Low contact resistivity at the 10⁻⁴ Ω cm² level fabricated directly on n-type AlN

Ultrawide bandgap aluminum nitride (AlN) stands out as a highly attractive material for high-power electronics. However, AlN power devices face performance challenges due to high contact resistivity exceeding 10⁻¹ Ω cm². In this Letter, we demonstrate achieving a low contact resistivity at the 10⁻⁴ Ω cm² level via refined metallization processes applied directly to n-AlN. The minimum contact resistivity reached 5.82 × 10⁻⁴ Ω cm². Our analysis reveals that the low contact resistance primarily results from the stable TiAlTi/AlN interface, resilient even under rigorous annealing conditions, which beneficially forms a thin Al-Ti-N interlayer, promotes substantial nitrogen vacancies, enhances the net carrier density at the interface, and lowers the contact barrier. This work marks a significant milestone in realizing superior Ohmic contacts for n-type AlN, paving the way for more efficient power electronic and optoelectronic devices.