Correlation between reflectivity and photoluminescent properties of porous silicon films Daisy Verma n , Firoz Khan, S.N. Singh, P.K. Singh Electronic Materials Division, National Physical Laboratory (CSIR), New Delhi-110012, India article info Keywords: Porous silicon Photoluminescence Reflectivity abstract Porous silicon (PS) layers were formed on p-type, /100S oriented, 1–5 O cm resistivity Cz silicon wafers by electrochemical etching in an HF:C 2 H 5 OH (1:2 by volume) electrolyte at room temperature at a constant current density 20 mA/cm 2 . The etching duration was varied to achieve PS layers of different morphologies and thicknesses. Both the photoluminescence (PL) and the total diffused reflectivity spectra of the PS layers were measured. It was found that for the PS layers grown for etching durations of less than 90 s the PL emission is insignificant and reflectivity is quite low. Such PS layers can be used as antireflection coatings (ARC) on solar cells. The PS layers formed for etching durations greater than 90 s show a significant PL emission in 500–800 nm range with peak lying in 630–660 nm wavelength range. When etching duration increases from 90 s to 8 min the PL intensity increases and the PL peak shows a blue shift. With further increase in etching duration the PL intensity decreases and PL peak shows a red shift. The reflectivity of the photoluminescent layers increases with etching duration showing a highest value for a sample grown for 8 min. Further increase in etching duration up to 20 min the reflectivity decreases and then increases. Striking observation is that both the PL emission intensity and reflectivity in the wavelength range of 550–800 nm are maximum for the PS layer grown for the etching duration of 8 min. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Porous silicon (PS) has been studied for last 50 years and its potential for various applications has been highlighted in several reports [1–3]. PS material and devices made out of it are being studied by researchers globally. This material can be broadly classified as nanometric and micrometric. The former is attractive for nanotechnology missions to produce photoluminescence (PL) [4] and photonic devices [5]. The latter finds applications in biocatalyst surface [6], solar glass [7], and antireflection coating (ARC) in solar photovoltaics (SPV) using silicon (Si) wafers. The exhibited unique structural, optical and electronic properties have made PS the most promising material systems in areas as diverse as optoelectronic, single electron devices, sensors and cold cathode field emission displays. In the past decades, numerous interesting silicon nanostructures such as PS, the arrays of nanocone, nanopillars, nanorods and nanowires have been developed by traditional or newly invented methods, and many interesting optical or electrical properties were obtained, but the space remained for constructing and developing novel silicon nanostructures is still tremendous [8]. The first application of photoelectrochemically formed PS layers grown on Si wafers as an ARC was reported by Prasad et al. [9]. Although different structures have been suggested to describe the morphology of the p-type PS a correlation of its optical properties like reflectivity with its structures and photolumines- cent property is not yet well established probably due to the complexity of the material. Attempts to correlate PL and reflectivity taking into account the structure of PS are very limited. One of the major problems is the deficiency of uniformity in the shape and size of the crystallites in PS. In this work we have prepared different PS layers electro- chemically by varying only one growth parameter, that is, the duration of PS formation, and have investigated its effect on reflectivity and PL of these layers. 2. Experimental The starting material was Cz grown single crystal silicon wafers of size 50 mm diameter and 300 mm thickness. Wafers were of p-type (B-doped) conductivity, /100S orientation and 1–5 O cm resistivity. They were mechanically lapped on both sides and then textured in a solution of NaOH:IPA:H 2 O at 85 1C for Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2010.05.030 n Corresponding author. Tel.: + 91 11 45608379; fax: + 91 11 45609310. E-mail address: daisy.physics@gmail.com (D. Verma). Solar Energy Materials & Solar Cells 95 (2011) 30–33