Combined optical, surface and nuclear microscopic assessment of porous silicon formed in HF-acetonitrile Z.C. Feng a, * , J.W. Yu a , K. Li b , Y.P. Feng c , K.R. Padmanabhan d , T.R. Yang e a Graduate Institute of Electro-Optical Engineering and Department of Electrical Engineering, National Taiwan University, Taipei, 106-17 Taiwan, ROC b Chartered Semiconductor Manufacturing Ltd., 60 Woodlands, Industrial Park D, Street 2, Singapore 738406, Singapore c Department of Physics, National University of Singapore, S0511, Singapore d Department of Physics and Astronomy, Wayne State University, Detroit, MI 48201, USA e Department of Physics, National Taiwan Normal University, Taipei, 116 Taiwan, ROC Available online 31 August 2005 Abstract A new type of HF solution, HF-acetonitrile (MeCN), has been employed to produce 10 – 30 Am thick porous silicon (P-Si) layers by photoelectrochemical etching of different types of Si wafers, Si(100), Si(111) and polycrystalline Si, with different resistivities. A combined optical, surface and nuclear microscopic assessment of these P-Si layers was performed using photoluminescence (PL), Raman scattering, X- ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. With increasing resistivity of the Si(100) wafers, the P-Si layers show a slight blue shift of their visible light emission peak energy, an up shift of the peak position and a narrowing of the band width of the dominant Raman band, and a decrease in the amount of residual elemental Si on the surface. Those Si(111) wafers, etched in HF-MeCN, showed no porous structures and no visible light emission. D 2005 Elsevier B.V. All rights reserved. Keywords: Porous silicon; PL; Raman; RBS; SEM; Raman scattering; XPS 1. Introduction The observations of the blue shift of the absorption edge [1] and the visible photoluminescence (PL) at room temperature (RT) [2] from porous silicon (P-Si) in the 1990s have attracted world-wide attention to P-Si and related materials [3–6]. These developments have led to the publication of a large number of reports and papers in various journals and conference proceedings [3–5] as well as review books [6–8]. After entering into the 21 century until current days, research on porous Si has been still very active [9–15]. Traditionally, Si is the dominant material for modern electronics and computers. But, its indirect band gap, which lies in the near infrared (NIR), and low light emission quantum efficiency had limited its use in visible optoelectronics. The recent developments in porous Si may, however, fortunately result in the use of the material in visible optoelectronics by merger of its optoelectronic properties and Si-based integrated processing techniques. This may open a new field of processed optoelectronic Si microelectronic devices. Porous Si can be formed easily by electrochemical etching of single crystalline Si in HF solutions containing electrolytes. The porous Si structures generate visible photoluminescent or electroluminescent light. Many authors [1,2] believe that quantum size effects, based upon the free standing quantum wire model, is the major reason for visible light emission, although several other mechanisms have also been proposed to explain the behavior of RT visible light emissions from P-Si, such as siloxene [16], oxidized Si [17], hydride complexes [18], and an amorphous phase of Si or its complexes [19]. We have used a combination of several sophisticated techniques to understand and distinguish different luminescent mechanisms [20–22]. Porous Si was indeed first described nearly half a century ago [23] and used as the anti-reflectance (AR) layer for solar 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.07.025 * Corresponding author. Tel.: +886 2 3366 3543; fax: +886 2 2363 7467. E-mail address: zcfeng@ee.cc.ntu.edu.tw (Z.C. Feng). Surface & Coatings Technology 200 (2006) 3254 – 3260 www.elsevier.com/locate/surfcoat