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Ge triple-junction solar cells for space use
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NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 745–749 www.elsevier.com/locate/nimb
Effects of 0.28–2.80 MeV proton irradiation on GaInP/GaAs/Ge triple-junction solar cells for space use Wang Rong a,b,c,*, Liu Yunhong b, Sun Xufang b a
Key Laboratory of Beam Technology and Materials Modification, Ministry of Education, Beijing Normal University, Beijing 100875, China b Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875, China c Beijing Radiation Center, Beijing 100875, China Received 6 October 2007; received in revised form 17 December 2007 Available online 28 December 2007
Abstract GaInP/GaAs/Ge triple-junction solar cells were irradiated with 0.28, 0.62 and 2.80 MeV protons with fluences ranging from 1 1010 cm 2 to 1 1013 cm 2. Their performance degradation is analyzed using current–voltage characteristics and spectral response measurements. The degradation rates of the short circuit current, open circuit voltage, and maximum power output increase with fluence, but decrease with increasing proton energy. It was also observed that the spectral response of the GaAs middle cell degrades more significantly than that of the GaInP top cell. Ó 2008 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 84.60.Jt Keywords: GaInP/GaAs/Ge solar cell; Proton irradiation; Spectral response
1. Introduction In recent years, with the development of satellites that require more power, high efficiency multi-junction (MJ) solar cells have been developed. GaInP/GaAs/Ge triplejunction (3J) solar cells have achieved a high conversion efficiency of over 31.7% (AM1.5) [1], and have great potential for space applications. For space applications it is important to investigate the radiation damage to the cells and clarify the degradation mechanism. The radiation environment near the Earth mainly consists of protons and electrons trapped in the Earth’s geomagnetic field and protons produced by solar flares. The degradation behavior of solar cells due to proton irradiation is stronger than that from electrons because the density of collision events per
* Corresponding author. Address: Key Laboratory of Beam Technology and Materials Modification, Ministry of Education, Beijing Normal University, Beijing 100875, China. E-mail address: [email protected] (W. Rong).
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.076
particle impact is several orders of magnitude higher. Furthermore, degradation induced by medium-energy protons is much larger than for high-energy protons [2,3]. It is thus necessary to investigate medium-energy proton irradiation effects on the GaInP/GaAs/Ge triple-junction solar cells. 2. Experiment Fig. 1 shows a schematic of the solar cells used in this study, which were fabricated by metal–organic chemical vapor deposition (MOCVD). The dimensions of each part of the solar cell are shown in detail in Fig. 1. The solar cells with no cover glass mainly consist of three sub-cells: a GaInP sub-cell (top part), GaAs sub-cell (middle part), and a Ge sub-cell (bottom part). The middle sub-cell is connected with the top and bottom ones in series through the tunnel junctions TJ1 and TJ2, respectively. The solar cells were irradiated with 0.28, 0.62 and 2.80 MeV protons (energies chosen mainly according to the depth of the induced damage in the cell and by
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W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
3. Results and discussion 3.1. I–V characteristics
Fig. 1. Schematic structure of GaInP/GaAs/Ge triple-junction solar cells.
Normalized Isc Normalized Voc Normalized Pmax
comparison with the results in [3]) using a 1.7 MV tandem accelerator. The fluences ranged from 1 1010 cm 2 to 1 1013 cm 2 with a flux of 5 108 cm 2 s 1, low enough to avoid heating of the cells during irradiation. I–V characteristics of the solar cells before and after irradiation were measured (25 °C) under AM0 using a LAPSS solar simulator with illumination at 136.7 mW cm 2. The spectral responses of the solar cells before and after irradiation were measured using a system consisting of a chopped light source, a bias light source, a monochromator, and a lock-in amplifier.
I–V characteristics of the initial and the irradiated solar cells were measured. Fig. 2 shows the degradation of the normalized short-circuit current (Isc), normalized open-circuit voltage (Voc), and normalized maximum power output (Pmax) as a function of proton irradiation fluence for different proton energies. From Fig. 2, one can see that proton irradiation at the lowest fluence leads to almost no performance degradation of the cells, but for fluences from 1 1011 cm 2 to 1 1013 cm 2, the degradation rates of Isc, Voc and Pmax increase with fluence, and Pmax has the most severe degradation. From Fig. 2(b) and (c) the degradation of Isc is much larger than that of Voc, that is, the overall irradiation response is primarily controlled by the degradation of Isc. This is indicative of a decrease in the minority-carrier diffusion length in the base region [4]. Table 1 lists the changes in the solar cells as a function of proton energy at a fluence of 1 1012 cm 2. From Table 1, the degradation rates of Isc, Voc, and Pmax decrease with proton energy, and irradiation with proton energies of 0.28 MeV produces the highest degradation rates. From Fig. 2 the degradation rates of all quantities also decrease for the other fluences not given in Table 1 as the proton energy increases. 3.2. Degradation of the spectral response Changes of the spectral responses of the middle and top sub-cells before and after irradiation at an energy of
1.0
a
0.8 0.6 0.4
0.28 MeV 0.62 MeV 2.80 MeV
0.2 0.0 1.0
b
0.8 0.6
0.28 MeV 0.62 MeV 2.80 MeV
0.4 0.2 0.0 1.0
c
0.8 0.6 0.28 MeV 0.62 MeV 2.80 MeV
0.4 0.2 0.0 10
10
11
10
12
10
Proton fluence/cm
13
10
-2
Fig. 2. Changes in electronic properties of GaInP/GaAs/Ge solar cells as a function of proton irradiation fluence and energy.
W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
The spectral response of the solar cells mainly drops in wavelength from 650 to 900 nm of the middle GaAs cell as the irradiation energy increases, since irradiation decreases the longer wavelength spectral response more significantly than that of the shorter wavelength in the middle GaAs cell. The spectral response hardly decreases in the wavelength range from 350 to 650 nm. Again, the spectral response of the middle GaAs cell degrades more than that of the top GaInP cell. The spectral response curves of the solar cells as a function of the proton energy can be explained with results of the irradiation-induced vacancies produced in the solar cells simulated by the Monte Carlo code SRIM [8]. The full damage cascades and displacement energies (10 eV for Ga and As, 6.7 eV for In, 8.7 eV for P, 27.5 eV for Ge) [9] have been used. The simulated results of the vacancies created in the solar cells after irradiation with energies of 0.28 MeV and 0.62 MeV are shown in Fig. 5. Both energies produce non-uniform vacancy depth distribution, and most are generated near the end of range. 0.28 MeV protons penetrate beyond the pn junction of the GaInP sub-cell and the pn junction of the GaAs sub-cell and mainly damage the base region of the GaAs sub-cell. The proton-induced atom displacements result in vacancies, interstitial atoms or complexes which capture charge carriers, thereby reducing the minority carrier diffusion length in the base region of the cell [4]. Irradiation thus degrades the spectral response primarily of the middle GaAs cell for wavelengths from 650 to 900 nm [10]. Protons (0.62 MeV) penetrate beyond the pn junctions of three sub-cells and mainly damage the base region of Ge sub-cell. The peak of 2.80 MeV protoninduced vacancies is far from the major active region of the triple-junction solar cell (omitted in Fig. 5).
Table 1 Changes in the properties of the solar cells as a function of proton energy Proton energy (MeV)
Isc degradation rate (%)
Voc degradation rate (%)
Pmax degradation rate (%)
0.28 0.62 2.80
60.4 40.1 18.6
23.4 17.6 13.1
74.8 55.9 36.8
747
0.62 MeV with different fluences are shown in Fig. 3. Since Isc of the bottom cell is much larger than that of the two others, its was not plotted [5]. From Fig. 3, the degradation of the spectral response increases with fluence, but the spectral response of the solar cells mainly drops in wavelength range from 650 to 900 nm (corresponding to the middle GaAs cell) as the fluence increases from 1 1010 to 1 1013 cm 2. Furthermore, irradiation decreases the longer wavelength spectral response more significantly than that of the shorter wavelength of the middle GaAs cell. The spectral response in the wavelength region from 350 nm to 650 nm (corresponding to the top GaInP sub-cell) hardly decreases for fluences less than 1 1013 cm 2, but is reduced remarkably from 350 to 550 nm after a high fluence of 1 1013 cm 2. This is mainly due to damage on the emitter layer and the interface of the top sub-cell, which increases the recombination velocity of the carriers and reduces the carrier life after a certain level of irradiation [6,7]. The spectral response of the middle GaAs cell degrades more than that of the top GaInP cell for 0.62 MeV irradiation. Changes of the spectral response before and after irradiation with different energies are shown in Fig. 4. The degradation of the spectral response decreases with proton energy, in agreement with the results of I–V characteristics.
1.0
GaAs middle cell
GaInP top cell
Quantum Efficiency
0.8
0.6
pre-irradiation
0.4
0.2
1*1 0
10
1*10
11
cm
-2
1*10
12
cm
-2
1*10
13
cm
-2
cm
-2
0.0 300
400
500
600
700
800
900
W avelength/nm Fig. 3. Spectral response of solar cells after irradiation with 0.62 MeV protons with different fluences.
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W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749 1.0
GaAs middle cell
GaInP top cell
Quantum Efficiency
0.8
0.6
0.4
pre-irradiation 0.28 MeV 0.62 MeV 2.80 MeV
0.2
0.0 300
400
500
600
700
800
900
Wavelength/nm
120
Ge
GaAs
GaInP
Fig. 4. Spectral response for different proton energies after a fluence of 1 1012 cm 2.
0.28 MeV 0.62 MeV
Vacancies/um/ion
100
80
60
40
20
0 0
1
2
3
4
5
6
7
8
Target Depth / um Fig. 5. Damage distribution of 0.28 and 0.62 MeV protons in the solar cell.
Therefore, irradiation with a proton energy of 0.28 MeV gives rise to the highest vacancy density near the pn junction in the middle GaAs cell. Thus, the largest degradation rates of Isc, Voc, and Pmax of the solar cells are related to the proton-induced vacancies near the pn junction in the middle GaAs sub-cell. That is, the maximum degradation of these parameters and the spectral response at 0.28 MeV was attributed to the middle GaAs sub-cell. In [3] we
obtained a similar degradation at 0.30 MeV, which was attributed to the entire GaAs/Ge cell. 4. Conclusions The degradation rates of Isc, Voc, Pmax and the spectral response increase with fluence, but the degradation rates decrease with proton energy, i.e. irradiation at 0.28 MeV
W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
gives rise to the highest degradation rates. The increasing degradation rates with decreasing energy are related to the location of the proton-induced Bragg peak with respect to the major active region of the solar cell. For the proton energies used in this study the spectral response of the middle GaAs cell degrades more significantly than that of the top GaInP cell. Thus, the irradiation tolerance of the triple-junction solar cells is dominated by the middle GaAs sub-cell. Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant No. 10675023, and by Beijing Excellent Personality Foundation. References [1] M. Yamaguchi, Multi-junction solar cells and novel structures for solar cell applications, Physica E 14 (2002) 84. [2] Wang Rong, Guo Zengliang, Zhang Xinghui, et al., 5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use, Sol. Energ. Mater. Sol. Cell. 77 (2003) 351.
749
[3] Wang Rong, Guo Zengliang, Wang Guangpu, Low energy proton irradiation effects on GaAs/Ge space solar cells, Sol. Energ. Mater. Sol. Cell. 90 (2006) 1052. [4] N. Dharmarasu, M. Yamaguchi, A. Khan, et al., High-radiationresistant InGaP, InGaAsP, and InGaAs solar cells for multijunction solar cells, Appl. Phys. Lett. 79 (15) (2001) 2399. [5] H. Cotal, R. King, M. Haddad, et al., The effects of electron on triplejunction GaInP/GaAs/Ge solar cells, Proc. IEEE 28th PVSC (2000) 1316. [6] T. Sumita, M. Imaizumi, S. Matsuda, et al., Proton radiation analysis of multi-junction space solar cells, Nucl. Instr. and Meth. Phys. Res. B 206 (2003) 448. [7] R. Kachare, B.E. Anspaugh, Spatial resolution and nature of defects produced by low-energy proton irradiation of GaAs solar cells, Appl. Phys. Lett. 49 (21) (1986) 1459. [8] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, The Stopping and Range of Ions in Matter, SRIM Version: SRIM-2006.01, downloaded from http://www.srim.org. [9] ESA-GSP Work Package 1 Study Report: Predicting Displacement Damage Effects in Electronic Components by Methods of Simulation. 2002, 15157/01/NL/PA. [10] N. Dharmarasu, A. Khan, M. Yamaguchi, et al., Effect of proton irradiation on n+ p InGaP solar cells, J. Appl. Phys. 91 (5) (2002) 3306.
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 745–749 www.elsevier.com/locate/nimb
Effects of 0.28–2.80 MeV proton irradiation on GaInP/GaAs/Ge triple-junction solar cells for space use Wang Rong a,b,c,*, Liu Yunhong b, Sun Xufang b a
Key Laboratory of Beam Technology and Materials Modification, Ministry of Education, Beijing Normal University, Beijing 100875, China b Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875, China c Beijing Radiation Center, Beijing 100875, China Received 6 October 2007; received in revised form 17 December 2007 Available online 28 December 2007
Abstract GaInP/GaAs/Ge triple-junction solar cells were irradiated with 0.28, 0.62 and 2.80 MeV protons with fluences ranging from 1 1010 cm 2 to 1 1013 cm 2. Their performance degradation is analyzed using current–voltage characteristics and spectral response measurements. The degradation rates of the short circuit current, open circuit voltage, and maximum power output increase with fluence, but decrease with increasing proton energy. It was also observed that the spectral response of the GaAs middle cell degrades more significantly than that of the GaInP top cell. Ó 2008 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 84.60.Jt Keywords: GaInP/GaAs/Ge solar cell; Proton irradiation; Spectral response
1. Introduction In recent years, with the development of satellites that require more power, high efficiency multi-junction (MJ) solar cells have been developed. GaInP/GaAs/Ge triplejunction (3J) solar cells have achieved a high conversion efficiency of over 31.7% (AM1.5) [1], and have great potential for space applications. For space applications it is important to investigate the radiation damage to the cells and clarify the degradation mechanism. The radiation environment near the Earth mainly consists of protons and electrons trapped in the Earth’s geomagnetic field and protons produced by solar flares. The degradation behavior of solar cells due to proton irradiation is stronger than that from electrons because the density of collision events per
* Corresponding author. Address: Key Laboratory of Beam Technology and Materials Modification, Ministry of Education, Beijing Normal University, Beijing 100875, China. E-mail address: [email protected] (W. Rong).
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.076
particle impact is several orders of magnitude higher. Furthermore, degradation induced by medium-energy protons is much larger than for high-energy protons [2,3]. It is thus necessary to investigate medium-energy proton irradiation effects on the GaInP/GaAs/Ge triple-junction solar cells. 2. Experiment Fig. 1 shows a schematic of the solar cells used in this study, which were fabricated by metal–organic chemical vapor deposition (MOCVD). The dimensions of each part of the solar cell are shown in detail in Fig. 1. The solar cells with no cover glass mainly consist of three sub-cells: a GaInP sub-cell (top part), GaAs sub-cell (middle part), and a Ge sub-cell (bottom part). The middle sub-cell is connected with the top and bottom ones in series through the tunnel junctions TJ1 and TJ2, respectively. The solar cells were irradiated with 0.28, 0.62 and 2.80 MeV protons (energies chosen mainly according to the depth of the induced damage in the cell and by
746
W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
3. Results and discussion 3.1. I–V characteristics
Fig. 1. Schematic structure of GaInP/GaAs/Ge triple-junction solar cells.
Normalized Isc Normalized Voc Normalized Pmax
comparison with the results in [3]) using a 1.7 MV tandem accelerator. The fluences ranged from 1 1010 cm 2 to 1 1013 cm 2 with a flux of 5 108 cm 2 s 1, low enough to avoid heating of the cells during irradiation. I–V characteristics of the solar cells before and after irradiation were measured (25 °C) under AM0 using a LAPSS solar simulator with illumination at 136.7 mW cm 2. The spectral responses of the solar cells before and after irradiation were measured using a system consisting of a chopped light source, a bias light source, a monochromator, and a lock-in amplifier.
I–V characteristics of the initial and the irradiated solar cells were measured. Fig. 2 shows the degradation of the normalized short-circuit current (Isc), normalized open-circuit voltage (Voc), and normalized maximum power output (Pmax) as a function of proton irradiation fluence for different proton energies. From Fig. 2, one can see that proton irradiation at the lowest fluence leads to almost no performance degradation of the cells, but for fluences from 1 1011 cm 2 to 1 1013 cm 2, the degradation rates of Isc, Voc and Pmax increase with fluence, and Pmax has the most severe degradation. From Fig. 2(b) and (c) the degradation of Isc is much larger than that of Voc, that is, the overall irradiation response is primarily controlled by the degradation of Isc. This is indicative of a decrease in the minority-carrier diffusion length in the base region [4]. Table 1 lists the changes in the solar cells as a function of proton energy at a fluence of 1 1012 cm 2. From Table 1, the degradation rates of Isc, Voc, and Pmax decrease with proton energy, and irradiation with proton energies of 0.28 MeV produces the highest degradation rates. From Fig. 2 the degradation rates of all quantities also decrease for the other fluences not given in Table 1 as the proton energy increases. 3.2. Degradation of the spectral response Changes of the spectral responses of the middle and top sub-cells before and after irradiation at an energy of
1.0
a
0.8 0.6 0.4
0.28 MeV 0.62 MeV 2.80 MeV
0.2 0.0 1.0
b
0.8 0.6
0.28 MeV 0.62 MeV 2.80 MeV
0.4 0.2 0.0 1.0
c
0.8 0.6 0.28 MeV 0.62 MeV 2.80 MeV
0.4 0.2 0.0 10
10
11
10
12
10
Proton fluence/cm
13
10
-2
Fig. 2. Changes in electronic properties of GaInP/GaAs/Ge solar cells as a function of proton irradiation fluence and energy.
W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
The spectral response of the solar cells mainly drops in wavelength from 650 to 900 nm of the middle GaAs cell as the irradiation energy increases, since irradiation decreases the longer wavelength spectral response more significantly than that of the shorter wavelength in the middle GaAs cell. The spectral response hardly decreases in the wavelength range from 350 to 650 nm. Again, the spectral response of the middle GaAs cell degrades more than that of the top GaInP cell. The spectral response curves of the solar cells as a function of the proton energy can be explained with results of the irradiation-induced vacancies produced in the solar cells simulated by the Monte Carlo code SRIM [8]. The full damage cascades and displacement energies (10 eV for Ga and As, 6.7 eV for In, 8.7 eV for P, 27.5 eV for Ge) [9] have been used. The simulated results of the vacancies created in the solar cells after irradiation with energies of 0.28 MeV and 0.62 MeV are shown in Fig. 5. Both energies produce non-uniform vacancy depth distribution, and most are generated near the end of range. 0.28 MeV protons penetrate beyond the pn junction of the GaInP sub-cell and the pn junction of the GaAs sub-cell and mainly damage the base region of the GaAs sub-cell. The proton-induced atom displacements result in vacancies, interstitial atoms or complexes which capture charge carriers, thereby reducing the minority carrier diffusion length in the base region of the cell [4]. Irradiation thus degrades the spectral response primarily of the middle GaAs cell for wavelengths from 650 to 900 nm [10]. Protons (0.62 MeV) penetrate beyond the pn junctions of three sub-cells and mainly damage the base region of Ge sub-cell. The peak of 2.80 MeV protoninduced vacancies is far from the major active region of the triple-junction solar cell (omitted in Fig. 5).
Table 1 Changes in the properties of the solar cells as a function of proton energy Proton energy (MeV)
Isc degradation rate (%)
Voc degradation rate (%)
Pmax degradation rate (%)
0.28 0.62 2.80
60.4 40.1 18.6
23.4 17.6 13.1
74.8 55.9 36.8
747
0.62 MeV with different fluences are shown in Fig. 3. Since Isc of the bottom cell is much larger than that of the two others, its was not plotted [5]. From Fig. 3, the degradation of the spectral response increases with fluence, but the spectral response of the solar cells mainly drops in wavelength range from 650 to 900 nm (corresponding to the middle GaAs cell) as the fluence increases from 1 1010 to 1 1013 cm 2. Furthermore, irradiation decreases the longer wavelength spectral response more significantly than that of the shorter wavelength of the middle GaAs cell. The spectral response in the wavelength region from 350 nm to 650 nm (corresponding to the top GaInP sub-cell) hardly decreases for fluences less than 1 1013 cm 2, but is reduced remarkably from 350 to 550 nm after a high fluence of 1 1013 cm 2. This is mainly due to damage on the emitter layer and the interface of the top sub-cell, which increases the recombination velocity of the carriers and reduces the carrier life after a certain level of irradiation [6,7]. The spectral response of the middle GaAs cell degrades more than that of the top GaInP cell for 0.62 MeV irradiation. Changes of the spectral response before and after irradiation with different energies are shown in Fig. 4. The degradation of the spectral response decreases with proton energy, in agreement with the results of I–V characteristics.
1.0
GaAs middle cell
GaInP top cell
Quantum Efficiency
0.8
0.6
pre-irradiation
0.4
0.2
1*1 0
10
1*10
11
cm
-2
1*10
12
cm
-2
1*10
13
cm
-2
cm
-2
0.0 300
400
500
600
700
800
900
W avelength/nm Fig. 3. Spectral response of solar cells after irradiation with 0.62 MeV protons with different fluences.
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W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749 1.0
GaAs middle cell
GaInP top cell
Quantum Efficiency
0.8
0.6
0.4
pre-irradiation 0.28 MeV 0.62 MeV 2.80 MeV
0.2
0.0 300
400
500
600
700
800
900
Wavelength/nm
120
Ge
GaAs
GaInP
Fig. 4. Spectral response for different proton energies after a fluence of 1 1012 cm 2.
0.28 MeV 0.62 MeV
Vacancies/um/ion
100
80
60
40
20
0 0
1
2
3
4
5
6
7
8
Target Depth / um Fig. 5. Damage distribution of 0.28 and 0.62 MeV protons in the solar cell.
Therefore, irradiation with a proton energy of 0.28 MeV gives rise to the highest vacancy density near the pn junction in the middle GaAs cell. Thus, the largest degradation rates of Isc, Voc, and Pmax of the solar cells are related to the proton-induced vacancies near the pn junction in the middle GaAs sub-cell. That is, the maximum degradation of these parameters and the spectral response at 0.28 MeV was attributed to the middle GaAs sub-cell. In [3] we
obtained a similar degradation at 0.30 MeV, which was attributed to the entire GaAs/Ge cell. 4. Conclusions The degradation rates of Isc, Voc, Pmax and the spectral response increase with fluence, but the degradation rates decrease with proton energy, i.e. irradiation at 0.28 MeV
W. Rong et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 745–749
gives rise to the highest degradation rates. The increasing degradation rates with decreasing energy are related to the location of the proton-induced Bragg peak with respect to the major active region of the solar cell. For the proton energies used in this study the spectral response of the middle GaAs cell degrades more significantly than that of the top GaInP cell. Thus, the irradiation tolerance of the triple-junction solar cells is dominated by the middle GaAs sub-cell. Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant No. 10675023, and by Beijing Excellent Personality Foundation. References [1] M. Yamaguchi, Multi-junction solar cells and novel structures for solar cell applications, Physica E 14 (2002) 84. [2] Wang Rong, Guo Zengliang, Zhang Xinghui, et al., 5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use, Sol. Energ. Mater. Sol. Cell. 77 (2003) 351.
749
[3] Wang Rong, Guo Zengliang, Wang Guangpu, Low energy proton irradiation effects on GaAs/Ge space solar cells, Sol. Energ. Mater. Sol. Cell. 90 (2006) 1052. [4] N. Dharmarasu, M. Yamaguchi, A. Khan, et al., High-radiationresistant InGaP, InGaAsP, and InGaAs solar cells for multijunction solar cells, Appl. Phys. Lett. 79 (15) (2001) 2399. [5] H. Cotal, R. King, M. Haddad, et al., The effects of electron on triplejunction GaInP/GaAs/Ge solar cells, Proc. IEEE 28th PVSC (2000) 1316. [6] T. Sumita, M. Imaizumi, S. Matsuda, et al., Proton radiation analysis of multi-junction space solar cells, Nucl. Instr. and Meth. Phys. Res. B 206 (2003) 448. [7] R. Kachare, B.E. Anspaugh, Spatial resolution and nature of defects produced by low-energy proton irradiation of GaAs solar cells, Appl. Phys. Lett. 49 (21) (1986) 1459. [8] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, The Stopping and Range of Ions in Matter, SRIM Version: SRIM-2006.01, downloaded from http://www.srim.org. [9] ESA-GSP Work Package 1 Study Report: Predicting Displacement Damage Effects in Electronic Components by Methods of Simulation. 2002, 15157/01/NL/PA. [10] N. Dharmarasu, A. Khan, M. Yamaguchi, et al., Effect of proton irradiation on n+ p InGaP solar cells, J. Appl. Phys. 91 (5) (2002) 3306.