An investigation was made, of the electrical properties of annealed C- and N-rich Czochralski-type crystals, by using optical absorption and electron spin resonance techniques. It was found that there was formation of a new kind of H-like donor. These were termed ultra-shallow thermal donors, and were made up of C, N and O, and had very shallow energy levels. The donor central-cell corrections were very small, and some of them involved a negative central-cell correction which was peculiar to large cluster size defects. On the basis of similarities between N-O donors and ultra-shallow thermal donors, a formation mechanism and atomic configuration were proposed for the latter. They were suggested to be defects that were caused by interstitial C atoms which diffused into the core of N-O donors and modified the electronic structure.

A.Hara: Japanese Journal of Applied Physics, 1995, 34[I-7A], 3418-25