Photoconductance-Based Excess Carrier Lifetime Measurements on Unpassivated Silicon Samples

Abstract

Measurement techniques which rely on the exact knowledge of the actual generation rate within a silicon sample (such as quasi-steady-state photoconductance measurements) are significantly affected by spectral variations of the illumination source. This is especially the case when using supplementary long-pass filters, in order to ensure a more symmetrical excess carrier profile within low- lifetime silicon samples. In this contribution the effect of different illumination spectra on photoconductance-based lifetime measurements will be investigated in detail. The calculations are based on actual measurements of the optical properties of the samples and the reference cell, as well as the used photo flash spectra. Two different simple approaches to calculate the excess carrier generation rate are presented and compared. Evaluations are exemplarily performed on a set of unpassivated thickness- varied silicon samples, revealing generation rate deviations as high as 21 % for different sample thicknesses and illumination spectra. Additionally, the effect of the different excitation spectra on the measured effective lifetime will be shown.