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 (τeff) is measured by the microwave photoconductance decay (μ-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 τeff whereas B–E solution passivation exhibits better stability in comparison with I–E solution. The τeff measured by the Sinton method (WCT-120) and using a Semilab system (μ-PCD, WT-2000) are comparable if injection levels are matched.

Effective minority carrier lifetime has strong injection level dependence as observed by the Sinton (injection level in the range 1011–1015) and μ-PCD (low injection level, i.e., Δn=1.2×1013 cm−3) methods.Figure optionsDownload as PowerPoint slideHighlights
► Silicon surface passivation is realized by ethanolic solution of iodine (I–E) and bromine (B–E).
► I–E solution provides better passivation compared to B–E solution; however, the latter exhibits better stability.
► Quality of surface passivation has surface pre-conditioning dependence.
► Minority carrier lifetime has strong injection level dependence.