Micro-spectroscopy on silicon wafers and solar cells

Abstract

Micro-Raman (RS) and micro-photoluminescence spectroscopy (PLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by PLS and RS. PLS utilizes the carrier diffusion from a point excitation source and RS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by RS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in RS measurements are analyzed for the determination of the doping density and the carri er lifetime in selective emitters, laser fired doping structures, and back surface fields, while PLS can show the micron-sized damage induced by the respective processes