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Abstract: Self-assembled InAs quantum dots (QDs) embedded close to the tunnel barrier in the upper well of the double quantum well system act as a sensitive probe to investigate the tunneling between the edge states. In the monolayer configuration, when the tunnel interaction between the edge states was absent, the Hall resistance exhibited well-developed and quantized Hall plateaus at integer filling factors. However, in bilayer configuration, no Hall plateaus were seen and an abrupt increase in the resistance was observed at B=2.1T, whereas no such anomalies were found in the control sample. This behavior appears to have its origin from the interaction between the edge state electrons and QDs as they tunnel across the barrier due to the difference in chemical potential between the upper and lower well. [Copyright &y& Elsevier]

We investigate the transport properties of two-dimensional electron gases (2DEG) formed in a GaAs/AlGaAs quantum well, where self-assembled InAs quantum dots were grown at the center of the GaAs well. Due to the resulting strain fields repulsive short-range scattering is experienced by the conduction electrons in the 2DEG. In a perpendicular magnetic field, there are transitions between quantum Hall liquids at filling factors ν=1 and 2 and the insulating phase. We show that the boundary of insulator–Quantum Hall transitions can be identified either by analysing the temperature-independent points in ρxx or from the peaks in σxx at low temperatures and both methods give similar results. [Copyright &y& Elsevier]

We present a study of magnetotransport properties in two-dimensional electron gases formed in a GaAs/Al0.33Ga0.67As quantum well, where self-assembled InAs quantum dots have been inserted into the centre of the GaAs well. In a perpendicular magnetic field there are transitions between quantum Hall liquids at filling factors ν=2 and 1 and the insulating phase from temperature independent points. In the insulating regime we observe ν=4 and 6 quantum Hall states due to Landau quantisation. We are able to construct a phase diagram in which Shubnikov–de Haas oscillations and insulating behaviour coexist. [Copyright &y& Elsevier]

Abstract: In the present report, ZnO nanoparticles of size ∼9nm have been assembled by optimized dielectrophoresis process on the pre-fabricated nanogap (60nm) electrodes. The fabricated ZnO nanoparticles based nano-device was studied for its I–V characteristic and typical non-linear semiconducting behavior was observed. When illuminated with ultraviolet (UV) radiation of wavelength 365nm, a tremendous change in conductivity of almost one order of magnitude was observed indicating a high sensitivity of the fabricated nano-device. Temporal photoresponse characteristics were studied at a fixed level of UV illumination intensity (1.0mW/cm2) and the response time under 10ms was recorded. The photoresponse curve exhibited a perfect rise and recovery without any slow component. Absence of slow component in the photoresponse characteristic suggested that shallow trapping centers were inactive and the photoconductivity could be due to the true quantum yield of photogenerated charge carriers through interband and deep trapping centers transitions. [Copyright &y& Elsevier]

Abstract: The metallic-like regime characterized by Shubnikov–de Haas (SdH) oscillations is investigated between localization-induced weak insulator and quantum Hall liquid in a gated two-dimensional GaAs electron system containing InAs dots. Multiple SdH crossing points are observed in the longitudinal resistivity before the appearance of the critical point of a plateau transition with increasing perpendicular magnetic field. In conductivities, however, there is no corresponding crossing in the metallic-like regime because of the T-dependent Hall slope under electron–electron interaction, which provides an explicit way to distinguish SdH crossing points from the critical point in our study. [Copyright &y& Elsevier]

It is now established that if there are an equal number of positively and negatively charged impurities, the quantum Hall plateaux in ρxy(B) are expected to be centred about the classical value ρxy=B/(en) where n is the 2D carrier density. It has also been shown that when repulsive or attractive scattering centres are deliberately introduced close to a two-dimensional electron gas (2DEG), the centres of the quantum Hall plateaux are shifted to higher or lower magnetic field, respectively. In this paper, we present magneto transport measurements on a high-quality GaAs electron system. We extend this concept to the composite fermions where each electron is bound to two magnetic flux quanta. We provide compelling evidence that the dominant scattering for the composite fermions is different from that for electrons. This is supported by studying the upshift of the ν=1 quantum Hall plateau within the composite fermion picture. [Copyright &y& Elsevier]

Abstract: Amorphous silicon oxide (SiO x ) nanowires were directly grown by thermal processing of Si substrates. Au and Pd–Au thin films with thicknesses of 3nm deposited on Si (001) substrates were used as catalysts for the growth of nanowires. High-yield synthesis of SiO x nanowires was achieved by a simple heating process (1000–1150°C) in an Ar ambient atmosphere without introducing any additional Si source materials. The as-synthesized products were characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy measurements. The SiO x nanowires with lengths of a few and tens of micrometers had an amorphous crystal structure. The solid–liquid–solid model of nanowire formation was shown to be valid. [Copyright &y& Elsevier]

We report the drastic enhancement of Shubnikov–de Haas (SdH) oscillations observed in a GaN/AlGaN heterostructure by microwave modulation. The dependence of the SdH pattern on microwave power and temperature are investigated. The underlying mechanism is attributed to the effect of carrier heating. This technique helps study the transport properties of two-dimensional electrons in a GaN/AlGaN heterostructure. In addition, this method has the advantage of keeping the carrier concentration fixed and not requiring expensive high-energy laser facilities compared with carrier-modulated SdH measurements. [Copyright &y& Elsevier]

We present a study of the transport and quantum lifetime dependence on electron density in two completely different kinds of two-dimensional electron gas systems. We observed that both the two scattering time increase with increasing the electron density. But the ratios of the transport to the quantum lifetime have different tendency with the electron density, which do not conform to the conventional theory. We speculate that the screening effects need to be considered in order to explain our experimental results. [Copyright &y& Elsevier]

We studied the insulator-quantum Hall conductor transition which separates the low-field insulator from the quantum Hall state of the filling factor ν=4 on a gated two-dimensional GaAs electron system containing self-assembled InAs quantum dots. To enter the ν=4 quantum Hall state directly from the low-field insulator, the two-dimensional system undergoes a crossover from the low-field localization to Landau quantization. The crossover, in fact, covers a wide range with respect to the magnetic field rather than only a small region near the critical point of the insulator-quantum Hall conductor transition. [Copyright &y& Elsevier]

We report the drastic enhancement of Shubnikov–de Haas (SdH) oscillations observed in a GaN/AlGaN heterostructure by microwave modulation. The dependence of the SdH pattern on microwave power and temperature are investigated. The underlying mechanism is attributed to the effect of carrier heating. This technique has the advantage of keeping the carrier concentration fixed and not requiring expensive high-energy laser facilities compared with carrier-modulated SdH measurements. Moreover, we have investigated the low-temperature transport properties of front-gated Al0.18Ga0.82N/GaN heterostructures. By changing the applied gate voltage, we can vary the carrier density in our sample. At high carrier densities (n>4.65×1012 cm−2), the measured mobility (μ) is found to be a decreasing function of carrier density as μ∼n−0.31. Loss of mobility with increasing carrier density is dominated by interface roughness scattering. At low carrier densities (n<4.24×1012 cm−2), the measured mobility is found to be an increasing function of carrier density as μ∼n0.34. This is consistent with remote ionized impurity scattering, although the measured exponent 0.34 is smaller than the typical value (0.7–1.5) observed in an AlGaN/GaN electron system. A possible reason is that our sample mobility is approximately five times lower than those in other devices for a similar electron density. [Copyright &y& Elsevier]

We have measured the low-temperature transport properties of front-gated GaAs/Al0.33Ga0.67As heterostructures. Collapse of spin-splitting and an enhanced Lande´ |g|-factor at Landau level filling factors both ν=3 and 1 are observed. Our experimental results show direct evidence that the electron–electron interactions are stronger at ν=3 than those at ν=1 over approximately the same perpendicular magnetic field range. [Copyright &y& Elsevier]

We report low-temperature magnetoresistivity measurements of high-quality gated two-dimensional (2D) electron systems. In the dilute electron density limit, we show evidence for spin polarisation in an in-plane magnetic field. Using a simple model, we estimate the Lande´ g-factor in this dilute two-dimensional electron gas to be about 3.32. The enhanced Lande´ g-factor compared with that of a bulk GaAs 2D electron system (0.44) is ascribed to electron–electron interaction effects at ultra-low electron densities. [Copyright &y& Elsevier]

We report low-temperature magnetoresistivity measurements of a high-quality gated two-dimensional electron gas (2DEG). In the dilute electron density limit, we show evidence for spin polarisation in an in-plane magnetic field. Using a simple model, we estimate the Lande´ g-factor in this dilute 2DEG to be about 3.32. This enhanced Lande´ g-factor compared with that of a bulk GaAs 2D electron system (0.44) is ascribed to electron–electron interaction effects at ultra-low electron densities and the fact that over the whole measurement range rs does not vary significantly. [Copyright &y& Elsevier]