In this
work a comprehensive model for the optical transmission as a function of
wavelength and thickness of ZnO :Al films deposited on glass substrates by
ultrasonic spray pyrolysis, is developed. The mathematical expression developed
for the transmission of the transparent conducting film on a transparent
substrate, considers: 1) the interference effects of multiple specular
reflections of coherent light from the front and the back of the
flat-parallel-sided interfaces film-air and filmglass substrate, 2) the
contribution of free carrier concentration (electrons in the conduction band
due to Al doping) to the weak absorption in the visible and nearinfrared range,
3) the Urbach tail absorption edge at the low wavelength region ( < 400 nm
), 4) the effect of surface diffuse scattering of light originated by the
roughness of these interfaces on the specular reflection and transmission
coefficients. The wavelength dependence of the coefficients of reflection and
transmission, and the absorption coefficient of the ZnO :Al film in the low
absorptionvisible region (400-800 nm), were calculated from the formulas
derived for the refractive index and extinction coefficient by using a
LorentzDrude expression to separate the contribution of the bound-electrons and
free-electrons, respectively, to the complex dielectric function. The carrier
concentration and dc-electrical conductivity of the ZnO : Al films were
measured using Hall effect and currentvoltage measurements in the van der Pauw
configuration. The optical transmission of the films, in the range of
wavelengths from 190 to 1100 nm, was measured using an Uv-Vis spectrometer. The
fitting of the semi-empirical formula for the optical transmission with the
experimental transmission spectrum for each film was good and the effects of
the different parameters involved in the model was evidenced. The formulas
derived here for the optical transmission can be used for a more precise
determination of previously defined figures of merit for these type of films
for their use as transparent conductive electrodes as a function of thickness
of ZnO : Al. The correctness of the figures of merits considered and the
usefulness of the model for selecting the optimal thickness for a transparent
conductive contact was discussed.
Author(s) Details
Juan Carlos Alonso-Huitron
Instituto
de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico.
Apartado Postal 70-360, Coyoacan 04510, Distrito Federal, Mexico.
Augusto Garcia-Valenzuela
Instituto
de Ciencias Aplicadas y Tecnologia, Universidad Nacional Autonoma de Mexico.
Apartado Postal 70-186, Coyoacan 04510, Distrito Federal, Mexico.
Please see
the book here:- https://doi.org/10.9734/bpi/cmsdi/v4/1269
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