Effect of substrate temperature on the structural, electrical and optical behaviour of reactively sputtered Ag–Cu–O films

Abstract

Thin films of Ag–Cu–O were deposited on glass substrates by radio frequency magnetron sputtering of an Ag70Cu30 target at an oxygen partial pressure of 2×10−2 Pa, a sputter pressure of 4 Pa and at different substrate temperatures in the range 303–548 K. The deposited films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy, ultraviolet–visible–infrared spectroscopy and four-probe techniques. The effect of substrate temperature on the core-level binding energies, crystallographic structure, surface morphology and electrical and optical properties of the deposited films was systematically studied. The films formed at room temperature (303 K) showed a core-level binding energy of Ag 3d5/2 of 367.9 eV due to the growth of single-phase Ag2Cu2O3 films, whereas those deposited at 523 K exhibited a lower energy value of 367.2 eV due to the presence of silver, silver oxides and copper oxide. The films formed at room temperature were nanocrystalline Ag2Cu2O3. The substrate temperature induced growth of a mixed phase of Ag2Cu2O3 and Ag2Cu2O4 in the temperature range 348–473 K. At higher temperatures the films were decomposed into silver and silver oxide. The electrical resistivity of the films decreased from 8.2 to 0.6 Ω cm with an increase in substrate temperature from 303 to 548 K due to an improvement in crystallinity and structural changes in the films. The optical band gap of the Ag–Cu–O films increased from 1.95 to 2.15 eV with an increase in substrate temperature from 303 to 523 K, whereas at a higher temperature of 548 K it decreased to 2.11 eV.