Electronic States and Luminescence in Porous Silicon Quantum Dots: The Role of Oxygen

TLDR

The photoluminescence of silicon quantum dots in porous silicon can be tuned from the near‑infrared to the ultraviolet by size and surface passivation with Si‑H bonds. A theoretical model predicts that forming Si=O bonds introduces new electronic states in the band gap of smaller quantum dots, matching experimental observations. Exposure to oxygen shifts the PL red by up to 1 eV, altering intensity and decay time, confirming that quantum confinement and surface passivation jointly determine electronic states and resolving the PL mechanism controversy.

Abstract

Depending on the size, the photoluminescence (PL) of silicon quantum dots present in porous silicon can be tuned from the near infrared to the ultraviolet when the surface is passivated with Si-H bonds. After exposure to oxygen, the PL shifts to the red by as much as 1 eV. This shift and the changes in PL intensity and decay time, show that both quantum confinement and surface passivation determine the electronic states of silicon quantum dots. A theoretical model in which new electronic states appear in the band gap of the smaller quantum dots when a $\mathrm{Si}=\mathrm{O}$ bond is formed, is in good agreement with experiments. This result clarifies the controversy regarding the PL mechanisms in porous silicon.