Effect of preparation conditions on the surface morphology and edge absorption of ZnGa2O4:Cr thin films

Thin ZnGa2O4:Cr films were obtained by RF ion-plasma sputtering in argon and argon-oxygen atmospheres mixtures on single-crystal NaCl and amorphous upsilon-SiO2 substrates. The surface morphology of the films was studied by atomic force microscopy. It was found that during the annealing of ZnGa2O4:Cr films on upsilon-SiO2 substrates in oxygen, the grains forming the film grow along the film surface, and during annealing in an argon atmosphere, the growth of grains is observed normal to the film surface. The region of the fundamental absorption edge was studied by optical spectroscopy. The variation of the optical band gap of E-g depending on the deposition and annealing atmosphere was determined. The total effective mass of free charge carriers and the concentration of free charge carriers are estimated. It is shown that the shift of the fundamental absorption edge in ZnGa2O4:Cr thin films after annealing in an argon atmosphere and when oxygen is added to the sputtering atmosphere is due to the Burstein-Moss effect.