High-Mobility 2D Hole Gas at a SrTiO₃ Interface

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Strontium titanate (SrTiO3 or STO) is a crucial substrate in oxide electronics, supporting superconductors, manganites, and multiferroics.
• STO interfaces host diverse phenomena like superconductivity and magnetism, often via a 2D electron gas (2DEG).
• The physics of 2D hole gases (2DHGs) at STO interfaces remain largely unexplored.

Purpose of the Study:

• To demonstrate a novel method for creating a high-mobility 2DHG at STO interfaces.
• To investigate the tunability of carrier type (p-type vs. n-type) at STO interfaces.
• To explore new avenues for oxide electronics utilizing 2DHGs.

Main Methods:

• Depositing sub-nanometer-thick iron (Fe) on STO substrates at room temperature to form amorphous FeOy layers.
• Characterizing the resulting STO/FeOy interface to confirm the presence and properties of a 2DHG.
• Varying Fe layer thickness to control the carrier type (p-type 2DHG or n-type 2DEG).

Main Results:

• Achieved an ultrahigh hole mobility of 24,000 cm2 V-1 s-1, the highest reported for holes in oxides.
• Demonstrated the ability to switch the interface carrier type from p-type (2DHG) to n-type (2DEG) by controlling Fe thickness.
• Established a simple, room-temperature method for fabricating STO-based 2DHGs.

Conclusions:

• A facile method for realizing high-mobility 2DHGs at STO interfaces has been developed.
• This technique opens pathways to investigate unexplored hole-related physics in STO systems.
• The findings pave the way for developing extremely low-cost and high-speed oxide electronic devices.