Method for the measurement of long minority carrier diffusion lengths exceeding wafer thickness

Abstract

A procedure is presented for determining long minority carrier diffusion lengths, L, from the measurement of the surface photovoltage (SPV) as a function of the light penetration depth. The procedure uses explicit SPV formulas adopted for diffusion lengths longer than the light penetration depths. Results obtained on high-purity silicon demonstrate new capability for noncontact wafer-scale measurement of L values in a mm range, exceeding the wafer thickness by as much as a factor of 2.5. This factor can be increased by increasing the accuracy of SPV signal measurement. The procedure does not have the fundamental limitations of previous SPV methods in which the diffusion lengths were limited to about 70% of the wafer thickness.