The role of ZnO in TeO2 thin films for optical and radiation dosimetry applications

The role of doping a p-type TeO₂ film with an n-type ZnO on its optical and X-ray dosimetric properties was investigated by experiments using (ZnO) _<i>x</i> (TeO₂)_1-<i>x</i> thin films (x = 0, 0.2, and 0.4 wt%). The physicochemical, optical, and electrical properties of (ZnO) _<i>x</i> (TeO₂) _<i>1-x</i> thin films grown on a soda-lime glass substrate by spray pyrolysis were studied. The XRD study revealed a polycrystalline structure of the films and weak diffraction peaks belonging to paratellurite TeO₂ in all film samples. A peak shift was observed in (ZnO)_0.2(TeO₂)_0.8 and (ZnO)_0.4(TeO₂)_0.6, indicating the presence of ZnO in the TeO₂ crystal lattice. The FESEM image revealed the grain size and roughness of the films, which decrease with increasing ZnO concentration. The film thickness determined by cross-sectional FESEM images are 14.00, 14.11, and 12.12 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>μ</mml:mi> <mml:mi>m</mml:mi></mml:mrow> </mml:math> for TeO₂, (ZnO)_0.2(TeO₂)_0.8, (ZnO)_0.4(TeO₂)_0.6, respectively. The UV-Vis study revealed high transparency in the visible light regions and a slight decrease in band gap values as ZnO concentration increased. The FTIR study showed resonances corresponding to the symmetrical equatorial and asymmetrical axial stretching frequencies of the Te-O bonds and a stretching mode of a Zn-O bond. Raman spectra detected the existence of Raman-active modes of TeO₂ for all films and ZnO in the ZnO-doped TeO₂ thin film samples. The current-voltage characteristics technique, which investigates the behaviour of electrical properties, was used to measure the change in current as a function of X-ray radiation dose. The I-V characteristics showed increased induced current at 100 and 200 cGy/min dose rates for all film samples. Consequently, we confirmed that the physicochemical properties of TeO₂ films could be improved by ZnO doping at a 40 % wt% concentration for maximum dose response and high transparency. These thin films have high sensitivity and can detect both low and high-energy radiation, making them useful in various radiation-related applications such as medical dosimetry, environmental monitoring, and radiation safety. TeO₂'s superior optical properties are enhanced by ZnO's wide bandgap high exciton binding energy, and radiation sensitivity making it a competitive candidate for the development of miniaturized thin-film dosimeter that can fit in portable gadgets such as smartphones.