Hutson, A. R.
Moiré Patterns of Ion Implantation by Channeling
at a lower T left [N] unchanged. This observation makes it impossible to interpret the annealing-induced increase of [N] to an equilibrium level [N.] simply in terms of the production of isolated N on P sites as a consequence of the thermal dissociation of a complex center containing N. For typical crystals which behave as in curve 3, annealing at 800Â°C gives [N.]=8,2XlO I5 cm-' after 0.5 hand 1.6XlOI6 cm-' after 16.5 h but upon reannealing for lO min at 900Â°C, [N.]=3.8XI0 16 cm-'. For a thermally activated process, the activation energy would be greater than 5 eV, a value inconsistent with the rapid change in [N.] upon reannealing at the higher T. The value of [N.] may depend upon the solubility of an unidentified impurity or defect, which is itself dependent upon the pressure of P in the heattreatment ambient. As [N] changes with annealing, the line at 2.3286 eV disappears and the Ax line grows in intensity. Figure 3 shows a plot of [N], measured after annealing for 2 h at lOOOÂ°C, versus the absorption coefficient at 2.3286 eV measured in the as-grown LEC crystals. The line drawn relates "'Ax and [N] in solution-grown crystals.' The
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