Diffusion of iridium in silicon: Changeover from a foreign-atom-limited to a native-defect-controlled transport mode

Diffusion of Ir into Si was investigated by annealing of front-side deposited floating-zone Si wafers at temperatures between 1000 and 1200 °C. Concentrations-depth profiles were measured by means of neutron activation analysis in conjunction with mechanical sectioning. The observed deep penetrations and anomalous profile shapes point to a diffusion process involving both highly mobile interstitial Ir_i as diffusion vehicle and immobile substitutional Ir_s as dominating species. The experimental findings are best reproduced by making allowance for Ir_i-Ir_s exchanges that simultaneously take place via Si self-interstitials (kickout mechanism) and Si vacancies (dissociative mechanism). As a unique property it is found that the Si:Ir system is subject to a gradual transition from a Ir_i-controlled diffusion mode at higher temperatures to a self-interstitial-controlled diffusion mode at lower temperatures.