Geometry and strain effects on single-electron charging in silicon nano-crystals

We investigate by numerical simulation the effects of geometry and strain on single-electron charging in 100-Å-diameter silicon (Si) nano-crystals of various shapes, embedded in silicon dioxide (SiO2). Our approach accounts for the Si band structure within the effective mass approximation and a continuum strain model based on the deformation potential theory. Electron–electron interactions in nano-crystals are treated within the density-functional theory. We show that the interplay between the Si nano-crystal geometry and the particular spatial symmetry generated by the strain potential enhances confinement in the quantum-dot and dramatically influences the electronic structure and single-electron charging behavior. In particular, for a Si(001)-oriented truncated-sphere and hemispherical nano-crystals, the 001-oriented orbitals (YY′ states) are relatively insensitive to nano-crystal strain compared to orbitals originating from conduction band valleys oriented in the other directions.