Influence of K-doping on the optical properties of ZnO thin films grown by chemical bath deposition method

The optical properties of potassium (K) doped zinc oxide (ZnO) thin films deposited onto glass substrate by chemical bath deposition (CBD) technique is investigated. The crystallinity, surface morphology and the element composition of the thin films were studied. The optical behavior of K-doped ZnO thin films were investigated by optical transmittance spectrum and photoluminescence (PL) studies. The energy band gap value determined from the optical transmittance spectrum decreases with the increase in the doping concentration. The optical band gap values of the doped thin films are large due to the small grain sizes. The optical constants such as refractive index, extinction coefficient, real and imaginary parts of dielectric constant as a function of wavelength were determined and our results are consistent with that of alkali doped ZnO thin films. The low extinction coefficient values reveal the good quality of the thin films. The thin films exhibit a high absorption coefficient values. The PL spectra show a UV emission and two weak blue emissions (deep level emissions) for all the films.

► Low cost chemical bath deposition method has been used for the growth of doped ZnO thin films.
► Controlling the optical constants by varying the potassium doping has been investigated.
► FESEM analysis indicates that the grain sizes are small and so the energy gap values are large.
► The doped ZnO thin films are found to be suitable for photovoltaic and optoelectronic applications.