Chemical surface passivation of silicon nanowires grown by APCVD Bhabani S. Swain a , Bibhu P. Swain b, * , Nong M. Hwang a a National Research Laboratory of Charged Nanoparticles, Department of Materials Science and Engineering, Seoul National University, Republic of Korea b Research Center for Photovoltaic, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan article info Article history: Received 2 November 2009 Accepted 2 December 2009 Available online 16 December 2009 Keywords: Silicon nanowires Surface passivations Photovoltics cells abstract Silicon nanowires (SiNWs) are attractive candidate for solar cells and surface passivation has been recog- nized an important fabrication steps solar cells. The SiNWs were grown on p-type Si (1 0 0) substrate by atmospheric pressure chemical vapour deposition. Field emission scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy were used to study the atomic bonding and microstructural aspect of silicon nanowires. Hydrogen and chlorine passivation were carried out by dilute HF and HCl solutions. The transient photoconductance decay and effective lifetime of SiNWs/c-Si were study by microwave photoconductance decay. The effective lifetime of SiNWs/p-Si were observed in between 0.5 and 0.8 ls. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years, nanowires including nanorods based solar cells have attractive interest due to their characteristics and processing benefits. The nanowires-enabled solar cells allow for decoupling the light absorption from the direction of carrier transport, such that in materials where the diffusion length of minority carriers is much shorter than the thickness of material required for optimal light absorption, current densities can be improved. Nanostructure solar cells, such as organic–inorganic materials, compound semi- conductor and many researchers [1–3] studied hetero or homo- junction silicon structures. These results indicate that the nano- wires are attractive to enhance charge transport in nanostructures solar cells compared with conventional solar cells or other nano- structured solar cells. In particular, silicon nanowires (SiNWs) are allows efficient charge transport. SiNWs can easily dope with various impurities to fabricate n- or p-type Si semiconductor [4] and [5]. The SiNWs have been synthesized by using various methods and metal cata- lysts via well-known vapor–liquid–solid (VLS) mechanism [6,7]. Moreover, various materials, such as Au, Al, Ga, In, Pb, Sn and Zn [6–13], have been used for synthesis of silicon nanowires. Recently, hetero-junction solar cell using SiNWs have been demonstrated by Tsakalakos et al. [2] and Thony et al. [3]. They fabricated an all- inorganic SiNWs solar cell using Au thin film and colloidal nano- particles. As mentioned above, Au nanoparticles are well-used me- tal catalyst and it easily synthesizes the SiNWs at low eutectic temperature. However, it is well-known that Au creates deep level defect when it incorporate with silicon. In contrast with Au, tin (Sn) appears to be the favorable catalyst because the Sn–Si alloy has relatively low eutectic temperature of 262 °C [2]. Moreover, Sn-catalyzed SiNWs were easily controlled by introducing hydro- gen flow ratios [14]. In this work, we synthesized SiNWs using Au nanoparticles on single crystalline silicon (p-type-Si) wafer for base layer for solar cell application and their characteristics are explored. In this present work, SiNWs were deposited on p-type c-Si by an atmospheric pressure chemical vapor deposition (APCVD). The structural and vibration properties of SiNWs were characterized by different SiH 4 flow rates. Diluted HF and HCl have been used for SiNWs passivation. Finally, we evaluated minority carrier life- time of SiNWs/p-type c-Si with different chemical treatments. 2. Experimental details Boron-doped p-type silicon (1 0 0) (1–3 X-cm) wafers were used for SiNWs deposition. The wafers were dipped in diluted hydrofluoric (2% HF) solution to remove native oxide layer and dried in N 2 atmosphere. The Au metal film was deposited on the Si wafer by spluttering technique at a rate of less than 1 nm/s. After deposition of Au film of approximately 5 nm thickness onto the Si wafer, the wafer was transferred into the experimental chamber and ageing at 700 °C. For synthesis of SiNWs, SiH 4 ,H 2 and N 2 were introduced into the CVD chamber. SiNWs were synthesized for 120 min at 800 °C. Details of other experiment conditions are sum- marized in Table 1. The SiNWs are characterized by Field emission scanning electron microscopy (FESEM-JEOL JSM-6700F), Fourier transform infrared (FTIR-Nicolet 2000) and micro-Raman Spectros- copy (HORIABA Jobin Yvon, FRANCE). The lifetime measurements 1567-1739/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2009.12.029 * Corresponding author. Tel.: +81 298615496; fax: +81 298615497. E-mail address: bp.swain@aist.go.jp (B.P. Swain). Current Applied Physics 10 (2010) S439–S442 Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap