JPH09129932A - Nitride semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the light transmissivity of a nitride semiconductor light emitting element by forming a translucent electrode containing at least vanadium on almost the entire surface of the p-type layer of the light emitting element on which the p-type layer is formed as the outermost layer. SOLUTION: After a buffer layer 2, an n-type contact layer 3, an active layer 4, a p-type clad layer 5, and a p-type contact layer 6 are successively grown on a sapphire substrate 1, a mask is formed in a prescribed shape on the surface of the topmost p-type GaN contact layer 6 and part of the contact layer 3 is exposed by etching the layers 4, 5, and 6. Then the mask is removed from the surface of the contact layer 6 and Pd is vapor-deposited to a film thickness of 30Å on almost the entire surface of the topmost GaN layer 6 as a p-electrode 10. The translucent electrode 10 containing Pd transmits visible light, especially, visible light of purple to green color more than the conventional translucent electrode does. Therefore, when the electrode 10 is formed on the surface of the p-type layer 6, the light transmissivity of a nitride semiconductor light emitting element can be improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitride semiconductor (In _XA).
L _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) The present invention relates to a light emitting device such as an LED, and particularly to a light emitting device in which a p-type nitride semiconductor layer is formed on the outermost surface. Regarding electrodes.

[0002]

2. Description of the Related Art At present, nitride semiconductors (In _X Al _Y Ga
Blue LE using _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1)
D and green LEDs have been put to practical use. The basic structure of these LEDs is, for example, n-type A on a transparent insulating substrate.
an n-type nitride semiconductor layer (hereinafter referred to as an n layer) made of l _Y Ga _{1 -Y} N (0 ≦ Y ≦ 1) and In _X Ga _1-X N (0 <X
≦ 1) active layer and p-type Al _Z Ga _1-Z N (0 ≦ Z
It has a double hetero structure in which a p-type nitride semiconductor layer of ≦ 1) (hereinafter referred to as a p layer) is sequentially stacked. Since this LED cannot take out the n-electrode from the substrate side, it is of a so-called flip-chip type in which the n-electrode and the p-electrode are taken out from the same surface side. Since the substrate is transparent on the emission observation surface side, it can be either the substrate side or the electrode side, but in many cases, the electrode side, that is, the p layer side is the emission observation surface.

An electrode made of a translucent metal is provided on the p-layer on the side of the light emission observation surface in order to take out the light emitted from the active layer to the outside. In addition, in Japanese Patent Application Laid-Open No. 6-314822, we have shown a light emitting device in which a transparent metal electrode is provided on the surface of a p-layer. However, the conventional translucent metal electrode has a poor transmissivity of the electrode for blue and green light, and the external quantum efficiency has not yet been sufficiently satisfactory.

By the way, an electrode used for a light emitting element made of a semiconductor material such as an LED needs to have a preferable ohmic contact with the semiconductor material in order to reduce the forward voltage. Also in the LED, a preferable ohmic contact is obtained with an electrode containing Ti and Al for the n layer and an electrode containing Ni and Au for the p layer.

In addition, as an electrode material for forming a nitride semiconductor, for example, tin oxide in JP-A-5-55631 is used.
Indium oxide and zinc oxide are shown. However, the material disclosed in this publication is an electrode formed on an i (insulater) type nitride semiconductor doped with an acceptor impurity, and a preferable ohmic property has not been obtained, and is not an electrode formed on a p layer. Further, in JP-A-5-315647, Ag, Au and P are preferred electrodes to be formed in the p layer.
Although t, Ir, Pd, Rh and the like are described, in reality, only the Au electrode is provided in the i layer of the light emitting device having the MIS structure instead of the p type.

[0006]

The p-layer is a material in which crystal growth is extremely difficult than in the past, and the physical properties thereof have not yet been clarified. LE with pn junction
Even if D is realized, there are still many points to be improved in the electrode formed in the p layer, and there is a demand for an electrode material having good compatibility with the p layer and excellent in various characteristics. Further, in LEDs, improvement in external quantum efficiency is desired. Therefore, an object of the present invention is to realize a light emitting device excellent in external quantum efficiency by providing a novel p-layer electrode useful as a light emitting device.

[0007]

The light emitting device of the present invention has p
In a nitride semiconductor light emitting device having a layer formed on the outermost surface, a translucent electrode containing at least palladium (Pd) is formed on almost the entire surface of the p layer.

In addition to Pd, the electrodes include at least platinum (Pt), rhodium (Rh), ruthenium (Ru),
It is characterized by containing at least one metal selected from the group consisting of osmium (Os), iridium (Ir), nickel (Ni), and gold (Au). Even if these elements are added to Pd, the translucency of the electrode can be maintained without impairing the ohmic property of Pd. The electrode structure after the addition may be a laminated structure in which thin films are laminated, a state in which the laminated structure is thermally annealed to be alloyed, or an alloy state from the beginning. Among them, Au is very preferable because it has good adhesiveness to the electrode of the bonding pad containing Au.

Further, when the electrode has a laminated structure, it is more preferable that the side in contact with the p-type layer is Pd. Pd
By making the first contact with the p layer, the ohmic property is hardly lost.

In the light emitting device of the present invention, by adjusting the film thickness of the p electrode formed on the p layer to 500 angstroms or less, more preferably 200 angstroms or less, a preferable light-transmitting property with respect to the emission wavelength of the light emitting device is obtained. It is possible to maintain This film thickness is the same as when other metal is contained in addition to Pd, and preferable translucency can be maintained by setting the total film thickness of the electrodes to 500 angstroms or less.

To form the p-electrode, vapor deposition, sputtering, etc.
A normal vapor phase film forming apparatus can be used. By controlling the film thickness with a film-forming device and setting the film thickness to 500 angstroms (0.05 μm) or less, and more preferably 200 angstroms or less as described above, a preferable light-transmitting property is obtained and light emitted from the light-emitting element is transmitted. To do. The translucency means that the electrode transmits the emission wavelength of the light emitting element, and does not necessarily mean colorless and transparent.

The light emitting device of the present invention includes MOVPE (metalorganic vapor phase epitaxy), HDVPE (halide vapor phase epitaxy), and MVPE.
It can be prepared by growing and stacking a crystal of a nitride semiconductor on a substrate using a vapor phase growth apparatus such as BE (Molecular Beam Vapor Deposition), MONBE (Metal Organic Molecular Beam Vapor Deposition). . Sapphire (Al ₂ O ₃ ), ZnO, spinel (MgAl ₂ O ₄ ), SiC, Si, GaN, etc. are used for the substrate, but sapphire or SiC is often used.
As a laminated structure, basically, an n layer is grown on a substrate, a p layer is laminated on the n layer, and the p layer is laminated on the outermost surface. The structure is such that electrodes can be formed. In addition, a light emitting element in which a p layer is the outermost surface through a p-i-n junction may be used. The n-type nitride semiconductor can be grown by doping a donor impurity such as Si, Ge, and Se. On the other hand, the p-type nitride semiconductor is Mg,
It can be grown by doping a nitride semiconductor with a group II element such as Zn and an acceptor impurity such as C. For example, when a nitride semiconductor doped with an acceptor impurity is grown by using the MOVPE method, there are some that show p-type characteristics without any treatment after the growth, but preferably,
By performing the annealing treatment at 400 ° C. or higher, more preferable p-type characteristics are exhibited. Note that the p-type is, for example, a nitride semiconductor doped with an acceptor impurity and has a resistivity of 10 ³ Ω · cm or less.

[0013]

The translucent electrode containing Pd is superior to the conventional translucent p electrode made of Ni and Au in the transmittance of visible light, particularly in the purple to green region. Therefore, when formed on the surface of the p layer, the light transmittance of the nitride semiconductor light emitting device is improved, and the external quantum efficiency is improved. Moreover, the ohmic property is also very excellent, and particularly when Pd is formed on the side in contact with the p layer, the ohmic property is maintained even if another metal thin film is formed on the Pd in a translucent state. be able to. Especially Pt, Rh, Ru, Os, Ir, Ni, Au
Even if such a metal is alloyed with Pd, good ohmic property can be maintained. Furthermore, since the p-electrode is formed on almost the entire surface of the p-layer, the current spreads uniformly over the entire p-layer, no local electric field concentration occurs, and uniform light emission can be obtained from the entire active layer.

FIG. 1 is a graph showing current-voltage characteristics of various electrodes formed on the p layer. Specifically, after forming the thin film described below on the p layer, annealing is performed at 400 ° C. or higher to p.
By forming electrodes and measuring the current-voltage characteristics of electrodes of the same type, the ohmic characteristics of the electrodes with respect to the p-layer were investigated. 2 is a graph showing the transmittance of the translucent electrode shown in FIG. The electrodes are as follows.

A: A transparent electrode in which Pd is formed in a film thickness of 40 Å. B: A conventional translucent electrode in which Ni and Ni have a film thickness of 60 angstroms and 200 angstroms are sequentially stacked.

As shown in FIG. 1, both show good ohmic properties, but it is further seen that Pd has very low ohmic properties with the p layer.

FIG. 2 shows the transmissivity of each electrode. The conventional electrode (B) containing Ni—Au has a transmissivity in the purple to green region which is a characteristic of the light emission of the nitride semiconductor light emitting device. Is bad. On the other hand, since the transmittance of the electrode A according to the light emitting device of the present invention is superior to that of B, the external quantum efficiency of the light emitting device can be improved.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the light emitting device of the present invention will be described below with reference to the drawings. 3 is a plan view of the light emitting device of the present invention as seen from the electrode side of the p layer, and FIG. 4 is a schematic cross-sectional view showing the structure of the light emitting device of FIG. 3 taken along the alternate long and short dash line shown in the figure. is there.

Example 1 Using a MOVPE reactor,
On a 2-inch φ sapphire substrate 1, a buffer layer 2 made of GaN is 200 angstroms, an n-type contact layer 3 made of Si-doped n-type GaN is 4 μm, and a single quantum well structure made of non-doped In0.2Ga0.8N is active. Layer 4 is 30 Å, Mg-doped p-type Al0.1G
a 0.9N p-type clad layer 5 with 0.2 μm, Mg
The p-type contact layer 6 made of doped p-type GaN is 0.5
The film is grown in order with a film thickness of μm.

Further, the wafer is placed in a reaction vessel,
Anneal at 600 ° C. in a nitrogen atmosphere to form the p-layer 5,
6 is further reduced in resistance. After the annealing, the wafer is taken out of the reaction container, a mask having a predetermined shape is formed on the surface of the uppermost p-type GaN, and the n-type contact layer 3 is etched as shown in FIG. Expose part of.

Next, the mask on the p-layer is removed, and Pd as the p-electrode 10 is formed on almost the entire surface of the uppermost p-type GaN layer.
Is vapor-deposited with a film thickness of 30 Å. P after vapor deposition
The d film is clearly transparent, and the sapphire substrate 1
I was able to see through. By forming the p-electrode 10 on almost the entire surface of the exposed p-layer in this way, the current can be uniformly spread over the entire p-layer, and since it is translucent, the electrode side can be used as the emission observation surface.

After forming the p-electrode 10, Au and N are formed at the corners of the electrode.
A pad electrode 13 for bonding including i is formed with a film thickness of 2 μm. The pad electrode 13 is not transparent.

After forming the p-electrode (10 + 11), the n-electrode 14 containing Ti and Al is formed to a film thickness of 2 μm on the exposed n-layer, and finally annealed at 400 ° C. or higher to heat the electrode. To alloy.

As described above, the wafer with electrodes formed on the n-type contact layer 3 and the p-layer contact layer 6 is
When cut into 50 μm square chips, the sapphire substrate side 1 of the light emitting chip was bonded to a lead frame, wire-bonded with an Au wire, and molded with an epoxy resin to form an LED element. If (forward current) 20 mA At Vf (forward voltage) of 3.4 V, emission wavelength of 460 nm
The emission output was about 30% higher than that of a conventional LED having the same structure having a translucent p electrode containing Ni and Au.

[Embodiment 2] In Embodiment 1, the p electrode 1
An LED element was obtained in the same manner except that Pd was 20 Å and Ni was 100 Å, and Vf was 3.4 V at If 20 mA, but the emission output was reduced by about 15% due to Ni. did.

[Third Embodiment] In the first embodiment, the p-electrode 1 is used.
An LED element was similarly obtained, except that Pd was 20 Å and Au was 100 Å, and Vf was 3.4 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[Embodiment 4] In Embodiment 1, the p electrode 1
An LED device was obtained in the same manner except that Pd was 20 angstroms and Rh was 100 angstroms in 0, and Vf was 3.5 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[Embodiment 5] In Embodiment 1, the p electrode 1
An LED element was similarly obtained, except that Pd was 20 Å and Ru was 100 Å, and Vf was 3.5 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[Sixth Embodiment] In the first embodiment, the p-electrode 1 is used.
An LED element was obtained in the same manner except that Pd was 20 angstroms and Pt was 100 angstroms in 0, and Vf was 3.5 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[Embodiment 7] In Embodiment 1, the p electrode 1
An LED element was obtained in the same manner except that Pd was stacked at 20 Å and Os was stacked at 100 Å at 0, and Vf was 3.5 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[Embodiment 7] In Embodiment 1, the p electrode 1 is used.
An LED element was obtained in the same manner except that Pd was laminated at 20 Å and Ir at 100 Å, and Vf was 3.5 V at If 20 mA. The light emission output was almost the same as that of Example 2.

[0032]

As described above, the light emitting device of the present invention can be formed on the surface of the p layer to effectively take out the light emitted from the active layer to the outside. Moreover, since the electrode is excellent in ohmic contact with the p layer, a practical light emitting device having a low Vf can be realized. When the light emitting device of the present invention is used for an LED device such as a full-color LED display, an LED traffic light, and a road information display board, a bright device with low power consumption can be realized, and its industrial utility value is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing current-voltage characteristics of various electrodes formed on a p-layer.

FIG. 2 is a diagram showing transmittances of various electrodes formed on a p-layer for respective wavelengths.

FIG. 3 is a plan view showing an electrode shape of a light emitting device according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view showing the structure of the light emitting device of FIG.

[Explanation of symbols]

 1 ... Sapphire substrate 2 ... Buffer layer 3 ... N-type contact layer 4 ... Active layer 5 ... P-type clad layer 6 ... P-type contact layer 10. ... P electrode 13 ... Pad electrode 14 ... N electrode

Claims (3)

[Claims] 1. A nitride semiconductor light-emitting device having a p-type nitride semiconductor layer formed on the outermost surface, wherein the p-type nitride semiconductor layer has a light-transmitting property including palladium (Pd) on substantially the entire surface. 2. A nitride semiconductor light emitting device, characterized in that the electrode is formed. 2. The electrode comprises, in addition to Pd, at least platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), nickel (N).
The nitride semiconductor light emitting device according to claim 1, comprising at least one metal selected from the group consisting of i) and gold (Au). 3. The electrode has at least a two-layer structure,
The nitride semiconductor light emitting device according to claim 2, wherein the side in contact with the p-type nitride semiconductor layer having a two-layer structure is Pd.