| 초록 |
Recently, Mott insulator such as LaMnO3, VO2, etc. has been widely studied because of their unusual properties. Especially, metal-insulator transition of Mott insulator has grate potential for novel electric device like non volatile memory device. Metal – insulator transition of LaTiO3+δ single crystal is widely investigated by many researchers. On the other hand, reports on metal-insulator transition of LaTiO3+δ thin film are much less than single crystal bulk LaTiO3+δ because stabilizing Ti 3+ state is difficult. Ohtomo et al. reported that LaTiO3+δ thin films grown on SrTiO3 substrate have mixed Ti valence and exhibit metallic behavior because of electronic reconstruction. In this study, we successfully fabricated insulating state LaTiO3+δ thin films on the LaAlO3 substrate. To prevent charge reconstruction and oxygen vacancy at the interface, LaAlO3 substrate is used. Structures of LaTiO3+δ thin films are studied by x-ray diffraction. Pseudo-cubic LaTiO3+δ thin films were epitaxially grown on LaAlO3 substrate at ambient oxygen pressures below 10-4 Torr. The transport property of LaTiO3+δ thin film was measured using the van der Pauw geometry in the temperature range 77 K＜T＜300 K. The resistivity versus temperature curves exhibit insulator behavior below 10-5 Torr of oxygen ambient pressure. With increasing oxygen content (δ), LaTiO3+δ thin film changes from insulator to metal with hole concentration of 2δ. When δ more increases, LaTiO3+δ changes to a band insulator. |
