STRUCTURAL CHANGES STUDIES OF a-Si:H FILMS DEPOSITED BY PECVD UNDER DIFFERENT HYDROGEN DILUTIONS USING VARIOUS EXPERIMEN

1. STRUCTURAL CHANGES STUDIES OF a-Si:H FILMS DEPOSITED BY PECVD UNDER DIFFERENT HYDROGEN DILUTIONS USING VARIOUS EXPERIMENTAL TECHNIQUES Veronika Vavruňková1Jarmila Müllerová2Rudolf Srnánek3, Pavol Šutta1 1 Department of Materials and Technology, New Technology Research Centre, University of West Bohemia, Univerzitní 8, Plzeň, 306 14, Czech Republic 2 Department of Engineering Fundamentals, Faculty of Electrical Engineering, University of Žilina, ul.kpt. J. Nálepku 1390, 031 01 Liptovský Mikuláš, Slovakia 3 Department of Microelectronics, Slovak University of Technology, Ilkovicova 3, Bratislava, 812 19, Slovak Republic Corresponding author: vavrunko@ntc.zcu.cz Introduction Experimental material • thin films of a-Si:H prepared using the hydrogen dilutionin silane source gas by plasma enhanced chemical vapour deposition (PECVD) belong to promising materials for low-cost solar cells • this deposition technique has been used to yield material with good opto-electrical properties, such as light stability (less light induced degradation known as Staebler-Wronski effect), higher optical band gap • the structure of films is necessary to understand and improve properties of the a-Si:H films which is significant for the application in solar cells • in this work, we focus on the effects of hydrogen dilution ration on the structural quality and evolution of c-Si in amorphous network • protocrystalline siliconconstitutestheevolutionfromamorphousto nanocrystalline silicon and contains the medium-range order (MRO) • a series of a-Si:H thin films were deposited using rf-PECVD under increasing dilution of silane plasma by hydrogen • the hydrogen to silane dilution ratio R = H2/SiH4 was varied from 5 to 40 • the samples were deposited on Corning glass 1737 substrates and on [100] oriented c-Si wafers • a reference sample was deposited using pure silane (R = 0) • the thickness of all films was approximately 300 nm X-ray diffraction • the XRD patterns were recordedusing automatic power diffractometer X´pertPro with the Cu X-ray tube ( = 0.154178 nm) and a thin film attachment • substrate and dilution influence • MRO was determined from thin films deposited on c-Si • lower value of FWHM indicates that films and contain MRO ~ 5-7 nm in size • evolution of the crystalline phase with increasing dilution on samples on glass substrate Raman spectroscopy • the Raman spectra were excited with a He-Ne laser generating the wavelength of 632.8 nm • grain size Si (220) 2D detector FTIR spectrometry • IR absorbance spectra were performed in the range of 650 – 4000 cm-1 using the ATR accessory with trapezoidal silicon crystal with a bevelled edge of 45 • mapping from the surface5 x 5 μm • integral intensity of Si crystalline peak • stretching vibrations of silicon hydrides SiH (2000cm-1) and SiH2 (2090cm-1) Conclusions • formation of the polycrystalline phase with increasing dilution – samples on glass • c-Si substrate - amorphous containing medium-range order • medium-range order determined from the films deposited on c-Si~ 5-7 nm • grain sizes calculated from Raman spectrometry increase with increasing dilutionabout ~ 3-5 nm • films - quite homogeneously • microstructure factor ~ 12 % in average, • material - slightly porous • microstructure factor and hydrogen concentration • the hydride configurations are agreeing with contribution to vacancies and void surfaces References [1] Van Elzakker, G.; Šutta, P.; Tichelaar, F.; Zeman, M. Phase control and stability of thin silicon films deposited from silane diluted with hydrogen. In MRS Symposium Proceedings. Vol. 989. Warrendale : 2007. ISBN 978-1-55899-949-7. [2] Park, Y. - B., Rhee, Y. – B. Microstructure and initial growth characteristics of the low temperature microcrystalline silicon films on silicon nitride surface J. Appl. Phys. 90, 217 – 221 (2001). [3] Stannowski, B., Schropp, R.E.I. Thin Solid Films, 383 (2001) p.125 – 128. [4] Vavruňková, V., Müllerová, J., Šutta, P. AEEE. 6 (2007), p. 108-111.