JPH118410A - Electrode of n-type nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an n-type electrode which provides a desired ohmic contact to an n-type layer and is hardly denatured, even under harsh operating conditions. SOLUTION: An electrode 23 formed on an n-type nitride semiconductor surface 12 contains at least a first electrode material composed of at least one of Ti, Zr and W, a second electrode material composed of at least one of Al, Si and Ge, and a third electrode material of Rh, and also contains the first through third materials and a fourth electrode material made of Au.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LE).
D), gallium nitride based compound semiconductors (In _x Al _Y Ga) used for laser diodes (LD) or other electronic devices, power devices, light receiving devices, etc.
_1-XYN , 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, X + Y ≦ 1), and is particularly formed on an n-type gallium nitride-based compound semiconductor layer (hereinafter referred to as an n-type layer). Electrode (negative electrode).

[0002]

2. Description of the Related Art In recent years, practically available blue light emitting diodes and blue lasers capable of continuous oscillation at room temperature have been realized. High-luminance full-color high-quality images using light-emitting diodes, and short-wavelength blue light-emitting elements for high-density recording of optical disks such as digital video disks (DVDs) or other electronic devices, power devices, and light-receiving devices using lasers. Further development is underway for realization. One of the developments is improvement of luminous efficiency. The luminous efficiency is such that when the contact resistivity between the nitride semiconductor layer and the electrode is low and the ohmic contact is good, the forward voltage decreases,
It improves. The present inventors have disclosed an electrode of an n-type layer having good ohmic contact with an n-type nitride semiconductor layer (hereinafter simply referred to as an n-type layer) (hereinafter referred to as an n-electrode) described in JP-A-7-45867. An n-electrode made of titanium and aluminum is disclosed. However, in the electrode described in this publication, since aluminum is easily oxidized, the bonding strength between the ball formed of a wire and the n-electrode at the time of bonding tends to be weak.

The present inventors have disclosed in Japanese Patent Laid-Open No. 7-2211.
No. 03 discloses titanium (Ti), aluminum (Al)
And an n-electrode made of a metal having a higher melting point than Al.
This technique has good ohmic contact and can improve the durability of the electrode.

[0004]

[0005] However, the above-mentioned technique is not suitable for L.
Although good in EDs, in LDs having a higher current density and larger heat generation at the electrodes than LEDs, the electrodes are apt to deteriorate, and the life of the element is reduced, which is not satisfactory. Accordingly, an object of the present invention is to provide an n-electrode formed on an n-type layer, which obtains a favorable ohmic contact with the n-type layer, and which is hardly deteriorated even under severe use conditions.

[0005]

That is, the object of the present invention is to
This can be achieved by the following configurations (1) to (3). (1) In an electrode formed on the surface of an n-type nitride semiconductor layer, the electrode is at least a first electrode material made of at least one of titanium (Ti), zirconium (Zr) and tungsten (W); Al), a second electrode material comprising at least one of silicon (Si) and germanium (Ge), and a third electrode material comprising rhodium (Rh). electrode. (2) As a fourth electrode material of the electrode, gold (Au)
The electrode of the n-type nitride semiconductor according to the above (1), comprising:

That is, according to the present invention, by using a combination of the above-mentioned specific metals, particularly Rh in combination as the material of the n-electrode, it is possible to prevent the electrode from being deteriorated due to good ohmic contact and oxidation and to improve the durability of the electrode. Improved. Also, by providing Au on the top of the electrode, deterioration of the electrode such as oxidation can be prevented well, and the adhesion between the ball and the n-electrode can be improved, which is preferable.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The n-electrode of the present invention is composed of first to third electrode materials, and further a fourth electrode material for improving the effect of the present invention. Other metals may be contained as long as the effects of the present invention are not impaired. The first electrode material is at least one of Ti, Zr, and W, the second electrode material is at least one of Al, Si, and Ge, and the third electrode material is Rh. As the first electrode material and the second electrode material composed of two or more kinds, one kind or two or more kinds of metals may be used.

[0008] The n-electrode of the present invention is formed by laminating a metal thin film comprising a first electrode material to a third electrode material. Here, any of the electrode materials in the present invention may be formed in contact with the n-type nitride semiconductor, and the stacking order of each electrode material is not particularly limited. Further, the same electrode material may be used twice or more when forming the electrodes. As the lamination order of the electrode materials, for example, the first electrode material is laminated in contact with the n-type layer,
The order in which the second electrode material is stacked on the first electrode material and the third electrode material is stacked last can be exemplified. In addition, as the stacking order in which the same electrode material is used twice or more, for example, a stacking order in which each electrode material is stacked in a first, second, first, and finally third order is exemplified.
Such lamination is preferable because ohmic contact can be obtained with good reproducibility. Further, when the third electrode material is farthest from the n-type layer in the above-described lamination order, that is, when the third electrode material is laminated on the uppermost layer of the n-electrode, Rh as the third electrode material has a higher melting point than the second electrode material. Since it is present and hardly oxidized, it is effective in preventing the oxidation of the electrode.

When two or more metals are used as the electrode material, for example, when two or more metals are used as the first electrode material, one metal may be laminated one by one at the time of forming the electrode to form a multilayer film. More than one kind of metal is alloyed and laminated. The first to third electrode materials may be in any combination. For example, [Ti, Al, Rh], [Ti, Si, Rh],
[Zr, Al, Rh], [(Ti-W), Ge, R
h], [W, (Al-Si), Rh], [Ti, Al,
Ti, Rh], and the like. The combinations of the above electrode materials are merely examples, and the present invention is not limited to these. In addition, the order of lamination at the time of electrode formation in the combination of the above-mentioned respective electrode materials can be variously changed. Further, in the above example, when the first and second electrode materials use two or more metals, for example, the first electrode material uses two metals of Ti and W, the ratio of each metal is particularly limited. It is not a thing and can be changed arbitrarily. Adjustment of the ratio of the metal, for example, in the case where two or more kinds of metals are used as the first electrode material, when each metal is laminated, the thickness of the metal thin film is adjusted or alloyed. When laminated, the proportion of each metal in the alloy is adjusted.

Further, the present invention preferably contains gold (Au) as a fourth electrode material of the electrode in order to obtain the effect. When forming an electrode together with the first to third electrode materials, the fourth electrode material made of Au is not particularly limited in the order of lamination of each material, but is preferably n farthest from the n-type layer.
Formed on top of the electrode. Au can prevent the oxidation of the electrode and increase the bonding strength with the ball formed from the wire.

After laminating the first electrode material to the third electrode material as described above, or laminating the first electrode material to the fourth electrode material, the laminated electrode material and the nitride semiconductor layer An annealing process is performed to improve the contact and obtain an ohmic contact. At this time, if the first and second electrode materials use two or more kinds of metals and each metal is laminated as a multilayer film, the multilayer film may have a multilayer structure depending on the annealing conditions (mainly heat) and the thickness of the electrode material. Part or all of the film is alloyed. In some cases, alloying may occur between the respective electrode materials stacked. The alloying according to the present invention is a state in which the metals are not mixed uniformly but are united. Even when it is not alloyed, the metal thin film is not necessarily separated clearly, and a small amount of metal movement occurs near the contact surface of each electrode material, and when viewed microscopically, each electrode material The alloying referred to in the present invention may occur on the contact surface.

In the present invention, the thickness of the n-electrode is the total thickness of each electrode material after lamination, and the thickness of the n-electrode is adjusted by changing the thickness of each electrode material. The film thickness of the first electrode material is 10 nm to 200 nm, preferably 10 nm to 50 nm. Within this range, an ohmic contact with the n-type layer is easily obtained. The film thickness of the second electrode material is
50 nm to 500 nm, preferably 100 nm to 200
nm. Within this range, a preferable ohmic with the n-type layer can be obtained, and an electrode that is stable against heat can be obtained. The thickness of the third electrode material is 100 nm to 1000 nm.
nm, preferably 300 nm to 500 nm. Within this range, oxidation of the electrode can be prevented, and the adhesive strength can be improved. The thickness of the fourth electrode material is 100 nm to 1 μm.
m, preferably 200 nm to 500 nm. Within this range, the prevention of oxidation of the electrodes will be good, and the use of the fourth electrode material on the top of the n-electrode will improve the bonding strength with the ball.

In the present invention, the method for forming the n-electrode is performed by laminating first to third or fourth electrode materials.
The order of lamination of each electrode material is not particularly limited as described above, and a preferable lamination order is to form an electrode by laminating first, second, third, and fourth electrode materials.
These electrode materials are laminated with a metal or an alloy using an apparatus such as vapor deposition or sputtering to form an electrode. In the case of the first and second electrode materials using two or more kinds of metals as electrode materials, a multilayer film in which one kind of metal is laminated,
It may be alloyed by annealing.

In the present invention, after laminating the first to third electrode materials or laminating the first to fourth electrode materials, an annealing treatment is performed to obtain a good ohmic contact. The annealing temperature is 400 ° C. or higher, preferably 6 ° C.
The temperature is not lower than 00 ° C, and the upper limit is not particularly limited, but is preferably not higher than 1200 ° C. Annealing at a temperature of 400 ° C. or higher is preferable because the resistivity starts to decrease and a preferable ohmic contact is obtained. When the temperature is 1200 ° C. or lower, decomposition of the nitride semiconductor can be prevented, which is preferable.

In the present invention, a nitride semiconductor on which an electrode is formed is formed by metal organic chemical vapor deposition (MOCVD, MOVP).
E), using a vapor phase growth method such as a hydride vapor phase growth method (HDCVD). The n-electrode is formed on an n-type nitride semiconductor, and the p-electrode is formed on a p-type nitride semiconductor. Here, n-type or p-type refers to a nitride semiconductor containing n-type or p-type impurities. Further, the n-electrode of the present invention can be applied to a nitride semiconductor having any layer configuration. In addition, p together with the n-electrode of the present invention
The p-electrode formed on the mold layer may be any one.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. [Embodiment 1] Embodiment 1 according to the present invention is an example of producing the nitride semiconductor device (LD device) shown in FIG. 4, and is produced by the following procedure. First, a substrate 1 made of sapphire (C-plane)
After 0 is set in the reaction vessel and the inside of the vessel is sufficiently replaced with hydrogen, the temperature of the substrate is increased to 1050 ° C. while flowing hydrogen to clean the substrate. Subsequently, the temperature was lowered to 510 ° C., and a buffer layer 11 made of GaN was formed on the substrate 10 to a film thickness of about 200 Å using hydrogen as a carrier gas, ammonia (NH ₃ ) and TMG (trimethylgallium) as a source gas. Grow with.

After growing the buffer layer 11, only TMG is stopped.
To raise the temperature to 1050 ° C. 1050 ℃
If you use TMG and ammonia gas as raw material gas
No, carrier concentration 1 × 10¹⁸/cm^ThreeUndoped GaN
A second buffer layer 112 having a thickness of 5 μm.
Let The second buffer layer 112 is made of In_XAl_YGa_1-XY
N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1)
The composition is not particularly limited, but is preferably undoped.
Al (Y value) of 0.1 or less_YGa_1-YN, most preferred
Or undoped GaN. Subsequently, 1050 ° C
Silane gas (Si) as TMG, ammonia, impurity gas
H _Four) Using 1 × 10¹⁹/cm^ThreeDoped n-type G
An n-side contact layer 12 of aN is formed with a thickness of 1 μm.
Lengthen. This n-side contact layer 12 is formed of a superlattice.
Is more preferable.

Next, the temperature is set to 800 ° C., and TMG, TMI (trimethylindium) and ammonia are used as raw material gases, silane gas is used as impurity gas, and Si is used as 5 × 10 ^18.
An anti-crack layer 13 made of In _0.1 Ga _0.9 N doped with / cm ³ is grown to a thickness of 500 Å.

Then, the temperature was raised to 1050 ° C.
(Trimethylaluminum), TMG, ammonia, silane gas and doped with Si at 5 × 10 ¹⁸ / cm ³
A first layer of type Al _0.2 Ga _0.8 N is grown to a thickness of 20 Å, followed by stopping TMA and silane, and a second layer of undoped GaN is grown to a thickness of 20 Å. This operation is repeated 100 times to grow the n-side cladding layer 14 composed of a superlattice layer having a total film thickness of 0.4 μm.

Then, at 1050 ° C., undoped GaN
The n-side light guide layer 15 is grown to a thickness of 0.1 μm.
Let Next, TMG, TMI, ammonia, silane gas
Is used to grow the active layer 16. The active layer 16
While maintaining the temperature at 800 ° C., first, 8 × 10¹⁸/cm^ThreeIn
In_0.2Ga_0.825 Å of N well layer
It is grown with a storm film thickness. Next, the molar ratio of TMI
8 × 10 ¹⁸/cm^Three
Doped In_0.01Ga_0.9950 barrier layers made of N
It grows with the thickness of the ungstrom. Repeat this operation twice.
Repeatedly, finally, a total thickness of 175 Å
The active layer 16 of the multiple quantum well structure (MQW)
Let it grow.

Next, the temperature was increased to 1050 ° C., and TMG, TMA, ammonia was used as a source gas, and Cp ₂ M was used as an impurity gas.
g (cyclopentadienyl magnesium), the band gap energy is larger than that of the active layer, and Mg is 1
A p-side cap layer 17 made of p-type Al _0.3 Ga _0.7 N doped with × 10 ²⁰ / cm ³ is grown to a thickness of 300 Å. Subsequently, at 1050 ° C., a p-side light guide layer 18 of undoped GaN having a band gap energy smaller than that of the p-side cap layer 17 is grown to a thickness of 0.1 μm.

Subsequently, TMG, TMA, ammonia, C
A first layer made of p-type Al _0.2 Ga _0.8 N doped with Mg at 1 × 10 ²⁰ / cm ³ at 1050 ° C. was formed using p ₂ Mg.
P-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ , grown only with Å thickness
A second layer is grown with a thickness of 20 Angstroms. And this operation is repeated 100 times,
P-side cladding layer 1 composed of a superlattice layer having a total thickness of 0.4 μm
9 is formed. Finally, at 1050 ° C., p-type G doped with 2 × 10 ²⁰ / cm ^{3 of} Mg is formed on the p-side cladding layer 19.
A p-side contact layer 20 made of aN is grown to a thickness of 150 Å.

After the reaction is completed, the temperature is lowered to room temperature, and the wafer is placed in a nitrogen atmosphere in a reaction vessel.
Anneal at ℃ to further reduce the resistance of the p-type layer. After the annealing, the wafer is taken out of the reaction container, and as shown in FIG. I do.

Next, a mask is formed on the surface of the ridge, and as shown in FIG. 1, the surface of the n-side contact layer 12 is exposed symmetrically with respect to the stripe-shaped ridge.

Next, a p-electrode 21 made of Ni and Au is formed on almost the entire outermost surface of the stripe ridge of the p-side contact layer 20.
To form On the other hand, Ti is 10 nm and Al is 200 n.
m, Rh are deposited in a thickness of 200 nm and Au is deposited in a thickness of 200 nm in this order, and an n-electrode 23 is formed on almost the entire surface of the n-side contact layer 12 in a stripe shape. After forming the p-electrode 14,
Remove the mask, put the wafer in the annealing equipment,
Anneal at 600 ° C. for 10 minutes in an inert gas atmosphere.

Next, as shown in FIG.
The surface of the nitride semiconductor layer exposed between the electrode 23 and Si
An insulating film 25 made of O ₂ is formed, and a p pad electrode 22 electrically connected to the p electrode 21 via the insulating film 25 is formed.
And an n-pad electrode 24 are formed. As described above,
The wafer on which the n-electrode and the p-electrode have been formed is transferred to a polishing apparatus, and the sapphire substrate 1 on which the nitride semiconductor is not formed is wrapped using a diamond abrasive to reduce the thickness of the substrate to 50 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm.

After the substrate is polished, the polished surface side is scribed,
Cleavage is performed in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. SiO ₂ and TiO ₂ on the resonator surface
A dielectric multilayer film was formed, and finally the bar was cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed on the heat sink face up (in a state where the substrate and the heat sink faced each other), and the respective electrodes were wire-bonded to produce an LD element. This LD
When the device was subjected to laser oscillation at room temperature, favorable ohmic contact was obtained at room temperature with a threshold current density of 2.9 kA / cm ² and a threshold voltage of 4.4 V. In addition, 100 LDs are randomly extracted from this LD element, and 40%, 90%
When continuous oscillation was performed in a high-temperature, high-humidity state of RH, it was found that all of the elements exhibited a life of 10 hours or more, and that the electrodes had sufficient durability even in high humidity without being deteriorated.

[Embodiment 2] In Embodiment 1, n-type Ga
An electrode formed on the surface of the N contact layer is formed by
m, Si 30 nm, Rh 200 nm, Au 200
A similar ohmic contact was obtained in the same manner except that the film was sequentially deposited with a film thickness of nm. Further, when continuous oscillation was performed in a high-temperature and high-humidity state as in Example 1, good results were obtained as in Example 1.

[Embodiment 3] In Embodiment 1, n-type Ga
The electrode formed on the surface of the N contact layer is
m, Al 150 nm, Ti 30 nm, Rh 200
When a similar ohmic contact was obtained, the same procedure was performed except that nm and Au were sequentially deposited to a thickness of 200 nm. Furthermore, when continuous oscillation was performed in a high-temperature and high-humidity state as in Example 1, almost the same results as in Example 1 were obtained.

Comparative Example 1 In Example 1, n-type Ga
An electrode formed on the surface of the N contact layer is made of 10n of Ti.
m, Si were deposited in the order of 50 nm and Au was deposited in the order of 200 nm. The same procedure was performed except that a good ohmic contact was obtained. Oscillation resulted in continuous oscillation for less than one hour.

[0031]

According to the present invention, an n-electrode which has a very favorable ohmic contact with an n-type nitride semiconductor layer, is hardly deteriorated even when a light emitting device is used under severe conditions, and has a good device life characteristic. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a nitride semiconductor light emitting device according to an embodiment in which an n-electrode according to the present invention can be provided.

[Explanation of symbols]

 10 substrate 11 buffer layer 112 second buffer layer 12 n-side contact layer 13 crack preventing layer 14 n-cladding layer ( ... N-side light guide layer 16... Active layer 17... Cap layer 18... P-side light guide layer 19. 20) p-side contact layer 21 p-electrode 22 p-pad electrode 23 n-electrode 24 n-pad electrode 25 insulating film

Claims (2)

[Claims] 1. An electrode formed on the surface of an n-type nitride semiconductor layer, wherein the electrode is at least one of a first electrode material made of at least one of titanium, zirconium and tungsten, and at least one of aluminum, silicon and germanium. An electrode of an n-type nitride semiconductor, comprising a second electrode material comprising: and a third electrode material comprising rhodium. 2. The n-type nitride semiconductor electrode according to claim 1, wherein gold is contained as a fourth electrode material of said electrode.