U.S. patent application number 11/100455 was filed with the patent office on 2005-10-13 for nanowire light emitting device.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Choi, Byoung-lyong, Jin, Young-gu, Kim, Jong-seob, Lee, Hyo-sug, Lee, Sung-hoon.
Application Number | 20050224780 11/100455 |
Document ID | / |
Family ID | 35059661 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050224780 |
Kind Code |
A1 |
Jin, Young-gu ; et
al. |
October 13, 2005 |
Nanowire light emitting device
Abstract
A nanowire light emitting device is provided. The nanowire light
emitting device includes a substrate, a first conductive layer
formed on the substrate, a plurality of nanowires vertically formed
on the first conductive layer, each nanowire comprising a p-doped
portion and an n-doped portion, a light emitting layer between the
p-doped portion and the n-doped portion, a second conductive layer
formed on the nanowires, and an insulating polymer in which a light
emitting material is embedded, filling a space between the
nanowires. The color of light emitted from the light emitting layer
varies according to the light emitting material.
Inventors: |
Jin, Young-gu; (Hwaseong-si,
KR) ; Lee, Sung-hoon; (Yongin-si, KR) ; Lee,
Hyo-sug; (Suwon-si, KR) ; Choi, Byoung-lyong;
(Seoul, KR) ; Kim, Jong-seob; (Suwon-si,
KR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
|
Family ID: |
35059661 |
Appl. No.: |
11/100455 |
Filed: |
April 7, 2005 |
Current U.S.
Class: |
257/13 ;
257/E33.003; 257/E33.008 |
Current CPC
Class: |
H01L 33/18 20130101;
B82Y 10/00 20130101; H01L 33/06 20130101; Y10S 977/762 20130101;
H01L 33/08 20130101 |
Class at
Publication: |
257/013 |
International
Class: |
H01L 029/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2004 |
KR |
10-2004-0023805 |
Claims
What is claimed is:
1. A nanowire light emitting device comprising: a substrate; a
first conductive layer formed on the substrate; a plurality of
nanowires vertically formed on the first conductive layer, each
nanowire comprising a p-doped portion and an n-doped portion; a
light emitting layer between the p-doped portion and the n-doped
portion; a second conductive layer formed on the nanowires; and an
insulating polymer in which a light emitting material is embedded,
filling a space between the nanowires, wherein a color of light
emitted from the light emitting layer varies according to the light
emitting material.
2. The device of claim 1, wherein the p-doped portion and n-doped
portion are doped with dopant atoms when the nanowires are grown or
are formed by adsorbing organic molecules onto a surface of the
nanowires.
3. The device of claim 1, wherein the light emitting layer
comprises a contact boundary between the p-doped portion and the
n-doped portion.
4. The device of claim 1, wherein the light emitting layer
comprises an undoped intrinsic portion formed between the p-doped
portion and the n-doped portion.
5. The device of claim 1, wherein the light emitting material
comprises a fluorescent material.
6. The device of claim 1, wherein the light emitting material
comprises a dye.
7. The device of claim 1, wherein the light emitting material
comprises a quantum dot.
8. The device of claim 1, wherein the insulating polymer in which
the embedded light emitting material comprises a colloidal quantum
dot.
9. The device of claim 1, further comprising a reflective layer
that reflects light emitted from the nanowires.
10. The device of claim 9, wherein the reflective layer is disposed
below the first conductive layer, and the substrate and the first
conductive layer are light transmitting materials.
11. The device of claim 9, wherein the reflective layer is disposed
on the second conductive layer, and the second conductive layer is
a transparent electrode.
12. The device of claim 2, wherein the p-doped portion is a portion
of the nanowires where molecules having a high electron affinity
are adsorbed on the surface of the nanowires.
13. The device of claim 12, wherein the p-doped portion is a
portion of the nanowires where molecules containing fluorine are
adsorbed.
14. The device of claim 13, wherein the molecules containing
fluorine are tetrafluoro-tetracyano-quinodimethane (F4-TCNQ).
15. The device of claim 2, wherein the n-doped portion is a portion
of the nanowires where molecules having a low ionization potential
are adsorbed on the surface of the nanowires.
16. The device of claim 15, wherein the n-doped portion is a
portion of the nanowires where organic electron donor molecules or
molecules containing at least one metal selected from the group
consisting of lithium, copper, and zinc is adsorbed.
17. The device of claim 16, wherein the n-doped portion is a
portion of the nanowires where at least one material selected from
the group consisting of copper phthalocyanine (CuPc), zinc
phthalocyanine (ZnPc), pentacene, and
bis(ethylenddithio)tetrathiafulvalene (BEDT-TTF) is adsorbed.
Description
BACKGROUND OF THE INVENTION
[0001] This application claims priority from Korean Patent
Application No. 10-2004-0023805, filed on Apr. 7, 2004, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
[0002] 1. Field of the Invention
[0003] The present invention relates to a nanowire light emitting
device, and more particularly, to a nanowire light emitting device
in which a light emitting material is formed to convert light
emitted by nanowires into different light.
[0004] 2. Description of the Related Art
[0005] A light emitting diode (LED) using a gallium nitride (GaN)
semiconductor is under study. Although the GaN-based LED has high
light emitting efficiency, it has a mismatch problem with a
substrate, thus making it difficult to produce a large-sized
device.
[0006] Technology in which a light emitting device uses a
nanostructure such as a nanowire is being developed. Japanese
Patent Laid-Open Publication No. Hei 10-326888 discloses a light
emitting device comprising a nanowire composed of silicon and a
method of fabricating the light emitting device. After a catalytic
layer such as gold is deposited on a substrate, the silicon
nanowire is grown from the catalytic layer by flowing silicon
tetrachloride (SiCl4) gas into a reactor. In the light emitting
device, emitting colors are controlled by controlling a diameter of
the nanowires.
[0007] The silicon nanowire light emitting device, although being
manufactured at a low cost, has a low light emitting
efficiency.
[0008] U.S. patent Publication No. 2003/0168964 discloses a
nanowire light emitting device having a p-n diode structure. In
this case, the lower portion of the nanowire is an n-type nanowire
and the upper portion is a p-type nanowire, and light is emitted
from the junction region between the two portions. Other components
are added using a vapor phase-liquid phase-solid phase (VLS) method
in order to fabricate a nanowire light emitting device having the
p-n junction structure. In the light emitting device of the U.S.
patent Publication, a predetermined fluorescent material is
disposed on a transparent substrate in order to provide a visible
ray of a desired color.
[0009] As the nanowire having the p-n junction structure is grown
on a catalytic layer, the n-type nanowire and the p-type nanowire
are sequentially formed, thus making it difficult to obtain a high
quality p-n junction structure.
SUMMARY OF THE INVENTION
[0010] The present invention provides a light emitting device,
including a material emitting a predetermined color filling a space
between nanowires.
[0011] According to an aspect of the present invention, there is
provided a nanowire light emitting device comprising: a substrate;
a first conductive layer formed on the substrate; a plurality of
nanowires vertically formed on the first conductive layer, each
nanowire comprising a p-doped portion and an n-doped portion; a
light emitting layer between the p-doped portion and the n-doped
portion; a second conductive layer formed on the nanowires; and an
insulating polymer in which a light emitting material is embedded,
filling a space between the nanowires, wherein a color of light
emitted from the light emitting layer varies according to the light
emitting material.
[0012] The p-doped portion and n-doped portion may be doped with
dopant atoms when the nanowires are grown or may be formed by
adsorbing organic molecules onto the surfaces of the nanowires. The
light emitting layer may be a contact boundary between the p-doped
portion and the n-doped portion. The light emitting layer may be an
undoped intrinsic portion formed between the p-doped portion and
the n-doped portion.
[0013] The light emitting material may be a fluorescent material.
Alternatively, light emitting material may be a dye or a quantum
dot.
[0014] The insulating polymer in which the light emitting material
is embedded may be a colloidal quantum dot. The nanowire light
emitting device may further comprise a reflective layer that
reflects light emitted from the nanowires.
[0015] The reflective layer may be disposed below the first
conductive layer and the substrate, and the first conductive layer
may be composed of a light transmitting material. Alternatively,
the reflective layer may be disposed on the second conductive
layer, and the second conductive layer may be a transparent
electrode.
[0016] The n-doped portion may be a portion of the nanowires where
molecules having a low ionization potential are adsorbed on the
surface of the nanowires.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0018] FIG. 1 is a cross-sectional view of a nanowire light
emitting device according to a first exemplary embodiment of the
present invention;
[0019] FIG. 2 is a diagram illustrating how a fluorescent material,
dye, or quantum dot, which is a light emitting material, is
embedded in the insulating polymer;
[0020] FIG. 3 is a diagram illustrating colloidal quantum dots in
which organic molecule chains are attached thereto; and
[0021] FIG. 4 is a cross-sectional diagram of a nanowire light
emitting device according to a second exemplary embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] A nanowire light emitting device according to the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings.
[0023] FIG. 1 is a cross-sectional view of a nanowire light
emitting device according to a first embodiment of the present
invention.
[0024] Referring to FIG. 1, a conductive layer (a first electrode
layer) 110 is formed on a substrate 100 and a plurality of
nanowires 120 are formed roughly at right angles to the conductive
layer 110. An insulating polymer 130, in which a light emitting
material is embedded, fills a space between the nanowires 120. An
electrode layer (a second electrode layer) 140 is formed on the
nanowires 120.
[0025] The nanowires 120 each have a p-type doped portion 122, an
n-type doped portion 126 and an intrinsic portion 124, which is a
light emitting layer between the p-type doped portion 122 and the
n-type doped portion 126. The intrinsic portion 124 is not
doped.
[0026] The substrate 100 may be a silicon wafer, a sapphire wafer,
or a flat metal film. If light is to be transmitted toward the
substrate 100, the substrate 100 may be a transparent substrate
such as a sapphire substrate, a quartz substrate, or a glass
substrate.
[0027] The first electrode layer 110 may be a transparent electrode
layer, for example, an ITO layer. The second electrode layer 140
may be formed of aluminum, gold, or magnesium by deposition. If
light is transmitted through the second electrode layer 140, the
second electrode layer 140 may be a transparent electrode layer
such as an ITO layer.
[0028] The nanowires 120 may emit ultraviolet light or blue light.
When the nanowires 120 are composed of ZnO, ultraviolet light is
emitted. When the nanowires are composed of Si, infrared light is
emitted. When the nanowires are composed of GaN, ultraviolet light
or blue light is emitted. When the nanowires are composed of InGaN,
blue light is emitted. The nanowires 120 may have a diameter of
20-100 nm and a length of 1 mm.
[0029] The nanowires have a p-i-n junction structure comprising the
p-doped portion 122, the n-doped portion 126, and the intrinsic
portion 124.
[0030] The p-type doped portion 122 is a portion formed by
adsorbing a p-type dopant into the surface of the nanowires 120. A
molecule having a high electron affinity such as
tetrafluoro-tetracyano-quinodimethane (F4-TCNQ), which is an
organic electron acceptor molecule, may be used as the p-type
dopant. Because the p-type dopant takes electrons from the
corresponding surfaces of the nanowires 120, holes are formed on
the surfaces of the nanowires where the p-type dopant is adsorbed.
Thus, the p-type doped portion 122 is formed. The p-type doped
portion 122 may contain electron acceptor atoms therein.
[0031] The n-type doped portion 126 is a portion formed by
adsorbing an n-type dopant onto the surface of the nanowires 120.
Molecules having a low ionization potential such as an organic
electron donor molecule or a molecule containing at least one of
lithium, copper, and zinc may be used as the n-type dopant. For
example, copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc),
pentacene, or bis(ethylenddithio)tetrathiafulvalen- e (BEDT-TTF)
may be used for the n-type dopant. Because the n-type dopant
provides electrons to the corresponding surfaces of the nanowires
120, free electrons are generated on the surfaces of the nanowires
where the n-type dopant is adsorbed. Thus, the n-type doped portion
126 is formed. The n-type doped portion 126 may contain electron
donor atoms therein.
[0032] The insulating polymer 130 prevents electric contact between
the nanowires 120. A fluorescent material is embedded inside the
insulating polymer 130 such that ultraviolet light emitted from the
nanowires 120 can be adsorbed onto the fluorescent material and a
predetermined visible wavelength can be emitted from the
fluorescent material. The polymer 130 may also be an insulating
polymer in which a dye or quantum dot is embedded. Most
semiconductor compounds, for example ZnS, CdS, ZnSe, CdSe, and InP,
may be used as the quantum dot. A photoresist can be the insulating
polymer 130 containing the fluorescent material, dye, or quantum
dot.
[0033] Ultraviolet light emitted from the nanowires 120 is adsorbed
by the fluorescent material, dye, or quantum dot that is embedded
in the insulating layer 130. The fluorescent material, dye, or
quantum dot that adsorbs the ultraviolet emits a predetermined
color.
[0034] A visible ray emitted from the fluorescent material, dye, or
quantum dot varies according to the fluorescent material, the color
of the dye, or the size of the quantum dot.
[0035] FIG. 2 is a diagram illustrating how a fluorescent material,
dye, or quantum dot, which is a light emitting material, is
embedded in the insulating polymer. A plurality of quantum dots 202
are embedded in the insulating polymer 200.
[0036] FIG. 3 is a diagram illustrating colloidal quantum dots in
which organic molecule chains 302 are attached to the quantum dots
300. Instead of using the polymer in which a fluorescent material,
a dye, or a quantum dot is embedded, the colloidal quantum dots of
FIG. 3 may be used by stacking them between the nanowires 120. The
organic molecule chain 302 may be composed of a material such as
trioctylphospine oxide (TOPO) or 1.6-hexanedithiol (HDT).
[0037] A reflective layer 112 may be interposed between the
substrate 100 and the first electrode layer 110. A long-wave pass
filter can be used as the reflective layer 112. When the reflective
layer 112 has a thickness equal to the wavelength of light emitted
from the nanowires 120, for example, the wavelength of ultraviolet
light, the reflective layer 112 reflects the ultraviolet light,
which is emitted from the intrinsic portion 124 of the nanowires
120, back inside the light emitting device and transmits only
visible rays to the outside. Therefore, the reflective layer 112
contributes all the ultraviolet light emitted from the nanowires
120 to emit visible rays, thus improving light emitting
efficiency.
[0038] The reflective layer 112 does not have to be disposed below
the first electrode layer 110. That is, the reflective layer 112
may be disposed above the first electrode layer 110 when the
reflective layer 112 is conductive. If the light of the light
emitting device is emitted through the second electrode layer 140,
the second electrode layer 140 may be composed of a transparent
electrode and the reflective layer 120 may be disposed on the
second electrode layer 140.
[0039] The operation of a light emitting device having the above
structure will be now described with reference to the attached
drawings.
[0040] First, holes from the p-type doped portion 122 and the
electrons from the n-type doped portion 126 combine in the
intrinsic portion 124 when a positive voltage is applied to the
first electrode layer 110 connected to the p-type doped portion 122
of the nanowires 120 and a negative voltage is applied to the
second electrode layer 140 connected to the n-type doped portion
126 of the nanowires 120, thus emitting light. The ultraviolet
light emitted from the intrinsic portion 124 disperses in every
direction. Some of the ultraviolet light that meets nearby
fluorescent material embedded in the insulating polymer 130 excites
the fluorescent material, which then emits visible rays. The
visible rays are transmitted through the transparent first
electrode layer 110, the reflective layer 112, and the transparent
substrate 100.
[0041] Some of the ultraviolet light emitted from the nanowires 120
that goes towards the second electrode layer 140 is reflected by
the second electrode layer 140, back into the light emitting
device, and adsorbed by the fluorescent material, which emits
visible rays. The ultraviolet light heading towards the first
electrode layer 110 is reflected by the reflective layer 112 into
the polymer containing the fluorescent material, and excites the
fluorescent material.
[0042] FIG. 4 is a cross-sectional view of a nanowire light
emitting device according to a second exemplary embodiment of the
present invention. Like reference numerals in FIGS. 1 and 2 denote
like elements, and their description will not be repeated.
[0043] Referring to FIG. 4, a conductive layer (a first electrode
layer) 110 is formed on a substrate 100 and a plurality of
nanowires 120' are formed roughly at right angles to the conductive
layer 110. An insulating polymer 130 in which a light emitting
material is embedded fills a space between the nanowires 120'. An
electrode layer (a second electrode layer) 140 is formed on the
nanowires 120'.
[0044] A reflective layer 112 may be interposed between the
substrate 100 and the first electrode layer 110. A long-wave pass
filter can be used as the reflective layer 112. When the reflective
layer 112 has a thickness equal to the wavelength of light emitted
from the nanowires 120', for example, the wavelength of ultraviolet
light, the reflective layer 112 reflects the ultraviolet light,
which is emitted from a light emitting layer 128 of the nanowires
120', back inside the light emitting device and transmits only
visible rays to the outside. Therefore, the reflective layer 112
contributes all the ultraviolet light emitted from the nanowires
120' to emit visible rays, thus improving light emitting
efficiency.
[0045] The nanowires 120' include a p-type doped portion 122 and an
n-type doped portion 126 contacting each other. A contact boundary
of the two doped portions 122 and 126 forms a light emitting layer
128. Such a light emitting structure is a p-n junction structure,
in comparison to the p-i-n junction structure of the first
exemplary embodiment.
[0046] The insulating polymer 130 prevents electric contact between
the nanowires 120'. A fluorescent material is embedded inside the
insulating polymer 130 such that ultraviolet light emitted from the
nanowires 120' can be adsorbed onto the fluorescent material and a
predetermined visible wavelength can be emitted from the
fluorescent material. The polymer 130 may also be an insulating
polymer in which a dye or quantum dot is embedded. Most
semiconductor compounds, for example ZnS, CdS, ZnSe, CdSe, and InP,
may be used as the quantum dot. A photoresist can be the insulating
polymer 130 containing the fluorescent material, dye, or quantum
dot.
[0047] Ultraviolet light emitted from the nanowires 120' is
adsorbed by the fluorescent material, dye, or quantum dot that is
embedded in the insulating layer 130. The fluorescent material,
dye, or quantum dot that adsorbs the ultraviolet emits a
predetermined color.
[0048] Ultraviolet light is emitted from the light emitting layer
128 when a direct current is supplied to both ends of the nanowires
220'. The ultraviolet light excites the fluorescent material, dye,
or quantum dot embedded in the polymer 130 and emits a
predetermined visible ray.
[0049] In the nanowire light emitting device according to exemplary
embodiments of the present invention, the colors of visible rays
emitted from a predetermined region can be controlled by
controlling the kind or size of a fluorescent material, dye, or
quantum dot inside an insulating layer. Also, the efficiency of
producing colored light is improved by inserting into the light
emitting device a material that controls colors.
[0050] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *