Self-assembling formation of silicon quantum dots with a germanium core bylow-pressure chemical vapour deposition

Abstract

The formation of nanometre-scale silicon dots with a germanium core on an ultrathin SiO2layer has been studied by controlling the early stages of low-pressure chemicalvapour deposition (LPCVD) alternately using pure monosilane and 5% germanediluted with helium. From atomic force microscope observations and x-rayphotoelectron spectroscopy measurements, the selective growth of Ge on pregrownSi dots and subsequent complete coverage with a Si cap have been confirmed.Cross-sectional transmission electron microscope images have shown theformation of isolated spherical nanocrystallites with Ge cores in contrastwith hemispherical pregrown Si dots, implying a high structural strain atthe interface between cladding Si and the Ge core. For multiply stackedstructures of the dots with a Ge core, Raman-scattering spectra indicate thatcompositional mixing occurs partly at the Si/Ge-core interface during LPCVD.