Lightly strained germanium quantum wells with hole mobility exceeding one million

We demonstrate that a lightly strained germanium channel (ε//=−0.41%) in an undoped Ge/Si0.1Ge0.9 heterostructure field effect transistor supports a two-dimensional (2D) hole gas with mobility in excess of 1×106 cm2/Vs and percolation density less than 5×1010 cm−2. This low disorder 2D hole system shows tunable fractional quantum Hall effects at low densities and low magnetic fields. The low-disorder and small effective mass (0.068me) defines lightly strained germanium as a basis to tune the strength of the spin–orbit coupling for fast and coherent quantum hardware.