Remarkably High-Performance Nanosheet GeSn Thin-Film Transistor.

Area of Science:

• Semiconductor Physics
• Materials Science
• Device Engineering

Background:

• High-performance p-type thin-film transistors (pTFTs) are essential for low-power displays and 3D integrated circuits.
• Achieving high hole mobility (>10 cm²/V·s) in pTFTs, even with materials like SnO, remains a challenge.
• Existing SnO TFTs, despite a unique band structure and small effective mass, struggle to meet performance demands.

Purpose of the Study:

• To demonstrate a high-performance Germanium-Tin (GeSn) pTFT.
• To investigate the relationship between channel thickness, mobility, and on/off current ratios in GeSn pTFTs.
• To explore the potential of GeSn as a material for advanced transistor applications.

Main Methods:

• Fabrication of ultra-thin (7 nm) nanosheet GeSn pTFTs.
• Characterization of field-effect hole mobility (μFE), subthreshold slope (SS), and on-current/off-current (ION/IOFF) ratios.
• First-principles electronic structure calculations to determine the hole effective mass of GeSn.

Main Results:

• Achieved a field-effect hole mobility (μFE) of 41.8 cm²/V·s in a 7 nm GeSn nanosheet pTFT.
• Obtained a sharp subthreshold slope (SS) of 311 mV/dec, enabling low-voltage operation.
• Demonstrated a high on-current/off-current (ION/IOFF) ratio of 8.9 × 10⁶.
• Higher mobility (103.8 cm²/V·s) was observed with thicker GeSn channels, but resulted in poor ION/IOFF ratios (>75).

Conclusions:

• Ultra-thin GeSn nanosheets are effective for high-performance pTFTs with excellent mobility and current ratios.
• The small hole effective mass of GeSn, confirmed by calculations, contributes to high mobility.
• GeSn pTFTs show significant promise for future low-power electronics and integrated circuit applications.