Dresden 2026 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 26: Poster II

HL 26.6: Poster

Wednesday, March 11, 2026, 09:30–11:30, P1

Optical loss characterization in UV multimode AlGaN waveguides with and without a backside absorbing layer — •leonardo wildenburg¹, verena kowallik¹, tim wernicke¹, and michael kneissl^{1, 2} — ¹Technische Universität Berlin, Berlin, Germany — ²Ferdinand-Braun-Institut (FBH), Berlin, Germany

Photonic integrated circuits (PICs) in the UV range enable complex optical functions on a chip-scale platform, e.g. for the detection of gases and biomolecules by absorption or Raman spectroscopy. The implementation of UV PICs requires wide-bandgap materials to ensure optical transparency. Among the available material systems, one promising candidate is AlGaN due to its application in UV-LEDs and laser diodes. In this work, the optical losses near 265 nm of n-Al_0.76Ga_0.24N waveguides with a width of 200 µm are investigated using a monolithically integrated UV-LED and UV-photodetector. The influence of straylight from the substrate backside was investigated with and without an absorbing 200 nm thin SiN layer. When operating the LEDs at a constant output power of 0.2 mW, the photocurrent decreases exponentially with increasing waveguide length according to Beer-Lambert-law. The reduction of scattered light was confirmed by measurements of photodetectors of the same wafer, but not connected to the emitting LED by a waveguide. Thus, optical losses of (40 ± 5) cm⁻¹ with an absorbing layer and (33 ± 5) cm⁻¹ without were measured for the n-Al_0.76Ga_0.24N waveguides. It was also determined that the optical losses strongly depend on the amount of scattered light from the UV-LED signal.

Keywords: optical losses; photonic integrated circuit; ultraviolet