Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2001-02-08
2002-11-19
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S103000, C372S046012
Reexamination Certificate
active
06483127
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device. Particularly, this invention relates to a structure of an InGaAlP-included semiconductor light emitting device, such as, a surface emission-type semiconductor light emitting device, suitable for optical linking devices.
Surface emission-type semiconductor light emitting devices fabricated using InGaAlP-group materials usually have light reflecting layers, each composed of semiconductor multi-films, located above and under a light emitting layer formed on an n-type GaAs-substrate.
Light emitting diodes (LEDs), among such surface emission-type semiconductor light emitting devices, with no laser oscillation, are called resonant cavity LEDs. These resonant cavity LEDs are superior to usual LEDs with no resonant structure on monochromatic emission.
Surface emission-type semiconductor light emitting devices with laser oscillation are, for example, called a vertical cavity surface emitting laser that generates a large spot laser beam.
FIG. 1
is a sectional view showing a schematic structure of a well-known surface emission-type semiconductor light emitting device.
Stacked on an n-type GaAs-substrate
101
are an n-type GaAs-buffer layer
102
, a multi-film light reflecting layer
103
made of n-type semiconductors, an n-type InGaAlP-clad layer
104
, an InGaAlP-active layer
105
, a p-type InGaAlP-clad layer
106
, and a multi-film light reflecting layer
107
made of p-type semiconductors.
Formed on the clad layer
106
and also under the clad layer
104
are current blocking layers
108
that exhibit high resistance by selective oxidation.
A current flow between a front surface electrode
110
and an rear surface electrode
111
is confined onto an opening formed on the current blocking layers
108
for light emission. The emitted light is extracted through an opening formed on the front surface electrode
110
.
FIG. 2
is a sectional view showing a schematic structure of another well-known surface emission-type semiconductor light emitting device.
Elements in this device that are the same as or analogous to elements in the former device (
FIG. 1
) are referenced by the same reference numbers and will not be explained in detail.
The device shown in
FIG. 2
is provided with current blocking layers
109
that exhibit high resistance by proton ion implantation instead of selective oxidation.
The well-known surface emission-type semiconductor light emitting devices shown in
FIGS. 1 and 2
have the following disadvantages:
The first disadvantage is caused by the multi-film light reflecting layer
107
made of p-type semiconductors formed over the active layer
105
.
In the devices shown in
FIGS. 1 and 2
, a current flows through the light reflecting layer
107
formed over the active layer
105
in the vertical direction and lately confined by the current blocking layer
108
. Electrical resistance of the light reflecting layer
107
is high in both vertical and horizontal directions.
Thus, these well-known devices have high series resistance and require a high operating voltage. Moreover, these devices exhibit insufficient temperature dependence characteristics depend on heat generation due to high resistance.
The second disadvantage is an extremely small margin of positioning of the openings of the current blocking layer
108
and the front surface electrode
110
.
FIGS. 3A
to
5
B illustrate current flow and current distribution for the well-known surface emission-type semiconductor light emitting device.
As shown in
FIG. 3A
, when an opening diameter d
2
of the current blocking layer
108
is extremely smaller than an opening diameter d
1
of the front surface electrode
110
(d
1
>>d
2
), a current injected from the electrode
110
flows through the p-type light reflecting layer
107
in the lateral direction and hardly reaches the center portion of the opening of the current blocking layer
108
.
As illustrated in
FIG. 3B
, the current mostly flows in the vicinity of the opening (d
2
) wall, thus exhibiting un-uniform emission distribution that deviates in the vicinity of the opening wall.
On the contrary, as shown in
FIG. 4A
, when an opening diameter d
1
of the front surface electrode
110
is smaller than an opening diameter d
2
of the current blocking layer
108
(d
1
<<d
2
), a current component that flows vertically from the front surface electrode
110
(the shortest passage) drastically increases.
As illustrated by a dot line in
FIG. 4B
, un-uniform emission distribution is exhibited that deviates in the vicinity of the opening wall. This emission is however blocked by the front surface electrode
110
and thus cannot be extracted. This results in un-uniform emission strength observed outside, as illustrated by a solid line.
Contrary to these devices,
FIGS. 5A and 5B
illustrate improvement in emission strength distribution. In detail, when an opening diameter d
1
of the front surface electrode
110
is little bit larger than an opening diameter d
2
of the current blocking layer
108
(d
1
>d
2
), a current injected from the surface electrode is diffused in a some extent in the vicinity of the center and the emission is extracted without being blocked by the front surface electrode
110
.
In order to extract such uniform emission, however, the current blocking layer
108
and the front surface electrode
110
require precise fabrication so that an opening diameter d
1
of the front surface electrode
110
is little bit larger than an opening diameter d
2
of the current blocking layer
108
at a predetermined size.
It is difficult to control the selective oxidation in forming the current blocking layer
108
shown in FIG.
1
. Thus, such a structure as shown in
FIG. 5A
is not always realized.
The other structure shown in
FIG. 2
can be realized with precise dimension control by means of proton ion implantation for forming the current blocking layer
108
. It is, however, difficult to form ohmic contact on the blocking layer
108
. In detail, proton ion implantated on the light emitting surface side often causes deterioration of the semiconductor layer on the blocking layer
108
. However, an arrangement such that the opening d
1
of the front surface electrode
110
is made smaller than the opening d
2
of the current blocking layer
10
, to solve the problem, poses the problems discussed with reference to
FIGS. 4A and 4B
.
SUMMARY OF THE INVENTION
In order to solve the problems discussed above, a purpose of the present invention is to provide a surface emission-type semiconductor light emitting device that picks up uniform emission at high efficiency.
The present invention provides a semiconductor light emitting device including: a substrate made of a semiconductor of a first conductivity-type; a first light reflecting layer made of a semiconductor of the first conductivity-type and provided on a main surface of the substrate; an active layer made of a semiconductor including InGaAlP and provided on the first reflecting layer; a second light reflecting layer made of a semiconductor of a second conductivity-type and provided on the active layer; a current blocking layer having an opening, only through the opening a current flowing into the active layer; a transparent electrode provided on the second light reflecting layer; a front surface electrode provided on the transparent electrode and having an opening through which emission from the active layer is extracted; and a rear surface electrode provided on a rear surface of the substrate, wherein the current supplied by the transparent electrode located under the opening of the front surface electrode and flowing into the active layer through the opening of the current blocking layer causes the active layer to emit light, the light being reflected repeatedly between the first and the second light reflecting layers and extracted via the transparent electrode under the opening of the front surface electrode.
Moreover, the present invention provides a semiconductor light emitting device includi
Crane Sara
Hogan & Hartson LLP
LandOfFree
Semiconductor light emitting device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor light emitting device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light emitting device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2968853