Reducing disorder in Ge quantum wells by using thick SiGe barriers.

We investigate the disorder properties of two-dimensional hole gases in Ge/SiGe heterostructures grown on Ge wafers, using thick SiGe barriers to mitigate the influence of the semiconductor–dielectric interface. Across several heterostructure field effect transistors, we measure an average maximum mobility of (4.4 ± 0.2) × 10 6 cm 2 / Vs at a saturation density of (1.72 ± 0.03) × 10 11 cm − 2 , corresponding to a long mean free path of (30 ± 1) μ m. The highest measured mobility is 4.68 × 10 6 cm 2 / Vs. We identify uniform background impurities and interface roughness as the dominant scattering mechanisms limiting mobility in a representative device, and we evaluate a percolation-induced critical density of (4.5 ± 0.1) × 10 9 cm − 2 . This low-disorder heterostructure, according to simulations, may support the electrostatic confinement of holes in gate-defined quantum dots. [ABSTRACT FROM AUTHOR]