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Optical investigations on the existence of phase transition in ZnO:Li thin films prepared by DC sputtering method
Author(s) -
Abu ELFadl A.,
ELMaghraby E. M.,
Yamazaki T.
Publication year - 2008
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.200710982
Subject(s) - absorption edge , sputtering , thin film , sapphire , wurtzite crystal structure , analytical chemistry (journal) , substrate (aquarium) , absorption (acoustics) , ion , materials science , band gap , semiconductor , phase transition , ferroelectricity , phase (matter) , chemistry , optoelectronics , zinc , optics , condensed matter physics , laser , nanotechnology , dielectric , physics , oceanography , organic chemistry , chromatography , geology , metallurgy , composite material
We investigated the effect of temperature on the absorption spectra of Zn 0.8 Li 0.2 O thin films (ZnO:Li), deposited at 573 K, in the wavelength range 190‐800 nm. The films were deposited on sapphire, MgO or quartz substrates by DC sputtering method. The results show a shift of the optical energy gap (E g ), with direct allowed transition type near the fundamental edge, to lower wavelengths as the temperature increases. The temperature rate of E g changes considerably showing an anomaly around 320 K depending on type of substrate. The founded results indicated that replacement of Zn ions with Li ions induces a ferroelectric phase in the ZnO wurtzite‐type semiconductor. The exponential dependence of the absorption coefficient on the incident photon energy suggests the validity of the Urbach rule. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)