U.S. patent application number 13/339984 was filed with the patent office on 2012-05-03 for solar cell.
This patent application is currently assigned to SAMSUNG SDI CO., LTD.. Invention is credited to Junhee CHOI, Jai Yong HAN, Andrei ZOULKARNEEV.
Application Number | 20120103405 13/339984 |
Document ID | / |
Family ID | 41132145 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120103405 |
Kind Code |
A1 |
CHOI; Junhee ; et
al. |
May 3, 2012 |
SOLAR CELL
Abstract
Disclosed are a relatively high-efficiency solar cell and a
method for fabricating the same using a micro-heater array. The
solar cell may include first and second micro-heaters intersecting
each other or being parallel to each other on a substrate, and a
plurality of In.sub.xGa.sub.1-xN p-n junction layers formed using
the first and second micro-heaters. The solar cell has improved
efficiency because sunlight with various wavelengths may be
effectively absorbed by the plurality of In.sub.xGa.sub.1-xN p-n
junction layers. Furthermore, relatively large-sized solar cells
may be fabricated, because the plurality of In.sub.xGa.sub.1-xN p-n
junction layers may be formed on a glass substrate using a
micro-heater array.
Inventors: |
CHOI; Junhee; (Seongnam-si,
KR) ; HAN; Jai Yong; (Suwon-si, KR) ;
ZOULKARNEEV; Andrei; (Suwon-si, KR) |
Assignee: |
SAMSUNG SDI CO., LTD.
Yongin-si
KR
SAMSUNG ELECTRONICS CO., LTD.
Suwon-si
KR
|
Family ID: |
41132145 |
Appl. No.: |
13/339984 |
Filed: |
December 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12320924 |
Feb 9, 2009 |
8138416 |
|
|
13339984 |
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Current U.S.
Class: |
136/255 ;
136/259 |
Current CPC
Class: |
H01L 31/1844 20130101;
H01L 31/0735 20130101; Y02E 10/544 20130101; H01L 31/03046
20130101 |
Class at
Publication: |
136/255 ;
136/259 |
International
Class: |
H01L 31/0687 20120101
H01L031/0687; H01L 31/0232 20060101 H01L031/0232 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2008 |
KR |
10-2008-0032072 |
Claims
1.-10. (canceled)
11. A solar cell comprising: a substrate; a first micro-heater
having a first heating portion and first supports, the first
heating portion being spaced apart from the substrate by the first
supports; a second micro-heater having a second heating portion and
second supports, the second heating portion arranged parallel to
the first heating portion while being spaced apart from the
substrate by the second supports; and a plurality of
In.sub.xGa.sub.1-xN p-n junction layers on at least one of the
first and second heating portions, x being a number from 0 to 1 and
each of the plurality of In.sub.xGa.sub.1-xN p-n junction layers
having a different value for x, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers being
electrically-connected to the first and second heating
portions.
12. The solar cell of claim 11, wherein the substrate is made of a
glass material.
13. The solar cell of claim 11, further comprising: a lens above at
least one of the first and second heating portions, the lens
focusing sunlight onto the plurality of In.sub.xGa.sub.1-xN p-n
junction layers.
14. The solar cell of claim 11, wherein the plurality of
In.sub.xGa.sub.1-xN p-n junction layers have a multilayer
structure, and an outer layer of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers has a smaller x value than
that of an inner layer of the plurality of In.sub.xGa.sub.1-xN p-n
junction layers.
15. The solar cell of claim 11, wherein the first supports are
between the substrate and the first heating portion, and the second
supports are between the substrate and the second heating
portion.
16. The solar cell of claim 11, wherein: the first micro-heater
further comprises first connecting portions extending from opposing
sides of the first heating portion and arranged along a length of
the first heating portion while being spaced apart from each other,
the second micro-heater further comprises second connecting
portions extending from opposing sides of the second heating
portion and arranged along a length of the second heating portion
while being spaced apart from each other, and the first supports
are between the substrate and the first connecting portions so as
to support the first heating portion and the first connecting
portions, and the second supports are between the substrate and the
second connecting portions so as to support the second heating
portion and the second connecting portions.
17. The solar cell of claim 11, wherein: the first micro-heater
further comprises first connecting portions extending from opposing
sides of the first heating portion and arranged along a length of
the first heating portion while being spaced apart from each other,
and the first supports are between the substrate and the first
connecting portions so as to support the first heating portion and
the first connecting portions, and the second supports are between
the substrate and the second heating portion so as to support the
second heating portion.
18.-25. (canceled)
26. The solar cell of claim 11, wherein the first and second
supports are directly disposed on the substrate.
Description
CROSS REFERENCE TO RELATED U.S. APPLICATION
[0001] This is a continuation application based on pending
application Ser. No. 12/320,924, filed Feb. 9, 2009, the entire
contents of which is hereby incorporated by reference.
CROSS-REFERENCE TO RELATED PRIORITY APPLICATION
[0002] This application claims priority under 35 U.S.C. .sctn.119
to Korean Patent Application No. 10-2008-0032072, filed Apr. 7,
2008, the entire disclosure of which is incorporated herein by
reference.
BACKGROUND
[0003] 1. Field
[0004] Example embodiments relate to solar cells and methods for
fabricating the same.
[0005] 2. Description of the Related Art
[0006] Conventionally, a p-n junction is used not only as a diode
for rectifying operations but also for opto-electronic devices
(e.g., solar cells, light emitting diodes (LEDs), and image
sensors). When fabricating p-n junctions for general-use
single-layered solar cells, silicon (Si) is used as the host
material, and phosphorous (P) and boron (B) may be added as n-type
and p-type doping materials, respectively. However, a
single-layered solar cell is disadvantageous, because it has low
efficiency.
[0007] The efficiency of a solar cell is affected by the band gap
(E.sub.g) of the host material. For example, a solar cell with a
host material having a large band gap is inefficient, because it
cannot absorb light having energy smaller than the band gap. In
contrast, a solar cell with a host material having a small band gap
is also inefficient, because (although it can absorb light having
energy larger than the band gap) the surplus energy beyond the band
gap is lost as heat. Of the host materials used in single-layered
solar cells, CdTe has the highest efficiency of 31%, but this is
still relatively low.
[0008] Because sunlight has a broad range of wavelengths, a host
material capable of absorbing the broad range of wavelengths is
required to effectively utilize sunlight as a source of electrical
energy. A large-sized, high-efficiency solar cell may be attained
by forming a high-quality p-n junction on a glass substrate.
However, a high temperature of 1000.degree. C. or more is typically
required to form a high-quality p-n junction. For this reason, the
substrate used to form the high-quality p-n junction is restricted
to relatively expensive substrates (e.g., silicon wafer,
Al.sub.2O.sub.3, SiC). Accordingly, there is increased difficultly
and costs associated with the manufacture of large-sized p-n
junctions and large-sized solar cells.
SUMMARY
[0009] Disclosed herein is a higher-efficiency, multi-stacked solar
cell that utilizes a micro-heater array. A solar cell using a
micro-heater array may include a substrate, a first micro-heater, a
second micro-heater, and a plurality of In.sub.xGa.sub.1-xN p-n
junction layers, x being a number from 0 to 1.
[0010] In example embodiments, the first micro-heater may include a
first heating portion spaced apart from the substrate and extending
in a first direction; and first supports provided on the substrate
so as to be spaced from one another and supporting the first
heating portion. The second micro-heater may include a second
heating portion extending in a second direction perpendicular to
the first direction so as to traverse the first heating portion;
and second supports provided on the substrate so as to be spaced
from one another and supporting the second heating portion. There
may be one or more of the first and second micro-heaters.
[0011] The plurality of In.sub.xGa.sub.1-xN p-n junction layers may
be formed on one or more of the first and second heating portions
at a juncture of the first and second heating portions (e.g.,
intersection area where the second heating portion traverses the
first heating portion) by the heat generated from the first or
second heating portion. The plurality of In.sub.xGa.sub.1-xN p-n
junction layers may be electrically connected to the first and
second heating portions and absorb sunlight from the external
environment. In the plurality of In.sub.xGa.sub.1-xN p-n junction
layers, each layer may have a different value for x.
[0012] In example embodiments, a solar cell may further include a
lens provided above the second heating portion and corresponding to
the area where the plurality of In.sub.xGa.sub.1-xN p-n junction
layers are formed so as to focus sunlight onto the plurality of
In.sub.xGa.sub.1-xN p-n junction layers.
[0013] In other example embodiments, a first micro-heater may
include a first heating portion spaced apart from the substrate and
extending in a first direction; and first supports provided on the
substrate so as to be spaced from one another and supporting the
first heating portion. A second micro-heater may include a second
heating portion spaced apart from the substrate and provided
parallel to the first heating portion; and second supports provided
on the substrate to be spaced from one another and supporting the
second heating portion. A plurality of In.sub.xGa.sub.1-xN p-n
junction layers may be formed on one or more of the first and
second heating portions by the heat generated from the first or
second heating portion. The plurality of In.sub.xGa.sub.1-xN p-n
junction layers may be electrically connected to the first and
second heating portions and absorb sunlight from the external
environment. In the plurality of In.sub.xGa.sub.1-xN p-n junction
layers, each layer may have a different value for x.
[0014] In example embodiments, a solar cell may further include a
lens provided above one or more of the first and second heating
portions and corresponding to the area where the plurality of
In.sub.xGa.sub.1-xN p-n junction layers are formed so as to focus
sunlight onto the plurality of In.sub.xGa.sub.1-xN p-n junction
layers.
[0015] In example embodiments, the substrate may be made of a glass
material. Furthermore, the first and second micro-heaters may be
operated independently of each other.
[0016] Also disclosed herein is a method for fabricating a
higher-efficiency, multi-stacked solar cell by forming a plurality
of In.sub.xGa.sub.1-xN p-n junction layers on a relatively
inexpensive and available substrate (e.g., glass substrate) using a
micro-heater array. A method for fabricating a solar cell using a
micro-heater array may include applying a first voltage to a
micro-heater array in the presence of source and doping gases, the
micro-heater array having a first heating portion extending in a
first direction and a second heating portion extending in a second
direction so as to traverse the first heating portion; and forming
a first plurality of In.sub.xGa.sub.1-xN p-n junction layers at a
juncture of the first and second heating portions, x being a number
from 0 to 1 and each of the first plurality of In.sub.xGa.sub.1-xN
p-n junction layers having a different value for x.
[0017] In other example embodiments, a method for fabricating a
solar cell using a micro-heater array may include applying a first
voltage to a micro-heater array in the presence of source and
doping gases, the micro-heater array having first and second
heating portions extending in parallel; and forming a first
plurality of In.sub.xGa.sub.1-xN p-n junction layers on one of the
first or second heating portions, x being a number from 0 to 1 and
each of the first plurality of In.sub.xGa.sub.1-xN p-n junction
layers having a different value for x.
[0018] In a method for fabricating a solar cell using a
micro-heater array according to example embodiments, the
micro-heater array may be provided in a chamber. A voltage may be
applied to one of the first or second micro-heaters. A source gas
and p-type doping gas may be injected into the chamber to grow a
p-type In.sub.xGa.sub.1-xN layer on the first heating portion or
the second heating portion heated by the applied voltage. A source
gas and an n-type doping gas may be injected into the chamber to
grow an n-type In.sub.xGa.sub.1-xN layer on the first heating
portion or the second heating portion heated by the applied
voltage. The process for growing the p-type In.sub.xGa.sub.1-xN
layer and the n-type In.sub.xGa.sub.1-xN layer may be repeated to
obtain a plurality of In.sub.xGa.sub.1-xN p-n junction layers,
wherein each layer has a different value for x. The p-type
In.sub.xGa.sub.1-xN layer and the n-type In.sub.xGa.sub.1-xN layer
may be grown sequentially, such that the p-type In.sub.xGa.sub.1-xN
layer is grown first and the n-type In.sub.xGa.sub.1-xN layer is
grown second or vice versa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The features and advantages of example embodiments may
become more apparent upon review of the attached drawings. The
accompanying drawings are merely intended to depict example
embodiments and should not be interpreted to limit the scope of the
claims.
[0020] FIG. 1A is a perspective view of a solar cell using a
micro-heater array according to an example embodiment.
[0021] FIG. 1B is a plan view of a solar cell using a micro-heater
array according to an example embodiment.
[0022] FIG. 1C is a cross-sectional view along line I-I' of FIG.
1B.
[0023] FIG. 2 is a cross-sectional view of a solar cell using a
micro-heater array according to another example embodiment.
[0024] FIGS. 3A and 3B are perspective and plan views,
respectively, of a solar cell using a micro-heater array according
to another example embodiment.
[0025] FIG. 4A is a plan view of a solar cell using a micro-heater
array according to another example embodiment.
[0026] FIG. 4B is a cross-sectional view along line II-II' of FIG.
4A.
[0027] FIG. 5A is a plan view of a solar cell using a micro-heater
array according to another example embodiment.
[0028] FIG. 5B is a cross-sectional view along line III-III' of
FIG. 5A.
[0029] FIG. 6A is a plan view showing a plurality of
In.sub.xGa.sub.1-xN p-n junction layers formed on the first and
second heating portions of FIG. 5A.
[0030] FIG. 6B is a cross-sectional view along line IV-IV' of FIG.
6A.
[0031] FIG. 6C is a cross-sectional view of a solar cell using the
micro-heater array illustrated in FIGS. 5A and 5B according to
another example embodiment.
[0032] FIG. 7 is a schematic view of a process of forming a solar
cell having a plurality of In.sub.xGa.sub.1-xN p-n junction layers
using a micro-heater array according to an example embodiment.
[0033] FIG. 8A through FIG. 8C are cross-sectional views along line
V-V' of
[0034] FIG. 7 illustrating an example of forming a plurality of
In.sub.xGa.sub.1-xN p-n junction layers at the juncture of the
first and second heating portions.
[0035] It should be understood that the appended drawings are not
necessarily to scale, while presenting a somewhat simplified
representation of various features illustrative of the basic
principles of example embodiments. The specific design features of
example embodiments as disclosed herein (e.g., specific dimensions,
orientations, locations, and shapes) may be determined in part by
the particular intended application and use environment.
DETAILED DESCRIPTION
[0036] A more detailed description of various example embodiments
is provided herein. However, specific structural and functional
details disclosed herein are merely representative for purposes of
describing example embodiments. Example embodiments may be embodied
in many alternate forms and should not be construed as limited to
only the embodiments set forth herein.
[0037] Accordingly, while example embodiments are capable of
various modifications and alternative forms, embodiments thereof
are shown by way of example in the drawings and will herein be
described in detail. It should be understood, however, that there
is no intent to limit example embodiments to the particular forms
disclosed, but to the contrary, example embodiments are to cover
all modifications, equivalents, and alternatives falling within the
scope of example embodiments. Like numbers refer to like elements
throughout the specification.
[0038] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of example embodiments.
[0039] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments. As used herein, the singular forms "a," "an,"
and "the" are intended to include the plural forms as well, unless
the context clearly indicates otherwise. It will be further
understood that the terms "comprises," "comprising," "includes,"
and/or "including," when used herein, specify the presence of
stated features, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, integers, steps, operations, elements,
components, and/or groups thereof.
[0040] It should also be noted that in some alternative
implementations, the functions/acts noted may occur out of the
order noted in the figures. For example, two figures shown in
succession may in fact be executed substantially concurrently or
may sometimes be executed in the reverse order, depending upon the
functionality/acts involved.
[0041] Although a plurality of first and second micro-heaters may
be illustrated according to example embodiments as being provided
on a substrate, a single (as opposed to a plurality of) first
and/or second micro-heater may instead be provided on a
substrate.
[0042] A solar cell using a micro-heater array according to an
example embodiment will be described in detail below. FIG. 1A is a
perspective view of a solar cell using a micro-heater array
according to an example embodiment, FIG. 1B is a plan view of a
solar cell using a micro-heater array according to an example
embodiment, and FIG. 10 is a cross-sectional view along line I-I'
of FIG. 1B.
[0043] Referring to FIG. 1A through FIG. 10, a solar cell 101
according to an example embodiment may include a micro-heater array
and a plurality of In.sub.xGa.sub.1-xN p-n junction layers 40. The
micro-heater array may include a substrate 10, a plurality of first
micro-heaters 20 arranged in parallel in a first direction D1 on
the substrate 10, and a plurality of second micro-heaters 30
provided in a second direction D2 perpendicular to the first
direction D1 so as to traverse the plurality of first micro-heaters
20. The plurality of first and second micro-heaters 20, 30 may be
operated independently of each other.
[0044] Each of the plurality of first micro-heaters 20 may include
a first heating portion 21 and first supports 22. The first heating
portion 21 may be spaced apart from the substrate 10 and may extend
in a first direction D1. The first supports 22 may be provided
between the substrate 10 and the first heating portion 21, and
support the first heating portion 21.
[0045] Each of the plurality of second micro-heaters 30 includes a
second heating portion 31 and second supports 32. The second
heating portion 31 extends in the second direction D2 perpendicular
to the first direction D1, and intersects the first heating portion
21 above the first heating portion 21. The second supports 32 may
be provided between the substrate 10 and the second heating portion
31 so as to support the second heating portion 31.
[0046] Each of the first and second supports 22, 32 may be arranged
so as to be spaced apart from one another along the length
direction of the first and second heating portions 21, 31, except
for the intersection area of the first and second heating portions
21, 31.
[0047] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may be formed at one or more of the first and second heating
portions 21, 31, at the intersection area of the first and second
heating portions 21, 31, by the heat generated from the first or
second heating portion 21, 31, and may be electrically connected to
the first and second heating portions 21, 31, respectively.
[0048] A more detailed description of each constituent is provided
below. In this example embodiment, the first and second
micro-heaters 20, 30 may be identical in structure and shape. But,
the first and second micro-heaters 20, 30 may have different
size.
[0049] As illustrated in FIG. 1A and FIG. 10, the second heating
portion 31 may be provided above the first heating portion 21, with
a predetermined spacing from the first heating portion 21. For the
first and second heating portions 21, 31 to be spaced from each
other at the intersection/juncture area, the spacing S1 between the
first heating portion 21 and the substrate 10 may be smaller than
the spacing S2 between the second heating portion 31 and the
substrate 10. Therefore, the height of the first supports 22 may be
lower than the height of the second supports 32. Meanwhile, the
spacing between the first and second heating portions 21, 31 may be
the same as the thickness of the plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40 formed between the first and second heating
portions 21, 31, so that the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 may be electrically connected to the first and
second heating portions 21, 31, respectively.
[0050] The first and second heating portions 21, 31 may be made of
a suitable material (e.g., molybdenum, tungsten, silicon carbide)
which emit light and generate heat when power is applied. The first
and second heating portions 21, 31 may be made of the same material
or different materials.
[0051] At the intersection area of the first and second heating
portions 21, 31, an opening 33 may be formed at the second heating
portion 31, or the second heating portion 31 may be formed of a
transparent electrode material. As such, the plurality of
In.sub.xGa.sub.1-xp-n junction layers 40 formed between the first
and second heating portions 21, 31 can absorb light. In this
example embodiment, the opening 33 may be formed at the second
heating portion 21, so that sunlight from outside can be
transmitted to the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 through the opening 33.
[0052] The first and second supports 22, 32 may be made of a
material having a relatively low thermal conductivity so as to
reduce or prevent the loss of heat generated from the first and
second heating portions 21, 31. For example, the first and second
supports 22, 32 may be made of an insulating material (e.g.,
SiO.sub.x, Si.sub.3N.sub.4).
[0053] The substrate 10 may be made of a glass material. If the
substrate 10 is made of a glass material, the first and second
heating portions 21, 31 may be heated to a high temperature of
600-2000.degree. C. while maintaining the temperature of the
substrate 10 at, for example, 50.degree. C., because radiation heat
(visible ray or IR) is transmitted. Accordingly, the micro-heater
array may be used to form a p-n junction requiring heating at high
temperature on a glass substrate. This enables the manufacture of
large-sized p-n junction devices.
[0054] In an example embodiment, as illustrated in FIG. 1B, each of
the first and second heating portions 21, 31 may be divided into
first areas A1 and second areas A2. The first areas A1 correspond
to contact areas CA at which the first and second heating portions
21, 31 are respectively in contact with the first and second
supports 22, 32, and each of the second areas A2 may be located
between the first areas A1. Here, the area of the contact area CA
needs to be decreased as much as possible while the first and
second supports 22, 32 maintain supporting of the first and second
heating portions 21, 31. The smaller the contact area CA, the less
heat is transferred between the first heating portion 21 and the
first supports 22 and between the second heating portion 31 and the
second supports 32. As a result, power consumption for driving the
micro-heater array may be reduced.
[0055] Although the first areas A1 and the contact areas CA are
shown as circular shapes in FIG. 1A through FIG. 10, the first
areas A1 and the contact areas CA may be etched to have a
rectangular shape or another suitable shape.
[0056] It may be beneficial for the width of the first areas A1 to
be greater than the width of the second areas A2. The reason is
that having the width of each of the first areas A1 greater than
the width of each of the second areas A2 may facilitate etching of
the first and second supports 22, 32, particularly at the contact
area CA. Another reason is that when the width of each of the
second areas A2 is smaller than the width of each of the first
areas A1, more light may be emitted and more heat may be generated
at the second areas A2 than at the first areas A1. Such a technical
configuration enables the control of light-emission and
heat-generation positions.
[0057] Each of the first and second heating portions 21, 31 may be
divided into the first areas A1 and the second areas A2, the light
emission and heat generation may be increased at the second areas
A2 but decreased at the first areas A1 respectively supported by
the first and second supports 22, 32, and unnecessary power
consumption may be reduced by minimizing the heat transfer area at
the first areas A1. Accordingly, the applied voltage may be
effectively used for high-temperature heating at the second areas
A1.
[0058] Because the first and second heating portions 21, 31
intersect each other at the second areas A2, a plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be formed between
the first and second heating portions 21, 31, at the intersection
area, using the high-temperature heat generated there.
[0059] As illustrated in FIG. 1A through FIG. 1C, the first
micro-heater 20 may be operated to generate heat at the first
heating portion 21 and form the plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40 at the first heating portion 21 using the
heat. Alternatively, the second micro-heater 30 may be operated to
form the plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 at
the second heating portion 31. Further, the first micro-heater 20
and the second micro-heater 30 may be operated sequentially to form
the plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 at both
the first heating portion 21 and the second heating portion 31.
Further, because each of the first heating portions 21 and the
second heating portions 31 included in the plurality of first and
second micro-heaters 20, 30 may be operated independently, it is
possible to form the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 only at some points selected from the intersection areas
of the first and second heating portions 21, 31.
[0060] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may be formed on the first heating portion 21. Because relatively
localized high temperature heating is possible at the second area
A2 of the first heating portion 21, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be formed at the
second area A2 of the first heating portion 21.
[0061] As illustrated in FIG. 1A and FIG. 1C, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 have a multilayer
structure. Each of the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 may include a p-type In.sub.xGa.sub.1-xN layer
and an n-type In.sub.xGa.sub.1-xN layer. And, in the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40, each x may have a
different value in the range from 0 to 1.
[0062] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may include three In.sub.xGa.sub.1-xN p-n junction layers 41, 42,
43. The first In.sub.xGa.sub.1-xN p-n junction layer 41 may include
a first p-type In.sub.xGa.sub.1-xN layer 41a and a first n-type
In.sub.xGa.sub.1-xN layer 41b, the second In.sub.xGa.sub.1-xN p-n
junction layer 42 may include a second p-type In.sub.xGa.sub.1-xN
layer 42a and a second n-type In.sub.xGa.sub.1-xN layer 42b, and
the third In.sub.xGa.sub.1-xN p-n junction layer 43 may include a
third p-type In.sub.xGa.sub.1-xN layer 43a and a third n-type
In.sub.xGa.sub.1-xN layer 43b.
[0063] The p-type In.sub.xGa.sub.1-xN layer and the n-type
In.sub.xGa.sub.1-xN layer may be formed sequentially to form the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40. However,
the n-type In.sub.xGa.sub.1-xN layer and the p-type
In.sub.xGa.sub.1-xN layer may be formed sequentially to form the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40.
[0064] In the plurality of In.sub.xGa.sub.1-xN p-n junction layers
40, each x may be adjusted to have different value so as to
effectively absorb sunlight incident on the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40. Because each host
material In.sub.xGa.sub.1-xN included in the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 forms a solid solution
of In and Ga, the x value may be controlled between 0 and 1 by
varying the contents of In and Ga, and, the band gap (E.sub.g) of
the x value.
[0065] By laminating In.sub.XGa.sub.1-XN p-n junction layers having
different x values, a plurality of In.sub.XGa.sub.1-XN p-n junction
layers 40 with different E.sub.g values may be formed, and each of
the plurality of In.sub.XGa.sub.1-XN p-n junction layers 40 may
absorb sunlight with different wavelength. Depending on the x
value, the E.sub.g of the In.sub.XGa.sub.1-XN may be varied from
0.7 eV (590 nm) to 3.4 eV (120 nm). This almost corresponds to the
spectrum of sunlight, which has a wide wavelength ranges.
Therefore, of the sunlight incident on the plurality of
In.sub.XGa.sub.1-XN p-n junction layers 40, the light with a short
wavelength may be absorbed by an In.sub.XGa.sub.1-XN p-n junction
layer with large E.sub.g, and the light with a long wavelength may
be absorbed by an In.sub.XGa.sub.1-XN p-n junction layer with small
E.sub.g. Consequently, the loss of the sunlight incident on the
plurality of In.sub.XGa.sub.1-XN p-n junction layers 40 may be
prevented. As a result, the efficiency of the solar cell 101 may be
improved. For instance, a solar cell having two In.sub.XGa.sub.1-XN
p-n junction layers 40 has a maximum efficiency of about 50%. The
maximum efficiency can be increased to about 56% with a solar cell
having three layers, and to about 72% with a solar cell having 36
layers.
[0066] If the x value in In.sub.XGa.sub.1-XN is 0, the
In.sub.XGa.sub.1-XN p-n junction layer has an E.sub.g of 3.4 eV. If
the x value in In.sub.XGa.sub.1-XN is 0.4, the In.sub.XGa.sub.1-XN
p-n junction layer has an E.sub.g of 1.0 eV. And, if the x value in
In.sub.XGa.sub.1-XN is 1, the In.sub.XGa.sub.1-XN p-n junction
layer has an E.sub.g of 0.7 eV. Thus, as the x value of the
In.sub.XGa.sub.1-XN increases, the In.sub.XGa.sub.1-XN p-n junction
layer has a smaller E.sub.g. Of the plurality of
In.sub.XGa.sub.1-XN p-n junction layers 40, the In.sub.XGa.sub.1-XN
p-n junction layer with a smaller x value absorbs shorter
wavelengths of sunlight. And, of the plurality of
In.sub.XGa.sub.1-XN p-n junction layers 40, the In.sub.XGa.sub.1-XN
p-n junction layer with a larger x value absorbs longer wavelengths
of sunlight.
[0067] Accordingly, by forming the plurality of In.sub.XGa.sub.1-XN
p-n junction layers 40 at the side where sunlight is incident such
that the In.sub.XGa.sub.1-XN p-n junction layers are aligned from
one having a larger E.sub.g to one having a smaller E.sub.g, it may
be configured such that the plurality of In.sub.XGa.sub.1-XN p-n
junction layers 40 can sequentially absorb the shorter to longer
wavelengths of sunlight.
[0068] For instance, if the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 includes the three In.sub.xGa.sub.1-xN p-n
junction layers 41, 42, 43 as illustrated in FIG. 1C, the third
In.sub.xGa.sub.1-xN p-n junction layer 43, which corresponds to the
outermost layer closest to the incident sunlight and contacts the
second heating portion 31, may have a x value of 0, the second (or
intermediate) In.sub.xGa.sub.1-xN p-n junction layer 42 may have a
x value of 0.4, and the first In.sub.xGa.sub.1-xN p-n junction
layer 41, which corresponds to the innermost layer and contacts the
first heating portion 21, may have a x value of 1. In this case,
sunlight may be absorbed from one with a shorter wavelength to one
with a longer wavelength, as it passes from the third
In.sub.xGa.sub.1-xN p-n junction layer 43 to the first
In.sub.xGa.sub.1-xN p-n junction layer 41.
[0069] Because the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 are directly grown on the first heating portion 21 by the
heat generated from the first heating portion 21 and are
electrically connected to the first and second heating portions 21,
31, respectively, the first and second heating portions 21, 31 may
be used as two electrodes of the solar cell 101 after the plurality
of In.sub.xGa.sub.1-xN p-n junction layers 40 have been formed.
Accordingly, the solar cell 101 may be made relatively thin and
light because no additional electrode layer is required.
[0070] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may be formed by the metal organic chemical vapor deposition
(MOCVD) method. TMIn, TEGa, and NH.sub.3 may be used as sources of
In, Ga, and N for forming the host In.sub.XGa.sub.1-XN,
respectively. Cp.sub.2Mg may be used as a p-type doping gas, and
SiH.sub.4 may be used as an n-type doping gas.
[0071] To grow In.sub.XGa.sub.1-XN, a growth temperature of about
1000.degree. C. or higher may be required. Because of the
high-temperature heating requirement, only expensive substrates
such as silicon wafer, Al.sub.2O.sub.3 substrate, SiC substrate,
etc. could be used, and there were limitations in manufacturing
large-sized solar cells. However, if In.sub.XGa.sub.1-XN is grown
using a micro-heater array, relatively high-temperature heating is
possible while maintaining the temperature of a glass substrate at
or around room temperature. As a result, In.sub.XGa.sub.1-XN p-n
junction layers may be formed on a glass substrate, and the
manufacture of large-sized solar cells becomes possible.
[0072] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may be formed symmetrically on the top and bottom surfaces of the
first heating portion 21. However, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be formed only on
the top surface of the first heating portion 21.
[0073] FIG. 2 is a cross-sectional view showing another aspect of a
solar cell using a micro-heater array according to an example
embodiment. Of the components illustrated in FIG. 2, the components
the same as those illustrated in FIG. 10 are designated by the same
reference numerals, and detailed descriptions thereof will be
omitted.
[0074] A solar cell 101 may further include a lens provided above
one or more of the first and second heating portions 21, 31,
corresponding to the area where the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 are formed, so as to
focus sunlight L onto the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40.
[0075] As illustrated in FIG. 2, in an example embodiment, the
solar cell 101 may further include a lens 60 provided above the
second heating portion 31. The lens 60 may be provided individually
at the intersection area of the first and second heating portions
21, 31, in the form of an array corresponding to the areas where
the plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 are
formed as in FIG. 1A. The lenses may be a cylinder-shape or
semicylinder-shape lenses, and may be aligned along the length
direction of the first heating portion 21 or the second heating
portion 31, corresponding to the areas where the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 are formed.
[0076] FIG. 3A and FIG. 3B are drawings of a solar cell using a
micro-heater array according to another example embodiment. Of the
components illustrated in FIG. 3A and FIG. 3B, the components the
same as those illustrated in FIG. 1A through FIG. 1C are designated
by the same reference numerals, and detailed descriptions thereof
will be omitted.
[0077] Referring to FIG. 3A and FIG. 3B, a solar cell 102 using a
micro-heater array according to another example embodiment may
include a micro-heater array and a plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40.
[0078] Each of a plurality of first and second micro-heaters 20',
30' may further include first and second connecting portions 27,
37. The construction of the micro-heater array and the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 according to this
embodiment may be the same as that of the micro-heater array and
the plurality of In.sub.xGa.sub.1-xN p-n junction layers
illustrated in FIG. 1A through FIG. 1C, except that the first and
second supports 26, 36 are not provided below the first and second
heating portions 25, 35 but below the first and second connecting
portions 27, 37.
[0079] Each of the plurality of first micro-heaters 20' may include
a first heating portion 25, first supports 26 and first connecting
portions 27. The first heating portion 25 may be spaced apart from
the substrate 10 and extends along the first direction D1. The
first connecting portions 27 extend from both sides of the first
heating portion 25 respectively, and are arranged along the length
direction of the first heating portion 25 while being spaced from
each other. The first supports 26 are provided between the
substrate 10 and the first connecting portions 27, and support the
first heating portion 25 and the first connecting portions 27.
[0080] Each of the plurality of second micro-heaters 30' may
include a second heating portion 35, second supports 36 and second
connecting portions 37. The second heating portion 35 may be spaced
apart from the substrate 10 and extends along the second direction
D2 perpendicular to the first direction D1 so as to intersect the
first heating portion 25 above the first heating portion 25. The
second connecting portions 37 may extend from both sides of the
second heating portion 35 respectively, and may be arranged along
the length direction of the second heating portion 35 while being
spaced from each other. The second supports 36 may be provided
between the substrate 10 and the second connecting portions 37, and
support the second heating portion 35 and the second connecting
portions 37.
[0081] At the intersection area of the first and second heating
portions 25, 35, the height of the first supports 26 may be smaller
than the height of the second supports 36, so that the first and
second heating portions 25, 35 may be spaced apart by a
predetermined distance. Each of the first and second heating
portions 25, 35 emits light and generates heat by the application
of voltage, and may be operated independently.
[0082] The second heating portion 35 may be formed of a transparent
electrode material, so that sunlight can be transmitted to the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 provided
below the second heating portion 35.
[0083] The construction and shape of the plurality of second
micro-heaters 30' may be the same as those of the plurality of
first micro-heaters 20', except that they may be provided above
substrate 10 in the direction perpendicular to that of the
plurality of first micro-heaters 20'. Hereinafter, the structure of
the plurality of first micro-heaters 20' will be described in
detail.
[0084] As illustrated in FIG. 3A and FIG. 3B, the first connecting
portions 27 may be provided on both sides of the first heating
portion 25, except for the intersection area of the first and
second heating portions 25, 35. In this example embodiment, the
first connecting portions 27 extend along the direction D2
perpendicular to the length direction D1 of the first heating
portion 25, and may be provided symmetrically on both sides of the
first heating portion 25. However, the first connecting portions 27
may be provided asymmetrically on both sides of the first heating
portion 25. The first connecting portions 27 may be formed of the
same material as the first heating portion 25, and formed
integrally with the first heating portion 25 for the following
processes.
[0085] The first supports 26 may be partially provided below the
first connecting portions 27, and partially contact the first
connecting portions 27. Here, each of the first connecting portions
27 may be divided into a third region A3 and a fourth region A4.
The third region A3 corresponds to a contact area CA where the
first connecting portions 27 contact the first supports 26. The
fourth region A4 may be between the first heating portion 25 and
the third region A3. In this example embodiment, the first supports
26 may be provided below each end portion of the first connecting
portions 27.
[0086] Because the first connecting portions 27 are supported by
the first supports 26, the first heating portion 25 formed
integrally with the first connecting portions 27 can be supported
by the first supports 26 without contacting the first supports 26.
Further, because the first heating portion 25 and the first
supports 26 are spaced apart from each other by the first
connecting portions 27, the shape of the first supports 26 has no
effect on the temperature distribution of the first heating portion
25. Hence, the first heating portion 25 can maintain a uniform
temperature distribution.
[0087] In the first micro-heater 20', by reducing the areas where
heat transfer occurs between the first heating portion 25 and the
first connecting portions 27 and between the first connecting
portions 27 and the first supports 26 (e.g., within the range where
the supporting is maintained), power consumption for driving the
first micro-heater 20' may be decreased.
[0088] Specifically, the thermal conductivity from both sides of
the first heating portion 25 to each of the first connecting
portions 27 decreases as the length L of the fourth area A4 of the
first connecting portions 27 increases and as the width W1, W2 of
the first connecting portions 27 decreases. Further, the thermal
conductivity from the first connecting portions 27 to the first
supports 26 decreases as the width of the contact area CA
decreases.
[0089] Accordingly, heat loss at the first heating portion 25 may
be reduced by maximizing the length L of the fourth area A4 of the
first connecting portions 27 or by minimizing the width W1, W2 of
the first connecting portions 27 and the contact area CA, within
the range where the supporting of the first heating portion 25 is
maintained. As a result, unnecessary power consumption by the first
micro-heater 20' may be reduced, and the applied voltage may be
effectively used for high-temperature heating of the first heating
portion 25.
[0090] For example, as illustrated in FIG. 3B, the width W2 of the
fourth area A4 of the first connecting portions 27 may be set
smaller than the width W3 of the first heating portion 25 in order
to reduce heat transfer from the first heating portion 25 to the
fourth region A4 of the first connecting portions 27. Further, in
order to reduce heat transfer from the first connecting portions 27
to the first supports 26, the width of the contact area CA may be
set smaller than the width W1 of the third area.
[0091] If the area of the contact area CA and the third area A3 of
the first connecting portions 27 is too small, a structural
stability may not be secured because the supporting by the first
supports 26 may be difficult. Accordingly, the area of the contact
area CA and the third region A3 may be large enough to ensure the
supporting of the first heating portion 25 and the first connecting
portions 27 by the first supports 26. Consequently, as illustrated
in FIG. 3B, the width W1 of the third region A3 and the width of
the contact area CA may be set larger than the width W2 of the
fourth region A4.
[0092] Similarly, as for the second micro-heater 30', power
consumption for the driving of the second micro-heaters 30' may be
reduced by adjusting the size of the area where heat transfer
occurs between the second heating portion 35 and the second
connecting portions 37 and between the second connecting portions
37 and the second supports 36.
[0093] Although the third area A3 and the contact area CA are shown
in a circular shape in FIG. 3A and FIG. 3B, the third region A3 or
the contact area CA may be etched to have a rectangular shape or
another shape.
[0094] Each of the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 may be directly grown on the first heating portion 25, at
the intersection area of the first and second heating portions 25,
35, using the heat generated from the first heating portion 25, and
may be electrically connected to the first and second heating
portions 25, 35, respectively. Because each of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 has different x value,
sunlight with various wavelengths may be effectively absorbed.
[0095] FIG. 4A is a plan view of a solar cell using a micro-heater
array according to still another example embodiment, and FIG. 4B is
a cross-sectional view along line II-II' in FIG. 4A. Of the
components illustrated in FIG. 4A and FIG. 4B, the components the
same as those illustrated in FIG. 1A through FIG. 1C are designated
by the same reference numerals, and detailed descriptions thereof
will be omitted.
[0096] A solar cell 103 using a micro-heater array according to
still another example embodiment may include a micro-heater array
and a plurality of In.sub.xGa.sub.1-xN p-n junction layers 40.
[0097] In this example embodiment, each of the plurality of first
micro-heaters 20 may include a first heating portion 21 and first
supports 22. The first heating portion 21 may be spaced apart from
the substrate 10 and extends in a first direction D1. The first
supports 22 may be provided partially between the substrate 10 and
the first heating portion 21 and support the first heating portion
21.
[0098] Each of the plurality of second micro-heaters 30' may
include a second heating portion 35, second supports 36 and second
connecting portions 37. The second heating portion 35 may be spaced
apart from the substrate 10 and extends in a second direction D2
perpendicular the first direction D1 to intersect the first heating
portion 21 above first heating portion 21. The second connecting
portions 37 may extend from both sides of the second heating
portion 35 respectively, and arranged along the length direction of
the second heating portion 35 while being spaced apart from each
other. The second supports 36 may be provided between the substrate
10 and the second connecting portions 37, and support the second
heating portion 35 and the second connecting portions 37.
[0099] At the intersection area of the first and second heating
portions 21, 35, the height of the first supports 22 may be lower
than the height of the second supports 36, so that the first and
second heating portions 21, 35 may be spaced apart by a
predetermined distance. Each of the first and second heating
portions 21, 35 emits light and generates heat by the applied
voltage, and may be operated independently. The second heating
portion 35 may be formed of a transparent electrode material.
[0100] As illustrated in FIG. 4A and FIG. 4B, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be formed on the
second heating portion 35 using the heat generated from the second
heating portion 35, and are electrically connected to the first and
second heating portions 25, 35, respectively. Because the plurality
of In.sub.xGa.sub.1-xN p-n junction layers 40 may include three
In.sub.xGa.sub.1-xN p-n junction layers 41, 42, 43 with different x
values, sunlight with various wavelengths may be effectively
absorbed.
[0101] FIG. 5A through FIG. 6B are drawings for illustrating a
solar cell using a micro-heater array according to further another
example embodiment. FIG. 5A is a plan view of a solar cell using a
micro-heater array according to another example embodiment, FIG. 5B
is a cross-sectional view along line III-III' in FIG. 5A, FIG. 6A
is a plan view showing a plurality of In.sub.xGa.sub.1-xN p-n
junction layers formed at the first and second heating portions of
FIG. 5A, and FIG. 6B is a cross-sectional view along line IV-IV' in
FIG. 6A.
[0102] Referring to FIG. 5A and FIG. 5B, the micro-heater array
according to this example embodiment may include a substrate 110,
and a plurality of first micro-heaters 120 and second micro-heaters
130 aligned in an alternating manner above the substrate 110 so as
to be parallel with each other.
[0103] Each of the plurality of first micro-heaters 120 may include
a first heating portion 121 and first supports 122. The first
heating portion 121 may be spaced apart from the substrate 110 and
extends in a first direction. The first supports 122 may be
provided partially between the substrate 110 and the first heating
portion 121, and support the first heating portion 121.
[0104] Like the first micro-heaters 120, each of the plurality of
second micro-heaters 130 include a second heating portion 131 and
second supports 132. The second heating portion 131 may be spaced
apart from the substrate 110 and may be aligned in parallel to the
first heating portion 121. The second supports 132 may be provided
partially between the substrate 110 and the second heating portion
131, and support the second heating portion 131.
[0105] Each of the first and second heating portions 121, 131 may
be divided into first areas A1 and second areas A2. The first areas
A1 correspond to contact areas CA at which the first and second
heating portions 121, 131 are respectively in contact with the
first and second supports 122, 132, and each of the second areas A2
may be located between the first areas A1. In the first and second
heating portions 121, 131, relatively high-temperature heating is
possible at the second areas A2 rather than the first areas A1.
[0106] As illustrated in FIG. 5A and FIG. 5B, the first
micro-heaters 120 and the second micro-heaters 130 may be aligned
in parallel, so that the first areas A1 and the second areas A2 of
the first heating portions 121 may be relatively close to the first
areas A1 and the second areas A2 of the second heating portions
131.
[0107] The first and second micro-heaters 120, 130 according to
this example embodiment have the same shape and structure as those
of the first micro-heaters 20 illustrated in FIG. 1A and FIG. 1B.
Therefore, detailed description of the first and second
micro-heaters 120, 130 according to this example embodiment will be
omitted.
[0108] Referring to FIG. 6A and FIG. 6B, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be formed on the
first heating portion 121 using the heat generated from the first
heating portion 121, and may be electrically connected to the first
and second heating portions 121, 131, respectively. Because the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 may include
three In.sub.xGa.sub.1-xN p-n junction layers 41, 42, 43 with
different x values, sunlight with various wavelengths may be
effectively absorbed.
[0109] The plurality of In.sub.xGa.sub.1-xN p-n junction layers 40
may contact the p-type In.sub.xGa.sub.1-xN layer 51a formed on the
second heating portion 131, and may be electrically connected with
the second heating portion 131. Of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40, the n-type
In.sub.xGa.sub.1-xN layer 43b of the third, i.e., the outermost,
In.sub.xGa.sub.1-xN p-n junction layer 43 contacts the p-type
In.sub.xGa.sub.1-xN layer 51a formed on the second heating portion
131.
[0110] If the outermost layer of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers formed on the first heating
portion 121 is a p-type In.sub.xGa.sub.1-xN layer, an n-type
In.sub.xGa.sub.1-xN layer may be formed on the second heating
portion 131 and contacted with the plurality of In.sub.xGa.sub.1-xN
p-n junction layer.
[0111] The construction of the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 may be the same as that of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers described referring to FIG.
1A through FIG. 1C. Therefore, detailed description thereof will be
omitted.
[0112] Although not illustrated in the drawings, the solar cell 111
according to this example embodiment may further include a lens
which is provided above the first heating portion 121,
corresponding to the area where the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 are formed, and focuses
sunlight from outside.
[0113] FIG. 6C is a cross-sectional view of the solar cell using a
micro-heater array illustrated in FIG. 5A and FIG. 5B according to
another example embodiment. Of the components illustrated in FIG.
6C, the components the same as those illustrated in FIG. 6A and
FIG. 6B are designated by the same reference numerals, and detailed
descriptions thereof will be omitted.
[0114] As illustrated in FIG. 6C, a solar cell 111' according to
another example embodiment may further include a plurality of
In.sub.xGa.sub.1-xN p-n junction layers 50 formed on a second
heating portion 131 using the heat generated from the second
heating portion 131. In this example embodiment, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 50 formed on the second
heating portion 131 may include two (first and second)
In.sub.xGa.sub.1-xN p-n junction layers 52, 53. In this case, the
outermost layer of the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 formed on the first heating portion 121, which
is the third n-type In.sub.xGa.sub.1-xN layer 43b, contacts the
outermost layer of the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 50 formed on the second heating portion 131, i.e.,
a p-type In.sub.xGa.sub.1-xN layer 53b. Accordingly, the plurality
of In.sub.xGa.sub.1-xN p-n junction layers 50 formed on the second
heating portion 131 has a structure in which a first n-type
In.sub.xGa.sub.1-xN layer 52a, a first p-type In.sub.xGa.sub.1-xN
layer 52b, a second n-type In.sub.xGa.sub.1-xN layer 53a and the
second p-type In.sub.xGa.sub.1-xN layer 53b are stacked in
sequence.
[0115] Although not illustrated in the drawings, the solar cell
111' according to this example embodiment may further include a
lens which may be provided above the first heating portion 121 and
the second heating portion 131, corresponding to the area where the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40, 50 are
formed, and focuses sunlight from outside.
[0116] FIG. 7 is a drawing for illustrating a process of forming a
solar cell having a plurality of In.sub.xGa.sub.1-xN p-n junction
layers using a micro-heater array according to an example
embodiment. In FIG. 7, the micro-heater array illustrated in FIG.
1A is drawn in a simplified version, for convenience of
illustration. FIG. 8A through FIG. 8c are cross-sectional views
along line V-V' in FIG. 7 for illustrating an example of forming a
plurality of In.sub.xGa.sub.1-xN p-n junction layers at the
intersection area of the first and second heating portions.
[0117] Referring to FIG. 7 through FIG. 8c, a method for forming a
plurality of In.sub.xGa.sub.1-xN p-n junction layer using a
micro-heater array according to an example embodiment is as
follows.
[0118] A micro-heater array may be provided in a chamber 210. A
voltage may be applied from an external power supply 220 to one of
first and second micro-heaters 20, 30. In this example embodiment,
a voltage may be applied to the first micro-heater 20 to heat a
first heating portion 21 to a relatively high temperature. The
first heating portion 21 generates high-temperature radiation heat,
commonly in the form of visible ray or IR.
[0119] Outside the chamber 210, a plurality of gas supply pipes 230
for supplying TMIn, TEGa and NH.sub.3, which are source gases of
In, Ga and N of the host material In.sub.xGa.sub.1-xN,
respectively, and for supplying Cp.sub.2Mg, which is a p-type
doping gas, and SiH.sub.4, which is an n-type doping gas, into the
chamber 210 are provided. By adjusting the supply amount of the
TMIn, TEGa and NH.sub.3, the plurality of In.sub.xGa.sub.1-xN p-n
junction layers 40 may be formed to have various compositions.
[0120] By supplying the source gases TMIn, TEGa and NH.sub.3, and
the p-type doping gas Cp.sub.2Mg into the chamber 210 via the gas
supply pipes 230 connected to the chamber 210, a first p-type
In.sub.xGa.sub.1-xN layer 41a may be grown on the first heating
portion 21 heated by the applied voltage, as illustrated in FIG.
8A.
[0121] The source gases and the p-type doping gas supplied into the
chamber 210 react directly on the first heating portion 21, which
is at a relatively high temperature, to grow the first p-type
In.sub.xGa.sub.1-xN layer 41a. The growth region of the first
p-type In.sub.xGa.sub.1-xN layer 41a may be controlled depending on
processing conditions, for example, by varying heating temperature
or heating time at the first heating portion 21. The first p-type
In.sub.xGa.sub.1-xN layer 41a may be formed on only the top surface
of the first heating portion 21 or on both the top and bottom
surfaces of the first heating portion 21.
[0122] Because relatively high-temperature heating is possible at
the second area of the first heating portion 21, which does not
directly contact the first supports 22, the first p-type
In.sub.xGa.sub.1-xN layer 41a may be grown mainly at the second
area of the first heating portion 21.
[0123] While maintaining the heating status of the first heating
portion 21, the source gases TMIn, TEGa and NH.sub.3, and the
n-type doping gas SiH.sub.4 may be supplied into the chamber 210,
so as to grow a first n-type In.sub.xGa.sub.1-x,N layer 41b on the
first p-type In.sub.xGa.sub.1-xN layer 41a, as illustrated in FIG.
8B. The source gases and the n-type doping gas supplied into the
chamber 210 react directly on the first heating portion 21, which
is at a relatively high temperature, and the first n-type
In.sub.xGa.sub.1-xN layer 41b is grown on the first p-type
In.sub.xGa.sub.1-xN layer 41a. As a result, a first
In.sub.xGa.sub.1-xN p-n junction layer 41 is formed between the
first and second heating portions 21, 31.
[0124] While controlling the supply amount of the source gases,
p-type doping gas and n-type doping gas, the process of growing the
p-type In.sub.xGa.sub.1-xN layer and the n-type In.sub.xGa.sub.1-xN
layer may be repeated to form a plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40 with different x values on the first heating
portion 21. Each of thus formed plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40 may be electrically connected with the first
and second heating portions 21, 31, respectively.
[0125] Also, as illustrated in FIG. 8c, after the formation of the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40, a process
of annealing the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 may be added. Through the annealing, the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 may be crystallized or
the contact resistance between the plurality of In.sub.xGa.sub.1-xN
p-n junction layers 40 and the first and second heating portions
21, 31 may be reduced.
[0126] A scrubber 250 may be provided below the chamber 210 to
absorb and neutralize the gas remaining in the chamber 210 after
the formation of the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40.
[0127] In the above, an example of forming the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 by an MOCVD process
using a micro-heater array according to an example embodiment has
been described. When the micro-heater array is used, only the first
or second heating portions 21, 31, at which the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 are formed, can be
locally heated at a relatively high temperature while maintaining
the temperature inside the chamber, particularly the temperature of
the substrate 10, at room temperature, unlike the typical MOCVD
process. Accordingly, In.sub.xGa.sub.1-xN p-n junction layers
requiring a high-temperature heating may be formed on a glass
substrate. Furthermore, since plasma or other complicated heating
tools are not required to form the In.sub.xGa.sub.1-xN p-n junction
layers, the fabrication process may be simplified and the solar
cell production cost may be reduced.
[0128] Because the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 may be directly grown on the first and second heating
portions 21, 31 using the relatively high-temperature heat
generated from the first and second heating portions 21, 31, the
solar cell fabrication process may be simplified.
[0129] A plurality of In.sub.xGa.sub.1-xN p-n junction layers may
be formed on the first heating portion 21 by forming an n-type
In.sub.xGa.sub.1-xN layer on the first heating portion 21 first,
and then growing a p-type In.sub.xGa.sub.1-xN layer on the n-type
In.sub.xGa.sub.1-xN layer.
[0130] As illustrated in FIG. 6B, after the formation of the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40, a process
of forming a p-type In.sub.xGa.sub.1-xN layer 51a which contacts
the plurality of In.sub.xGa.sub.1-xN p-n junction layers 40 may be
added. Specifically, by applying a voltage to the second
micro-heater 130 and supplying source gases and a p-type doping gas
into the chamber 210, the p-type In.sub.xGa.sub.1-xN layer 52a,
which contacts the outermost layer of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40, may be formed on the
second heating portion 131 heated by the applied voltage.
[0131] As illustrated in FIG. 6C, after the formation of the
plurality of In.sub.xGa.sub.1-xN p-n junction layers 40, a process
of forming a plurality of In.sub.xGa.sub.1-xN p-n junction layers
50, which contact the plurality of In.sub.xGa.sub.1-xN p-n junction
layers 40 formed on the first heating portion 121, on the second
heating portion 131 may be further added. Specifically, by applying
a voltage to the second micro-heater 130 and supplying source gases
and an n-type doping gas into the chamber 210, a first n-type
In.sub.xGa.sub.1-xN layer 52a may be formed on the second heating
portion 131 heated by the applied voltage. Then, source gases and
p-type doping gas may be supplied into the chamber 210 to grow a
first p-type In.sub.xGa.sub.1-xN layer 52b on the first n-type
In.sub.xGa.sub.1-xN layer 52a.
[0132] While controlling the supply amount of source gases, n-type
doping gas and p-type doping gas, the process of growing a second
n-type In.sub.xGa.sub.1-xN layer 53a and a second p-type
In.sub.xGa.sub.1-xN layer 53b may be repeated to form the plurality
of In.sub.xGa.sub.1-xN p-n junction layer 50 with different x
values on the second heating portion 131.
[0133] The outermost layer of the plurality of In.sub.xGa.sub.1-xN
p-n junction layer 50 formed on the second heating portion 131
contacts the outermost layer of the plurality of
In.sub.xGa.sub.1-xN p-n junction layers 40 formed on the first
heating portion 121. The outermost layers may be different type of
In.sub.xGa.sub.1-xN layers. Accordingly, a plurality of
In.sub.xGa.sub.1-xN p-n junction layers may be provided
continuously between the first and second heating portions 121,
131.
[0134] As described, in the example embodiments, because a
plurality of In.sub.xGa.sub.1-xN p-n junction layers are formed
using a micro-heater array, the temperature of the substrate may be
maintained near the room temperature during the formation of the
plurality of In.sub.xGa.sub.1-xN p-n junction layers. Accordingly,
it is possible to form the plurality of In.sub.xGa.sub.1-xN p-n
junction layers on a glass substrate, and, therefore, to fabricate
relatively large-sized, high-efficiency solar cells.
[0135] While example embodiments have been disclosed herein, it
should be understood that other variations may be possible. Such
variations are not to be regarded as a departure from the spirit
and scope of example embodiments of the present application, and
all such modifications as would be obvious to one skilled in the
art are intended to be included within the scope of the following
claims.
* * * * *