Gettering impurities from crystalline silicon by aluminum diffusion using a porous silicon layer

Abstract

PACS 66.30.Jt, 81.05.Rm, 81.40.Rs, 81.65.Tx In this paper, we report a study on the possibility of gettering transition metal impurities from solar grade crystalline silicon (Si). Porous silicon layers were formed by the stain-etching method on both sides of the Si wafer. Aluminum diffusion was done throughout the PS layer in an infrared furnace under a (N 2 /O 2 ) controlled atmosphere. This enables to getter eventual metal impurities towards the PS layer. The gettering effect was evaluated by measuring the majority carrier density and mobility and the minority carrier diffusion length (L d ) of the Si substrate. For this purpose, Wander Pauw and Hall Effect measurements together with the Light Beam Induced Current (LBIC) technique were used. We noticed that the best gettering corresponds to a heat treatment at 850 ˚C for 30 min; in that case an evident decrease of the majority carrier density and an enhancement of the mobility were observed. After gettering, we found an apparent improvement of the minority carrier diffusion length. These results give evidence of the effectiveness of external gettering treatments by combining (Al -PS) layer for an efficient gettering effect in solar grade monocrystalline Si.