Size dependence of phosphorus doping in silicon nanocrystals

Abstract

Doping of silicon nanocrystals (Si-NCs) is one of the major challenges for silicon nanoscale devices. In this work, phosphorus (P) doping in Si-NCs which are embedded within an amorphous silicon matrix is realized together with the growth of Si-NCs by plasma-enhanced chemical vapor deposition under a tunable substrate direct current (DC) bias. The variation of phosphorus concentration with substrate bias can be explained by the competition of bonding processes of Si–Si and P–Si bonds. The formation of Si–Si and P–Si bonds is differently influenced by the ion bombardment controlled by the substrate bias, due to their bonding energy difference. We have studied the influences of grain size on P doping in Si-NCs. Free carrier concentration, which is provided by activated P atoms, decreases with decreasing grain size due to increasing formation energy and activation energy of P atoms incorporated in Si-NCs. Furthermore, we have studied the P locations inside Si-NCs and hydrogen passivation of P in the form of P–Si–H complexes using the first-principles method. Hydrogen passivation of P can also contribute to the reduced free carrier concentration in smaller Si-NCs. These results provide valuable understanding of P doping in Si-NCs.