Surface Morphology and Structure in ZnO films doped with Ga and In impurities

The ZnO:Ga:In nanocrystal (NC) films co-doped with Ga and In donor type impurities have been investigated The films were produced by spray pyrolysis ultrasonic on Si substrates kept at 400°C. The group of samples was grown with permanent In content of 1at% in the films, and with various Ga contents of 0.5 at% up to 2.5 at% Ga. All samples for better crystallization have been further annealed in a nitrogen flow (5 L/min) at 400°C during 4h. The non-monotonous varying the surface morphology has been detected in ZnO:Ga:In NC films. With a small Ga content (≤1.0 at%) and a high Ga content (≥2.0 at%), the grains have the form of small sheets distributed randomly on the surface. The sheet like shape changes to nanorod with hexagonal cross sections of the size 50-100 nm in films with 1.5 at% Ga. With all Ga concentrations the ZnO films studied demonstrated the crystal structures of wurtzite. However, the XRD peak positions and ZnO lattice parameters change non monotonically versus Ga contents. The factors that favor the non-monotonic change of the parameters of the ZnO crystal lattice have been analysed. The Ga/In doping concentrations necessary to obtain ZnO films with low roughness and flat surface morphology have been estimated.