Limiting factors of gettering treatments in mc-Si wafers from the metallurgical route

摘要

Gettering treatments such as phosphorus diffusion and aluminium-silicon alloying have been applied to multicrystalline silicon wafers prepared from upgraded metallurgical feedstock. Purification of the feedstock results of plasma torch treatment and directional solidification. Minority carrier diffusion lengths L_n are close to 40μm in the raw wafers and increase up to 150μm after phosphorus plus Al-Si getter-ings. Improvements are limited by the presence of residual metallic impurities, mainly slow diffusers like aluminium, and also by the high doping level.