Transition-metal-related quantum emitters in wurtzite AlN and GaN

Transition-metal centers in wide-bandgap semiconductors are paramagnetic and can be optically manipulated, making them promising for quantum information applications. We have investigated the electronic structure and magneto-optical properties of Cr, Mn, Co, Ni, and Cu substitutional centers in AlN and GaN. We use hybrid density functional theory calculations to determine level structure, stability, optical signatures, and magnetic properties of these centers. The excitation energies are calculated using a constrained occupation approach that accounts for the multideterminant nature of the excited states and was verified with the complete active space configuration interaction approach. In analogy with the emission from Cr in sapphire, it has been suggested that Cr would be the source of ~1.8 eV optical emission observed in nitrides. Our results contradict this, which we explain this based on the different local environment (tetrahedral vs. octahedral coordination) in nitrides vs. oxides. Our simulations of photoluminescence spectra indicate that, instead, Cr is responsible for the observed emission near 1.2 eV. We outline an optical spin polarization protocol, demonstrating that these centers are promising candidates for spin qubits.