A comparative study of silicon surface passivation using ethanolic iodine and bromine solutions

We report the surface passivation studies made on p-type single-crystalline silicon wafers using ethanolic solution of iodine and bromine. Minority carrier lifetime (tau(eff)) is measured by the microwave photoconductance decay (mu-PCD) method and using a Sinton's lifetime tester. Measurements are carried out at different molar concentrations of iodine-ethanol (I-E) and bromine-ethanol (B-E) solutions to optimize the process parameters. It is found that good passivation (+/-5% of measured maximum lifetime) could be achieved for certain ranges of concentration, which in the case of I-E and B-E are 0.07-0.12 M and 0.05-0.07 M, respectively. The effect of pre-conditioning steps on surface passivation (silicon surfaces with and without native oxide) is investigated. It is shown that the quality of surface passivation can be improved by an optimized wet-chemical pre-conditioning treatment. The effect of bias light and passivation time is also studied. I-E solution provides better passivation than B-E solution in terms of tau(eff) whereas B-E solution passivation exhibits better stability in comparison with I-E solution. The tau(eff) measured by the Sinton method (WCT-120) and using a Semilab system (mu-PCD. WT-2000) are comparable if injection levels are matched. (C) 2011 Elsevier B.V. All rights reserved.