Fabrication of Si Thermoelectric Nanomaterials Containing Ultrasmall Epitaxial Ge Nanodots with an Ultrahigh Density

A Si-based nanomaterial is proposed for use as a thermoelectric material. Ultrasmall epitaxial Ge nanodots (NDs) with an ultrahigh density are introduced into Si films as phonon scatterers using an ultrathin SiO 2 film technique. The nanomaterial has the stacked structure Si/Ge NDs/Si on Si substrates. Reflection high-energy electron diffraction reveals epitaxial growth of the Ge NDs and Si layers in all of the stacking stages. Sharp interfaces of the Ge NDs/Si in the stacked structures were observed by high-angle annular field scanning transmission electron microscopy. The Ge NDs were controlled in terms of their composition and strain: main parts of the NDs did not alloy with Si, and the elastic strain was relaxed. These features were confirmed by Raman scattering and x-ray diffraction measurements. The fabrication techniques used to make the simple Si-based stacked structure with strain-relaxed almost pure Ge NDs are useful to develop thermoelectric nanomaterials.