Holes Outperform Electrons in Group IV Semiconductor Materials

A record-high mobility of holes, reaching 4.3 × 10⁶ cm² V^-1 s^-1 at 300 mK in an epitaxial strained germanium (s-Ge) semiconductor, grown on a standard silicon wafer, is reported. This major breakthrough is achieved due to the development of state-of-the-art epitaxial growth technology culminating in superior monocrystalline quality of the s-Ge material platform with a very low density of background impurities and other imperfections. As a consequence, the hole mobility in s-Ge appears to be ≈2 times higher than the highest electron mobility in strained silicon. In addition to the record mobility, this material platform reveals a unique combination of properties, which are a very large and tuneable effective g*-factor (>18), a very low percolation density (5 × 10⁹ cm^-2) and a small effective mass (0.054 m ₀). This long-sought combination of parameters in one material system is important for the research and development of low-temperature electronics with reduced Joule heating and for quantum-electronics circuits based on spin qubits.