Metal-Insulator Transition inSrTiO3−xThin Films Induced by Frozen-Out Carriers

Abstract

We report optical, electrical and magnetotransport properties of oxygen deficient SrTiO(3) (SrTiO(3-x)) thin films fabricated by pulsed laser deposition technique. The oxygen vacancies (O(vac)) in the thin film are expected to be uniform. By comparing its electrical properties to those of bulk SrTiO(3-x), it was found that O(vac) in bulk SrTiO(3-x) is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the SrTiO(3-x) film was found to be induced by the carrier freeze-out effect. The low temperature frozen state can be reexcited by Joule heating, electric and intriguingly magnetic field.

Enhanced carrier density in Nb-doped SrTiO3 thermoelectrics

“…A similar transition recently has been reported at 78 K for O-deficient STO thin films. 29 The carrier concentrations of the 12% and 20% Nb-doped films are estimated to be 3.9 Á 10 20 cm À3 and 8.0 Á 10 20 cm À3 , respectively, at 300 K. Insight into the temperature dependence of the carrier concentration as well as mobility at high temperature would require Hall effect measurements. Generally speaking, the intrinsic charge carrier concentration at 0 K is n ¼ Ð E F E c DOSðEÞdE, where E c is the lower edge of the conduction band.…”

Bandgap Control of the Oxygen‐Vacancy‐Induced Two‐Dimensional Electron Gas in SrTiO3

“…[38,39] Therefore, the oxygen-vacancy-induced 2D conduction is more localized in STO-filmbased 2DEG-V and that is also why the oxygen-vacancy-induced 3D conduction shows the low-temperature semiconducting phase in oxygen-deficient STO films. [17][18][19][20] Now looking back into the growth-temperature-dependent bandgap in Figure 3, we can draw a conclusion that a high growth temperature is useful to suppress point defect such as Sr/Ti defects. For example, the STO single crystal growth temperature is more than 1500 °C, which helps to minimize point defects.…”

“…Instead, oxygen-deficient STO films are typically semiconducting at low temperatures. [17][18][19][20] Besides, the 2DEG at the LAO/STO interface fabricated on STO films [21][22][23][24] is more localized at low temperatures than that fabricated on STO single crystals; [7] it was found that the insertion of a STO film layer degrades the LAO/STO interface significantly; [25,26] the fully metallic state of the LAO/STO interface based on STO films is achieved when STO films are deposited at a very high temperature of 1100 °C. [27] These perhaps indicate the presence of point defects/disorder in the STO films deposited at the typical temperature range of 600-800 °C.…”

Influence of Reoxidation on Silica-Containing Barium Titanate Ceramics for PTCR Thermistors Prepared by Tape Casting

“…The composition of the ceramics was Ba 1.004 Y 0.004 TiO 3 . Silica was added to promote liquid phase sintering and its effect could be found in the previous discussion [8], which illustrated the optimized silica doping amount in the present composition.…”

“…Langhammer et al divided the oxygen adsorption at different temperatures into three stages: (a) annihilation of surface oxygen vacancies (250 -800°C), (b) oxidation of grain boundaries (800 -1250°C and (c) oxidation of inner grain bulk (above 1250°C) [2]. The presence of defects in oxides is very important for electronic device applications, because they deter-mine the electrical properties [3]. For example, antisite defects were found responsible for the large bandgap enhancement in SrTiO 3 thin films [4].…”