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.

Localized surface plasmon-enhanced light emission using platinum nanorings in deep ultraviolet-emitting AlGaN quantum wells.

We report the enhancement of deep ultraviolet emissions from AlGaN-based quantum wells (QWs) using energy-matched localized surface plasmons (LSPs) in platinum (Pt) nanoring arrays. The peak resonances of the extinction spectra were shifted to the red spectral region as the nanoring diameters increased, and the Pt nanorings with a diameter of 325 nm exhibited strong photoluminescence (PL) resonance at 279 nm. The emission enhancement ratio was calculated to be 304% in peak PL intensity when compared to that of the bare AlGaN QWs; this is attributed to the strong coupling of QWs with LSPs from the Pt nanorings.

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter: A Universal Approach Toward High-Performance Blue TADF Top Emission OLED.

A novel device structure for thermally activated delayed fluorescence (TADF) top emission organic light-emitting diodes (TEOLEDs) that improves the viewing angle characteristics and reduces the efficiency roll-off is presented. Furthermore, we describe the design and fabrication of a cavity-suppressing electrode (CSE), Ag (12 nm)/WO3 (65 nm)/Ag (12 nm) that can be used as a transparent cathode. While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency (EQE) and improved angular dependency than the device fabricated using the microcavity-based Ag electrode, it suffers from low color purity and severe efficiency roll-off. These drawbacks can be reduced by using an optimized multi-quantum well emissive layer (MQW EML). The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE (18.05%), high color purity (full width at half maximum ~ 59 nm), reduced efficiency roll-off (~ 46% at 1000 cd m-2), and low angular dependence. These improvements can be attributed to the synergistic effect of the CSE and MQW EML. An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence, and the MQW EML effectively confines charges and excitons, thereby improving the color purity and EQE significantly. The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

Work Function-Tunable Amorphous Carbon-Silver Nanocomposite Hybrid Electrode for Optoelectronic Applications.

Parameters such as electrode work function (WF), optical reflectance, electrode morphology, and interface roughness play a crucial role in optoelectronic device design; therefore, fine-tuning these parameters is essential for efficient end-user applications. In this study, amorphous carbon-silver (C-Ag) nanocomposite hybrid electrodes are proposed and fully characterized for solar photovoltaic applications. Basically, the WF, sheet resistance, and optical reflectance of the C-Ag nanocomposite electrode are fine-tuned by varying the composition in a wide range. Experimental results suggest that irrespective of the variation in the graphite-silver composition, smaller and consistent grain size distributions offer uniform WF across the electrode surface. In addition, the strong C-Ag interaction in the nanocomposite enhances the nanomechanical properties of the hybrid electrode, such as hardness, reduced modulus, and elastic recovery parameters. Furthermore, the C-Ag nanocomposite hybrid electrode exhibits relatively lower surface roughness than the commercially available carbon paste electrode. These results suggest that the C-Ag nanocomposite electrode can be used for highly efficient photovoltaics in place of the conventional carbon-based electrodes.

Chromium/Nickel-Doped Silicon Oxide Thin-Film Electrode: Mechanism and Application to Microscale Light-Emitting Diodes.

Light extraction of microscale light-emitting diodes (µLEDs) is fundamentally limited by p-type metal electrodes for current injection due to the small pixel size of the LEDs. We propose Cr/Ni-doped silicon oxide (CN-SiOX) films as p-type contact electrodes for blue µLEDs to increase the light-output power under the same emitting areas. The conductivity of CN-SiOX electrode originates from the diffusion of top Cr/Ni atoms via electric-field-induced doping treatments, which allows for effective hole injection into the active layer. Consequently, we achieved a 62% improvement in the current density and a 47% increase in the light-output power compared to ITO-based µLEDs.

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.