Effect of over-oxidized surface layer on metal insulator transition characteristics of VO2 films grown by thermal oxidation method

We have investigated the effect of over oxidized surface layer on the characteristics of metal-insulator transition (MIT) of vanadium dioxide (VO2) films grown by thermal oxidation method. During the oxidation, the over-oxidized V6O13 layer was formed, which increased contact resistance and thus reduced the resistivity ratio before and after MIT. The contact resistivity of the VO2 film with over-oxidized surface layer was in the range 4.2 × 10−2 ∼ 9.4 × 10−4 Ωcm2. Interestingly, the over-oxidized surface layer was removed by simply cooling the film under reduced oxygen pressure. Upon the removal of the over-oxidized layer, the resistivity ratio across MIT increased up to 1.2 × 104. The ratio of contact resistance to sample resistance was small (large) at low (high) temperature.