U.S. patent application number 11/143993 was filed with the patent office on 2006-09-14 for semiconductor light emitting device and semiconductor light emitting apparatus.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yasuhiko Akaike, Shuji Itonaga, Kenichi Ohashi, Yasuharu Sugawara.
Application Number | 20060202219 11/143993 |
Document ID | / |
Family ID | 36969898 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060202219 |
Kind Code |
A1 |
Ohashi; Kenichi ; et
al. |
September 14, 2006 |
Semiconductor light emitting device and semiconductor light
emitting apparatus
Abstract
A semiconductor light emitting device comprises: a substrate; a
semiconductor stacked structure; a first electrode; a second
electrode; and a reflective film. The substrate has a top face and
a rear face electrode forming portion opposed thereto, and is
translucent to light in a first wavelength band. The rear face
electrode forming portion is surrounded by a rough surface. The
semiconductor stacked structure is provided on the top face of the
substrate and includes an active layer that emits light in the
first wavelength band. The first electrode is provided on the
semiconductor stacked structure, and the second electrode is
provided on the rear face electrode forming portion. The reflective
film is coated on at least a portion of the rough surface.
Inventors: |
Ohashi; Kenichi; (Kanagawa,
JP) ; Sugawara; Yasuharu; (Kanagawa, JP) ;
Itonaga; Shuji; (Kanagawa, JP) ; Akaike;
Yasuhiko; (Kanagawa, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
36969898 |
Appl. No.: |
11/143993 |
Filed: |
June 3, 2005 |
Current U.S.
Class: |
257/98 ;
257/E33.068; 257/E33.073; 257/E33.074 |
Current CPC
Class: |
H01L 2224/45144
20130101; H01L 33/38 20130101; H01L 2224/45015 20130101; H01L
2224/45144 20130101; H01L 2924/181 20130101; H01L 2924/00014
20130101; H01L 2924/00 20130101; H01L 2224/48472 20130101; H01L
2924/01322 20130101; H01L 2224/48247 20130101; H01L 33/22 20130101;
H01L 2224/48091 20130101; H01L 2224/48472 20130101; H01L 24/32
20130101; H01L 33/54 20130101; H01L 2924/00014 20130101; H01L
2924/20752 20130101; H01L 2224/48247 20130101; H01L 2924/20753
20130101; H01L 2224/48091 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2224/45015 20130101; H01L 2924/00 20130101;
H01L 2224/45015 20130101; H01L 2924/3025 20130101; H01L 2924/3025
20130101; H01L 2224/8592 20130101; H01L 2924/181 20130101; H01L
2224/48472 20130101; H01L 33/20 20130101; H01L 33/46 20130101; H01L
2224/73265 20130101; H01L 24/45 20130101; H01L 2224/48091 20130101;
H01L 2924/1815 20130101 |
Class at
Publication: |
257/098 ;
257/E33.068 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2005 |
JP |
2005-065589 |
Claims
1. A semiconductor light emitting device comprising: a substrate
having a top face and a rear face electrode forming portion opposed
thereto, the substrate being translucent to light in a first
wavelength band, the rear face electrode forming portion being
surrounded by a rough surface; a semiconductor stacked structure
provided on the top face of the substrate and including an active
layer that emits light in the first wavelength band; a first
electrode provided on the semiconductor stacked structure; a second
electrode provided on the rear face electrode forming portion; and
a reflective film coated on at least a portion of the rough
surface.
2. A semiconductor light emitting device according to claim 1,
wherein the rear face electrode forming portion is provided
selectively on a bottom face opposed to the top face, and the rough
surface is provided around the rear face electrode forming portion
on the bottom face.
3. A semiconductor light emitting device according to claim 1,
wherein the rear face electrode forming portion has a smaller area
than the top face, the substrate has a side face that obliquely
extends from the top face to the rear face electrode forming
portion, the rough surface is formed on the side face, and the
reflective film is provided on the side face selectively in a
region close to the rear face electrode forming portion.
4. A semiconductor light emitting device according to claim 1,
wherein the rear face electrode forming portion has a smaller area
than the top face, the substrate has a first side face extending
generally vertically from the top face and a second side face that
obliquely extends from the first side face to the rear face
electrode forming portion, the rough surface is formed on the first
and second side faces, and the reflective film is provided on the
second side face.
5. A semiconductor light emitting device comprising: a substrate
being translucent to light in a first wavelength band; and a
semiconductor stacked structure provided on a major surface of the
substrate and including an active layer that emits light in the
first wavelength band, the substrate having a recess on a mounting
surface opposed to the major surface.
6. A semiconductor light emitting device according to claim 5,
further comprising: a first electrode provided on the semiconductor
stacked structure; and a second electrode provided on an inner wall
of the recess.
7. A semiconductor light emitting device according to claim 6,
wherein the second electrode is provided selectively near the
center of the recess, and the semiconductor light emitting device
further comprises a reflective film coated on the recess around the
second electrode.
8. A semiconductor light emitting device according to claim 5,
wherein the recess is shaped as a polygonal pyramid.
9. A semiconductor light emitting device according to claim 5,
wherein the recess is shaped as a circular cone.
10. A semiconductor light emitting device according to claim 5,
wherein the recess does not overlap a side face of the
substrate.
11. A semiconductor light emitting device comprising: a substrate
having first and second major surfaces and being translucent to
light in a first wavelength band; a semiconductor stacked structure
provided on the first major surface of the substrate and including
an active layer that emits light in the first wavelength band, at
least a portion of the semiconductor stacked structure having a
first rough surface formed thereon; a dielectric film provided on
the first rough surface; a bonding pad provided on the dielectric
film; a thin line electrode portion provided on the semiconductor
stacked structure and electrically connected to the semiconductor
stacked structure and the bonding pad; and an electrode provided on
the second major surface of the substrate.
12. A semiconductor light emitting device according to claim 11,
wherein a second rough surface is formed on a side face of the
substrate.
13. A semiconductor light emitting device according to claim 11,
wherein the substrate has an oblique side face, and the second
major surface is smaller than the first major surface.
14. A semiconductor light emitting apparatus comprising: a
packaging member; a semiconductor light emitting device mounted on
the packaging member; and a wire connected to the semiconductor
light emitting device, the semiconductor light emitting device
including: a semiconductor stacked structure including an active
layer that emits light; and a bonding pad provided on the
semiconductor stacked structure and connected to a fusion bonding
portion for the wire, the bonding pad having a smaller pattern than
the fusion bonding portion.
15. A semiconductor light emitting apparatus according to claim 14,
wherein the semiconductor light emitting device further comprises
an extended electrode portion formed on the semiconductor stacked
structure and connected to the bonding pad.
16. A semiconductor light emitting apparatus according to claim 15,
wherein the extended electrode portion radially extends from the
bonding pad.
17. A semiconductor light emitting apparatus according to claim 14,
wherein a transparent film is provided below the fusion bonding
portion where the bonding pad is not provided.
18. A semiconductor light emitting apparatus according to claim 17,
further comprising: sealing resin configured to cover the
semiconductor light emitting device, the transparent film having a
smaller refractive index than the sealing resin.
19. A semiconductor light emitting apparatus according to claim 15,
wherein the semiconductor light emitting device further comprises a
thin line electrode portion connected to the extended electrode
portion and extending to its periphery.
20. A semiconductor light emitting apparatus according to claim 14,
wherein the semiconductor light emitting device further includes a
substrate underlying the semiconductor stacked structure and being
translucent to light emitted from the active layer, and the
packaging member includes a reflective portion that reflects light
emitted from a side face of the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2005-065589, filed on Mar. 9, 2005; the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a semiconductor light emitting
device and a semiconductor light emitting apparatus, and more
particularly to a semiconductor light emitting device and a
semiconductor light emitting apparatus having improved extraction
efficiency for light emitted from the active layer.
[0003] Semiconductor light emitting devices such as LEDs (light
emitting diodes) and LDs (laser diodes) provide various emission
wavelengths, high emission efficiency, and long lifetime while
being compact in size. For this reason, they are widely used for
display, lighting, communication, sensor, and other devices.
[0004] In such a semiconductor light emitting device, a
semiconductor multilayer film including an n-type cladding layer,
active layer, p-type cladding layer, and the like is formed on a
substrate of GaAs or sapphire by direct epitaxial growth, or by
lamination with a heterogeneous substrate. Electrodes are further
formed on the n-type and p-type layers, respectively (e.g.,
Japanese Laid-Open Patent Applications 2002-353502 and
2001-217467).
[0005] However, this type of semiconductor light emitting device
does not have sufficiently high extraction efficiency for light
emitted from the active layer.
[0006] More specifically, the light emitted downward from the
active layer is incident on the electrode provided under the
substrate. However, the substrate has an alloyed region formed with
the electrode material near the interface with the electrode. This
causes a problem that the light emitted from the active layer is
prone to absorption, which leads to a certain loss inside the
chip.
[0007] In addition, the light reflected from the lower electrode is
attenuated by optical absorption in passing through the active
layer. This causes a problem that the reflected light cannot be
fully exploited.
[0008] There is another problem that total reflection is likely to
occur at the side face and the like of the chip. More specifically,
the above-described LED is typically processed into a rectangular
parallelepiped shape having six smooth faces by cleavage and
dicing, and covered with mold resin or the like. However, due to
the large difference between a high refractive index of the
semiconductor crystal (about 3.5) and a low refractive index of the
mold resin (about 1.5), total reflection is likely to occur at the
interface therebetween. This decreases the probability that the
light emitted inside the chip is extracted outside the chip.
[0009] An approach to improving the decrease of light extraction
efficiency is to roughen the surface by wet etching or the like to
form asperities (e.g., Japanese Laid-Open Patent Application
2001-217467). However, surface roughening is not effective for
extracting light emitted toward the bottom face inside the chip
mounted on a packaging member.
SUMMARY OF THE INVENTION
[0010] According to an aspect of the invention, there is provided a
semiconductor light emitting device comprising:
[0011] a substrate having a top face and a rear face electrode
forming portion opposed thereto, the substrate being translucent to
light in a first wavelength band, the rear face electrode forming
portion being surrounded by a rough surface;
[0012] a semiconductor stacked structure provided on the top face
of the substrate and including an active layer that emits light in
the first wavelength band;
[0013] a first electrode provided on the semiconductor stacked
structure;
[0014] a second electrode provided on the rear face electrode
forming portion; and
[0015] a reflective film coated on at least a portion of the rough
surface.
According to other aspect of the invention, there is provided a
semiconductor light emitting device comprising:
[0016] a substrate being translucent to light in a first wavelength
band; and
[0017] a semiconductor stacked structure provided on a major
surface of the substrate and including an active layer that emits
light in the first wavelength band,
[0018] the substrate having a recess on a mounting surface opposed
to the major surface.
[0019] According to other aspect of the invention, there is
provided a semiconductor light emitting device comprising:
[0020] a substrate having first and second major surfaces and being
translucent to light in a first wavelength band;
[0021] a semiconductor stacked structure provided on the first
major surface of the substrate and including an active layer that
emits light in the first wavelength band, at least a portion of the
semiconductor stacked structure having a first rough surface formed
thereon;
[0022] a dielectric film provided on the first rough surface;
[0023] a bonding pad provided on the dielectric film;
[0024] a thin line electrode portion provided on the semiconductor
stacked structure and electrically connected to the semiconductor
stacked structure and the bonding pad; and
[0025] an electrode provided on the second major surface of the
substrate.
[0026] According to other aspect of the invention, there is
provided a semiconductor light emitting apparatus comprising:
[0027] a packaging member;
[0028] a semiconductor light emitting device mounted on the
packaging member; and
[0029] a wire connected to the semiconductor light emitting
device,
[0030] the semiconductor light emitting device including: [0031] a
semiconductor stacked structure including an active layer that
emits light; and [0032] a bonding pad provided on the semiconductor
stacked structure and connected to a fusion bonding portion for the
wire, the bonding pad having a smaller pattern than the fusion
bonding portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device according to a
first embodiment of the invention;
[0034] FIG. 2 is a schematic view illustrating extraction paths of
light emitted from the active layer 3;
[0035] FIGS. 3A to 3C and 4A to 4C are process cross-sectional
views showing part of a process of manufacturing a semiconductor
light emitting device according to the embodiment of the
invention;
[0036] FIG. 5 is a micrograph showing the rough surface 9 formed on
the rear face of the GaP substrate 1;
[0037] FIGS. 6 to 9 are schematic views illustrating the
configuration of the rear face of the substrate 1 in the embodiment
of the invention;
[0038] FIG. 10 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of the
embodiment of the invention;
[0039] FIG. 11 is a schematic view for describing light extraction
at the rough surface 9;
[0040] FIG. 12 is a schematic view illustrating light extraction
paths in the variation of the embodiment of the invention;
[0041] FIG. 13 is a schematic view showing a semiconductor light
emitting device according to another variation of the embodiment of
the invention;
[0042] FIG. 14 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device of the
embodiment of the invention which is mounted on a packaging
member;
[0043] FIGS. 15A to 15C and 16A to 16C are process cross-sectional
views illustrating a formation process by dry etching;
[0044] FIG. 17 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of the
embodiment of the invention;
[0045] FIG. 18 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device according to the
embodiment of the invention;
[0046] FIG. 19 is a plan view illustrating an electrode pattern
formed on the surface of the semiconductor light emitting
device;
[0047] FIG. 20 is a schematic cross-sectional view of a
semiconductor light emitting device investigated by the inventors
in the course of reaching the invention;
[0048] FIG. 21 is a schematic view illustrating a situation where
the light scattered below the bonding pad 7A is reflected toward
the side face of the device and extracted outside;
[0049] FIG. 22 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of the
embodiment of the invention;
[0050] FIG. 23 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a second variation
of the embodiment of the invention;
[0051] FIG. 24 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device of the
embodiment of the invention;
[0052] FIG. 25 is an enlarged view of a bonding pad portion of the
semiconductor light emitting device;
[0053] FIG. 26 is a schematic view illustrating a situation where
part of the light emitted below the fusion bonding portion 80 is
extracted outside through a gap between the extended electrode
portions 7D;
[0054] FIG. 27 is a schematic view illustrating an electrode
pattern in the embodiment of the invention;
[0055] FIG. 28 is a schematic view showing another example
electrode pattern in the embodiment of the invention;
[0056] FIGS. 29A and 29B are schematic views showing a
semiconductor light emitting device according to a variation of the
embodiment of the invention;
[0057] FIG. 30 is a schematic cross-sectional view showing a
semiconductor light emitting device according to another variation
of the embodiment of the invention;
[0058] FIG. 31 is a schematic cross-sectional view showing a
semiconductor light emitting device according to still another
variation of the embodiment of the invention;
[0059] FIG. 32 is a schematic cross-sectional view showing a
semiconductor light emitting apparatus of the embodiment of the
invention;
[0060] FIG. 33 is a schematic cross-sectional view showing another
example of the semiconductor light emitting apparatus; and
[0061] FIGS. 34 to 36 are schematic cross-sectional views showing
still another example of the semiconductor light emitting
apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0062] Embodiments of the invention will now be described with
reference to the drawings.
First Embodiment
[0063] FIG. 1 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device according to a
first embodiment of the invention.
[0064] More specifically, the semiconductor light emitting device
of this example has a structure comprising a substrate 1 on which a
cladding layer 2, active layer 3, cladding layer 4, and current
diffusion layer 5 are stacked in this order. An electrode 7 is
provided on the current diffusion layer 5 via a contact layer (not
shown). On the other hand, an electrode 8 is formed on part of the
rear side of the substrate 1. The remaining portion is formed into
a rough surface 9 with asperities, the surface of which is coated
with a reflective film 10.
[0065] The substrate 1 is translucent to light emitted from the
active layer 3. For example, the substrate 1 is made of p-type GaP.
The cladding layer 2 can be formed from p-type InAlP, the active
layer 3 from InGaAlP, the cladding layer 4 from n-type InAlP, and
the current diffusion layer 5 from n-type InGaAlP. In this case,
the contact layer provided between the current diffusion layer 5
and the electrode 7 may be made of n-type GaAs.
[0066] Epitaxial growth of an InGaAlP-based compound semiconductor
layer directly on the GaP substrate 1 is difficult. For this
reason, a stacked structure 6 of InGaAlP-based compound
semiconductor is first epitaxially grown on a GaAs substrate. The
p-type GaP substrate 1 is laminated thereon by wafer bonding
technology. The GaAs substrate can then be removed by etching or
the like to form the stacked structure of the present example.
[0067] The reflective film 10 may be made of, for example, metal
such as gold (Au), or dielectric. In this respect, for example,
silicon oxide or silicon nitride may be used to form the so-called
"HR (High Reflectance) coating" in which the relationship between
the refractive index and the thickness yields a maximal
reflectance. Alternatively, the reflective film 10 may be made of a
DBR (Distributed Bragg Reflector) in which two kinds of
semiconductor layers having different refractive indices are
alternately stacked.
[0068] In this embodiment, the extraction efficiency for light
emitted downward from the active layer 3 can be improved by
providing the rough surface 9 and the reflective film 10 on the
rear face of the substrate 1.
[0069] FIG. 2 is a schematic view illustrating extraction paths of
light emitted from the active layer 3.
[0070] The light emitted from the active layer 3 is scattered
toward the side face 1S of the substrate 1 by the rough surface 9
and the reflective film 10 as shown by arrows in this figure. Since
the scattered light is incident on the side face 1S of the
substrate 1 at a relatively small angle (i.e., at a nearly
perpendicular angle with respect to the side face 1S), it is
emitted outside at the side face 1S without total reflection. As
described above, this type of semiconductor light emitting device
is typically sealed with translucent resin having a refractive
index of about 1.5. Therefore the light emitted from inside the
chip is susceptible to total reflection at the interface between
the semiconductor layer and the resin. On the contrary, in the
present embodiment, the light can be scattered by the rough surface
9 and the reflective film 10 and made incident on the side face 1S
of the substrate 1 at a small angle. Therefore the light can be
extracted outside without total reflection.
[0071] If a flat reflective film is provided without the rough
surface 9 on the rear face of the substrate 1, the light emitted
downward from the active layer 3 is reflected upward by this
reflective film. In this case, however, the reflected light passes
through the active layer 3, leading to a certain loss due to
reabsorption. On the contrary, in the present embodiment, the rough
surface 9 serves to scatter the light toward the side face 1S,
reducing the loss due to absorption.
[0072] Furthermore, if the electrode 8 is formed entirely on the
rear face of the substrate 1, an alloyed region is formed at the
interface between the substrate 1 and the electrode 8, and absorbs
the light emitted from the active layer 3, leading to a certain
loss. In contrast, according to the present embodiment, no alloyed
region is present on the rough surface 9, which reflects the light
in conjunction with the reflective film 10 with high efficiency. As
a result, the loss due to absorption is reduced.
[0073] Next, the present embodiment will be described with
reference to a method of manufacturing an InGaAlP-based light
emitting device by way of example.
[0074] FIGS. 3A to 3C and 4A to 4C are process cross-sectional
views showing part of a process of manufacturing a semiconductor
light emitting device according to this embodiment.
[0075] First, as shown in FIG. 3A, an InAlP etch stop layer 94,
GaAs contact layer 26, InGaAlP current diffusion layer 5, n-type
InAlP cladding layer 4, InGaAlP active layer 3, p-type InAlP
cladding layer 2, InGaP bonding layer 34, and InAlP cover layer 96
are grown on an n-type GaAs substrate 92. The n-type GaAs substrate
92 may be a mirror-finished substrate having a diameter of 3 inches
and a thickness of 350 .mu.m, and doped with silicon (Si) at a
carrier concentration of about 1.times.10.sup.18/cm.sup.3.
[0076] The etch stop layer 94 may have a thickness of 0.2 .mu.m.
The GaAs contact layer 26 has a thickness of 0.02 .mu.m and a
carrier concentration of 1.times.10.sup.18/cm.sup.3. The InGaAlP
current diffusion layer 5 is made of InGaAlP and may have a
thickness of 1.5 .mu.m. The n-type cladding layer 4 is made of
InAlP and may have a thickness of 0.6 .mu.m. The active layer 3 is
made of InGaAlP and may have a thickness of 0.4 .mu.m. The p-type
cladding layer 2 is made of InAlP and may have a thickness of 0.6
.mu.m. The InGaP bonding layer 34 may have a thickness of 0.1
.mu.m, and the InAlP cover layer 96 may have a thickness of 0.15
.mu.m.
[0077] Next, this epitaxial wafer is washed with surfactant,
immersed in a mixture of ammonia and hydrogen peroxide solution
with a volume ratio of 1:15 to etch the rear side of the GaAs
substrate 92, thereby removing any reaction products and the like
produced in the epitaxial growth and attached to the rear face of
the epitaxial wafer.
[0078] Next, the epitaxial wafer is washed again with surfactant.
The topmost InAlP cover layer 96 is then removed with phosphoric
acid to expose the InGaP bonding layer 34.
[0079] Subsequently, as shown in FIG. 3B, a GaP substrate 1 is
laminated. In the following, a process of direct lamination will be
described.
[0080] The GaP substrate 1 may be, for example, a mirror-finished,
(100)-oriented p-type substrate having a diameter of 3 inches and a
thickness of 300 .mu.m. A high concentration layer may be formed on
the surface of the GaP substrate 1 to lower the electric resistance
at the bonding interface. As a preprocess for direct bonding, the
GaP substrate 1 is washed with surfactant, immersed in dilute
hydrofluoric acid to remove natural oxidation film on the surface,
washed with water, and then dried using a spinner. With regard to
the epitaxial wafer, after the cover layer 96 on the surface
thereof is removed, it is treated with dilute hydrofluoric acid,
washed with water, and spin-dried, in the same way as for the GaP
substrate 1. Preferably, these preprocesses are entirely performed
under a clean atmosphere in a clean room.
[0081] Next, the preprocessed epitaxial wafer is placed with the
InGaP bonding layer 34 turned up, on which the GaP substrate 1 is
mounted with its mirror surface turned down, and closely contacted
at room temperature.
[0082] Next, as a final step of direct bonding, the wafers
contacted at room temperature are set up in a line on a quartz
boat, and placed in a diffusion oven for heat treatment. The heat
treatment may be performed at a temperature of 800.degree. C. for a
duration of one hour in an atmosphere of argon containing 10%
hydrogen. This heat treatment integrates the GaP substrate 1 with
the InGaP bonding layer 34, thereby completing the bonding.
[0083] Next, as shown in FIG. 3C, the GaAs substrate 92 of the
epitaxial wafer is removed. More specifically, the bonded wafer is
immersed in a mixture of ammonia and hydrogen peroxide solution to
selectively etch the GaAs substrate 92. This etching step stops at
the InAlP etch stop layer 94. Next, etching is performed with
phosphoric acid at 70.degree. C. to selectively remove the InAlP
etch stop layer 94.
[0084] The foregoing process results in a bonded substrate for LED
in which the GaP transparent substrate 1 is bonded to the stacked
structure 6 of InGaAlP-based semiconductor.
[0085] Next, as shown in FIG. 4A, an n-side electrode 7 is formed
on the GaAs contact layer 26, and a p-side electrode 8 is formed on
the rear face of the GaP substrate 1.
[0086] The contact layer 26 surrounding the n-side electrode 7 is
etched away in order to avoid absorption by the GaAs contact layer
26.
[0087] The n-side electrode 7 may be a stacked structure of, for
example, AuGe (250 nm)/Mo (150 nm)/AuGe (250 nm)/Au (300 nm) from
the contact layer 26 side. The p-side electrode 8 may be made of,
for example, metal containing gold (Au) with 5% zinc (Zn). In
addition, a eutectic solder layer such as AuSn (1000 nm) may be
provided via Au (100 nm) on the surface of the p-side electrode
8.
[0088] Next, as shown in FIG. 4B, a rough surface 9 is formed on
the rear face of the substrate 1.
[0089] First, protection films 11 are formed on the n-side
electrode 7 and the p-side electrode 8, respectively. The
protection film 11 may be made of material such as resist, silicon
oxide, or silicon nitride, for example.
[0090] Subsequently, a rough surface 9 is formed by etching the
rear face of the GaP substrate 1 exposed around the periphery of
the p-side electrode 8. The etching condition may be, for example,
immersion in concentrated hydrofluoric acid for about 10
minutes.
[0091] FIG. 5 is an electron micrograph showing the rough surface 9
formed on the rear face of the GaP substrate 1 according to this
process. As a result of hydrofluoric acid etching, the rear face of
the substrate 1 is covered with pyramids having a width and height
of generally 1 micrometer. The rough surface 9 composed of a
collection of such pyramids provides a high scattering effect on
the light emitted downward from the active layer 3.
[0092] Subsequently, as shown in FIG. 4C, the rough surface 9 is
coated with a reflective film 10.
[0093] More specifically, for example, the reflective film 10 can
be formed by depositing gold (Au) using vacuum deposition.
Subsequently, the protection films 11 provided on both sides of the
wafer are removed. Chips are separated by dicing or otherwise to
result in a semiconductor light emitting device of the present
embodiment.
[0094] When metal is used for the material of the reflective film
10, alloying with the substrate 1 decreases the reflectance and
leads to a certain loss. For this reason, when heat treatment
(sinter) is needed to lower the contact resistance of the n-side
electrode 7 and the p-side electrode 8, the reflective film 10 is
formed preferably after this heat treatment.
[0095] Alternatively, ohmic metal can be used for the material of
the reflective film 10. More specifically, when light absorption
due to alloying with the substrate 1 is not substantial, ohmic
metal may be used for the material of the reflective film 10.
[0096] As described above, in this embodiment, the rear face of the
GaP substrate 1 is etched by hydrofluoric acid to form a rough
surface 9 that provides a high scattering effect, which allows
improvement of light extraction efficiency.
[0097] FIGS. 6 to 9 are schematic views illustrating the
configuration of the rear face of the substrate 1 in this
embodiment.
[0098] More specifically, the p-side electrode 8 may be formed near
the center of the rear face of the substrate 1 in a circular shape
as shown in FIG. 6, or in a square shape as shown in FIG. 7. In
addition, as shown in FIG. 8, the p-side electrode 8 may be divided
into a plurality of portions. Division of the electrode into a
plurality of portions serves to alleviate concentration of current
and to uniformly inject current into the active layer 3, which
leads to light emission in a wide region.
[0099] Alternatively, as shown in FIG. 9, a first portion 8A
provided near the center of the rear face of the substrate 1 may be
connected to a second portion 8B shaped in a thin line extending
around the periphery. This can also result in uniform injection of
current into the active layer 3 and light emission in a wide
region.
[0100] It is to be understood that FIGS. 6 to 9 are illustrative
only. For example, the p-side electrode 8 may have a pattern of
polygon, ellipse, or any other shapes. Similarly, the number and
arrangement thereof may be varied. Such variations are encompassed
within the scope of the invention.
[0101] FIG. 10 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of
this embodiment. With regard to this figure, the elements similar
to those described above with reference to FIGS. 1 to 9 are marked
with the same reference numerals and will not be described in
detail.
[0102] In this variation, the side face 1S of the substrate 1 is
tapered, and thus the substrate 1 is shaped like a truncated
pyramid. A rough surface 9 is formed on the side face 1S.
Furthermore, a reflective film 10 is provided on the rough surface
9 in a region extending from the bottom face of the substrate 1,
that is, the lower face with a p-side electrode 8 provided thereon,
to halfway the side face 1S.
[0103] The rough surface 9 not covered with the reflective film 10
has an effect of increasing light extraction efficiency.
[0104] FIG. 11 is a schematic view for describing light extraction
at the rough surface 9.
[0105] More specifically, the rough surface 9 made of pyramids is
formed on the side face 1S of the substrate 1. The light traveling
inside the substrate 1 along the arrow A is totally reflected along
the arrow B when the light is incident on the rough surface 9 at an
angle greater than the critical angle. However, this reflected
light is incident on the opposed rough surface 9 at an angle less
than the critical angle and can be extracted outside from the
substrate 1. In this manner, when the light traveling inside the
substrate 1 enters a salient portion of the rough surface 9, it is
subjected to one or more total reflections and can be extracted
outside as shown by the arrow C.
[0106] FIG. 12 is a schematic view illustrating light extraction
paths in this variation.
[0107] As described above with reference to FIG. 11, light can be
extracted with high efficiency at the rough surface 9 not covered
with the reflective film 10.
[0108] However, when this semiconductor light emitting device is
mounted with an adhesive 30 such as silver paste or solder, the
adhesive 30 may climb up on the side face of the chip as shown.
Light cannot be extracted in the portion where the adhesive 30
climbed up in this manner. On the contrary, in this variation,
light extraction is facilitated by coating the rough surface 9 with
the reflective film 10 near the mounting surface of the chip. More
specifically, in the region where the adhesive 30 climbs up, the
light inside the chip is reflected by the reflective film 10 to
allow external extraction. As a result, the light extraction
efficiency can be improved.
[0109] The tapered side face 1S of the substrate 1 in this
variation can be formed, for example, by dicing. More specifically,
a dicing blade having a V-shaped cross section can be used to dice
the substrate 1 from the rear side for forming a V-shaped groove.
Alternatively, the V-shaped groove may be formed by etching. Chips
are separated along the V-shaped groove thus formed to result in
the tapered side face 1S. In this case, the rough surface 9 can be
formed by applying the roughening treatment as described above with
reference to FIG. 4B when the V-shaped grooves have been formed, or
after the chips are separated.
[0110] FIG. 13 is a schematic view showing a semiconductor light
emitting device according to another variation of this
embodiment.
[0111] More specifically, in this variation, only the lower portion
of the substrate 1 is tapered. A rough surface 9 is formed on the
side face 1S of the substrate 1. The rough surface 9 in the tapered
portion is coated with a reflective film 10.
[0112] This can avoid shielding light due to climbing up of the
adhesive 30, and simultaneously help the light reflected by the
reflective film 10 be incident on the vertical side face 1S as
illustrated by the arrow A. As a result, the light extraction
efficiency can be further increased.
[0113] The semiconductor light emitting device of this variation
can be manufactured by adjusting the depth of the groove when the
V-shaped grooves are formed on the rear face of the substrate 1 by
using a dicing blade having a V-shaped cross section or by etching.
After the V-shaped grooves are formed, a scriber or a thin dicing
blade is used to cut off the remaining portion. In this way, the
side face of the V-shaped groove becomes a tapered portion, and the
remaining portion becomes the vertical side face.
Second Embodiment
[0114] Next, as a second embodiment of the invention, a
semiconductor light emitting device having a recess on the rear
face of the chip will be described.
[0115] FIG. 14 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device of this
embodiment which is mounted on a packaging member.
[0116] More specifically, the semiconductor light emitting device
of this embodiment also has a substrate 1 and a semiconductor
stacked structure 6. The semiconductor stacked structure 6 includes
an active layer and cladding layers as appropriate, and emits light
in response to injection of current via electrodes 7 and 8. The
semiconductor light emitting device is mounted on a packaging
member 28 such as a lead frame or mounting board with an adhesive
30.
[0117] In this embodiment, a pyramidal or conical recess 20 is
provided on the rear face of the semiconductor light emitting
device so as not to overlap the side face 1S of the substrate. The
recess 20 may be shaped as a pyramid or a circular cone. The
electrode 8 is provided, for example, near the center of the
recess. Such a recess 20 can increase the light extraction
efficiency. This point will be described with reference to a
comparative example.
[0118] More specifically, consider a comparative example of the
semiconductor light emitting device having a flat rear face where
an electrode is provided near the center. When such a semiconductor
light emitting device is mounted on a packaging member, an adhesive
such as silver paste or solder may run off around the device and
climb up on the side face of the device. It is thus impossible to
extract light in the portion where the adhesive climbed up. On the
other hand, the light emitted downward from the active layer is
reflected by the flat rear face of the device, and the reflected
light is absorbed in the active layer, which leads to a certain
loss.
[0119] On the contrary, in the present embodiment, a pyramidal or
conical recess 20 is provided on the rear face of the semiconductor
light emitting device. Therefore, as shown in FIG. 14, the light
emitted from the active layer can be reflected toward the side face
1S of the substrate and extracted outside without passing through
the active layer. That is, the loss due to absorption by the active
layer can be reduced.
[0120] Furthermore, the recess 20 absorbs any excess of the
adhesive 30. Thus the adhesive 30 can be prevented from climbing up
on the side face 1S of the device. Therefore the light reflected
from the recess 20 toward the side face 1S is extracted outside
without being shielded by the adhesive 30.
[0121] The side face of the recess 20 in the semiconductor light
emitting device of this embodiment has an oblique angle of, for
example, about 25 to 45 degrees relative to the mounting surface of
the device. Such a recess 20 can be formed by, for example, dry
etching or laser processing.
[0122] FIGS. 15A to 15C and 16A to 16C are process cross-sectional
views illustrating a formation process by dry etching.
[0123] More specifically, first, as shown in FIG. 15A, a mask layer
40 made of relatively soft material such as resist is formed on the
rear face of the substrate 1 where a recess is to be formed.
[0124] Next, as shown in FIG. 15B, a press 42 is forced on the mask
layer 40. The press 42 has protrusions 42P each corresponding to
the recess 20 to be formed.
[0125] Forced by the press 42, as shown in FIG. 15C, recesses 44
corresponding to the protrusions 42P are formed on the mask layer
40.
[0126] Next, as shown in FIG. 16A, anisotropic etching such as ion
milling or RIE (reactive ion etching) is used to etch the mask
layer 40 from above. The etching pattern of the mask layer 40 is
then transferred to the underlying substrate 1. Etching of the mask
layer 40 proceeds as shown in FIG. 16B. When the mask layer 40 is
completely etched as shown in FIG. 16C, the recesses 20 have been
formed on the surface of the underlying substrate 1.
[0127] As an alternative to the process described above, for
example, laser processing may be used to form a recess 20 on the
rear face of the substrate 1. In this case, the rear face of the
substrate 1 is irradiated with a scanned laser beam to successively
etch a certain amount. A pyramidal or conical recess 20 can be
formed by gradually reducing the scanning field of the laser
beam.
[0128] FIG. 17 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of the
present embodiment.
[0129] In this variation, the portion of the recess 20 outside the
electrode 8 is coated with a reflective film 10. The reflective
film 10 may be any one of the various films described above with
reference to the first embodiment.
[0130] The reflective film 10 can further increase light
reflectance at the recess 20. As a result, the light emitted
downward from the active layer can be reflected with high
efficiency and extracted outside via the side face 1S.
[0131] Furthermore, in this embodiment, a rough surface as
described above with reference to FIG. 11 may be provided on the
side face 1S.
Third Embodiment
[0132] Next, as a third embodiment of the invention, a
semiconductor light emitting device having a reduced loss of light
below the bonding pad will be described.
[0133] FIG. 18 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device according to
this embodiment.
[0134] FIG. 19 is a plan view illustrating an electrode pattern
formed on the surface of this semiconductor light emitting
device.
[0135] With regard to these figures again, the elements similar to
those described above with reference to FIGS. 1 to 17 are marked
with the same reference numerals and will not be described in
detail.
[0136] In this embodiment, the electrode 7 formed on the
semiconductor stacked structure 6 has a bonding pad 7A and a thin
line electrode portion 7B connected thereto. The bonding pad 7A is
a connecting portion for gold wire or the like that is connected to
an external circuit (not shown). The thin line electrode portion 7B
is a portion for electrical contact with the semiconductor layer
via an ohmic GaAs layer 26. The chip may measure generally 200
micrometers to 1 millimeter per side. The bonding pad 7A may have a
diameter of generally 100 to 150 micrometers. The thin line
electrode portion 7B may have a line width of generally 2 to 10
micrometers.
[0137] In this embodiment, a rough surface 9 is formed on the
surface of the semiconductor stacked structure 6 below the bonding
pad 7A, and a dielectric layer 50 is provided thereon. The rough
surface 9 may be similar to that described above with reference to
the first embodiment. The dielectric layer 50 may be formed by, for
example, SOG (spin on glass). Such structure below the bonding pad
7A can improve the extraction efficiency for light from the
semiconductor light emitting device. This point will be described
with reference to a comparative example.
[0138] FIG. 20 is a schematic cross-sectional view of a
semiconductor light emitting device investigated by the inventors
in the course of reaching the invention.
[0139] In this comparative example, the semiconductor stacked
structure 6 has a flat surface, on which a current block layer 52
made of semiconductor is provided. For example, when the
semiconductor stacked structure 6 is made of InGaAlP-based compound
semiconductor that emits red light, the current block layer 52 may
be made of non-doped InGaP or the like. The current block layer 52
serves to block the injection of current from the bonding pad 7A
into the underlying semiconductor layer. That is, it is difficult
to extract externally the light emitted below the bonding pad 7A
because it is shielded by the bonding pad 7A. For this reason, the
current block layer 52 is provided to turn the portion below the
bonding pad 7A into a non-emitting region NE.
[0140] However, the structure of this comparative example has a
problem that, when the light emitted by current injection from the
thin line electrode region 7B is directed below the bonding pad 7A
as shown by the arrow A, it is absorbed by the GaAs contact layer
26 to result in a certain loss. In addition, the light reflected
below the bonding pad 7A travels toward the opposed electrode 8 as
shown by the arrow B, and is absorbed in the alloyed region formed
in the vicinity of the electrode 8, which leads to another loss.
Furthermore, since the light emitted below the thin line electrode
7B is incident on the side face 1S of the substrate 1 at a
relatively large incident angle, it is prone to total reflection at
the side face 1S. This causes another problem of decreasing light
extraction efficiency.
[0141] On the contrary, in the present embodiment, first, a
dielectric layer 50 is provided below the bonding pad 7A, which has
a current blocking effect and an effect of increasing reflectance.
More specifically, since the dielectric layer 50 is insulator, it
can definitely block current and ensure that light emission below
the bonding pad 7A is reduced.
[0142] Furthermore, the dielectric layer 50 serves to reflect the
light emitted from the active layer 3 with high efficiency. For
example, if the dielectric layer 50 is made of silicon oxide, and
assuming that the underlying InGaAlP layer has a refractive index
of n=3.2 and silicon oxide has a refractive index of n=1.45, then
the critical angle for total reflection at the interface
therebetween is as small as about 27 degrees. That is, of the light
emitted from the active layer and being incident on the dielectric
layer 50, the light having an incident angle above 27 degrees is
totally reflected. Additionally, in this case, the light having an
incident angle below 27 degrees is also subjected to about 14%
reflection. In this way, the dielectric layer 50 serves to reflect
the light emitted from the active layer 3 with high efficiency.
[0143] Furthermore, according to this embodiment, a rough surface 9
can be provided on the surface of the semiconductor stacked
structure 6 to scatter light. As a result, as shown in FIG. 21 by
the arrow A, the light scattered below the bonding pad 7A can be
reflected toward the side face 1S of the device and extracted
outside.
[0144] FIG. 22 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a variation of
this embodiment.
[0145] More specifically, in this variation, a rough surface 9 is
provided on the side face 1S of the substrate 1. Such a rough
surface 9 serves to increase the light extraction efficiency by
taking advantage of multiple reflections as described above with
reference to FIG. 11. That is, the light emitted below the thin
line electrode portion 7B or the light scattered at the rough
surface 9 below the bonding pad 7A can be extracted via the side
face 1S with high efficiency.
[0146] FIG. 23 is a schematic cross-sectional view showing a
semiconductor light emitting device according to a second variation
of this embodiment.
[0147] More specifically, in this variation, the side face 1S of
the substrate 1 is tapered. This enables the light emitted below
the thin line electrode portion 7B or the light reflected below the
bonding pad 7A to be incident on the side face 1S at a smaller
incident angle. As a result, total reflection at the side face 1S
can be reduced to further increase the light extraction efficiency.
Additionally, in this variation, a rough surface 9 similar to that
shown in FIG. 22 may be provided on the side face 1S.
Fourth Embodiment
[0148] Next, as a fourth embodiment of the invention, a
semiconductor light emitting device having an improved extraction
efficiency for light from below the bonding pad will be
described.
[0149] FIG. 24 is a schematic view illustrating the cross-sectional
structure of a semiconductor light emitting device of this
embodiment.
[0150] FIG. 25 is an enlarged view of a bonding pad portion of this
semiconductor light emitting device. With regard to these figures,
the elements similar to those described above with reference to
FIGS. 1 to 23 are marked with the same reference numerals and will
not be described in detail.
[0151] In this embodiment, the electrode 7 formed on the top face
of the device is composed of a bonding pad 7C and extended
electrode portions 7D. However, the bonding pad 7C has a smaller
pattern area than a fusion bonding portion 80 for gold (Au) or
other wire to be connected thereto. For example, when a gold wire
having a diameter of about 20 to 30 micrometers is ball bonded, the
fusion bonding portion 80 will have a generally circular shape
having a diameter of about 80 to 120 micrometers. In contrast, the
diameter of the bonding pad 7C of the light emitting device of this
embodiment is set to, for example, about 40 to 70 micrometers. In
addition, extended electrode portions 7D are extended from the
bonding pad 7C in order to secure strength against wire bonding and
to diffuse current over a wide range. The structure below the
bonding pad 7C and the extended electrode portions 7D is made to
allow current injection via a contact layer or the like (not
shown).
[0152] FIG. 26 is a schematic view illustrating a situation where
part of the light emitted below the fusion bonding portion 80 is
extracted outside through a gap between the extended electrodes
7D.
[0153] Typically, the light emitted below the bonding pad 7C is
shielded by the bonding pad 7C and cannot be directly extracted
outside. In addition, in a structure where current is injected into
a semiconductor layer below the bonding pad 7C, an alloyed region
18 of metal and semiconductor is formed below the bonding pad 7C.
Absorption of light emission by this alloyed region 18 leads to a
certain loss. Therefore the bonding pad 7C formed larger than the
size of the wire fusion bonding portion 80 decreases the light
extraction efficiency.
[0154] In contrast, according to this embodiment, the size of the
bonding pad 7C is made smaller than the wire fusion bonding portion
80. As shown in FIG. 26, this enables part of the light emitted
below the fusion bonding portion 80 to be extracted outside through
a gap between the extended electrode portions 7D. Therefore, in
this embodiment, the substrate 1 does not necessarily need to be
transparent to the light emitted from the active layer 3. Of
course, this embodiment has a similar advantageous effect when
applied to a semiconductor light emitting device having a
transparent substrate 1.
[0155] FIG. 27 is a schematic view illustrating an electrode
pattern in this embodiment.
[0156] More specifically, a bonding pad 7C smaller than the wire
fusion bonding portion 80 is provided. Extended electrode portions
7F having a narrow width are radially connected to the bonding pad
7C. The light emitted below the fusion bonding portion 80 can be
extracted outside between the extended electrode portions 7F. In
addition, thin line electrode portions 7E having an even narrower
width can be extended to the periphery of the chip to uniformly
inject current over a wide range and produce light emission.
[0157] FIG. 28 is a schematic view showing another example
electrode pattern in this embodiment.
[0158] More specifically, in this example, extended electrode
portions 7D having a wider width are formed below the fusion
bonding portion 80, and extended electrode portions 7F having a
narrower width are formed otherwise. Formation of extended
electrode portions 7D having a wider width below the fusion bonding
portion 80 facilitates increasing strength against wire bonding.
That is, semiconductor layers can be protected more definitely
against pressure, ultrasonic waves, and the like applied during
wire bonding. In addition, formation of extended electrode portions
7F having a narrow width and thin line electrode portions 7E having
an even narrower width outside the fusion bonding portion 80 serves
to uniformly inject current over a wide range and to extract light
emission at high efficiency without shielding.
[0159] FIG. 29A is an enlarged schematic plan view showing the
electrode 7 of the semiconductor light emitting device according to
a variation of this embodiment, and FIG. 29B is a schematic
cross-sectional view thereof.
[0160] More specifically, in this variation, the surface of the
semiconductor layer below the fusion bonding portion 80 (e.g., the
fusion bonding portion 80 shown by a dot-dashed line in FIGS. 27
and 28) outside the electrode 7 (extended electrode portions 7D and
7F, bonding pad 7C, etc.) is covered with a transparent film 21
being translucent to light emission. Such a transparent film 21
serves to increase strength against wire bonding. It also serves to
protect the semiconductor layer when the semiconductor light
emitting device is sealed with resin. Furthermore, the transparent
film 21 allows part of the light emitted below the bonding pad 7C
to be extracted outside more efficiently. That is, as shown in FIG.
29B by the arrow A, the light emitted below the bonding pad 7C can
be made incident on the transparent film 21 and reflected at the
surface of the transparent film 21 to propagate in the transparent
film 21. In this way, the light emitted below the fusion bonding
portion 80 can be extracted by propagating in the transparent film
21.
[0161] In this case, the transparent film 21 is preferably formed
from material having a smaller refractive index than the
transparent resin (having a refractive index of about 1.5) for
sealing the light emitting device. Such a transparent film 21 can
be formed by, for example, the SOG (Spin On Glass) method. In the
SOG method, liquid SOG raw material based on, for example,
inorganic silicates or organic silicates such as methyl siloxanes
is applied to the surface of a wafer using the spin coating method.
Subsequently, a transparent silicon oxide film can be obtained by,
for example, applying heat treatment at 300 to 400.degree. C. The
silicon oxide film thus obtained has a refractive index of 1.4 or
less, which can be used as a transparent film 21 in this
variation.
[0162] Furthermore, the strength against wire bonding can be
increased when the transparent film 21 and the electrode 7 have a
comparable thickness. However, the advantageous effect of light
extraction is achieved even when the transparent film 21 has a
smaller thickness than the electrode 7.
[0163] Additionally, in this variation again, the light extraction
efficiency can be further improved by forming a rough surface of
asperities on the rear face of the translucent substrate as
described above with reference to the first embodiment, or by
providing a recess on the rear face of the translucent substrate as
described above with reference to the second embodiment.
[0164] FIG. 30 is a schematic cross-sectional view showing a
semiconductor light emitting device according to another variation
of this embodiment.
[0165] More specifically, in this variation, a rough surface 9 is
formed on the surface of the semiconductor layer. Formation of the
rough surface 9 serves to increase the light extraction efficiency
by taking advantage of multiple reflections as described above with
reference to FIG. 11. That is, the light emitted from the active
layer 3 can be extracted with high efficiency whether the light is
emitted below the fusion bonding portion 80 or in other light
emitting regions.
[0166] FIG. 31 is a schematic cross-sectional view showing a
semiconductor light emitting device according to still another
variation of this embodiment.
[0167] More specifically, this variation has a combined structure
of the variations shown in FIGS. 29 and 30. The transparent film 21
and the rough surface 9 provided below the fusion bonding portion
80 facilitate reflecting and scattering effects, which allow the
light emitted below the fusion bonding portion 80 to be extracted
outside with higher efficiency.
Fifth Embodiment
[0168] Next, as a fifth embodiment of the invention, a
semiconductor light emitting apparatus equipped with the
semiconductor light emitting device of the embodiment of the
invention will be described. More specifically, a semiconductor
light emitting apparatus with high brightness can be obtained by
packaging the semiconductor light emitting device described above
with reference to the first to fourth embodiments on a lead frame,
mounting board, or the like.
[0169] FIG. 32 is a schematic cross-sectional view showing a
semiconductor light emitting apparatus of this embodiment. The
semiconductor light emitting apparatus of this example is a
resin-sealed semiconductor light emitting apparatus called the
"bullet-shaped" type.
[0170] A cup portion 102C is provided on top of a lead 102. The
semiconductor light emitting device 101 is mounted on the bottom
face of the cup portion 102C with an adhesive or the like. It is
connected to another lead 103 using a wire 104. The inner wall of
the cup portion 102C constitutes a light reflecting surface 102R,
which reflects the light emitted from the semiconductor light
emitting device 101 and allows the light to be extracted above. In
this example, in particular, the light emitted from the side face
and the like of the transparent substrate of the semiconductor
light emitting device 101 can be reflected by the light reflecting
surface 102R and extracted above.
[0171] The periphery of the cup portion 102C is sealed with
translucent resin 107. The light extraction surface 107E of the
resin 107 forms a condensing surface, which can condense the light
emitted from the semiconductor light emitting device 101 as
appropriate to achieve a predetermined light distribution.
[0172] FIG. 33 is a schematic cross-sectional view showing another
example of the semiconductor light emitting apparatus. More
specifically, in this example, the resin 107 sealing the
semiconductor light emitting device 101 has rotational symmetry
about its optical axis 107C. It is shaped as set back and converged
toward the semiconductor light emitting device 101 at the center.
The resin 107 of such shape results in light distribution
characteristics where light is scattered at wide angles.
[0173] FIG. 34 is a schematic cross-sectional view showing still
another example of the semiconductor light emitting apparatus. More
specifically, this example is called the "surface mounted" type.
The semiconductor light emitting device 101 is mounted on a lead
102, and connected to another lead 103 using a wire 104. These
leads 102 and 103 are molded in first resin 109. The semiconductor
light emitting device 101 is sealed with second translucent resin
107. The first resin 109 has an enhanced light reflectivity by
dispersing fine particles of titanium oxide, for example. Its inner
wall 109R acts as a light reflecting surface to guide the light
emitted from the semiconductor light emitting device 101 to the
outside. That is, the light emitted from the side face and the like
of the semiconductor light emitting device 101 can be extracted
above.
[0174] FIG. 35 is a schematic cross-sectional view showing still
another example of the semiconductor light emitting apparatus. More
specifically, this example is also what is called the "surface
mounted" type. The semiconductor light emitting device 101 is
mounted on a lead 102, and connected to another lead 103 using a
wire 104. The tips of these leads 102 and 103, together with the
semiconductor light emitting device 101, are molded in translucent
resin 107.
[0175] FIG. 36 is a schematic cross-sectional view showing still
another example of the semiconductor light emitting apparatus. In
this example, a structure similar to that described above with
reference to FIG. 32 is used. In addition, the semiconductor light
emitting device 101 is covered with phosphor 108. The phosphor 108
serves to absorb the light emitted from the semiconductor light
emitting device 101 and convert its wavelength. For example,
ultraviolet or blue primary light is emitted from the semiconductor
light emitting device 101. The phosphor 108 absorbs this primary
light and emits secondary light having different wavelengths such
as red and green. For example, three kinds of phosphor may be
mixed, and the phosphor 108 may absorb ultraviolet radiation
emitted from the semiconductor light emitting device 101 to emit
white light composed of blue, green, and red light.
[0176] The phosphor 108 may be applied to the surface of the
semiconductor light emitting device 101, or may be contained in the
resin 107.
[0177] In any semiconductor light emitting apparatus shown in FIGS.
32 to 36, a semiconductor light emitting apparatus with high
brightness can be offered by providing the semiconductor light
emitting device described above with reference to the first to
fourth embodiments to extract light from the top and/or side faces
of the semiconductor light emitting device 101 with high
efficiency.
[0178] Embodiments of the invention have been described with
reference to specific examples. However, the invention is not
limited to the specific examples. For example, various variations
of the semiconductor light emitting device and the semiconductor
light emitting apparatus with respect to their structure and the
like are also encompassed within the scope of the invention.
[0179] For example, any details of the layered structure
constituting the semiconductor light emitting device modified as
appropriate by those skilled in the art are also encompassed within
the scope of the invention, as long as they comprise the feature of
the invention. For instance, the active layer may be made of
various materials in addition to InGaAlP-based material, including
Ga.sub.xIn.sub.1-xAs.sub.yN.sub.1-y-based (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1), AlGaAs-based, and InGaAsP-based materials.
Similarly, the cladding layers and optical guide layer may also be
made of various materials.
[0180] In addition, the wafer bonding described as a typical
example of the method of manufacturing a LED having a
light-transmitting substrate may also be applied to conventionally
known LEDs such as AlGaAs-based LEDs in which the transparent
substrate is obtained by thick epitaxial growth.
[0181] Any shape and size of the semiconductor light emitting
device modified as appropriate by those skilled in the art are also
encompassed within the scope of the invention, as long as they
comprise the feature of the invention.
[0182] Furthermore, a semiconductor light emitting device and a
semiconductor light emitting apparatus obtained from any
combination of two or more of the embodiments of the invention are
also encompassed within the scope of the invention. More
specifically, for example, a semiconductor light emitting device
and a semiconductor light emitting apparatus obtained by combining
the first embodiment of the invention with any of the second to
fourth embodiments of the invention are also encompassed within the
scope of the invention. The third and the fourth embodiments may
also be combined. Any other combinations that are technically
feasible are also encompassed within the scope of the
invention.
[0183] Any other semiconductor light emitting devices and
semiconductor light emitting apparatuses that can be modified and
implemented as appropriate by those skilled in the art on the basis
of the semiconductor light emitting devices and semiconductor light
emitting apparatuses described above as the embodiments of the
invention also belong to the scope of the invention.
* * * * *