High-quality Ge/SiGe heterostructure with atomically sharp interface grown by molecular beam epitaxy

Germanium is a versatile material for realization of spin and topological quantum computing. Here, we report on the epitaxial growth of an undoped Ge/SiGe heterostructure in which a hole quantum well is formed in the sandwiched Ge layer. The heterostructure is grown on Si (001) via molecular beam epitaxy (MBE). Atomic force microscopy characterizations display a flat surface with a root mean square roughness of 0.956 nm, and spherical aberration corrected transmission electron microscopy data show a sharp interface with a characteristic length of 0.49 nm. A mobility of up to 1.2 x 10(5) cm(2) V-1 s(-1) was achieved in the SiGe/Ge/SiGe two-dimensional hole gas (2DHG). The low percolation density of 3.70 x 10(10) cm(-2), light effective mass of 0.079 m(0) (where m(0) is the free electron mass), and large effective g-factor of 9.5 were obtained. These results show the potential of MBE-grown Ge 2DHG for semiconductor quantum computing.