Single donors in highly strained silicon

Strain is a common ingredient in solid-state systems which has been widely used to enhance electronic devices performances, both electrically and optically, via a change in the band structure of materials. Consequently, strain also induces a change in the properties of single dopants, and schemes have now emerged to use strain to define or tune qubits for quantum technology purposes. Ensemble measurements of donors in strained silicon have been carried out, but yet to date no experiment down to the single atom level has been performed. Here a thin layer of highly strained silicon (~0.7%) was doped and overgrown, and the ground state of single donors were imaged using a scanning tunneling microscope. They reveal a strong valley repopulation with the ground state mostly composed of z-valleys for such large strain, as opposed to the unstrained case where the ground state is evenly distributed between the 6 valleys. This result, supported by atomistic calculations and X-ray measurements, shows that strain engineering is compatible with the future development of quantum technologies in solid-state systems.