Silicon-based qubits are highly promising for scalable high compatibility with the existing semiconductor industry. However, a major challenge in utilizing 2-dimensional electron gas (2DEG) quantum well (QW) structures for qubits is maintaining high electron mobility ($\mu$) while achieving significant valley splitting ($E_v$). In this study, by employing a thorough chemical cleaning process for the chemical mechanical polish (CMP)-processed buffer layer, we minimized QW interface disorder in a $\mathrm{Si}/{\mathrm{Si}}_{0.77}{\mathrm{Ge}}_{0.23}$ 2DEG heterostructure, achieving record-high electron mobility of $750000{\mathrm{cm}}^2/\mathrm{Vs}$, a transport scattering time (${\tau }_t$) over 80 ps, and a valley splitting energy of $204\mu \mathrm{eV}$ simultaneously from magnetotransport measurements. These results highlight the heterostructure's low disorder and superior material properties, affirming the critical role of interface optimization in achieving high-mobility 2DEG systems. Our findings demonstrate that optimizing the quantum well interface in low-strain Si/SiGe structures can achieve both high mobility and a large in-plane $g$ factor conducive to quantum dot tuning, and a significant valley splitting calculated from the $g$ factor.

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• Functional materials
• Growth
• Interfaces
• Quantum wells
• Semiconductor compounds
• Two-dimensional electron gas
• Hall bar
• Resistivity measurements
• Shubnikov-de Haas effect