Optical Bandgap Tunability of Silicon Nanocrystals Fabricated by Inductively Coupled Plasma CVD for Next Generation Photovoltaics

Superior optical properties of Si-nanocrystals (Si-NCs) compared with bulk Si, particularly tunability of bandgap by controlling size, can be exploited for realizing next-generation Si tandem solar cells. In view of this, optical bandgap tunability of Si-NCs fabricated by Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPCVD) is presented. The SiO_x<;2/SiO₂ superlattice approach was used for realizing Si-NCs with tight size control. Deposition time of SiOx sublayer and, hence, the related thickness (TSRO), was used as a variable parameter to realize Si-NCs of varying sizes. Formation of Si-NCs was verified by transmission electron microscopy and Raman spectroscopy. Using XPS analysis, the stoichiometry parameter x was estimated to be 0.82 for SiO_x sublayer. The optical bandgap E_Tauc estimated using Tauc analysis was observed to be tunable from 1.57 to 2.52 eV as the size of Si-NCs was varied from 5.8 (±0.5) to 2 (±0.4) nm, respectively.