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

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 Ln are close to 40 μm in the raw wafers and increase up to 150 μm after phosphorus plus Al–Si getterings. Improvements are limited by the presence of residual metallic impurities, mainly slow diffusers like aluminium, and also by the high doping level.