Sains Malaysiana 41(8)(2012): 993–1000

Effects of Rf Power on Structural Properties of Nc-Si:H Thin FilmsDeposited

by Layer-By-Layer (LbL) Deposition Technique

(Kesan Kuasa Rf Terhadap Sifat-Sifat Struktur Filem Nipis Nc-Si:H yang dimendapkan denganMenggunakan Teknik Lapisan Demi Lapisan (LbL)

Goh Boon Tong*, Muhamad Rasat Muhamad & Saadah Abdul Rahman

Low Dimensional Materials Research Centre, Department of Physics

University of Malaya, 50603 Kuala Lumpur, Malaysia

Received: 5 October 2011 / Accepted: 15 March 2012

ABSTRACT

The effects of rf power on the structural properties of hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited using layer-by-layer (LbL) deposition technique in a home-built plasma enhanced chemical vapor deposition (PECVD) system were investigated. The properties of the films were characterized by X-ray diffraction (XRD), micro-Raman scattering spectroscopy, high resolution transmission electron microscope (HRTEM) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the films consisted of different size of Si crystallites embedded within an amorphous matrix and the growth of these crystallites was suppressed at higher rf powers. The crystalline volume fraction of the films was optimum at the rf power of 60 W and contained both small and big crystallites with diameters of 3.7 nm and 120 nm, respectively. The hydrogen content increased with increasing rf power and enhanced the structural disorder of the amorphous matrix thus decreasing the crystalline volume fraction of the films. Correlation of crystalline volume fraction, hydrogen content and structure disorder of the films under the effect of rf power is discussed.

Keywords: Crystalline volume fraction; hydrogen content; layer-by-layer deposition; ncSi:H; XRD

ABSTRAK

Dalam penyelidikan ini, kesan kuasa rf terhadap struktur filem nipis nanohablur silikon berhidrogen (nc-Si:H) yang dimendapkan menggunakan teknik lapisan demi lapisan (LbL) daripada sistem pemendapan wap kimia secara peningkatan plasma (PECVD) buatan sendiri telah dikaji. Sifat-sifat struktur filem nipis ini dikaji dengan kaedah belauan sinar-X (XRD), spektroskopi penyebaran mikro-Raman, mikroskopi elektron imbasan beresolusi tinggi (HRTEM) dan spektroskopi transformasi Fourier inframerah (FTIR). Keputusan menunjukkan bahawa filem nipis ini mengandungi hablur nano Si yang berlainan saiz yang terbenam dalam matriks amorfus. Pertumbuhan hablur nano Si ini terbantut pada kuasa rf yang lebih tinggi. Pecahan isi padu hablur filem nipis ini mencapai nilai optimum pada kuasa rf 60 W yang mengandungi kristalit silikon yang bersaiz kecil dan besar dengan diameter 3.7 and 120 nm. Kandungan hidrogen meningkat dengan menambahkan kuasa rf. Ini meningkatkan struktur tak tertib matriks amorfus dan pecahan isi padu hablur dalam filem nipis dapat dikurangkan. Korelasi di antara pecahan isi padu hablur, kandungan hidrogen dan struktur tak tertib filem nipis dengan kesan kuasa rf dibincangkan.

Kata kunci: Kandungan hydrogen; nc-Si:H; pemendapan LbL; XRD; pecahan isipadu hablur

REFERENCES

Adhikary, K. & Ray, S. 2007. Characteristics of p-type nanocrystalline silicon thin films developed for window layer of solar cells. J. Non-Cryst. Solids 353: 2289-2294.

Ali, A.M. 2006. Mechanisms of the growth of nanocrystalline Si:H films deposited by PECVD. J. Non-Cryst. Solids 352: 3126-3133.

Alpuim, P. & Chu, V. 1999. Amorphous and microcrystalline silicon films grown at low temperatures by radio-frequency and hot-wire chemical vapor deposition. J. Appl. Phys. 86: 3812-10.

Ambrosone, G., Coscia, U., Lettieri, S., Maddalena, P. & Minarini, C. 2003. Optical, structural and electrical properties of μc-Si:H films deposited by SiH4+H2. Mater. Sci. & Eng. B 101: 236-241.

Baghdad, R., Benlakehal, D., Portier, X., Zellama, K., Charvet, S., Sib, J.D., Clin, M. & Chahed, L. 2008. Deposition of nanocryctalline silicon thin films: Effect of total pressure and substrate temperature. Thin Solid Films 516: 3965-3970.

Bhattacharya, E. & Mahan, A.H. 1988. Microstructure and the light-induced metastability in hydrogenated amorphous silicon. Appl. Phys. Lett. 52: 1587-3.

Brodsky, M.H., Cardona, M. & Cuomo, J.J. 1977. Infrared and Raman spectra of the silicon-hydrogen bonds in amorphous silicon prepared by glow discharge and sputtering. Phys. Rev. B 16: 3556-3571.

Cabarrocas, P. & Roca, I. 2004. New approaches for the production of nano-, micro-, and polycrystalline silicon thin films. Phys. Status Solidi (c) 1(5): 1115-1130.

Chen, X.Y., Chen, W.Z., Chen, H., Zhang, R. & He, Y.L. 2006. High electron mobility in well ordered and lattice-strained hydrogenated nanocrystalline silicon. Nanotechnology 17: 595-599.

Choi, W.C., Kim, E.K., Min, S.-K., Park, C.Y., Kim, J.H. & Seong, T.-Y. 1997. Direct formation of nanocrystalline silicon by electron cyclotron resonance chemical vapor deposition. Appl. Phys. Lett. 70: 3014-3.

Goh, B.T. & Rahman, S.A. 2006. Effect of substrate temperature on the properties of hydrogenated nanocrystalline silicon thin film grown by layer-by-layer technique. Proceeding of the IEEE International Conference on Semiconductor Electronics 2006 (ICSE2006). Kuala Lumpur. Malaysia: IEEEXplore. pp. 472-476.

Goh, B.T., Gani, S.M. Ab. & Rahman, S.A. 2008. Influence of hydrogen dilution of silane on the properties of nc-Si:H films grown by layer-by-layer deposition technique. Adv. Mater. Res. 31: 80-82.

Goh, B.T., Gani, S. M. Ab. & Rahman, S.A. 2008b. Crystallinity and Si-H Bonding Configuration of nc-Si:H films grown by layer-by-layer (LBL) deposition technique at different rf power. Sains Malaysiana 37(3): 233-237.

Goh, B.T., Gani, S.M. Ab., Muhamad, R.M. & Rahman, S.A. 2009. Influence of bias voltage on the optical and structural properties of nc-Si:H films grown by layer-by-layer (LBL) deposition technique. Thin Solid Films 517: 4945-4949.

Goswani, R. & Ray, S. 2007. Study of Medium-Range Order and Defects in Hydrogenated Protocrystalline Silicon Films Deposited by Radio Frequency Plasma Enhanced Chemical Vapor Deposition. Jpn. J. Appl. Phys. 46(11): 7188-7193.

Hatzopoulos, A.T., Pappas, I., Tassis, D.H., Arpatzanis, N., Dimitriadisa, C.A., Templier, F. & Oudwan, M. 2006. Analytical current-voltage model for nanocrystalline silicon thin-film transistors. Appl. Phys. Lett. 89: 193504-3.

Hazra, S., Saha, S.C. & Ray, S. 1999. Polycrystalline silicon thin films prepared by plasma enhanced chemical vapour deposition at 200°C using fluorinated source gas. J. Phys. D: Appl. Phys. 32: 208-212.

Huet, S., Viera, G. & Boufendi, L. 2002. Effect of small crystal size and surface temperature on the Raman spectra of amorphous and nanostructured Si thin films deposited by radiofrequency plasmas. Thin Solid Films 403-404: 193-196.

Itoh, T., Yamamoto, K., Ushikoshi, K., Nonomura, S. & Nitta, S. 2000. Characterization and role of hydrogen in nc-Si:H. J. Non-Cryst. Solids 266-269: 201-205.

Klung, H.P. & Alexander, L.E. 1974. X-ray Diffraction Procedures. New York: Wiley.

Knights, J.C., Lujan, R.A., Rosenblum, M.P., Street, R.A., Bieglesen, D.K. & Reimer, J.A. 1981. Effects of inert gas dilution of silane on plasma-deposited a-Si:H films. Appl. Phys. Lett. 38: 331-3.

Lin, C.-Y., Fang, Y.-K., Chen, S.-F., Lin, P.-C., Lin, C.-S., Chou, T.-H., Hwang, J.S. & Lin, K.I. 2006. Growth of nanocrystalline silicon thin film with layer-by-layer technique for fast photo-detecting applications. Mater. Sci. & Eng. B 127: 251-254.

Lucovksy, G., Nemanich, R.J. & Knights, J.C. 1979. Structural interpretation of the vibrational spectra of a-Si: H alloys. Phys. Rev. B 19: 2064-2073.

Raha, D. & Das, D. 2008. Hydrogen induced promotion of nanocrystallization from He-diluted SiH4 plasma. J. Phys. D: Appl. Phys. 41: 085303-9.

Ruther, R. & Livingstone, J. 1994. Hydrogenated amorphous silicon: Hydrogen content, bonding configurations and morphology in sputter-deposited, in-chamber annealed thin films. Thin Solid Films 251: 30-35.

Swain, B.P& Hwang, N.M. 2009. Effect of negative substrate bias on HWCVD deposited nanocrystalline silicon (nc-Si) films. Solid State Sci. 11: 467-471.

Torchynska, T.V. 2009. Emission of Si nanoclusters of different phases in amorphous hydrogenated silicon. Superlattices & Microstructures 45: 267-270.

Viera, G., Huet, S. & Boufendi, L. 2001. Crystal size and temperature measurements in nanostructured silicon using Raman spectroscopy. J. Appl. Phys. 90: 4175-9.

Wang, J.L. & Wu, E.X. 2007. Characterization of doped hydrogenated nanocrystalline silicon films prepared by plasma enhanced chemical vapour deposition. Chin. Phys. 16: 848-06.

Wang, K., Canning, A., Weinberg-Wolf, J.R., Harley, E.C.T & Han, D. 2004. Correlation of Hydrogenated Nanocrystalline Silicon Microstructure and Solar Cell Performance. Mat. Res. Soc. Symp. Proc. 808: A9.53.1-6.

Yue, G., Yan, B., Ganguly, G., Yang, J., Guha, S. & Teplin, C.W. 2006. Material structure and metastability of hydrogenated nanocrystalline silicon solar cells. Appl. Phys. Lett. 88: 263507-3.

*Corresponding author; email: boontong77@yahoo.com