Single dopants in semiconductors.

The controlled introduction of dopant atoms to semiconducting host materials is the corner stone of electronic device fabrication. Dopant atoms provide a means to modulate the electronic, optical, and magnetic properties of semiconductors [1], and it is now possible to control dopant profiles with true atomic-scale precision in the laboratory [2]. Moreover, industrial fabrication methods are now capable of producing features with sub-10 nm precision [3] which therefore contain only a small numbers of dopants. This extraordinary control of dopant atom placement and semiconductor feature patterning provides exciting possibilities for the creation of quantum (opto)electronic devices including devices for quantum information processing. Furthermore, it can be argued that building such devices in semiconductor hosts provides a more straightforward route for their incorporation with conventional semiconductor electronics compared with competing quantum device architectures. At the same time there are new challenges for conventional devices at these length scales; the very small number of dopants involved in sub-10 nm structures means the position of individual dopants has a dramatic effect on charge transport due to the effects of scattering, quantisation, and tunnelling [4]. The present challenge is to develop a deeper understanding of the physics underpinning small numbers of dopant atoms in device-relevant atomic-scale architectures. This will necessarily include the further development of methods for fabricating such structures and the refinement of the theoretical tools appropriate for modelling them.