Features of the Shubnikov-de Haas oscillations of the conductivity of a high-mobility two-dimensional hole gas in a SiGe/Ge/SiGe quantum well

The Shubnikov-de Haas oscillations in a two-dimensional hole gas in a quantum well of pure germanium in a SiGe/Ge/SiGe heterostructure with a hole concentration p(H)=5.68x10(11) cm(2) and mobility mu=4.68x10(4) cm(2)V(-1)s(-1) are investigated in magnetic fields up to 15 T at temperatures from 40 mK to 4 K. The observed deviation from the known relation describing the conductivity oscillations in the Shubnikov-de Haas effect are explained by additional broadening of the Landau levels due to the existence of a nonuniform distribution of the concentration of charge carriers, and, accordingly, of their energy, in the plane of the two-dimensional gas. It is assumed that the latter is due to natural atomic-step variations of the well width. The effective hole mass (m(*)=0.112m(0)) is determined from the temperature dependence of the oscillation amplitude, and its dependence on magnetic field is used to determine the quantum scattering time and the value of the carrier concentration fluctuations. (c) 2006 American Institute of Physics.