Practical measurement of bulk lifetime and surface recombination by using wavelength dependence

In a quasi-steady state photoconductance (QSSPC) lifetime measurement, the lifetime that is measured depends on the minority-carrier profile within the wafer during illumination. This has been applied by Bail et al. to uniquely determine the bulk lifetime and surface recombination velocity on a single wafer by using two different wavelengths of light. This paper presents recent data from the literature for passivated and unpassivated wafers in the industrially-relevant context of a 1 Ohm-cm, 300-/spl mu/m-thick wafer. Instances where the technique may have useful industrial applications in R&D or process control are identified. Cases are also shown where there is no spectral dependence in the measured lifetime, justifying a simple measurement and analysis for white light or a single wavelength. Optimized methodologies for measuring unpassivated multi-crystalline wafers and blocks are presented and tested with new experimental data.