Single Dopant Placement for Quantum Applications:Reacting Phosphine withAtomic PrecisionDangling Bond Structures

The use of STM-based hydrogen depassivation lithography (HDL) to position P atoms in silicon is now a proven platform for quantum devices (e.g. qubit and analog quantum simulation architectures). The electronic and nuclear properties at key sites of these devices such as spin, on site Coulomb repulsion, local chemical potential, etc., depend critically on the precise number of P atoms at a site. Despite the high degree of positional control demonstrated by HDL of +/-1 nm, it has proven difficult to ensure true single P atom placement as opposed to small clusters of P atoms. To address this, we experimentally explore two lithographic structures capable of hosting the P precursor molecule, phosphine, and develop strategies for using them to incorporate single P atoms. By perfecting these strategies we hope to achieve precision control over both P atom position and number in silicon enabling a higher complexity of quantum devices than what is currently possible.