Effective bulk doping concentration of diffused and undiffused silicon wafers obtained from combined photoconductance and photoluminescence measurements

Abstract

The effective doping concentration of the bulk of a silicon wafer is an important material parameter for photovoltaic applications. The techniques commonly used to measure the effective doping concentration are based on conductance or resistivity measurements and include both contacted methods, such as the four-point probe, and contactless approaches, such as eddy current measurements. Applying these techniques to diffused wafers is complicated by the fact that the total conductance is the sum of the bulk conductance and the diffused layer conductance. Without further information about the emitter properties, a clear separation of these two parameters is not possible. This paper demonstrates a contactless method for specifically measuring the effective doping concentration of the bulk without significant influence from diffused layers. Copyright © 2012 John Wiley & Sons, Ltd. A new contactless method to detrmine the bulk doping concentration is presented. The method can be used throughout the solar cell fabrication process and on a wide variety of silicon substrates, without being affected by diffused or passivation layers. An excelent agreement was demonstrated between the post-diffusion doping concentration as obtained by the new method and the pre-diffusion doping concentration from dark conductance measurements. Copyright © 2012 John Wiley & Sons, Ltd.