Optimized ITO/Ag/ITO multilayers as a current spreading layer to enhance the light output of ultraviolet light-emitting diodes

ITO/Ag/ITO multilayers were optimized at different annealing conditions and were employed as a current spreading layer (CSL) for 365 nm UVLEDs. The ITO (40 nm) layer gave a transmittance of 83.9% at 365 nm, while the ITO/Ag/ITO (13 nm/14 nm/23 nm) multilayers annealed at 600 °C in N₂ ambient had 92.3%. The ITO/Ag/ITO multilayer annealed at 600 °C in N₂ ambient yielded a sheet resistance of 3.8 Ω/sq., while the ITO layer had 186.8 Ω/sq. The ITO/Ag/ITO multilayers annealed at 600 °C had a Haacke's figure of merit (FOM) of 106.1 × 10⁻³ Ω⁻¹, which was far larger than that of the ITO layer (1.5 × 10⁻³ Ω⁻¹). The annealed multilayers revealed optical bandgaps of 3.74–3.94 eV. The high-angle annular dark-field images showed that unlike the N₂-annealed samples, the Ag layer of the air-annealed sample experienced agglomeration. Ultraviolet light-emitting diodes (UVLEDs) fabricated with the 600 °C-annealed ITO/Ag/ITO CSL displayed 68.5% higher light output at 100 mA than the reference ITO UVLED. Unlike the UVLED with reference ITO, the UVLEDs with the annealed multilayers exhibited uniform light emission across the chip area. The higher light output was attributed to the combined effects of the high transmittance, and better current injection and current spreading of the annealed multilayers.