Suppression of near-edge optical absorption band in sputter deposited HfO2–Al2O3 nanolaminates containing nonmonoclinic HfO2

Nanolaminates of polycrystalline (tetragonal+orthorhombic) HfO2 and amorphous Al2O3 are sputter deposited on unheated fused SiO2, air annealed at 573–1273K, and analyzed by x-ray diffraction and spectrophometry. Significant O 2p→Hf 5d interband absorption occurs in all films at energy E⩾6.2eV. For E<6.2eV, films annealed below 1273K retain a featureless optical absorption edge despite further crystallization. A band with a 5.65eV onset concurrently develops with m-HfO2 crystallization after a 1273K anneal, indicating this phase and not nanocrystallinity per se is responsible for increased absorption.