Epitaxial relationships and electrical properties of vanadium oxide films on r-cut sapphire

By activated reactive evaporation (ARE) at 500 degrees C vanadium dioxide ( VO2) films could be grown epitaxially on r-cut sapphire. It is shown that t here are two significantly different growth orientations of the VO2 relativ e to the substrate. These orientations exhibit, however, a similar matching , which, in both cases, results in an additional small angle splitting. The corresponding domains can be: described by the following epitaxial relatio n: (a) (100)VO2//(01 (1) over bar 2)Al2O3 with [010]VO2//[0 (1) over bar (1 ) over bar 2]Al2O3 +/- 1.85 degrees (b) (111)VO2//(01 (1) over bar 2)AlO3, with [10 (1) over bar]VO2// [2 (1) over bar (1) over bar 0]Al2O3 + 1.4 degr ees, and [(1) over bar 01]VO2//[(2) over bar 110]Al2O3 + 1.4 degrees. These multidomain films show a well defined metal-to-insulator transition at 64 degrees C with an accompanying resistivity change by four orders ol magnitu de. The related IR-reflectivity can be switched in this way by 67%, (C) 199 9 Elsevier Science S.A, All rights reserved.