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Lippmaa Group

Professor LIPPMAA, Mikk
Research Associate MORI, Taizo

Research Subjects

  • Growth of thin oxide films and heterostructures by pulsed laser deposition
  • Development of oxide photoelectrode materials for photocatalytic water splitting
  • Synthesis of nanostructures and nanocomposite thin films
  • In situ tracking of molecular motions and orientations at the air-water interface

Two-dimensional electron gas (2DEG) layers can form at various oxide interfaces. Some of the best known oxide 2DEGs occur in heterostructures that combine SrTiO3 with LaAlO3 or LaTiO3. In our recent work, we have studied the effects of crystal defects on the accumulation of carriers in quantum wells that form at such interfaces.

In particular, we find that the low-temperature resistivity of the 2DEG layer often shows an upturn below about 10 K (left) and this upturn is dependent on the particular thin film growth conditions and thin film thicknesses.

This type of behavior is related to the presence of multiple parallel layers of carriers in the heterostructure.

As shown on the right, the resistivity of the heterostructures can be changed by applying an electric field with a gate electrode. However, the resistivity behavior is not monotonic and shows a memory effect, which indicates that some of the carriers are trapped and permanently removed from the heterostructure. In our work we attempt to determine where the trapping occurs and find methods of eliminating the effect of carrier traps on the low-temperature transport characteristics of the oxide 2DEG heterostructures.

Variation of the low-temperature resistivity of SrTiO3/LaTiO3/SrTiO3 heterostructures with different cap layer thicknesses.
Memory effect caused by carrier trapping in SrTiO3 in two SrTiO3/LaTiO3/SrTiO3 heterostructures with different total carrier densities.

Publications and Research Highlights