Texture of tetragonal α-FeSi₂ films on Si(001)

Synchrotron radiation was used to measure pole figures of α-FeSi₂ films on Si(001) substrates. The pole figures consist of complex, though symmetrical patterns of narrow lines. These lines are indicative of axiotaxy, a peculiar type of preferential orientation which has been recently reported to occur in NiSi films on Si(001). The patterns of lines are created by grains for which the α-FeSi₂(110) or (102)-type planes are parallel to Si(110)-type planes in the substrate. As a direct consequence of the constraint that a set of planes in the film is aligned to a set of planes in the substrate, the texture manifests itself as though it were a fiber texture, with the fiber axis normal to the Si(110)-type planes (i.e., at 45° and 90° from the surface normal). The spacing of 1.905Å between α-FeSi₂(110) planes is almost identical to the spacing of 1.920Å between Si(220) planes. Hence, if α-FeSi₂(110)-type planes are parallel to Si(110)-type planes, the resulting interface with the Si(001) substrate is periodic along the Si(100)-type directions in the plane of the interface. The brightest spots along the lines are caused by grains which are epitaxially aligned with the Si substrate. In addition to the axiotaxy, four different types of epitaxial texture components could be identified within the same film.