Effect of Cu–Li Co-Doping on the Structural, Optical, and Optoelectronic Properties of Sol-Gel ZnO Thin Films

Abstract

The effect of Cu–Li co-doping for 0.1% Cu and 2–7% Li on the structural, optical, and optoelectronic properties of sol–gel ZnO thin films deposited on glass substrates has been investigated. X-ray diffraction studies show that the co-doped films have ZnO wurtzite structure with random orientations. With 2% Li doping in 0.1% Cu-doped ZnO, an initial increase in the parameter is observed followed by a decrease for a higher Li incorporation. The surface morphology shows that the co-doped films are composed of grains, which decrease in size with Li co-doping. A systematic decrease in the current level in the current–voltage measurements confirms that Li is incorporated into the ZnO lattice. The excitonic absorption peak is very prominent in a 2% Li co-doped film while it is broadened for higher Li content. As 2% Li is introduced, the sharp green emission peak at around 515 nm observed in only 0.1% Cu-doped film is broadened and becomes asymmetric. With further increase in the Li content, the green emission is gradually diminished due to the formation of a Li-related defect complex that acts as the nonradiative path for the luminescence. The photocurrent spectra also indicate the formation of complex defects in the co-doped films.