Study of annealing influence on electrical and morphological properties of ZnO:Ga thin films

Abstract

In this study, the influence of thermal annealing in different ambients on the electrical and morphological properties of Ga-doped ZnO films with 1wt.% gallium acetylacetonate in the precursor mix is investigated systematically. As-grown samples were prepared on c-plane Al2O3 by PEMOCVD with a substrate temperature of 300 °C and possess a resistivity of about 10–2 Ω cm. The annealing was realized in isochronal steps between 300 to 1000 °C for 1 hour in argon and air ambient, respectively. The resistivity of the films was found to be dependent on the annealing atmosphere. During annealing in air, the resisitivity increases monotically with an abrupt reduction at 800 °C, whereas the annealing in argon does not induce significant changes but results in two clear minima at 300 °C and 800 °C. These effects are explained with crystal improvement at low temperature (300 °C) and successive dopant activation at higher temperature (800 °C). Furthermore, an anomalous surface flattening at 800°C was observed. The obtained results suggest that the annealing procedure does allow to decrease the resistivity and roughness of as-grown ZnO:Ga films, what would be beneficial for the application of PEMOCVD-grown ZnO thin films for the formation of abrupt junctions in p–n device structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)