Interface-engineering enhanced light emission from Si/Ge quantum dots

We show that the space confinement mechanism is dominant in both Si and Ge indirect bandgap quantum dots, and the interface-induced intervalley coupling mechanism plays a minor role

Zhi-Min Ji; Jun-Wei Luo; Shu-Shen Li

2020

Scholarcy highlights

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  • Si quantum dots have a significant improvement in luminous efficiency compared with bulk Si, achieved by alleviating the forbiddance of no-phonon Γ–Γ radiative transition determined by the law of momentum conservation
  • Two divergent mechanisms have been proposed to account for the breakdown of momentum conservation in Si QDs, one is due to the space-confinement-induced spread of k-space wave functions associated with Heisenberg uncertainty principle Δr · Δk > 1/2, and the other is due to the interface-effect-induced intervalley mixing between indirect and direct bandgap states
  • Both mechanisms could cause a small overlap of the electron and hole wave functions in k-space and make vertical transitions allowed, which leads to the zero-phonon light emission
  • We unravel the hierarchical relationship between these two primary mechanisms in the process of zero-phonon light emission from indirect bandgap QDs, by performing semiempirical pseudopotential calculation including many-body interaction on the room-temperature luminescent properties of a series of Si, Ge, and Ge/Si core/shell QDs
  • We demonstrate that the interface engineering can enhance light emission in indirect bandgap QDs substantially and regulate the intervalley coupling mechanism as the primary factor over the space confinement mechanism in breaking the momentum conservation law

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