Numerical evaluation of the scanning method for the determination of minority carrier diffusion length in p-n junctions

A numerical model for the scanning method for determining minority carrier diffusion length is presented to include the effect of the built-in field and high-level injection. A numerical simulation is presented which shows that the scanning method for diffusion length measurements will not give accurate results for minority carrier diffusion length in the region where the presence of a built-in field is significant. No matter how poor the junction is made, the accuracy of the measurement method increases away from the depletion region. The problem of low magnitude in the induced short circuit current away from the physical junction could be overcome by increasing the generation level. For substrate dopant concentrations between 2.0 × 10¹⁵cm⁻³ and 6.0 × 10¹⁶cm⁻³ the distance into the device from the surface where the error of the measurement will be greater than 10% is expressed as a semi-empirical formula relating dopant concentration. When there are irregularities in minority carrier lifetime closer to the physical junction, the measurement method will accurately determine the minority carrier diffusion length in a particular region only if the width of that region is much larger than its diffusion length.