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

HfO2 has been widely used in the electronics industry as a dielectric material with excellent properties. It has attracted much attention since HfO2 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 HfO2 thin films were grown on SrTiO3 substrates by pulsed laser deposition (PLD). Atomic force microscopy investigation suggests that the surface roughness of HfO2 thin films increases as the film thickness increases. X-ray photoelectron spectroscopy analyses indicate that the HfO2 thin film has a high purity and contain only Hf4+ ions. The band gap of HfO2 was measured by valence EELS and UV-visible spectra. Atomic structures of the HfO2/SrTiO3 heterointerface have been studied by the aberration-corrected transmission electron microscopy and energy-dispersive X-ray spectroscopy. The HfO2/SrTiO3 heterointerface is atomically abrupt and incoherent. Our findings suggest that non-doped HfO2 films with o-phase structure through PLD technology.