Valley Splitting in Silicon from the Interference Pattern of Quantum Oscillations

Area of Science:

• Condensed Matter Physics
• Materials Science
• Semiconductor Physics

Background:

• Two-dimensional electron systems (2DES) in silicon metal-oxide-semiconductor (MOS) structures are fundamental to modern electronics.
• Understanding the energy levels and interactions within these systems is critical for device performance.
• Valley degeneracy in silicon's conduction band can impact electron transport properties.

Purpose of the Study:

• To experimentally determine the energy splitting of conduction-band valleys in high-quality 2D electrons confined in silicon MOS Hall-bar transistors.
• To investigate the relationship between valley splitting and electron density at the semiconductor-oxide interface.
• To compare experimental findings with theoretical predictions for valley splitting.

Main Methods:

• Fabrication of high-quality silicon MOS Hall-bar transistors on 300 mm wafers.
• Measurement of Shubnikov-de Haas oscillations in a low-disorder 2DES.
• Analysis of oscillation beating patterns to extract valley splitting energy (ΔE_VS).

Main Results:

• Achieved high electron mobility (17.6×10^3 cm²/Vs) and low percolation density (3.45×10^10 cm⁻²).
• Observed clear beatings in Shubnikov-de Haas oscillations, indicative of valley splitting.
• Estimated a maximum valley splitting of ΔE_VS = 8.2 meV at an electron density of 6.8×10^12 cm⁻².
• Found that valley splitting increases with electron density, consistent with theoretical models for near-ideal interfaces.

Conclusions:

• The energy splitting of conduction-band valleys in silicon 2DES can be accurately measured using Shubnikov-de Haas oscillations in high-quality devices.
• The observed valley splitting behavior supports theoretical predictions, particularly for interfaces with low disorder.
• These findings provide valuable insights into the fundamental physics of electrons in silicon-based nanostructures.