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Monitoring of Incoming Silicon PV Wafers with Modified Surface Photovoltage (SPV) Minority Carrier Diffusion Length Method
M. Wilson, A. Savtchouk, F. Buchholz, S. Olibet, R. Kopecek, K. Peter
Minority Carrier Diffusion Length, SPV, Incoming Wafers
Wafer-based Silicon Solar Cells and Materials Technology
Subtopic: Silicon Feedstock, Crystallisation and Wafering
Event: 26th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2BO.7.6
979 - 983
ISBN: 3-936338-27-2
Paper DOI: 10.4229/26thEUPVSEC2011-2BO.7.6
0,00 EUR
Document(s): paper


The noncontact ac-surface photovoltage technique is modified to enable reliable measurement of the minority diffusion length in incoming silicon PV wafers. The modifications to overcome very low SPV signal in wafers with saw damage include three elements; 1- increased photon flux in a range that still maintains advantages of low injection level; 2- elevated frequency light modulation with increased averaging that enhances signal to noise ratio and 3- thermal preconditioning of surface to create depletion layer SPV. The technique is tested using comparative measurements on Cz wafers and MC wafers with saw damage and after a saw damage removal etch. Consistently similar results were obtained before and after etching for diffusion length L, and for iron and boronoxygen defect concentrations. The results demonstrate excellent repeatability that for a L of about 100μm is 0.1%. The repeatability data for Fe and boron-oxygen enable to evaluate defect detection limits in low e9 atoms/cm3 range. To our knowledge, no other techniques can match such sensitivity for as-cut saw damaged wafers.