Unveiling the vibrational fingerprints of ferroelectric HfO₂

Experimental observation of ferroelectricity in hafnia (HfO2) has sparked a lot of research interest on this material, mainly due to its promising applications in complementary metal-oxide-semiconductor (CMOS) technology and negative capacitance heterostructures [1,2]. A thorough understanding of lattice dynamics and vibrational properties of this emerging material is vital for identification of various distinct phases of hafnia and their technological integration. Using density-functional theory calculations, we systematically investigate the lattice dynamics of five known phases of hafnia (i.e., cubic, tetragonal, orthorhombic polar, orthorhombic antipolar, and monoclinic) and identify their spectroscopic fingerprints. Our theoretical results are in remarkable agreement with the measured Raman and infrared reflectance spectra of distinct phases of bulk hafnia stabilized by Y substitution and rapid cooling. We uncover a number of signature infrared- and Raman-active phonon modes for each phase. We especially focus on the recently reported “flat-band” polar phonon mode in ferroelectric hafnia [3].

References:

[1] Böscke et al., Appl. Phys. Lett. 99, 102903 (2011).

[2] Xu et al., Nat. Mater. 20, 826-832 (2021).

[3] Lee et al., Science 369, 6509: 1343-1347 (2020).