Detection of bottom depletion layer and its influence on surface photovoltage measurement in mu c-Si : H

The surface photovoltage (SPV) measurement is a very suitable method to ass ess the minority carrier diffusion length in microcrystalline silicon (muc- Si:H). Surface states create space charge region, needed for the SPV techni que and diffusion length evaluation, but additionally another space charge region, the bottom one, can appear. We present results of monitoring experi mentally the bottom space charge region by SPV technique in thick layers of undoped muc-Si:H grown on different substrates. In layers grown on p(+) cr ystalline silicon substrate and a-Si:H sublayers the surface photovoltage a s a function of the absorption coefficient is characterised by a distinct p eak at low absorption. Mathematical modelling prescribes the experimental d ata to a photovoltage signal originating in the bottom interface muc-Si:H/s ubstrate. (C) 2001 Elsevier Science B.V. All rights reserved.