Very high mobility two-dimensional hole gas in Si/GexSi1−x/Ge structures grown by molecular beam epitaxy

Modulation-doped Si/GexSi1−x/Ge/GexSi1−x structures were fabricated in which a thin Ge layer was employed as the conduction channel for the two-dimensional hole gas. The strained heterostructure was fabricated on top of a low threading dislocation density, totally relaxed, GexSi1−x buffer layer with a linearly graded Ge concentration profile. The best mobility of the two-dimensional hole gas is 55 000 cm2/V s at 4.2 K with a concentration-dependent hole effective mass of ≤0.10m0. The effect of the Ge/GeSi interface roughness on the 2DHG mobility was studied.