Size Dependence And Role Of Decoherence In Hot Electron Relaxation Within Fluorinated Silicon Quantum Dots: A First-Principles Study

Reeves et al. in their recent work on small silicon quantum dots [Reeves, et al. Nano Lett., 2015, 15, 6429-6433] found that surface passivation with fluorine atoms results in a significant slow down of hot electron relaxation because there exist particular electronic states that retain the hot electron for an extended time, and the relaxation time scale is largely influenced by shuttling of the hot electron between energetically adjacent states by such unique electronic states. In this work, we investigate how the quantum dot size changes this observation associated with the fluorine passivation and also consider the effect of decoherence. With the larger size of silicon quantum dot, the distinct hot electron shuttling behavior is no longer observed, and the relaxation time constant is much shorter. At the same time, decoherence can significantly slow down the hot electron relaxation by a factor of two or more. Our study reveals that slow hot electron relaxation can result from the quantum Zeno effect, in addition to the surface-specific vibronic effect for small quantum dots.