Preferred orientation and anisotropic growth in polycrystalline ZnO:Al films prepared by magnetron sputtering

A thorough growth study of thin polycrystalline ZnO:Al samples prepared by DC magnetron sputtering is presented. The atomic areal density as a function of deposition time t was determined by Rutherford backscattering (RBS), from which a growth rate G(t) can be defined. It was found, that in the initial stages of film growth G(t) increases with increasing deposition time up to a thickness of about 300 nm, although the process conditions were kept constant. In addition, the preferred orientation of each sample, as characterized by a < 00.l > fiber texture, was quantified by evaluating the texture index J for each sample. The course of J(t) was identified to concomitantly increase with G(t). The variation of both, growth rate and preferred orientation, with deposition time is interpreted to be caused by an anisotropic growth velocity of ZnO grains. It seems that such a close correlation between growth rate and texture has not been observed so far.