Thermodynamics of Phosphorus in Molten Silicon

Research Project

Project/Area Number	07650866
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	Metal making engineering
Research Institution	The University of Tokyo
Principal Investigator	SUZUKI Kichiya The University of Tokyo, Graduate School of Engineering, Lecturer, 大学院・工学系研究科, 講師 (00092247)
Project Period (FY)	1995 – 1996
Project Status	Completed (Fiscal Year 1996)
Budget Amount *help	¥2,200,000 (Direct Cost: ¥2,200,000) Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000) Fiscal Year 1995: ¥1,500,000 (Direct Cost: ¥1,500,000)
Keywords	Silicon / Phosphorus / Iron / Titanium / Solar Cell / Chemical Equilibrium / 気体輸送法 / 溶解平衡
Research Abstract	Removal of phophorus is one of the major problems on the purification of molten silicon for solar cell. The Gibbs energy change of phosphorus dissolution into molten silicon was determined in the temperature range from 1723 to 1848 K by equilibrating a molten silicon-phosphorus alloy in a controlled phosphorus partial pressue and is expressed by the following equations. 1/(P_2(g)=P__-(mass pct, in Si) DELTAGﾟ=-139,000((]SY.+-。[)2,000)+43.4((]SY.+-。[)10.1T)(J/mol) Possibility of removing phosphorus from silicon melts by vacuum treatment and the accompanying yield of silicon during the refining process are discussed. Titanium and iron in silicon are known as harmful "life time killer" impurities which shorten the life time of excited carriers in silicon solar cell and disturb power generation. Therefore, the removal of titanium and iron is one of the most important topics for the production of solar grade silicon. Thermodynamic properties of titanium and iron in molten silicon were determined at 1723K by equilibrating molten silicon-titanium alloys or molten silicon-iron alloys with molten lead, which has a limited mutual solubility for both alloys. The activity coefficients of infinite dilution, self-interaction coefficients of titanium and iron in molten silicon, and the Gibbs energy change of mixing for silicon-titanium and silicon-iron at 1723K relative to pure liquid silicon, titanium, and iron, were determined.