Effect of annealing on the electrical properties of nitrogen-doped silicon single crystals grown by crucibleless zone melting

The electrical properties of nitrogen-doped silicon single crystals of the n and p types grown by crucibleless zone melting and annealed at 680°C have been studied. It is shown that the annealing brings about the appearance, in the crystals, of nitrogen-containing centers, which form deep donor and acceptor levels in the band gap. The process is accompanied by an increase in the electrical resistivity; the increase is particularly substantial in the initially high-resistance single crystals. On the other hand, in slightly boron-doped single crystals of the n and p types, the conversion of the conduction type is observed. In a converted material of the n-type, the electron mobility is anomalously low, which demonstrates its high electrical spatial inhomogeneity. The energy of the deep acceptor level near E _c ? 0.35 eV introduced during annealing has been determined. The model explaining the phenomena observed is proposed.