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SEMI Auxiliary Information: Contactless Carrier Lifetime Measurements in Silicon Wafers, Ingots, and Blocks

Abstract: This white paper was written in an effort to create a concise summary of a common framework for contactless carrier lifetime measurement in silicon photovoltaics. The goal was to document methodologies that will allow for comparisons of results taken at various institutes, manufacturers, and universities that may use different measurement instruments. A description of lifetime measurements is discussed in terms of the device physics, focusing on the physical excess carrier lifetimes and (charge-)carrier densities that form the basis for any lifetime measurement. A standard analysis is presented. The application of this measurement methodology is described in the context of lifetime measurements on wafers, ingots, and blocks. Commonly-used interpretations of the measured lifetime to determine surface recombination velocities, emitter saturation current densities, and bulk lifetimes are described. The results of this white paper apply to any lifetime measurement technique that can demonstrate a calibration of measured data to excess-carrier density within the sample. One specific example that applies the methodology developed in this white paper is presented, using an eddy-current sensor to determine photoconductance. In this case, the calibration to absolute photoconductance is done with a traceable calibration of the instrument against wafers measured by four-point-probe. Standard equations for silicon mobility vs. carrier density are then used to convert conductance data into carrier density vs. time during a measurement. This data is then sufficient to evaluate carrier lifetimes and report the results as a function of the carrier density in the sample using the methods described in the white paper. 

edited by Ron Sinton: http://www.sintonconsulting.com, http://www.semi.org

20.06.10

35th IEEE Photovoltaic specialists...

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05.05.10

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27.04.10

Photon's 6th, Photovoltaic Technology Show...

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