Doping, the controlled and intentional addition of impurities to a semiconductor, is one of the most important steps in a semiconductor
device fabrication process. Ion implantation has been the preferred method for doping semiconductor devices for many decades, but the technique suffers from a number of drawbacks at sub-10-nm dimensions. The ion implantation process is inherently high energy, due to the acceleration of heavy dopant ions toward the semiconductor crystal lattice at tens to hundreds of keV, often causing damage to the semiconductor’s crystal structure which must be recrystallized through a further annealing step. While the dose and concentration the dopant species may be finely adjusted, the spatial distribution of the implanted ions is quite difficult to control; controlling the depth and abruptness of ions to within 1 nm is particularly problematic. Combined with the general incompatibility of ion implantation with nanostructured materials, there is a clear need for new doping approaches to counter these
drawbacks.