Preferential positioning of dopants and co-dopants in embedded and freestanding Si nanocrystals

TL;DR

This study uses ab-initio calculations to explore how dopants and co-dopants preferentially position themselves in silicon nanocrystals, revealing surface binding tendencies and the formation of stable electric dipoles with potential applications.

Contribution

It provides new insights into dopant positioning and the formation of electric dipoles in Si nanocrystals, highlighting differences between embedded and freestanding structures.

Findings

Dopants prefer surface binding in co-doped nanocrystals.

B-P bonds form stable electric dipoles pointing inward.

Dopant positioning affects nanocrystal properties.

Abstract

In this work we aim at understanding the effect of n-type and p-type substitutional doping in the case of matrix-embedded and freestanding Si nanocrystals. By means of ab-initio calculations we identify the preferential positioning of the dopants and its effect on the structural properties with respect to the undoped case. Subsequently, we consider the case of phosphorus and boron co-doped nanocrystals showing that, against the single-doping situation, the energetics strongly favors the binding of the impurities at the NC surface. Indeed we demonstrate that the polar B-P bond forms a stable permanent electric dipole that radially points inwards the nanocrystal. Such noteworthy characteristic and its physical consequences are discussed alongside new potential applications.