Аннотация
A detailed structural and optical band gap characterization study for more
than 40 epitaxial bismuth ferrite (BiFeO3 —BFO) thin films, measured by
X-ray diffraction, atomic force microscopy, and optical transmission spec-
troscopy, is reported. The films are grown in different deposition systems to
varying thicknesses (10–140 nm), on several substrates, and under different
growth and cooling conditions. Using the results and literature data, first it is
shown that the band gap measured by transmission is systematically lower
than the gap found by ellipsometry, suggesting that sufficient caution must
be exercised when comparing optical properties of BFO thin films. Then,
statistical analysis is used to look for correlations between the band gap and
structural parameters. While earlier works show the band gap to be sensitive
to epitaxial (homogeneous) strain, it is found that it appears not to exhibit a
dependence on inhomogeneous strain, out-of-plane lattice constant, or sub-
strate/film interface roughness. Rather, it is found that surface roughness as
well as film thickness generally tends to enhance the gap. Overall, the insen-
sitivity of the band gap to structural parameters—aside from homogeneous
strain—makes BiFeO3 largely immune to deviations in processing param-
eters, which should be an asset for photonic devices based on this material.
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