Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
2001-04-19
2003-04-29
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S078000
Reexamination Certificate
active
06555847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gallium nitride based compound semiconductor light emitting element capable of emitting light beams in the blue to ultraviolet ranges, and more specifically to an electrode structure thereof.
2. Description of the Background Art
A schematic cross sectional view of
FIG. 5
shows a stacked structure of an example of a conventional gallium nitride based compound semiconductor light emitting element (see Japanese Patent Laying-Open No. 9-129919). In this light emitting element, on an insulating sapphire substrate
100
, an n type contact layer
200
, a light emitting layer
300
, a p type clad layer
400
and a p type contact layer
410
are stacked in this order. On a main region on a top surface of p type contact layer
410
, a first p type electrode layer
500
of metal is formed. On a first region on the top surface of the first p type electrode layer
500
, a second p type electrode layer
600
of a transparent conductive film containing oxide is formed, and on the remaining second region, a pad electrode
700
is formed. Further, a portion of n type contact layer
200
is exposed by anisotropic etching, and an n type electrode
800
is formed on the exposed region.
In the electrode structure of the light emitting element such as shown in
FIG. 5
, the top surface of the first p type electrode
500
is covered either by the second p type electrode layer
600
or the pad electrode
700
. Side surfaces of the first p type electrode
500
, however, are exposed to the atmosphere. Further, portions of the top surface of p type contact layer
410
that are not covered by the first p type electrode
500
are exposed.
The inventors of the present invention performed a conduction test of the light emitting element having such an electrode structure in the atmosphere and in a lump state formed of a mold resin, and it was found that when the first p type electrode layer
500
contains palladium (Pd), local bumps generate at the upper surface of p type contact layer
410
on the side surfaces and near the side surfaces of the first p type electrode layer, resulting in a particular phenomenon that the bumps turned out to be dark spaces of the light emitting region. More specifically, such a bump portion is a cause of unevenness of the light emitting pattern from the light emitting region, deteriorating reliability of the light emitting element. Further, it was found that when p type and n type pad electrodes are arranged at diagonal directions of the light emitting element, such bumps are more frequently generated on the side surfaces of the first p type electrode layer and the top surface regions of the p type contact layer
410
near the side surfaces, nearer to the region having high current density along the shortest distance between the pad electrodes.
SUMMARY OF THE INVENTION
In view of the problems experienced in the conventional light emitting element found by the inventors, an object of the present invention is to provide a nitride based semiconductor light emitting element having high reliability capable of uniform light emission in the overall light emitting regions under a low forward voltage.
According to the present invention, the nitride based semiconductor light emitting element includes at least a gallium nitride based compound semiconductor layer of a first conductivity type and a gallium nitride based compound semiconductor layer of a second conductivity type stacked on a substrate, a Pd-containing electrode is formed on a main region on the top surface of the semiconductor layer of the second conductivity type, and the top surface and side surfaces of the Pd-containing electrode as well as the surface of the semiconductor layer of the second conductivity type in an area of at least a prescribed width W from the side surfaces are covered by a conductive shielding film to be shielded from the atmosphere or a mold resin.
The Pd-containing electrode may be formed as a transparent electrode, and the conductive shielding film may be formed by a transparent conductive film.
A pad electrode may be formed on a region on the top surface of the Pd-containing electrode and, in that case, it is preferred that the conductive shielding film additionally covers the side surfaces and the peripheral portion of the top surface of the pad electrode.
A Pd-containing electrode may be formed as an ohmic electrode, and the conductive shielding film may be formed to serve additionally as the pad electrode.
The Pd-containing electrode may be formed as a single-layer or multi-layered metal thin film.
When the conductive shielding film is formed by a transparent conductive film, the thickness thereof should preferably be 0.1 &mgr;m to 30 &mgr;m and the aforementioned width W should preferably be at least 5 &mgr;m.
When the conductive shielding film is formed to serve additionally as the pad electrode, it should preferably contain at least gold (Au), and the thickness thereof should be 0.3 &mgr;m to 1.5 &mgr;m and the aforementioned width should preferably be at least 5 &mgr;m.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 6456639 (2002-09-01), Ishibashi et al.
patent: A9129919 (1997-05-01), None
patent: A10321913 (1998-12-01), None
Fudeta Mayuko
Hata Toshio
Tatsumi Masaki
Yamamoto Kensaku
Birch Stewart Kolasch & Birch, LLP.
Meier Stephen D.
Sharp Kabushiki Kaisha
LandOfFree
Nitride based semiconductor light emitting element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nitride based semiconductor light emitting element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nitride based semiconductor light emitting element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017264