Advanced modeling of the effective minority carrier lifetime of passivated crystalline silicon wafers

A strong injection level dependence of the effective minority carrier lifetime (τeff) is typically measured at low injection levels for undiffused crystalline silicon (c-Si) wafers symmetrically passivated by a highly charged dielectric film. However, this phenomenon is not yet well understood. In this work, we concentrate on two of those possible physical mechanisms to reproduce measured τeff data of c-Si wafers symmetrically passivated by atomic layer deposited Al2O3. The first assumes the existence of a defective region close to the c-Si surface. The second assumes asymmetric electron and hole lifetimes in the bulk. Both explanations result in an adequate reproduction of the injection dependent τeff found for both n- and p-type c-Si wafers. However, modeling also predicts a distinctly different injection dependence of τeff for the two suggested mechanisms if the polarity of the effective surface charge is inverted. We test this prediction by experimentally inverting the polarity of the effective surface charge using corona charges. From the experiments and simulations, it is concluded that surface damage is the most likely cause of the significant reduction of τeff at low injection levels.