Oxygen plasma treated epitaxial ZnO thin films for Schottky ultraviolet detection

Abstract

The effects of oxygen plasma treatment on epitaxial ZnO thin films grown by molecular beam epitaxy were studied. The Au–ZnO–In junction exhibiting ohmic behaviour before the treatment gradually changes to a Schottky junction with the increase in oxygen plasma treatment time. The crystallinity and the surface microstructure did not change to any great extent after the treatment. However, the x-ray photoelectron spectroscopy studies show the removal of conductive OH layer from the surface of ZnO films and the current–voltage characteristics of Au–ZnO–In junction exhibit the rectifying behaviour after oxygen plasma treatment. The fabricated Au–ZnO–Au ultraviolet (UV) detector was successfully tested and was observed to be sensitive to the two UV sources used. The photoresponsivities of the UV detector for the irradiation of two different power densities 350 (λ = 356 nm) and 420 µW cm−2 (λ = 254 nm) are 13.5 A W−1, 15.3 A W−1 at 5 V and 128.9 A W−1, 160 A W−1 at 10 V, respectively.