Electrical properties of the multi-crystalline silicon ingots grown with UMG (upgraded metallurgical grade) silicon materials

To estimate the axial variation of resistivity in the silicon ingot directionally solidified with n-type UMG silicon material, the actual axial dopant concentration variations were measured and compared with simulated results. The simulation was conducted with segregation equations. It was found that the segregation coefficients (keff) of the doping impurities in this directional solidification were very close to the segregation coefficients of doping impurities in normal freezing (k0). With these segregation coefficients, the axial variation of resistivity was estimated with the PC1D program for various combinations of boron and phosphorous content in a silicon material. It was expected that the phosphorous content in the silicon material would be more determinative than the boron content in the enlargement of the useful portion of the silicon ingot for solar cell fabrication.

► In this investigation, calculation of the axial variations of the boron and phosphorous concentrations employing Scheil's law was conducted first.
► Actual measurement of the axial variations of the boron and phosphorous concentrations for the silicon ingot grown with raw material with 7 and 15 ppma of boron and phosphorous, respectively, was conducted with ICP.
► Comparison of this measurement with the simulation was conducted to determine the effectiveness of the calculation method.
► Once the axial variations of the dopants are known, the axial variation of resistivity of this silicon ingot can be simulated with the PC1D program.
► Employing this procedure, the usable portion of the silicon ingot for solar cell fabrication can be estimated when using lower grade silicon materials.