Stark effect, polarizability and electroabsorption in silicon nanocrystals

The experimental quantum-confined Stark effect data in embedded Si nanocrystals (NCs) is unambiguously explained with an atomistic pseudopotential theory. The majority of the Stark shift comes from the valence states which undergo a level crossing with respect to the applied field. The nonmonotonic behavior of the experimental data as well as the peak intensity appearing around 0.5~MV/cm and the subsequent fall off are well reproduced by the theory. However, for small Stark fields, the 300~K emission comes out to be stronger in the theoretical estimation due to thermally-activated nonradiative processes not accounted in the theory that possibly degrade the emission rate at higher temperatures. The polarizability of embedded Si NCs is obtained over a diameter range of 2.5--6.5~nm which unveils the importance of Coulombic effects for larger NCs. The intraband electroabsorption analysis asserts that p-doped Si NCs will benefit from a wider voltage tunability. Finally, the spin-orbit interaction is considered as a function of NC size which begins to have an impact on the results for large Stark fields.