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

Abstract

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.