Optimization of p-type contact for electrical injection and light extraction for 365nm UV-A LEDs

This paper demonstrates low-resistance and high-transparency p-type contact materials for UV micro-LEDs at 365 nm. As a commonly used p-type LED contact, Indium tin oxide (ITO) and nickel/indium tin oxide (Ni/ITO) contacts were studied before and after rapid thermal annealing (RTA) treatments. The transmittance at 365 nm wavelength of 200 nm thick ITO films increased from approximately 57% to 90% after RTA at a temperature exceeding 400°C, while the Ni/ITO film had a transmittance of about 73% after annealing. Micron-sized UV-LEDs (light-emitting diodes) with Ni/ITO p-contact were fabricated. Electrical characterization shows that Ni/ITO films annealed at 600°C demonstrated good ohmic contact behavior and the highest on-wafer external quantum efficiency (EQE), despite slightly lower transmittance. This paper shows the potential of annealed Ni/ITO films as promising p-contact materials for high-performance 365 nm UV-LEDs.