Transparent electrode Number:7,417,263 from the United States Patent and Trademark Office (PTO) owispatent In order to emit a light from an electrode side, in semiconductor light emitting devices such as LED and the like, and liquid crystal, the electrode is formed of a transparent material so as to transmit a light through the transparent electrode and exit the light. A ZnO, which constitutes a material for the transparent electrode, is subject to erosion by acid and alkali, thus, as the case may cause loss of a reliability of the electrode under the influence of ion-containing moisture. In order to solve such a problem, this invention has as its aim a transparent electrode film provided with stability capable of preventing any degradation under the influence of any ion-containing moisture, while being kept acid-proof and alkali-proof. In order to accomplish the above-mentioned aim, this invention provides a transparent electrode made up of a ZnO as its main material, wherein its surface is covered with a Mg-doped ZnO film.<H Transparent, electrode, Transparent, ele, 7417263.html, Patent, pto, 7417263

Title: Transparent electrode

Abstract: In order to emit a light from an electrode side, in semiconductor light emitting devices such as LED and the like, and liquid crystal, the electrode is formed of a transparent material so as to transmit a light through the transparent electrode and exit the light. A ZnO, which constitutes a material for the transparent electrode, is subject to erosion by acid and alkali, thus, as the case may cause loss of a reliability of the electrode under the influence of ion-containing moisture. In order to solve such a problem, this invention has as its aim a transparent electrode film provided with stability capable of preventing any degradation under the influence of any ion-containing moisture, while being kept acid-proof and alkali-proof. In order to accomplish the above-mentioned aim, this invention provides a transparent electrode made up of a ZnO as its main material, wherein its surface is covered with a Mg-doped ZnO film.

Patent Number: 7,417,263 Issued on 08/26/2008 to Nakahara

Inventors: Nakahara; Ken (Kyoto, JP)
Assignee: Rohm Co., Ltd. (Kyoto, JP)

Appl. No.: 10/748,734

Filed: December 30, 2003

Foreign Application Priority Data


Feb 25, 2003 [JP]			2003-048065

Current U.S. Class: 257/99 ; 257/100; 257/102; 257/103

Current International Class: H01L 33/00 (20060101); H01L 23/29 (20060101)

Field of Search: 257/79-103 372/43-50 349/42-53

References Cited [Referenced By]

U.S. Patent Documents


4888202	December 1989	Murakami et al.
5625202	April 1997	Chai
5804834	September 1998	Shimoyama et al.
6057561	May 2000	Kawasaki et al.
6084899	July 2000	Shakuda
6320207	November 2001	Furukawa et al.
6416888	July 2002	Kawamura et al.
6423983	July 2002	Narayan et al.
6541797	April 2003	Udagawa
6674098	January 2004	Niki et al.
6787435	September 2004	Gibb et al.
6806503	October 2004	Hosono et al.
2001/0028062	October 2001	Uemura et al.
2002/0030196	March 2002	Iwata et al.
2002/0105279	August 2002	Kimura
2002/0126719	September 2002	Kadota
2002/0127853	September 2002	Hubacek et al.
2003/0209723	November 2003	Sakai
2004/0051109	March 2004	Ishizaki et al.
2004/0079947	April 2004	Lan et al.
2004/0104392	June 2004	Ishizaki
2004/0112278	June 2004	Yoshida et al.
2004/0235212	November 2004	Ishizaki
2005/0224825	October 2005	Ishizaki

Foreign Patent Documents


11-070610	Mar., 1999	JP
2000-353820	Dec., 2000	JP
2001-210867	Aug., 2001	JP
2002-076356	Mar., 2002	JP
2002-011059	Apr., 2002	JP
2002-164570	Jun., 2002	JP
2002-170993	Jun., 2002	JP
2002-222991	Aug., 2002	JP
2003037268	Feb., 2003	JP
WO 01/08229	Aug., 2002	WO
WO-02-070793	Sep., 2002	WO
WO-02/89223	Nov., 2002	WO

Other References

Wada et al, "Thin Film Materials Technology--Sputtering of Compound Materials", publisher: William Andrew Publishing / Noyes (2004), p. 306 (Table 5.28). cited by examiner .
S. M. Sze, "Modern Semiconductor Device Physics", John Wiley & Sons, Inc., New York ; p. 537 (Appendix F)(ISBN: 0-471-15237-4 (1998)). cited by examiner .
Merriam-Webster's Collegiate Dictionary, tenth Edition, p. 811; Merriam-Webster, Incorporated, Springfield, MA (USA) (1999). cited by examiner .
Japanese language office action and its English translation for corresponding Japanese application No. 2003-048065 list the reference above. cited by other.

Primary Examiner: Mondt; Johannes P
Attorney, Agent or Firm: Hogan & Hartson LLP

Claims

What is claimed is:

1. A light emitting device comprising: a semiconductor layer formed on a substrate of a semiconductor device; a ZnO transparent electrode formed on the semiconductor layer; and an Mg-doped ZnO film disposed on a light emission side of an outer surface of the ZnO transparent electrode that is opposite to the substrate, wherein the semiconductor layer comprises an n-type GaN system semiconductor layer formed on the substrate, an emission layer formed on the n-type GaN system semiconductor layer, and a p-type GaN system semiconductor layer formed on the emission layer.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transparent electrode provided with stability capable of preventing any degradation due to ion-containing moistures, while being kept acid-proof and alkali-proof.

2. Description of the Related Art

Conventionally, in semiconductor light emitting devices such as LED, and liquid crystal, the electrode is formed, for emitting a light from an electrode side, of a transparent material to allow light to transmit through the transparent electrode and exit it (for example, refer to related art document 1 below). ZnO, which is material as the transparent electrode, is subject to erosion by acid and alkali, and thus may cause loss of a reliability of the electrode under the influence of ion-containing moistures. Moreover, when employed as a white light source utilizing an emission of LED, a semiconductor light emitting device is covered with an epoxy resin mixed with a fluorescent material.

In FIG. 4 there is shown an arrangement of a light emitting device module as a conventional white light source. In FIG. 4, a reference numeral 51 refers to a semiconductor light emitting device, 52 refers to an epoxy resin, 53 refers to a module substrate and 54 refers to moisture. As shown in FIG. 4, the entire semiconductor light emitting devices 51, which is mounted on the module substrate 53 of the light emitting device module, is covered with the epoxy resin 52. The fluorescent material mixed with the epoxy resin 52 is excited by emission from the semiconductor light emitting devices 51 and thus emits white light. However, the moisture is liable to penetrate the epoxy resin 52 so that when any moisture contained inside the epoxy resin 52 or the moisture 54 from the outside penetrates, or in particular, the moisture 54 contains ions, it exhibits acidity or alkalinity, thus, as the case may be, resulting in an erosion of a ZnO transparent electrode employed for the semiconductor light emitting device. It is probably assumed that a high ionization tendency of Zn causes said phenomenon.

[Related Art Document 1]

Japanese patent laid-open publication 11-70610, (FIG. 3, page 3-4)

SUMMARY OF THE INVENTION

In order to solve such a problem, the object of the invention is to provide a transparent electrode film provided with stability capable of preventing any degradation due to penetration of ion-containing moistures.

The inventor has discovered that doping ZnO, which is employed as a transparent electrode of a light emitting device, with Mg leads to a greatly improved acid resistance. In FIG. 1, an experimental result of a measured acid resistance of Mg-doped ZnO transparent electrodes with a doped-Mg amount as parameter is shown. In FIG. 1, a horizontal axis shows etching time, a vertical axis shows an etching depth, and a parameter of Mg shows weight % of the Mg to be doped to ZnO. In this experiment, the etching depth was measured by dipping the ZnO transparent electrode into an acid liquid with a volume ratio of a 35% concentration hydrochloric acid to water of 1:100. FIG. 1 shows that the etching depth decreases to one fourth or less as compared with the non-Mg doped transparent electrode, when doping Mg of 12 mol % or more. This also indicates that the Mg-doped ZnO can prevent any degradation of reliability due to ion-containing moistures.

Then, in order to accomplish the object mentioned above, the invention provides a transparent electrode made up of ZnO as its main material, wherein its surface is covered with a Mg-doped ZnO film.

According to the invention, in the transparent electrode, an acid-resistance can be increased and any degradation of reliability due to ion-containing moistures can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating measured acid resistance of Mg-doped ZnO on which the present invention is based.

FIG. 2 is a view showing an arrangement of an embodiment in which the invention is applied to a GaN system semiconductor light emitting device, and explaining a ZnO transparent electrode wherein a top surface is covered with a Mg-doped ZnO film.

FIG. 3 is a view showing an arrangement of an embodiment in which the invention is applied to a GaN system semiconductor light emitting device, and explaining a ZnO transparent electrode wherein surfaces are covered with a Mg-doped ZnO film.

FIG. 4 is a view explaining an arrangement of a conventional light emitting device module employed as a white light source.

REFERENCE NUMERALS

11: Mg-doped ZnO film 12: ZnO transparent electrode 13: metal pattern 14: metal electrode 15: Sapphire substrate 20: GaN system semiconductor layer 21: p type GaN system semiconductor layer 22: emission layer 23: n type GaN system semiconductor layer

DETAILED DESCRIPTION OF THE INVENTION

Hereafter embodiments of the present invention will be described with reference to accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

A first embodiment of the invention is shown in FIG. 2. FIG. 2 is an embodiment of a GaN system semiconductor light emitting device to which the invention is applied. In FIG. 2, 11 is a Mg-doped ZnO film, 12 is a ZnO transparent electrode, 13 is a metal pattern, 14 is a metal electrode, 15 is a sapphire substrate, 21 is a p type GaN system semiconductor layer, 22 is an emission layer, 23 is an n type GaN system semiconductor layer, and 20 is a GaN system semiconductor layer which includes the p type GaN system semiconductor layer 21, the emission layer 22, and the n type GaN system semiconductor layer 23. In the present invention, the GaN system semiconductor layer refers to a semiconductor layer, which includes at least one layer of In.sub.pGa.sub.qAl.sub.rN (p+q+r=1, p.gtoreq.0, q.gtoreq.0, r.gtoreq.0).

In such a GaN system semiconductor light emitting device, first of all, the n type GaN system semiconductor layer 23 is formed on the top surface of the sapphire substrate 15 with MOCVD (metal organic chemical vapor deposition) method and the like. It is suitable that the n type GaN system semiconductor layer 23 is contained of an n type GaN and a GaN buffer layer. The n type GaN system semiconductor layer 23 may be formed with ELO (Epitaxial Lateral Overgrowth). The emission layer 22 is formed on the top surface of the n type GaN system semiconductor layer 23. The emission layer 22 consists of In.sub.xGa.sub.1-xN (0.ltoreq.x<1) or/and Al.sub.yGa.sub.1-yN (0.ltoreq.y<1). Moreover, the emission layer 22 may be in the form of a multi-quantum well structure of In.sub.xGa.sub.1-xN/GaN (0.ltoreq.x<1) by adjusting the ratio of In and Ga, or a multi-quantum well structure of Al.sub.yGa.sub.1-yN/GaN (0.ltoreq.y<1) by adjusting the ratio of aluminum and Ga. Furthermore, a multi-quantum well structure of In.sub.pGa.sub.qAl.sub.rN/GaN (p+q+r=1, p.gtoreq.0, q.gtoreq.0, r.gtoreq.0) may as well be realized by adjusting the ratio of In, Ga and aluminum. Moreover, a layer consisting of an n type Al.sub.yGa.sub.1-yN (0.ltoreq.y<1) may be formed on the n type GaN system semiconductor layer 23 side of the emission layer 22, or a layer consisting of Al.sub.yGa.sub.1-yN (0.ltoreq.y<1) may be formed on the p type GaN system semiconductor layer 21 side of the emission layer 22.

Next, the p type GaN system semiconductor layer 21 is formed on the top surface of the emission layer 22. After having formed the ZnO transparent electrode 12 on the top surface of the p type GaN system semiconductor 21, a part of the ZnO transparent electrode 12, the p type GaN system semiconductor layer 21, the emission layer 22, and the n type GaN system semiconductor layer 23 is removed by etching, respectively. The n type GaN system semiconductor layer 23 is etched down to the midway of the layer thereof. Next, the Mg-doped ZnO film 11 is formed, and then the metal electrode 14 is formed on the top surface of the exposed n type GaN system semiconductor layer 23, and the metal pattern 13 is formed on the top surface of the Mg-doped ZnO film 11 with an evaporation method or a sputtering method.

Or after having formed the p type GaN system semiconductor layer 21 on the top surface of the emission layer 22, a part of the p type GaN system semiconductor layer 21, the emission layer 22, and the n type GaN system semiconductor layer 23 is removed by etching, respectively. The n type GaN system semiconductor layer 23 is etched down to the midway of the layer thereof. Next, the ZnO transparent electrode 12 is formed on the top surface of the p type GaN system semiconductor layer 21, and furthermore, on the top thereof, the Mg-doped ZnO film 11 is formed. The metal electrode 14 is formed on the top surface of the exposed n type GaN system semiconductor layer 23, while the metal pattern 13 is formed on the top surface of the Mg-doped ZnO film 11 with the evaporation method or the sputtering method.

The above-mentioned Mg-doped ZnO film 11 is formed with a sputtering method by using a target of a baked compound of mixed MgO and ZnO powders, an ion plating method and the like. Moreover, an evaporation method similar to a molecular beam epitaxial method, which provides metal Mg and metal Zn having been heated by a heater as a molecular beam, and provides oxygen using an RF radical cell, may also provide the same.

Moreover, as for the material, which constitutes the metal pattern 13, either of Al, Ti, Cr, Ni, Cu, Mo, Pd, W, Pt, or Au, or an alloy of these metals is as well available. The metal pattern includes a metal pad for bonding.

If the ZnO transparent electrode is covered with the Mg-doped ZnO film as described according to the embodiment, the Mg-doped ZnO film and the ZnO transparent electrode can be prevented from being eroded by moisture. Because Mg-doped ZnO has the same light transmittance and conductivity as ZnO, light emitted from a portion of the GaN system semiconductor layer transmits through the Mg-doped ZnO film, and then the conductivity between the metal pattern 13 formed on the Mg-doped ZnO film 11 and the ZnO transparent electrode 12 is also secured.

According to the embodiment, although the GaN system semiconductor layer 20 is formed on the top surface of the sapphire substrate 15, the GaN system semiconductor layer 20 may be formed on a conductive substrate in place of the sapphire substrate 15. Moreover, although the embodiment in which the transparent electrode is formed on the top surface of the GaN system semiconductor layer 20 has been described, the invention may be applicable not only to GaN system semiconductor layers but to semiconductor layers like those constituting semiconductor light emitting devices, and furthermore to devices which form a ZnO transparent electrode such as electronic devices including a liquid crystal.

Embodiment 2

A second embodiment of the invention is shown in FIG. 3. FIG. 3 is an embodiment of a GaN system semiconductor light emitting device to which the invention is applied. In FIG. 3, 11 is a Mg doped ZnO film, 12 is a ZnO transparent electrode, 13 is a metal pattern, 14 is a metal electrode, 15 is a sapphire substrate, 21 is a p type GaN system semiconductor layer, 22 is a emission layer, 23 is an n type GaN system semiconductor layer, and 20 is a GaN system semiconductor layer which includes the p type GaN system semiconductor layer 21, the emission layer 22, and the n type GaN system semiconductor layer 23.

As for material, which constitutes the metal pattern 13, either of Al, Ti, Cr, Ni, Cu, Mo, Pd, W, Pt, or Au, or an alloy of these metals is as well available. The metal pattern includes a metal pad for bonding.

A point of a difference exists between the second embodiment and the first embodiment in that not only the top surface of the ZnO transparent electrode 12 but also the side surface thereof are covered with the Mg-doped ZnO film 11. Such a GaN system semiconductor light emitting device can be manufactured by the same process as the first embodiment.

As shown in FIG. 3, because not only the top surface of the ZnO transparent electrode 12 but the side surface thereof are covered with the Mg-doped ZnO film 11, the Mg-doped ZnO film 11 and the ZnO transparent electrode 12 can be prevented more effectively from being eroded by moisture, while ensuring light transmittance and conductivity. Moreover, when forming a metal pattern on the Mg-doped ZnO film 11 by etching, the Mg-doped ZnO film 11 and the ZnO transparent electrode 12 can be protected based upon further improvements of an acid resistance.

According to the embodiment, although the GaN system semiconductor layer 20 is formed on the top surface of the sapphire substrate 15, the GaN system semiconductor layer 20 may be formed on a conductive substrate in place of the sapphire substrate 15. Moreover, although the embodiment in which the transparent electrode is formed on the top surface of the GaN system semiconductor layer 20 has been described, the invention may be applicable not only to GaN system semiconductor layers but to semiconductor layers like those constituting semiconductor light emitting devices, and furthermore to devices which form a ZnO transparent electrode such as electronic devices including a liquid crystal.

[Effect of the Invention]

As described above, according to the invention, there can be achieved a transparent electrode, provided with stability capable of preventing any degradation due to penetration of ion-containing moistures, while being kept acid-proof and alkali-proof.

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