Three families of shallow thermal donors have been identified in annealed C
zochralski silicon from measurements of their infrared electronic transitio
ns using Fourier transform spectroscopy. Donors produced in Al-doped Si inc
orporate an Al impurity; centers produced in hydrogenated material contain
an H (or D) atom; a third set of donors labeled STD(X)N produced in nitrida
ted or irradiated pre-hydrogenated samples may incorporate a lattice vacanc
y rather than a nitrogen atom. A critical review of the literature is made
and some rationalization has been effected. Comments are included about the
formation of donor centers following anneals of heavily damaged neat-zone
Si that also contains hydrogen.