Microstructural association of diverse chemical constituents in nc-SiOx:H network synthesized by spontaneous low temperature plasma processing

Abstract

The nc-SiOx:H films have been synthesized via single step, spontaneous and low temperature (∼250 °C) RF (13.56 MHz) plasma processing of (SiH4 + CO2) diluted by H2 and He. Continued incorporation of oxygen hinders the nanocrystalline growth and limits the crystallinity in nc-SiOx:H. In the nc-SiOx:H network, mostly spherical nc-Si–QDs are embedded in the a-SiOx matrix. The overall crystallinity is comprised of the nanocrystalline grains and the ultra-nanocrystalline component (unc-Si) located mostly at the grain boundaries. Each crystalline core i.e., the nc-Si grain along with its ultra-nanocrystalline dominated grain boundary is covered by a shell which is a part of the a-SiOx matrix that again has its two-phase structure: Si-rich a-SiOx and O-rich a-SiOx. By detail experimental evidences it is envisaged that the shell layer surrounding the nc-Si–QDs consists of the O-rich a-SiOx component which acts as the protective layers for the QDs within the pool of amorphous matrix belonging to the Si-rich a-SiOx phase. At enhanced oxygen incorporation into the silicon network elevated O-rich a-SiOx component contributes thicker oxide shell that introduces enhanced stress around the Si crystalline core and, thereby, induces smaller size of nc-Si–QDs. At reduced core size of the Si-ncs, the proportional grain boundary to core volume increases simultaneous to increased Xunc-Si/Xnc-Si ratio with increasing O-content (CO) in the network. At elevated oxygen incorporation in the overall nc-SiOx:H network, therefore, a trade-off relation between the reduced core diameter and the enhanced shell thickness is evident, simultaneous to the advanced population of ultra-nanocrystalline fraction of crystallinity at the grain boundary. A consolidated microstructural model involving association of different chemical constituents in the overall nc-SiOx:H network has been proposed.