Evaluation of Silicon Optical Absorption Data for Use in Minority‐Carrier‐Diffusion‐Length Measurements by the SPV Method

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Abstract
We have examined and evaluated the published data for the optical absorption coefficient α of crystalline silicon as a function of the wavelength λ for use in the measurement of minority‐carrier‐diffusion length by the SPV method. We have compared the ASTM‐recommended expression for with (i) Runyan's data on which it is based, (ii) the data of Swimm and Dumas, and (iii) the data of Weakliem and Redfield, and find systematic disagreement that can result in significant differences in the values of determined by the SPV method. We have proposed (i) a set of compromise data based on an average between the extremes of the published data and (ii) an expression for that agrees with the compromise data to within about 1%. The use of this expression, , where is per centimeter and λ is in micrometers, reduces the uncertainty in resulting values of by a factor of approximately two. For , a further reduction in uncertainty can be achieved by lowering the maximum value of λ used for the measurements. Finally, we believe that the compromise data that we propose should be considered as an interim choice pending further experimental results that more clearly remove the present uncertainty in the value of .

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