Applied Surface Science 258 (2012) 8889–8894 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Implications of alkaline solutions-induced etching on optical and minority carrier lifetime features of monocrystalline silicon N. Bachtouli a , S. Aouida a,∗ , R. Hadj Laajimi b,c , M.F. Boujmil a , B. Bessais a a Photovoltaic Laboratory, Research and Technology Centre of Energy, Borj-Cedria Science and Technology Park, BP 95, 2050 Hammam-Lif, Tunisia b Water Researches and Technologies Center, Science and Technology Park, BP 273, route touristique Soliman Borj-Cedria, 8020 Soliman, Tunisia c Department of Chemistry, College of Science, University of Hail, P.O. Box 1560, Hail, Saudi Arabia a r t i c l e i n f o Article history: Received 6 February 2012 Received in revised form 19 May 2012 Accepted 21 May 2012 Available online 29 May 2012 Keywords: Silicon Surface texturization QSSPC lifetime spectroscopy a b s t r a c t In this work, we search to optimize the surface textures of monocrystalline silicon (c-Si) intended to be used in silicon solar cells. For this purpose, we studied the morphology of formed etch hillocks during anisotropic etching of silicon using alkaline solutions based on sodium hydroxide (NaOH), potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH). Such treatments lead to the formation of various pyramids-like textures that can be well optimized to improve the photocurrent of c-Si-based solar cells. The produced textures were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible optical reflectivity and minority carrier lifetime measurements. These investigations allow evaluating the size and density of the formed pyramidal textures; the apex angles vary between 75 ◦ and 82 ◦ , while the heights and bases of the pyramids range from a few hundred nanome- ters to several micrometers. A minimum reflectivity value of about 6% was obtained at specific conditions using NaOH, whereas it was found that the apparent effective minority carrier lifetime ( eff ) is sensitive to the injection level (n), which shows an apparent increase from 1.2 s to 2.4 s for a minority carrier density of about n = 210 14 cm -3 . © 2012 Elsevier B.V. All rights reserved. 1. Introduction The anisotropic etching of silicon bulk using weak alkaline solu- tions presents an orientation-dependent process. Depending on the atomic packing density, the etching of some planes is much faster than others [1]. Such treatment on (1 0 0) oriented silicon surface yields the appearance of hillocks having facets formed by resistant planes, generally (1 1 1) planes or neighboring orienta- tion leading to the formation of three dimensional microstructures like pyramids. This etching behavior is beneficial in silicon sur- face micromachining and can be used in the fabrication of different devices. Many studies proved that it is possible to tune the sur- face geometry of the silicon wafer using appropriate experimental conditions [2,3]. In photovoltaic processing the formation of uni- form pyramidal texture is an important step as regard to the whole solar cell manufacturing; it allows to minimize the surface reflec- tivity and to enhance the optical absorption via light trapping [4].Many successful approaches based on silicon surface texturing utilize sodium hydroxide (NaOH), potassium hydroxide (KOH) [5] and tetramethylammonium hydroxide ((CH 3 ) 4 NOH = TMAH) [6]. In general, isopropyl alcohol (IPA) is added to the alkaline etchants to ∗ Corresponding author. Tel.: +216 22575720; fax: +216 79325825. E-mail addresses: salma.aouida@crten.rnrt.tn, saouida2002@yahoo.fr (S. Aouida). improve the uniformity of the textured surface by removing hydro- gen bubbles sticking on the etched surface [7]. Indeed, hydrogen bubbles can inhibit chemical reaction between alkaline etchants and silicon surface via the formation of the Si(OH) 4 complex, which can form a mask preventing the etching process. This experiment is carried out at temperatures ranging from 70 ◦ C to 90 ◦ C and under magnetic agitation to accelerate the diffusion and migration of etchant and then the reaction products, enabling to improve the etching rate and the roughness quality [7]. In this work, we perform a systematic study on the influence of some silicon etching parameters (types and concentrations of etchants and etching time) on the morphological and optical fea- tures of the formed pyramids and their apparent effect on the effective minority carrier lifetime. The shape, size and density of pyramids were estimated using microscopic investigations. The value of the apex angle varies slightly from 76 ◦ to 82 ◦ , heights and bases of pyramids can vary from a few hundred nanometers to a few tens of micrometers. Furthermore, we analyze the values of the minority carrier lifetime of etched Si substrates as regard to un-etched ones. 2. Experimental The etching experiments were carried out on p-type boron doped (1 0 0) oriented Cz-monocrystalline silicon (c-Si), with a thickness of about 350 ± 50 m and a resistivity of 1–2  cm. After 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.05.110