Realization of p-type non-polar a-plane ZnO films via doping of Na acceptor

Abstract

p-Type non-polar ZnO films have been realized via doping of Na acceptor on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The film is (112¯0) oriented (a-plane) as identified by the X-ray diffraction pattern. Structural properties are anisotropic and surfaces of films show stripes running along the ZnO [0001] direction. Secondary ion mass spectroscopy confirmed that Na has been doped into ZnO films. The chemical states of Na were analyzed by x-ray photoelectron spectroscopy. Deep level emission is dominant in room-temperature photoluminescence, which is mainly due to oxygen vacancy. With an effective incorporation of Na, Na-doped non-polar ZnO film exhibits p-type conductivity with a hole concentration of 1.81×1015cm−3, a Hall mobility of 0.402cm2V−1s−1, and a resistivity of 8575Ωcm, respectively. The origin of weak p-type behavior is most likely a certain amount of oxygen vacancies existed in the film, which partly compensates Na acceptor.