Probing the p-Ge1-xSix/Ge/p-Ge1-xSix quantum wellby means of the quantum Hall effect

Abstract

We have measured the temperature (0.1⩽T⩽15 K)and magnetic field (0⩽B⩽32 T) dependences oflongitudinal and Hall resistivities for the p-Ge0.93Si0.07/Ge multilayers with different Ge layer widths 10⩽dw⩽38 nm and hole densities ps = (1-5)×1015 m-2. An extremely high sensitivity ofthe experimental data (the structure of magnetoresistance traces,relative values of the inter-Landau-level (LL) gaps deduced from theactivation magnetotransport etc) to the quantum well (QW)characteristics has been revealed in the cases when the Fermilevel reached the second confinement subband. The backgrounddensity of states (5-10)×1014 m-2 meV-1 deduced from the activation behaviour of themagnetoresistance was too high to be attributed to the LLtails, but may be accounted for within a smooth randompotential model. The hole gas in the Ge QW was foundto separate into two sublayers for dw>~35 nm and ps≈5×1015 m-2. Concomitantly thepositive magnetoresistance emerged in the weakest fields, fromwhich different mobilities in the sublayers were deduced. Amodel is suggested to explain the existence of the plateauxclose to the fundamental values in a system of two parallellayers with different mobilities.