An advanced annealing method was proposed to enhance the lifetime of minority carriers by obtaining larger defect-free zone and keeping an amount of oxygen precipitates. We investigated the influence of annealing process on the defect-free zone and oxygen precipitates. In our experiments, the thickness of defect-free zone reached up to 100 mu m. And an amount of oxygen precipitates, which play a great role on impurity gathering, were kept at the same time. It was found that the lifetime of minority-carrier was proportional to the thickness of defect-free zone. The lifetime of minority carriers was enhanced by reducing the grown-in defects in the defect-free zone. (c) 2005 Elsevier B.V. All rights reserved.