JP2001035810A - Nitride semiconductor device, and method for forming electrode therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a nitride semiconductor device having between an electrode and it a contacting resistance of a good characteristic and facilitate the forming of an electrode in a nitride semiconductor, by providing between the nitride semiconductor and the electrode an ohmic contacting layer made of an arsenic or phosphoric compound. SOLUTION: In a wafer for a nitride semiconductor device, after growing epitaxially on a sapphire substrate 1 an undoped GaN layer 2 and a p-type or n-type GaN layer 3, an ohmic contacting layer 4 made of an arsenic or phosphoric compound having a predetermined composition is further grown epitaxially thereon to form by a deposition an Au electrode 5 on the ohmic contacting layer 4. In the nitride semiconductor device, as its raw materials, there are used trimethylgallium, trimethylindium, trimethylaluminum, ammonia, bi-cyclo-pentane magnesium, arsine, and phosphine, and they are obtained by growing them epitaxially through an organic-metal vapor-phase growth method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor device and a method of forming an electrode on the nitride semiconductor, and more particularly, to a nitride semiconductor device in which electrodes are ohmic-connected under a low contact resistance, and a method of forming the same. The present invention relates to a method for forming an electrode on a semiconductor.

[0002]

2. Description of the Related Art Forming an ohmic electrode in a compound semiconductor is indispensable for applying the compound semiconductor to various uses. Normally, when an electrode based on ohmic contact is formed, heat treatment is performed to create a good junction state at the contact interface between the electrode and the semiconductor, but from the viewpoint of not diffusing impurities from the semiconductor, It is desirable that no heat treatment be performed, or that the heat treatment be performed at as low a temperature as possible.

[0003]

However, according to a conventional nitride semiconductor and a method of forming an electrode on the same, 600 nm
Heat treatment at a high temperature of not less than ℃ is indispensable, and the contact resistance with the formed electrode is not always satisfactory. In particular, it is difficult to make a good ohmic contact on the p-type electrode side. Have.

The reason that it is difficult to form an ohmic contact between a nitride-based compound semiconductor and a metal electrode is that the crystal of this semiconductor is thermally and chemically stable, and it is difficult to form an alloy at a contact interface with the metal. Further, it is considered that the bandgap is wide due to a high Schottky barrier at the interface between the p-type layer and the metal.

For this reason, many proposals have been made to lower the barrier, but there is no drastic measure, and at present the high temperature heat treatment is inevitable. Performing the heat treatment not only has an effect on the semiconductor characteristics but also increases the number of steps due to the heat treatment, and is not preferable in terms of cost.

Accordingly, an object of the present invention is to provide a nitride semiconductor device having good characteristics in contact resistance with an electrode and a method of easily forming an electrode on a nitride semiconductor.

[0007]

According to the present invention, there is provided a nitride semiconductor device having an electrode in ohmic contact with a nitride semiconductor. A nitride semiconductor device characterized by having an ohmic contact layer of the compound of

According to another aspect of the present invention, there is provided a method of forming an electrode on a nitride semiconductor, the method comprising forming an electrode based on ohmic contact with the nitride semiconductor. It is another object of the present invention to provide a method for forming an electrode on a nitride semiconductor, wherein an ohmic contact layer of an arsenic or phosphorus compound is formed at a place to be formed, and the electrode is brought into ohmic contact with the ohmic contact layer.

As the arsenic compound, for example,
GaNAs, InGaNAs or AlGaNAs is used. As the phosphorus compound layer, for example, GaN
P, InGaNP or AlGaNP is used.

As a method of forming an ohmic contact layer made of these compounds on a nitride semiconductor, when epitaxially growing a crystal of a nitride semiconductor, an ohmic contact layer is formed at a predetermined position of the grown crystal, for example, at the top of the grown crystal. It is preferable to perform epitaxial growth. In that case, it is possible to grow the ohmic contact layer according to the position and size of the electrode formation.

As another method, an arsenic or phosphorus gas is allowed to act on the nitride semiconductor, and arsenic or phosphorus is thermally diffused into the nitride semiconductor to make this portion an ohmic contact layer. An effective method is to use an alloy containing arsenic or phosphorus as a constituent material, thereby thermally diffusing arsenic or phosphorus from an electrode into a nitride semiconductor and using the diffused layer as an ohmic contact layer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of a nitride semiconductor device and a method of forming an electrode on a nitride semiconductor according to the present invention will be described. FIGS. 1 to 7 show a configuration example of a nitride semiconductor device manufactured according to the present invention, using trimethylgallium, trimethylindium, trimethylaluminum, ammonia, biscyclopentamagnesium, arsine and phosphine as raw materials, It is one grown epitaxially by metal organic chemical vapor deposition.

In each case, an undoped GaN layer 2 and a 200 nm-thick p-type or n-type G
After the aN layer 3 is epitaxially grown, different nitride semiconductors are epitaxially grown.
On top of this, the wafer has a configuration in which an ohmic contact layer 4 made of a compound of arsenic or phosphorus having a predetermined composition is epitaxially grown. On the ohmic contact layer 4, an Au electrode 5 is formed by vapor deposition.

FIG. 1 shows a GaN layer 3 having a p-type, and a GaN layer 3 having a thickness of 5 nm made of a p-type GaNAs compound containing arsenic.
nm ohmic contact layer 4 is formed, and p-type Ga
The X value of the composition of NAs is designed to gradually change in the thickness direction in the range of 0 to 0.25, and is set so that the lowermost portion of the layer 4 is 0 and the uppermost portion is 0.25. Have been.

FIG. 2 shows that a p-type GaN layer 3 is grown on an undoped GaN layer 2 and an ohmic contact layer 4 of p-type GaNP containing phosphorus having a thickness of 5 nm is grown thereon. The X value of the p-type GANP is set to gradually change from 0 at the bottom in the thickness direction to 0.5 at the top.

FIG. 3 shows a p-type GaN layer 3 having a thickness of 10 μm.
a Au electrode 5 is formed by growing a 2 nm thick ohmic contact layer 4 of p-type InGaNAs containing arsenic, and forming an X value of the p-type InGaNAs. Is set at 0 at the bottom of the compound layer 4 and at 0.25 at the top.

FIG. 4 shows the p-type InGaNAs shown in FIG.
In place of the ohmic contact layer 4, the ohmic contact layer 4 made of phosphorus-containing p-type InGaP is formed. The X value of the p-type InGaP is 0 at the bottom of the ohmic contact layer 4 and 0.1 at the top. 5 is set.

FIG. 5 shows that p-type Al is formed on the p-type GaN layer 3.
The wafer configuration is such that a GaN layer 7 is grown to a thickness of 10 nm, and an ohmic contact layer 4 of p-type AlGaNAs containing arsenic is grown thereon to a thickness of 2 nm.

FIG. 6 shows the p-type AlGaNAs shown in FIG.
Instead of the ohmic contact layer 4, the ohmic contact layer 4 of p-type AlGaNP containing phosphorus is grown, and the X value of the p-type AlGaNP is 0 at the bottom of the compound layer 4 and 0.1 at the top. 5 is set.

FIG. 7 shows a structure in which the pn relationship of FIG. 5 is reversed, and a 200 nm-thick n-type layer is formed on the undoped GaN layer 2.
Type GaN layer 3 is grown, and an n-type AlGaN layer 8 having a thickness of 10 nm and an n-type arsenic-containing n-type
It has a configuration in which ohmic contact layers 4 of type AlGaNAs are sequentially grown.

FIG. 8 shows a structure of a conventional nitride semiconductor device manufactured for comparison with the present invention. On a sapphire substrate 1, an undoped GaN layer 2 and a 200 nm thick p
The GaN layer 3 is epitaxially grown in order by a metal organic chemical vapor deposition method, and an Au electrode 5 is formed on the p-type GaN layer 3 by vapor deposition.

FIG. 9 shows another conventional nitride semiconductor device. In FIG. 7, the Au electrode 5 is directly deposited on the n-type AlGaN layer 8 without forming the n-type AlGaNAs compound layer 4. It is an example. In FIGS. 1 to 9 described above, the n-type GaN layer between the undoped GaN layer 2 and the p-type GaN layer 3 is omitted in FIGS.
7 and 9, the undoped GaN layer 2 and the n-type G
The illustration of the p-type GaN layer between the aN layers 3 is omitted.

Under the conditions that the pretreatment for Au deposition after removing the wafer from the epitaxial growth furnace and the heat treatment after depositing the Au electrode 5 are completely omitted, FIG.
Table 1 shows the results of manufacturing the nitride semiconductor devices of FIGS.

[0024]

[Table 1]

According to Table 1 which summarizes the measurement results of the contact resistance by the TLM method, the conventional one in which the Au electrode 5 is of the p-type (FIG. 8) shows an unmeasurable contact resistance exceeding 10 ⁵ . In contrast, in the case of FIGS. 1 to 6 of the p-type electrode, it is recognized that the contact resistance is markedly low, that is, 8 × 10 ^{−8 to} 1.1 × 10 ⁻⁶ Ωcm ² .

Further, also in FIGS. 7 and 9 to form an n-type electrode 5, compared to the case of FIG. 9 is a conventional nitride semiconductor indicates a high contact resistance of 1.2Omucm ^2, the present invention In the case of FIG. 7 based on the above, 5 × 10 ⁻⁷ Ωcm
^It shows a low level of contact resistance of ² .

The difference between both the p-type and the n-type is clear, and the effect of the present invention for forming an ohmic contact layer of a compound of arsenic or phosphorus is clearly shown. Note that the method for forming an electrode according to the present invention does not exclude the heat treatment after the electrode is formed. Naturally, heat treatment at a low or moderate temperature is possible and is included in the embodiments of the present invention.

[0028]

As described above, according to the nitride semiconductor device and the method for forming an electrode on a nitride semiconductor according to the present invention, an ohmic contact layer made of an arsenic or phosphorus compound is formed on the nitride semiconductor. Since an electrode is brought into ohmic contact with this layer, an electrode with low contact resistance can be formed. Further, since heat treatment before and after electrode formation is not required, a simplified method for forming an electrode can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a nitride semiconductor device and a method for forming an electrode on a nitride semiconductor according to the present invention.

FIG. 2 is an explanatory view showing another embodiment of the present invention.

FIG. 3 is an explanatory view showing another embodiment of the present invention.

FIG. 4 is an explanatory view showing another embodiment of the present invention.

FIG. 5 is an explanatory view showing another embodiment of the present invention.

FIG. 6 is an explanatory view showing another embodiment of the present invention.

FIG. 7 is an explanatory view showing another embodiment of the present invention.

FIG. 8 is an explanatory view showing a conventional nitride semiconductor device and a method for forming an electrode on the nitride semiconductor.

FIG. 9 is an explanatory view showing another conventional nitride semiconductor device and a method for forming an electrode on a nitride semiconductor.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 undoped GaN layer 3 GaN layer (p or n-type) 4 ohmic contact layer 5 Au electrode 6 p-type InGaN layer 7 p-type AlGaN layer 8 n-type AlGaN layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M104 AA04 AA07 AA09 BB09 CC01 DD28 DD34 HH15 5F041 AA21 CA34 CA40 CA58 CA65 CA72 CA83 CA98

Claims (9)

[Claims] 1. A nitride semiconductor device having an electrode in ohmic contact with a nitride semiconductor layer, comprising an ohmic contact layer of an arsenic or phosphorus compound between the nitride semiconductor layer and the electrode. Semiconductor device. 2. The method of claim 1, wherein the arsenic compound is GaNAs, InG
2. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is aNAs or AlGaNAs. 3. The nitride semiconductor device according to claim 1, wherein said phosphorus compound is GaNP. 4. A method for forming an electrode on a nitride semiconductor, wherein the electrode is formed on the nitride semiconductor based on ohmic contact, wherein an ohmic contact of a compound of arsenic or phosphorus is formed at a position where the electrode of the nitride semiconductor is to be formed. A method for forming an electrode on a nitride semiconductor, comprising: forming a layer; and bringing the electrode into ohmic contact with the ohmic contact layer. 5. The arsenic compound is GaNAs, InG
5. The method for forming an electrode on a nitride semiconductor according to claim 4, wherein the method is aNAs or AlGaNAs. 6. The method according to claim 1, wherein the compound of phosphorus is GaNP, InGa.
5. The method for forming an electrode on a nitride semiconductor according to claim 4, wherein the method is NP or AlGaNP. 7. The semiconductor according to claim 4, wherein said ohmic contact layer is grown by being incorporated at a predetermined position in said nitride semiconductor when said nitride semiconductor is epitaxially grown. Method of forming an electrode on a substrate. 8. The semiconductor device according to claim 4, wherein said ohmic contact layer is formed by causing a gas of arsenic or phosphorus to act on said nitride semiconductor and thermally diffusing said arsenic or phosphorus into said nitride semiconductor. The method for forming an electrode on a nitride semiconductor according to the above item. 9. The method according to claim 1, wherein the ohmic contact layer is formed by using an alloy containing arsenic or phosphorus as the electrode and thermally diffusing the arsenic or phosphorus from the alloy into the nitride semiconductor. Item 5. The method for forming an electrode on a nitride semiconductor according to Item 4.