The continuous downscaling of transistor has required replacing the SiO2 gate dielectric with high dielectric gate materials. Therefore, it is a key problem to explore new high dielectric gate materials. Among the materials investigated,La-based rare earth materials have being emerging as one of the most promising candidates as the new gate dielectrics due to its relatively high dielectric constant , wide band gap, and high thermal stability. However, the structure and dielectric property of these materials are considerable limited. In this study, we grew LaxHf(1-x)Oy and LaLuO3 thin film by pulsed laser deposition method. Combining Synchrotron Infrared spectroscopy and XAFS techniques, the structure, infrared phonon modes and dielectric property are studied. For the LaxHf(1-x)Oy thin film, we revealed the dependence of structure and dielectric constant on La concentration. The thin film with 10% La/(La + Hf) atom ratio forms a cubic HfO2 phase and it has the largest static dielectric constant. More La atoms introduced cause amorphous phase formed and the static dielectric constants increase with the La content. The infrared phonon modes with most contribution to the static dielectric constant move to lower frequency, which results in the component dependence of the dielectric constant. For the LaLuO3 thin film, we found that the crystalline thin film keeps the main infrared phonon modes and preserves the static dielectric constant as crystal bulk sample. But the infrared phonon modes of amorphous thin film reduce and cause the static dielectric constant to decrease. The result is closely related to the local structure as revealed by XAFS. The crystalline thin film has the similar local structure as crystal bulk sample, while the amorphous thin film presents obvious change. This study indicates that synchrotron infrared spectroscopy and XAFS techniques can provide very important information for understanding the dielectric property physics origin of high dielectric gate materials. 

Fig1. (a).Infrared transmission spectra (Left) and Radial structure function(Right) of LaxHf(1-x)Oythin film;(b).Infrared transmission spectra (Left) and Radial structure function(Right) of LaLuO3thin film;