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Chemically etched porous silicon as an anti-reflection coating for high efficiency solar cells
Thin Solid Films 297 (1997) 296–298
Chemically etched porous silicon as an anti-reflection coating for high efficiency solar cells L. Schirone, G. Sotgiu, F.P. Califano Universita` di Roma Tre, Dipartimento di Ingegneria Elettronica, Via della Vasca Navale, 84, 00146 Roma, Italy
Abstract
Porous silicon was formed on mono- and multicrystalline Si substrates by stain etching in aqueous HF/HNO3 solutions. Optical properties of the resulting films were investigated by reflectance spectroscopy and related to the main etch parameters. Porous Si films have been shown able to reduce surface reflectance to under 3% in a wavelength range larger than 400–800 nm. Efficient anti-reflection coatings were developed and used in multicrystalline Si solar cells with area up to 12.8=12.8 cm2. Photovoltaic conversion efficiency up to 12% was obtained under standard AM1.5G simulated sunlight. q 1997 Elsevier Science S.A. Keywords:
Silicon; Porous; Stain etch; Coatings; Solar cells
1. Introduction
Chemical etching of Si in a variety of solutions is known to produce stain layers [1]. These films consist of porous material similar to that resulting from anodic etching of Si in HF solutions [2]. We demonstrate here their use as antireflection (AR) coatings of large area solar cells, enabling a photovoltaic conversion efficiency comparable to commercially available devices. Several authors considered the possible use of porous silicon in PV devices and photo detectors [3–13], and a few groups reported appreciable photovoltaic conversion [9,11,13]. Most of the authors prepared porous Si by electrochemical process in HF/EtOH aqueous solutions [2]. We prefer to use chemical etching in aqueous HF/HNO3 solutions [1], since this technology is more suitable for massive industrial production [12]. This work focuses on the reflective properties of porous films formed on the outermost region of p/nq junctions and relates them to performance of the resulting solar cells.
icon with grain size in millimetres range, obtained by a cheap casting process from waste monocrystalline materials [24]. Silver paste was deposited on the surface by screen printing and sintered at 700 8C in order to provide ohmic contacts. The metal lines were then protected by a screen-printed polymeric film, and the outermost region of the junctions was converted into porous Si by stain etching in aqueous HF/ HNO3 solutions. The starting concentration for our freshsolutions was H2O:HF:HNO3s1:1:0.01 vol., and HNO3 or HF(50%) were then added to increase or decrease the growth rate. Finally, the protecting film was removed in acetone. Further details on the preparation process have been published elsewhere [14]. Integrated reflectance of porous films was measured by a Lambda 9 Perkin–Elmer spectrophotometer. Measurements were taken at 1 nm intervals, 400 A˚ miny1 scan rate. Film thickness was deduced from fitting reflectance data by a model based on a monolayer film. Solar cell efficiency was measured under standard AM1.5G conditions. The quantum yield was measured at 10 nm intervals.
2. Experimental details 3. Results and discussion
Substrates were B-doped multi- and monocrystalline Si wafers, thermally diffused to form 0.5 mm deep junctions, consisting of a shallow 0.1 mm nq region with approximately constant 1020 cmy3 phosphorus concentration and a deeper decreasing erfc-shaped profile. Multicrystalline is a poly-sil-
3.1. Porous Si anti-reflection layers
Porous Si is a sponge-like material, consisting of nanometer-sized voids and monocrystalline columns, with a large,
0040-6090/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S0040-6090(96)09436-9
Journal: TSF (Thin Solid Films)
Article: 9436
297
L. Schirone et al. / Thin Solid Films 297 (1997) 296–298
hydrogenated surface [15]. Therefore, the refractive index is controlled by the volume fraction of void with respect to the crystalline skeleton (porosity) [16,17], and it can be adjusted to optimise optical matching between air and Si [12]. The parameters which are known to affect the material porosity are solution composition and porous film growth rate [20,21]. Moreover, properties of the resulting porous films depend on substrate doping profile, as it is well known for anodically etched porous films [18,19]. Reflectance of a porous Si-coated surface is also affected by film thickness, which was monitored by surface colouring during the etch process. A decrease in reagent concentrations results in a proportionally decreased reaction rate. Fig. 1 shows reflectance spectra of porous films produced in solutions where HNO3 concentration was varied by a factor 8 in order to obtain growth rates ranging from 9.2 to 64 A˚ sy1. All the samples were formed on monocrystalline substrates and are 1500– 1800 A˚ thick. The lowest mean reflectance in UV spectral region was obtained in the sample grown at 36 A˚ sy1. Results obtained at larger growth rates were somewhat irreproducible. The spectra reported above were measured from samples grown on monocrystalline substrates, with no particular surface pre-treatment. Light trapping effects by texturization (i.e. formation of pyramidal micro structures on the surface) allowed us to further reduce the reflectance to 1.2% minimum. As shown in Fig. 2, the integrated reflectance was lower than 3% in a wavelength range larger than 400–800 nm. 3.2. Photovoltaic devices
Solar cells were carried out on multicrystalline substrates by giving a stain etch treatment to p/nq junctions, 0.5 mm deep, after an Ag grid was deposited by screen printing and protected by a screen printed polymeric film. Porous Si films
Fig. 1. Reflectance spectra of porous films produced on monocrystalline substrates at growth rates ranging from 9.2 to 64 A˚ sy1. Thickness of the film grown at 64 A˚ sy1 is about 1500 A˚. Other films are approximately 1800 A˚ thick. Measurements were taken at 1 nm intervals. To identify the different spectra a few markers have been added to the curves.
Fig. 2. Integrated reflectance of porous films grown on a monocrystalline texturized substrates: it is lower than 3% in a wavelength range larger than 400–800 nm.
Fig. 3. Reflected power from 1300 and 1500 A˚ thick porous films, under solar AM1.5G radiation. Substrates were multicrystalline, texturized p/nq junctions.
were formed in the regions between the metal lines, resulting in anti-reflection (AR) coating and passivating the surface [3]. The lowest effective reflectance was obtained by 1500 A˚ thick porous films, with refractive index nf2.0. Thus, by using such films for solar cell AR coatings, the highest photocurrent was obtained. Unfortunately, etching themostheavily doped portion of the nq region causes open circuit voltage of the resulting solar cells to be reduced [22,23]. Therefore, optimum porous layer thickness results from a compromise between separate optimisation of either current or voltage and was found to be 1300 A˚ for 35 V/h junctions. In Fig. 3, reflectance data of 1300 A˚ and 1500 A˚ samples are multiplied by power density of AM1.5G radiation, in order to take into account the solar energy spectral distribution. The lattereffect limits photovoltaic conversion efficiency to 11.8% under AM1.5G simulated illumination for 10=10 cm2, 35 V/h multicrystalline solar cells. By using junctions with a thinner emitter (40 V/h, 12.8=12.8 cm2), our best result was 10.1% efficiency. On the other hand, by using double-dielectric coatings, consisting of a thin (f500 A˚) porous layer and
Journal: TSF (Thin Solid Films)
Article: 9436
298
L. Schirone et al. / Thin Solid Films 297 (1997) 296–298
F. Rallo for continuous encouragement. A particular acknowledgement is due to F. Galluzzi for fruitful discussions. Moreover, we are indebted to G. Di Francia for helpful suggestions. References
Fig. 4. Quantum yield spectra of multicrystalline solar cells with porous Si and standard TiO2 AR coatings. Measurements were taken at 10 nm intervals.
a superimposed TiO2 film, a small improvement of photovoltaic efficiency (up to 12%) was obtained. A porous Si-coated solar cell is compared to a commercial TiO2 coated solar cell in Fig. 4, where quantum yield spectra are reported (QY(l)scarriers collected in external circuit/ impinging photons). Our device shows an improved QY in IR region, which can be described in terms of the light scattering produced by roughness at the PS/bulk interface [11,22]. We also observe an improvement in UV region, associated to reduced surface recombination due to hydrogen passivation. 4. Conclusions
Porous Si films have been used as AR coatings in solar cells. The principle objective was the achievement of photovoltaic conversion efficiency comparable to standard commercially available devices. A strong effort was necessary and work is currently in progress in order to optimise the manifold parameters affecting performance of porous silicon coated solar cells (among others, etching solution, surface treatments and doping profile of the substrate). Further variables are introduced by additional TiO2 coatings in doubledielectric devices. Nevertheless, 12% photovoltaic conversion efficiency under AM1.5G simulated sunlight was achieved for a 10=10 cm2 multicrystalline device. To our knowledge, this is the best result reported in the literature for porous Si-based solar cells [13]. Acknowledgements
We wish to acknowledge M. D’Ovidio for preparing substrates, M. Montecchi for providing spectrophotometer and
[1] R.J. Archer, J. Phys. Chem. Solids, 14 (1960) 104. [2] K.H. Jung, S. Shih and D.L. Kwong, J. Electrochem. Soc., 140 (1993) 3046. [3] A. Prasad, S. Balakrishnan, S.K. Jain and G.C. Jain, J. Electrochem. Soc., 129 (1982) 596. [4] J.P Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson and H.S. Kwok, Appl. Phys. Lett., 61 (1992) 459. [5] C. Levy-Clement, A. Lagoubi, M. Neumann-Spallat, M. Rodot and R. Tenne, J. Electrochem. Soc., 138 (1991) L69; also in 11th EPVSEC Proc., Montreux, CH, Harwood Academic Publ., CHUV, CH, 1992, p. 250. [6] G. Smestad, M. Kunst and C. Vial, Solar Energy Mater. Solar Cells, 26 (1992) 277; G. Smestad and H. Reis, Solar Energy Mater. Solar Cells, 25 (1992) 51. [7] Y.S. Tsuo, M.J. Heben, X. Wu, Y. Xiao, C.A. Moore, P. Verlinden and S.K. Deb, Mater. Res. Soc. Proc. 256, Pittsburg, PA, USA (1992); also in Y.S. Tsuo, M.J. Heben, X. Wu, Y. Xiao, F.J. Pern and S.K. Deb, 23rd IEEE PVSC Proc., Louisville, KY, 1993, p. 287. [8] H.P. Maruska, F. Navamar and N.M. Kalkoran, Appl. Phys. Lett., 63 (1993) 45; also in H.P. Maruska, N. Kalkoran and W.D. Halverson, 1st World Conf. on PV Energy Conversion, Waikoloa, HI, 1994. [9] S. Bastide, M. Cuniot, P. Williams, N. Le Quang, D. Sarti and C. LevyClement, 12th EPSECE, Amsterdam, 1994, p. 4A25. [10] W. Guang-Pu, Z. Yi-Ming, H. Zhao-Jian, L. Yu, F. Jing-Wei and M. Yio-Wu, Solar Energy Mater. Solar Cells, 35 (1994) 319. [11] K. Grigoras, A. Krotus, V. Pacebutas, J. Kavaliauskas and I. Simkiene, EMRS Conf Proc., Strasbourg, Elsevier, Amsterdam, 1995. [12] P. Menna, G. Di Francia and V. La Ferrara, Solar Energy Mater. Solar Cells, 37 (1995) 13. [13] E. Vazsonyi, M. Fried, T. Lohner, M. Adam, T. Mohacsy, I. Barsoni, J. Szlufcik, F. Duerinckx and J. Nijs, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 37. [14] L. Schirone, G. Sotgiu F. Rallo and F.P. Califano, Il Nuovo Cimento, Vol. 18 (Oct. 1996) pp. 1225–1232. [15] V. Lehman and U. Gosele, Appl. Phys. Lett., 58 (1991) 856. [16] D.E. Aspnes, J.B. Theeten and F. Hottier, Phys. Rev. B, 20 (1979) 3292. [17] W. Theiss, Adv. Solid State Phys., 33 (1993) 149. [18] M.G. Berger, C. Dieker, M. Thonissen, L. Vescan, H. Luth, H. Munder, W. Theiss, M. Wernke and P. Grosse, J. Phys D, Appl. Phys., 27 (1994) 1333. [19] R. Herino, G. Bomchil, K. Barla and C. Bertrand, J. Electrochem. Soc., 134 (1987) 1994. [20] R.W. Fathauer, T. George, A. Ksendzov and R.P. Vasquez, Appl. Phys. Lett., 60 (1992) 995. [21] K.H. Jung, S. Shih, D.L. Kwong, C.C. Cho and B.E. Gnade, Appl. Phys. Lett., 61 (1992) 2467. [22] S. Bastide, S. Strehlke, M. Cuniot, A. Boutry-Forveille, Q.N. Le, D. Sarti and C. Levy-Clement, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 1280. [23] L. Schirone, G. Sotgiu F. Rallo and F.P. Califano, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 2447. [24] F. Ferrazza, D. Margadonna, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, pp. 3–8.
Journal: TSF (Thin Solid Films)
Article: 9436
Chemically etched porous silicon as an anti-reflection coating for high efficiency solar cells L. Schirone, G. Sotgiu, F.P. Califano Universita` di Roma Tre, Dipartimento di Ingegneria Elettronica, Via della Vasca Navale, 84, 00146 Roma, Italy
Abstract
Porous silicon was formed on mono- and multicrystalline Si substrates by stain etching in aqueous HF/HNO3 solutions. Optical properties of the resulting films were investigated by reflectance spectroscopy and related to the main etch parameters. Porous Si films have been shown able to reduce surface reflectance to under 3% in a wavelength range larger than 400–800 nm. Efficient anti-reflection coatings were developed and used in multicrystalline Si solar cells with area up to 12.8=12.8 cm2. Photovoltaic conversion efficiency up to 12% was obtained under standard AM1.5G simulated sunlight. q 1997 Elsevier Science S.A. Keywords:
Silicon; Porous; Stain etch; Coatings; Solar cells
1. Introduction
Chemical etching of Si in a variety of solutions is known to produce stain layers [1]. These films consist of porous material similar to that resulting from anodic etching of Si in HF solutions [2]. We demonstrate here their use as antireflection (AR) coatings of large area solar cells, enabling a photovoltaic conversion efficiency comparable to commercially available devices. Several authors considered the possible use of porous silicon in PV devices and photo detectors [3–13], and a few groups reported appreciable photovoltaic conversion [9,11,13]. Most of the authors prepared porous Si by electrochemical process in HF/EtOH aqueous solutions [2]. We prefer to use chemical etching in aqueous HF/HNO3 solutions [1], since this technology is more suitable for massive industrial production [12]. This work focuses on the reflective properties of porous films formed on the outermost region of p/nq junctions and relates them to performance of the resulting solar cells.
icon with grain size in millimetres range, obtained by a cheap casting process from waste monocrystalline materials [24]. Silver paste was deposited on the surface by screen printing and sintered at 700 8C in order to provide ohmic contacts. The metal lines were then protected by a screen-printed polymeric film, and the outermost region of the junctions was converted into porous Si by stain etching in aqueous HF/ HNO3 solutions. The starting concentration for our freshsolutions was H2O:HF:HNO3s1:1:0.01 vol., and HNO3 or HF(50%) were then added to increase or decrease the growth rate. Finally, the protecting film was removed in acetone. Further details on the preparation process have been published elsewhere [14]. Integrated reflectance of porous films was measured by a Lambda 9 Perkin–Elmer spectrophotometer. Measurements were taken at 1 nm intervals, 400 A˚ miny1 scan rate. Film thickness was deduced from fitting reflectance data by a model based on a monolayer film. Solar cell efficiency was measured under standard AM1.5G conditions. The quantum yield was measured at 10 nm intervals.
2. Experimental details 3. Results and discussion
Substrates were B-doped multi- and monocrystalline Si wafers, thermally diffused to form 0.5 mm deep junctions, consisting of a shallow 0.1 mm nq region with approximately constant 1020 cmy3 phosphorus concentration and a deeper decreasing erfc-shaped profile. Multicrystalline is a poly-sil-
3.1. Porous Si anti-reflection layers
Porous Si is a sponge-like material, consisting of nanometer-sized voids and monocrystalline columns, with a large,
0040-6090/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved PII S0040-6090(96)09436-9
Journal: TSF (Thin Solid Films)
Article: 9436
297
L. Schirone et al. / Thin Solid Films 297 (1997) 296–298
hydrogenated surface [15]. Therefore, the refractive index is controlled by the volume fraction of void with respect to the crystalline skeleton (porosity) [16,17], and it can be adjusted to optimise optical matching between air and Si [12]. The parameters which are known to affect the material porosity are solution composition and porous film growth rate [20,21]. Moreover, properties of the resulting porous films depend on substrate doping profile, as it is well known for anodically etched porous films [18,19]. Reflectance of a porous Si-coated surface is also affected by film thickness, which was monitored by surface colouring during the etch process. A decrease in reagent concentrations results in a proportionally decreased reaction rate. Fig. 1 shows reflectance spectra of porous films produced in solutions where HNO3 concentration was varied by a factor 8 in order to obtain growth rates ranging from 9.2 to 64 A˚ sy1. All the samples were formed on monocrystalline substrates and are 1500– 1800 A˚ thick. The lowest mean reflectance in UV spectral region was obtained in the sample grown at 36 A˚ sy1. Results obtained at larger growth rates were somewhat irreproducible. The spectra reported above were measured from samples grown on monocrystalline substrates, with no particular surface pre-treatment. Light trapping effects by texturization (i.e. formation of pyramidal micro structures on the surface) allowed us to further reduce the reflectance to 1.2% minimum. As shown in Fig. 2, the integrated reflectance was lower than 3% in a wavelength range larger than 400–800 nm. 3.2. Photovoltaic devices
Solar cells were carried out on multicrystalline substrates by giving a stain etch treatment to p/nq junctions, 0.5 mm deep, after an Ag grid was deposited by screen printing and protected by a screen printed polymeric film. Porous Si films
Fig. 1. Reflectance spectra of porous films produced on monocrystalline substrates at growth rates ranging from 9.2 to 64 A˚ sy1. Thickness of the film grown at 64 A˚ sy1 is about 1500 A˚. Other films are approximately 1800 A˚ thick. Measurements were taken at 1 nm intervals. To identify the different spectra a few markers have been added to the curves.
Fig. 2. Integrated reflectance of porous films grown on a monocrystalline texturized substrates: it is lower than 3% in a wavelength range larger than 400–800 nm.
Fig. 3. Reflected power from 1300 and 1500 A˚ thick porous films, under solar AM1.5G radiation. Substrates were multicrystalline, texturized p/nq junctions.
were formed in the regions between the metal lines, resulting in anti-reflection (AR) coating and passivating the surface [3]. The lowest effective reflectance was obtained by 1500 A˚ thick porous films, with refractive index nf2.0. Thus, by using such films for solar cell AR coatings, the highest photocurrent was obtained. Unfortunately, etching themostheavily doped portion of the nq region causes open circuit voltage of the resulting solar cells to be reduced [22,23]. Therefore, optimum porous layer thickness results from a compromise between separate optimisation of either current or voltage and was found to be 1300 A˚ for 35 V/h junctions. In Fig. 3, reflectance data of 1300 A˚ and 1500 A˚ samples are multiplied by power density of AM1.5G radiation, in order to take into account the solar energy spectral distribution. The lattereffect limits photovoltaic conversion efficiency to 11.8% under AM1.5G simulated illumination for 10=10 cm2, 35 V/h multicrystalline solar cells. By using junctions with a thinner emitter (40 V/h, 12.8=12.8 cm2), our best result was 10.1% efficiency. On the other hand, by using double-dielectric coatings, consisting of a thin (f500 A˚) porous layer and
Journal: TSF (Thin Solid Films)
Article: 9436
298
L. Schirone et al. / Thin Solid Films 297 (1997) 296–298
F. Rallo for continuous encouragement. A particular acknowledgement is due to F. Galluzzi for fruitful discussions. Moreover, we are indebted to G. Di Francia for helpful suggestions. References
Fig. 4. Quantum yield spectra of multicrystalline solar cells with porous Si and standard TiO2 AR coatings. Measurements were taken at 10 nm intervals.
a superimposed TiO2 film, a small improvement of photovoltaic efficiency (up to 12%) was obtained. A porous Si-coated solar cell is compared to a commercial TiO2 coated solar cell in Fig. 4, where quantum yield spectra are reported (QY(l)scarriers collected in external circuit/ impinging photons). Our device shows an improved QY in IR region, which can be described in terms of the light scattering produced by roughness at the PS/bulk interface [11,22]. We also observe an improvement in UV region, associated to reduced surface recombination due to hydrogen passivation. 4. Conclusions
Porous Si films have been used as AR coatings in solar cells. The principle objective was the achievement of photovoltaic conversion efficiency comparable to standard commercially available devices. A strong effort was necessary and work is currently in progress in order to optimise the manifold parameters affecting performance of porous silicon coated solar cells (among others, etching solution, surface treatments and doping profile of the substrate). Further variables are introduced by additional TiO2 coatings in doubledielectric devices. Nevertheless, 12% photovoltaic conversion efficiency under AM1.5G simulated sunlight was achieved for a 10=10 cm2 multicrystalline device. To our knowledge, this is the best result reported in the literature for porous Si-based solar cells [13]. Acknowledgements
We wish to acknowledge M. D’Ovidio for preparing substrates, M. Montecchi for providing spectrophotometer and
[1] R.J. Archer, J. Phys. Chem. Solids, 14 (1960) 104. [2] K.H. Jung, S. Shih and D.L. Kwong, J. Electrochem. Soc., 140 (1993) 3046. [3] A. Prasad, S. Balakrishnan, S.K. Jain and G.C. Jain, J. Electrochem. Soc., 129 (1982) 596. [4] J.P Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson and H.S. Kwok, Appl. Phys. Lett., 61 (1992) 459. [5] C. Levy-Clement, A. Lagoubi, M. Neumann-Spallat, M. Rodot and R. Tenne, J. Electrochem. Soc., 138 (1991) L69; also in 11th EPVSEC Proc., Montreux, CH, Harwood Academic Publ., CHUV, CH, 1992, p. 250. [6] G. Smestad, M. Kunst and C. Vial, Solar Energy Mater. Solar Cells, 26 (1992) 277; G. Smestad and H. Reis, Solar Energy Mater. Solar Cells, 25 (1992) 51. [7] Y.S. Tsuo, M.J. Heben, X. Wu, Y. Xiao, C.A. Moore, P. Verlinden and S.K. Deb, Mater. Res. Soc. Proc. 256, Pittsburg, PA, USA (1992); also in Y.S. Tsuo, M.J. Heben, X. Wu, Y. Xiao, F.J. Pern and S.K. Deb, 23rd IEEE PVSC Proc., Louisville, KY, 1993, p. 287. [8] H.P. Maruska, F. Navamar and N.M. Kalkoran, Appl. Phys. Lett., 63 (1993) 45; also in H.P. Maruska, N. Kalkoran and W.D. Halverson, 1st World Conf. on PV Energy Conversion, Waikoloa, HI, 1994. [9] S. Bastide, M. Cuniot, P. Williams, N. Le Quang, D. Sarti and C. LevyClement, 12th EPSECE, Amsterdam, 1994, p. 4A25. [10] W. Guang-Pu, Z. Yi-Ming, H. Zhao-Jian, L. Yu, F. Jing-Wei and M. Yio-Wu, Solar Energy Mater. Solar Cells, 35 (1994) 319. [11] K. Grigoras, A. Krotus, V. Pacebutas, J. Kavaliauskas and I. Simkiene, EMRS Conf Proc., Strasbourg, Elsevier, Amsterdam, 1995. [12] P. Menna, G. Di Francia and V. La Ferrara, Solar Energy Mater. Solar Cells, 37 (1995) 13. [13] E. Vazsonyi, M. Fried, T. Lohner, M. Adam, T. Mohacsy, I. Barsoni, J. Szlufcik, F. Duerinckx and J. Nijs, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 37. [14] L. Schirone, G. Sotgiu F. Rallo and F.P. Califano, Il Nuovo Cimento, Vol. 18 (Oct. 1996) pp. 1225–1232. [15] V. Lehman and U. Gosele, Appl. Phys. Lett., 58 (1991) 856. [16] D.E. Aspnes, J.B. Theeten and F. Hottier, Phys. Rev. B, 20 (1979) 3292. [17] W. Theiss, Adv. Solid State Phys., 33 (1993) 149. [18] M.G. Berger, C. Dieker, M. Thonissen, L. Vescan, H. Luth, H. Munder, W. Theiss, M. Wernke and P. Grosse, J. Phys D, Appl. Phys., 27 (1994) 1333. [19] R. Herino, G. Bomchil, K. Barla and C. Bertrand, J. Electrochem. Soc., 134 (1987) 1994. [20] R.W. Fathauer, T. George, A. Ksendzov and R.P. Vasquez, Appl. Phys. Lett., 60 (1992) 995. [21] K.H. Jung, S. Shih, D.L. Kwong, C.C. Cho and B.E. Gnade, Appl. Phys. Lett., 61 (1992) 2467. [22] S. Bastide, S. Strehlke, M. Cuniot, A. Boutry-Forveille, Q.N. Le, D. Sarti and C. Levy-Clement, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 1280. [23] L. Schirone, G. Sotgiu F. Rallo and F.P. Califano, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, p. 2447. [24] F. Ferrazza, D. Margadonna, 13th EPVSCE Proc., Nice, France, Stephens and Associates, Bedford, UK, 1995, pp. 3–8.
Journal: TSF (Thin Solid Films)
Article: 9436