High mobility 2-D hole gases in strained Ge channels on Si substrates studied by magnetotransport and cyclotron resonance

High mobility two-dimensional hole gases have been achieved in p-type modulation doped Ge/SiGe heterostructures grown by MBE on a relaxed graded SiGe buffer. Hall mobilities of up to 15,500 cm²/Vs at carrier densities of 1.04 × 10¹²cm^-2 are observed at 0.4 K in magnetotransport. The cyclotron resonance (CR) shows a narrow (FWHM 15 cm^-1) and strong absorption of up to 15%. Quantum transitions are resolved. A splitting of the CR is observed, attributed to the lifting of the spin degeneracy of the ±3/2 states at B = 0 due to the asymmetric confinement potential. Mean CR masses of 0.14 m₀ up to 0.20 m₀ are found depending on well width and carrier density.