Implantation and activation of ultra-shallow boron in germanium

The physical scaling associated with integrated circuits is exhausting the properties of Si and requires that advanced materials be used for future device generations. Ge is widely regarded as a possible replacement for Si due to its enhanced mobility and reduced contact resistance. Due to the extensive use of SixGe1-x in current devices, the implementation of Ge into future devices could be considered a mere evolution from Si rather than a revolutionary change. However, the information regarding technologically relevant ultra-shallow dopant implants into Ge and their associated activation behavior is currently sparse and must be fully understood prior to implementation into future devices.;The activation behavior of ultra-shallow B+ implants in Ge has been investigated using micro Hall effect and micro four point probe techniques. It has been observed that the activation behavior of ultra-shallow B+ implants are anomalous in that the electrically active dopant fraction is independent of the implanted B+ fluence for both crystalline and pre-amorphized Ge. Ion beam analysis techniques have been employed which have confirmed that a small fraction of B is located substitutionally and the substitutional fraction does not increase appreciably with thermal processing for temperatures ≤ 600°C. Activation is observed to increase with increasing B+ energy which is attributed to the effect of the surface proximity and its associated effect on vacancy annihilation.;The activation behavior is further explained through the largely immobile B atoms which have a distinctly low probability of recombining with a vacant site due to the overwhelmingly large population of interstitials created during implantation as simulated by SRIM. The excess interstitial population increases competition for B recombination on a vacant lattice site and thereby reduces B activation. B+ implantation at increased energy increases the number of vacancies created and reduces the effect of the surface on vacancy annihilation which explains the observed increase in activation.;The observed activation behavior in this work is a strong departure from what has been observed previously for B in Si. The results suggests that previous activation and dopant solubility models implemented for activation in Si do not apply for shallow B+ implantation in Ge.