Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2000-10-06
2003-08-05
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S013000, C257S080000, C257S082000, C257S089000, C257S093000, C257S098000, C257S099000, C257S103000, C257S918000
Reexamination Certificate
active
06603146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor light-emitting device, which is capable of emitting light from the visible region to the ultraviolet region of the light spectrum, and more specifically, the present invention relates to a gallium nitride group compound semiconductor light-emitting device having a semiconductor layer which it formed on a substrate and includes a light-emitting region.
2. Description of the Related Arts
FIG. 10
Illustrates a conventional gallium nitride group compound semiconductor light-emitting device
600
.
The gallium nitride group compound semiconductor light-emitting device
600
includes: a insulative sapphire substrate
61
; an N-type gallium nitride group compound semiconductor layer
62
and a P-type gallium nitride group compound semiconductor layer
63
formed on the substrate in this order and a light-transmittable thin film electrode
64
for the P-type gallium nitride group compound semiconductor layer
63
, an insulation layer
65
, and a fluorescent material layer
66
formed thereon in this order.
Light emitted from the semiconductor layers
62
and
63
is transmitted through the light-transmittable thin film electrode
64
and the insulation layer
65
, and then enters the fluorescent material layer
66
, where the light is converted into visible light having a different wavelength and then is emitted to the outside of the device.
However, the conventional gallium nitride group compound semiconductor light-emitting device
600
has the following problems.
The gallium nitride group compound semiconductor light-emitting device
600
is characterized by having the light-transmittable thin film electrode
64
formed on the surface of the P-type gallium nitride group compound semiconductor layer
63
, and the insulation layer
65
and the fluorescent material layer
66
formed thereon in this order.
Therefore, in order to increase the light-emitting power of the respective N-type and P-type gallium nitride group compound semiconductor layers
62
and
63
, which are positioned under the fluorescent material layer
66
, the light-transmittable thin film electrode
64
is required to maintain a light-transmitting characteristic from the visible region to the ultraviolet region of the light spectrum. Therefore, the light-transmittable thin film electrode
64
has to be practically formed as a thin film having a film thickness of about 10 nm.
In addition, in the case where the wavelength of the light is transformed by the fluorescent material layer
66
, the fluorescent material layer
66
has to be formed as a layer having a thickness of 2 &mgr;m or more. This causes a problem in that the light-transmittable thin film electrode
64
cracks due to the heat strain created during the formation of the fluorescent material layer
66
.
If the light-transmittable thin film electrode
64
cracks, the current flowing in the light-transmittable thin film electrode
64
becomes irregular, thereby making the emission of the gallium nitride group compound semiconductor light-emitting device
600
irregular.
Furthermore, the cracks increase the resistance of the light-transmittable thin film electrode
64
. As a result, the driving voltage of the device increases and the reliability of the device is reduced.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a semiconductor light-emitting device including: a substrate; a semiconductor layer including at least a light-emitting region; a metal layer having a light transmitting characteristic; a first fluorescent material layer for transforming at least a portion of first light emitted from the light-emitting region into second light having a different wavelength from the first light; and an oxide semiconductor layer formed between the metal layer and the first fluorescent material layer and having alight transmitting characteristic.
In one embodiment of the invention, the semiconductor layer is formed of a gallium nitride group compound semiconductor.
In another embodiment of the invention, the metal layer to formed of an ohmic metal thin film.
According to the structure described above, the oxide semiconductor layer which has a light transmitting characteristic is provided between the metal thin film (which has a light transmitting characteristic and is formed on the semiconductor layer) and the first fluorescent material layer. Therefore, even if a crack is created on the metal thin film, the current flows evenly in the metal thin film via the oxide semiconductor layer, thereby enabling a uniform emission from the light-emitting region and improving the reliability of the device.
Furthermore, the oxide semiconductor layer has a good adhesion, a good mechanical strength, a low moisture transmission, and a good thermal stability. Therefore, when the fluorescent material layer is formed, the oxide semiconductor layer is capable of acting as a protection layer for the metal thin film.
In addition, by forming the oxide semiconductor layer which acts as a layer for protecting the metal thin film and improving the conductivity, and providing the fluorescent material layer thereon, a gallium nitride group compound semiconductor light-emitting device is provided which is suitable for mass-production and effectively emits light to the outside of the device.
In still another embodiment of the invention, a thickness of the metal layer is from about 1 nm to about 10 nm.
According to the structure described above, the metal thin film formed on the semiconductor layer is designed to have a suitable thickness, thereby making it possible to provide a metal thin film having good transmittance without reducing an ohmic characteristic between the semiconductor layer and the metal thin film. As a result, a uniform light-emitting pattern is obtained in the light-emitting region of the semiconductor layer.
In still another embodiment of the invention, a thickness of the oxide semiconductor layer is from about 0.1 &mgr;m to about 1 &mgr;m.
In still another embodiment of the invention, the oxide semiconductor layer includes at least one of the materials selected from the group consisting of In
2
O
3
, SnO
2
, ZnO, Cd
2
SnO
4
, and CdSnO
3
.
According to the structure described above, the oxide semiconductor layer having a light transmitting characteristic formed on the metal thin film is designed to have a suitable thickness, thereby mating it possible to provide an oxide semiconductor layer which is excellent in conductivity and durability, and transmits a large portion of light emitted from the light-emitting region. As a result, a highly efficient and highly reliable device is provided, in which a uniform light-emitting pattern is obtained in the light-emitting region of the semiconductor layer.
In still another embodiment of the invention, a first electrode is formed on a portion of the metal layer.
According to the structure described above, the first electrode is formed directly on the metal thin film. Therefore, it is possible to inject the current effectively and directly into the device.
In still another embodiment of the invention, a second electrode is formed on a portion of the oxide semiconductor layer.
According to the structure described above, the oxide semiconductor layer is formed on the entire surface of the metal thin film, thereby a better ohmic characteristic between the semiconductor layer and the metal thin film is achieved. As a result, it is possible to inject the current evenly from the second electrode.
In still another embodiment of the invention, a conductive wire is formed on a portion of the oxide semiconductor layer.
According to the structure described above, external connection means, such as an Au wire is directly provided on the oxide semiconductor layer, so as to eliminate the second electrode. Therefore, the manufacturing process of the device is simplified, thereby reducing the manufacturing time and the device cost.
In still another embodiment of the invention, a
Hata Toshio
Kamikawa Takeshi
Morimoto Taiji
Yamamoto Kensaku
Louie Wai-Sing
Morrison & Foerster / LLP
Pham Long
Sharp Kabushiki Kaisha
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