U.S. patent application number 13/394049 was filed with the patent office on 2013-08-15 for photoelectric conversion device and characteristic inspection method for same.
The applicant listed for this patent is Yoshihiro Ishitani, Kazuhide Kusakabe, Akihiko Yoshikawa. Invention is credited to Yoshihiro Ishitani, Kazuhide Kusakabe, Akihiko Yoshikawa.
Application Number | 20130208267 13/394049 |
Document ID | / |
Family ID | 44563646 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130208267 |
Kind Code |
A9 |
Yoshikawa; Akihiko ; et
al. |
August 15, 2013 |
PHOTOELECTRIC CONVERSION DEVICE AND CHARACTERISTIC INSPECTION
METHOD FOR SAME
Abstract
Disclosed is a photoelectric conversion device which inhibits
characteristic degradation caused by crystal defects, and an
inspection method for crystal defects in photoelectric conversion
devices. The photoelectric conversion device is provided with an
active layer, and a deactivator contained in the active layer.
Inventors: |
Yoshikawa; Akihiko;
(Chiba-shi, JP) ; Ishitani; Yoshihiro; (Chiba-shi,
JP) ; Kusakabe; Kazuhide; (Chiba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yoshikawa; Akihiko
Ishitani; Yoshihiro
Kusakabe; Kazuhide |
Chiba-shi
Chiba-shi
Chiba-shi |
|
JP
JP
JP |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130016345 A1 |
January 17, 2013 |
|
|
Family ID: |
44563646 |
Appl. No.: |
13/394049 |
Filed: |
March 14, 2011 |
PCT Filed: |
March 14, 2011 |
PCT NO: |
PCT/JP2011/055882 PCKC 00 |
371 Date: |
September 24, 2012 |
Current U.S.
Class: |
356/237.1;
257/103; 257/461; 257/E31.02; 257/E33.023 |
Current CPC
Class: |
H01L 31/03046 20130101;
Y02P 70/521 20151101; H01S 2301/17 20130101; H01L 31/0368 20130101;
H01L 33/32 20130101; H01S 5/34333 20130101; Y02E 10/548 20130101;
B82Y 20/00 20130101; H01L 31/105 20130101; H01L 31/075 20130101;
H01L 33/025 20130101; H01L 33/18 20130101; Y02P 70/50 20151101;
H02S 50/10 20141201; Y02E 10/544 20130101 |
Class at
Publication: |
356/237.1;
257/103; 257/461; 257/E33.023; 257/E31.02 |
International
Class: |
G01N 21/956 20060101
G01N021/956; H01L 31/0304 20060101 H01L031/0304; H01L 33/32
20100101 H01L033/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2010 |
JP |
2010-055388 |
Claims
1. A photoelectric conversion device comprising: a photoelectric
conversion unit; and a dislocation deactivation unit included in
the photoelectric conversion unit.
2. The photoelectric conversion device according to claim 1,
wherein the dislocation deactivation unit is formed to have a
crystal fault.
3. The photoelectric conversion device according to claim 1,
wherein the dislocation deactivation unit includes a photoelectric
conversion function.
4. The photoelectric conversion device according to claim 1,
further comprising: a first conductive unit formed above the
dislocation deactivation unit; and a second conductive unit formed
below the dislocation deactivation unit, wherein the first
conductive unit includes a first bandgap energy, the second
conductive unit includes a second bandgap energy, and the
dislocation deactivation unit includes a third bandgap energy, and
wherein the third bandgap energy is smaller than any of the first
bandgap energy and the second bandgap energy.
5. A photoelectric conversion device comprising: a first
In.sub.xGa.sub.yAl.sub.1-x-yN layer having a first conduction type;
an In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit
formed on the first In.sub.xGa.sub.yAl.sub.1-x-yN layer; and a
second In.sub.xGa.sub.yAl.sub.1-x-yN layer formed on the In
.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit and
having a second conduction type, wherein ranges of x and y are
defined as 0 x, y 1, and the In.sub.xGa.sub.yAl.sub.1-x-yN
photoelectric conversion unit includes an InN dislocation
deactivation unit.
6. The photoelectric conversion device according to claim 5,
wherein the InN dislocation deactivation unit has a layer thickness
equal to or less than a bimolecular layer thickness.
7. The photoelectric conversion device according to claim 5,
wherein the InN dislocation deactivation unit is formed to have a
crystal fault.
8. A crystal fault detection method of a photoelectric conversion
device comprising: a first In.sub.xGa.sub.yAl.sub.1-x-yN layer
having a first conduction type; an In.sub.xGa.sub.yAl.sub.1-x-yN
photoelectric conversion unit formed on the first
In.sub.xGa.sub.yAl.sub.1-x-yN layer; and a second
In.sub.xGa.sub.yAl.sub.1-x-y N layer formed on the
In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit and
having a second conduction type, wherein ranges of x and y are
defined as 0 x, y 1, the In.sub.xGa.sub.yAl.sub.1-x-yN
photoelectric conversion unit includes an InN dislocation detection
unit, the InN dislocation detection unit is formed to have a
crystal fault, and a crystal fault is detected based on
light-emitting property of the InN dislocation detection unit.
9. The crystal fault detection method according to claim 8, wherein
the InN dislocation detection unit has a layer thickness equal to
or less than a bimolecular layer thickness.
10. The crystal fault detection method according to claim 8,
wherein a crystal fault is detected based on cathodoluminescence
from the InN dislocation detection unit.
Description
TECHNICAL FIELD
[0001] The present invention relates to a photoelectric conversion
device and a test method of its property, and in particular, it
relates to a photoelectric conversion device that can inhibit
property deterioration due to a crystal fault and a detection
method of a crystal fault that is inherent in the photoelectric
conversion device.
BACKGROUND ART
[0002] As a photoelectric conversion element by a semiconductor,
light-emitting elements such as a light-emitting diode and a
semiconductor laser as well as light-receiving elements such as a
solar cell have been known.
[0003] The matter required for practical use and high performance
of a light-emitting element is a high-power optical output and an
increased longevity of an element. On the other hand, in a case of
a receiving element, improvement of conversion efficiency is
required. However, it is well known that a crystal fault
(dislocation) that is inherent in a semiconductor crystal
constituting a photoelectric conversion element inhibits the above
high performance and deteriorates operation property.
[0004] With reference to FIG. 8, the condition that a crystal fault
in a semiconductor crystal deteriorates operation property of a
photoelectric conversion element will be explained.
[0005] FIG. 8 is a block diagram showing the configuration of a
photoelectric conversion element 100 as one example. The
photoelectric conversion element 100 includes an n-type
semiconductor layer 101, an active layer (photoelectric conversion
unit) 102 formed on the n-type semiconductor layer 101 and a p-type
semiconductor layer 103 formed on the active layer 103. These are
formed as a basic structure of a photoelectric conversion device by
a well known semiconductor manufacture technique etc.
[0006] Here, a basic operation of the photoelectric conversion
element 100 will be briefly explained with an example of a
light-emitting element.
[0007] When a current is injected in the photoelectric conversion
element 100, an electron is injected from the n-type semiconductor
layer 101 and a hole is injected from the p-type semiconductor
layer 103. The injected electron and hole are converted to a light
by a luminescence recombination process in the active layer 102 and
output a light to the outside.
[0008] However, the photoelectric conversion element may include a
crystal fault (threading dislocation) 201 as shown in FIG. 8 due to
configuration imperfection of a semiconductor crystal. FIG. 8
schematically shows a crystal fault which is inherent in a
semiconductor crystal constituting the photoelectric conversion
element 100 and there exist a threading dislocation 201 and a
nonluminescence center 202. For example, the threading dislocation
201 that generates at an interface between a growth substrate and a
growth layer and propagates from below to the photoelectric
conversion element 100 behaves as the nonluminescence center 202
that inhibits photoelectric conversion in the active layer 102.
[0009] In particular, in a nitride semiconductor, the threading
dislocation is commonly included with a high density of 1 10.sup.8
cm.sup.-2 to 1 10.sup.10 cm.sup.-2, which becomes a major obstacle
of high performance of a light-emitting element.
[0010] As a technology to reduce influence of this crystal fault,
for example, Patent Literatures 1 and 2 below can be listed.
CITATION LIST
Patent Literature
[0011] Patent Literature1: Japanese Unexamined Patent Application
Publication No. 2006-13547A [0012] Patent Literature2: Japanese
Unexamined Patent Application Publication No. 2006-5044A
Technical Problem
[0013] The crystal fault reduction technology disclosed in Patent
Literatures 1 and 2 belongs to crystal growth technology called as
selective growth or lateral growth for those skilled in the art. In
this lateral growth process, accompanied with a normal crystal
growth, a surface treatment process such as mask formation is
required. This causes increase of the number of steps, a problem
occurs in terms of yield or manufacture cost.
[0014] The present invention is made considering these
circumstances, and an object of the present invention is to provide
a photoelectric conversion device that inhibits property
deterioration due to a crystal fault without increasing the number
of manufacture steps and a detection method of a crystal fault
which is inherent in the photoelectric conversion device.
Solution to Problem
[0015] An electric conversion device according to a first aspect of
the present invention includes a photoelectric conversion unit and
a dislocation deactivation unit included in the photoelectric
conversion unit.
[0016] In the photoelectric conversion device according to the
first aspect of the present invention, the dislocation deactivation
unit may be formed to have a crystal fault.
[0017] In the photoelectric conversion device according to the
first aspect of the present invention, the dislocation deactivation
unit may be formed to have a photoelectric conversion function.
[0018] In the photoelectric conversion device according to the
first aspect of the present invention, the photoelectric conversion
device includes a first conductive unit formed above the
dislocation deactivation unit, and a second conductive unit formed
below the dislocation deactivation unit, wherein the first
conductive unit includes a first bandgap energy, the second
conductive unit includes a second bandgap energy, and the
dislocation deactivation unit includes a third bandgap energy, and
wherein the third bandgap energy is smaller than any of the first
bandgap energy and the second bandgap energy.
[0019] Moreover, a photoelectric conversion device according to the
second aspect of the present invention includes a first
In.sub.xGa.sub.yAl.sub.1-x-yN layer having a first conduction type,
an In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit
formed on the first In.sub.xGa.sub.yAl.sub.1-x-yN layer, and a
second In.sub.xGa.sub.yAl.sub.1-x-y N layer formed on the
In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit and
having a second conduction type, wherein ranges of x and y are
defined as 0 x, y 1, and the In.sub.xGa.sub.yAl.sub.1-x-yN
photoelectric conversion unit includes an InN dislocation
deactivation unit.
[0020] In the photoelectric conversion device according to the
second aspect of the present invention, the InN dislocation
deactivation unit may be formed to have a layer thickness equal to
or less than a bimolecular layer thickness.
[0021] In the photoelectric conversion device according to the
second aspect of the present invention, the InN dislocation
deactivation unit may be formed to have a crystal fault.
[0022] In a crystal fault detection method of a photoelectric
conversion device according to the third aspect of the present
invention, the photoelectric conversion device includes a first
In.sub.xGa.sub.yAl.sub.1-x-yN layer having a first conduction type,
an In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit
formed on the first In.sub.xGa.sub.yAl.sub.1-x-yN layer, and a
second In.sub.xGa.sub.yAl.sub.1-x-yN layer formed on the
In.sub.xGa.sub.yAl.sub.1-x-yN photoelectric conversion unit and
having a second conduction type, wherein ranges of x and y are
defined as 0 x, y 1, the In.sub.xGa.sub.yAl.sub.1-x-yN
photoelectric conversion unit includes an InN dislocation detection
unit, the InN dislocation detection unit is formed to have a
crystal fault and a crystal fault is detected based on
light-emitting property of the InN dislocation detection unit.
[0023] In the crystal fault detection method of a photoelectric
conversion device according to the third aspect of the present
invention, the InN dislocation detection unit has a layer thickness
equal to or less than a bimolecular layer thickness.
[0024] In the crystal fault detection method of a photoelectric
conversion device according to the third aspect of the present
invention, a crystal fault is detected based on cathodoluminescence
from the InN dislocation detection unit.
[0025] As explained above, according to the present invention,
property deterioration due to a crystal fault can be inhibited
without increasing the number of manufacture steps even when a
crystal fault is inherent in the photoelectric conversion device.
Moreover, detection of a crystal fault is made easy, which
facilitates a product test of the photoelectric conversion
device.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a block diagram of a configuration example of a
photoelectric conversion device according to an embodiment of the
present invention.
[0027] FIG. 2 is a block diagram showing the configuration of a
photoelectric conversion unit according to an embodiment of the
present invention.
[0028] FIG. 3 is experimental data by cathodoluminescence
measurement showing operation and effects of a dislocation
deactivation unit of the present invention.
[0029] FIG. 4 is a block diagram showing the configuration of the
photoelectric conversion unit according to an embodiment of the
present invention.
[0030] FIG. 5 is a block diagram showing a configuration example of
the photoelectric conversion device according to an embodiment of
the present invention.
[0031] FIG. 6 is a block diagram showing a configuration example of
the photoelectric conversion device according to an embodiment of
the present invention.
[0032] FIG. 7 is a block diagram showing a configuration example of
the photoelectric conversion device according to an embodiment of
the present invention.
[0033] FIG. 8 is a block diagram showing a configuration example of
a photoelectric conversion device of the prior art.
DESCRIPTION OF EMBODIMENTS
[0034] Hereafter, the embodiments of the present invention will be
described below referring to the accompanying drawings.
[0035] However, the descriptions don't limit the range of the
present invention and they indicate only an example of
explanation.
First Embodiment
[0036] FIG. 1 is a block diagram showing a configuration example of
a photoelectric conversion device 10 according to the first
embodiment of the claimed invention of the present application. In
FIG. 1, the photoelectric conversion device 10 includes an n-type
gallium nitride (hereinafter, it is referred to as "n-GaN".) layer
11, a photoelectric conversion unit (Active layer) 12 formed on the
n-GaN layer 11, a p-type gallium nitride (hereinafter, it is
referred to as "p-GaN".) layer 13 formed on the photoelectric
conversion unit 12 and a dislocation deactivation unit 14 included
in the photoelectric conversion unit 12, and is formed by well
known semiconductor manufacture technology etc. Additionally, since
there is little appropriate growth substrate in a nitride-based
semiconductor, when the photoelectric conversion element 10 is
constituted, crystal faults 21 such as threading dislocation
emitted from an interface between the N--GaN layer 11 and a
substrate (figure is omitted) are included with high density of
approximately 1 10.sup.8 cm.sup.-2 to 1 10.sup.10 cm.sup.-2.
[0037] The n-GaN layer 11 is used to transport an electron, and the
p-GaN layer 13 is used to transport a hole. Accordingly,
resistivity and layer thickness of the n-GaN layer 11 and the p-GaN
layer 13 are respectively appropriately adjusted in the viewpoint
of carrier transport and a collection rate.
[0038] When the photoelectric conversion unit 12 is a
light-emitting element, an injected electron-hole is converted to a
light by a recombination process, and when it is a light receiving
element, an absorbed light is converted to electron-hole. As long
as this function is included, the photoelectric conversion unit 12
is not limited, but it preferably includes gallium nitride (GaN),
indium gallium nitride (InGaN) or indium nitride (InN) for example,
and has a forbidden band width (bandgap energy) which is smaller
than any of the n-GaN layer 11 and the p-GaN layer 13.
[0039] Here, the dislocation deactivation unit 14 will be
explained. Here, an explanation will be made with an example that
the dislocation deactivation unit 14 is an InN ultrathin film and
the photoelectric conversion unit 12 is GaN.
[0040] When InN is subjected to epitaxy growth on GaN, in a case of
growth of a surface c for example, as there is the degree of
lattice mismatch of approximately 11% between InN and GaN, a
crystal fault of high density could be newly introduced during
crystal growth. This crystal fault significantly deteriorates
conversion efficiency in a photoelectric conversion element.
However, the inventors have found that, if InN has a bimolecular
layer (2ML) or less, elastic deformation is maintained without
introducing any crystal fault and coherent growth is possible to
GaN as an underlayer.
[0041] Moreover, in this ultrathin InN film with a bimolecular
layer thickness or less, crystal growth with highly excellent
structural perfection can be performed due to immiscibility with
GaN. As a result, a formation process with self order and self stop
can be performed, and a precipitous InN/GaN interface is formed in
the atomic layer order.
[0042] When the ultrathin InN film is inserted in the photoelectric
conversion unit 12, a quantum well structure in which the ultrathin
InN film is a well layer and GaN is a barrier layer is formed. That
is, the ultrathin InN film quantum well layer may function as a
part of the photoelectric conversion unit 12.
[0043] As shown in FIG. 2, when the crystal fault 21 penetrates
through the ultrathin InN film in the photoelectric conversion unit
12, in a normal concept, it is believed that this becomes
nonluminescence center and reduces conversion efficiency (quantum
efficiency) in the photoelectric conversion unit 12. However,
contrary to the common knowledge, the inventors have found that
this penetration point does not become nonluminescence center even
if the ultrathin InN film is penetrated by the crystal fault 21.
That is, the inventors have found that the ultrathin InN film not
only constitutes a part of the photoelectric conversion unit 12 by
itself but also constitutes the dislocation deactivation unit 14
that eliminates nonluminescence due to a crystal fault.
[0044] Operation and effects of the dislocation deactivation unit
14 which depart from the conventional common knowledge will be
explained with property which is particular to the ultrathin InN
film.
[0045] FIG. 3 shows a result of cathodoluminescence (CL)
observation (CL image) of a sample which is grown on a GaN
underlayer of a quantum well structure constituted by an ultrathin
InN film well layer whose thickness is limited to a monomolecular
layer thickness (1ML-InN) and a GaN layer. The CL observation
refers to irradiating an accelerated electron beam from a sample
surface to execute spectrofluorometric measurement from a sample.
By controlling accelerating voltage of the accelerated electron
beam Vacc, the insertion depth of an electron beam is controlled to
obtain luminescence distribution information of a desired layer
structural region (depth position).
[0046] FIG. 3 shows respective CL image when an observation region
is 19 19 m.sup.2 and accelerating voltage Vacc is varied in the
same field of view. The accelerating voltage Vacc of 3 kV, 6 kV, 14
kV and 18 kV respectively correspond to the electron beam insertion
length of 48 nm, 160 nm, 710 nm and 1100 nm. That is, when the
accelerating voltage Vacc is 3 kV and 6 kV, mainly luminescence
distribution from 1ML-InN quantum well is observed, and when the
accelerating voltage Vacc is 14 kV and 18 kV, mainly luminescence
distribution from GaN underlayer is observed.
[0047] In the CL images, white contrast corresponds to a
luminescence region, and black contrast corresponds to a
nonluminescence region (nonluminescence center), that is, the
crystal fault 21 exists.
[0048] First, the CL images with the accelerating voltage Vacc is
14 kV and 18 kV are focused. Several scotomas are observed, and
these are considered as crystal faults included in the GaN
underlayer. Circular frames as a mark are applied to these
scotomas.
[0049] On the other hand, in FIG. 3, focusing on the CL images with
the accelerating voltage Vacc of 3 kV and 6 kV, it is found that
regions of the circular frames as a mark applied to the crystal
faults illuminate relatively brighter than its circumference.
Conventionally, it has been considered that, in a region in which
the crystal fault 21 is included in the GaN underlayer,
luminescence efficiency of a quantum well grown on the region is
deteriorated due to influence of the crystal fault 21. However,
contrary to this common knowledge, it is firstly shown that
luminescence efficiency of the ultrathin InN film is not
deteriorated irrespective of the existence of the crystal fault 21.
This surprisingly experimental fact clearly shows that the
ultrathin InN film not only constitutes a part of the photoelectric
conversion unit 12 by itself but also constitutes the dislocation
deactivation unit 14 that eliminates nonluminescence due to a
crystal fault.
[0050] Moreover, when the experimental results shown in FIG. 3 are
interpreted from another point of view, it can be thought that the
ultrathin InN film is formed in an island shape whose surface
coverage is 1 or less.
[0051] Hereinafter, forming of this island ultrathin InN film and
its operation and effects will be explained.
[0052] In FIG. 3, in the CL images with the accelerating voltage
Vacc of 3 kV ad 6 kV, that is, luminescence distribution images of
a 1ML-InN quantum well region, the matter that the region shown by
the circular frames as a mark is relatively brighter than the
circumference can also be understood as improvement of luminescence
strength because a quantum well structure is formed only in this
region. That is, it can be thought that the ultrathin InN film is
selectively grown to include the crystal fault 21 and an island
structure as shown in FIG. 4 is formed.
[0053] That is, the dislocation deactivation unit 14 is not
necessarily a sequential film whose surface coverage is 1, and it
can eliminate nonluminescence due to the crystal fault 21 if it is
an island including the crystal fault 21, that is, in a
configuration with surface coverage is 1 or less.
[0054] As stated above, according to the first embodiment, property
deterioration due to the crystal fault 21 can be inhibited even
when the crystal fault 21 is inherent in the photoelectric
conversion unit 12 of the photoelectric conversion device 10.
APPLIED EXAMPLE 1
[0055] As the first application of a photoelectric conversion
element by nitride semiconductor, a light-emitting diode (LED) in
an ultraviolet wavelength region has received attention. In
particular, in a short wavelength region less than 365 nm which is
a band edge wavelength of GaN, accompanied with a shorter
wavelength of luminescence wavelength, luminescence efficiency is
rapidly deteriorated. Here, efficiency improvement of an
ultraviolet LED due to a nonluminescence center inhibition effect
of the ultrathin InN film will be explained.
[0056] FIG. 5 is a block diagram showing a configuration example of
a photoelectric conversion device 30 which is Applied Example 1
related to the first embodiment of the claimed invention of the
present application. In FIG. 5, the photoelectric conversion device
30 includes an n-type aluminum gallium nitride (hereinafter, it is
referred to as "n-AlGaN") layer 31, a photoelectric conversion unit
(Active layer) 32 formed on the n-AlGaN layer 31, a p-type aluminum
gallium nitride (hereinafter, it is referred to as "p-AlGaN") layer
33 formed on the photoelectric conversion unit 32 and the
photoelectric conversion unit 32 including a dislocation
deactivation unit 34, and is formed by well known semiconductor
manufacture technology etc.
[0057] The photoelectric conversion unit 32 is preferably
constituted by gallium nitride (GaN), aluminum gallium nitride
(AlGaN) or aluminum indium gallium nitride (AlInGaN) for example,
and has a forbidden band width (bandgap energy) which is smaller
than any of the n-AlGaN layer 31 and the p-AlGaN layer 33. The
dislocation deactivation unit 34 is constituted by ultrathin InN
film.
[0058] The n-AlGaN layer 31 is used to transport an electron. The
p-AlGaN layer 33 is used to transport a hole. Accordingly,
resistivity and layer thickness of the n-AlGaN layer 31 and the
p-AlGaN layer 33 are respectively appropriately adjusted to perform
efficient carrier transport. The photoelectric conversion unit 32
converts injected electron-hole into ultraviolet light by a
recombination process.
[0059] Next, inhibition of nonluminescence center and efficiency
improvement of ultraviolet LED by the dislocation deactivation unit
34 will be explained. Here, a case where the photoelectric
conversion unit 32 is AlGaN will be explained.
[0060] By increasing Al composition of AlGaN constituting the
n-AlGaN layer 31, the p-AlGaN layer 33 and the photoelectric
conversion unit 32, the luminescence wavelength of an ultraviolet
LED becomes shorter. However, generally, when Al composition of
AlGaN is increased, difficulty of crystal growth is more
significant, and density of the crystal fault 21 included in the
photoelectric conversion device 30 increases. Consequently,
luminescence efficiency is deteriorated.
[0061] However, when ultrathin InN film is inserted in the
photoelectric conversion unit 32, as shown in FIG. 3,
nonluminescence due to the crystal fault 21 is reduced. That is, in
the photoelectric conversion device 30 which is an ultraviolet LED,
deterioration of luminescence efficiency accompanied by decrease of
the luminescence wavelength can be inhibited by configuring the
dislocation deactivation unit 34 by ultrathin InN film.
[0062] As described above, according to the applied example 1,
property deterioration due to a crystal fault 21 can be inhibited
even when a crystal fault 21 is inherent in the photoelectric
conversion unit 32 of the photoelectric conversion device 30.
APPLIED EXAMPLE 2
[0063] As the second application of the photoelectric conversion
element by nitride semiconductor, a green laser and red-infrared
wavelength region light-emitting diode (LED) has received
attention. In particular, in a long wavelength region more than 500
nm, accompanied with a longer wavelength of luminescence
wavelength, luminescence efficiency is sharply deteriorated. Here,
efficiency improvement of a green laser and red-infrared wavelength
region LED due to a nonluminescence center inhibition effect of the
ultrathin InN film will be explained.
[0064] FIG. 6 is a block diagram showing a configuration example of
a photoelectric conversion device 40 which is Applied Example 2
related to the first embodiment of the claimed invention of the
present application. In FIG. 6, the photoelectric conversion device
40 includes an n-type indium gallium nitride (hereinafter, it is
referred to as "n-InGaN") layer 41, a photoelectric conversion unit
(Active layer) 42 formed on the n-InGaN layer 41, a p-type indium
gallium nitride (hereinafter, it is referred to as "p-InGaN") layer
43 formed on the photoelectric conversion unit 42 and a dislocation
deactivation unit 44 included in the photoelectric conversion unit
42, and is formed by well known semiconductor manufacture
technology etc.
[0065] The photoelectric conversion unit 42 is preferably
constituted by indium nitride (InN), indium gallium nitride (InGaN)
or aluminum indium gallium nitride (AlInGaN) for example, and has a
forbidden band width (bandgap energy) which is smaller than any of
the n-InGaN layer 41 and the p-InGaN layer 43. The dislocation
deactivation unit 44 is constituted by ultrathin InN film.
[0066] The n-InGaN layer 41 is used to transport an electron. The
p-InGaN layer 43 is used to transport a hole. Accordingly,
resistivity and layer thickness of the n-InGaN layer 41 and the
p-InGaN layer 43 are respectively appropriately adjusted to perform
efficient carrier transport. The photoelectric conversion unit 42
converts injected electron-hole into a light by a recombination
process.
[0067] Next, inhibition of nonluminescence center and efficiency
improvement of the green laser and red-infrared wavelength region
LED by the dislocation deactivation unit 44 will be explained.
Here, a case where the photoelectric conversion unit 42 is InGaN
will be explained.
[0068] By increasing In composition of InGaN constituting the
n-INGaN layer 41, the p-InGaN layer 43 and the photoelectric
conversion unit 42, the luminescence wavelength of the green laser
and red-infrared wavelength region LED becomes longer. However,
generally, when In composition of InGaN is increased, difficulty of
crystal growth is more significant, and density of the crystal
fault 21 included in the photoelectric conversion device 40
increases. Consequently, luminescence efficiency is
deteriorated.
[0069] However, when ultrathin InN film is inserted in the
photoelectric conversion unit 42, as shown in FIG. 3,
nonluminescence due to the crystal fault 21 is reduced. That is, in
the photoelectric conversion device 40 which is a green laser and
red-infrared wavelength region LED, deterioration of luminescence
efficiency accompanied by increase of the luminescence wavelength
can be inhibited by configuring the dislocation deactivation unit
44 by ultrathin InN film.
[0070] As described above, according to the applied example 2
property deterioration due to a crystal fault 21 can be inhibited
even when a crystal fault 21 is inherent in the photoelectric
conversion unit 42 of the photoelectric conversion device 40.
APPLIED EXAMPLE 3
[0071] As the third application of the photoelectric conversion
element by nitride semiconductor, a solar cell corresponding to a
wide solar light spectrum is has received attention. In particular,
since the nitride semiconductor includes a high density crystal
fault, junction property of a solar cell is inferior. Here,
efficiency improvement of a nitride solar cell due to a dislocation
deactivation effect of the ultrathin InN film will be
explained.
[0072] FIG. 7 is a block diagram showing a configuration example of
a photoelectric conversion device 50 which is Applied Example 3
related to the first embodiment of the claimed invention of the
present application. In FIG. 7, the photoelectric conversion device
50 includes an n-type aluminum indium gallium nitride (hereinafter,
it is referred to as "n-AlInGaN") layer 51, a photoelectric
conversion unit (Depletion layer) 52 formed on the n-AlInGaN layer
51, a p-type aluminum indium gallium nitride (hereinafter, it is
referred to as "p-AlInGaN") layer 53 formed on the photoelectric
conversion unit 52 and a dislocation deactivation unit 54 included
in the photoelectric conversion unit 52, and is formed by well
known semiconductor manufacture technology etc.
[0073] The photoelectric conversion unit 52 is preferably
constituted by gallium nitride (GaN), indium gallium nitride
(InGaN), aluminum indium nitride (AlInN) or aluminum indium gallium
nitride (AlInGaN) for example, and has a forbidden band width
(bandgap energy) which is smaller than any of the n-AlInGaN layer
51 and the p-AlInGaN layer 53. The dislocation deactivation unit 54
is constituted by the ultrathin InN film.
[0074] The n-AlInGaN layer 51 is used to transport an electron. The
p-AlInGaN layer 53 is used to transport a hole. Accordingly,
resistivity and layer thickness of the n-AlInGaN layer 51 and the
p-AlInGaN layer 53 are respectively appropriately adjusted in the
viewpoint of carrier transport and a collection rate. The
photoelectric conversion unit 52 converts an absorbed light into
electron-hole.
[0075] Next, improvement of junction property of the solar cell and
efficiency improvement of the nitride solar cell by the dislocation
deactivation unit 54 will be explained. Here, a case where the
photoelectric conversion unit 52 is InGaN will be explained.
[0076] By increasing In composition of InGaN constituting the
n-AlInGaN layer 51, the p-AlInGaN layer 53 and the photoelectric
conversion unit 52, a solar cell that covers substantially the
entire region of solar spectrum is configured. However, generally,
when In composition of AlInGaN and InGaN is increased, difficulty
of crystal growth is more significant, and density of the crystal
fault 21 included in the photoelectric conversion device 50
increases. Consequently, junction property of a solar cell is
deteriorated and conversion efficiency of a solar cell is
deteriorated.
[0077] However, when ultrathin InN film is inserted in the
photoelectric conversion unit 52, as shown in FIG. 3, a dislocation
deactivation effect due to the crystal fault 21 is generated. That
is, in the photoelectric conversion device 50 which is a solar
cell, a decrease of conversion efficiency accompanied by
deterioration of conjunction property of a solar cell can be
inhibited by configuring the dislocation deactivation unit 54 by
ultrathin InN film.
[0078] As described above, according to the applied example 3
property deterioration due to a crystal fault 21 can be inhibited
even when a crystal fault 21 is inherent in the photoelectric
conversion unit 52 of the photoelectric conversion device 50.
Second Embodiment
[0079] In the first embodiment, operation and effects of the
dislocation deactivation unit by ultrathin InN film have been
stated. Incidentally, when an experimental result shown in FIG. 3
is interpreted from another viewpoint, it is found that ultrathin
InN film can be used as a dislocation detection unit 15.
Hereinafter, operation and effects of the dislocation detection
unit 15 by ultrathin InN film will be explained.
[0080] A growth mechanism of ultrathin InN film is a self-order and
self-stop process in which an excessive InN than designed film
thickness is provided to be evaporated and removed on a growth
surface. However, it can be thought that InN is fixed by a pin in a
region in which a crystal fault exists, and thus an evaporation and
removal rate is inhibited to regions that include no crystal
fault.
[0081] Accordingly, as shown in FIG. 4, it is interpreted that
ultrathin InN film grows as a fractional layer InN only in a region
in which a crystal fault exists. The fractional layer InN means
that a surface coverage is 1 or less. For example, 0.5 molecular
layer corresponds to an island structure with monomolecular layer
thickness and surface coverage of 50%, that is, a quantum disk
structure.
[0082] Generally, to detect crystal dislocation, observation means
by a transmission electron microscope or pit detection by etching
process (etch pit) are known. Any of these methods belong to
destruction inspection of a sample, and their processes are
complicated.
[0083] However, cathodoluminescence (CL) observation basically
belongs to nondestructive inspection, and no previous process to a
sample is needed. Consequently, detection of a crystal fault
becomes easy, which makes a product test of the photoelectric
conversion device simple.
[0084] Moreover, in the conventional CL observation, a crystal
fault has been evaluated as a scotoma in a CL image. This is not
problematic since a high contrast ratio to a scotoma can be
obtained in a sample with high luminescence efficiency. However, in
a sample with low luminescence efficiency, that is, in a case where
dislocation detection is highly needed, a scotoma exists in a
relatively dark field of vision, so that a light-dark contrast of
the CL image cannot be fully obtained.
[0085] However, in this embodiment, by inserting ultrathin InN film
in the photoelectric conversion unit 12 of the photoelectric
conversion device 10, the ultrathin InN film is formed to have the
crystal fault 21 and shows luminescence property. Consequently, the
ultrathin InN film may be used as the dislocation detection unit
15.
[0086] As stated above, according to the second embodiment, by
observing the dislocation detection unit 15 in a case where a
crystal fault 21 is inherent in the photoelectric conversion unit
12 of the photoelectric conversion device 10, the crystal fault 21
can be easily detected. This makes a product test of the
photoelectric conversion device 10 simple.
[0087] Additionally, in each embodiment described above, an example
in which the ultrathin InN film is constituted by 1 layer has been
explained. However, not limited to this, for example, a
configuration in which a number of ultrathin films InN are inserted
is also acceptable.
[0088] Furthermore, the present invention shall not be limited by
the above-described embodiments, and modification, substitution,
and abbreviation are possible within the range which is not
deviated from the intention of the present invention.
[0089] Moreover, as it is clear from the above embodiments, layers
including nitride which sandwich the photoelectric conversion unit
have conductivity and are expressed as a first conductive unit and
a second conductive unit. In addition, focusing on materials, the
first and second conductive units are respectively expressed as a
In.sub.xGa.sub.yAl.sub.1-x-yN layer, and in particular, the first
conductive unit is expressed as a first conduction type
In.sub.xGa.sub.yAl.sub.1-x-yN layer and the second conductive unit
is expressed as a second conduction type
In.sub.xGa.sub.yAl.sub.1-x-yN layer. Additionally, in such a case,
x and y may be the same or different, and a range of x and y may be
0 x, y 1.
[0090] Also, as it is clear from the above embodiments, the
photoelectric conversion unit can be expressed as an
In.sub.xGa.sub.yAl.sub.1-x-yN layer.
[0091] Moreover, as it is clear from the above embodiments, the
first conductive unit, the second conductive unit and the
photoelectric conversion unit respectively include bandgap energy.
In addition, it is preferable that bandgap energy of a third
conductive unit (the third bandgap energy) is smaller than any of
bandgap energy of the first conductive unit (the first bandgap
energy) and bandgap energy of the second conductive unit (the first
bandgap energy).
INDUSTRIAL APPLICABILITY
[0092] The photoelectric conversion device according to the present
of the invention is applicable for a light-emitting element and a
light-receiving element which are available with a
ultraviolet-infrared light, especially a solar cell.
EXPLANATION OF NUMERALS
[0093] 10, 30, 40, 50, 100 . . . photoelectric conversion device
[0094] 11 . . . n-type gallium nitride layer [0095] 13 . . . p-type
gallium nitride layer [0096] 12, 32, 42, 52, 102 . . .
photoelectric conversion unit [0097] 14, 34, 44, 54 . . .
dislocation deactivation unit [0098] 15 . . . dislocation detection
unit [0099] 31 . . . n-type aluminum gallium nitride layer [0100]
33 . . . p-type aluminum gallium nitride layer [0101] 41 . . .
n-type indium gallium nitride layer [0102] 43 . . . p-type indium
gallium nitride layer [0103] 51 . . . n-type aluminum indium
gallium nitride layer [0104] 53 . . . p-type aluminum indium
gallium nitride layer [0105] 101 . . . n-type semiconductor layer
[0106] 103 . . . p-type semiconductor layer [0107] 21, 201 . . .
crystal fault [0108] 202 . . . nonluminescence center
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