Microdisplays based on an array of micro-sized GaN-based light emitting diodes (μLEDs) are very promising for high brightness applications. As the size of Micro-LED decreases, the sidewall damage caused by plasma etching becomes an important factor in reducing the luminescence efficiency. Here, the photoluminescence, scanning electron microscope (SEM) and high‑resolution transmission electron microscopy (HR‑TEM) were combined to reveal physical defects on the sidewall surface, such as plasma-induced lattice disorder, the enrichment of impurity atoms such as oxygen, and the destruction of the exposed part of the quantum well during etching. The structure of the 20 um mesa after inductively coupled plasma (ICP) dry etching was characterized optically, and the luminescence intensity begins to decrease gradually at 5 um from the sidewall, which was caused by the surface non-radiative recombination. Finally, through the combination of tetramethylammonium hydroxide (TMAH) treatment and SiO2 passivation, the sidewall passivation process is optimized, and the luminous efficiency of Micro-LED edge is effectively improved 4.5 times. These results have reference significance for reducing sidewall defects to improve Micro-LEDs luminescence efficiency in the future.
In the visible and near infrared regions, graphene is essentially transparent with a constant absorptivity of 2.3%. On contrast, in longer wavelengths, the absorptivity can be enhanced by graphene plasmons motivated by simple nanostructures. Besides, the graphene plasmons can be further enhanced via electrostatic doping when voltage is applied. This work numerically demonstrates that in optimized configuration the absorptance in monolayer graphene can be greatly enhanced and reach to 98.6% of the impinging light for transverse magnetic (TM) polarizations. Graphene can interact with light via plasmonic resonance. Towards this, we utilize a subwavelength-thick optic cavity, which composed of graphene grating, a dielectric spacing layer and a metal film to further enhance the interaction. When we use the TM mode source, the incident light matched the graphene plasmons, a strong drastic cut in the energy of the reflected light, which means obvious resonance absorption occurred. Meanwhile, the reflection can approach 0 when voltage applied. Finally, great absorption in 6.94 μm has been achieved by the graphene grating with the addition of a subwavelength-thick optic cavity via different voltage.
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