The Effect of Lewis Base Chemisorption on the Luminescence of Porous Silicon
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THE EFFECT OF LEWIS BASE CHEMISORPTION ON THE LUMINESCENCE OF POROUS SILICON Jeffery L. Coffer, Sean C. Lilley, and Rebecca A. Martin, Department of Chemistry, Texas ChristianUniversity, Ft. Worth, TX 76129. Leigh Ann Files-Sesler, CentralResearch Laboratories,Texas Instruments, Dallas, TX, 75265
Abstract We report here studies on the effects of Lewis base addition on the observed luminescence of porous silicon generated non-anodically from a stain etch of p-type wafers and whose surface morphology has been characterized by atomic force microscopy (AFM). Addition of dilute heptane solutions of alkyl amines such as n-butyl amine (C 4H 7NH 2) results in dramatic quenching of the steady-state photoluminescence (PL) near 625 nm. The observed fractional changes in integrated PL intensity as a function of amine concentration have been fit to a simple equilibrium model demonstrating Langmuir-type behavior from which adduct formation constants have been calculated. These steady-state PL measurements are complemented by Fourier Transform Infrared (FT IR) spectroscopic measurements monitoring the effect of amine adsorption on the silicon hydride stretching modes [v(Si-Hx)] near 2100 cm- 1 . Based on these results, a physical model for the amine interactions with the porous silicon surface is presented.
Introduction Studies regarding the role of surface structure and composition in the luminescent properties of porous siliconl are important to assisting in an elucidation of the fundamental origin(s) of the observed light emission. 2 -4 Such efforts are also crucial to evaluating the ability of this material to be employed in any sensor-type devices. 5 Given the inherent 6 reactivity of the silicon hydride bonds which are prevalent at the porous silicon surface, these moeities should be quite sensitive to the effect of Lewis base (strong electron donor) addition. In turn, the effects of this chemical perturbation of the porous silicon surface should significantly alter the observed PL if the surface chemical composition is vital to the magnitide of the luminescence. Thus, judicious choice of the Lewis base adsorbate should reflect the geometric accessibility and fundamental acid/base character of this technologically interesting interface. Described below are a series of experiments illustrating the effect of addition of a class of Lewis base molecules known as organoamines on the observed photoluminescence (PL) of porous silicon, as well as concomitant effects on the Si-Hx (x = 1, 2 ) vibrational modes.
Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
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Experimental 7 Luminescent porous silicon samples were prepared employing stain etch methods from boron-doped p-type wafers possessing a resistivity of 6-8 Q cm. Samples of dimension 5 x 40 mm were etched horizontally in a 1/5/10 HF/HNO 3/H 20 solution in polypropylene beakers for 20 minutes, rinsed briefly in absolute ethanol, then dried in a stream of dry nitrogen. Photoluminescence spectra were recorded using a SPEX Fluorolog-2 system with doubl
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