Control of a- and c-plane preferential orientations of ZnO thin films

We report orientation-controllable growth of ZnO thin films and their orientation-dependent electrical characteristics. ZnO thin films were deposited on single-crystalline (1 0 0) LaAlO3 and (1 0 0) SrTiO3 substrates using pulsed laser deposition (PLD) at different substrate temperatures (400–800 °C). It was found that the orientation of ZnO films could be controlled by using different substrates of single-crystalline (1 0 0) LaAlO3 and (1 0 0) SrTiO3. The a-plane (image) and c-plane (0 0 0 2) oriented ZnO films are formed on LaAlO3 and SrTiO3, respectively. In both cases, the degree orientation increased with increasing deposition temperature Ts. Both the surface free energy and the degree of lattice mismatch are ascribed to play an important role for the orientation-controllable growth. Further characterization show that the grain size of the films with both orientations increases for a substrate temperature increase (i.e. from Ts = 400 °C to Ts = 800 °C), whereas the electrical properties of ZnO thin films depend upon their crystalline orientation, showing lower electrical resistivity values for a-plane oriented ZnO films.