\textit{Ab initio} calculations for the electronic properties of zinc-doped indium phosphide nanowires*

$p$-type indium phosphide nanowires are known to function as working devices when assembled with $n$-type nanowires, and thus are seen as very promising building blocks for highly integrated electronic devices within the semiconductor industry. In this work, we have characterized the impurity state responsible for current flow in zinc-doped indium phosphide nanowires through first-principles calculations based on a real-space implementation of density-functional theory and pseudopotentials. The binding energy of the acceptor state is predicted to range from the value of the acceptor state in the bulk to up to values of approximately 0.2 eV in the thinner nanowires as a result of the two-dimensional quantum confinement. Our results show that, in thin nanowires, quantum confinement can move the defect level deep into the energy gap.