A deep level was found in crystals which had been annealed at 750 to 1000C in N, and then quenched to room, or liquid N, temperatures. The energy level and cross-section of the deep level, which acted as a majority carrier trap, were deduced to be Ec - 0.44eV and 10-16cm2, respectively. The depth profile of the trap could be described by a complementary error function. The coefficient which was estimated from the profile corresponded with that for N in Si. It was suggested that the traps were generated by N and vacancy complexes, as the traps appeared only in quenched samples. In order to confirm this assumption, an attempt was made to control the trap density by changing the vacancy concentration. Annealing in N and O gas mixtures caused the vacancy concentration to decrease, since the oxidation of Si introduced excess interstitial Si atoms from the oxidized Si surface. The results clearly showed that the trap density near to the surface gradually decreased with annealing time in N and O gas mixtures.

N.Fuma, K.Tashiro, K.Kakumoto, Y.Takano: Materials Science Forum, 1995, 196-201, 797-802