Theory and Experiment on the Surface Photovoltage Diffusion Length Measurement in Thin Silicon Wafers

Abstract

A simplified theoretical model for the constant-magnitude steady-state surface photovoltage (SPV) technique is developed. Emphasis is placed on the determination of the minority carrier diffusion length L in the particular case for which the sample thickness is quite lower than the true value of L. The model is derived from the theoretical basis with the assumption that incidental light flux varies linearly in the explored range. This model fits very well to experimental data points obtained from both FZ and CZ mono-silicon crystals. We showed that in the case of thin wafers, SPV technique is not adapted to L measurements. It leads only to extracting a short length proportional to the sample thickness. However, if the recombination velocities and the minority carrier diffusion coefficient are known, then we could reach the true value of L by a computer calculation.