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Using spin-polarized density functional theory supercells, this study investigates the defect thermodynamics and magnetic ordering of Cr-, Ru-, and Rh-doped wurtzite aluminum nitride (w-AlN) for dilute magnetic semiconductor applications. The calculations reveal that Cr dopants uniquely favor a stable ferromagnetic state across 1.85% to 16.67% concentration, transitioning from an insulator to a high-spin half-metal between 7.40% and 12.96% before becoming a normal metal. These findings establish Cr-doped w-AlN as a viable wide-bandgap material platform for room-temperature spintronic devices.
Cr doping reliably stabilizes a high-spin half-metallic phase in wide-bandgap w-AlN between 7.4% and 13%, sidestepping the antiferromagnetic collapse seen with Ru and Rh dopants.
Spintronics drives the search for functional materials, pursuing room-temperature dilute magnetic semiconductors to realize practical, energy-efficient devices. This paper presents a theoretical investigation into the magnetic properties of w-AlN doped with Cr, Ru, and Rh atoms, using spin-polarized density functional theory calculations with supercell models. Calculations of point-defect formation energies as a function of the Fermi level predict that Cr4+, Ru4+, and Rh3+ are the most favorable charge states substituting Al in w-AlN. With these preferred charge states, Cr-doped AlN is stable in the ferromagnetic state, preferable for spintronic devices, across a wide concentration range (1.85 to 16.67% of Al). Conversely, Ru- and Rh-doped AlN are unstable in the ferromagnetic state relative to the antiferromagnetic state. Further investigation into the electronic density of states reveals a fascinating evolution: for Cr concentrations below 5.56%, the Fermi level resides within the band gap directly above the valence band maximum, keeping the system insulating. It transitions to a high-spin half-metallic state between 7.40% and 12.96%, and finally transforms into a normal metal at 16.67% Cr. This behavior is absent in the DOS of the antiferromagnetic model of Ru- and Rh-doped systems, where insulating and metallic behaviors instead appear non-sequentially with varying concentrations.