Metal-Insulator-Insulator-Metal Diodes with Responsivities Greater Than 30 A W⁻¹ Based on Nitrogen-Doped TiO_x and AlO_x Insulator Layers

Metal-insulator-insulator-metal diodes based on nitrogen-doped titanium dioxide (NTiO_x) and aluminum oxide (NAlO_x) are fabricated and characterized for the first time. Pt/TiO_x-NTiO_x/Pt and Pt/TiO_x-NAlO_x/Pt diodes with 30 nm of TiO_x or NTiOx and 5 nm of NAlO_x are compared to undoped Pt/TiO_x/Pt and Pt/TiO_x-AlO_x/Pt diodes of similar thickness. The nitrogen atoms are expected to modify the barrier heights and produce electron traps in the insulators. This changes the conduction mechanisms of the doped diodes, including the introduction of unidirectional, defect-mediated Poole–Frenkel transport and trap-assisted tunneling, which increase the performance of the doped diodes. The representative figures of merit observed for a Pt/TiO_x-NAlO_x/Pt diode at 0.5 V include an asymmetry of 8.76 × 10³, nonlinearity of 4, and zero-bias responsivity of 22.3 A W⁻¹. Zero-bias responsivities as high as 36.8 A W⁻¹ are obtained, which surpass the 19.4 A W⁻¹ theoretical limit for Schottky diodes. Notably, this defect-engineering approach is found to improve the figures of merit without an unwanted increase in diode resistance. A thinner Pt/NTiO_x-NAlO_x/Al diode is also produced, which has a low zero-bias resistance of 36 Ω, nonlinearity of 3.7, and zero-bias responsivity of 1.7 A W⁻¹.