Holes in silicon are heavier than expected: Transport properties of extremely high mobility electrons and holes in silicon MOSFETs

Abstract

The quality of the silicon-oxide interface plays a crucial role in fabricating reproducible silicon spin qubits. In this work we characterize interface quality by performing mobility measurements on silicon Hall bars. We find a peak electron mobility of nearly 40000cm2/Vs in a device with a 21nm oxide layer, and a peak hole mobility of about 2000cm2/Vs in a device with 8nm oxide, the latter being the highest recorded mobility for a p-type silicon MOSFET. Despite the high device quality, we note an order-of-magnitude difference in mobility between electrons and holes. By studying additional n-type and p-type devices with identical oxides, and fitting to transport theory, we show that this mobility discrepancy is due to valence band nonparabolicity. The nonparabolicity endows holes with a density-dependent transverse effective mass ranging from 0.6⁢𝑚0 to 0.7⁢𝑚0, significantly larger than the usually quoted band-edge mass of 0.22⁢𝑚0. Finally, we perform magnetotransport measurements to extract electron momentum and quantum scattering lifetimes.