Work function control of functionally graded ZnO+Ga2O3 thin film for OLED applications

ZnO+Ga2O3 functionally graded thin films (FGTFs) were examined for their potential use as organic light emitting diodes (OLEDs). FGTF transparent conducting oxides (TCO) were fabricated by combinatorial RF magnetron sputtering. The composition gradient was controlled up to 10% by changing the plasma power of the two sputter guns. A Ga2O3+ZnO graded region was placed on the top layer of ZnO. The FGTFs showed up to 80% transmittance. Their surface resistances were reduced to <10% by increasing the Ga2O3: pure ZnO ratio in the TCO. The FGTFs’ work functions could be controlled within a range of 0.18 eV. The controlled work function is a very promising technology because it reduces the contact resistance between the anode and Hall transport layers of OLED devices.