Distinguishing the Rhombohedral Phase from Orthorhombic Phases in Epitaxial Doped HfO Ferroelectric Films.

Epitaxial strain plays an important role in the stabilization of ferroelectricity in doped hafnia thin films, which are emerging candidates for Si-compatible nanoscale devices. Here, we report on epitaxial ferroelectric thin films of doped HfO deposited on LaSrMnO-buffered SrTiO substrates, LaSrMnO SrTiO-buffered Si (100) wafers, and trigonal AlO substrates. The investigated films appear to consist of four domains in a rhombohedral phase for films deposited on LaSrMnO-buffered SrTiO substrates and two domains for those deposited on sapphire. These findings are supported by extensive transmission electron microscopy characterization of the investigated films. The doped hafnia films show ferroelectric behavior with a remanent polarization up to 25 μC/cm and they do not require wake-up cycling to reach the polarization, unlike the reported polycrystalline orthorhombic ferroelectric hafnia films.