Other information

There is various other important kinetic, electronic and impurity-complex related information that is relevant to this work. The initial total TD formation rate at 450$^\circ$C is proportional to [O_i]ⁿ, n=4 [179] initially suggesting early TDs contained 4 O atoms; later work has shown this to be a function of both [O_i][242] (for [O_i] $\leq 8 \times 10^{17}$cm^-3 n was close to 1), and temperature[243]. At lower temperatures (T $\leq$ 400$^\circ$C) n=2, and this increases at 450$^\circ$C to n=4 as seen earlier. This suggests that at lower temperatures, oxygen dimerisation is the rate dominating step, but at higher temperatures this is replaced with simple O_i diffusion. At 500$^\circ$C, n increases further.

Uniaxial stress measurements on the electronic IR absorption associated with the TDs has also allowed symmetry assignments. This also showed C_2v symmetry [244,245], with the effective-mass like donor state constructed from a single pair of conduction band valleys [246] along [001] [247]. The C₂ axis is compressive and lies along [001] [248].