Bandgap study of quantum dot-sized SiGe alloy nanocrystals prepared in a nonthermal capacitively-coupled plasma by ambient scanning tunneling spectroscopy

The manuscript aims to elucidate the evolution of the bandgap and the semiconducting nature of quantum dot-sized SiGe alloy nanocrystals prepared at different plasma conditions in VHF PECVD. The technique of scanning tunneling spectroscopy (STS) is used for this, considering its highly localized nature, and to study the individual NCs. The STS analysis gives the density of states (DOS) spectrum of the SiGe alloy NCs. The present STS study reveals a dependence of the bandgap of SiGe alloy NCs on plasma parameters. The SiGe alloy NCs also exhibited a shallow p-type character despite the fact that no dopants were used during the deposition. Besides this, the midgap defect states are also observed in some of the samples. Further, a comparative bandgap study of the SiGe alloy NCs with its bulk indicates quantum confinement. These new findings from the QD-sized SiGe alloy NCs are important for the conceptual design and practical development of quantum dot-based third-generation solar cells

Sensitivity of germanium content on growth conditions of silicon-germanium nanoparticles prepared in nonthermal capacitively-coupled plasmas

We report on the synthesis of Si1−x Ge x alloy nanocrystals by very-high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique at different silane to germane gas flow ratio (R) in a mixture of (H2+Ar) dilution gas and H2 dilution gas alone. TEM, SAED, EDS studies and HAADF-STEM mapping of the samples were done to investigate the NCs' size, crystallinity and distribution of Si and Ge in the Si1−x Ge x alloy NCs. The average estimated size of the NCs in all the samples are in the order of exciton Bohr radius of Ge (24.3 nm), thereby indicating the probability of good quantum confinement. The alloy nature of NCs was confirmed in Raman study. The content of Ge in SiGe NCs was evaluated from Raman spectra which show a direct correlation with the fraction of hydrogen flow in the dilution gas mixture