Spectroscopic Ellipsometry Studies of nc-Si/a-Si and nc-Si/SiOx Systems: Optical Characterization of Crystallization

Third generation solar cells are expected to utilize the quantum size effect occurring in the semiconductor quantum dots fabricated in an appropriate matrix. A promising and well-studied material system is the Si nanocrystals fabricated in an oxide matrix such as SiO2. In spite of extensive research efforts on this material system, a successful device realization has not been possible due to the difficulties in the device fabrication and the electronic transport in the dielectric matrix that forms an insulating medium for the charge transport. In order to overcome the problems related to the electronic transport while not losing the quantum size effect, the use of a sponge-like nanostructure has recently been proposed. Si nanosponge is composed of tiny interconnected Si nanostructures embedded in an oxide matrix. These nanostructures form an interconnected quantum structure where the charge transport does not require the tunneling current which needs well positioned quantum dots. The band gap of the material can still be engineered by process parameters for tandem solar cell fabrication. Sinanosponge is then a promising candidate for the fabrication of third generation photovoltaic (PV) solar cells. In this work, Si-nanosponge structures were fabricated successfully in a SiOx matrix in a wide range of x values (0