Electronic properties, doping and defects in chlorinated silicon nanocrystals

TL;DR

This study uses density functional theory to analyze how chlorination affects the electronic properties, doping behavior, and defect states of silicon nanocrystals, revealing stability and altered electronic characteristics compared to hydrogenated counterparts.

Contribution

It provides the first detailed comparison of chlorinated versus hydrogenated silicon nanocrystals, highlighting stability and electronic property modifications due to surface passivation.

Findings

Chlorinated nanocrystals are stable with higher electron affinity.

Chlorination lowers optical absorption energy threshold.

Doping requires high activation energy in chlorinated nanocrystals.

Abstract

Silicon nanocrystals with diameters between 1 and 3 nm and surfaces passivated by chlorine or a mixture of chlorine and hydrogen were modeled using density functional theory, and their properties compared with those of fully hydrogenated nanocrystals. It is found that fully and partially chlorinated nanocrystals are stable, and have higher electron affinity, higher ionization energy and lower optical absorption energy threshold. As the hydrogenated silicon nanocrystals, chlorinated silicon nanocrystals doped with phosphorus or boron require a high activation energy to transfer an electron or hole, respectively, to undoped silicon nanocrystals. The electronic levels of surface dangling bonds are similar for both types of surface passivation, although in the chlorinated silicon nanocrystals some fall outside the narrower energy gap.