It was fOlllld as long ago as 1954 that heating oxygen rich silicon to
around 450°C produced electrical active defects - the so called thermal
donors. The inference was that the donors were created by some defect
produced by the aggregation of oxygen. Since then, there has been an
enor- mous amount of work carried out to elucidate the detailed
mechanism by which they, and other defects, are generated. This task has
been made all the more relevant as silicon is one of the most important
technological ma- terials in everyday use and oxygen is its most common
impurity. However, even after forty years, the details of the processes
by which the donors and other defects are generated are still obscure.
The difficulty of the problem is made more apparent when it is realised
that there is only one oxygen atom in about ten thousand silicon atoms
and so it is difficult to devise experiments to 'see' what happens
during the early stages of oxygen precipitation when complexes of two,
three or four 0xygen atoms are formed. However, new important new
findings have emerged from experiments such as the careful monitoring of
the changes in the infra- red lattice absorption spectra over long
durations, the observation of the growth of new bands which are
correlated with electronic infra-red data, and high resolution ENDOR
studies. In addition, progress has been made in the improved control of
samples containing oxygen, carbon, nitrogen and hydrogen.