A two-center model is developed to explain the electronic structure of
thermal double donors (TDD) in silicon. Calculations of 2p levels of
singly ionized TDD's are performed in the effective mass approximation
. From a comparison of the calculated results with the experimental da
ta, the internuclear distance between the two electrically active atom
s is evaluated as 0.75-0.95 nm for the TDD1-TDD3 and 1.35-1.75 nm for
the next four species:TDD4-TDD7. (C) 1997 American Institute of Physic
s.