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

Abstract

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 SiOx<;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 SiOx sublayer. The optical bandgap ETauc 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.