Effect of film thickness on phase structure of epitaxial non-doped hafnium oxide films.

HfO has been widely used in the electronics industry as a dielectric material with excellent properties. It has attracted much attention since HfO was first reported to be ferroelectric in 2011. With the continuous advancement of research, various methods such as oxygen vacancy control and interface control have been proven to be able to stabilize the metastable polar o-phase structure in doped hafnium oxide thin films. However, there are still some shortcomings in the relevant issues concerning non-doped hafnium oxide thin film materials. Here, polycrystalline non-doped HfO thin films were grown on SrTiO substrates by pulsed laser deposition (PLD). Atomic force microscopy investigation suggests that the surface roughness of HfO thin films increases as the film thickness increases. X-ray photoelectron spectroscopy analyses indicate that the HfO thin film has a high purity and contain only Hf ions. The band gap of HfO was measured by valence EELS and UV-visible spectra. Atomic structures of the HfO/SrTiO heterointerface have been studied by the aberration-corrected transmission electron microscopy and energy-dispersive X-ray spectroscopy. The HfO/SrTiO heterointerface is atomically abrupt and incoherent. Our findings suggest that non-doped HfO films with o-phase structure through PLD technology.