Seminarium Fizyki Ciała Stałego

Hexagonal boron nitride (hBN) is a wide bandgap semiconductor which was synthesized already in the 19th century, but only recently a high quality, single crystals with macroscopic millimetric size were produced [1], leading to the realization of a light-emitting device operating in the deep UV [2]. This achievement paved the way for applications of hBN to advanced optoelectronics, making it to be considered a challenger of aluminum nitride [3]. Furthermore, Bourrelier et al. reported in 2016 single photon emission of color centers emitting at 4.1 eV [4]. However, the question of the nature of the defect giving rise to this behavior is still under debate. In order to contribute to the elucidation of the origin of such emission, we performed high hydrostatic pressure studies of the low-temperature photoluminescence of bulk h-BN crystals and other BN stacking sequences, i.e. the Bernal bBN) and rhomboedral (rBN) forms (polytypes) in the ~ 3 – 4 eV spectral region using the diamond anvil cell technique. The results showed that the emission energy decreased with pressure less sensitively than the bandgap [5,6]. This behavior, distinct from the shift of the bandgap is typical of deep traps.Theoretical calculations of pressure dependencies of various defect levels in hBN and other BN polytypes demonstrated that some of the observed UV lines are associated with carbon-related defects, and their pressure behavior depends strongly on BN polytype. Our results show that tuning the stacking sequence in different polytypes of a given crystal provides unique “fingerprints” contributing to the identification of defects in 2D materials.[1] K. Watanabe et al., Nat. Mater., 3, 404 (2004). [2] K. Watanabe et al., Int. J. Appl. Ceram. Technol., 8, 977 (2011). [3] H.X. Jiang et al., ECS J. Solid State Sci. Technol., 6, Q3012 (2017).[4] R. Bourrellier et al., Nano Lett,. 16 4317 (2016). [5] K. Koronski et al., Superlattices and Microstructures, 131, 1 (2019).[6] J. Plo et al, https://arxiv.org/pdf/2405.20837, submitted to Phys. Rev. X (2024).