Capping-layer-mediated lattice mismatch and redox reaction in SrTiO₃-based bilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Traditional two-dimensional electron systems (2DES) on SrTiO3 substrates are sensitive to capping layer modifications.
• SrTiO3-layer-carried 2DES (bilayer 2DES) offers unique transport properties relevant for thin-film devices but is less explored regarding capping layer engineering.

Purpose of the Study:

• To investigate the effect of various crystalline and amorphous oxide capping layers on the electronic properties of SrTiO3 bilayer 2DES.
• To understand the distinct roles of crystalline versus amorphous capping layers in forming and tuning bilayer 2DES.

Main Methods:

• Fabrication of SrTiO3 bilayers with diverse crystalline and amorphous oxide capping layers on epitaxial SrTiO3 films.
• Characterization of interfacial conductance, carrier mobility, and carrier density in the fabricated bilayer 2DES.
• Analysis of the influence of lattice mismatch and capping layer composition (e.g., Al concentration) on electronic transport.

Main Results:

• For crystalline capping layers, increasing lattice mismatch with SrTiO3 monotonically reduced interfacial conductance and carrier mobility, highlighting the role of interfacial disorders.
• Amorphous capping layers with higher Al concentration showed increased conductivity and carrier mobility, suggesting interfacial charge screening and band bending effects beyond simple redox reactions.
• Crystalline capping layers with large lattice mismatch were more insulating than their amorphous counterparts, and vice versa, indicating different dominant formation mechanisms.

Conclusions:

• The nature (crystalline vs. amorphous) and properties (lattice mismatch, composition) of oxide capping layers significantly influence the formation and electronic transport of SrTiO3 bilayer 2DES.
• Interfacial disorders and charge screening/band bending effects are crucial for understanding transport in crystalline and amorphous bilayer 2DES, respectively.
• These findings provide insights for designing functional oxide interfaces and heterostructures for advanced electronic devices.