Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2002-01-28
2002-11-26
Chaudhuri, Olik (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S081000, C257S079000
Reexamination Certificate
active
06486500
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a structure and a manufacturing method of light emitting diode (LED), and more particularly relates to a LED structure having an electrode with a schottky contact and to a manufacturing method thereof. By reducing the quantity of carriers in an area under the electrode, the carriers can be distributed over the active region efficiently. Thus, the output intensity of light can be enhanced.
BACKGROUND OF THE INVENTION
Nowadays, because LED has advantages of low manufacturing cost, low manufacturing difficulty level, easy and convenient installation and good development future, LED is used widely in daily life, such as electronic bulletin boards, indicator lights and car taillights, etc. However, how to further enhance the irraidation efficiency of LED is still a target on which engineers are working.
Referring to
FIG. 1
,
FIG. 1
is a cross-sectional view showing the structure of a conventional LED. The conventional LED is grown by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). First, a buffer layer
102
, a first confining layer
104
, an active layer
106
, a second confining layer
108
and a window layer
110
are formed on a substrate
100
sequentially, and then, by performing an evaporation step, a upper metal electrode
112
is formed on the window layer
110
and a backside electrode
114
is formed by evaporation beneath the substrate
100
.
Current leaves or enters the window layer
110
through the upper metal electrode
112
of LED
90
, and then the carriers arrive the active layer
106
after passing the second confining layer
108
uniformly by diffusion. Therefore, due to the carrier recombination, the active layer
106
ejects out photons thereby emitting light for the LED
90
.
As the aforementioned description, the main current flow path is an area under the upper metal electrode
112
, and the area contains plenty of carriers, so that the carriers can not be spread efficiently to the whole window layer
110
and to the whole chip. Hence, the main radiation combining area
116
is located on the center of the active layer
106
(the area beneath the upper metal electrode
112
).
However, since most of carriers are only injected to the position under the upper metal electrode
112
during the operation of LED, and due to the Current Crowding Phenomenon that the carriers are concentrated under the upper metal electrode
112
, there are no enough carriers to perform radiative recombination in the other position of the active layer
106
. Thus, most of light emitted from the active layer
106
is either blocked and reflected by the upper metal electrode
112
, or is absorbed by semiconductor, so that the emitting efficiency of LED
90
is decreased and is not be satisfied.
Referring to
FIG. 2
,
FIG. 2
is a cross-sectional view showing the structure of another conventional LED. In order to resolve the aforementioned problem, the thickness of the window layer is increased for enhancing the spreading current. Another method of improving the Current Crowding Phenomenon is to formed a current blocking layer
118
beneath the upper metal electrode
112
in the subsequent process as shown in the
FIG. 1
after forming the second confining layer
108
as shown in the FIG.
1
. The carriers are blocked from moving downward by using the energy barrier and the electric field induced in the depletion region in the current blocking layer
118
, so that the carriers beneath the upper metal electrode
112
are forced to be distributed allover the chip, and the main radiation combining area
116
is located on the active layer
106
's other areas which are not under the upper metal electrode
112
. Therefore, the photons emitted from the active layer
106
will not be blocked by the opaque upper metal electrode
112
, so that the light output intensity is enhanced.
Nevertheless, in the method of increasing the thickness of the window layer
110
for enhancing the spreading current, the thickness of the window layer
110
has to be about 5 &mgr;m or over, which takes longer production time for forming the epitaxy and thus increases the production cost. In the other method of forming the current blocking layer
118
on the second confining layer
108
, the current blocking layer has to be formed by using MOCVD twice. After the second confining layer
108
is formed, the chip needs to be moved out of the chamber for forming the current blocking layer
118
, and after the current blocking layer
118
is formed, the chip is moved into the chamber again for performing the subsequent steps to complete the remaining structure. The additional step for forming the current blocking layer
118
results the extension of production time, the increase of production cost and the decrease of yield.
SUMMARY OF THE INVENTION
In view of the background of the invention described above, the LED with high efficient is urgently needed, so that many conventional methods for improving the light efficiency of LED are developed. In a conventional LED manufacturing process, for improving the current crowding phenomenon, a current blocking layer is formed on the second confining layer for blocking the carriers from moving downward and for forcing the carriers to spread around the chip. However, forming the current blocking layer has to employ MOCVD twice, before performing the subsequent steps. Because of additional step for forming the current blocking layer in the conventional manufacturing process of LED, the production time is extended, and the production cost is increased.
It is the principal object of the present invention to provide a LED structure and a manufacturing method thereof, and more particularly to provide a LED structure having an electrode with a schottky contact, and to provide a method for manufacturing the LED structure. In the present invention, by forming the schottky contact between the metal electrode and the window layer, the carriers are blocked from moving downward by using the energy barrier, and are forced to spread out, thereby enhancing the light output intensity.
In accordance with the aforementioned purposes of the present invention, the present invention provides a structure and a manufacturing method of LED, and the manufacturing method comprises: providing a first-type substrate; forming a first-type buffer layer on the first-type substrate; forming a first-type first confining layer on the first-type buffer layer; forming an active layer on the first-type first confining layer; forming a second-type confining layer on the active layer; forming a second-type window layer on the second-type confining layer; forming a first metal electrode beneath the first-type substrate, wherein there is a first ohmic contact surface between the first metal electrode and the first-type substrate; forming a second metal electrode on the second-type window layer, wherein there is a schottky contact surface between the second metal electrode and the second-type window layer; forming a third metal electrode on the second metal electrode, wherein the third metal electrode has a feature of high melting point; forming a fourth electrode on the third metal electrode and the second-type window layer, wherein there is a second ohmic contact surface between the fourth electrode and the second-type window layer; and forming a fifth metal electrode on the fourth electrode, wherein the fifth metal electrode has a feature of good adhesion, and when the first-type substrate, the first-type buffer layer and the first-type first confining layer are n-type, the second-type second confining layer and the second-type window layer are p-type, and when the first-type substrate, the first-type buffer layer and the first-type first confining layer are p-type, the second-type second confining layer and the second-type window layer are n-type.
Since there is a schottky contact surface between the second metal electrode and the second-type window layer, and the third metal electrode having the feature of high meltin
Chaudhuri Olik
Epitech Corporation, Ltd.
Powell Goldstein Frazer & Murphy LLP
Vesperman William C
LandOfFree
Led structure having a schottky contact and manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Led structure having a schottky contact and manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Led structure having a schottky contact and manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2930597