Electrical properties and oxygen sensing ability of Zn1-xCoxO epitaxial films

Abstract

While Co-doped ZnO has been much studied from the viewpoint of dilute magnetic semiconductors, we offer a new perspective by shedding light on the oxygen sensing ability of Co-doped ZnO. Epitaxial Zn1 xCoxO (x ¼ 0.0,0.05,0.1,0.15) thin films are grown on a-Al2O3 (0001) by pulsed laser deposition. We successfully optimize growth conditions of Zn1 xCoxO films to prevent Co clustering and also to obtain high crystallinity. As Co content (x) increases, the c-axis lattice constant of Zn1 xCoxO films linearly increases. We particularly pay attention to the effect of oxygen annealing and dynamic response under reduction gas (2% hydrogen in Ar) and oxygen gas environment in electrical properties of Zn1 xCoxO. It is shown that the resistance of Zn0.85Co0.15O changes more than two orders of magnitude reversibly as it is reduced and oxidized alternatively. Thus, the present work demonstrates a potential of Zn1 xCoxO as an oxygen sensor at high temperatures. Oxygen (oxygen vacancy and/or oxygen interstitial) and Co in the system appear to play a role cooperatively in determining the electrical properties of Zn1 xCoxO.