Ion beam analysis of porous silicon layers Sanjiv Kumar, J.V. Ramana, Christopher David, V.S. Raju * National Centre for Compositional Characterisation of Materials, E.C.I.L.Post), Hyderabad 500 062, India Received 1 August 2000; received in revised form 16 January 2001 Abstract The composition of porous silicon layers prepared by anodising silicon in HF±methanol medium has been studied using a combination of nuclear resonance reaction analysis NRRA) and non-Rutherford backscattering spectrometry. The 1 H 15 N; ac 12 C resonance reaction has been used for determining depth distribution of hydrogen in the ®lms. The distribution of other low Z elements like C, O and Si has been probed and the ratio of their atomic concentrations determined using 12 Ca; a 12 C and 16 Oa; a 16 O scattering. Anodisation resulted in the formation of Si 1 C x H y layers. The composition and thickness of the layers depend on the conditions of preparation. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Porous silicon has emerged as a promising material for the fabrication of silicon-based light emitting and optoelectronic devices since the dis- covery of its room temperature photoluminescence properties [1]. Porous silicon layers are formed by electrochemical anodisation of silicon wafers in HF-based media [1,2]. From the number of cou- lombs consumed and the weight changes in the bulk material, it has been proposed that the elec- trochemistry proceeds in the divalent state which undergoes chemical disproportionation to produce elemental and tetravalent silicon [3]. However, the exact nature of the anodised silicon layer is not known. The composition and the nature of bonding among the constituents of the layer have been studied using dierent analytical techniques like Fourier transform infrared spectroscopy FT- IR), Auger electron spectroscopy AES) and X- Ray photoelectron spectroscopy XPS), etc. [4±6]. Some researchers have suggested the layers to be composed of pure crystalline silicon whereas oth- ers have proposed the formation of dierent chemical substances like silicon hydrides [7], sil- oxenes [8] and its derivatives and non-bridging oxygen hole complexes during anodisation [9]. However, techniques like AES and XPS cannot determine hydrogen hence these techniques do not yield exact composition of ®lms containing hy- drogen. In contrast, ion beam techniques provide more sensitive methods for the determination of low Z elements including hydrogen. The scope of the present work has been to use ion beam analysis for the compositional characterisation of porous Nuclear Instruments and Methods in Physics Research B 179 2001) 113±120 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: +91-40-71-21-365; fax: +91- 40-71-25-463. E-mail addresses: rajucccm@hotmail.com, raju@cccm1.er- net.in V.S. Raju). 0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0168-583X01)00385-8