Probing the p-Ge_1-xSi_x/Ge/p-Ge_1-xSi_xquantum well by means of the quantum Hall effect

Abstract

Abstract. We have measured the temperature (0.1 ≤ T ≤ 15 K) and magnetic field (0 ≤ B ≤ 32 T) dependences of longitudinal 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)·10 15 m -2 . An extremely high sensitivity of the experimental data (the structure of magnetoresistance traces, relative values of the inter-Landau-level (LL) gaps deduced from the activated magnetotransport etc) to the quantum well (QW) characteristics has been revealed in the cases when the Fermi level reached the second confinement subband. The background density of states (5÷10)·10 14 m -2 meV -1 deduced from the activation behavior of the magnetoresistance was too high to be attributed to the LL tails, but may be accounted for within a smooth random potential model. The hole gas in the Ge quantum well was found to separate into two sublayers for dw > ~35 nm and ps ≈ 5·10 15 m -2 . Concomitantly the positive magnetoresistance emerged in the weakest fields, from which different mobilities in the sublayers were deduced. A model is suggested to explain the existence of the plateaux close to the fundamental values in a system of two parallel layers with different mobilities.

Activation transport under quantum Hall regime in HgTe-based heterostructure

“…The main result that D(E) is practically constant and comparable with D 0 within the energy interval between adjacent LL's is consistent with the data for structures with n-type conductivity: Si-MOSFET [3], high-mobility [4] and intermediate-mobility [29] AlGaAs/GaAs, InGaAs/InP [5] as well as for multilayer p-Ge/Ge 1-x Si x heterostructures [6].…”

“…The DOS in mobility gaps may be evaluated from the data on activation energy E A as a function of the LL filling factor ν [3][4][5][6]. As / B n n ν = (n is the electron density, B n = / eB hc = is the degree of LL degeneracy), the filling factor can be tuned by the change of either a carrier density [3] or a magnetic field [4][5][6].…”

“…As / B n n ν = (n is the electron density, B n = / eB hc = is the degree of LL degeneracy), the filling factor can be tuned by the change of either a carrier density [3] or a magnetic field [4][5][6].…”

“…From the E A (B) dependences the background density of states in the mobility gap may be constructed [4,6,29]: Figure 5 shows the results for the DOS at mobility gaps ∆ 1 , ∆ 2 , and ∆ 3 (see also Table 1). The following features of the mobility gap DOS as a function of energy, D(E), should be mentioned.…”

“…Distances between adjacent LLs can be extracted and a density of localized states in the mobility gaps may be determined from scanning them by the Fermi level in experiments of this kind [3][4][5][6][7]. Experimental reconstruction of the energy spectrum is especially important for systems with a complex band structure where the LL picture is determined not only by the cyclotron energy with a given effective mass as for a simple parabolic conduction band system.…”