Regensburg 2022 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 25: Poster 1

HL 25.2: Poster

Mittwoch, 7. September 2022, 18:00–20:00, P2

Enhancement of Raman and Defect Photoluminescence Emission in Hexagonal Boron Nitride (h-BN) — •Felix Schaumburg, Marcel Zöllner, Vasilis Dergainlis, Axel Lorke, Martin Geller, and Günther Prinz — Faculty of Physics and CENIDE, University Duisburg-Essen, Germany

Optical spectroscopy, especially Raman- and photoluminescence (PL)-spectroscopy, is commonly used to study the optical properties of two-dimensional materials. In order to obtain the highest Raman/PL-signals, it is important to reduce the reflection of the excitation laser. We studied a number of exfoliated h-BN flakes with different thicknesses on a Si substrate with a 300 nm SiO₂ top-layer. By changing the h-BN layer-thickness, we found a specific thickness, where all Raman signals showed maximum intensity, whereas the backscattered laser light was almost completely suppressed. To explain the increased intensities, we calculated the reflectivity of the layer system (air, h-BN, SiO₂, Si) for different h-BN layer thicknesses and used the transfer-matrix-algorithm. For our 532 nm excitation laser, the minimum reflectivity was found for a h-BN flake thickness of about 160 nm. Using AFM measurements, we were able to confirm that the thickness of the h-BN flakes having the strongest Raman signals correspond almost exactly to the calculated thickness. Our results suggest, that the PL from defects will also be strongly enhanced for an h-BN thickness of 160 nm and an excitation laser wavelength of 532 nm. This optimal thickness for the defect state PL emission can easily be calculated for other excitation laser wavelengths, as well as for other materials.