Crystal structures and band offsets of ultrathin HfO₂-Y ₂O₃ composite films studied by photoemission and x-ray absorption spectroscopies

The authors have investigated ultrathin Hf O2 - Y2 O3 composite films by photoemission spectroscopy and x-ray absorption spectroscopy (XAS) to elucidate the Y2 O3 composition dependence of crystallization and band offsets. The authors have found that the crystal structure of ultrathin films can be predicted by the detailed spectral structure between 540 and 550 eV in XAS. Photoemission spectroscopy and XAS reveal that the films of x=0 and 0.05 are mainly in a monoclinic phase, while those of x=0.10 and 0.20 are in a cubic phase. Regardless of the crystal structure changes by adding Y2 O3 to Hf O2, the band gap and band offsets remain almost unchanged.