Aluminum-nanosphere-stacked MgNiO metal-semiconductor-metal ultraviolet photodetectors

Because MgO and NiO materials have the same rock-salt cubic structure and similar lattice constants, the MgNiO absorption layers of metal–semiconductor–metal ultraviolet photodetectors (MSM-UVPDs) were deposited by alloying MgO and NiO. To improve the properties of the MgNiO films, the films were annealed at various temperatures. The grain size of 18.5 nm for the as-deposited MgNiO films was improved to 23.4 nm and 24.8 nm for the MgNiO films annealed at 500 °C and 600 °C for 60 min, respectively. For the film-structured MSM-UVPDs with 500 °C-annealed MgNiO films operated at a bias voltage of 5 V, the photoresponsivity, average noise current, noise equivalent power, and specific detectivity were 1.78 × 10⁻² A/W, 3.74 × 10⁻¹² A, 2.10 × 10⁻¹⁰ W, and 1.50 × 10⁹ cmHz^0.5W⁻¹, respectively. Aluminum (Al) nanospheres were stacked on the film-structured MgNiO MSM-UVPDs. The performance of the resulting Al-nanosphere-stacked MgNiO MSM-UVPDs was improved by increasing the density of the Al nanospheres. With an Al nanosphere density of approximately 2.0 × 10⁷/mm², when the Al-nanosphere-stacked MgNiO MSM-UVPDs operated at a bias voltage of 5 V, the photoresponsivity, average noise current, noise equivalent power, and specific detectivity were 2.00 × 10⁻¹ A/W, 7.71 × 10⁻¹² A, 3.88 × 10⁻¹¹ W, and 8.16 × 10⁹ cmHz^0.5W⁻¹, respectively. Despite the noise induced by the Al nanospheres, the performance of the Al-nanosphere-stacked MgNiO MSM-UVPDs was better than that of the film-structured MgNiO MSM-UVPDs. The improved detective performance was attributed to the increase in absorbance induced by the surface plasmon resonance and the optical scattering effect of the stacked Al nanospheres.