U.S. patent application number 12/262353 was filed with the patent office on 2009-03-05 for stacked three diminesional photonic crystal, light emitting device, and image display apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Hikaru HOSHI, Akinari TAKAGI.
Application Number | 20090060410 12/262353 |
Document ID | / |
Family ID | 34940773 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090060410 |
Kind Code |
A1 |
HOSHI; Hikaru ; et
al. |
March 5, 2009 |
STACKED THREE DIMINESIONAL PHOTONIC CRYSTAL, LIGHT EMITTING DEVICE,
AND IMAGE DISPLAY APPARATUS
Abstract
Provided is a light emitting structure which can emit light
having a plurality of wavelength distributions from a single light
emitting structure, can be integrated at high density, and can
control a radiation mode pattern of radiation light and
polarization thereof. A stacked three-dimensional photonic crystal
is composed of a plurality of three-dimensional photonic crystals
having photonic band gaps different from one another, which are
stacked. Each of the plurality of three-dimensional photonic
crystals includes a resonator in which a point defect is
formed.
Inventors: |
HOSHI; Hikaru; (Tochigi-ken,
JP) ; TAKAGI; Akinari; (Utsunomiya-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
34940773 |
Appl. No.: |
12/262353 |
Filed: |
October 31, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11100588 |
Apr 7, 2005 |
7462873 |
|
|
12262353 |
|
|
|
|
Current U.S.
Class: |
385/2 ;
250/458.1; 257/98; 257/E33.067 |
Current CPC
Class: |
H01S 5/18397 20130101;
H04N 9/3129 20130101; H01S 5/3086 20130101; H01S 5/4093 20130101;
H01S 5/36 20130101; H04N 9/30 20130101; H01S 5/11 20210101; H01S
5/426 20130101; H01S 5/327 20130101 |
Class at
Publication: |
385/2 ; 257/98;
250/458.1; 257/E33.067 |
International
Class: |
G02F 1/035 20060101
G02F001/035; H01L 33/00 20060101 H01L033/00; G01J 1/58 20060101
G01J001/58 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2004 |
JP |
2004-116806 |
Mar 31, 2005 |
JP |
2005-102596 |
Claims
1.-13. (canceled)
14. A stacked three-dimensional photonic crystal including an
active medium, comprising: a first three-dimensional photonic
crystal for emitting light of a first wavelength; and a second
three-dimensional photonic crystal which is located on a light
emitting side with respect to the first three-dimensional photonic
crystal, for emitting light of a second wavelength which is shorter
than the first wavelength.
15. A stacked three-dimensional photonic crystal according to claim
14, wherein the active medium emits light through current
injunction.
16. A stacked three-dimensional photonic crystal according to claim
14, wherein the active medium emits light through excitation light
irradiation.
17. A light emitting device comprising: the stacked
three-dimensional photonic crystal according to claim 14; and
excitation means for exciting the active medium.
18. A light emitting device according to claim 17, further
comprising switching means for controlling a light emitting state
of the light emitting device.
19. A light emitting device according to claim 18, wherein the
switching means controls a drive signal supplied to the excitation
means.
20. A light emitting device according to claim 18, wherein the
first three-dimensional photonic crystal and the second
three-dimensional photonic crystal include corresponding
resonators, and the switching means changes a resonant wavelength
of each of the resonators to control the light emitting state of
the light emitting device.
21. A light emitting device according to claim 18, wherein the
first three-dimensional photonic crystal and the second
three-dimensional photonic crystal include corresponding
resonators, and the switching means cuts off an optical path of
light emitted from each of the resonators to control the light
emitting state of the light emitting device.
22. A light emitting device according to claim 17, wherein the
light emitting device emits light in a wavelength region
corresponding to at least one of colors of R, G, and B.
23. An image display apparatus, comprising a plurality of arranged
light emitting devices, each of which is the light emitting device
according to claim 17.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a structure capable of
selectively emitting multiple-wavelength light using a photonic
crystal.
[0003] 2. Related Background Art
[0004] Up to now, several methods of selectively emitting light
having a predetermined wavelength have been known. Such a method is
broadly classified into an active light emitting method and a
passive light emitting method. With respect to the active light
emitting method, there are, for example, a method using a light
emitting diode and a method using plasma light emission. Light is
emitted with a specific wavelength determined according to a medium
to be used. A method of applying excitation energy to a fluorescent
material to obtain light having a desirable wavelength has been
also known. A method using a wavelength selective filter capable of
transmitting only light having a specific wavelength, of light
having a relatively wide wavelength region, such as white light has
been known as the passive light emitting method.
[0005] In any of the above-mentioned methods, light having a
predetermined wavelength distribution is emitted from a light
emitting structure. Therefore, for example, when a display
apparatus is to be produced using such a conventional light
emitting structure, a plurality of conventional light emitting
structures for emitting light having different wavelengths are
arranged to compose a group, thereby expressing the entire group by
an arbitrary color. Thus, for example, when a display apparatus is
composed of a combination of pixels, each of which has a structure
for emitting light in color of R, G, or B, it is necessary to
alternately arrange the pixels, so that the resolution of an image
which can be displayed thereon corresponds to 1/3 of the number of
actual pixels.
[0006] Japanese Patent Application Laid-Open No. H06-283812
discloses a structure for extracting multiple-wavelength laser
light from a single light emitting device. More specifically, there
is disclosed a structure in which a plurality of semiconductor
lasers each having a multi-layer film resonator structure is
stacked to extract multiple-wavelength laser light.
[0007] On the other hand, it has been known that a photonic crystal
is used for a light-emitting device. A photonic band gap (PBG) that
allows almost no transmission of light having a predetermined
wavelength region is used to confine light in a point defect
provided in the photonic crystal, with the result that light energy
can be concentrated to emit light with high efficiency (U.S. Pat.
No. 5,784,400 B). When a light emitting device having a high light
confining effect and high light emitting efficiency is to be
realized, it is particularly effective to use a three-dimensional
photonic crystal having a PBG in all directions. Such a light
emitting device can be applied to various applications such as
optical communications and display apparatuses, so that a structure
having a wide operating wavelength band is required therefor
because of its wide application range. For example, when the
display apparatus is constructed, a light-emitting device for
generating light having wavelengths corresponding to the
wavelengths of R, G, and B which are three primary colors of light
is required.
[0008] Assume that the structure in which the plurality of
semiconductor lasers each having the multi-layer film resonator
structure are stacked as disclosed in Japanese Patent Application
Laid-Open No. H06-283812 is used to selectively extract
multiple-wavelength light from the single light-emitting device. In
this case, reflectance of a reflection multi-layer film is
insufficient to light having a specific wavelength. Therefore, in
each unit light-emitting device, high light emitting efficiency is
not obtained and a heating value is likely to increase. In
addition, because the reflection multi-layer film of each unit
light-emitting device has predetermined reflectance to light
emitted from other light emitting devices, light emission is
mutually inhibited. Therefore, light-emitting efficiency becomes
lower and a heating value is likely to increase. As a result, for
example, when a plurality of light emitting devices, each of which
can emit light having a plurality of wavelength regions are
integrated to form a display apparatus, it is hard to sufficiently
improve an integration density because of an increase in heating
value.
[0009] In the conventional technique, the resonator structure using
the reflection multi-layer film is a one-dimensional thin film
structure. Therefore, it is hard to perform mode pattern control of
light confined in a resonator in-plane direction.
[0010] In contrast to this, when the photonic crystal is used for
the light emitting structure, it is hard to control a wavelength
region of a complete photonic band gap which can be realized by the
three-dimensional photonic crystal. For example, in the case of a
photonic crystal having an inverse diamond opal structure
(refraction index of high-refraction index material: 2.33,
refraction index of low-refraction index material: 1.00, and PBG
central wavelength: 550 nm), the complete photonic band gap can be
obtained in only a band of about 50 nm. Therefore, it is hard to
control all light corresponding to the wavelengths of R, G, and B
using the single three-dimensional photonic crystal.
[0011] It has been known that the PBG widens as a difference of
refraction index between a high-refraction index material and a
low-refraction index material that composes the photonic crystal
becomes larger. However, a material that is transparent in a
visible wavelength region generally has a low refraction index, so
that it is hard to obtain a wide PBG (material: refraction index,
TiO.sub.2: 2.3, Ta.sub.2O.sub.5: 2.1, CeO.sub.2: 2.05, ZrO.sub.2:
2.03, GaN: 2.4, LiNbO.sub.3: 2.2, LiTaO.sub.3: 2.1, and
BaTiO.sub.3: 2.3). The above-mentioned materials each have a lower
refraction index than that of each of materials generally used in
an infrared wavelength region (material: refraction index, Si: 3.4,
GaAs: 3.6, and Ge: 4.0). Therefore, it is hard to realize wide band
operation in the case where a use wavelength region is particularly
the visible wavelength region.
SUMMARY OF THE INVENTION
[0012] A stacked three-dimensional photonic crystal of the present
invention is a stacked three-dimensional photonic crystal in which
a plurality of three-dimensional photonic crystals having photonic
band gaps different from one another are stacked. Each of the
plurality of three-dimensional photonic crystals has a resonator
formed from a point defect. A light-emitting device of the present
invention includes the stacked three-dimensional photonic crystal
and excitation means for exciting an active medium thereof. An
image display apparatus of the present invention includes a
plurality of stacked three-dimensional photonic crystals which are
arranged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic view showing a stacked light emission
structure for emitting light having a plurality of wavelength
distributions;
[0014] FIG. 2 is a schematic view showing diffraction caused by a
diffraction grating;
[0015] FIG. 3 is a schematic view showing diffraction on a surface
of a photonic crystal;
[0016] FIG. 4 is a graph showing a relationship between a PBG and a
resonant wavelength;
[0017] FIG. 5 is a graph showing a relationship between a PBG and a
resonant wavelength with respect to two kinds of photonic
crystals;
[0018] FIG. 6 is a graph showing a relationship between a lattice
period and reflectance of a photonic crystal;
[0019] FIGS. 7A and 7B are explanatory views showing means for
extracting light from a point defect resonator;
[0020] FIG. 8 is a schematic view showing a light emitting
structure in which an inorganic light emitting material is used as
a light emitting material;
[0021] FIG. 9 is a schematic view showing a light emitting
structure in which an organic light emitting material is used as
the light emitting material;
[0022] FIG. 10 is a schematic view showing a light emitting
structure in which a conductive transparent electrode material is
used for a current injection electrode;
[0023] FIG. 11 is a schematic view showing an optical excitation
light emitting structure;
[0024] FIG. 12 is a schematic view showing a stacked light emitting
structure using a current injection light emitting structure;
[0025] FIG. 13 is a graph showing a relationship between a photonic
band gap and resonant wavelength of each layer of the stacked light
emitting structure;
[0026] FIGS. 14A1, 14A2, 14B, 14C, 14D1, 14D2, 14E1, 14E2, 14F1,
and 14F2 are explanatory views showing means for performing light
extraction switching;
[0027] FIG. 15 is an explanatory graph showing a change in photonic
band gap, which is caused by a switching mechanism;
[0028] FIG. 16 is a schematic view showing a stacked light emitting
structure using the optical excitation light emitting
structure;
[0029] FIG. 17 is a schematic view showing a stacked
three-dimensional photonic crystal;
[0030] FIG. 18 is an explanatory view showing a stack order of a
three-dimensional photonic crystal; and
[0031] FIGS. 19A, 19B, 19C, 19D, 19E and 19F are explanatory views
showing three-dimensional photonic crystal structures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] FIG. 1 is a schematic view showing a light emission
structure for emitting a plurality of light beams having wavelength
distributions different from one another. The light emission
structure for emitting the plurality of light beams having the
different wavelength distributions is obtained by stacking a
plurality of three-dimensional photonic crystals (a first photonic
crystal 1, a second photonic crystal 2, and a third photonic
crystal 3) having photonic band gaps different from one another in
a light emitting direction. The photonic crystals 1, 2, and 3
include a first resonator structure 7, a second resonator structure
8, and a third resonator structure 9, respectively, each of which
serves as a light emitting region. With respect to an optical state
between the plurality of photonic crystals, it is required that a
structure located in an upper layer is transparent to the light
beams (a first light beam 4, a second light beam 5, and a third
light beam 6) emitted from the structures located in lower layers.
Therefore, the light beams from the respective lower layers
transmit through the upper layers and are exited from the uppermost
surface of the stacked structure. As a result, it is possible to
obtain a light emitting structure in which the plurality of light
beams having the different wavelength distributions are
superimposed on one another and emitted therefrom.
[0033] For describing the present invention, the photonic crystal
will be first described. It has been cleared by Yablonovitch that
the photonic crystal is a structure having a predetermined periodic
refraction index distribution and the behavior of light having a
wavelength longer than a period of refraction index can be
controlled in the photonic crystal (Physical Review Letters, Vol.
58, pp. 2059, 1987).
[0034] FIG. 2 is a schematic view showing a state of diffraction
caused by a diffraction grating. Light 51 incident on the
diffraction grating is diffracted in a plurality of directions
(zero-order, first-order, . . . ) determined according to a period
of the diffraction grating, an incident angle .theta. of the light
on the diffraction grating, a wavelength of the light, and the
like. FIG. 2 shows, for example, zero-order reflection and
diffraction light 53, positive first-order transmission and
diffraction light 54, and zero-order transmission and diffraction
light 55 when a diffraction angle is given by .theta.'. Directions
of diffraction caused at this time are directions in which phases
of light scattered at each point are enhanced.
[0035] FIG. 3 is a schematic view showing a state of diffraction on
a surface of the photonic crystal. The photonic crystal has a
periodic refraction index structure, which is shorter than the
wavelength of the incident light. Therefore, incident light 11 is
diffracted to produce diffraction light (reflection) 52. In
particular, in the case of the photonic crystal, the periodic
structure is used such that all enhancement directions of
diffraction light caused by the periodic structure are distributed
on an opposite side even when incident light having a specific
wavelength is incident on the crystal in any direction. When a
structure is used such that all diffraction directions of the
incident light having the specific wavelength exist on the opposite
side regardless of an incident angle of the incident light and no
diffraction light transmitting through the surface of the crystal
exists, the photonic crystal acts as a reflection mirror with
respect to the light having the wavelength and is transparent to
light having another wavelength.
[0036] The feature of the photonic crystal is that light having a
specific wavelength region determined according to the structure
thereof cannot be existed in the photonic crystal. As compared with
an energy band gap of a general crystal substance, a wavelength
region in which light cannot be existed in the photonic crystal is
called a photonic band gap (PBG).
[0037] A photonic band gap obtained with respect to incident light
from all directions is expressed as a complete photonic band gap.
FIGS. 19A, 19B, 19C, 19D, 19E and 19F show examples of known
three-dimensional photonic crystals, in each of which the complete
photonic band gap is obtained. With respect to a three-dimensional
structure in which the complete photonic band gap is obtained,
there are diamond structures in which a high refractive index
material is located at each atomic position of a diamond crystal
structure in a low refractive index material (FIG. 19A: a diamond
opal structure, FIG. 19E: an inverse structure, and FIG. 19F: a
diamond wood pile structure). In addition, there is a woodpile
structure in which columnar lattice layers composing the high
refractive index material are stacked at predetermined intervals in
the low refractive index material (FIG. 19B). Further, there are a
spiral structure (FIG. 19C), a specific three-dimensional periodic
structure (FIG. 19D), and the like. Of the three-dimensional
structures such as the diamond structures, the inverse structure in
which the high refractive index material is located in the low
refractive index material (FIG. 19E) has a relatively wide complete
photonic band gap.
[0038] When dielectric constants of the high refractive index
material and the low refractive index material, a size of the
structure, a period, and the like are set as appropriate for each
of the three-dimensional structures, a central wavelength of the
PBG and a wavelength width thereof can be determined.
[0039] On the other hand, light having a predetermined wavelength,
which is existed in the photonic crystal is suppressed by the
periodic refractive index structure. Therefore, a portion that the
periodic refractive index structure is disturbed (point defect) is
provided in the photonic crystal. As a result, an effective
refractive index changes at the vicinity of the point defect, so
that light can be existed in the point defect to confine the light
therein.
[0040] When a shape of the point defect is suitably formed, it is
possible to resonate only light having a specific wavelength.
Therefore, when a structure of the point defect and a size thereof
are suitably designed, an optical resonator structure which is
operable at an arbitrary wavelength can be realized in the photonic
crystal. Such a structure has been known as a point defect
resonator structure.
[0041] The features of the point defect resonator (defect resonator
structure) are that (1) light having an arbitrary wavelength within
the PBG can be confined in a resonator by controlling a minute
periodic structure and a point defect resonator and (2) a
high-efficiency resonator can be realized based on a high
efficiency reflection characteristic using the PBG. When the point
defect resonator is used to produce and extract the light having
the specific wavelength, it is possible to realize a light emitting
structure capable of emitting the light having the arbitrary
wavelength at high efficiency and a light-emitting device using the
light emitting structure.
[0042] As disclosed in U.S. Pat. No. 5,784,400, the point defect
resonator is provided in the photonic crystal having the complete
photonic band gap and a light-emitting region is provided in the
point defect resonator, so that laser oscillation can be performed
by light emission made by arbitrary excitation means.
[0043] FIG. 4 shows an example of a relationship between a photonic
band gap and a resonant wavelength of a point defect resonator for
resonating light having a specific wavelength in a photonic
crystal. A periodic structure and a point defect resonator in the
photonic crystal having characteristics shown in FIG. 4 are a
structure shown in Table 1 and a structure shown Table 2,
respectively.
TABLE-US-00001 TABLE 1 Grating structure Inverse diamond opal
structure Constituent Material 1 TiO.sub.2 (n = 2.33) (refraction
index) Constituent Material 2 Air or Vacuum (n = 1.00) (refraction
index) lattice period a = 365 nm Radius of Constituent 0.30 a
Material 2
TABLE-US-00002 TABLE 2 Shape of point defect Substantial sphere
resonator Material of a point defect TiO.sub.2 (n = 2.33) resonator
(refraction index) Resonator diameter 231.7 nm (effective
value)
[0044] The point defect resonator is obtained by filling air
located at lattice points as point defects with TiO.sub.2
(refraction index=2.33).
[0045] As shown in FIG. 4, the photonic crystal acts as a
reflection mirror with respect to the light having the specific
wavelength, so that transmittance 13 thereof can be substantially
reduced to zero. A wavelength region that the transmittance 13 of
the photonic crystal becomes substantially zero is a photonic band
gap (PBG) 12. On the other hand, it is necessary to reflect light
having the resonant wavelength of the point defect resonator in the
photonic crystal. Therefore, as shown in FIG. 4, the resonant
wavelength is present in the photonic band gap 12.
[0046] As shown in FIG. 4, the photonic crystal with the periodic
structure has the photonic band gap in a wavelength band of 525 nm
to 575 nm and reflects light having the wavelength region. In the
point defect resonator, it is possible to resonate light having a
wavelength close to 540 nm which is within the photonic band
gap.
[0047] A structure and a material of the photonic crystal that has
the point defect resonator to resonate the light having the
specific wavelength are not limited to the above-mentioned ones.
Therefore, it is possible to suitably determine a structure and a
material which are capable of obtaining the point defect resonator
having the resonant wavelength within the photonic band gap.
[0048] When a light emitting structure capable of selectively
emitting light having plurality of wavelengths is to be obtained
using the photonic crystal and the point defect resonator included
therein, it is required that at least a portion located in the
upper layer be transparent to light emitted from a structure
located in the lower layer.
[0049] FIG. 5 is a graph showing a relationship between a photonic
band gap and a resonant wavelength with respect to two kinds of
photonic crystals having different point defect resonators.
Periodic refraction index structures and point defect resonators in
first and second photonic crystals having characteristics shown in
FIG. 5 are structures shown in Table 3 and structures shown Table
4.
TABLE-US-00003 TABLE 3 First photonic Second photonic crystal
crystal Grating structure Inverse diamond Inverse diamond opal
structure opal structure High refraction TiO.sub.2 (n = 2.33)
TiO.sub.2 (n = 2.33) index material (refraction index) Low
refraction Air or vacuum Air or vacuum index material (n = 1.00) (n
= 1.00) (refraction index) Lattice period a = 365 nm a = 432 nm
Radius of low 0.30 a 0.30 a refractive index material (air) PBG
wavelength 525 nm to 575 nm 625 nm to 685 nm
TABLE-US-00004 TABLE 4 First photonic Second photonic crystal
crystal Shape of a point Substantial Substantial defect resonator
sphere sphere Material of a TiO.sub.2 (n = 2.33) TiO.sub.2 (n =
2.33) point defect resonator (refraction index) Resonator 231.7 nm
274.7 nm diameter (effective value) Central resonant 540 nm 640 nm
wavelength
[0050] In any photonic crystal, each of the point defect resonators
shown in Table 4 is obtained by filling low refraction index
materials (air) located at lattice points as point defects with
media (n=2.33).
[0051] When a lattice period the photonic crystal is changed as
shown in Table 3, it is possible to shift photonic band gaps 12 and
12a as shown in FIG. 5.
[0052] As described above, when the photonic crystals having the
photonic band gaps which are not overlapped with each other are
stacked, the light emitting structure capable of selectively
emitting the light having the plurality of wavelengths can be
obtained without blocking light emitted from the respective
photonic crystals. In addition, when the effective diameter of the
point defect resonator is changed as shown in Table 4, the
resonance wavelength can be shifted within the photonic band
gap.
[0053] When light emission caused by resonating the light having
the specific wavelength by the point defect resonator in the
photonic crystal is to be used, it is necessary to extract a part
of the resonated light from the photonic crystal to the
outside.
[0054] FIG. 6 is a graph showing a relationship between a period of
a three-dimensional photonic crystal and reflectance in a photonic
band gap. The horizontal axis indicates a period of the crystal as
a unit. When a thickness of the three-dimensional photonic crystal
is equal to about several periods, a certain percentage of light
transmits therethrough. Therefore, when the photonic crystal
including the point defect resonator is thinned to the extent that
a certain percentage of light transmits therethrough, light can be
extracted from the point defect resonator.
[0055] FIGS. 7A and 7B show other structures for extracting light
from a point defect resonator 23 in photonic crystals. A part of
the photonic crystals including the point defect resonator is
irregularly formed to obtain a waveguide. Therefore, light can be
extracted through the waveguide. Various waveguide such as a linear
defect waveguide 24 having a guided mode including a wavelength to
be extracted and a point defect coupling waveguide 25 can be used
for the waveguide.
[0056] With respect to an excitation method of exciting a light
emitting medium of the point defect resonator to emit light, there
are optical excitation using an external light source, excitation
using current injection, and the like. In the case of the
excitation using current injection, when a metallic material such
as Al or Cr or a transparent conductive material such as an ITO is
used for electrodes, the light-emitting medium can be sandwiched
between the electrodes to emit light. In addition, when electrodes
which are separately operated are formed for a plurality of point
defect resonators, it is possible to separately control light
having respective wavelengths.
[0057] FIG. 8 shows an example of a light emitting structure in
which an inorganic light emitting material is used as a light
emitting material. In this light emitting structure, a light
emitting layer 803 made of an inorganic light emitting material is
sandwiched by upper and lower insulating layers 802 and 804.
Electrodes 801 and 805 are provided so as to sandwich the
light-emitting layer 803 and the upper and lower insulating layers
802 and 804. Therefore, it is possible to produce a light-emitting
portion that emits light having a wavelength determined according
to a light emitting material. When such a light-emitting portion is
provided in the point defect resonator, light having a wavelength
determined by the point defect resonator can be resonated for
extraction. It is desirable to use a transparent material such as
an indium tin oxide (ITO) for the electrodes. A metal such as Al or
Cr may be used for the electrode. ZnS:Mn, ZnMgS:Mn, ZnS:Sm, ZnS:Tb,
ZnS:Tm, CaS:Eu, SrS:Ce, SrS:Cu, SrGa.sub.2S.sub.4:Ce,
BaAl.sub.2S.sub.4:Eu, or the like can be used as an example of the
inorganic light emitting material. SiO.sub.2, SiN, Al.sub.2O.sub.3,
Ta.sub.2O.sub.5, SrTiO.sub.3, or the like can be used for the
insulating layers. The inorganic light emitting material and the
insulating material are not limited to those. When a structure that
causes light emission by current injection is obtained, other
materials can be used. A light-emitting structure using the
inorganic light emitting material may be a structure other than
that shown in FIG. 8.
[0058] FIG. 9 shows an example of a light-emitting structure in
which an organic light emitting material is used as the
light-emitting material. In this light-emitting structure, a
light-emitting layer 903 containing an organic light-emitting
material is sandwiched by an electron transporting layer 902 and a
hole transporting layer 904. Upper and rear electrodes 901 and 905
are provided so as to sandwich the light-emitting layer 903, the
electron transporting layer 902, and the hole transporting layer
904. Therefore, a light-emitting structure for emitting light
having a wavelength determined according to a light-emitting
material is obtained. There is a structure including the
electron-injected layer and the hole injected layer, other than
such a structure. It is desirable to use a transparent electrode
material such as an indium tin oxide (ITO) for the upper electrode
901 through which light caused by light emission transmits. An
indium tin oxide (ITO) or a metal such as Al or Cr, which is not
transparent, can be used for the rear electrode 905.
[0059] Alq, Eu(DBM)3(Phen), BeBq, DPVBi, or the like may be used as
a typical low-molecular organic light emitting material. TPD,
.alpha.-NPD, TPT, or Spiro-TPD may be used as a typical hole
transporting low-molecular material. PBD, TAZ, OXD, or Bphen may be
used as a typical electron transporting low-molecular material. A
conductive polymer using polythiophene, polyaniline, or the like,
which is doped with acid such as polystyrene sulfonate or camphor
sulfonate may be used as a typical polymer organic light emitting
material for the light emitting layer. Various materials other than
the above-mentioned materials can be used.
[0060] In addition to the structures shown in FIGS. 8 and 9, a
current injection type light-emitting structure is provided in the
point defect resonator by using a light-emitting medium including a
compound semiconductor material, an inorganic light-emitting
material, an organic light-emitting material, a polymer
light-emitting material, a quantum dot, and a nanocrystal.
Therefore, light having a desirable wavelength can be resonated for
extraction.
[0061] FIG. 10 shows a structural example in the case where a
conductive transparent electrode material such as an ITO is
particularly used as a current injection electrode material. When
an ITO or the like is used as the current injection electrode
material, it is possible to obtain a simple structure in which the
waveguide for extracting light from the point defect resonator in
the photonic crystals is also served for current injection
electrodes. A current is injected for light emission into a light
emitting material 1004 which is inserted into a point defect
resonator 1001 using transparent electrodes 1003 passing through
photonic crystals 1002. At this time, the transparent electrodes
1003 become line defects to a period of the photonic crystal 1002.
In addition, the transparent electrodes 1003 become the waveguide.
Therefore, a part of light resonated by the point defect resonator
1001 is guided to the outside of the photonic crystals through the
transparent electrodes 1003.
[0062] When the optical excitation is caused using the external
light source, a wavelength outside the photonic band gap is used,
with the result that the light-emitting medium in the photonic
crystals can be efficiently excited for light emission.
[0063] FIG. 11 shows an example of a light-emitting structure 1100
in the case where the light-emitting layer is optically excited
using the external light source. A resonator 1103 containing a
fluorescent material that emits fluorescent light having a
wavelength within the PBG is provided in the photonic crystals
1102. In order to excite the fluorescent material of the resonator
structure 1103 for light emission, an ultraviolet light source 1104
that emits light having a wavelength shorter than the PBG of the
photonic crystals 1102 is provided below the photonic crystals
1101. A wavelength selective filter 1101 that transmits light
emitted from the resonator 1103 and cuts off only excitation light
emitted from the ultraviolet light source 1104 is provided on the
photonic crystals 1102.
[0064] According to the structure shown in FIG. 11, when an ON/OFF
state of the ultraviolet light source 1104 is controlled by a
control circuit which is externally provided, it is possible to
control an output of light which is resonated by the resonator 1103
and emitted to an upper side of the light emitting structure. When
such a structure is used, it is unnecessary to form, for example,
the current injection electrodes in the photonic crystals 1102.
Therefore, it is possible to obtain a light emitting structure
using a photonic crystal having a more complete PBG. When light
having a plurality of wavelengths is to be arbitrarily selectively
emitted from the light emitting structure having the plurality of
photonic crystals, a switching mechanism for freely selecting
ON/OFF of emission of light from each unit light emitting structure
is required.
[0065] With respect to a mechanism for switching between ON/OFF of
light emission caused by each photonic crystal, there are a method
of switching between ON/OFF of emission of light from the light
emitting medium and a method of switching between ON/OFF of
extraction of light from the point defect resonator (or unit light
emitting structure). When the excitation is caused by the current
injection, the ON/OFF of light emission can be switched with a
relatively high response. Therefore, it is preferable to perform
switching according to an injected current. On the other hand, when
the optical excitation is caused using the external light source,
it is preferable to perform switching of extraction of light from
the point defect resonator or the photonic crystal while the
emission of light from the light-emitting medium continues.
[0066] Next, a method of producing a three-dimensional photonic
crystal will be described. When a structure located at each lattice
point is sphere as in the case of the diamond opal structure, the
three-dimensional photonic crystal can be produced by suitably
stacking a member made of a predetermined material on a
three-dimensional lattice structure. In the case of the inverse
structure in which a dielectric constant of a member located at a
lattice point is higher than that of each of other members located
around the member and particularly the member located at the
lattice point is made of a low-refraction index material, the
following method has been known. First, a three-dimensional lattice
structure (such as a face centered cubic structure or a diamond
opal structure) is obtained using silica spheres and polymer
spheres. Then, a gap between the spheres is filled with a lattice
material such as a dielectric material. Finally, the silica spheres
and the polymer spheres are removed. With respect to a lattice
material filling method, there are a sol-gel method and a
nanoparticle filling method, and the like. With respect to a method
of removing the silica sphere and the polymer sphere, there are a
dissolving method using a solvent and a removal method with
baking.
[0067] On the other hand, in the cases of the woodpile structure
and the like, each layer thereof can be formed by application of a
general semiconductor process including lithography, film
formation, and etching. When a crystal structure having a large
number of layers is to be obtained, a predetermined number of pile
structures are obtained by the general semiconductor process and
then a process for bonding the pile structures to each other using
a wafer bonding method is repeated.
[0068] Hereinafter, stacked three-dimensional photonic crystal
structures according to embodiments of the present invention, which
is produced by the above-mentioned technique will be described.
Embodiment 1
[0069] FIG. 12 is a schematic view showing a stacked light-emitting
structure of a current injection excitation type. Three photonic
crystal layers that resonate light beams 1201a to 1201c having
wavelengths different from one another and emit the light beams are
stacked. Each of the photonic crystals has a light-emitting region
that includes a point defect resonator and a light emitting medium.
Tables 5 and 6 show photonic crystal structures 1204a to 1204c and
point defect resonators 1205a to 1205c.
TABLE-US-00005 TABLE 5 First Second Third photonic photonic
photonic crystal crystal crystal structure structure structure
Grating Inverse Inverse Inverse structure diamond diamond opal
diamond opal opal structure structure structure Constituent
TiO.sub.2 TiO.sub.2 (n = 2.33) TiO.sub.2 Material 4 (n = 2.33) (n =
2.33) (refraction index) Constituent Air or Air or vacuum Air or
Material 5 vacuum (n = 1.00) vacuum (refraction (n = 1.00) (n =
1.00) index) Lattice a = 300 nm a = 365 nm a = 432 nm period Radius
of 0.30 a 0.30 a 0.30 a constituent Material 5 Band gap 428 nm to
521 nm to 579 nm 617 nm to region 476 nm 686 nm
TABLE-US-00006 TABLE 6 First Second Third resonator resonator
resonator structure structure structure Shape of Substantial
Substantial Substantial defect sphere sphere sphere resonator
Material of TiO.sub.2 TiO.sub.2 TiO.sub.2 defect (n = 2.33) (n =
2.33) (n = 2.33) resonator (refraction index) Resonator 190.4 nm
231.7 nm 274.7 nm diameter (effective value) Central 443 nm 540 nm
640 nm resonant wavelength
[0070] In this embodiment, light emission is caused from the
structure using the inorganic light emitting material for each
light-emitting region 1211 as shown in FIG. 8. A current is
injected from the outside to the light-emitting region provided in
the resonator of each of the layers through electrodes 1210.
Therefore, light having a specific wavelength can be generated.
[0071] There are the following existing light-emitting materials.
When a rare-earth ion as light-emitting center is added to a
material such as ZnS, CaS, or SrS, which is used as a host, an EL
material that emits light having various wavelengths is obtained.
For example, in the case of red, there have been known
ZnS:Sm.sup.3+ in which Sm.sup.3+ is added to ZnS used as a host and
CaS:Ce.sup.3+. In the case of green, ZnS:Tb.sup.3+ and
SrS:Ce.sup.3+ have been known. In the case of blue, ZnS:Tm.sup.3+
and SrS:Cu.sup.+ have been known. In order to cause the light
emission using those inorganic light-emitting materials, for
example electroluminescence can be used. For example, a
light-emitting layer is sandwiched by insulating layers, electrodes
are located to sandwich the light-emitting layer and the insulating
layers, and a high electric field is stably applied to the
light-emitting layer. Therefore, light emission can be caused by
electric field excitation. In addition to the above-mentioned
materials, a light emitting medium including a compound
semiconductor material, an organic light-emitting material, a
polymer light-emitting material, a quantum dot, and a nanocrystal
may be used.
[0072] When the number of photonic crystal layers located above
each of the resonators is reduced to a value smaller than the
number of photonic crystal layers located below the corresponding
resonator, resonated light is emitted to only the upper side. The
structure of the light-emitting region is not limited to this and
thus a suitable structure can be used for applications.
[0073] FIG. 13 shows a relationship between a photonic band gap and
a resonant wavelength of each of the layers of the stacked
light-emitting structure according to this embodiment. The
respective layers are designed so as to emit light having
wavelengths corresponding to general colors of R, G, and B. The
photonic band gap (PBG) of the photonic crystal composing one of
the layers is formed so as not to include the wavelengths of light
emitted from the other layers, so that the respective layers are
transparent to one another.
[0074] When a current injected to the light-emitting region of each
of the layers is ON/OFF-controlled by switching means 1212a to
1212c if necessary, a light flux having a desirable color which is
a combination of colors of R, G, and B can be emitted from the
uppermost surface of a light emitting device. In this embodiment,
the ON/OFF of light emission is controlled by ON/OFF switching of
the current injected to the light-emitting region of the photonic
crystal. However, light emitted from each of the photonic crystals
can be ON/OFF-controlled by using other switching methods described
below.
[0075] FIGS. 14A1, 14A2, 14B, 14C, 14D1, 14D2, 14E1, 14E2, 14F1,
and 14F2 show examples of a method of performing extraction
switching of light from the point defect resonator or the photonic
crystal. FIGS. 14A1 and 14A2 show an example in which a photonic
crystal layer using liquid crystal as each of constituent mediums
221 and 222 is a switching layer. When an orientation of a liquid
crystal molecule is controlled based on a voltage applied through
electrodes provided outside the switching layer, a dielectric
constant of the liquid crystal molecule is significantly changed
according to the orientation. Therefore, a dielectric constant
distribution of the photonic crystal is changed to shift the
photonic band gap thereof.
[0076] As shown in FIG. 14A1, when a voltage is applied to the
switching layer using liquid crystal through transparent
electrodes, the orientations of liquid crystal molecules in each
dispersed particle are aligned. Therefore, characteristics of
liquid crystal molecules and a size and a frequency of a dispersion
layer are set so as to produce a photonic band gap for a wavelength
of light resonated by the point defect resonator located in the
lower layer with the alignment state.
[0077] In contrast to this, as shown in FIG. 14A2, when no voltage
is applied in the above-mentioned structure, the orientations of
liquid crystal molecules in each dispersed particle become random.
Therefore, the dielectric constant distribution of the switching
layer is deviated from an ideal distribution required for producing
the photonic band gap, so that power for reflecting light having a
specific wavelength reduces. As a result, constant transmittance is
provided for light resonated by the point defect resonator. Thus,
light scattered by the dispersion layer is exited through the
switching layer. In the above-mentioned structure, it is preferable
that the photonic crystals located between the point defect
resonator and the switching layer have several layers, the point
defect resonator be well maintained, and a part of light resonated
by the point defect resonator reach the switching layer.
[0078] FIG. 15 shows an example of a change in photonic band gap
produced in the switching layer shown in FIGS. 14A1 and 14A2. When
a voltage is applied to the switching layer, a relative large
photonic band gap 151 is produced. Therefore, the switching layer
acts as a reflection mirror with respect to light 11 emitted from
the point defect resonator. On the other hand, when no voltage is
applied to the switching layer, a photonic band gap 152 produced in
the switching layer becomes incomplete. Therefore, the switching
layer transmits the light 11 emitted from the point defect
resonator.
[0079] When a desirable photonic band gap is obtained in the
switching layer using the liquid crystal as shown in FIGS. 14A1 and
14A2, the constituent medium 211 may be made of the same material
as that of a constituent medium 21 of a photonic crystal composing
the light-emitting structure located in the lower layer or a
material different from that of the constituent medium 21. FIGS.
14A1 and 14A2 show the case where the liquid crystal layer is
located in the constituent medium 211. It is also possible to use a
structure in which arrangement is reversed, that is, an inverse
type structure in which the constituent medium is located in the
liquid crystal layer.
[0080] FIG. 14B shows an example in which a photonic crystal layer
using a ferroelectric material for a dispersion layer is provided
as a switching layer. A voltage is applied to the switching layer
through electrodes provided outside the switching layer to apply an
electric field to a layer of the ferroelectric material, thereby
finely deforming ferroelectric material. Therefore, a dielectric
constant distribution of the photonic crystal is changed to shift
the photonic band gap thereof.
[0081] Even when the ferroelectric material is used for the
switching layer, as in the above-mentioned case where the liquid
crystal is used, the photonic band gap is shifted according to an
applied voltage to switch between the case where the switching
layer has a surface reflecting light emitted from the point defect
resonator located in the lower layer and the case where the
switching layer has a surface transmitting the light.
[0082] In FIG. 14B, the ferroelectric material is used for the
dispersion layer. A photonic crystal constituent medium may be the
ferroelectric material when the material is sufficiently
transparent to light to be used.
[0083] FIG. 14C shows an example of a photonic crystal in which a
multi-layer film including a layer whose dielectric constant is
variable is used as the switching layer. In the multi-layer film
serving as the switching layer, for example, liquid crystal is used
and an electric field is applied to the liquid crystal to change a
dielectric constant with respect to a specific direction.
Therefore, switching is performed between the case where the
multi-layer film becomes a reflective film reflecting light emitted
from the point defect resonator located in the lower layer and the
case where the multi-layer film becomes a transmission film
transmitting the light. When the case where the multi-layer film
does not act as the reflective film depending on an angle of light
incident thereon is to be prevented, it is preferable to use a
switching method as shown in FIG. 14C for light extracted through
the waveguide as shown in FIG. 8.
[0084] FIG. 14D1 shows an example in which a dielectric constant is
changed by heat energy supplied from the outside to shift the PBG,
thereby performing switching. When a heater 1410 is made in contact
with a photonic crystal 1400, heat energy can be supplied thereto
to control the PBG based on a change in dielectric constant which
is caused by heating. As shown in FIG. 14D2, means for emitting
light corresponding to a absorption wavelength of the photonic
crystal or a Peltier element may be used as the heat energy
supplying means.
[0085] FIGS. 14E1 and 14E2 shows an example in which the photonic
crystal is deformed by external force to shift the PBG, thereby
performing switching. An example of a deformation mechanism in
which a drive mechanism 1420 is connected with a photonic crystal
1400 is shown. When the external force is applied to the photonic
crystal structure due to extension or constriction of the drive
mechanism 1420, the photonic crystal 1400 is extended or
constricted. Therefore, structural parameters such as a lattice
period of the photonic crystal and a filling ratio (volume ratio
between a high-refraction material and a low-refraction material)
changes, thereby changing an effective refraction index. Thus, the
PBG can be controlled for light switching.
[0086] In FIGS. 14E1 and 14E2, the external force is applied to the
entire photonic crystal to deform it. The external force may be
applied to a portion of the structure. For example, the external
force may be applied to the waveguide to perform switching.
[0087] A waveguide may be formed for switching as shown in FIGS.
14F1 and 14F2. FIGS. 14F1 and 14F2 show a structure in which only
the waveguide is connected with the drive mechanism 1420 in the
photonic crystal 1400.
[0088] When the drive mechanism 1420 is extended, a waveguide is
located in the photonic crystal structure to produce the PBG, so
that light does not leak to the outside. On the other hand, when
the drive mechanism 1420 is constricted, the waveguide is taken
from the photonic crystal structure to the outside to form a linear
defect waveguide, so that light can be extracted from the photonic
crystal to the outside. Therefore, switching can be performed.
[0089] The stacked light-emitting structure of the current
injection type can be realized using the stacked three-dimensional
photonic crystal provided with the above-mentioned light-emitting
region. In this embodiment, the example in which only the three
photonic crystal layers corresponding to the colors of R, G, and B
are stacked is described. The number of photonic crystal layers is
not limited to three. An arbitrary number of photonic crystal
layers can be stacked if necessary. As described above, according
to this embodiment, it is possible to realize a light-emitting
device for full-color operation.
[0090] When stacked three-dimensional photonic crystals, each of
which corresponds to a pixel are arranged, it is possible to obtain
an image display apparatus capable of expressing an arbitrary color
by combination of colors of R, G, and B based on an external
signal.
Embodiment 2
[0091] FIG. 16 shows a stacked light-emitting structure 1600 of an
ultraviolet light excitation type. Three photonic crystal layers
are stacked. A first photonic crystal layer is composed of a
photonic crystal 1602a, a point defect resonator 1603a, and a
switching layer 1601a. A second photonic crystal layer is composed
of a photonic crystal 1602b, a point defect resonator 1603b, and a
switching layer 1601b. A third photonic crystal layer is composed
of a photonic crystal 1602c, a point defect resonator 1603c, and a
switching layer 1601c. An ultraviolet light source 1605 that emits
light having a wavelength capable of exciting fluorescent materials
provided in the point defect resonators 1603a to 1603c is located
in the lowest layer of the structure 1600. A wavelength selective
filter 1604 that cuts off only light emitted from the ultraviolet
light source 1605 is provided in the uppermost layer of the
structure 1600.
[0092] The fluorescent materials provided in the point defect
resonators 1603a to 1603c of the respective photonic crystal layers
are excited by ultraviolet light emitted from the ultraviolet light
source 1605 to cause light emission. Light beams having respective
wavelengths, which are resonated by the point defect resonators
1603a to 1603c and extracted, travel toward the upper side of the
stacked light emitting structure 1600 according to states of the
switching layers 1601a to 1601c. At this time, the light beams
extracted from the point defect resonators 1603a to 1603c are
designed to the respective wavelengths corresponding to colors of
R, G, and B, it is possible to realize a light-emitting device of
the ultraviolet light excitation type for full-color operation.
[0093] The photonic crystal structures 1602a to 1602c and the point
defect resonators 1603a to 1603c are identical to those shown in
Tables 5 and 6. A relationship between a photonic band gap and a
resonant wavelength is identical to that shown in FIG. 16. Note
that each of the point defect resonators 1603a to 1603c has a
fluorescent material that emits fluorescent light having a
desirable wavelength through ultraviolet excitation. When a
wavelength of 400 nm or less is used for the ultraviolet light
source 1605, ultraviolet light can excite the fluorescent materials
in the respective point defect resonators 1603a to 1603c because
the respective photonic crystals shown in Table 5 are transparent
to the ultraviolet light.
[0094] As an example of the fluorescent material that emits the
fluorescent light through ultraviolet excitation,
Y.sub.2O.sub.2S:Eu in which an Eu ion as an impurity is added to
Y.sub.2O.sub.2S used as a host crystal can be used for red.
Similarly, existing materials such as ZnS:Cu and Al can be used for
green and existing materials such as ZnS:Ag and Cl can be used for
blue.
[0095] Each of the switching layers 1601a to 1601c is the switching
layer using the liquid crystal as described above using FIGS. 14A1
and 14A2. When liquid crystal is aligned to a predetermined state,
a PBG including a wavelength of light emitted from a corresponding
point defect resonator is produced in response to a signal inputted
from an outside to prevent the light from being emitted from the
unit light emitting structure to an outside. When the liquid
crystal is not aligned, each of the switching layers transmits
light from a corresponding point defect resonator to exit the light
toward the upper side. Any switching layer has a PGB in which it is
transmissive of light emitted from each of other unit light
emitting structures and light emitted from the ultraviolet light
source 1605.
[0096] A structure of each of the switching layers 1601a to 1601c
is not limited to the above-mentioned structure and can be selected
as appropriate from a structure using a ferroelectric material, and
the like.
[0097] The wavelength selective filter 1604 located in the
uppermost layer prevents light emitted from the ultraviolet light
source 1605 from being exited from the stacked light emitting
structure to the outside. The wavelength selective filter 1604 may
be made of a known ultraviolet absorbing material or a photonic
crystal having a PBG including a wavelength of light emitted from
the ultraviolet light source 1605. In particular, when a photonic
crystal having a predetermined PBG is used for the wavelength
selective filter 1604, use efficiency of an excitation light beam
can be improved.
[0098] The stacked light emitting structure of the optical
excitation type can be realized using the above-mentioned stacked
three-dimensional photonic crystal. In this embodiment, the example
in which only the three photonic crystal layers corresponding to
the colors of R, G, and B are stacked is described. The number of
photonic crystal layers is not limited to three. An arbitrary
number of photonic crystal layers can be stacked if necessary. As
described above, according to this embodiment, it is possible to
realize a light-emitting device for full-color operation.
[0099] When stacked three-dimensional photonic crystals, each of
which corresponds to a pixel are arranged, it is possible to obtain
an image display apparatus capable of expressing an arbitrary color
by combination of colors of R, G, and B based on an external
signal.
Embodiment 3
[0100] Next, a deviation in light extraction efficiency due to a
change in stack order of photonic crystal layers will be described.
FIG. 17 is a schematic view showing a stacked three-dimensional
photonic crystal. Three-dimensional photonic crystal layers 1701b,
1701g, and 1701r including point defect resonators 1702b, 1702g,
and 1702r are stacked on a substrate 1700. Table 7 shows the three
three-dimensional photonic crystal structures (1701b, 1701g, and
1701r).
TABLE-US-00007 TABLE 7 Structure 1701b 1701g 1701r Grating Inverse
Inverse Inverse structure diamond diamond diamond opal opal opal
Constituent TiO.sub.2 TiO.sub.2 TiO.sub.2 Material 6 (n = 2.33) (n
= 2.33) (n = 2.33) (refraction index) Constituent Air (or Air (or
Air (or Material 7 vacuum) vacuum) vacuum) (refraction (n = 1.00)
(n = 1.00) (n = 1.00) index) Dispersion layer 0.30 a 0.30 a 0.30 a
radius (a means (a means (a means lattice lattice lattice period.)
period.) period.) Lattice period 300 nm 365 nm 432 nm (a) Resonant
450 nm 530 nm 640 nm wavelength
[0101] The case where the three three-dimensional photonic crystal
layers are stacked in the normal direction of the substrate and
light is extracted from the air side is assumed. At this time, it
can be assumed that the number of combinations of the order in
which the layers are stacked on the substrate is six. Combinations
that light is more efficiently extracted from the air side are
examined. FIG. 18 shows six kinds of combinations. In FIG. 18, an
arrow indicates a light extraction direction.
[0102] Because the three three-dimensional photonic crystal layers
having lattice periods different from one another are stacked, the
respective structures thereof have photonic band gap regions
different from one another. In the photonic band gap region,
substantially 100% of light is reflected. For example, when a
thickness of the structure 1701g described in Table 7 is set
corresponding to eight frequencies, transmittance at a wavelength
of 530 nm is 0.099%.
[0103] In the six kinds of combinations, it is examined how far
light emitted from each of the three-dimensional photonic crystal
layers travels toward the air side. A period of each of the
photonic crystal structures is set to eight. Table 8 shows a result
obtained by comparison based on transmittances to respective
resonant wavelengths. With respect to G in the case of a stack
order of (1) substrate-R-G-B, transmittance when light emitted from
the photonic crystal layer 1701g is transmitted through the
photonic crystal layer 1701b is 68.25% (G transmittance).
Similarly, With respect to R, transmittance when light emitted from
the photonic crystal layer 1701r is transmitted through the
photonic crystal layers 1701g and 1701b is 67.15% (R
transmittance).
TABLE-US-00008 TABLE 8 Transmittance Transmittance Transmittance
Stack order B (450 nm) G (530 nm) R (640 nm) (1) Substrate-R-G-B --
68.25% 67.15% (2) Substrate-G-R-B -- 0.99% 83.95% (3)
Substrate-R-B-G 2.98% -- 67.15% (4) Substrate-B-R-G 0.23% -- 79.98%
(5) Substrate-G-B-R 7.86% 0.99% -- (6) Substrate-B-G-R 0.23% 1.45%
--
[0104] As shown in Table 8, the transmittance to each light is
changed according to the order in which the photonic crystal layers
are stacked on the substrate. Therefore, it is important to
determine a suitable stack order.
[0105] In particular, in a region in which a wavelength of light is
substantially equal to or several times longer than a lattice
period, a phenomenon that diffraction efficiency becomes unstable
in a wavelength band other than the photonic band gap has been
known as an anomaly. For example, transmittance when light of blue
is transmitted through the photonic crystal layer 1701r becomes
lower.
[0106] As is apparent from Table 8, the case where the stack order
is (1) substrate-R-G-B is best. In other words, when light
extraction efficiency is to be improved, it is important to shift
the wavelength of the light which becomes a light extraction object
and a photonic band gap from each other and to stack the layers
such that the central wavelengths of the respective photonic band
gaps are successively shifted to a short wavelength side in a stack
direction.
[0107] With respect to R, G, and B which are three primary colors
of light in the above-mentioned description of the present
invention, light whose central wavelength of light emitting
spectrum is within a range of 600 nm to 670 nm is set to R (red),
light whose central wavelength is within a range of 500 nm to 600
nm is set to G (green), and light whose central wavelength is
within a range of 380 nm to 500 nm is set to B (blue).
[0108] As described above, according to the present invention, it
is possible to provide a light-emitting structure which can emit
light having a plurality of wavelength distributions over a wide
wavelength region from a single structure, can be integrated at
high density, and can control a radiation mode pattern of radiation
light.
[0109] This application claims priority from Japanese Patent
Application No. 2004-116806 filed Apr. 12, 2004, and Japanese
Patent Application No. 2005-102596 filed Mar. 31, 2005 which are
hereby incorporated by reference herein.
* * * * *