Kyung Rock Son

Highly Efficient Deep-UV Light-Emitting Diodes Using AlN-Based Deep-UV-Transparent Glass Electrodes

Many studies have set out to develop electrodes that are both highly conductive and transparent across a wide spectral region, from visible to deep UV (DUV). However, few solutions have been proposed because these two properties are mutually exclusive. In this paper, an AlN-based glass electrode film with a conducting filament formed by the application of an ac pulse is proposed as a solution, which exhibits a high transmittance in the DUV region (over 95.6% at 280 nm) and a 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 the p-Al0.4Ga0.6N layers is fully examined using various analytical tools. This AlN film is finally applied to a 280 nm top-emitting light-emitting diode, to verify the validity of the method, which exhibits very stable operations with a forward voltage of 7.7 V at 20 mA, a light output power of 7.49 mW at 100 mA, and, most importantly, a record high external quantum efficiency of 2.8% after packaging.

Nitride-Based Microlight-Emitting Diodes Using AlN Thin-Film Electrodes with Nanoscale Indium/Tin Conducting Filaments

Microlight-emitting diodes (µLEDs) are emerging solutions for both high-quality displays and lighting technologies. However, the overall light output power density of these devices is low, as the emission area is shielded by the p-electrodes required for current injection. In this study, instead of the more conventionally used indium tin oxide (ITO), an AlN thin film with nanoscale conducing filaments (CFs) is used, referred to as CF-AlN, as a transparent conducting electrode (TCE), to enhance the output power density from the same emission area. As a result of this modification, the electroluminescence intensity is enhanced by 10% at an injection current of 10 mA, and the current density is improved by 13% at a forward voltage of 4.9 V, in comparison to the parameters observed with ITO-based µLEDs. This improvement is attributed to the higher transmittance of CF-AlN TCEs, together with efficient hole injection from the p-electrode into the light-emitting layer, through the CFs formed in the AlN layer. In addition, using transmission electron microscopy analyses, the origin of the CFs is directly identified as the diffusion of In and Sn ions, which provides critical insight into the conduction mechanism of AlN-based TCEs.

Highly-efficient top-emitting UV A-to-C LEDs using AlN-based glass electrodes (Conference Presentation)

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.

AlN/ITO hybrid electrodes with conducting filament for 365 nm ultraviolet light-emitting diodes

Hybrid transparent conductive electrodes (TCEs) consisting of AlN rods with conducting filaments (CFs) and ITO films was proposed to improve the current injection, spreading effect, and optical transmittance for 365 nm p-AlGaN based LEDs, and we demonstrated their electrical and optical properties. When comparing the performance of the LEDs with proposed hybrid TCE with reference LEDs having conventional ITO-TCEs, we observed the increased light-output powers of 6% and the reduced forward voltages of 8%, which may result from the improvement of ohmic contact behavior on the p-AlGaN layers by employing filament-embedded TCE, i.e., AlN/ITO hybrid electrodes.

Localized surface plasmon resonance from pt-based split ring structures

We fabricated split ring (SR) nanostructures to enhance the interaction with resonant photons caused by an excitation of localized surface plasmon resonance (LSPR) in the deep-ultraviolet region. Also, the effect of SR diameter size and split gap angle on the coherent plasmon coupling was investigated in 2D arrays of Pt based SR. The absorption resonance of the fabricated Pt-based SR depends on its diameter, and shifts toward shorter wavelength for the SR with larger diameter.