JP2001044503A - Algainp light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart superior ohmic contact property with an oxide window layer by a method, wherein a downmost layer of an electrode is constituted by a layer containing an oxide of a transition metal, and also the upper most layer of the electrode is constituted by a metal layer. SOLUTION: An n-type ohmic electrode 107 is provide on a window layer 106 provided in an upper part of a lamination structure 30, and a lowermost part 107a joined to a ZnO layer of the ohmic electrode 107 is structured by adhering Ni through vacuum deposition. An Au film is placed on top of the Ni film as an upmost layer 107b by the vacuum deposition. After an electrode material composed of a gold and zinc alloy is adhered on a reverse face of a substrate 101 by the vacuum deposition, it is heated to form a (p) type ohmic electrode 108. In parallel thereto, oxygen diffusing from a zinc oxide layer is made to be absorbed into the Ni film of the lowermost layer 107a, thereby changing it into a NiO film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-brightness (Al _X Ga _{1 -x} ) _Y In _{1 -Y} P (0 ≦ X ≦
1, 0 <Y ≦ 1) (hereinafter abbreviated as AlGaInP) The present invention relates to a configuration of an electrode for providing a light emitting diode.

[0002]

2. Description of the Related Art An AlGaInP light emitting diode (LED) having a pn junction type double hetero (DH) junction structure is known as a light emitting element in a green, yellow to red-orange band (Appl. Phys. Lett., 61). (1
5) (1992), pp. 1775-1777). In particular, the indium composition ratio is set to about 0.5 (Al _X G
_{a 1-X) 0. 5 In} 0.5 P (0 ≦ X ≦ 1) is gallium arsenide (GaAs) single crystal and for lattice matching (Appl.P
hys. Lett. , 57 (27) (1990), 29
(See pages 37 to 2939), which is used for forming a clad layer and a light emitting layer (active layer) which form a light emitting portion of a DH junction structure (Appl. Phys. Let).
t. , 58 (10) (1991), 1010-1012.
Page).

In a conventional AlGaInP high-brightness LED,
A window layer (window layer) for efficiently extracting light emitted from the light emitting section to the outside is disposed on the upper clad layer in the direction of extracting light (SPIE, Vol. 30).
02 (1997), pp. 110-118). In a conventional example, a window layer is formed of indium-tin oxide (indium-t).
An example comprising an in oxide (abbreviated as ITO) is known (see US Pat. No. 5,481,122). Further, there is disclosed a technical means for providing a transparent oxide layer made of indium oxide, tin oxide, zinc oxide or magnesium oxide as a contact layer (see Japanese Patent Application Laid-Open No. 11-17220).

It is known that zinc oxide (ZnO) to which aluminum (Al) is added exhibits a low specific resistance (resistivity) of less than 1 × 10 ⁻³ Ω · cm (Technical Research of the Institute of Electronics, Information and Communication Engineers). Report, Vol.99, No.63 (1999)
May 20, 2000), pages 83-88). This Al-doped ZnO layer is also used as a window layer of a group III nitride semiconductor LED (see US Pat. No. 5,889,295).

A conventional high-luminance AlGaInPLED is constructed by laying an ohmic electrode on a window layer or a contact layer made of the above-mentioned oxide. The ohmic electrode is gold (Au) or nickel (Ni) / gold (indicating that nickel and gold are stacked, nickel is in the lower layer, and gold is in the upper layer; the same applies hereinafter). Alternatively, it is composed of platinum (Pt) / gold (see US Pat. No. 5,889,295).

[0006]

However, even if a metal electrode having a conventional structure is directly joined to an oxide layer of ITO or the like, a low ohmic contact resistance cannot be stably obtained. This is a practical problem.

In addition, in the case of a conventional electrode composed of a single metal or a multi-layer structure, it is not possible to sufficiently secure adhesion to an oxide film such as zinc oxide or ITO. This insufficient adhesion causes the metal electrode to peel off from the oxide layer at the time of connection (bonding) to the electrode, resulting in a disadvantage of lowering the production yield of the LED.

The present invention has been made to overcome the above-mentioned problems of the prior art, and has as its object to provide a pn junction type double hetero (DH) structure AlGaInP having an oxide window layer.
It is an object of the present invention to provide a configuration of an electrode in an LED that (1) can achieve good ohmic contact with an oxide window layer and (2) does not peel off from the surface of the oxide window layer.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have reached the present invention.
That is, in the present invention, [1] the light-emitting layer is (Al _X Ga _{1 -x} ) _Y I
An LED having a pn junction type double hetero structure composed of n _{1 -Y} P (0 ≦ X ≦ 1, 0 <Y ≦ 1), having a window layer containing n-type zinc oxide in a light emission direction, and the window layer An AlGaInP light-emitting diode, comprising an electrode composed of a plurality of layers in contact with the lower electrode, wherein the lowermost layer of the electrode is formed of a layer containing a transition metal oxide, and the uppermost layer of the electrode is formed of a metal layer. [2] The AlGaInP light-emitting diode according to [1], wherein the window layer and the electrode are in contact with each other;
[3] The AlGaInP light-emitting diode according to [1] or [2], wherein the transition metal is one selected from titanium, nickel, chromium, and cobalt;
[4] The thickness of the lowermost layer of the electrode is 5 nm or more and 100 nm
The AlGaInP light emitting diode according to any one of [1] to [3], wherein the metal in the uppermost layer of the electrode [5] is aluminum. AlGaI according to any one of [4]
The nP light emitting diode, [6] the AlGaInP light emitting diode according to any one of [1] to [4], wherein the metal of the uppermost layer of the electrode is gold; AlGa according to [6], further comprising a layer made of molybdenum or platinum between the lowermost layer and the lowermost layer.
An InP light emitting diode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The light emitting section of the present invention is composed of an AlGaInP mixed crystal having a pn junction type DH junction structure. In particular, the indium composition ratio is set to about 0.5 (Al _X
Ga _1-x ) _0.5 In _0.5 P (0 ≦ X ≦ 1) is particularly preferable because of lattice matching with a GaAs single crystal substrate. In the electrode of the present invention, the lowermost layer of the electrode on the oxide window layer containing n-type zinc oxide is composed of a layer containing a metal oxide of a transition metal. Examples of the configuration of the electrode include nickel oxide (NiO) (lowest layer) / Au (top layer) or titanium oxide (TiO ₂ ) /
There are multi-layer electrodes made of Al or the like. The multilayer electrode having such a configuration can be configured based on a laminated structure of a single film of Ni or titanium (Ti), which is a metal element forming the lowermost oxide layer, and a metal film forming the uppermost layer. That is, Ni / Au
Alternatively, it can be configured based on a Ti / Al multilayer structure. Heat treatment for imparting ohmic properties to electrodes (alloying)
Alternatively, with the heat treatment in the LED manufacturing process, in the single-metal multilayer structure electrode configured as described above, the lowermost Ni layer or Ti layer is oxidized by oxygen entering from the underlying oxide window layer. As a result, an oxide-containing layer is formed, and as a result, an electrode having a NiO / Au or TiO ₂ / Al multilayer structure is obtained. The lowermost layer containing a transition metal oxide is preferably a transition metal oxide alone or a layer containing 15% or more by weight of a transition metal oxide. This lowermost constituent layer diffuses from the oxide window layer side,
It is preferable that the oxide window layer and the lowermost layer of the electrode are in contact with each other because they have a function of capturing invading oxygen.

The electrode having the above-mentioned multilayer structure of a single metal layer can be formed by a metal film applying means such as a high frequency sputtering method, an ion plating method, an electron beam (EB) evaporation method, or a vacuum evaporation method. From the beginning, there is also a means for depositing an oxide film such as NiO or TiO ₂ as the lowermost layer. However, when the oxide is previously deposited in the form of an oxide, the ability to capture oxygen is inferior to that of a single metal film.

The ability to capture oxygen that is released and diffused from the oxide window layer is better exhibited in the layer composed of the transition metal. This is interpreted as having an excellent affinity for oxygen. In the embodiment of the present invention, the lowermost oxide layer is composed of a transition metal oxide layer, and in particular, Ti, Ni,
It is preferable to constitute the chromium (Cr) or cobalt (Co) oxide layer.

If the thickness of the oxide layer is extremely thick to several μm or more, there is a problem in reducing the forward voltage (so-called Vf) of the LED. For this reason, in the present invention, the thickness of the oxide layer constituting the lowermost layer is set to 5 nm or more and 100 nm or less in order to ensure sufficient conduction between the uppermost layer of the electrode and the oxide window layer. Defined in If the thickness exceeds 100 nm, it is difficult to reduce the forward voltage.

Since the oxide layer forming the lowermost layer of the electrode has a function of catching oxygen entering from the oxide window layer, a good ohmic contact is provided especially when the oxide window layer and the electrode are in contact with each other. It is. In addition, the adhesion between the lowermost layer and the oxide window layer is increased by this action. Furthermore, the adhesion between the lowermost layer and the uppermost layer of the electrode is increased, and an ohmic electrode that does not easily peel off from the oxide window layer is provided. In particular, in the Au electrode, an Au electrode layer having remarkably excellent adhesion can be formed as compared with the conventional method of laying directly on the oxide window layer.

In the present invention, the uppermost metal electrode of the electrode is
It is preferable to be composed of Al or Au. Either metal can be easily bonded and the manufacture of the LED is simplified. When a multilayer electrode is formed by stacking a plurality of layers on the lowermost layer, Al and Au are arranged so as to form the outermost layer. This is to maintain the easiness of the connection possessed by these metals.

Further, in the present invention, it is preferable that a layer made of molybdenum (Mo) or Pt is provided between the lowermost layer and the uppermost layer in the multilayer electrode having Au as the uppermost layer. As described above, when the intermediate layer made of a high melting point metal is inserted, oxygen atoms are prevented from being concentrated in a region near the bonding interface with the Au electrode layer, and the multilayer electrodes that are firmly adhered to each other are formed. There are benefits brought.

The electrode having the multilayer structure as described above has n
It functions best when it is configured in contact with a window layer containing zinc oxide, but is also applicable when it is provided on another oxide layer. For example, even if the electrode of the present invention is laid on a conductive ITO film provided as a protective film on a ZnO film that is the outermost layer of the window layer, an ohmic electrode with secured adhesion to the window layer can be formed. .

[0018]

EXAMPLE Zinc (Zn) inclined 4 ° in the [110] direction
Doped p-type (001) -GaAs single crystal substrate 101, Z
n-doped p-type GaAs buffer layer (carrier concentration (p) = 4
× 10¹⁸cm^-3, Layer thickness (d) = 3 μm) 102, Zn
P-type (Al_0.7Ga_0.3)_0.5In_0.5P lower cladding
Layer (p = 3 × 10¹⁸cm^-3, D = 1 μm) 103, en
Doped n-type (Al_0.2Ga_0.8)_0.5In_0.5P light emitting layer
(Carrier concentration n = 3 × 10¹⁷cm^-3, D = 0.5μ
m) 104, Si-doped n-type (Al_0.7Ga_0.3) _0.5I
n_0.5P upper cladding layer (n = 1 × 10¹⁸cm^-3, D =
5 μm) 105, and a window layer composed of an Al-doped ZnO film
In each of the following examples,
AlGaInPLED as a common host material
Was.

The Al-doped zinc oxide layer forming the window layer 106 was applied by a general magnetron sputtering method. The carrier concentration of the zinc oxide layer at room temperature is about 2 × 1
And 0 ²⁰ cm ^-3, the resistivity was about 3 × 10 ^-3 Ω · cm. The mobility was about 12 cm ² / V · s. The layer thickness was about 250 nm. Sheet resistance is about 56
Ω / □. According to a general X-ray diffraction analysis method, the zinc oxide layer forming the window layer 106 has a <0001> direction (C axis).
It was shown to be a polycrystal consisting of an aggregate of single crystal bodies grown in the above.

(Embodiment 1) FIG. 1 shows an LE according to this embodiment.
It is a schematic diagram which shows the cross-section of D10. Laminated structure 30
An n-type ohmic electrode 107 was laid on the window layer 106 provided on the top of the substrate. Zn of the n-type ohmic electrode 107
First, the lowermost layer 107a to be joined to the O layer was formed by applying Ni by a general vacuum deposition method. The layer thickness of the Ni film was about 10 nm. An Au film was overlaid on the Ni film as the uppermost layer 107b by a general vacuum deposition method. Au
The thickness of the film was about 1.5 μm.

Next, an electrode material made of a gold-zinc alloy (Au 98% by weight-Zn 2% by weight) was applied to the back surface of the p-type GaAs substrate 101 by a general vacuum deposition method. Thereafter, an alloy heat treatment at 420 ° C. for 5 minutes in an argon (Ar) gas flow is performed to form a p-type ohmic electrode 1.
08.

At the same time as the alloying process for forming the p-type ohmic electrode 108, oxygen diffused from the zinc oxide layer is absorbed by the Ni film of the lowermost layer 107a, and the Ni film is converted to the NiO film. Changed. Thus, the laminated structure of the n-type ohmic electrode 107 was NiO / Au.
Further, after the above alloying, the multilayer structure electrode 10
7 was visually observed.

The n-type ohmic electrode 1 having the above configuration
In No. 07, since the outermost layer was an Au layer, an Au wire could be easily bonded. Further, the electrode did not peel off from the oxide window layer 106 during bonding. When a forward current was passed between the n-type and p-type ohmic electrodes 107 and 108, substantially uniform red-orange light emission was obtained from almost the entire surface of the ZnO window layer 106. The emission wavelength measured by the spectrometer was about 620 nm. The half width of the light emission spectrum was about 18 nm, and light emission having excellent monochromaticity was obtained. Reflecting the good ohmic contact between the n-type ohmic electrode 107 and the ZnO window layer 106, the forward voltage when a forward current of 20 mA (mA) flows is about 1.95 volts (V). became. Further, the change width of the forward voltage between the LEDs was 1.95 V ± 0.03 V, and the forward voltage was uniform. The emission intensity in a chip state reached about 54 millicandela (mcd).

(Embodiment 2) Only the structure of the n-type ohmic electrode is different from that of the embodiment 1, and the other parts are the same.
A PLED was fabricated.

In this embodiment, the n-type ohmic electrode is made of Ti
It was composed of a titanium oxide / Al multilayer structure based on the / Al multilayer structure. The conversion from the Ti layer to the titanium oxide layer made of TiO, TiO _2, or the like utilized the above-described alloy processing.

A connection was made by ultrasonic bonding to an n-type ohmic electrode having a titanium oxide / Al multilayer structure, and the characteristics of the LED were evaluated. No peeling of the electrode from the ZnO window layer during bonding was observed.
The characteristics of the obtained LED were substantially the same as those described in Example 1.

Example 3 An AlGaInPLED 20 shown in FIG. 2 was constructed using the above-mentioned laminated structure 30.
The same components as those in the first embodiment (see FIG. 1) are denoted by the same reference numerals, and description thereof will be omitted.

The window layer 10 made of ZnO described in Example 1
On 6, a protective film 109 made of ITO was laminated.
The protective film 109 was formed of an ITO film having a carrier concentration of about 1 × 10 ²⁰ cm ⁻³ and a specific resistance of about 4 × 10 ⁻⁴ Ω · cm. The layer thickness was about 200 nm.

An electrode material having a three-layer structure of a Ti layer / Pt layer / Au layer was deposited on the ITO protective film 109 by using a normal electron beam evaporation method. Ti of the bottom layer
The thickness of the layer 107a was about 8 nm. The thickness of the intermediate layer 107c was set to about 0.1 μm, and the thickness of the Au layer of the uppermost layer 107b was set to about 1.2 μm. p-type GaAs substrate 1
01 was applied with the p-type electrode material described in Example 1.

Thereafter, a heat treatment was performed in a nitrogen stream at 420 ° C. for 3 minutes to give ohmic properties to the above-mentioned p-type electrode material to form a p-type ohmic electrode 108. At the same time, the ZnO window layer 106 or ITO
Oxygen atoms diffused from the protective film 109 are replaced with Ti in the lowermost layer.
The layer 107a was captured. Thus, the Ti layer was converted to an oxide layer made of TiO or TiO ₂ .

An Au wire can be easily connected to the n-type ohmic electrode 107 having a multilayer structure of titanium oxide / Pt / Au.
No peeling from No. 9 was observed. When a forward current was passed between the n-type and p-type ohmic electrodes 107 and 108, substantially uniform red-orange light emission was obtained from almost the entire surface of the ITO protective film 109. The emission wavelength measured by the spectrometer is about 6
20 nm. The half width of the emission spectrum is about 18n
m, and luminescence excellent in monochromaticity was obtained. Reflecting good ohmic contact between the n-type ohmic electrode 107 and the ITO protective layer 109, the forward voltage when a forward current of 20 mA flows was about 1.98V. Also, L
The change width of the forward voltage between EDs is 1.98 V ± 0.04
V, which was a uniform forward voltage. The light emission intensity in the chip state was about 50 mcd.

[0032]

As described in the present invention, when an electrode is formed from a multilayer structure, good ohmic characteristics can be achieved with an oxide window layer, so that a forward voltage is reduced and a high-luminance AlG
An aInPLED is obtained.

Further, when the electrode having the multilayer structure according to the present invention is used, an ohmic electrode having excellent adhesion to the oxide window layer can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a cross-sectional structure of an LED described in Example 1.

FIG. 2 is a schematic diagram illustrating a cross-sectional structure of the LED described in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 AlGaInPLED 20 AlGaInPLED 30 Laminated structure 101 p-type GaAs single crystal substrate 102 p-type GaAs buffer layer 103 p-type lower cladding layer 104 light emitting layer 105 upper cladding layer 106 oxide window layer 107 n-type ohmic electrode 107a lowermost layer 107b uppermost layer 107c Intermediate layer 108 p-type ohmic electrode 109 protective layer

Continuation of the front page F term (reference) 5F041 AA03 CA04 CA23 CA34 CA35 CA41 CA49 CA53 CA57 CA66 CA67 CA71 CA73 CA82 CA85 CA92 DA07

Claims (7)

[Claims] The light-emitting layer is composed of (Al _X Ga _{1 -X} ) _Y In _{1 -Y} P (0
≦ X ≦ 1, 0 <Y ≦ 1) a pn junction type double heterostructure LED having a window layer containing n-type zinc oxide in a light emission direction, and comprising a plurality of layers on the window layer An AlGaInP light-emitting diode, comprising: an electrode, wherein the lowermost layer of the electrode comprises a layer containing a transition metal oxide, and the uppermost layer of the electrode comprises a metal layer. 2. The AlGaInP light emitting diode according to claim 1, wherein the window layer and the electrode are in contact with each other. 3. The transition metal is titanium, nickel, chromium,
The AlGaInP light emitting diode according to claim 1, wherein the AlGaInP light emitting diode is one selected from cobalt. 4. The method according to claim 1, wherein the lowermost layer of the electrode has a thickness of 5 nm or more and
The AlGaInP light emitting diode according to any one of claims 1 to 3, wherein the thickness of the AlGaInP light emitting diode is 0 nm or less. 5. The AlGaInP light-emitting diode according to claim 1, wherein the metal in the uppermost layer of the electrode is aluminum. 6. The AlGa according to claim 1, wherein the metal in the uppermost layer of the electrode is gold.
InP light emitting diode. 7. The AlGaInP light emitting diode according to claim 6, further comprising a layer made of molybdenum or platinum between the uppermost layer and the lowermost layer of the electrode.