Abstract
For bulk doping, boron and phosphorus are usually used as p-type and n-type dopants, respectively. The distribution of these dopant concentrations in a silicon crystal along the vertical direction is governed by the segregation phenomena. As the segregation coefficient of phosphorus is small, phosphorus concentration distribution in a silicon crystal becomes inhomogeneous; inhomogeneous phosphorus concentration distribution affects the distribution of resistivity in the crystal. Therefore, it is important to control the phosphorus concentration distribution in a silicon crystal and make it uniform. In this study, by numerical analysis, we investigated the effect of the evaporation flux at the melt surface on phosphorus concentration distribution during the directional solidification process. To obtain a homogeneous phosphorus concentration distribution in the silicon crystal, we had to control the phosphorous evaporation flux at the melt surface and maintain approximately the same phosphorus concentration in the melt during the entire solidification process even though the growth rate was always changing.
Highlights
The photovoltaic market has rapidly advanced over the last two decades
Ingots grown by most manufacturers have an inhomogeneous phosphorus concentration distribution along their height because of the small segregation coefficient of phosphorus
A small segregation coefficient leads to the low production yield and high production cost of silicon crystals because of the specific range of resistivity required in the crystals by industrial manufacturers
Summary
The photovoltaic market has rapidly advanced over the last two decades. Compared with multicrystalline materials, single-crystalline silicon has proven advantages such as high quality and very low dislocation density, but the production cost of single-crystalline silicon is high. The enhancement of dopant evaporation at the melt surface, is effective in controlling the vertical resistivity distribution of grown crystals.
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