Papers by Author: M.A. Falkenberg

Abstract: This contribution summarizes recent efforts to apply transmission electron microscopy (TEM) techniques to recombination-active extended defects present in a low density. In order to locate individual defects, electron beam induced current (EBIC) is applied in situ in a focused ion beam (FIB) machine combined with a scanning electron microscope. Using this approach defect densities down to about 10cm^-2 are accessible while a target accuracy of better than 50nm is achieved. First applications described here include metal impurity related defects in multicrystalline silicon, recombination and charge collection at NiSi₂ platelets, internal gettering of copper by NiSi₂ precipitates and site-determination of copper atoms in NiSi₂.

Abstract: The efficiency of solar cells produced from crystalline silicon materials is considerably affected by the presence of metal impurities. In order to reduce the concentration of metal impurities, gettering processes as phosphorus diffusion gettering (PDG) and aluminum gettering (AlG) are routinely included in solar cell processing. Further development and optimization of gettering schemes has to ground on physics-based simulations of gettering processes. In this contribution we use quantitative simulations to compare the efficiency and kinetics of PDG and AlG in the presence of precipitates for interstitially dissolved metals, like iron, at different gettering conditions. Recently measured segregation coefficients of iron in liquid AlSi with respect to crystalline silicon are used in order to compare with PDG under typical conditions. It is shown that kinetics of both, PDG and AlG, can be separated into two regimes: (i) at low temperatures kinetics are limited by precipitate dissolution, and (ii) at high temperatures kinetics of AlG is mainly limited by metal impurity diffusion while phosphorus in-diffusion is the limiting factor of PDG.