Raman Spectroscopy of the Trapezoidal Bi₂O₂Se

Abstract The 2D Bi₂O₂Se has recently attracted significant interest with large Hall mobility at low temperature due to the depressed electron–phonon scattering. However, the phonon properties of Bi₂O₂Se are not well explored, and some Raman modes are under debate. Here, substrate engineering is used to grow an unexplored trapezoidal Bi₂O₂Se, which facilitates the Raman measurements in different orientation planes. Two additional Raman modes at 55 and 429 cm⁻¹ are detected on the slope of the trapezoid besides the 159 and 362 cm⁻¹ modes found on the top plane of the trapezoidal Bi₂O₂Se. Based on the polarized Raman spectroscopy, density functional theory calculations, and group theory analysis, the Raman modes of 55, 159, 362, and 429 cm⁻¹ are assigned to the E_g, A_1g, B_1g, and E_g modes, respectively. There are two distinct types of angle‐resolved polarized Raman spectroscopy for the A_1g mode on the top and edge planes of Bi₂O₂Se, which can be used to determine the crystal orientation unambiguously. Furthermore, strong thermal anisotropy is found in the top and edge planes of trapezoidal Bi₂O₂Se, as reflected from the first‐order temperature coefficient of A_1g phonon mode. The novel growth strategy and interesting anisotropic phonon properties may open up potential applications of Bi₂O₂Se in nanoelectronics.