Fig. 1. Schematic illustration of (a) the flip-chip sub-250 nm DUV LEDs using distributed n-contact rods and embedded plasmonic pads for light extraction improvement, and (b) mechanism of photon propagation manipulation by plasmonic pads. (c) Simulated I-V curves for the Plasmonic device with comparison to that of Control one. (d) Comparison of current distribution (@100 mA) between the Control and Plasmonic devices (D=8  μm), where the black arrows indicate both direction and magnitude of current flow in the 2D plane. (e) Evolution of average current density in the active layer with increasing plasmonic pad size, in comparison to the pads’ area ratio to the active layer. (f) Comparative surface emission intensity for the Control and Plasmonic devices (D=8  μm), and (g) the plasmonic-pad-size-dependent LEE and related enhancement. The insets in (d) and (f) present a detailed view of the typical regions from their corresponding figures, and the plasmonic pads are indicated by the red arrows.

Fig. 2. (a) EL spectra comparison between Plasmonic DUV LEDs with different plasmonic pad sizes and the Control device without the plasmonic pads in the p-GaN layer. (b) Optical output power distribution for a batch of Plasmonic devices based on different sizes of plasmonic pads (D=8, 16, 20, and 24 μm) with comparison to the Control devices. (c) I-V and LOP curves for the typical Control and Plasmonic DUV LEDs with different sizes of plasmonic pads; (d) the corresponding angular emission pattern for the devices shown in (c).

Fig. 3. (a) 2D surface near-field EL emission pattern of the flip-chip DUV LEDs: Control and Plasmonic structure with different plasmonic pad sizes (i–v), and (b) the corresponding intensity distribution plotted in 3D mode. (c)–(e) Representative local emission patterns from regions highlighted in (i), (iv), and (v) of (a), shown referring to their OM images. The n-contact rod (n-rod) and plasmonic pad are labeled in the images. The scale bar is 100 μm.

Fig. 4. (a) Schematic illustration of the photon transmission within the epitaxy layer of the Control LED without plasmonic pads. Simulated near-field distribution for the Control LED under (b) TE mode and (c) TM mode dipole excitation. (d) Illustration of the photon transmission within the epitaxy layer of the Plasmonic LED. (e), (f) Corresponding simulation results for the Plasmonic LED incorporating plasmonic pads. (g), (h) Simulated near-field distribution for the Plasmonic LED under TM mode dipole excitation at various distances (0, 2, and 3 μm) from the plasmonic pad edge.

Fig. 5. (a) Schematic illustration of the FDTD simulation configuration for calculating angle-dependent reflective spectra using a plane wave light source with variable incident angles. (b) Extracted reflectance values as a function of incident angle. (c), (d) Simulated near-field distribution patterns within the device model at incident angles of 0° and −30°, respectively.

Fig. 6. (a) Schematic diagram of the experiment setup for measuring DOP in edge-emitting EL from DUV LEDs. (b), (c) EL spectra under TE and TM polarization for Control and Plasmonic LEDs, respectively. (d) Calculated DOP values for both samples.

Fig. 7. (a) EL spectra of the typical DUV LEDs with and without encapsulation of quartz lens using fluorine resin as binding material; (b) the corresponding I-V and LOP curves for the devices.

Fig. 8. Schematic illustration of the epitaxy structure for sub-250 nm DUV LEDs and the fabrication steps for the devices: i) Epitaxial growth of the layers and standard cleaning; ii) definition of the mesa and isolation trenches by dry etching; iii) etching of p-GaN holes for the embedding of plasmonic pads; iv) deposition of the n-contact metal; v) deposition of the p-contact metal; vi) deposition of the first SiO2 passivation layer; vii) formation of the p and n metal electrodes; viii) deposition of the second SiO2 passivation layer; ix) deposition electrode pads. During the fabrication process, step ii) established a pattern of distributed circular n-contact areas within the chip, which later developed into n-contact rods after the deposition of n-contact metals in step iv). Meanwhile, in step vii), an Al film was deposited simultaneously to form the embedded structure within p-GaN holes.

Fig. 9. OM images of the (a) electrode side and (b) sapphire side of the fabricated flip-chip DUV LED, providing a clear depiction of the distribution of the n-contact rods and plasmon pads. The chip size and the diameter of the n-contact rods are also illustrated.

Fig. 10. Simulated EL spectrum of the AlGaN DUV LED using the similar quantum structure in the experimental work, showing a center emission wavelength about 249 nm.

Fig. 11. Simulated I-V curves for the designed Plasmonic device with diffident size of plasmonic pads, in comparison with that of Control one without plasmonic pads.

Fig. 12. Extracted current distribution (@100 mA) for the Plasmonic device with pad’s diameter of (a) 8 μm, (b) 16 μm, (c) 20 μm, and (d) 24 μm, respectively. The direction and intensity of the current in the 2D plane are also indicated by the direction and magnitude of the black arrows.

Fig. 13. The surface emission intensity distribution for Plasmonic device with plasmonic pad’s diameter of (a) 8 μm, (b) 16 μm, (c) 20 μm, and (d) 24 μm, respectively. The driving current on the devices was 100 mA. The insets show a detailed view of the typical regions in the corresponding figure.

Fig. 14. The far-field emission patterns for the (a) Control and (b)–(e) Plasmonic devices with plasmonic pad’s diameter of 8 μm, 16 μm, 20 μm, and 24 μm, respectively.