S. V. Gudina

Application of the high-pressure thermoelectric technique for characterization of semiconductor microsamples: PbX-based compounds

In this paper the technique of thermoelectric measurements at high pressure was applied for characterization of semiconductor microsamples based on lead chalcogenide compounds (p-PbSe, n-Pb1−xSnxSe). The Raman scattering technique at ambient pressure was used as an alternative tool for testing of the samples. Raman measurements have revealed broad peaks at 135 and 265 cm−1 for PbSe and Pb1−xSnxSe. Analogous spectra were obtained for PbS, and PbTe-based ternary compounds at higher and lower frequencies, respectively. The peaks have been attributed to the first- and second-order Raman modes. From resistivity and thermoelectric power data the linear decrease in the pressure of the NaCl → GeS structural phase transition with increasing Sn content has been established and the thermopower of high-pressure GeS phases have been determined. Thermoelectric properties of the samples at high pressure have shown high sensitivity to a small variation in the composition of the ternary Pb1−xSnxSe compounds, which makes it possible to distinguish semiconductor microsamples whose compositions are very similar.

The effect of infrared radiation on quantum magnetotransport in n-InGaAs/GaAs with two strongly coupled quantum wells

Longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are measured as a function of transverse magnetic field in n-InGaAs/GaAs nanostructures with strongly coupled double quantum wells in the temperature range T = 0.05–60 K and magnetic fields B = 0–16 T before and after low-temperature infrared irradiation. The appearance of persistent photoconductivity causes the type of the temperature dependence of resistance to be changed: from insulator-like (dρ/dT 0) at higher temperatures. It is shown that this is related to the temperature dependence of electron density. The strong temperature dependence of electron mobility observed before the illumination practically disappears after infrared irradiation.

Features of quantum effects in two-dimensional GaAs∕n‐InGaAs∕GaAs structures with double quantum wells

In an n‐InxGa1−xAs∕GaAs double quantum well (x≈0.2) the temperature dependence of the longitudinal resistance ρxx(T) of a 2D electron gas with low mobility and with an electron density close to the B=0 metal–insulator transition is of an “insulator” character in the temperature interval T=1.8–70K(kBTτ∕ℏ=0.1–3.8). Anomalous temperature dependence of σxy(B,T) in the region ωcτ=1 leads to a number of features of the transition from the regime of weak localization and electron–electron interaction to the quantum Hall effect regime at low magnetic fields.

Scaling in the quantum Hall effect regime in n-InGaAs/GaAs nanostructures

The longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are investigated experimentally in the integer quantum Hall effect (QHE) regime in n-InGaAs/GaAs double quantum well nanostructures in the range of magnetic fields B = (0–16) T and temperatures T = (0.05–70) K before and after IR illumination. The results are evaluated within the scaling hypothesis with regard to electron-electron interaction.

Contributions of the electron–electron interaction and weak localization to the conductance of p‐Ge∕Ge1−xSix heterostructures

We separate the contributions to the conductance from disorder-modified electron–electron interaction and weak localization for p‐Ge∕Ge1−xSix heterostructures with low carrier mobility at magnetic fields 0⩽B⩽2T for fixed temperatures 0.2K⩽T⩽4.2K. The contribution of the Zeeman splitting to the magnetoresistance is taken into account in the electron–electron interaction, making it possible to get reasonable values of the energy relaxation time (dephasing time τφ) and to obtain its theoretically predicted power-law temperature dependence. Values are estimated for the parameters of these effects: Hartree interaction constant F0σ=−0.51, amplitude of the Fermi-liquid interaction λ=0.40, and Lande factor g=12.0.

Quantum Hall plateau-plateau transitions in n-InGaAs/GaAs heterostructures before and after IR illumination

The longitudinal ρxx(B,T) and Hall ρxy(B,T) magnetoresistances in n-InGaAs/GaAs heterostructures with a single quantum well are studied experimentally before and after IR illumination in the quantum Hall regime in magnetic fields B = 0–12 T and at temperatures T = 0.4–4.2 K. The temperature dependence of the width of quantum Hall plateau-plateau transitions is analyzed in terms of a two-parameter scaling theory.

Temperature dependence of the bandwidth of delocalized states for n-InGaAs/GaAs in the quantum Hall effect regime

Temperature and magnetic-field dependences of longitudinal ρxx(B,T) and Hall ρxy(B,T) resistivities of n-InxGa1−xAs/GaAs nanostructures with single and double quantum wells are investigated in the quantum Hall regime at B = 0–16 Т and T = 0.05–70 K, before and after IR illumination. The temperature dependence of the QHE plateau-plateau transition width is analyzed and information about temperature dependences of the bandwidth of delocalized states in the center of Landau subbands is obtained.

Temperature dependence of quantum lifetime in n-InGaAs/GaAs structures with strongly coupled double quantum wells

Longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are experimentally investigated as a function of in-plane and transverse magnetic fields in n-InGaAs/GaAs nanostructures with strongly-coupled double quantum wells in the temperature range T = 1.8–70 K and magnetic fields B = 0–9.0 T. Experimental data on the temperature dependence of quantum lifetime in diffusive (kBT/τtr ≪ 1) and ballistic (kBT/τtr ≫ 1) regimes are reported. It has been found that in the ballistic regime in the temperature range where kBT/EF < 0.1, the observed quadratic temperature dependence of quantum lifetime is determined by inelastic electron–electron scattering. However, the temperature dependence of quantum lifetime cannot be quantitatively described by the existing theories in the whole temperature range.

Quantum Hall effect and hopping conductivity in n-InGaAs/InAlAs nanoheterostructures

The longitudinal and Hall magnetoresistances are measured in the quantum Hall effect regime in the n-InGaAs/InAlAs heterostructures at temperatures of T = (1.8–30) K in magnetic fields up to B = 9 T. Temperature-induced transport in the region of the longitudinal resistance minima, corresponding to the plateau regions at Hall resistance, is investigated within the framework of the concept of hopping conductivity in a strongly localized electron system. The analysis of variable-range hopping conductivity in the region of the second, third, and fourth plateau of the quantum Hall effect provides the possibility of determining the localization length exponent.The longitudinal and Hall magnetoresistances are measured in the quantum Hall effect regime in the n-InGaAs/InAlAs heterostructures at temperatures of T = (1.8–30) K in magnetic fields up to B = 9 T. Temperature-induced transport in the region of the longitudinal resistance minima, corresponding to the plateau regions at Hall resistance, is investigated within the framework of the concept of hopping conductivity in a strongly localized electron system. The analysis of variable-range hopping conductivity in the region of the second, third, and fourth plateau of the quantum Hall effect provides the possibility of determining the localization length exponent.

Temperature scaling in the quantum-Hall-effect regime in a HgTe quantum well with an inverted energy spectrum

The longitudinal and Hall magnetoresistances of HgTe/HgCdTe heterostructures with an inverted energy spectrum (the HgTe quantum well width is d = 20.3 nm) are measured in the quantum-Hall-effect regime at T = 2–50 K in magnetic fields up to B = 9 T. Analysis of the temperature dependences of conductivity in the transition region between the first and second plateaus of the quantum Hall effect shows the feasibility of the scaling regime for a plateau–plateau quantum phase transition in 2D-structures on the basis of mercury telluride.