- Email: [email protected]
Preparation and properties of amorphous silicon produced by a consecutive, separated reaction chamber method
Journal of Non-Crystalline Solids 59 & 60 (1983) 1107-1110 North-Holland PublishingCompany
| 107
PREPARATION AND PROPERTIES OF AMORPHOUS SILICON PRODUCED BY A CONSECUTIVE, SEPARATED REACTION CHAMBER METHOD
M. Ohnishi, H. Nishiwaki, K. Enomoto, Y. Nakashima, S. Tsuda, T. Takahama, H. Tarui, M. Tanaka, N. Dojo, and Y. Kuwano Research Center, SANYO Electric Co., Ltd. 1-18-13 Hashiridani, Hirakata City, Osaka, Japan A new fabrication apparatus was developed from the consecutive, separated reaction chamber method in order to fabricate the multi-gap amorphous solar cell. In this fabrication process, the different amorphous materials are deposited in different reaction chambers. It was confirmed by IMA measurement that the intermixing of different amorphous materials was clearly avoided. The space charge density (Ni) of the films, into which a slight amount of ~ r o n is doped in this method, was measure d . The minimum Ni was about 2xl0-~cm -3 at the gas ratio B2H6/SiH A of 2xi0 -v. The best conversion efficiency of p-i-n amorphous solar cells fabricated by this method was 10.0%. I. INTRODUCTION Since Spear and Le Comber succeeded in the substitutional doping of amorphous silicon (a-Si) deposited by a glow discharge in SiH 4 in 1975, I) extensive research on a-Si solar cells and many other devices has been done by many workers. The conventional glow discharge method for the deposition of a-Si uses a single reaction chamber method.
This method involves the problem of the unde2) In order to solve this problem,
sirable intermixing of residual impurities.
the authors have developed a now fabrication apparatus from the consecutive, separated reaction chamber method. In this paper, the intermixing of host materials in amorphous solar cells is described, and impurity intermixing in amorphous solar cells whose i-layer only was prepared from a glow discharge decomposition of disilane (Si2H6) is also described.
The properties of a-Si films obtained by a fine control of the
slight amount of dopant, and the photovoltaic characteristics of amorphous solar cells fabricated by this method are presented.
2. CONSECUTIVE, SEPARATED REACTION CHAMBER METHOD FOR FABRICATING MULTI-GAP AMORPHOUS SOLAR CELLS Multi-gap amorphous solar cells, in which two or three amorphous solar cells which have different band gaps are stacked, have been proposed to improve the efficiency of a-Si Solar cells. 3)"
The apparatus for the fabrication of multi-
gap amorphous solar cells, which was developed from the consecutive, separated
0022-3093/83/0000-0000/$03.00 © 1983 North-Holland/Physical Society of Japan
M. Olmishi et al. / Preparation and properties o f amorphous silk'oH
1108
reaction chamber method, is shown in Fig. i.
In this apparatus, the a-SiN,
a-SiC, a-SiGe and a-SiSn films are deposited in different reaction chambers.
I Sill44- SnH4l I SiH,+GeH; I ~ Shutte r k ' ~ Substrate ~
,
~
|~'~
[1~ :II~ '
~
SiH4*C'H,~2H6 SiH4+NH3
~
I'
[1~::~::~ ~.,~
~
~
'
l.
Fig.
' k._L~
Consecutive, separated reaction chamber apparatus for the multi-gap amorphou~ solar cell.
~
Vacuum 3. INTERMIXING OF HOST MATERIALS IN AMORPHOUS SOLAR CELLS The intermixing of the host materials in the multi-gap amorphous solar cells was investigated with an ion microanalyzer (IMA).
The
IMA depth profile of
carbon (C) and nitrogen (N) atoms contained in the front cell and that of germanium (Ge) and tin (Sn) atoms contained in the back cell in the two-band multi-gap amorphous solar cell are shown in Fig. 2 (a) and (b), respectively. The intermixing of the host materials, in the case of the multi-gap solar cell prepared by the consecutive, separated reaction chamber method (represented by the solid line) decreases sharply and is very small compared with that of the single reaction chamber method (represented by the broken line), as shown in Fig. 2 (a) and (b).
The intermixing of Ge and Sn is still smaller than that of
C and N in the case of the separate chamber method, as is also shown in Fig. 2 (a) and (b).
These results indicate that the separated reaction chamber method
is superior to the single reaction chamber method for preventing of the unde-
p(SiC) TCO Glass
sirable mixing of host materials,
nJ
nl ' H01, s,dl I ~"- -
i g
,
--
'ff]
,2%+ t.U I---
Separated
. . . . Single
_z Z
Separated ...... Single 0!2 I 01.6 0,4 Depth(pro) -
0
0.2 0.4 0.6 Depth(pm) (a)
}'1/I 'II
--Separated t .... ?inglT_. . . . C . = ~
42SIN* 12c"
i
i
"(SigH6) i I J
TCO
o(s,c!\G,~.
-
_o
f 0.2
(b)
Fig. 2. IMA depth profile of carbon and nitrogen (a) and germanium and tin (b) in multi-gap amorphous solar cells.
0.4
0.6
Depth (/Jm) Fig, 3, 1MA depth profile of carbon and boron in p-i-n amorphous solar cell deposited from Si2H 6 .
M. Ohtlishi ¢'t al. / Prcl~arat#m aml properties" ~)/ atm)rph~)u.~ silic~m
1109
The authors have also investigated the intermixing of impurities in the a-S| solar cell fabricated from a glow discharge decomposition of Si2H 6.
The ib~
depth profile of boron (B) and carbon (C) atoms in Glass/TCO/p(SiC)-i-n cells whose i-layer only is deposited from a glow discharge decomposition of Si2H 6 by using the consecutive, separated reaction chamber method and the single reaction chamber method is shown in Fig.3.
B and C are intermixed undesirably to the
i-layer in the cell prepared by the single reaction chamber method, while the intermixing of B and C is prevented in the case of the separated chamber method. In order to fabricate good quality films trom a glow discharge decomposition of Si2H6, a higher RF power and a higher substrate temperature than those of SiH 4 are necessary.
It seems that these reaction conditions increase the mixing of
the residual impur[ties which remain on the surface of the electrode and the reaction chamber wails in the case of the single chamber method. This result shows that the undesirable mixing can be also avoided by using the separated chamber method in the case of Si2H 6 as well as in the case of SiH 4,
4. PROPERTIES OF THE A-SI FILMS AND PHOTOVOLTAIC PROPERTIES OF THE A-SI SOLAR CELLS in order to improve the quality of a-S| films, the authors have investigated the difference in properties between a-S| film deposited by the conventional single reaction chamber method and a-S| film deposited by the consecutive, separated reaction chamber method from the C-V characteristics of Schottky barrier diodes.
The Schottky diodes have a structure of n+ o-Si/a-Si/Au.
a-S| films were deposited by both methods.
The
Before the experiment, a p-i-n cell
was prepared by both methods, in order to duplicate the conventional preparation of the a-S| solar cell. The C-V characteristics of these two Schottky barrier diodes are shown in Fig.4.
The space charge density (Ni) of a-S| was estimated from the I/C 2 vs.V
characteristics of the Schottky barrier diodes.
The value of Ni obtained by the
separated reaction chamber method (6.62 x |014cm-3) was smaller than that of the single chamher method (3.39 x |015cm-3). The Ni of the a-S| films, into which a slight amount of boron was doped in the separated reaction chamber method, was investigated. function of the gas ratio B2H6/SiH 4 is shown in Fig.5. 2x1014 cm -3 at the gas ratio of 2x~O -6. about 1.5 ~m.
The value of Ni as a The minimum Ni was about
The depletion width of this diode is
This result shows that high quality films can be obtained in this
method by making possible a fine control of the slight amount of dopant, which was difficult in the conventional single reaction chamber method.
l l l0
M. Ohnishi et al. / Preparation and properties o f amorphous silicon
( X l O -9) Separated ........ Single
20
~
Single
e ~" (3.93X tO t5 )
E o
1~6.62X 1014(cm-3)
d(1/c~)=_2__
?
Separated
10
~, (6.62X 1014)
qeNI
°--~.%
10 .E o (=
(2!01XtO TM
10 14 - 1.0 - 0 . 8 - 0 . 6 - 0 . 4 - 0 . 2
V
0
o
2
3
B2H6/SiH 4 (XtO -6)
(V)
Fig. 4. C-V characteristics of n c-Si/a-Si/Au Schottky barrier diodes.
Fig. 5. Space charge density of the a-Si films as a function of the gas ratio B2H6/SiH 4.
p-i-n amorphous solar cells were fabricated using the consecutive, separated reaction chamber apparatus. Glass/TCO/p(SiC)in/Me lO0mW/cm 2 (AM-I).
The best conversion efficiency of
solar cells was 10.0% with a size of 4mm 2 in sunlight of
The open circuit voltage (Voc), the short circuit current
density (Isc), and the fill factor (F.F.) were 0.847V, 17.3mA/cm 2, and 0.682, respectively.
5. CONCLUSION A new fabrication apparatus was developed from the consecutive, reaction chamber method.
separated
It was confirmed by IMA measurement that intermixing
of various materials in multi gap amorphous solar cells and that of impurities in a-Si solar cells deposited from Si H can be avoided with this method. 2 6 The mlnlmum value of NI was about 2 x 1 ol4cm -3 at the B2H6/SiN 4 gas ratio of •
2 x
"
'
10-6. The best conversion efficiency of p-i-n a-Si solar cells fabricated by this
method was 10.0%.
ACKNOWLEDGEMENT This work was supported in part by the Agency of Industrial Science and Technology under the sunshine project. REFERENCES 1) W.E.Spear and P.G.Le Comber:Solid State Commun. 17 (1975) 1193 2) Y.Kuwano, M.Ohnishi et al.:16th IEEE Photovol. Spec.Conf. (1981) 698 3) S.Tsuda, N.Nakamura et al.:Jpn.J.Appl. Phys. 21 (1982) Suppl. 21-2, 251
| 107
PREPARATION AND PROPERTIES OF AMORPHOUS SILICON PRODUCED BY A CONSECUTIVE, SEPARATED REACTION CHAMBER METHOD
M. Ohnishi, H. Nishiwaki, K. Enomoto, Y. Nakashima, S. Tsuda, T. Takahama, H. Tarui, M. Tanaka, N. Dojo, and Y. Kuwano Research Center, SANYO Electric Co., Ltd. 1-18-13 Hashiridani, Hirakata City, Osaka, Japan A new fabrication apparatus was developed from the consecutive, separated reaction chamber method in order to fabricate the multi-gap amorphous solar cell. In this fabrication process, the different amorphous materials are deposited in different reaction chambers. It was confirmed by IMA measurement that the intermixing of different amorphous materials was clearly avoided. The space charge density (Ni) of the films, into which a slight amount of ~ r o n is doped in this method, was measure d . The minimum Ni was about 2xl0-~cm -3 at the gas ratio B2H6/SiH A of 2xi0 -v. The best conversion efficiency of p-i-n amorphous solar cells fabricated by this method was 10.0%. I. INTRODUCTION Since Spear and Le Comber succeeded in the substitutional doping of amorphous silicon (a-Si) deposited by a glow discharge in SiH 4 in 1975, I) extensive research on a-Si solar cells and many other devices has been done by many workers. The conventional glow discharge method for the deposition of a-Si uses a single reaction chamber method.
This method involves the problem of the unde2) In order to solve this problem,
sirable intermixing of residual impurities.
the authors have developed a now fabrication apparatus from the consecutive, separated reaction chamber method. In this paper, the intermixing of host materials in amorphous solar cells is described, and impurity intermixing in amorphous solar cells whose i-layer only was prepared from a glow discharge decomposition of disilane (Si2H6) is also described.
The properties of a-Si films obtained by a fine control of the
slight amount of dopant, and the photovoltaic characteristics of amorphous solar cells fabricated by this method are presented.
2. CONSECUTIVE, SEPARATED REACTION CHAMBER METHOD FOR FABRICATING MULTI-GAP AMORPHOUS SOLAR CELLS Multi-gap amorphous solar cells, in which two or three amorphous solar cells which have different band gaps are stacked, have been proposed to improve the efficiency of a-Si Solar cells. 3)"
The apparatus for the fabrication of multi-
gap amorphous solar cells, which was developed from the consecutive, separated
0022-3093/83/0000-0000/$03.00 © 1983 North-Holland/Physical Society of Japan
M. Olmishi et al. / Preparation and properties o f amorphous silk'oH
1108
reaction chamber method, is shown in Fig. i.
In this apparatus, the a-SiN,
a-SiC, a-SiGe and a-SiSn films are deposited in different reaction chambers.
I Sill44- SnH4l I SiH,+GeH; I ~ Shutte r k ' ~ Substrate ~
,
~
|~'~
[1~ :II~ '
~
SiH4*C'H,~2H6 SiH4+NH3
~
I'
[1~::~::~ ~.,~
~
~
'
l.
Fig.
' k._L~
Consecutive, separated reaction chamber apparatus for the multi-gap amorphou~ solar cell.
~
Vacuum 3. INTERMIXING OF HOST MATERIALS IN AMORPHOUS SOLAR CELLS The intermixing of the host materials in the multi-gap amorphous solar cells was investigated with an ion microanalyzer (IMA).
The
IMA depth profile of
carbon (C) and nitrogen (N) atoms contained in the front cell and that of germanium (Ge) and tin (Sn) atoms contained in the back cell in the two-band multi-gap amorphous solar cell are shown in Fig. 2 (a) and (b), respectively. The intermixing of the host materials, in the case of the multi-gap solar cell prepared by the consecutive, separated reaction chamber method (represented by the solid line) decreases sharply and is very small compared with that of the single reaction chamber method (represented by the broken line), as shown in Fig. 2 (a) and (b).
The intermixing of Ge and Sn is still smaller than that of
C and N in the case of the separate chamber method, as is also shown in Fig. 2 (a) and (b).
These results indicate that the separated reaction chamber method
is superior to the single reaction chamber method for preventing of the unde-
p(SiC) TCO Glass
sirable mixing of host materials,
nJ
nl ' H01, s,dl I ~"- -
i g
,
--
'ff]
,2%+ t.U I---
Separated
. . . . Single
_z Z
Separated ...... Single 0!2 I 01.6 0,4 Depth(pro) -
0
0.2 0.4 0.6 Depth(pm) (a)
}'1/I 'II
--Separated t .... ?inglT_. . . . C . = ~
42SIN* 12c"
i
i
"(SigH6) i I J
TCO
o(s,c!\G,~.
-
_o
f 0.2
(b)
Fig. 2. IMA depth profile of carbon and nitrogen (a) and germanium and tin (b) in multi-gap amorphous solar cells.
0.4
0.6
Depth (/Jm) Fig, 3, 1MA depth profile of carbon and boron in p-i-n amorphous solar cell deposited from Si2H 6 .
M. Ohtlishi ¢'t al. / Prcl~arat#m aml properties" ~)/ atm)rph~)u.~ silic~m
1109
The authors have also investigated the intermixing of impurities in the a-S| solar cell fabricated from a glow discharge decomposition of Si2H 6.
The ib~
depth profile of boron (B) and carbon (C) atoms in Glass/TCO/p(SiC)-i-n cells whose i-layer only is deposited from a glow discharge decomposition of Si2H 6 by using the consecutive, separated reaction chamber method and the single reaction chamber method is shown in Fig.3.
B and C are intermixed undesirably to the
i-layer in the cell prepared by the single reaction chamber method, while the intermixing of B and C is prevented in the case of the separated chamber method. In order to fabricate good quality films trom a glow discharge decomposition of Si2H6, a higher RF power and a higher substrate temperature than those of SiH 4 are necessary.
It seems that these reaction conditions increase the mixing of
the residual impur[ties which remain on the surface of the electrode and the reaction chamber wails in the case of the single chamber method. This result shows that the undesirable mixing can be also avoided by using the separated chamber method in the case of Si2H 6 as well as in the case of SiH 4,
4. PROPERTIES OF THE A-SI FILMS AND PHOTOVOLTAIC PROPERTIES OF THE A-SI SOLAR CELLS in order to improve the quality of a-S| films, the authors have investigated the difference in properties between a-S| film deposited by the conventional single reaction chamber method and a-S| film deposited by the consecutive, separated reaction chamber method from the C-V characteristics of Schottky barrier diodes.
The Schottky diodes have a structure of n+ o-Si/a-Si/Au.
a-S| films were deposited by both methods.
The
Before the experiment, a p-i-n cell
was prepared by both methods, in order to duplicate the conventional preparation of the a-S| solar cell. The C-V characteristics of these two Schottky barrier diodes are shown in Fig.4.
The space charge density (Ni) of a-S| was estimated from the I/C 2 vs.V
characteristics of the Schottky barrier diodes.
The value of Ni obtained by the
separated reaction chamber method (6.62 x |014cm-3) was smaller than that of the single chamher method (3.39 x |015cm-3). The Ni of the a-S| films, into which a slight amount of boron was doped in the separated reaction chamber method, was investigated. function of the gas ratio B2H6/SiH 4 is shown in Fig.5. 2x1014 cm -3 at the gas ratio of 2x~O -6. about 1.5 ~m.
The value of Ni as a The minimum Ni was about
The depletion width of this diode is
This result shows that high quality films can be obtained in this
method by making possible a fine control of the slight amount of dopant, which was difficult in the conventional single reaction chamber method.
l l l0
M. Ohnishi et al. / Preparation and properties o f amorphous silicon
( X l O -9) Separated ........ Single
20
~
Single
e ~" (3.93X tO t5 )
E o
1~6.62X 1014(cm-3)
d(1/c~)=_2__
?
Separated
10
~, (6.62X 1014)
qeNI
°--~.%
10 .E o (=
(2!01XtO TM
10 14 - 1.0 - 0 . 8 - 0 . 6 - 0 . 4 - 0 . 2
V
0
o
2
3
B2H6/SiH 4 (XtO -6)
(V)
Fig. 4. C-V characteristics of n c-Si/a-Si/Au Schottky barrier diodes.
Fig. 5. Space charge density of the a-Si films as a function of the gas ratio B2H6/SiH 4.
p-i-n amorphous solar cells were fabricated using the consecutive, separated reaction chamber apparatus. Glass/TCO/p(SiC)in/Me lO0mW/cm 2 (AM-I).
The best conversion efficiency of
solar cells was 10.0% with a size of 4mm 2 in sunlight of
The open circuit voltage (Voc), the short circuit current
density (Isc), and the fill factor (F.F.) were 0.847V, 17.3mA/cm 2, and 0.682, respectively.
5. CONCLUSION A new fabrication apparatus was developed from the consecutive, reaction chamber method.
separated
It was confirmed by IMA measurement that intermixing
of various materials in multi gap amorphous solar cells and that of impurities in a-Si solar cells deposited from Si H can be avoided with this method. 2 6 The mlnlmum value of NI was about 2 x 1 ol4cm -3 at the B2H6/SiN 4 gas ratio of •
2 x
"
'
10-6. The best conversion efficiency of p-i-n a-Si solar cells fabricated by this
method was 10.0%.
ACKNOWLEDGEMENT This work was supported in part by the Agency of Industrial Science and Technology under the sunshine project. REFERENCES 1) W.E.Spear and P.G.Le Comber:Solid State Commun. 17 (1975) 1193 2) Y.Kuwano, M.Ohnishi et al.:16th IEEE Photovol. Spec.Conf. (1981) 698 3) S.Tsuda, N.Nakamura et al.:Jpn.J.Appl. Phys. 21 (1982) Suppl. 21-2, 251