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Type: Article × Subject: Light emitting diodes ×

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    Strain induced power enhancement of far-UVC LEDs on high temperature annealed AlN templates
    (Melville, NY : American Inst. of Physics, 2023) Knauer, A.; Kolbe, T.; Hagedorn, S.; Hoepfner, J.; Guttmann, M.; Cho, H.K.; Rass, J.; Ruschel, J.; Einfeldt, S.; Kneissl, M.; Weyers, M.
    High temperature annealed AlN/sapphire templates exhibit a reduced in-plane lattice constant compared to conventional non-annealed AlN/sapphire grown by metalorganic vapor phase epitaxy (MOVPE). This leads to additional lattice mismatch between the template and the AlGaN-based ultraviolet-C light emitting diode (UVC LED) heterostructure grown on these templates. This mismatch introduces additional compressive strain in AlGaN quantum wells resulting in enhanced transverse electric polarization of the quantum well emission at wavelengths below 235 nm compared to layer structures deposited on conventional MOVPE-grown AlN templates, which exhibit mainly transverse magnetic polarized emission. In addition, high temperature annealed AlN/sapphire templates also feature reduced defect densities leading to reduced non-radiative recombination. Based on these two factors, i.e., better outcoupling efficiency of the transverse electric polarized light and an enhanced internal quantum efficiency, the performance characteristic of far-UVC LEDs emitting at 231 nm was further improved with a cw optical output power of 3.5 mW at 150 mA.
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    High-Resolution Inkjet Printing of Quantum Dot Light-Emitting Microdiode Arrays
    (Weinheim : Wiley-VCH Verlag, 2020) Yang, P.; Zhang, L.; Kang, D.J.; Strahl, R.; Kraus, T.
    The direct printing of microscale quantum dot light-emitting diodes (QLEDs) is a cost-effective alternative to the placement of pre-formed LEDs. The quality of printed QLEDs currently is limited by nonuniformities in droplet formation, wetting, and drying during inkjet printing. Here, optimal ink formulation which can suppress nonuniformities at the pixel and array levels is demonstrated. A solvent mixture is used to tune the ejected droplet size, ensure wetting, and provoke Marangoni flows that prevent coffee stain rings. Arrays of green QLED devices are printed at a resolution of 500 pixels in.−1 with a maximum luminance of ≈3000 cd m−2 and a peak current efficiency of 2.8 cd A−1. The resulting array quality is sufficient to print displays at state-of-the-art resolutions.