Lightly-strained germanium quantum wells with hole mobility exceeding one million

Abstract

We demonstrate that a lightly-strained germanium channel (${\epsilon }_{//}$ = -0.41%) in an undoped Ge/Si${}_{0.1}$Ge${}_{0.9}$ heterostructure field effect transistor supports a 2D hole gas with mobility in excess of 1$\times$10${}^6$ cm${}^2$/Vs and percolation density less than 5$\times$10${}^{10}$ cm${}^{-2}$. This low disorder 2D hole system shows tunable fractional quantum Hall effect at low density and low magnetic field. The low-disorder and small effective mass (0.068$m_e$) defines lightly-strained germanium as a basis to tune the strength of the spin-orbit coupling for fast and coherent quantum hardware.