Electrical and structural characterization of nitrogen doped ZnO layers grown at low temperature by atomic layer deposition

Stable silver Schottky contacts are formed on nitrogen-doped thin ZnO films grown by the atomic layer deposition technique. The IV characteristics show the rectification ratio of about 4 and the leakage current of about 10⁻³ A cm⁻² in as-grown samples. The electrical properties of the Schottky diodes can be significantly improved by annealing the samples in oxygen or nitrogen atmosphere at 400 °C. We correlate this observation with the reduction of free carrier concentration in thin ZnO films after the heat treatment. We rule out that hydrogen at the bond-centred lattice site or hydrogen bond in an oxygen vacancy are dominant donors in our samples. Our findings confirm the model where the vacancy of oxygen acts as a dominant donor in nitrogen-doped as-grown samples. From DLTS measurements three deep levels (E130, E220 and E305) are present in the samples annealed in oxygen atmosphere. We assign E130 to an extended defect, whereas E220 and E305 are tentatively attributed to an impurity unintentionally introduced during the growth process. (paper)