Influence of orientation on the electro-optic effect in epitaxial Y-doped HfO₂ferroelectric thin films

Recently, we reported linear electro-optic (EO) effects in (100)-epitaxial yttrium-doped hafnium dioxide (Y-HfO2) ferroelectric thin films. In this study, we have investigated the influence of orientation on the EO effect in Y-HfO2 thin-film. (111)-epitaxial undoped HfO2 and Y-HfO2 films were deposited on Sn-doped In2O3/yttria-stabilized zirconia (111) substrates at room temperature through radiofrequency magnetron sputtering. Although the undoped HfO2 film showed typical paraelectric characteristics, ferroelectricity was observed in the (111)-Y-HfO2 film. Remnant polarization in the (111)-Y-HfO2 film was higher than that in the (100)-Y-HfO2 film. The (111)-Y-HfO2 film exhibited a linear EO effect based on ferroelectricity, which is consistent with that of the (100)-Y-HfO2 film. The average EO coefficient r c of the (111)-Y-HfO2 film was 0.67 pm V-1, which is higher than that of the (100)-Y-HfO2 film. This result is reasonable considering the difference in remnant polarization between the (100)-Y-HfO2 and (111)-Y-HfO2 films.