Defects in AlN as candidates for solid-state qubits

We investigate point defects and defect complexes in AlN for potential applicability as single-spin centers and solid-state qubits analogous to those observed in diamond and SiC. We find that isolated anion vacancies (VN) meet many of the criteria for an individually addressable quantum system, but their states are too close to the conduction-band edge. We therefore investigate how the properties can be tuned by complexing of the vacancy with substitutional impurities on neighboring lattice sites. Based on our comprehensive investigation, the transition-metal dopants Ti and Zr emerge as the best candidates: They favorably substitute on the Al site and form complexes with VN that possess the desired array of electronic and optical properties. Favorable charge and spin states, binding energies, and optical excitation energies are reported. Our results indicate that implantation of Ti or Zr into single-crystal AlN substrates can lead to the formation of individually addressable solid-state qubits in this material.