Materials Science and Engineering B 127 (2006) 255–260 Short communication Role of surface texturization in the formation of highly luminescent, stable and thick porous silicon films Shailesh N. Sharma a,∗ , G. Bhagavannarayana b , R.K. Sharma a , S.T. Lakshmikumar a a Materials Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110 012, India b Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110 012, India Received 26 June 2005; received in revised form 1 October 2005; accepted 1 October 2005 Abstract Porous silicon (PS) films were prepared by anodization on polished and textured substrates of (1 0 0) Si at different current densities for a fixed anodization time of 30 min. Using scanning electron microscopy (SEM), high-resolution X-ray diffractometry (HRXRD) and photoluminescence (PL) decay measurements, we have demonstrated that the texturization of silicon surface is a simple and effective method for the formation of mechanically stable thick porous silicon films. The PS formed on textured substrates exhibits higher porosity, negligible PL decay, better adherence to the substrate and non-fractured surface morphology compared to that formed on polished silicon substrates under the same preparation conditions. The morphology of the PS film as observed by SEM indicates the formation of highly porous vertical layers separating macroscopic domains of nanoporous silicon. The lattice mismatch or strain measurements from HRXRD revealed that a variety of good quality PS films having different strain values (by varying the current density) corresponding to wide range of band gaps suitable for sensor applications can be formed on textured substrate. © 2005 Elsevier B.V. All rights reserved. Keywords: Porous silicon; Photoluminescence; Surface morphology; Textured substrate; Polished substrate 1. Introduction Porous silicon (PS) is investigated for use as chemical sen- sors, optoelectronic devices, displays and photodetectors [1–4]. The nanoscale structure of PS leads to an enormous increase in surface area and the presence of large number of unpaired bonds at the surface which alter surface reactivity and stability [5,6]. Stress produced during the fabrication process including anodization, drying and storage leads to fracture, fragility and long term failure [7] inhibiting commercial utilization. Even when used as a sacrificial layer in silicon micro machining, the stress often causes mechanical curling, fracture and device failures [7]. From micro-Raman spectroscopy, which offers a non-destructive method for the measurement of local stresses in PS layers, stress attributed to lattice mismatch between PS and crystalline silicon, has been identified and shown to relax faster for samples of higher porosity [8,9]. Using X-ray techniques, ∗ Corresponding author. Tel.: +91 11 25742609–14x2409; fax: +91 11 25726938/52. E-mail address: shailesh@mail.nplindia.ernet.in (S.N. Sharma). lattice mismatch is shown to lead to an elastic curvature and stress [10]. The origin of the initial expansion of lattice has been variously attributed to size effects [11], to the presence of SiO 2 [12], and coverage of silicon crystallites by SiH x [13]. Recently, by means of computer supported finite element modeling (FEM) technique to investigate the origin of residual strain in thermally oxidized PS structures, it has been found that the residual strain is mainly due to the intrinsic stress formed at the Si–SiO 2 interface [14]. PS is formed in a liquid medium and drying is a key step for obtaining uniform, good quality layers for device applications [15]. When the material is allowed to dry by evaporation, the liquid vapor interfaces formed can generate enormous capillary tensions [16,17]. If the material’s skeleton is not strong enough, these forces can induce cracking, shrinkage, reduction in PL efficiency [18] and even complete disintegration [3]. A simple method to reduce this is to replace water with a miscible liquid of lower surface tension such as pentane [15]. Alternatives such as freeze drying [18] or polymerization of pore liquids [16] have been suggested. Supercritical drying [19,20] where the removal of liquid in the pores takes place above its critical point so as to avoid the occurrence of liquid vapor interfaces is the most supe- rior. Capillary forces are completely removed in this process, 0921-5107/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2005.10.001