Spatially resolved modeling of the combined effect of dislocations and grain boundaries on minority carrier lifetime in multicrystalline silicon

Abstract

A model for the combined effect of dislocations and grain boundaries on minority carrier lifetime has been developed. Lifetime varies with dislocation density, grain boundary misorientation, and the coincidence site lattice (CSL) nature of the boundaries. Minority carrier lifetime was measured with high spatial resolution (50 mu m) using the carrier density imaging (CDI) technique on a silicon nitride passivated multicrystalline sample. Dislocation density was measured on the same sample by image recognition of optical microscope pictures of a Secco etched surface. Grain boundaries were then mapped and characterized by electron backscatter diffraction (EBSD). Lifetime was simulated based on the dislocation and grain boundary measurements. Parameters were chosen to match closely the simulated and measured maps. Very good two-dimensional (2D) correlation was obtained by assigning roughly equal importance to recombination at dislocations and grain boundaries. The value for the capture cross section, which gives the best correlation, is 4x10(-14) cm(-3). This is in the range of values reported for interstitial transition metals like, for instance, iron. It appears necessary to include also the effect of grain boundaries to explain recombination in low lifetime areas. Sub grain boundaries were particularly recombination active and are dominating the number of active grain boundaries

Grain boundary effect on lifetime in high performance multicrystalline silicon during solar cell processing

“…The lifetime-prediction model, designed in Comsol, is based on Donolato's theory on dislocation recombination strength [15,16]. The model has been designed to fit the predicted lifetime to linescans perpendicular to GBs.…”

Solidification of silicon for electronic and solar applications

“…Structural defects will also influence the electrical properties, and dislocations need to be avoided completely in single crystals, whereas the dislocation density in multicrystalline ingots needs to be kept to a minimum. 2 Crystallization processes for semiconductor silicon, therefore, tend to be quite demanding. The present article will briefly review the most important silicon crystallization processes for applications in integrated circuits and in solar cells.…”

High Temperature Annealing of Dislocations in Multicrystalline Silicon for Solar Cells

“…Since multicrystalline silicon is cooled very slowly after crystallisation, it is not likely that much of the stored energy is due to point defects. In this case we are interested in the mechanisms involving dislocations, and the interesting effect in question is reducing the impact of dislocations on carrier recombination (Rinio et al 2002;Stokkan et al 2007), therefore also processes that do not directly influence the actual dislocation density, but only their configuration are of interest. …”