Photoluminescence and dielectric properties of (Al/Cu) and (In/Cu) co-doped ZnO sprayed thin films under the oxygen deficiency conditions

This work focuses on the study of the transport of charge carriers in Al (1%)/Cu (1%) and
In (1%)/Cu (1%) co-doped ZnO thin films prepared on glass substrates heated at 460°C using
the spray pyrolysis method. Each ratio of doping element is equal to 1% (M/Zn=1%, M=Al,
In, Cu) in the starting solutions. First, SEM and AFM micrographs confirm that the surface
samples are rough. Second, the impedance spectroscopy was used to investigate the transport
of charge carriers through grains and grain boundaries regions. Indeed, the ε »(T) plots show
the appearance of a peak when the temperature increases showing the detrapping phenomenon
which may promote the conductive behavior of these co-doped-ZnO thin layers. This
behavior was well approved by an increase of the Ac conductivity with temperature for such
co-doped films. Finally, PL investigations showed that these doping elements increase the
defects density and promote the presence of shallow traps levels close to the conduction band
edge which can contribute to the increase of the electrical conductivity. Finally, it is found
that indium doping enhances the blue emission intensity by increasing the charge carrier’s
concentration in oxygen vacancy levels. These oxygen deficiencies have an important effect
on the transport of charge carriers and pave the way for various applications such as
photocatalysis and bio-sensors.