Electrical properties of silicon nanodots embedded in a SiC matrix for photovoltaic applications

The Scanning Probe Microscopy is a very useful technique that provides a variety of information about the surface of materials. Atomic Force Microscopy (AFM) is used in this work in order to investigate the topography and the local conductivity of a system composed of silicon nano-crystals (Si NCs) embedded in a dielectric matrix (SiC). This system is studied in view of its application as a tunable band-gap absorber in all-silicon multi-junction photovoltaic cells. SiC/Silicon Rich Carbide (SRC) multilayers are produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) and are subsequently annealed in order to obtain NCs formation. The properties of the multilayers have been studied as a function of the NCs size. Macroscopical as well as microscopical characterization are carried out in order to understand the properties of the multilayers. AFM maps are obtained in tapping mode in order to investigate the topography of the layers and the energy dissipated between the tip and the sample. Conductivity measurements as a function of temperature show that the conductivity increases with SRC layer thickness. Local IV measurement are performed with the AFM in contact mode with a conducting probe and the measurements show a similar trend with respect to SRC layer thickness. Conductive-AFM is performed to identify conductive paths at the nano-scale. Regions with different conductivity have been observed, which could be related to compositional variations (Si content) and unintentional doping by contamination with nitrogen and oxygen. The results are correlated with crystalline fraction and structural properties of the layers as obtained by optical analyses and transmission electron microscopy measurements, respectively.