In this study, a highly conductive and transparent AlN–based glass electrode, fabricated by either DC or AC-pulse-based electrical breakdown processes, is introduced, and applied to AlGaN–based UV-A and UV-C light-emitting diodes with p-AlxGa1-xN contact layers (x = 0.05, 0.1, 0.4). This AlN–based glass electrode with a conducting filament exhibited high transmittance in the deep-UV region (over 95.6 % at 280 nm) and low contact resistance with a p-Al0.4Ga0.6N layer (ρc = 3.2 × 10-2 Ω·cm2). The ohmic conduction mechanism at the interface between the AlN film and p-Al0.4Ga0.6N layers was then examined using various analytical tools. One of the 280-nm top-emitting LEDs with the AlN-based glass electrodes operated stably with a forward voltage of 7.7 V at 20 mA and a light-output power of 7.49 mW at 100 mA after packaging. The external quantum efficiency was measured to be a record-high 2.8. This report is the first demonstration of top emission from DUV LEDs, and the proposed method may be used extensively in various areas of optoelectronic devices and sensors.
Micro-light-emitting diodes (µLEDs) have attracted much attention in recent decades on account of their diverse applications, such as light sources for transparent displays, a headlamp for automobiles, a head-up display for military and aerospace areas. However, µLEDs suffered from a trade-off between fill factor (the ratio of emission area to pixel size) and the current density because each pixel of µLEDs is screened by p-electrode for current injection, reducing the effective emission area. We can expand the emission area by reducing the p-type electrode area, but it decreases the current density of the µLED. During the past few decades, many efforts have been attempted to enhance the light output power of the µLED by changing the size and shape of the pixel. However, there have been few fundamental breakthroughs in this trade-off issue.
In this study, we offered the so-called ‘glass electrodes’ to solve this problem in µLEDs. AlN rod-shaped glass electrodes with high transmittance and local current path (nanofilaments) were applied as top electrodes of the µLEDs, to improve the fill factor by enhancing the light emission of the µLED. The current path in AlN thin film was produced by an electrical breakdown process. Compared to the µLEDs with ITO electrodes, our µLEDs with AlN rod-shaped electrodes exhibited higher light output power density (105 % at 300 mA) and brighter light emission per area (110 % at 10 mA). More details including the ohmic transport mechanism for current injection and analysis of nanofilament will be presented at the conference.