Germanium doping challenges

Ideal source and drain regions rely on high dopant solubility in the crystalline substrate, in order to boost activation and reduce sheet resistance, and low dopant diffusivity, to facilitate device scaling. High-concentration doping of Ge can be quite a substantial problem, as it is difficult to activate impurity atoms to a high enough level, prevent them escaping during thermal treatments, while maintaining good crystalline integrity of the semiconductor substrate. With future FET devices fabricated with nanowire, fin, or ultra-thin-body architectures, as reiterated by The International Technology Roadmap for Semiconductors, this problem may be challenging for many years to come. In this paper Ge doping challenges will be reviewed, including our ability to model such materials, as well as looking at potential future solutions.