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In this report, we have investigated optical constants and thickness of nanostructured ZnO films grown on a glass substrate by sol-gel spin coating technique using zinc acetate as precursor. Optical constants such as complex refractive index ñ and dielectric constant ϵ determined from the transmittance spectrum in the ultraviolet, visible, near infrared (UV-VIS, NIR) region by envelope method. The value of refractive index decreases from 2.34 to 1.86 and extinction coefficient increases from 0.28 to 0.64 with increasing wavelength. The decreasing behavior of refractive index is attributed due to the increase in transmission and decrease in absorption coefficient with increasing wavelength. The film exhibits reasonably high transmittance (>80%) in the visible region. Absorbance coefficient α and film thickness (d) were calculated from the interference of fringes of transmittance spectrum. The band gap and thickness of the film were found 3.02 eV and 275nm, respectively. The thickness of the film measured by envelope method is validated with cross-section micrograph of SEM images which is about 285 nm. The real part of the dielectric function of nanostructured ZnO decreases with increasing wavelength where as the imaginary part of dielectric constant increases with increasing wavelength. The observed high value of refractive index n and real part of dielectric constant ϵ at lower wavelength is due to band edge absorption of carriers. The dispersion relation shows the increase of complex refractive index and dielectric constant at the high frequency regime is due to the discharging of defect levels using optical excitation of carriers in the visible region.

The fabrication of electric double layer thin film transistors (EDLTFTs) using polymeric electrolyte as gate dielectric on chemically grown polycrystalline ZnO thin film channel has the lower threshold voltage at 0.4 V and the saturation current at 3 µA in the dark. The lower threshold voltage is -1 V and the saturation current is 10 µA in the UV illumination. In the dark and under UV light, the off state ID is 1 nA and 0.3 µA respectively and under gate and UV illumination the on current shows more than 3 times enhancement. This improvement in photocurrent is due to the combined effect of gate and UV illumination. The field effect mobility of the TFT is 0.06 cm2/Vs in the dark and 0.16 cm2/Vs under UV illumination. This increase in mobility under illumination and gate bias is due to the increase in carrier concentration and reduction of charged defects in the channel length.

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