SKM 2021 – scientific programme

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DS: Fachverband Dünne Schichten

DS 4: Poster

DS 4.21: Poster

Tuesday, September 28, 2021, 10:00–13:00, P

Enhancement of the Raman Emission in Hexagonal Boron Nitride — •Felix Schaumburg, Marcel Ney, Vasilis Dergianlis, Günther Prinz, Martin Paul Geller, and Axel Lorke — 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 signal, it is important to reduce spurious effects, such as backscattered laser light.

We studied a number of exfoliated h-BN flakes with different thicknesses on a silicon (Si) substrate with a 300 nm silicon dioxide (SiO₂) top-layer. With 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 signal, we calculated the reflectivity of the layer system (air, h-BN, SiO₂, Si) for different h-BN layer thickness, by using the transfer-matrix-algorithm. For our 532 nm excitation laser, the minimum surface reflectivity was found for a layer thickness of around 160 nm. With AFM measurements, we were able to confirm that the thickness of the samples, with the strongest Raman signal, corresponds 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.