peeling of the first electrode and the p-layer are provided on the first electrode. This can be prevented by the fact that the second electrode formed in the window portion is more strongly bonded to the p-layer than the first electrode.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light emitting device according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view of a light emitting device according to an embodiment of the present application as viewed from a p-layer side, that is, a light emission observation surface side. FIG. 2 is a schematic cross-sectional view of the plan view of FIG. It is. This element is a sapphire substrate 1
Is a light emitting device having a homo structure in which an n-type layer 2 and a p-type layer 3 are sequentially stacked on the light emitting element.

Since the first electrode 11 formed on the p-layer 3 is translucent, light emitted from the pn junction interface can be effectively extracted to the light-emitting surface side. In addition, since it is formed on almost the entire surface of the p layer 3, the electric field spreads uniformly, and uniform light emission can be obtained over almost the entire pn junction surface. Electrode 1
Au, Pt, Al, Sn, C
This can be realized by forming the electrode materials such as r, Ti, and Ni very thin. Specifically, it is possible to form a thin film directly by a technique such as vapor deposition or sputtering so that the electrode is translucent, or to form a thin film and then anneal to make the electrode translucent. it can. The electrode 11 is preferably formed with a thickness of 0.001 μm to 1 μm. If the thickness is less than 0.001 μm, the contact resistance increases, which is not preferable. On the other hand, if the thickness is more than 1 μm, the electrode is unlikely to be light-transmitting and is not practical. The electrode is almost transparent, hardly hinders light emission, and has a low contact resistance, and a particularly practical range is preferably 0.005 μm to 0.2 μm.

Ni and Au are particularly preferably used as metals that can provide good ohmic contact between the first electrode 11 and the p-type gallium nitride compound semiconductor. When these metals are used as the material of the first electrode 11 and formed to be translucent, ohmic contact with the p-layer can be obtained, Vf (forward voltage) of the light-emitting element can be reduced, and luminous efficiency can be improved. it can. FIG. 4 shows Ni and Au on the p-type GaN layer.
FIG. 4 is a diagram showing that the electrodes were alloyed by vapor-depositing them in order with a film thickness of 0.1 μm and then annealed to measure the current-voltage characteristics. As shown in this figure, the first electrode 11 made of Ni and Au has a good ohmic contact with the p layer 3.

Next, the light emitting device of the present invention comprises a first electrode 11
A window 13 for forming the second electrode 12 for bonding is formed in a part of the substrate. The window 13 is preferably provided at a position farthest from the n-layer electrode 4 when viewed from the same plane, that is, at a diagonal line. This is because, by setting the position, the current spreads over the entire p layer, and the entire p layer can emit light uniformly. The window 13 needs to penetrate the first electrode 11 to expose the p layer 3 so that the bonding electrode, that is, the second electrode 12 is in contact with the p layer 3. To form the window 13,
After forming the first electrode 11, a mask may be used for etching, or a mask of a predetermined shape may be formed on the surface of the p-layer 3 from the beginning, and the first electrode 11 may be formed thereon. After that, the mask can be formed even by removing the mask.

Further, in the light emitting device according to the present invention, the window 1
3, a second electrode 12 for bonding electrically connected to the first electrode 113 is formed. Moreover, since the second electrode 12 is more firmly adhered to the p-layer 3 than the first electrode 11, even if a force pulling on the second electrode 12 is applied during bonding, the first electrode 11 will not move. It does not come off.

The second electrode 12 may be in ohmic contact with the p-layer 3, but need not be in ohmic contact since the ohmic is obtained by the first electrode 11. Therefore, any material may be used as long as the second electrode 12 is in electrical contact with the first electrode 11 and is firmly attached to the p-layer 3.

As a means for electrically connecting the second electrode 12 to the first electrode 11 and bonding the second electrode 12 to the p-layer 3 more strongly than the first electrode 11, for example, the following method can be used. First, as a material of the second electrode 12, a material having better adhesiveness to the p-type gallium nitride-based compound semiconductor layer than the first electrode (11) is selected, and the second electrode 12 is formed of the material. There is a method of forming. According to this method,
The thickness of the second electrode 12 can be freely formed, and the second electrode 12 can be formed to be extremely thin to be light-transmitting. For example, as a material having very good adhesion to the p layer 3, for example, Cr, Al, Au
And the like, or at least two of them, or Al alone can be used. These materials do not provide good ohmic contact with the p-type layer, but have very good adhesion and tend not to peel off during bonding. Therefore, when the second electrode 12 is formed of these materials, it is difficult to peel off the light-transmitting thin film. Alternatively, the second electrode may have a multilayer structure, the side in contact with the p-layer may be made of a material having good adhesion to the p-layer, and the uppermost layer may be made of a material having good adhesion to the bonding material.

[0017] Therefore, on the same p-type GaN layer, Ni-
Translucent electrode 10 deposited with Au to a thickness of 0.01 μm
And 1000 pieces of Cr-Al, Al-Au, Cr-Au, and Al each having a thickness of 0.01 μm.
When a gold wire was wire-bonded to the individually deposited translucent electrode, and when the gold wire was released, the number of peeled electrodes was checked and the yield of the electrodes was tested. While the yield was about 60%, all the other electrodes made of Cr and the like had a yield of 98% or more.
Note that the electrode areas are all the same, Ni-Au and the like are indicated by Ni on the side in contact with the p layer and A on the bonding side.
u indicates a multilayer film structure. As described above, there is a difference in adhesion between the first electrode 11 and the p-layer depending on the type of the metal, and the first electrode 11 can be prevented from peeling by selecting a material having a large adhesion to the second electrode 12.

As the next means, there is a method in which the second electrode 12 is formed to have a large thickness, thereby naturally increasing the adhesion to the p-layer 3 so that the second electrode 12 is hardly peeled off during bonding. According to this method, the second electrode 12 becomes a thick film and is not light-transmitting. However, for example, by forming the second electrode 12 from a thick film using the same material as the first electrode 11,
2, an ohmic contact can be obtained.

FIG. 3 is a perspective view showing a light emitting device according to another embodiment of the present invention. The light emitting device has a window 13 formed by cutting out a corner of a first electrode 11. The portion 13 and the n-layer electrode 4 are arranged diagonally. In this figure, the second electrode 12 is not formed so that the window 13 can be easily understood.

The light emitting device having the homo structure in which the n-layer and the p-layer are sequentially stacked has been described above. However, the present invention is directed to a gallium nitride-based compound semiconductor light-emitting device having the p-layer as a light-emission observation surface. It can be applied to any structure regardless of the structure of the light emitting element such as a single hetero structure.

[0021]

As described above, in the light emitting device of the present invention, the first electrode formed on the p layer is formed as a translucent electrode, and the light emitting element is formed substantially over the entire surface even when the light emission observation surface is on the p layer side. As a result, the current spreads uniformly, and light emission at the pn junction interface can be sufficiently extracted to the outside. Further, the first electrode and the second electrode for bonding are formed separately, and the adhesive force of the p-layer of the bonding electrode is made larger than that of the first electrode. The separation of the two electrodes can be prevented, and an element having excellent reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a light emitting device according to one embodiment of the present invention as viewed from a p-layer side.

FIG. 2 is a schematic cross-sectional view when the light-emitting element of FIG. 1 is cut along a dashed line.

FIG. 3 is a perspective view showing a light emitting device according to another embodiment of the present invention.

FIG. 4 is a diagram showing current-voltage characteristics of a Ni—Au electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... N-type gallium nitride-based compound semiconductor layer 3 ... P-type gallium nitride-based compound semiconductor layer 4 ... N-layer electrode 11 ... First electrode 12 ... Second electrode 13: Window

Continuation of the front page (56) References JP-A-5-129658 (JP, A) JP-A-57-10280 (JP, A) JP-A-49-122294 (JP, A) JP-A-63-244689 (JP) , A) JP-A-63-56967 (JP, A)

Claims (5)

(57) [Claims] 1. An insulating substrate (1) comprising at least an n-type gallium nitride-based compound semiconductor layer (2) and a p-type gallium nitride-based compound semiconductor layer (3) laminated in order.
A gallium nitride-based compound semiconductor light emitting device having a light emission observation surface on the side of the p-type gallium nitride-based compound semiconductor layer (3), wherein substantially all of the surface of the p-type gallium nitride-based compound semiconductor layer (3) is transparent. A first electrode (11) is formed, and the first electrode (11) has a window (13) formed through a part of the first electrode (11). Further, the window (13) has a first electrode (1).
A second electrode (12) for bonding electrically connected to 1) is formed, and the second electrode (12) is more strongly p-type gallium nitride than the first electrode (11). A gallium nitride-based compound semiconductor light emitting device, which is bonded to the based compound semiconductor layer (3). 2. The semiconductor device according to claim 1, wherein the second electrode is formed of a material having better adhesiveness to the p-type gallium nitride-based compound semiconductor layer than the first electrode. 2. The gallium nitride-based compound semiconductor light emitting device according to 1. 3. The method according to claim 1, wherein the second electrode (12) comprises Cr, Al,
The gallium nitride-based compound semiconductor light-emitting device according to claim 1, wherein the gallium nitride-based compound semiconductor light-emitting device is made of at least two kinds of materials selected from Au or Al alone. 4. The gallium nitride-based compound according to claim 1, wherein the thickness of the second electrode (12) is larger than the thickness of the first electrode (1). Semiconductor light emitting device. 5. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein said first electrode is made of Ni and Au.