Low-dimensional structures in high magnetic fields
Zusammenfassung der Projektergebnisse
In this work the electron and holes dynamics of low-dimensional structures were investigated in pulsed magnetic fields up to 50 T. The developed high precision measurement system provides simultaneous magnetoresistance and Hall effect measurements during 80 ms magnetic field pulse as well current-voltage characteristic measurements at the top of the field pulse where magnetic field varies slightly, ± 0.5 %. Investigation of size-dependent magnetoresistance in 3D structures, 2D electron/hole gas in quantum wells and transport mechanisms via quasi 0D and 1D states helps to make a next step to understand the nature. This research was encouraged not only by fundamental interest but also possible future applications of investigated materials. Study of size-dependent magnetoresistance effect in inhomogeneous conductors: Size-dependent positive magnetoresistance effect was investigated on narrow band gap (energy Eg = 0.3 eV at T = 300 K) and high electron mobility (μ > 1m2V-1s-1 at T = 300 K) InAs grown on GaAs. It was shown that the room temperature transverse magnetoresistance is linear at magnetic fields up to 50 T; it is weakly affected by temperature and can be controlled by incorporation of nitrogen substitutional impurities (~1 %) and/or sample geometries. The electron dynamics in the presence of electrical and magnetic fields were analyzed by Monte Carlo simulations. This study revealed that the linear magnetoresistance arises from the stochastic behavior of the electronic cycloidal trajectories around low-mobility islands in high-mobility inhomogeneous conductors. The size-dependent magnetoresistance effect in inhomogeneous materials was observed in the case an average distance between neighbor low-mobility islands becomes comparable with sample geometry. The observed effects are attractive features for several applications ranging from infrared gas sensing and security devices to low-power, sensitive Hall sensors and magnetoresistors. This work was done in collaboration with A. Patanè, O. Makarovsky, L. Eaves (the University of Nottingham, UK), and N. Mori (Osaka University, Japan). Study of 2D electron/hole gas in quantum wells: Resistance and Hall effect of low-mobility 2D electron gas in GaAs quantum wells (QWs) were studied in tilted magnetic field up to 50 T. The low-mobility systems are widely used for study of electron-electron interaction contribution to the conductivity in the diffusion regime when kBT << ħζ where ζ is transport relaxation time. Since the interaction contribution depends on the µBgB to kBT ratio, where µB is the Bohr magneton, the knowing of the g-factor is important for the quantitative analysis. Analyzing the angle dependent amplitude of the Shubnikov-de Haas oscillations the value of g-factor, g = 0.9 ± 0.1, was calculated. The g-factor obtained from resistance and Hall Effect measurements is noticeably larger than that predicted theoretically and obtained from optical experiments. This work was done in collaboration with A. Germanenko (Ural Federal University, Ekaterinburg, Russian Federation). The study of temperature dependent Shubnikov-de Haas pattern and cyclotron resonance of p-type Ge channels of strained Ge/Si1−xGex QWs measured up to 47 T revealed that the effective masses of holes in the channels depend on energy and the strain. These are promising materials for high performance CMOS (Complementary Metal Oxide Semiconductor) devices. In comparison to Si channels, p-type Ge channels have much higher mobility. It was shown that the built-in compressive strain in the quantum well leads to the reduction of the effective mass and the suppression of the interband phonon scattering. This work was done in collaboration with N. Miura (National Institute for Materials Science, Tsukuba, Japan) and O. Drachenko (Helmholtz Forschungszentrum Dresden). Quantum transport via quasi 0 D and 1 D sates in Au nanoparticle-cellulose films: The magnetotransport properties of hybrid cellulose films containing of 27 wt % to 44 wt % of gold nanoparticles (Au NPs) with diameter of about 10 nm were investigated in a wide temperature range (1.7 K < T < 300 K). This study showed that the mechanism of electronic conduction in Au NP-cellulose films is strongly dependent on the resistivity and changes from tunneling via intermediate quasi 0D and 1D virtual states in a sequence of Au NPs to metallic-like with decreasing resistivity of the films. In the highly resistive films, the high magnetic field experiments revealed negative magnetoresistance. This is attributed to the spin polarization of the Au NPs and the magnetic field induced suppression of electron spin-flips during spin-polarized tunneling in the NP network. These findings on transport properties of Au NP-cellulose are relevant to future applications that require environmentally benign and flexible conducting materials. This work was done in collaboration with L. Turyanska, O. Makarovsky and Amalia Patanè (University of Nottingham, UK).
Projektbezogene Publikationen (Auswahl)
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g-Factor of low mobility 2D GaAs electron gas as determined from high magnetic field experiments, Physica E 42 (2010) 960–963
V. Germanenko, N. Kozlova, G. M. Minkov, O. E. Rut, A. A. Sherstobitov, J. Freudenberger
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Cyclotron Resonance Mass and Fermi Energy Pinning in the In(AsN) Alloy, Applied Physics Letters 98 (2011) 162109
O. Drachenko, A. Patanè, N. Kozlova, Q. D. Zhuang, A. Krier, L. Eaves, M. Helm
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High magnetic field quantum transport in Au nanoparticle–cellulose films, Nanotechnology 23 (2012) 045702 (5pp)
L. Turyanska, O. Makarovsky, A Patanè, N. V. Kozlova, Z. Liu, M. Li, and S. Mann
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Linear magnetoresistance due to multiple-electron scattering by low-mobility islands in an inhomogeneous conductor, Nature Communications 3:1097 (2012)
N. V. Kozlova, N. Mori, O. Makarovsky, L. Eaves, Q. D. Zhuang, A. Krier, A. Patanè
