Valley splitting and density-driven scattering in undoped Si/SiGe two-dimensional electron system
Lucky Donald Lyngdoh Kynshi1, Umang Soni1, Chithra H Sharma2,3
1Department of Physics, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India.
Summary
This study reveals how scattering mechanisms and valley splitting in undoped silicon/silicon-germanium (Si/SiGe) affect quantum computing. Understanding these factors is key for developing scalable silicon quantum devices.
Area of Science:
- Quantum Computing
- Condensed Matter Physics
- Materials Science
Background:
- Undoped Si/SiGe two-dimensional electron gas (2DEG) is a promising platform for quantum-dot spin qubits due to long spin dephasing times and CMOS compatibility.
- Strained Si quantum wells reduce valley degeneracy, but near-degenerate valley states can compromise gate fidelity.
- Uniform valley splitting is essential for scalable and reliable quantum computing architectures, yet is degraded by imperfections like interface broadening and alloy disorder.
Purpose of the Study:
- Investigate scattering mechanisms and valley splitting in high-mobility undoped Si/SiGe 2DEG.
- Determine the impact of carrier density and magnetic fields on valley splitting.
- Provide insights into scattering-dominated regimes for advancing silicon-based quantum devices.
Main Methods:
- Low-temperature magnetotransport measurements were used to probe the Si/SiGe 2DEG.
- Carrier density and temperature variations were employed to analyze scattering and valley splitting.
- The temperature activation method was utilized to quantify valley splitting.
Main Results:
- Transport is limited by remote charged impurities at low carrier densities and background impurities at higher densities.
- Both transport and quantum lifetimes increase with carrier concentration due to enhanced screening.
- Magnetic-field-induced orbital confinement enhances valley splitting, which was measured at 95±4 μeV at n=2.98×10^11 cm⁻².
Conclusions:
- Scattering mechanisms in undoped Si/SiGe 2DEG are density-dependent.
- Valley splitting is sensitive to carrier density, magnetic fields, and scattering effects.
- These findings are crucial for optimizing Si/SiGe platforms for scalable quantum computing.
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