On growth of epitaxial vanadium oxide thin film on sapphire (0001)

摘要

We report the characteristics of epitaxial growth and properties of vanadium oxide (VO_2) thin films on sapphire (0001) substrates. Pulsed laser deposition was used to grow (002) oriented VO_2 films on sapphire (0001). Transmission electron microscopy studies showed that the orientation relationship between the substrate and the thin film is: (002)_(f2)||(0006)_(sub3) and [010]_(f2) ||[2110]_(sub). It was also established that VO_2 has three different orientations in the film plane which are rotated by 60° from each other. The epitaxial growth of vanadium oxide on sapphire (0001) has been explained in the framework of domain matching epitaxy (DME). Electrical resistivity measurements as a function of temperature showed a sharp transition with a hysteresis width ～5℃, and large resistance change (～1.5 × 10~4) from the semiconductor phase to the metal phase. It is interesting to note that in spite of large angle twin boundaries in these VO_2 films, the SMT characteristics are better than those observed for polycrystalline films. The higher width of thermal hysteresis for the VO_2 film on c-sapphire compared to a bulk single VO_2 crystal and a single-crystal VO_2 film on r-sapphire can be attributed to the existence of these large-angle twin grain boundaries. These findings can provide insight into the phase transformation characteristics of VO_2, which has important applications in switching and memory devices.