Magnetotransport studies of SiGe-based p-type heterostructures: Problems with the determination of effective mass

The use of Shubnikov-de Haas oscillations for determining effective mass is illustrated by a study of the magnetotransport properties of the two-dimensional hole gas in Si1-xGex (x = 0.13, 0.36, 0.95, 0.98) quantum wells. For some samples the data cannot be fitted to standard theoretical curves in which the scattering of charge carriers is described by the conventional Dingle factor. The reasons for the discrepancies between the experiment the theory are: (i) the effect of spin splitting on the amplitude of the peak in the SdH oscillations; (ii) extra broadening of the Landau levels attributable to an inhomogeneous distribution of the carrier concentration; (iii) the coexistence of short and long-range scattering potentials; and, (iv) population of the second energy level in the quantum well. Ways of calculating the effective hole masses m* for all these cases are presented and values of m* are found for the heterostructures studied here. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770520]