Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device
Reexamination Certificate
2002-08-26
2004-09-21
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
C257S189000, C257S200000, C257S228000, C257S293000, C257S432000
Reexamination Certificate
active
06794690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Group III nitride compound semiconductor light-emitting element. Particularly, it relates to improvement of a p-side electrode in a Group III nitride compound semiconductor light-emitting element provided with the p-side electrode and an n-side electrode both formed on one surface side.
2. Description of the Related Art
A so-called flip chip type light-emitting element provided with a p-side electrode and an n-side electrode both formed on one surface side is known as a Group III nitride compound semiconductor light-emitting element. The flip chip type light-emitting element is generally configured as shown in FIG.
4
. That is, an n-type semiconductor layer
102
, a light-emitting layer
103
and a p-type semiconductor layer
104
are formed successively on a light-transmissive substrate
101
such as a sapphire substrate. A p-side electrode
105
and a protective film
106
are formed on the p-type semiconductor layer
104
. An n-side electrode
107
is formed on the n-type semiconductor layer
102
. Light emitted from the light-emitting layer
103
is radiated out through the substrate
101
. On this occasion, apart of light emitted from the light-emitting layer
103
moves toward the electrode side. To improve external radiation efficiency (luminance), it is therefore preferable that the part of light moving toward the electrode side is efficiently reflected by the p-side electrode
105
so as to be used as external radiating light. Hence, there has been a proposal for a configuration in which Ag (or Ag alloy) exhibiting high reflectance to the light emitted from a Group III nitride compound semiconductor light-emitting element is used as the material of the p-side electrode.
When the p-side electrode is made of such an Ag-based material, a high-luminance light-emitting element can be achieved but there arises a problem in reliability. That is, when the Ag-based material is used, there arises a problem that lowering of intensity of emitted light or reduction of the lifetime is caused by migration of Ag.
In the related-art example shown in
FIG. 4
, Ag in the p-side electrode
105
is distributed all over the p-side electrode
105
at a point of time when the protective film
106
is formed by heating after the p-side electrode
105
is formed. Further, a window
108
is provided in the protective film
106
to secure a bonding region. Accordingly, a region in which Ag is substantially exposed is present, so that migration of Ag occurs easily. On the other hand, another configuration (
FIG. 5
) has been disclosed in Unexamined Japanese Patent Publication No. Hei. 11-220171. In the disclosed configuration, a p-side electrode
111
made of an Ag-based material is covered with a metal layer
112
not containing Ag. A protective film
113
is further formed on the metal layer
112
. Hence, the disclosed configuration can be expected to considerably suppress migration of Ag from the p-side electrode
111
. A plasma CVD method in a high-temperature state is, however, used exclusively for forming a protective film
113
good in passivation. By this process history, Ag in the p-side electrode
111
is diffused into the metal layer
112
not containing Ag and provided just above the p-side electrode
111
. For this reason, similarly to the configuration shown in
FIG. 4
, migration of Ag cannot be suppressed to a practical level because Ag is diffused into the metal layer surface where the window
114
of the protective film
113
is formed although the Ag concentration is low.
SUMMARY OF THE INVENTION
The invention is designed to solve the problem and an object of the invention is to provide a Group III nitride compound semiconductor light-emitting element with both high luminance and high reliability achieved by suppressing migration of Ag in a p-side electrode.
To achieve the foregoing object, the invention is configured as follows. That is,
a Group III nitride compound semiconductor light-emitting element is provided with a p-side electrode and an n-side electrode both formed on one surface side, wherein the p-side electrode includes: a first metal layer containing Ag and formed on a p-type semiconductor layer; an electrically insulating protective film with which the first metal layer except a part region is covered; and a second metal layer not containing Ag and formed on the protective film.
According to this configuration, first, the light-emitting element can be provided as a light-emitting element high in external radiation efficiency because the use of the first metal layer containing Ag makes the semiconductor layer side surface of the p-side electrode have high reflectance so that light emitted from the light-emitting layer can be efficiently reflected by this surface. Moreover, migration of Ag from the first metal layer to the second metal layer can be suppressed effectively because the first metal layer and the second metal layer are electrically insulated from each other by the protective film except a part region. In other words, migration of Ag from the first metal layer to the p-side electrode surface (that is, the surface of the second metal layer) can be suppressed greatly, so that a highly reliable light-emitting element can be formed. On the other hand, electrical contact between the first metal layer and the second metal layer can be still sustained by the part region which is not shielded by the protective film. In this manner, a light-emitting element with both high luminous intensity and high reliability can be provided according to the configuration.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.
REFERENCES:
patent: 5767581 (1998-06-01), Nakamura et al.
patent: 6281524 (2001-08-01), Yamamoto et al.
patent: 6410162 (2002-06-01), White et al.
patent: 59-228776 (1984-12-01), None
patent: 02-068968 (1990-03-01), None
patent: 05-013816 (1993-01-01), None
patent: 05-129658 (1993-05-01), None
patent: 11-220171 (1999-08-01), None
Abraham Fetsum
McGinn & Gibb PLLC
Toyoda Gosei Co,., Ltd.
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