Formation of piezoelectric domains in epitaxial BN grown by MOVPE

Jakub Iwa?ski
University of Warsaw, Warsaw, Poland _______________________________________

Layered sp²-bonded boron nitride (BN) consists of atomic layers that can adopt various stacking sequences, resulting in polytypism. While hexagonal boron nitride (hBN) remains the most extensively studied polytype, alternative structures such as AB-stacked (bBN) and ABC-stacked (rBN) configurations have recently gained significant attention within the BN research community. These less common polytypes lack a center of symmetry, enabling unique physical properties, including second harmonic generation and piezoelectricity, which are absent in the widely studied hBN [1,2].

In this study, we report the growth of triangular rBN domains embedded within hBN films synthesized via metal-organic vapor phase epitaxy. The material quality and its polytype was examined by a set of experimental techniques such as X-ray diffraction, Fourier-transform infrared and Raman spectroscopy, photoluminescence, cathodoluminescence and transmission electron microscopy [3]. Fig. 1 presents piezoresponse force microscopy results, showing triangular domains consistently aligned along a single crystallographic orientation (Fig. 1a) with a pronounced piezoelectric response of approximately 2 pm/V (Fig. 1b), oriented out-of-plane (Fig. 1c). These triangular domains are composed of rBN (Fig. 1d). In contrast, most of the surrounding hBN regions display no significant piezoelectricity, apart from small domains with antiparallel piezoelectric responses. We will discuss the mechanisms underlying the formation of these oppositely oriented piezoelectric domains and their implications. Furthermore, we will demonstrate that these piezoelectric domains may influence properties of other 2D materials integrated into heterostructures using graphene as an example.

[1] Jiajie Qi, et al., Adv. Mater. 2024, 36, 2303122.https://doi.org/10.1002/adma.202303122
[2] Li Wang, et al., Nature 629, 74–79 (2024).https://doi.org/10.1038/s41586-024-07286-3
[3] Jakub Iwa?ski, et al., npj 2D Mater Appl 8, 72 (2024).https://doi.org/10.1038/s41699-024-00511-7

Email: Jakub.Iwanski@fuw.edu.pl