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To light emitting diodes (LEDs), solving the common non-uniform current injection and efficiency degradation issues in (0001) plane micro-LED is essential. Herein, we investigated the light emission characteristics of various mesa sizes and different p-electrode areas toward the realization of coaxial GaInN/GaN multi-quantum-shell (MQS) nanowires (NWs)-based micro-LEDs. As the mesa area was reduced, the current leakage decreases, and further reduction of the area showed a possibility of realizing micro-LED with less current leakage. The large leakage path is mainly associated with the defective MQS structure on the (0001) plane area of each NW. Therefore, more NWs involved in an LED chip will induce higher reverse leakage. The current density-light output density characteristics showed considerably increased electroluminescence (EL) intensity as the mesa area decreased, owing to the promoted current injection into the efficient NW sidewalls under high current density. The samples with a mesa area of 50 × 50 µm2 showed 1.68 times higher light output density than an area of 100 × 100 µm2 under a current density of 1000 A/cm2. In particular, the emission from (1-101) and (10-10) planes did not exhibit an apparent peak shift caused by the quantum-confined Stark effect. Furthermore, by enlarging the p-electrode area, current can be uniformly injected into the entire chip with a trade-off of effective injection to the sidewall of each NW. High performance of the MQS NW-based micro-LED can be expected because of the mitigated efficiency degradation with a reducing mesa area and an optimal dimension of p-electrode.

GaInN/GaN multi-quantum-shell (MQS) nanowires (NWs) are gaining increasing attention as promising materials for developing highly efficient long-wavelength micro-light emitting diodes (LEDs). To improve the emission properties in GaInN/GaN MQS NWs, it is necessary to suppress the emission from the (0001) c-plane MQS at the apex region, which featured with low crystalline quality. In this study, we investigated the enhancement of optical properties and the realization of micro-LEDs by confirming the effect of the (0001) plane region. A 7.9-fold enhancement of the electroluminescence (EL) intensity was demonstrated by removal the (0001) plane region via inductively coupled plasma (ICP) dry etching, owing to the promoted current injection into the (1–101) semi-polar and (10–10) non-polar sidewall area. To investigate the effect of the emission area on the samples with and without truncated (0001) plane region, devices with three different mesa areas (50 × 50, 100 × 100, and 100 × 200 μm2) were fabricated. An increased EL intensity with the reduced mesa areas was observed in the samples without dry etching of the (0001)-plane area, because more current can be injected into the sidewall region with higher crystalline quality and luminous efficiency than the (0001)-plane MQS. Under the same injection current density, the truncated samples’ light output was increased for more than ten times as compared to the samples without (0001)-plane etching. Therefore, it confirms the possibility of realizing highly efficient GaInN/GaN MQS NWs LEDs by eliminating the (0001) plane MQS region. A precise etching and surface passivation of the apex region is expected to further reduce the reverse leakage current and improve the performance in NW-LEDs.

In this study, a nitride‐based blue PEDOT‐LED is fabricated and a preliminary assessment of the device characteristics is done. To prevent detaching of the PEDOT/PSS layer from the LED substrate when immersing in water or developing solution, Ag was deposited on top of the PEDOT/PSS layer. Additionally, exfoliation is suppressed by reducing the developing time and protecting the wafer edge with a photoresist. Different etching methods for Ag and PEDOT/PSS are investigated. The Ar ion‐beam etching resulted in uniform and flat‐etched surfaces. Regarding the performance of the PEDOT‐LEDs, a high Mg‐doping concentration of 1.0 × 1020 cm−2 leads to a relatively low threshold current voltage in the V–I characteristics. However, for the PEDOT‐LED with p‐Al0.25Ga0.75 N EBL, a steep light output saturation is observed at high current density when analyzing the L–I characteristics. [ABSTRACT FROM AUTHOR]

Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

The superior crystalline quality of coaxial GaInN/GaN multiple-quantum shell (MQS) nanowires (NWs) was demonstrated by employing an AlGaN undershell during metal-organic chemical vapor deposition. Scanning transmission electron microscopy (STEM) results reveal that the NW structure consists of distinct GaInN/GaN regions on different positions of the NWs and the cores were dislocation-free. High-resolution atomic contrast STEM images verified the importance of AlGaN undershells in trapping the point defects diffused from n-core to MQSs (m-planes), as well as the improvement of the grown crystal quality on the apex region (c-planes). Time-integrated and time-resolved photoluminescence (PL) measurements were performed to clarify the mechanism of the emission within the coaxial GaInN/GaN MQS NWs. The improved internal quantum efficiency in the NW sample was attributed to the unique AlGaN undershell, which was able to suppress the point defects diffusion and reduce the dislocation densities on c-planes. Carrier lifetimes of 2.19 ns and 8.44 ns were derived from time-resolved PL decay curves for NW samples without and with the AlGaN undershell, respectively. Hence, the use of an AlGaN undershell exhibits promising improvement of optical properties for NW-based white and micro light-emitting diodes.

In this study, we aim to understand the thermodynamics inside the junctions of GaInN-based LEDs through optical operation of the device (the wavelength of the pumping laser is 405 nm for quasi-resonant optical excitation). First, to achieve this goal, the short-circuit current vs the open-circuit voltage curve and photoluminescence spectrum are carefully analyzed and compared with the current–voltage curve and electroluminescence spectrum. By this comparative study, we experimentally demonstrate the electrical–optical energy conversion efficiency (ECE) > 100% under optical excitation. Second, the intra-band phonon absorption and emission inside and/or outside the junction (PPeltier and PHC) are investigated through the power-loss analysis. In so doing, we ascertain that the carriers in the multiple quantum wells are energized by phonons, which introduces the ECE > 100%. Specifically, after the energization, the Boltzmann carrier distribution is no longer controlled by the ambient lattice temperature but by higher temperature, namely, that of the carriers themselves. Based on the analysis, we propose a thermally enhanced effective temperature for the Boltzmann distribution. Finally, we compare the junction efficiency by photoluminescence (PL), composed of the internal quantum efficiency by PL and the ECE by PL, of the sample at various temperatures to investigate the effect of PHC on the overall PL efficiency. [ABSTRACT FROM AUTHOR]