Conductivity measurement of nanocrystalline silicon thin films grown by LEPECVD fot photovoltaic applications

Abstract

Low Energy Plasma-Enhanced Chemical Vapor Deposition (LEPECVD) is one of the new techniques available to grow hydrogenated microcrystalline silicon (μc-Si:H) at high growth rate. μc-Si:H is long known as a promising material for photovoltaic applications, however, more accurate correlations between growth conditions, microstructure and physical properties are to be found in order to exploit its full potential. In this framework, μc-Si:H i-layers grown at low silane dilution ([SiH4]/[SiH4+H2]) were deposited on oxidized silicon wafers at different temperatures and dilutions and current voltage characteristics were measured in a 2 point configuration at various temperatures. At low voltage we extracted the activation energy and the conductivity at room and infinite temperature. At high voltage the conduction is due to Space Charge Limited Currents (SCLC) and excess carriers will fill the conduction bandtail traps and their distribution can then be determined around the Fermi level. The discovery of a Meyer-Neldel rule in these μc-Si:H layers seems to be consistent with a conduction mechanism involving the amorphous tissue. The study of SCLC is consistent with a widely distributed exponential conduction bandtail in correlation with the conduction in the amorphous tissue and low photogain performances.