Silicon quantum dot formation in SiC/SiOx hetero-superlattice

All-Silicon tandem solar cells make use of the quantum confinement of silicon nanocrystals (Si-NCs) embedded in silicon oxide, carbide or nitride for the band gap engineering required to achieve efficiencies beyond the Shockley-Queisser-Limit while relying exclusively on abundant and non-toxic materials. A promising approach to the realization of the silicon quantum dot absorbers is the fabrication of superlattice structures with controlled mono-disperse size and spacing of the Si-NCs. Here we introduce the SiC/SiOx hetero-superlattice with near-stoichiometric SiC as barrier layer for the electrical transport and silicon rich SiOx as matrix layer for the quantum dot formation. Due to the competing nature of carrier localization and transport, the choice of different materials for matrix and barrier is indicated. We consider SiOx (x<2) as a promising matrix layer, since the phase separation is thermodynamically favourable, the quantum confinement pronounced and the amorphous matrix phase stable at high temperature. The SiC with low band gap should lead to low band offset between Si and SiC and thus give rise to high tunnel probability and easy carrier transport. In this work we deposited samples with various layer thicknesses and compositions using PECVD, followed by thermal annealing. We show HRTEM, Raman and GIXRD measurements for structural evaluation and present PL and PDS results for optical evaluation. In addition, we carried out electron spin resonance experiments addressing the defect creation during annealing. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Organizers of European Materials Research Society (EMRS) Conference: Symposium on Advanced Inorganic Materials and Concepts for Photovoltaics.