Valence force field analysis on nitrogen in silicon

Nitrogen doping attracts attention because it reduces void defects drastically. But the mechanism has not been clarified yet. Various configurations of nitrogen have been proposed by using the first principles calculation but there is no description how the stress plays a role in determining these nitrogen configurations. We reveal normal vibration modes corresponding to well-known infrared absorption peaks at 766 and 963 cm(-1) of nitrogen split interstitial (N-N) and derive force constants for bond stretching and bond bending. Local strain energy near nitrogen is calculated for the optimized structures of N-N, nitrogen-vacancy complex, substitutional N and interstitial N. As a result, it is found that in structures of N-N and N-2-V-2 with filled electron orbitals, strain energy plays an important role in the determination of the stable structure. (C) 2001 Published by Elsevier Science B.V.