Influence of different excitation spectra on the measured carrier lifetimes in quasi-steady-state photoconductance measurements

Abstract

The interpretation of lifetime measurements on unpassivated silicon wafers by means of the quasi-steady-state photoconductance (QSSPC) technique is a practically highly relevant, but challenging task. We investigate QSSPC measurements on damage-etched samples with five different resistivities from 0.25 Ω cm p-type to 100 Ω cm n-type float-zone material with four different thicknesses each, ranging from 105 to 250 μm. The influence of different excitation spectra, realized by adding different long pass filters to the standard QSSPC Xenon flash spectrum, on the injection-dependent effective excess carrier lifetime is studied in detail. We observed that the measured effective lifetime is significantly dependent upon the excitation spectrum in use and is augmented by increasing the long pass filter cut-off wavelength, the latter being equivalent to more symmetrical excess carrier density profiles. Furthermore, the size and the injection dependency of the dominating surface recombination channels are investigated. Finally, two different approaches to accurately calculate the excess carrier generation rate within the sample are presented and compared.