Electron Transport In Nanowires Research Articles

The interplay between Zeeman splitting and spin-orbit coupling in InAs nanowires.

Coupling of the electron orbital motion and spin, i.e., spin-orbit coupling (SOC) leads to nontrivial changes in energy-level structures, giving rise to various spectroscopies and applications. The SOC in solids generates energy-band inversion or splitting under zero or weak magnetic fields, which is required for topological phases or Majorana fermions. Here, we examined the interplay between the Zeeman splitting and SOC by performing the transport spectroscopy of Landau levels (LLs) in indium arsenide nanowires under a strong magnetic field. We observed the anomalous Zeeman splitting of LLs, which depends on the quantum number of LLs as well as the electron spin. We considered that this observation was attributed to the interplay between the Zeeman splitting and the SOC. Our findings suggest an approach of generating spin-resolved chiral electron transport in nanowires.

Fano resonances in high energy electron transport in nanowires of variable cross-section

Electron ballistic transport in 2D quantum waveguide with two narrowings is considered. For longitudinal electron motion such narrowings play the role of effective potential barriers and conditions for resonant tunneling arise. If the electron energy is sufficiently high the electron wave can scatter into different quantum states (transverse channels of the leads) which results in complicated E-dependence of the scattering amplitudes. Numerical simulations have shown that the scattering amplitudes resonances are of Fano type. The form of the transmission probability curve is conditioned by interference of the quantum states into which the electron wave is scattered by the narrowings. The suggested interference model makes possible to find the resonance parameters with high precision and to link them to the closed resonator eigenvalues.

Analysis of surface states in ZnO nanowire field effect transistors

Nanowires (NWs) have attracted considerable interests for scaled electronic and optoelectronic device applications. However, NW based semiconductor devices normally suffer from surface states due to the existence of dangling bonds or surface reconstruction. Because of their large surface-to-volume ratio, surface states in NWs can easily affect the metallic contacts to NWs and electron transport in NW. Here, we present ZnO NW surface analysis by performing current–voltage characterization on ZnO NW Schottky barrier field effect transistors with different metal contacts (Ti, Al, Au) at both room temperature and cryogenic temperature. Our results show that three metal contacts are all Schottky contacts to ZnO NWs due to surface states. Our further study reveals: (a) the surface states related Schottky barrier height (SBH) can be extracted from a back to back Schottky diodes model and the SBH values are in the range of 0.34–0.37eV for three metal contacts; (b) the trap activation energy determined from the Arrhenius plots of different Schottky metal contacts is in the range of 0.23–0.29eV, which is oxygen vacancies related; and (c) based on the space-charge-limited model, the surface state density of ZnO NW is in the range of 1.04×1010–1.24×1010/cm2.

Charge Transport in 1-D Nanostructured CdS Dye Sensitized Solar Cell

Charge transport in eosin yellow sensitized CdS 1-D nanostructures is studied. Direct conduction pathway for electron transport in nanowires enhances Voc in CdS nanowires compared to nanorods and nanoparticles. J-V characterization of nanowires results in improved efficiency of 0.184% due to fewer interparticle connections. Increase in Jsc is observed by coating CdS 1-D nanostructures on TiO2 substrate which reduces rate of recombination and photocorrosive nature of CdS photoanodes. Enhancement in efficiency up to 0.501% is achieved for CdS 1-D nanostructures DSSCs on TiO2 substrate.

Dye-sensitized solar cells based on nitrogen-doped TiO2–B nanowire/TiO2 nanoparticle composite photoelectrode

TiO2–B nanowire/TiO2 nanoparticle composite is an ideal nanomaterial for dye-sensitized solar cell photoelectrode because it combines the advantages of rapid electron transport in nanowires and high surface area of nanoparticles. Meanwhile, nitrogen doping is also an effective method for enhancing the photo-electrical conversion efficiency. In this work, nitrogen-doped TiO2–B nanowires are obtained using NH3 as a gaseous precursor under middle pressures. And the nitrogen-doped naowire/nanoparticle composite electrodes are fabricated. The conversion efficiency of nitrogen-doped nanowire/nanoparticle cells (7.21%) is higher than that of undoped nanowire/nanoparticle cells (6.10%) and nitrogen-doped nanoparticle cells (5.37%).

Microwave realization of quasi-one-dimensional systems with correlated disorder

A microwave setup for mode-resolved transport measurement in quasi-one-dimensional (quasi-1D) structures is presented. We will demonstrate a technique for direct measurement of the Green's function of the system. With its help we will investigate quasi-1D structures with various types of disorder. We will focus on stratified structures, i.e., structures that are homogeneous perpendicular to the direction of wave propagation. In this case the interaction between different channels is absent, so wave propagation occurs individually in each open channel. We will apply analytical results developed in the theory of one-dimensional (1D) disordered models in order to explain main features of the quasi-1D transport. The main focus will be selective transport due to long-range correlations in the disorder. In our setup, we can intentionally introduce correlations by changing the positions of periodically spaced brass bars of finite thickness. Because of the equivalence of the stationary Schr\"odinger equation and the Helmholtz equation, the result can be directly applied to selective electron transport in nanowires, nanostripes, and superlattices.

Self-similarity of single-channel transmission for electron transport in nanowires

We demonstrate that the single-channel transmission in the resonance tunneling regime exhibits self-similarity as a function of the nanowire length and the energy of incident electrons. The self-similarity is used to design the nonlinear transformation of the nanowire length and energy which, on the basis of known values of transmission for a certain region on the energy-length plane, yields transmissions for other regions on this plane. Test calculations with a one-dimensional tight-binding model illustrate the described transformations. Density function theory based transport calculations of Na atomic wires confirm the existence of the self-similarity in the transmission.

Effect of wire length on Coulomb blockade in ultrathin wires of recrystallized hydrogenated amorphous silicon

Electron transport in nanowires of hydrogenated amorphous silicon recrystallized by electron beam annealing has been studied. Wire length dependent electrical characteristics have been measured at low temperatures. Evidence for single electron effects with I–V characteristics has been presented. Transmission electron microscopy and photoluminescence data are used to support the electrical results. The Coulomb blockade effect is modeled as a combination of hopping conduction between a limited number of trapping sites in amorphous regions or at grain boundaries with additional Coulomb blockade effects as well as a confinement due to potential fluctuations arising from dopant distribution.

Nonlinear electron transport characteristics in ultrathin wires of recrystallized hydrogenated amorphous silicon

Electron transport in nanowires of hydrogenated amorphous silicon recrystallized by electron beam annealing has been studied. Evidence for single electron effects with I–V characteristics at low temperature has been presented. The region of the nonlinear I–V characteristics is modeled as a hopping conduction between limited number of trapping sites in amorphous regions or at grain boundaries with Coulomb blockade effect. Transmission electron microscopy is used to support this hypothesis.