Effect of thermal annealing on properties of polycrystalline ZnO thin films

Electrical properties (density, carriers mobility, resistivity), optical absorption and photoluminescence spectra of ZnO, grown by MOCVD and hydrothermal methods, have been investigated depending on the annealing and treatment modes in a hydrogen plasma. It has been shown that the electrical and photoluminescent (PL) properties of ZnO are strongly dependent on gas atmosphere during annealing. The annealing in oxygen atmosphere causes a sharp drop of carrier mobility and films conductivity due to the absorption of oxygen on grain boundaries. The process of ZnO electrical properties recovery by the thermal annealing in inert atmosphere (nitrogen), in oil (2×10−2 mbar) and oil-free (1×10−5 mbar) vacuum has been investigated. The hydrogen plasma treatment influence on the intensity of near-band-gap emission (NBE) has been studied. The effect of annealing and subsequent plasma treatment on PL intensity depends on the gas atmosphere of preliminary thermal annealing.