The use of heater-magnet module for Czochralski growth of PV silicon crystals with quadratic cross section

The first experimental results show single crystalline Si crystals with reproducible square cross sections up to 91×91 mm2 including rounded corners. Until now TMF frequencies of f=180 and 300 Hz and a phase shift of φ=90° were applied. For high-purified material an average facet undercooling of ΔT≈2 K has been deduced from the observed rectangular side plane widths. According to high-resolution transmission electron microscopy (HRTEM) the four macroscopically flat faces are microscopically composed of {1 1 0} sub-facets and {1 1 1} macrosteps. Etch pit densities (EPD) between 0 and 104 cm−2 were ascertained. Due to the magnetically induced high-speed melt flow toroid around the growing crystal a relatively low and homogeneously distributed oxygen concentration can be achieved. A minimum value of 7.5×1017 cm−3 was measured in high-purity as-grown crystals at a TMF frequency of f=300 Hz.