Correlation between phase and optical properties of yttrium-doped hafnium oxide nanocrystalline thin films

Yttrium-doped hafnium oxide (YDH) nanocrystalline films were produced by sputter-deposition at a substrate temperature of 400 degrees C. The deposition was made onto Si (100) and optical grade quartz substrates with variable deposition time to produce YDH films in a wide range of thickness, d(YDH) similar to 25 nm to 1.1 mu m. The effect of d(YDH) on the crystal structure, surface/interface morphology and optical properties of YDH films was investigated. X-ray diffraction analyses revealed the formation of monoclinic phase for relatively thin films (<150 nm). The evolution towards stabilized cubic phase with increasing d(YDH) is observed. The scanning electron microscopy results indicate the dense, columnar structure of YDH films as a function of d(YDH). Spectrophotometry analyses indicate that the grown YDH films are transparent. The band gap was found to be similar to 5.60 eV for monoclinic YDH films while distinct separation and an increase in band gap to similar to 6.03 eV is evident with increasing d(YDH) and formation cubic YDH films. A correlation between growth conditions, phase evolution, and optical properties of the YDH nanocrystalline films is established. (C) 2013 Elsevier B.V. All rights reserved.