Electronic transport characterization of silicon wafers by laterally resolved free-carrier absorption and multiparameter fitting

Laterally resolved modulated free-carrier absorption (MFCA) is applied to the simultaneous determination of the electronic transport properties of semiconductor wafers. A rigorous three-dimensional carrier diffusion model is used to fit the observed dependences of the MFCA signal amplitude and phase on the separation between the pump and probe laser spots, measured at several modulation frequencies covering an appropriate range. This leads to a simultaneous and unambiguous determination of the values of three transport parameters, namely, the minority-carrier lifetime τ, the carrier diffusivity D, and the front surface recombination velocity s1. The extracted values for a n-type Si wafer with a resistivity of 7–10Ωcm are 53μs (τ), 16.6cm2∕s (D), and <200cm∕s (s1), respectively.