  In the present theoretical work we have considered impurities, either boron
or phosphorous, located at different substitutional sites in silicon quantum
dots (Si-QDs) with diameters around 1.5\,nm, embedded in a SiO2 matrix.
Formation energy calculations reveal that the most energetically-favored doping
sites are inside the QD and at the Si/SiO2 interface for P and B impurities,
respectively. Furthermore, electron and hole transport calculations show in all
the cases a strong reduction of the minimum voltage threshold, and a
corresponding increase of the total current in the low-voltage regime. At
higher voltage, our findings indicate a significant increase of transport only
for P-doped Si-QDs, while the electrical response of B-doped ones does not
stray from the undoped case. These findings are of support for the employment
of doped Si-QDs in a wide range of applications, such as Si-based photonics or
photovoltaic solar cells.
