RETRACTED: Grain size and strain effects on the optical and electrical properties of hafnium oxide nanocrystalline thin films (Retracted article. See vol. 109, artn no. 109903, 2011)

Nanocrystalline hafnium oxide (HfO2) thin films with an average crystal size similar to 5-50 nm have been produced under controlled temperature and pressure and their structural, optical and electrical properties have been evaluated. Structural investigations indicate that the monoclinic HfO2 nanocrystals are highly oriented along the ((1) over bar 11) direction. The lattice expansion increases with a reduction in size while minimum strain energy occurs at maximum lattice expansion. The strain factor increases linearly from 2.4% to 4% with increasing HfO2 crystal dimensions from 10 to 40 nm. The optical absorption measurements indicate that the band gap (E-g) changes are not very significant with size reduction. The interband absorption corresponding to O 2p -> Hf 5d transitions dominate the optical absorption edge at E similar to 6.25 eV; E-g varied in the range 5.42-5.60 eV for a variation in crystal dimension in the range 10-40 nm. Room temperature electrical conductivity increases from 1.08 X 10(-3) to 1.7 X 10(-3) (Omega cm)(-1) with increasing size from 10 to 40 nm. The frequency dispersion of the electrical resistivity reveals the hopping conduction mechanism. The functional relationship derived between geometric and electronic structure for HfO2 suggest that tuning properties for desired applications can be achieved by controlling the grain size and, hence, the strain at the nanoscale dimensions. (C) 2010 American Institute of Physics. [doi:10.1063/1.3499325]