IMPROVEMENT OF MINORITY CARRIER DIFFUSION LENGTH IN SOLAR GRADE SILICON:A NEW METHOD

摘要

Metallic impurities in solar grade silicon act generally as recombination centers for minority carriers and degradesignificantly their diffusion length and thereafter solar cell efficiency. It is needful to remove these impurities from externalgettering techniques. In this work we present a study on the possibility of reducing the amount of metallic impurities in solargrade silicon wafers in order to improve the solar cell efficiency. The gettering technique used is a combination of porous siliconand silicon tetrachloride. This technique consists of heating a silicon substrate with a porous layer on both sides under SiCl4/N2atmosphere. The gettering effect was studied using the Hall Effect and the Van Der Pauw methods in order to perform mobilityand resistivity measurements, respectively. We obtained a significant improvement of the majority carrier mobility after suchthermo-chemical treatment. The gettering efficiency was also evaluated, using the light beam induced current (LBIC) that enablesus to estimate the minority carrier diffusion length L, which reaches a value of about 210 μm.