First principles analysis on void-reduction mechanism and impact of oxygen in nitrogen-doped CZ-Si crystal

•Stable structures and formation processes of N-V and N-O-V complexes in Si was theoretically studied.•Void-reduction mechanism by N-doping was clarified.•The reason O atoms weaken the void-reduction effect by N-doping is explained. During silicon (Si) crystal growth with the Czochralski method, nitrogen (N) doping at a concentration of about 1013–1015 atoms/cm3 decreases the size of void defects. This is related to the trapping of vacancies (Vs) by N atoms. The effect by N-doping is weakened with an increase in oxygen (O) concentration. The stable structures and formation processes of N-V and N-O-V complexes were investigated systematically by conducting density functional theory calculations, and the void-reduction mechanism by N-doping and the impact of O atoms were clarified. The results indicate that two interstitial N atoms form N2 which reacts with Vs to change its structure to N2-V and N2-V2. The dissociation of a V from stable N-V complexes requires a large amount of energy. Furthermore, the stabilized O atoms around the N atoms in N-O-V complexes restrict the movement of Si atoms. The energy required for a V to dissociate from N-O-V complexes is reduced, resulting in an increase in the number of free Vs. This is the reason O atoms weaken the void-reduction effect by N-doping.