Orientation control of phase transition and ferroelectricity in Al-doped HfO2 thin films

Binary ferroelectric materials such as hafnium oxide have been intensively studied, which are expected to exhibit robust ferroelectricity comparable to the perovskite-based ferroelectrics at nanoscale. Here, using the combination of X-ray diffraction (XRD) associate with Transmission Electron Microscope (TEM), we reveal the epitaxial growth of Al-doped HfO2 possessing various phase structures on different oriented SrTiO3 substrates. The well-oriented films show different ferroelectricity indicated by piezoresponse force microscopy (PFM). The film grown on the (111) SrTiO3 substrate shows the largest electromechanical effect. These results, with the analyses of structural characterizations, demonstrate the orientation control of phase transitions and ferroelectricity in Al-doped HfO2 thin films.