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High-rate deposition of hydrogenated amorphous silicon films using inductively coupled silane plasma
Solar Energy Materials & Solar Cells 66 (2001) 337}343
High-rate deposition of hydrogenated amorphous silicon "lms using inductively coupled silane plasma Nobuki Sakikawa*, Yoshinori Shishida, Seiichi Miyazaki, Masataka Hirose Department of Electrical Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima 739-8527, Japan
Abstract Inductively coupled plasma (ICP) generated at 13.56 MHz has been employed for high-rate deposition of device-quality hydrogenated amorphous silicon (a-Si:H). It has been shown that an increase in the #ow rate of a monosilane gas enhances the generation rate of deposition precursors, while the ion #ux decreases and becomes saturated. The defect density reaches the minimum at a deposition rate of 2.3 nm/s. It has also been demonstrated that even at deposition rates around 4 nm/s, a-Si:H deposited at 1503C exhibits a subgap defect density lower than &6;10 cm\ after 12 h AM1 (100 mW/cm) light soaking. 2001 Published by Elsevier Science B.V. All rights reserved. Keywords: Inductively coupled plasma; Hydrogenated amorphous silicon; High deposition rate; Silane #ow rate
1. Introduction In large-scale manufacturing of hydrogenated amorphous silicon (a-Si:H) solar cells, there has been an increasing need for uniform deposition of device-quality "lms at high rates at temperatures below 2003C. At such low temperatures, the a-Si:H deposition by the conventional plasma-enhanced chemical vapor deposition (PECVD) method, in which a capacitively coupled plasma (CCP) is generated at
* Corresponding author. 0927-0248/01/$ - see front matter 2001 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 0 ) 0 0 1 9 2 - 6
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N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
13.56 MHz, limits the rates to 0.3 nm/s, above which the "lm quality deteriorates [1]. Increasing the RF power and gas pressure in a CCP accelerates the deposition rate, resulting in the generation of particles in the reactor [2]. The particle generation is known to deteriorate the "lm quality and to limit the yield of a-Si:H devices such as solar cells [3,4]. Therefore, a-Si:H "lms have usually been produced at a low deposition rate of around 0.1 nm/s. In order to increase the deposition rate, alternative techniques have been developed, such as using electron cyclotron resonance (ECR) [5], helicon wave (HW) plasma [6], very high-frequency (VHF) plasma [7] and inductively coupled plasma (ICP) [8]. ICP is especially promising; since it enables us to easily obtain a high plasma density under a relatively low pressure without an external magnetic "eld, a higher uniformity and less particle formation in the plasma can be expected. However, the feasibility of ICP with an RF source for high-rate deposition of device-quality a-Si:H at a temperature as low as 1503C has not yet been established. In this work, we have investigated high-rate a-Si:H deposition using ICP as a function of SiH #ow rate, and we have examined the corresponding structural, optical and electrical properties of a-Si:H.
2. Experimental An external single-turn antenna with a diameter of 120 mm was placed on a quartz cooling tube in contact with a 10-mm-thick quartz plate that was attached to a deposition chamber. RF power at 13.56 MHz was supplied to the antenna through a matching box to generate the ICP of pure SiH . Films of a-Si:H about 500 nm thick were deposited on quartz, sapphire and Si(1 0 0) (o"20}30 ) cm) substrates at 1503C. The distance between the antenna and the grounded substrate susceptor was "xed at 45 mm in the axial direction. The SiH #ow rate was varied from 7.5 to 110 sccm. During the "lm growth, the RF power and the gas pressure were maintained at 400 W and 50 mTorr, respectively. The current passing through the substrate was monitored by an oscilloscope trace at the inductance terminal [9]. No signi"cant di!erence in the IR spectra among deposited "lms on c-Si and sapphire substrates was observable, presumably because the surface conductance is high enough once an a-Si:H "lm starts to grow [9,10], and hence the e!ect on "lm growth of charge-up on an insulating substrate is negligible. The structural inhomogeneity has been probed by Raman scattering [11] and small-angle X-ray scattering (SAXS) [12]. The Raman scattering spectra were measured under a right-angle scattering geometry in which a p-polarized 441.6 nm light from an He}Cd laser was incident to the sample surface in Ar ambient at a glancing angle of about 103 for directly characterizing the a-Si:H network structure. SAXS analysis was carried out using slit-collimated Cu K radiation combined with a scintillation counter. The SAXS a spectrum reveals the size and the quantity of microvoids and/or low-density regions in a-Si:H. The defect density was evaluated by a constant photocurrent method (CPM) [13].
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
339
Fig. 1. (a) The deposition rate and the normalized deposition rate by 414 nm emission intensity due to the SiH; (b) the emission intensity ratio of H (486 nm) to H (656 nm) and the emission intensity of H ; (c) ion @ a @ current (I ) and electron current (I ) measured at the substrate electrode are plotted as a function of the SiH #ow rate, respectively.
3. Results and discussion The deposition rate increases monotonically up to 4.1 nm/s with increasing SiH #ow rate to 110 sccm, although it tends to level o! at higher SiH #ow rates, as shown in Fig. 1(a). Note that the ratio of the deposition rate to the 414 nm emission intensity due to excited SiH species is constant regardless of the #ow rates. The emitting species SiH are created through the one-electron impact dissociations of SiH being similar to the case of non-emissive SiH radicals, which are considered to be possible deposition precursors [14]. Therefore, the intensity of the emitting SiH is well correlated with the concentration of the deposition precursors. A similar correlation between the deposition rate and the SiH emission intensity was reported on a conventional CCP [15,16]. These results indicate that the "lm growth from ICP is controlled by the generation rate of deposition precursors in the gas phase as in the case of CCP. Note that even at a deposition rate as high as 4.1 nm/s no powder formation was observed on the substrate susceptor 120 mm in diameter and on the quartz plate beneath the antenna. Furthermore, the emission intensity ratio of H (486 nm)/ @ H (656 nm) decreases gradually with an increase in the SiH #ow rate although the a emission intensity of H is kept constant, as shown in Fig. 1(b). This suggests that the @ electron temperature is decreased at higher SiH #ow rates. Fig. 1(c) shows current #owing to the substrate electrode during "lm growth as a function of the SiH #ow rate, where ion and electron components in the measured AC current were evaluated
340
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Fig. 2. (a) The absorption intensity ratio of dihydrides to monohydrides (SiH /SiH); (b) total bonded hydrogen content (C ) and optical band gap (E ); (c) the intensity ratio of TA-like phonon mode & (150 cm\) to TO-like phonon mode (480 cm\) in the a-Si network and the FWHM of TO-like phonon mode as a function of the deposition rate.
separately. Both ion (I ) and electron (I ) currents decrease with increasing SiH #ow rate in the region below 25 sccm, and then increase slightly with the SiH #ow rate. Taking into account an increase in the deposition rate with the SiH #ow rate as represented in Fig. 1(a), it is suggested that the #ux ratio of ions or electrons to deposition precursors to the growing surface signi"cantly decreases with increasing SiH #ow rate. The content of bonded hydrogen in the deposited "lms decreases from 16.5 to 12 at% with an increase in the deposition rate from 1.2 to 2.3 nm/s, and correspondingly the optical band gap decreases from 1.82 eV by about 0.1 eV, as indicated in Fig. 2. An increase in the #ux ratio of deposition precursors to hydrogen ions and hydrogen radicals impinging onto the growing "lm under a high-rate deposition condition might be responsible for the decrease in the hydrogen content. For "lms deposited at rates higher than 2.3 nm/s, the bonded hydrogen content tends to slightly increase while the optical band gap remains almost unchanged. Since the observed change in the hydrogen content is mainly caused by the change in the amount of SiH bonds, a fairly homogeneous a-Si network with a low defect density is expected to be formed at deposition rates around 2 nm/s. In fact, for "lms deposited at rates of 2}3 nm/s structural #uctuation and/or inhomogeneity evaluated by Raman scattering [11] and SAXS measurements [12] appreciably reduces as shown in Figs. 2(c) and 3. Both the intensity ratio of the TA-like phonon mode at 150 cm\ to the TO-like mode at 480 cm\ (TA/TO) as obtained from Raman scattering, which roughly re#ects the bond-angle variations in the a-Si network, and the full-width at half-maximum (FWHM) of the TO phonon mode, which is correlated to variations in both the bond angle and bond length [17], reach their minima for a-Si:H deposition at 2}3 nm/s, indicating that network #uctuation is reduced by increasing deposition rate up to 2}3 nm/s. As for the structural inhomogeneity such as microvoids evaluated by SAXS measurements [12], its total amount becomes fairly small for a-Si:H deposited at
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
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Fig. 3. Relative volume fraction of low-density region, which was evaluated by SAXS measurements, versus radius of gyration for "lms deposited at di!erent deposition rates.
Fig. 4. (a) The defect densities obtained from CPM before and after AM1 (100 mW/cm) light soaking for 12 h; (b) dark conductivity (p ), initial and degraded photoconductivity (p ) and the photosensitivity (p /p ); (c) conductivity activation energy (E ) versus deposition rate.
2.3 nm/s compared with "lms deposited at 1.3 or 3.8 nm/s, although no signi"cant change in the size distribution is observable (Fig. 3). In addition, the defect density evaluated by CPM takes its minimum (&1;10 cm\ for the annealed state and &3;10 cm\ for a light-soaked state) for "lms deposited at &2 nm/s [Fig. 4(a)], while the defect density as high as 4;10 cm\ is obtained for an a-Si:H "lm
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deposited at 1.2 nm/s presumably because of the ion bombardment during the "lm growth. It is interesting to note that, even for the "lm deposited at a rate of 4.1 nm/s, the defect state density remains below 6;10 cm\ after 12 h light soaking (AM1, 100 mW/cm). A slight increase in the defect states observed at deposition rates higher than &2 nm/s might be correlated with microvoid formation. The dark conductivity is increased by about two orders of magnitude by increasing the deposition rate up to 2.3 nm/s because its activation energy is decreased from 0.89 eV by 0.1 eV, as shown in Figs. 4(b) and (c). For a further increase in the deposition rate, an increase in the activation energy attributable to a small increment of the defect density results in a decrease in the dark conductivity down to &2;10} S/cm at a deposition rate of 4.1 nm/s. Since the change in the photoconductivity under AM1 (100 mW/cm) illumination is smaller by about one order of magnitude than the change in the dark conductivity, a photosensitivity as high as 1.3;10 is obtained even for the "lm deposited at 4.1 nm/s.
4. Conclusions We have demonstrated that the use of ICP is a promising way to achieve a higher deposition rate of device-quality a-Si:H "lms. It is found that a moderate SiH supply is of great importance in increasing the deposition rate and decreasing the hydrogen content and the defect density e$ciently at a substrate temperature of 1503C, presumably because the #ux ratio of ions to deposition precursors on the growing surface is decreased at higher SiH #ow rates. Acknowledgements This work was supported in part by a Grant-in-Aid for Scienti"c Research and Development Program in the New Sunshine Project for the Ministry of International Trade and Industry.
References [1] T. Kamei, G. Ganguly, N. Hata, A. Matsuda, J. Non-Cryst. Solids 164}166 (1993) 43. [2] R.I. Patel, J.R. Shirck, D.J. Tran, K.A. Epstein, Proceedings of the 18th IEEE Photovoltaic Specialists Conference, IEEE, New York, 1985, p. 499. [3] G. Ganguly, A. Matsuda, Jpn. J. Appl. Phys. 31 (1992) L1269. [4] Y. Watanabe, M. Shiratani, Jpn. J. Appl. Phys. 32 (1993) 3074. [5] M. Kitagawa, K. Setsune, Y. Manabe, T. Hirao, Jpn. J. Appl. Phys. 27 (1988) 2026. [6] R.W. Boswell, Proceedings of the 21th International Conference on Phenomena in Ionized Gases, Bochum, 1993, p. 118. [7] F. Finger, U. Kroll, V. Viret, A. Shah, W. Beyer, X.-M. Tang, J. Weber, A. Howling, Ch. Hollenstein, J. Appl. Phys. 71 (1992) 5665. [8] M. Goto, H. Toyoda, M. Kitagawa, T. Hirao, H. Sugai, Jpn. J. Appl. Phys. 36 (1997) 3714. [9] N. Sakikawa, Y. Shishida, S. Miyazaki, M. Hirose, Jpn. J. Appl. Phys. 37 (1998) L774.
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343 [10] [11] [12] [13] [14] [15]
343
C.A.M. de Vries, W. G. M. van den Hoek, J. Appl. Phys. 58 (1985) 2074. S. Miyazaki, N. Fukuhara, M. Hirose, J. Non-Cryst. Solids, to be published. N. Sakikawa, T. Tamao, S. Miyazaki, M. Hirose, Jpn. J. Appl. Phys. 37 (1998) 432. M. Vanecek, J. Kocka, J. Stuchlik, Z. Kozisek, O. Stika, A. Triska, Sol. Energy Mater. 8 (1983) 411. G. Ganguly, A. Matsuda, J. Non-Cryst. Solids 31&36 (1993) 164. T. Hamasaki, M. Hirose, Y. Osaka, Proceedings of the Seventh International Conference on Vac. Metallugry, Tokyo, 1982, p. 472. [16] A. Matsuda, K. Nakagawa, K. Tanaka, M. Matsumura, S. Yamasaki, H. Okushi, S. Iizima, J. Non-Cryst. Solids 35&36 (1980) 183. [17] J.S. Lanni, in: J.I. Pankove (Ed.), Semiconductors and Semimetals, Vol. 21, Part B, Academic Press, London, 1984 (Chapter 6).
High-rate deposition of hydrogenated amorphous silicon "lms using inductively coupled silane plasma Nobuki Sakikawa*, Yoshinori Shishida, Seiichi Miyazaki, Masataka Hirose Department of Electrical Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima 739-8527, Japan
Abstract Inductively coupled plasma (ICP) generated at 13.56 MHz has been employed for high-rate deposition of device-quality hydrogenated amorphous silicon (a-Si:H). It has been shown that an increase in the #ow rate of a monosilane gas enhances the generation rate of deposition precursors, while the ion #ux decreases and becomes saturated. The defect density reaches the minimum at a deposition rate of 2.3 nm/s. It has also been demonstrated that even at deposition rates around 4 nm/s, a-Si:H deposited at 1503C exhibits a subgap defect density lower than &6;10 cm\ after 12 h AM1 (100 mW/cm) light soaking. 2001 Published by Elsevier Science B.V. All rights reserved. Keywords: Inductively coupled plasma; Hydrogenated amorphous silicon; High deposition rate; Silane #ow rate
1. Introduction In large-scale manufacturing of hydrogenated amorphous silicon (a-Si:H) solar cells, there has been an increasing need for uniform deposition of device-quality "lms at high rates at temperatures below 2003C. At such low temperatures, the a-Si:H deposition by the conventional plasma-enhanced chemical vapor deposition (PECVD) method, in which a capacitively coupled plasma (CCP) is generated at
* Corresponding author. 0927-0248/01/$ - see front matter 2001 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 0 ) 0 0 1 9 2 - 6
338
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
13.56 MHz, limits the rates to 0.3 nm/s, above which the "lm quality deteriorates [1]. Increasing the RF power and gas pressure in a CCP accelerates the deposition rate, resulting in the generation of particles in the reactor [2]. The particle generation is known to deteriorate the "lm quality and to limit the yield of a-Si:H devices such as solar cells [3,4]. Therefore, a-Si:H "lms have usually been produced at a low deposition rate of around 0.1 nm/s. In order to increase the deposition rate, alternative techniques have been developed, such as using electron cyclotron resonance (ECR) [5], helicon wave (HW) plasma [6], very high-frequency (VHF) plasma [7] and inductively coupled plasma (ICP) [8]. ICP is especially promising; since it enables us to easily obtain a high plasma density under a relatively low pressure without an external magnetic "eld, a higher uniformity and less particle formation in the plasma can be expected. However, the feasibility of ICP with an RF source for high-rate deposition of device-quality a-Si:H at a temperature as low as 1503C has not yet been established. In this work, we have investigated high-rate a-Si:H deposition using ICP as a function of SiH #ow rate, and we have examined the corresponding structural, optical and electrical properties of a-Si:H.
2. Experimental An external single-turn antenna with a diameter of 120 mm was placed on a quartz cooling tube in contact with a 10-mm-thick quartz plate that was attached to a deposition chamber. RF power at 13.56 MHz was supplied to the antenna through a matching box to generate the ICP of pure SiH . Films of a-Si:H about 500 nm thick were deposited on quartz, sapphire and Si(1 0 0) (o"20}30 ) cm) substrates at 1503C. The distance between the antenna and the grounded substrate susceptor was "xed at 45 mm in the axial direction. The SiH #ow rate was varied from 7.5 to 110 sccm. During the "lm growth, the RF power and the gas pressure were maintained at 400 W and 50 mTorr, respectively. The current passing through the substrate was monitored by an oscilloscope trace at the inductance terminal [9]. No signi"cant di!erence in the IR spectra among deposited "lms on c-Si and sapphire substrates was observable, presumably because the surface conductance is high enough once an a-Si:H "lm starts to grow [9,10], and hence the e!ect on "lm growth of charge-up on an insulating substrate is negligible. The structural inhomogeneity has been probed by Raman scattering [11] and small-angle X-ray scattering (SAXS) [12]. The Raman scattering spectra were measured under a right-angle scattering geometry in which a p-polarized 441.6 nm light from an He}Cd laser was incident to the sample surface in Ar ambient at a glancing angle of about 103 for directly characterizing the a-Si:H network structure. SAXS analysis was carried out using slit-collimated Cu K radiation combined with a scintillation counter. The SAXS a spectrum reveals the size and the quantity of microvoids and/or low-density regions in a-Si:H. The defect density was evaluated by a constant photocurrent method (CPM) [13].
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
339
Fig. 1. (a) The deposition rate and the normalized deposition rate by 414 nm emission intensity due to the SiH; (b) the emission intensity ratio of H (486 nm) to H (656 nm) and the emission intensity of H ; (c) ion @ a @ current (I ) and electron current (I ) measured at the substrate electrode are plotted as a function of the SiH #ow rate, respectively.
3. Results and discussion The deposition rate increases monotonically up to 4.1 nm/s with increasing SiH #ow rate to 110 sccm, although it tends to level o! at higher SiH #ow rates, as shown in Fig. 1(a). Note that the ratio of the deposition rate to the 414 nm emission intensity due to excited SiH species is constant regardless of the #ow rates. The emitting species SiH are created through the one-electron impact dissociations of SiH being similar to the case of non-emissive SiH radicals, which are considered to be possible deposition precursors [14]. Therefore, the intensity of the emitting SiH is well correlated with the concentration of the deposition precursors. A similar correlation between the deposition rate and the SiH emission intensity was reported on a conventional CCP [15,16]. These results indicate that the "lm growth from ICP is controlled by the generation rate of deposition precursors in the gas phase as in the case of CCP. Note that even at a deposition rate as high as 4.1 nm/s no powder formation was observed on the substrate susceptor 120 mm in diameter and on the quartz plate beneath the antenna. Furthermore, the emission intensity ratio of H (486 nm)/ @ H (656 nm) decreases gradually with an increase in the SiH #ow rate although the a emission intensity of H is kept constant, as shown in Fig. 1(b). This suggests that the @ electron temperature is decreased at higher SiH #ow rates. Fig. 1(c) shows current #owing to the substrate electrode during "lm growth as a function of the SiH #ow rate, where ion and electron components in the measured AC current were evaluated
340
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
Fig. 2. (a) The absorption intensity ratio of dihydrides to monohydrides (SiH /SiH); (b) total bonded hydrogen content (C ) and optical band gap (E ); (c) the intensity ratio of TA-like phonon mode & (150 cm\) to TO-like phonon mode (480 cm\) in the a-Si network and the FWHM of TO-like phonon mode as a function of the deposition rate.
separately. Both ion (I ) and electron (I ) currents decrease with increasing SiH #ow rate in the region below 25 sccm, and then increase slightly with the SiH #ow rate. Taking into account an increase in the deposition rate with the SiH #ow rate as represented in Fig. 1(a), it is suggested that the #ux ratio of ions or electrons to deposition precursors to the growing surface signi"cantly decreases with increasing SiH #ow rate. The content of bonded hydrogen in the deposited "lms decreases from 16.5 to 12 at% with an increase in the deposition rate from 1.2 to 2.3 nm/s, and correspondingly the optical band gap decreases from 1.82 eV by about 0.1 eV, as indicated in Fig. 2. An increase in the #ux ratio of deposition precursors to hydrogen ions and hydrogen radicals impinging onto the growing "lm under a high-rate deposition condition might be responsible for the decrease in the hydrogen content. For "lms deposited at rates higher than 2.3 nm/s, the bonded hydrogen content tends to slightly increase while the optical band gap remains almost unchanged. Since the observed change in the hydrogen content is mainly caused by the change in the amount of SiH bonds, a fairly homogeneous a-Si network with a low defect density is expected to be formed at deposition rates around 2 nm/s. In fact, for "lms deposited at rates of 2}3 nm/s structural #uctuation and/or inhomogeneity evaluated by Raman scattering [11] and SAXS measurements [12] appreciably reduces as shown in Figs. 2(c) and 3. Both the intensity ratio of the TA-like phonon mode at 150 cm\ to the TO-like mode at 480 cm\ (TA/TO) as obtained from Raman scattering, which roughly re#ects the bond-angle variations in the a-Si network, and the full-width at half-maximum (FWHM) of the TO phonon mode, which is correlated to variations in both the bond angle and bond length [17], reach their minima for a-Si:H deposition at 2}3 nm/s, indicating that network #uctuation is reduced by increasing deposition rate up to 2}3 nm/s. As for the structural inhomogeneity such as microvoids evaluated by SAXS measurements [12], its total amount becomes fairly small for a-Si:H deposited at
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343
341
Fig. 3. Relative volume fraction of low-density region, which was evaluated by SAXS measurements, versus radius of gyration for "lms deposited at di!erent deposition rates.
Fig. 4. (a) The defect densities obtained from CPM before and after AM1 (100 mW/cm) light soaking for 12 h; (b) dark conductivity (p ), initial and degraded photoconductivity (p ) and the photosensitivity (p /p ); (c) conductivity activation energy (E ) versus deposition rate.
2.3 nm/s compared with "lms deposited at 1.3 or 3.8 nm/s, although no signi"cant change in the size distribution is observable (Fig. 3). In addition, the defect density evaluated by CPM takes its minimum (&1;10 cm\ for the annealed state and &3;10 cm\ for a light-soaked state) for "lms deposited at &2 nm/s [Fig. 4(a)], while the defect density as high as 4;10 cm\ is obtained for an a-Si:H "lm
342
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deposited at 1.2 nm/s presumably because of the ion bombardment during the "lm growth. It is interesting to note that, even for the "lm deposited at a rate of 4.1 nm/s, the defect state density remains below 6;10 cm\ after 12 h light soaking (AM1, 100 mW/cm). A slight increase in the defect states observed at deposition rates higher than &2 nm/s might be correlated with microvoid formation. The dark conductivity is increased by about two orders of magnitude by increasing the deposition rate up to 2.3 nm/s because its activation energy is decreased from 0.89 eV by 0.1 eV, as shown in Figs. 4(b) and (c). For a further increase in the deposition rate, an increase in the activation energy attributable to a small increment of the defect density results in a decrease in the dark conductivity down to &2;10} S/cm at a deposition rate of 4.1 nm/s. Since the change in the photoconductivity under AM1 (100 mW/cm) illumination is smaller by about one order of magnitude than the change in the dark conductivity, a photosensitivity as high as 1.3;10 is obtained even for the "lm deposited at 4.1 nm/s.
4. Conclusions We have demonstrated that the use of ICP is a promising way to achieve a higher deposition rate of device-quality a-Si:H "lms. It is found that a moderate SiH supply is of great importance in increasing the deposition rate and decreasing the hydrogen content and the defect density e$ciently at a substrate temperature of 1503C, presumably because the #ux ratio of ions to deposition precursors on the growing surface is decreased at higher SiH #ow rates. Acknowledgements This work was supported in part by a Grant-in-Aid for Scienti"c Research and Development Program in the New Sunshine Project for the Ministry of International Trade and Industry.
References [1] T. Kamei, G. Ganguly, N. Hata, A. Matsuda, J. Non-Cryst. Solids 164}166 (1993) 43. [2] R.I. Patel, J.R. Shirck, D.J. Tran, K.A. Epstein, Proceedings of the 18th IEEE Photovoltaic Specialists Conference, IEEE, New York, 1985, p. 499. [3] G. Ganguly, A. Matsuda, Jpn. J. Appl. Phys. 31 (1992) L1269. [4] Y. Watanabe, M. Shiratani, Jpn. J. Appl. Phys. 32 (1993) 3074. [5] M. Kitagawa, K. Setsune, Y. Manabe, T. Hirao, Jpn. J. Appl. Phys. 27 (1988) 2026. [6] R.W. Boswell, Proceedings of the 21th International Conference on Phenomena in Ionized Gases, Bochum, 1993, p. 118. [7] F. Finger, U. Kroll, V. Viret, A. Shah, W. Beyer, X.-M. Tang, J. Weber, A. Howling, Ch. Hollenstein, J. Appl. Phys. 71 (1992) 5665. [8] M. Goto, H. Toyoda, M. Kitagawa, T. Hirao, H. Sugai, Jpn. J. Appl. Phys. 36 (1997) 3714. [9] N. Sakikawa, Y. Shishida, S. Miyazaki, M. Hirose, Jpn. J. Appl. Phys. 37 (1998) L774.
N. Sakikawa et al. / Solar Energy Materials & Solar Cells 66 (2001) 337}343 [10] [11] [12] [13] [14] [15]
343
C.A.M. de Vries, W. G. M. van den Hoek, J. Appl. Phys. 58 (1985) 2074. S. Miyazaki, N. Fukuhara, M. Hirose, J. Non-Cryst. Solids, to be published. N. Sakikawa, T. Tamao, S. Miyazaki, M. Hirose, Jpn. J. Appl. Phys. 37 (1998) 432. M. Vanecek, J. Kocka, J. Stuchlik, Z. Kozisek, O. Stika, A. Triska, Sol. Energy Mater. 8 (1983) 411. G. Ganguly, A. Matsuda, J. Non-Cryst. Solids 31&36 (1993) 164. T. Hamasaki, M. Hirose, Y. Osaka, Proceedings of the Seventh International Conference on Vac. Metallugry, Tokyo, 1982, p. 472. [16] A. Matsuda, K. Nakagawa, K. Tanaka, M. Matsumura, S. Yamasaki, H. Okushi, S. Iizima, J. Non-Cryst. Solids 35&36 (1980) 183. [17] J.S. Lanni, in: J.I. Pankove (Ed.), Semiconductors and Semimetals, Vol. 21, Part B, Academic Press, London, 1984 (Chapter 6).