JP3322301B2 - Nitride semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor device having a p-type gallium nitride based semiconductor layer.

[0002]

2. Description of the Related Art In recent years, light emitting devices capable of emitting blue light using nitride semiconductors have been developed and used for various purposes. The development of a nitride semiconductor device represented by this light emitting device has greatly contributed to the fact that a gallium nitride based semiconductor layer having p-type conductivity can be formed. In order to further improve the characteristics of the nitride semiconductor device in the future, while developing a technology that can form a better p-type gallium nitride-based semiconductor layer, The development of a positive electrode that can make an ohmic contact and that can reduce resistance in a broad sense including connectivity with an external circuit is positioned as one of the important issues.

In a conventional nitride semiconductor device, as a positive electrode, an electrode obtained by laminating Ni and Au capable of making good ohmic contact with a p-type gallium nitride based semiconductor layer is widely used. The electrode in which Ni and Au are laminated is formed such that the Ni layer is in contact with the p-type gallium nitride based semiconductor layer, and the Au layer is formed on the Ni layer. It is known that the stacked structure changes (reversed), whereby the Au layer is located below the p-type gallium nitride-based semiconductor layer and the Ni layer is located on the surface (Japanese Patent Application Laid-Open No. 9-1997). No. 64337).

[0004]

However, in the conventional nitride semiconductor device, the surface of the Ni layer, which has been moved upward by the heat treatment, is oxidized in the positive electrode having the Ni layer and the Au layer laminated thereon, so that, for example, an Au wire or the like can be used. When performing wire bonding using, for example, or performing flip-chip bonding using, for example, an Ag paste, there is a problem that contact resistance between the positive electrode and the Au wire or the Ag paste increases. Further, even in a structure in which a lead electrode (pad electrode) is provided on the positive electrode, there is a problem that the contact resistance between the positive electrode and the lead electrode increases. For this reason, the conventional nitride semiconductor device could not sufficiently improve the current-voltage characteristics due to the loss caused by the relatively large contact resistance. In addition, since the surface of the Ni layer is oxidized, the wire-bonded Au wire and the Ag paste or the extraction electrode in the case of flip-chip bonding are easily peeled from the positive electrode, so that sufficient connection reliability at the connection portion is ensured. For this purpose, there is a problem in that various measures are required in manufacturing and fine process control is required.

An object of the present invention is to solve the above-mentioned problems of the conventional example and to provide a nitride semiconductor device having good current-voltage characteristics and easy manufacture.

[0006]

As a result of intensive studies to solve the above-mentioned problems of the prior art, the present invention
By using a positive electrode having a Pt layer formed on the layer,
The present invention has been completed by finding that good ohmic contact with the p-type gallium nitride based semiconductor layer can be obtained and that there is no problem as in the conventional example. That is, the nitride semiconductor device according to the present invention is formed on the p-type gallium nitride-based semiconductor layer having p-type conductivity and the gallium nitride-based semiconductor layer, and is in ohmic contact with the p-type gallium nitride-based semiconductor layer. A nitride semiconductor device comprising: a first electrode layer containing Mo as a main component and formed in contact with the p-type gallium nitride-based semiconductor layer; A second electrode layer containing Pt as a main component and formed on the electrode layer. Here, in this specification, gallium nitride based semiconductors are GaN and GaN.
Refers to a semiconductor in which part of gallium is replaced with one or more other elements.

Further, by using the present invention, it is possible to form a nitride light emitting element which is a light emitting element which is formed so that the positive electrode has a light transmitting property and outputs light generated through the positive electrode.

Further, in the nitride semiconductor device of the present invention, it is preferable that the first electrode layer contains oxygen, whereby the adhesion strength between the p-type gallium nitride based semiconductor layer and the positive electrode is improved. When the positive electrode is formed to have a light transmitting property, the light transmitting property can be improved.

Further, in the nitride semiconductor device of the present invention, it is preferable that the heat treatment is performed after the formation of the positive electrode, thereby further increasing the ohmic contact between the positive electrode and the p-type gallium nitride-based semiconductor layer. Can be good.

Further, in the nitride semiconductor device of the present invention, an extraction electrode for connection to an external circuit may be formed on a part or the entire surface of the positive electrode.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. The nitride semiconductor device according to the first embodiment of the present invention is a light-emitting device, and as shown in FIG. 1, an n-type gallium nitride-based AlInGaN doped with, for example, Si on a substrate 11 made of, for example, sapphire. The semiconductor layer 12 has a semiconductor layer structure in which a light emitting layer 10 made of, for example, InGaN and a p-type gallium nitride-based semiconductor layer 13 made of, for example, AlInGaN doped with Mg are sequentially stacked. Formed. That is, the n-side negative electrode 14 is formed on the upper surface of the n-type gallium nitride-based semiconductor layer 12 which is exposed by removing the p-type gallium nitride-based semiconductor layer to a predetermined width from one side surface (first side surface), A p-side positive electrode 15 is formed on almost the entire upper surface of the p-type gallium nitride based semiconductor layer 13. In the nitride semiconductor device of the first embodiment, the extraction electrode 16 is further provided on the positive electrode 15 at a position away from the negative electrode 14.
Is formed, and an insulating film 17 is formed so as to cover each electrode and each semiconductor layer, except for openings on the negative electrode 14 and the extraction electrode 16.

Here, in the nitride semiconductor device of the first embodiment, as shown in FIG.
A first electrode layer 1 made of Mo (molybdenum) formed to be in contact with the p-type gallium nitride based semiconductor layer 13 and a second electrode made of Pt (platinum) formed on the first electrode layer 1 It has a two-layer structure with the electrode layer 2, and has various advantages described later.

In the first embodiment, it is preferable to perform a heat treatment at a predetermined temperature after forming the first electrode layer 1, whereby the p-type gallium nitride-based semiconductor layer 13 can be further improved. Ohmic contact is obtained. Further, in the present embodiment, even if the first electrode 1 is formed while heating the substrate at a predetermined temperature, the same effect as that obtained by heat treatment after formation is obtained, and a good ohmic contact is obtained.

Hereinafter, the present invention will be described in more detail, including examples studied by the present inventors. In the following examination examples, the first electrode layer 1 was formed to have a thickness of 200 ° using a sputtering device, and the second electrode layer 2 was formed to have a thickness of 3000 ° using a sputtering device. And formed continuously. FIG. 2 is a graph showing current-voltage characteristics when heat treatment is performed at various temperatures after the positive electrode 15 is formed. In this study, the best current-voltage characteristics were obtained at a temperature of 700 ° C., as shown in FIG. If the heat treatment temperature exceeds 700 ° C., GaN may deteriorate, and if the heat treatment temperature is lower than 450 ° C., the linearity of the voltage-current characteristics deteriorates.

FIG. 3 shows the p-type gallium nitride based semiconductor layer 13 from the surface of the positive electrode 15 after the above-described heat treatment.
2 shows the results of elemental analysis in the depth direction using Auger electron spectroscopy up to the vicinity of the surface. As shown in FIG. 3, in the nitride semiconductor device of the first embodiment, the positive electrode 1
In No. 5, no reversal phenomenon as in the conventional positive electrode using the Ni layer and the Au layer was observed, there was no change in the laminated structure, and the surface of Pt as the second electrode layer 2 was also oxidized. It turns out there is no.

As described in detail above, in the nitride semiconductor device of the first embodiment, the positive electrode 15 is made of Mo (molybdenum).
A positive electrode 15 and a p-type gallium nitride are formed by forming a laminated structure of a first electrode layer 1 made of Pt and a second electrode layer 2 made of Pt (platinum) formed on the first electrode layer 1. Good ohmic contact with the system semiconductor layer 13 can be achieved. Further, since the second electrode layer 2 made of Pt formed on the upper layer of the positive electrode 15 is not oxidized, the contact resistance between the positive electrode 15 and the extraction electrode 16 can be reduced, and the nitride semiconductor element In this case, the voltage drop due to the contact resistance can be reduced. by this,
In the nitride semiconductor device of the first embodiment, the forward voltage can be reduced as compared with the conventional example because of the small voltage drop. Therefore, when the present invention is applied to a nitride semiconductor element such as a light emitting element or a laser diode, a lower driving voltage and higher luminance can be achieved.

In the nitride semiconductor device of Embodiment 1 described above, the positive electrode 15 is formed by using the first electrode layer 1 made of Mo and the second electrode layer 2 made of Pt. The present invention is not limited thereto, and the Mo layer and the Pt layer may be partially alloyed, or the Mo layer and / or the Pt layer may contain Si or another metal. Even with the above configuration, the same operation and effect as those of the first embodiment can be obtained. That is, in the present invention, the first electrode layer 1 contains Mo as a main component,
It suffices that the electrode layer 2 contains Pt as a main component.

Embodiment 2 FIG. The nitride semiconductor device of the second embodiment according to the present invention is characterized in that the Mo layer of the first electrode layer 1 contains oxygen in the first embodiment, and is otherwise configured in the same manner as the first embodiment. You. Thus, in the nitride semiconductor device of Embodiment 2, the adhesion strength between the positive electrode 15 and the p-type gallium nitride semiconductor layer can be increased. In the second embodiment, for example, by performing sputtering of Mo in a mixed atmosphere of Ar and O ₂ , oxygen can be contained in the Mo layer.
O layer can contain oxygen.

According to our studies, it has been confirmed that the light transmittance of the Mo layer can be improved by adding oxygen to the Mo layer. So, for example,
The thickness of the second electrode layer 2 made of Pt is set to 300 ° or less, the positive electrode 1 is made translucent, and light is output through the positive electrode 1 (so-called semiconductor-side emission). )
In this case, it is effective to include oxygen in the first electrode layer 1 made of Mo from the viewpoint of improving the light transmission. The light-emitting element for emitting light on the semiconductor side has, for example, an electrode structure in which a negative electrode and an extraction electrode are arranged on a diagonal line in order to output luminous efficiency and emitted light effectively. That is, the negative electrode is formed on the surface of the n-type gallium nitride-based semiconductor layer 12 where the p-type gallium nitride-based semiconductor layer is removed at one corner and exposed, and the positive electrode is formed on the p-type gallium nitride-based semiconductor layer. And the extraction electrode is formed at a position diagonal to the negative electrode.

The nitride semiconductor device according to the second embodiment configured as described above has the same effect as that of the first embodiment, and also has an improved adhesion strength between the positive electrode 15 and the p-type gallium nitride semiconductor layer as described above. The light transmittance can be improved.

In the first and second embodiments, the nitride semiconductor layer device including the n-type gallium nitride-based semiconductor layer 12, the active layer 10, and the p-type gallium nitride-based semiconductor layer 13 has been described. It goes without saying that other semiconductor layers such as a buffer layer may be provided.
The present invention can be applied even if another semiconductor layer is provided, and has the same operation and effect as the embodiment.

[0022]

As described above in detail, the nitride semiconductor device according to the present invention is formed on a p-type gallium nitride-based semiconductor layer having p-type conductivity and in contact with the gallium nitride-based semiconductor layer. A first electrode layer containing Mo as a main component;
A second layer mainly composed of Pt formed on the first electrode layer;
And a positive electrode having the above electrode layer. Thus, according to the present invention, it is possible to provide a nitride semiconductor device having good current-voltage characteristics and easy manufacture.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a nitride semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a graph showing voltage-current characteristics when a heat treatment temperature is changed in the first embodiment.

FIG. 3 is a graph showing a result of Auger analysis in a depth direction of a positive electrode in the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st electrode layer made of Mo, 2 ... 2nd electrode layer made of Pt, 10 ... active layer, 11 ... substrate, 12 ... Reference numeral 14 denotes a negative electrode, 15 denotes a positive electrode, 16 denotes an extraction electrode, and 17 denotes an insulating film.

Claims (5)

(57) [Claims] 1. A nitride comprising: a p-type gallium nitride-based semiconductor layer having p-type conductivity; and a positive electrode formed on the p-type gallium nitride-based semiconductor layer and in ohmic contact with the gallium nitride-based semiconductor layer. A semiconductor device, wherein the positive electrode is formed on a first electrode layer mainly composed of Mo formed in contact with the p-type gallium nitride based semiconductor layer, and formed on the first electrode layer. A nitride semiconductor device comprising: a second electrode layer containing Pt as a main component. 2. The nitride semiconductor device according to claim 1, wherein said positive electrode has a light transmitting property and outputs light generated through said positive electrode. 3. The nitride semiconductor device according to claim 1, wherein said first electrode layer contains oxygen. 4. The nitride semiconductor device according to claim 1, wherein the heat treatment is performed after the formation of the positive electrode. 5. The nitride semiconductor device according to claim 1, wherein said nitride semiconductor device further has an extraction electrode for connecting to an external circuit on a part or the entire surface of said positive electrode. element.