Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2003-06-20
2004-10-26
Hu, Shouxiang (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S098000
Reexamination Certificate
active
06809345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a semiconductor light emitting element and a semiconductor light emitting device.
2. Related Background Art
Semiconductor light emitting elements are elements that make use of luminescent recombination of electrons and holes injected into pn junctions to emit light from their active layers. They are remarked as inexpensive, long-lifetime light emitting elements.
An issue with such semiconductor light emitting elements is enhancement of light output by enhancing the internal emission efficiency and the light extraction efficiency. Semiconductors in general have higher refractive indices than air. Therefore, only a part of light output inside a semiconductor light emitting element can be extracts externally, and the remainder is reflected back at the interface between the semiconductor light emitting element and air. Therefore, enhancement of the light extraction efficiency is one of issues of semiconductor light emitting elements.
FIG. 20
shows an existing light emitting element disclosed in Japanese Patent Laid-Open Publication No. hei 3-35568. The element includes a bonding substrate
31
transparent to its own emission wavelength, light emitting diode layer
32
and silica layer
33
that are sandwiched between ohmic electrodes
34
,
35
. A method usable for manufacturing such a semiconductor light emitting element is briefly explained below.
In the first step, the light emitting diode layer
32
is grown on an opaque substrate not shown. Then a bondage substrate
31
transparent to the wavelength of light emitted in the light emitting diode layer
32
is bonded to the light emitting diode layer
32
on the substrate. After that, the opaque substrate, not shown, is removed to obtain an intermediate semiconductor light emitting element. In the next step, the silica layer
33
for concentrating the current to a central part of the light emitting diode layer
32
is formed on the light emitting diode layer
32
as shown in FIG.
20
. Thereafter, one of the electricity-conducting ohmic electrodes is formed on the transparent substrate
31
, and the other electricity-conducting ohmic electrode
35
is formed over the light emitting diode layer
32
and the silica layer
33
, as shown in FIG.
20
. After that, through dicing and/or other steps, the semiconductor light emitting element is finally configured quasi hemispherical as shown in FIG.
20
.
The semiconductor light emitting element shown in
FIG. 20
enhances the light extraction efficiency to some extent by configuring quasi hemispherical.
However, the semiconductor light emitting element shown in
FIG. 20
suffers partial blockage of light emitted in the light emitting diode layer
32
by the opaque ohmic electrode
34
. Therefore, it could not be sufficiently enhanced in light extraction efficiency.
FIG. 21
shows another existing semiconductor light emitting element disclosed in Japanese Patent Laid-Open Publication No. hei 4-96381. The element includes an AlGaAs thick-film substrate
37
, p-type AlGaAs clad layer
38
, AlGaAs active layer
39
, and n-type AlGaAs clad layer
40
as shown in FIG.
21
. This semiconductor light emitting element further includes a semiconductor multi-layered reflective film
41
, cap layer
42
, Zn-diffused portions
43
, p-side electrode
44
, and n-side electrode
45
. For the purpose of efficiently extracting light emitted in the AlGaAs active layer
39
, the semiconductor light emitting element is configured to induce emission of light in a central part of the hemispherical dome.
The semiconductor light emitting element shown in
FIG. 21
uses the substrate
37
that is transparent and hemispherical, and locates the opaque electrodes
44
,
45
on the surface opposite from the light-extracting surface. Therefore, the semiconductor light emitting element of
FIG. 21
is higher in light extraction efficiency than the element of FIG.
20
.
However, the element of the type shown in
FIG. 21
involves the problem that the production yield or productivity is inevitably low because of extreme difficulty of its mounting. In greater detail, for manufacturing the semiconductor light emitting element of
FIG. 21
, grooves must be made for isolating the p-side electrode
44
from the n-side electrode
45
, and a manufacturing process of Zn-diffused portions
43
is indispensable. These factors made the manufacturing process of the element of
FIG. 21
very difficult. Additionally, since the p-side electrode
44
and the n-side electrode
45
are closely located, these electrodes
44
,
45
are liable to be short-circuited by a spread of an electrically conductive mounting material during or after the mounting of the element. Furthermore, since those two electrodes
44
,
45
need simultaneous positioning, severe preciseness is required for positioning the electrode on the part of the reflector (mounting stem) and the electrodes
44
,
45
of the element. These factors inevitably worsened the production yield and the productivity. Furthermore, in the semiconductor light emitting element shown in
FIG. 1
, a current is injected abeam to the light emitting portion in the central portion of the dome, and this caused uneven emission of light.
As explained above, it has been impossible heretofore to obtain a semiconductor light emitting element high in light extraction efficiency, uniform in emission of light and high in production yield and productivity.
SUMMARY OF THE INVENTION
According to embodiments of the present invention, there is provide a semiconductor light emitting element comprising:
a transparent first conduction type substrate having a first surface and a second surface opposed to each other and being transparent to light of a wavelength &lgr;;
a semiconductor epitaxial layer formed on a location of the first surface of the substrate directly or via a buffer layer, and including a semiconductor layer of a first conduction type formed in electrical connection with the substrate, an active layer formed on the semiconductor layer of the first conduction type to emit light of the wavelength &lgr; and a semiconductor layer of a second conduction type formed on the active layer;
a first electrode formed in electrical connection with the semiconductor layer of the second conduction type of the semiconductor epitaxial layer on a location of a surface of the semiconductor epitaxial layer opposite from the substrate;
a second electrode formed in electrical connection with the substrate on a location of the second surface of the substrate offset from alignment with the first electrode; and
a groove formed to indent from the second surface of the substrate toward the first surface thereof in a location between the first electrode and the second electrode.
According to embodiments of the present invention, there is provide a semiconductor light emitting device comprising:
a semiconductor light emitting element having:
a transparent first conduction type substrate having a first surface and a second surface opposed to each other and being transparent to light of a wavelength &lgr;;
a semiconductor epitaxial layer formed on a location of the first surface of the substrate directly or via a buffer layer, and including a semiconductor layer of a first conduction type formed in electrical connection with the substrate, an active layer formed on the semiconductor layer of the first conduction type to emit light of the wavelength &lgr; and a semiconductor layer of a second conduction type formed on the active layer;
a first electrode formed in electrical connection with the semiconductor layer of the second conduction type of the semiconductor epitaxial layer on a location of a surface of the semiconductor epitaxial layer opposite from the substrate;
a second electrode formed in electrical connection with the substrate on a location of the second surface of the substrate offset from alignment with the first electrode; and
a groove formed to indent from the second surface of the substrate toward the first surface ther
Hogan & Hartson LLP
Hu Shouxiang
Kabushiki Kaisha Toshiba
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