Semiconductor–metal phase transition and “tristable” electrical switching in nanocrystalline vanadium oxide films on silicon

Temperature dependences of the ac conductivity of nanocrystalline mixed vanadium oxide films on silicon revealed a multistep shape of the hysteresis loop observed during the semiconductor–metal phase transition in VO$_2$, which was not manifested in the case of dc measurements. These peculiarities are related to the size effect, heterophase character of vanadium oxide films, and different types of charge carriers in the bulk of nanocrystallites and on their surfaces. The appearance of steps is explained by the phase transition taking place in separate groups of crystallites with close dimensions. The phenomenon of “tristable” electrical switching in these vanadium oxide films was observed for the first time.