C. Reimann

Dependence of phosphorus gettering and hydrogen passivation efficacy on grain boundary type in multicrystalline silicon

This investigation analyzes the dependency of minority charge carrier lifetime values at grain boundaries in multicrystalline silicon on the grain boundary type after P gettering and/or firing of SiNx:H layers deposited by plasma enhanced chemical vapor deposition. To get a broad statistics, a new method to determine the coincidence site lattice grain boundary types on large scale throughout entire 50 × 50 mm2 samples is combined with spatially resolved lifetime-calibrated photoluminescence measurements and mappings of the interstitial iron concentration. As an evaluation of the lifetime data at grain boundaries in comparison to the recombination activity of the bordering grains, lifetime contrast values are calculated. The correlation of this dependency on the grain boundary type with the impurity concentration is analyzed by the investigation of multicrystalline samples from two different ingots grown by directional solidification with different crucible material qualities. A dependency of the efficacy ...

The importance of convective heat and mass transfer for controlling material properties in ingot casting of multi-crystalline-silicon for photovoltaic applications

This contribution deals with the development of a species transfer model in the hot zone region of a laboratory scale crystal growth facility for the directional solidification of multi-crystalline silicon ingots with a diameter of 6 cm and a length of 4–5 cm in a Si3N4 coated silica crucible. A coupled local global modeling approach is used to compute the convective heat and mass transfer especially for C, N, O and the precipitate formation of SiC and Si3N4 during crystallization. The experimentally obtained data (C, N and O distributions) are compared with numerical results. It will be shown that the amount of contaminants in the silicon ingot is mainly influenced by the initial feed stock quality, the Si3N4 coating, the incorporation of CO and the evaporation of SiO over the free melt surface. It will be demonstrated that melt convection plays an important role in the transport of the species in the silicon melt and that convection can explain the experimentally observed O, C, and N distributions as well as the formation of the SiC and Si3N4 precipitates.