In order to make a Schottky contact between metal and semiconductor material. The work function of the metal must be greater than to the work function of semiconductor material, for example, Silver (with a work function of 4.24-4.71) will form an ohmic contact to Zinc oxide material (with a work function of approx. 5) and Gold will form Schottky contact (5.11). However based on some related literature (doi: 1757-899X/149/1/012069). Silver contact form rectifying behavior on Zinc Oxide film deposited on a polymeric substrate. So I'm not sure if Silver can form Schottky contact with zinc oxide film (assume that the substrate is glass)?