Studies on al and Mg Co-Doped ZnO Thin Films Grown by Sol-Gel Technique

ZnO thin films were grown by sol-gel process on glass substrates and were doped with Mg and Al by introduction of their respective salts in the solution. A series of samples were deposited by maintaining the same dopant concentration in the solution, but by varying the substrate temperature employed in the final annealling step. The concentration of dopant elements in the final ZnO film was estimated using Energy Dispersive X-ray Spectroscopy (EDS) measurements. Surface morphology was observed by using Scanning Electron Microscope (SEM). The energy band-gap was measured using optical absorption studies. Photoluminescence (PL) measurements were carried out at room temperature. Photocurrent measurements were carried out using Ag contacts by exposure to ultraviolet radiation. The results indicate that with increase of substrate temperature from 500 to 650 °C, the band gap reduced from 3.37 to 3.34 eV, along with an evolution of the PL peak. The dark and photocurrent levels were also reduced significantly with increased substrate temperature. A corresponding reduction in photocurrent switching transient times was also observed. The results indicate that higher substrate temperatures cause a precipitation or segregation of dopants into clusters thereby reducing their effectiveness.