Smoothing and passivation of special Si(111) substrates: studied by SPV,PL, AFM and SEM measurements |
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Authors: | H. Angermann J. Rappich I. Sieber K. Hübener J. Hauschild |
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Affiliation: | Abteilung Siliziumphotovoltaik, Hahn-Meitner-Institut, 12489, Berlin, Germany. angermann@hmi.de |
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Abstract: | Surface sensitive techniques, the field-modulated surface photovoltage, photoluminescence measurements, atomic force microscopy and scanning electron microscopy, were employed to yield detailed information on the influence of wet-chemical treatments on the preparation induced microroughness and electronic properties of wet-chemically passivated Si(111) substrates with special surface morphology. Stepped substrates with evenly distributed atomically flat terraces were prepared and passivated by thin oxide layers, which were used as a starting point for the subsequent H-termination after long storage in air. It was shown that their surface morphology and electronic properties do not degrade. Applying this preparation method to solar cell substrates with randomly distributed Si(111) pyramids, we achieved significantly lower densities of surface states and reduced recombination loss at a-Si:H/c-Si interfaces, compared with conventional pretreatments. The surface microroughness, the density of rechargeable states and the resulting recombination loss on a-Si:H/c-Si heterojunctions were found to be mainly influenced by two steps of surface pretreatment: firstly, the wet-chemical smoothing procedure of structured substrates and, secondly, the removal of native and wet-chemical oxides during the final etching in HF- or NH4F- containing solutions. Figure After wet-chemical oxidation in H2SO4/H2O2 and storage in air |
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Keywords: | Surface photovoltage Photoluminescence Atomic force microscopy Electron microscopy Interface state density Wet-chemical surface pretreatment |
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