Deposition of nanocryctalline silicon thin films: Effect of total pressure and substrate temperature R. Baghdad a,1 , D. Benlakehal b , X. Portier c , K. Zellama a, ⁎ , S. Charvet a , J.D. Sib b , M. Clin a , L. Chahed b a Laboratoire de Physique de la Matière Condensée, Faculté des Sciences, Université de Picardie Jules Verne, 33 Rue Saint-Leu, 80039 Amiens, France b Laboratoire de Physique des Couches Minces et de Microélectronique, Département de Physique, Université d'Oran Es-sénia, 31000 Oran, Algeria c SIFCOM-ENSICAEN, UMR 6176-CNRS, 6 Blvd. Maréchal Juin, 14050 Caen, France Received 22 December 2006; received in revised form 2 July 2007; accepted 30 July 2007 Available online 8 August 2007 Abstract The structural changes in intrinsic silicon thin films are investigated as a function of the total pressure (2 to 4 Pa) and substrate temperature (room temperature to 200 °C). Infrared absorption, Raman spectroscopy and high resolution transmission electron microscopy are applied to characterize the films. The results indicate that the films grown at 2 Pa are completely amorphous, while at 3 and 4 Pa, crystallization occurs at temperature as low as room temperature. These structural changes are well correlated to the variation of the room temperature conductivity, which increases up to about eight orders of magnitude for the nanocrystallized films. A crystalline volume fraction varying from 71 to about 90% is also observed. The growth mechanism of the nanocrystalline films is also discussed in the framework of the reported models. © 2007 Elsevier B.V. All rights reserved. PACS: 81.07.Bc; 78.30.-j; 68.37.Lp Keywords: Nanocrystalline silicon; Infrared spectroscopy; Raman spectroscopy; Transmission electron microscopy; Electrical properties and measurements 1. Introduction Over the past few years, hydrogenated nanocrystalline silicon (nc-Si:H) films have become the subject of great attention due to their remarkable optoelectronic properties for microeletronics and solar cells technology [1–3]. It has been reported that these films exhibit a reduced light-induced degradation as compared to the amorphous silicon based materials [4,5]. The challenge is now to grow nc-Si:H with good electronic properties at relatively low temperature (b 200 °C) compatible with the use of flexible polymeric substrates that cannot withstand elevated temperatures, which makes these materials potential candidates for further industrial applications. Numerous studies have been conducted on these films grown using a combination of various deposition parameters and techniques including plasma enhanced chemical vapour deposition (PECVD), hot wire CVD (HWCVD), VHFCVD and radiofrequency magnetron sputtering (RFMS) [1–9]. The latter is a simple and promising low cost technique as it has the advantage to control the hydrogen incorporation and to grow crystallized doped films without using toxic gases. It has been found that the deposition conditions such as the total pressure, partial hydrogen and argon dilution, substrate temperature and radiofrequency (RF) power are of crucial importance for the growth of nc-Si:H and their optoelectronic properties [1–12]. However, the relationship between the deposition parameters and the growth mechanisms of nc-Si:H is still a subject of debate [1,6,8,13]. Different growth mechanisms have been proposed including surface diffusion of adsorbed precursors, selective etching or hydrogen chemical annealing [1,6,8,10,14–16]. It is also found that the use of high total pressure may lead to the growth of porous films [3,17]. The aim of this work is to get more insight into the effect of the total pressure and the substrate temperature on the structural and electrical properties of the nc-Si:H films. Also, the possibility to grow nc-Si:H, using RFMS, at relatively low pressure (below 4 Pa) and at temperature as low as room temperature, in keeping good Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 3965 – 3970 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +33 3 22 82 75 97; fax: +33 3 22 82 78 91. E-mail address: Kacem.Zellama@sc.u-picardie.fr (K. Zellama). 1 Permanent address: Laboratoire de Génie Physique, Université Ibn Khaldoun, 14000 Tiaret, Algeria. 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.07.190