Sains Malaysiana 37(3):  233-237 (2008)

Crystallinity and Si-H Bonding Configuration of nc-Si:H Films Grown by Layer-by-layer (LBL) Deposition Technique at Different RF Power

(Kehabluran dan Konfigurasi Ikatan Filem nc-Si: H yang ditumbuhkan dengan

Teknik Mendapan Lapisan Demi Lapisan (LBL) pada Kuasa RF yang berlainan)

Goh Boon Tong, Siti Meriam Ab. Gani & Saadah Abdul Rahman

University of Malaya

50603 Kuala Lumpur, Malayssia

Received:  12 June 2007 / Accepted:  4 December 2007

ABSTRACT

A set of hydrogenated nanocrystalline silicon (nc-Si:H) films prepared in a home-built plasma enhanced chemical vapour deposition (PECVD) system using the layer-by-layer (LBL) deposition technique have been studied. The 13.56 MHz rf power was varied from 20 W to 100 W to study the influence of rf power on the structural properties of the nc-Si:H films. The structure of the films was studied by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Appearance of XRD peaks at 2q angles of 28^o and 56^o  which correspond to silicon orientation of (111) and (311) respectively were observed in all films deposited on c-Si substrate indicating evidence of crystallinity in the films. The crystallite sizes were in the range of 8 to 100 nm as determined using the Scherrer technique. The integrated intensities of absorption bands at 630 cm^-1, 780 - 880 cm^-1 and 2000 – 2090 cm^-1 from FTIR spectrum which corresponds to various Si-H bonding configurations in the films were studied and were related to the presence of small clusters of nanocrystallites embedded in an amorphous matrix. Based on the dependence of amplitudes of Si-H vibrational modes on crystallite size and rf power, the properties and the role of hydrogen in nc-Si:H films prepared using the LBL technique were discussed.

Keywords: nc-Si:H; XRD; crystallite size; FTIR

ABSTRAK

Satu set sampel filem nipis nanohablur silikon berhidrogen (nc-Si:H) dihasilkan daripada sistem pemendapan wap kimia secara peningkatan plasma (PECVD) buatan sendiri dengan menggunakan teknik lapisan demi lapisan (LBL) telah dikaji. Kuasa frekuensi radio (rf) yang berfrekuensi 13.56 MHz diubah daripada 20 W ke 100 W untuk mengkaji kesan kuasa rf ke atas sifat struktur filem nipis nc-Si:H. Sifat struktur filem nipis ini dikaji oleh belauan sinar-X (XRD) dan spektroskopi Transformasi Fourier Inframerah (FTIR). Daripada keputusan XRD, semua filem nipis yang termendap di atas hablur silikon menunjukkan kemunculan puncak pada 2q di 28^o dan 56^o adalah bersepadan dengan silikon yang berorientasi (111) dan (311). Cara ini dapat memastikan sifat hablur dalam filem nipis tersebut. Saiz hablur tersebut adalah berada dalam julat 8 nm sehingga 100 nm yang dikira dengan menggunakan persamaan Scherrer. Keamatan terkamil bagi jalur penyerapan pada 630 cm^-1, 780 – 880 cm^-1 dan 2000 – 2090 cm^-1 daripada spektrum FTIR dalam nc-Si:H filem nipis dikaji. Jalur-jalur ini adalah bersepadan dengan pelbagai jenis susunan bagi ikatan Si-H dan dihubungkan dengan kehadiran kelompok kecil nanohablur yang terbenam dalam matriks amorfus. Dengan mengasaskan kebersandaran di antara amplitud bagi mod getaran Si-H dengan saiz hablur dan kuasa rf, sifat-sifat filem nipis nc-Si:H dan peranan hydrogen dalam filem nipis tersebut yang dihasilkan melalui teknik LBL dibincangkan.

Kata kunci: nc-Si:H; XRD; saiz hablur; FTIR

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

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

Ali, Atif Mossad, Inokuma, Takao & Hasegawa, Seiichi 2006. Structural and photo-luminescence properties of nanocrystalline silicon films deposited at low temperature by plasma-enhanced chemical vapor deposition. Appl. Surf. Sci. 253: 1198-1204.

Asano, A. 1990. Effects of hydrogen atoms on the network structure of hydrogenated amorphous and microcrystalline silicon thin films. Appl. Phys. Lett. 56: 533-535.

Bhattacharya, E. & Mahan, A. H. 1988. Microstructure and the light-induced metastability in hydrogenated amorphous silicon. Appl. Phys. Lett. 52: 1587-1589.

Binetti, S., Acciarri, M., Bollani, M., Fumagalli, L., Von Kanel, H. & Pizzini, S. 2005. Nanocrystalline silicon films grown by Low Energy Plasma Enhanced Chemical Vapor Deposition for optoelectronic applications. Thin Solid Films 487: 19-25.

Chen, X.Y., Shen, 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.

Godet, C., Layadi, N. & Roca I Cabarrocas, P. 1995. Role of mobile hydrogen in the amorphous silicon recrystallization. Appl. Phys. Lett. 66: 3146-3148.

Goh, Boon Tong & Rahman, S.A. 2006. Effects of Substrate Temperature on The Properties of Hydrogenated Nanocrystalline Silicon Thin Film Grown by Layer-by-Layer technique, Proceedings of the IEEE International Conference on Semiconductor Electronics 2006 (ICSE2006). Kuala Lumpur, Malaysia: IEEE Xplore. pp. 472-476.

Gudovskikh, A.S., Kleider, J.P., Afanasjev, V.P., Kazak-Kazakevich, A.Z. & Sazanov, A.P. 2004. Investigation of nc-Si inclusions in multilayer a-Si:H films obtained using the layer by layer technique. J. Non-Cryst. Solids 338-340: 135-138.

Harun, Roszairi and Rahman, S.A. in: Proceedings of the IEEE International Conference on Semiconductor Electronics 2002 (ICSE 2002), Penang, Malaysia, 19^th – 21^th Dec 2002, pp. 300. 

Langford, A.A., Fleet, M.L., Nelson, B.P., Lanford, W.A. & Maley, N. 1992. Infrared absorption strength and hydrogen content of hydrogenated amorphous silicon. Phys. Rev. B 45: 13367-13377.

Lebib, S. & Roca I.C, P. 2005. Effects of ion energy on the crystal size and hydrogen bonding in plasma-deposited nanocrystalline silicon thin films. J. Appl. Phys. 97: 104334.

Lin, Chun-Yu, Fang, Yean-Kuen, Chen, Shih-Fang, Lin, Ping-Chang, Lin, Chun-Sheng, Chou, Tse-Heng, Hwang, Jenn Shyong & Lin, Kuang 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.

Liu, X.-N., Tong, Song, Wang, L.-C., Chen, G.-X. & Bao, X.-M. 1995. Photoluminescence of nanocrystallites embedded in hydrogenated amorphous silicon films. J. Appl. Phys. 78: 6193-6196.

Nussield, E.W. 1966. X-Ray Diffraction Methods. New York: John Wiley & Sons.

Wang, Jin-Liang & Wu, Er-Xing 2007. Characterization of doped hydrogenated nanocrystalline silicon films prepared by plasma enhanced chemical vapour deposition. Chin. Phys. 16: 848-853.