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Author: Einfeldt, S. × DDC: 530 ×

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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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    Low resistance n-contact for UVC LEDs by a two-step plasma etching process
    (Bristol : IOP Publ., 2020) Cho, H.K.; Kang, J.H.; Sulmoni, L.; Kunkel, K.; Rass, J.; Susilo, N.; Wernicke, T.; Einfeldt, S.; Kneissl, M.
    The impact of plasma etching on the formation of low-resistance n-contacts on the AlGaN:Si current spreading layer during the chip fabrication of ultraviolet light-emitting diodes (UV LEDs) emitting at 265 nm is investigated. A two-step plasma etching process with a first rapid etching using BCl3/Cl2 gas mixture and a second slow etching step using pure Cl2 gas has been developed. The etching sequence provides smooth mesa side-walls and an n-AlGaN surface with reduced surface damage. Ohmic n-contacts with a contact resistivity of 3.5 10-4 Ωcm2 are obtained on Si-doped Al0.65Ga0.35N layers and the operating voltages of the UVC LEDs were reduced by 2 V for a current of 20 mA. © 2020 The Author(s). Published by IOP Publishing Ltd.