J. Rass, S. Hagedorn, H.K. Cho, T. Kolbe, M. Guttmann, S. Breuer, J. Ruschel and S. Einfeldt

Published in:

Semicond. Sci. Technol., vol. 40, no.1, pp. 015019, doi:10.1088/1361-6641/ad9fa0 (2025).

Abstract:

Arrays of far-UVC micro light emitting diodes (LEDs) based on AlGaN and emitting at 233–235 nm have been fabricated on different types of AlN-sapphire templates and the optical polarization, output power, and efficiencies have been studied in dependence of the template technology and the mesa diameter of the micro-pixels. While LEDs fabricated on metal organic vapor phase epitaxy (MOVPE) AlN-sapphire templates show dominant TM polarized emission with a degree of polarization (DoP) of −0.2, LEDs on high temperature annealed AlN-sapphire templates show dominant TE polarized emission with a DoP of 0.2–0.3. The output power and external quantum efficiency increases with decreasing diameter of the slanted and reflective micro LED mesa. Peak output powers of 18 mW at 200 mA and peak external quantum efficiencies of up to 2.7% for mesa diameters of 1.5 μm on annealed templates were measured, corresponding to peak wall plug efficiencies of 1.7%, while conventional LEDs with large mesa areas on the same template showed maximum EQEs of 1.1%. The relative increase in output power by using the micro LED approach as compared to a conventional large area emitter is stronger for LEDs on MOVPE AlN templates than on annealed templates (about a factor of 3.7 vs. 2.3, respectively, at 50 mA) which is attributed to the polarization dependence of the light extraction.

Keywords:

LED, far-UVC, light extraction, optical polarization, AlN-template, AlGaN

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