Transparent conductive films of 2 at% Ga-doped ZnO films were prepared on C-plane sapphire substrates by e-beam evaporation in vacuum. The optical absorption, reflectance, structural and electrical properties of 2 at% Ga-doped ZnO films were investigated. The films are highly transparent (>80%) in visible-NIR ranges, and the optical bandgap exhibits a blue shift for the as-deposited films from 3.30 eV to 3.83 eV and for heat treatment from 3.27 eV to 3.60 eV for 2 at% Ga-doped ZnO films with respect to pure ZnO films. Through resistivity, optical constants (ε, σ , -Im ε −1 and ω p ) and carrier concentration obtained from reflectivity and transmittance spectra for 2 at% Ga-doped ZnO films, we found that these films behave as n-type semiconductors exhibiting high carrier concentration N ∼ 10 21 cm −3 . This also gives an opportunity to predict electrical behaviour of transparent conductive films on the basis of the analysis of absorption and reflection measurements.
Lithium doped (0–10 at. % Li) ZnO films were grown in the wurtzite structure on sapphire (001) substrates and investigated in the 200–1200 cm−1 frequency range at 300 K by far-infrared reflectivity spectroscopy using polarized oblique (45°) incidence. This technique has enabled us to determine the longitudinal optical phonon frequency E1(LO) at 576 cm−1 of the fundamental lattice vibration at the center of the Brillouin zone, as well as to investigate the LO phonon-plasmon coupling in the low carrier density (N⩽1018 cm−3) ZnO films. The energy shift and halfwidth broadening of the LO phonon band in comparison with the uncoupled mode in high-ohmic ZnO:0.8 at. % Li (ρdc=0.6×106 Ω cm) film have been analyzed to get the concentration and “optical” mobility of charge carriers in the Li doped ZnO films. The results of optical, x-ray diffraction and dc resistivity measurements are discussed.
We report the preparation and investigation of heterostructures based on ferroelectric crystals and semiconductor films. The ferroelectric field effect transistor with high transparency for visible light and high field mobility of the charge carriers has been fabricated using ZnO:Li films as a transistor channel. The possibility of use of ferroelectric field effect transistor based on ZnO:Li films as bistable element for information writing has been shown.
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