Deep levels are found in n-type silicon that is annealed in N2 and quenched to room temperature. The energy level and capture cross section of the deep levels are estimated to be about E c-0.42 eV and of the order of 10-17 cm2, respectively. The charge state of the deep levels is determined to be acceptor type by measuring the temperature dependence of the Schottky junction capacitance made in the specimen with the deep levels. The depth profile of the deep level density is found to correspond to that of the complementary error function, and the diffusion coefficient calculated from the profile is in good agreement with that of nitrogen in silicon. It is assumed that generation of deep levels is due to the formation of nitrogen-vacancy complexes, because quenching to room temperature and several hours' storage after quenching are required to form the deep levels. In order to confirm this assumption, we attempted to control the deep level density by changing the vacancy concentration. Oxidation of the specimen surface and formation of oxygen precipitates in silicon are known to decrease the vacancy concentration, since they supply excess interstitials from the oxide and silicon interface. Experimental results clearly show that the deep level density observed in these specimens is very low.

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A deep level of E c-0.46 eV (E1) was observed in commercially available Si epitaxial layers. The deep level decreased gradually at room temperature and eventually vanished completely 8 months after growth, and new levels, E c-0.08 eV, E c-0.10 eV, E c-0.14 eV and E c-0.21 eV, were observed. After annealing at 750° C, E1 level appeared again and all of the new levels disappeared. All levels, including E1, disappeared upon high-temperature annealing (>1000° C) in a O2 ambient. It was confirmed that these deep levels were due to contamination by Fe in epitaxial layer.