Fig. 1. (a) Schematics of the processing steps used to fabricate Al nanoring arrays using SiO2 nanospheres. (b)–(d) SEM images showing top views of Al nanoring arrays fabricated using SiO2 nanospheres with diameters of 150, 300, and 450 nm, respectively. (e)–(g) Experimental absorbance spectra of the Al nanorings with outer diameters of 165, 385, and 520 nm, respectively.

Fig. 2. (a) Schematic of the AlGaN/GaN-based near-UV LED structure with Al nanorings to capture both AFM and TEM images. (b) AFM image of the top surface of the near-UV LED with 385 nm Al nanorings that have an HCP array structure and height distribution. (c) STEM cross-sectional image of the AlGaN/GaN-based near-UV LED with Al nanorings and (d) the corresponding EDS mapping image of Al element (green color).

Fig. 3. 3D FDTD simulations of the Al nanoring array, which has an HCP structure with outer diameters of 385 nm, plasmonic system. (a) Schematic of the simulated Al nanoring array–HCP unit cell structure. (b) Simulated absorbance spectra of the Al nanoring array with an HCP unit cell on the glass substrate, when the incident light was both TE and TM polarized. Top views of the local electric field distributions of Al nanorings with HCP unit cell on the Al0.1Ga0.9N substrate, when using dipole modes of (c) TE and (d) TM at z=0  nm, and (e) TE at z=−16  nm, respectively, at 365 nm. (f) Intensity profile of the magnetic field at 365 nm.

Fig. 4. (a) Power-dependent PL measurements with source power of 0.03, 0.1, 0.5, 2, and 8 mW from bottom to top. (b) Time-resolved PL spectra of the AlGaN/GaN MQW structure with and without Al nanorings at room temperature.

Fig. 5. (a) Temporal evolution of MQW emissions obtained at different temperatures for AlGaN/GaN MQW samples with and without Al nanoring structures. For both samples, temporal curves are normalized and vertically shifted for comparison. Measured PL lifetime τm and radiative and nonradiative lifetimes (τr and τnr) (b) without Al nanorings and (c) with Al nanorings inferred from the temperature-dependent time-resolved PL result and integrated PL intensity.

Fig. 6. TDPL measurements. PL spectra of AlGaN/GaN MQW structures (a) without Al nanorings (b) with Al nanorings at temperatures from 12 to 300 K. (c) Arrhenius plot of the normalized integrated PL intensities for AlGaN/GaN MQWs with and without Al nanorings.