Reversal of the Charge Transfer between Host and Dopant Atoms in Semiconductor Nanocrystals

TL;DR

This study uses ab initio calculations to reveal a size-dependent reversal of dopant charge in silicon nanocrystals, challenging traditional bulk semiconductor doping principles and suggesting similar effects in other semiconductor nanocrystals.

Contribution

It predicts a novel size-dependent reversal of dopant charge in semiconductor nanocrystals, supported by ab initio density functional calculations.

Findings

Dopant atoms in nanocrystals can have opposite charge signs compared to bulk silicon.

Reversal occurs at nanocrystal sizes around 100 silicon atoms.

The phenomenon is likely applicable to most semiconductor nanocrystals.

Abstract

We present ab initio density functional calculations that show P (Al) dopant atoms in small hydrogen-terminated Si crystals to be negatively (positively) charged. These signs of the dopant charges are reversed relative to the same dopants in bulk Si. We predict this novel reversal of the dopant charge (and electronic character of the doping) to occur at crystal sizes of order 100 Si atoms. We explain it as a result of competition between fundamental principles governing charge transfer in bulk semiconductors and molecules and predict it to occur in nanocrystals of most semiconductors.