Tilted InSb nanostructures fabricated by off-normal ion beam irradiation

ABSTRACT

Using a two-step focused ion beam irradiation process, tilted InSb nanostructures have been fabricated using a off-normal angle of irradiation. In the first step, a well-focused ion beam was used to irradiate the surface of the structure to achieve top-down sputtering. In the second step, the ion beam was used to irradiate the entire surface to promote bottom-up nanostructure growth through the migration of ion-beam-induced interstitial atoms. The formation of a nanostructure with a 46° tilt and an aspect ratio of 0.5 was achieved using ion beam irradiation at an angle of 45° in both steps of the process. The 2% concentration of point defects obtained by changing the volume of the nanostructure before and after irradiation contributed to the growth of the structure. The results showed that many point defects did not recombine, and survived to contribute toward the growth of the wall structure.     

Tunable wave-vector filtering in a two-dimensional electron gas modulated by magnetic barriers and δ-doping

We report a theoretical investigation on the control of wave-vector filtering (WVF) in a two-dimensional electron gas modulated by realistic magnetic barriers and δ-doping, which can be experimentally realised by depositing a ferromagnetic stripe on the surface of a GaAs/Al_xGa_1?xAs heterostructure and using atomic layer doping. Theoretical analysis demonstrates that a sizeable WVF effect still exists even if δ-doping is introduced into the device. Numerical calculation reveals that the WVF efficiency is related closely to the δ-doping. Thus, the WVF effect in a magnetic nanostructure can be conveniently manipulated by properly adjusting the weight and/or the position of the δ-doping, giving rise to a tunable momentum filter for nanoelectronics applications.     

A novel method for measurement of electronic work function of micro/nanostructure materials using a Kelvin probe system

Work function (WF) can be measured using the Kelvin probe (KP) technique to characterize surface behavior of micro/nanostructures grown on substrates such as metals or semiconductors. However, for such micro/nanostructures, substrates with different WF can strongly affect the measurements if they are exposed directly to face the Kevin probe tip. In this article, a model is proposed to investigate the WF of sparse ZnO nanorods grown on an Si substrate. It is demonstrated that theoretical results from the model are consistent with experimental observations performed using a KP system.     

Electrically-manipulable spin filter based on a novel magnetic nanostructure

In order to achieve a controllable spin-polarized source, we have applied a transverse electric field to a spin filter based on a novel magnetic nanostructure with zero average magnetic field. We have analytically calculated the transmission coefficient, conductance and spin polarization for electrons to transit the device in the presence of a transverse electric field. The results demonstrate that the transmission, the conductance and the spin polarization vary sensitively with the electric field. It is shown that the performance of the spin filter can be manipulated expediently by adjusting the transverse electric field. Thus, the spin filter can be utilized as an electrically controllable spin-polarized source for spintronics applications.     

Controllable electron-momentum filter in a δ-doped magnetically modulated semiconductor nanostructure

ABSTRACT

We have theoretically investigated the control of wave-vector filtering (WVF) by introducing δ-doping into a magnetically modulated nanostructure fabricated by depositing ferromagnetic stripes on top and bottom of a GaAs/Al_xGa_{1 ?x}As heterostructure. With the help of an improved transfer matrix method, the Schrödinger equation for electrons in this semiconductor nanostructure is solved exactly and the transmission efficient calculated numerically. We demonstrate that the WVF efficiency is associated closely with the weight and position of the δ-doping, which may be helpful for designing a controllable electron-momentum filter based on such a magnetically modulated semiconductor nanostructure.     

Transient photoconductivity in n-type a-Si: H

Abstract

The long-time transient photocurrent decay in annealed and light-exposed P-doped a-Si: H is examined experimentally and by numerical modelling. The decay is a dispersive power law with sublinear index, extending to times longer than 1s, and the decay rate increases with temperature. Light exposure dramatically decreases the decay amplitude but does not affect the rate of decay. The phenomenon is discussed in terms of a comprehensive multiple-trapping model in which transport of thermalized electrons is essentially non-dispersive, and recombination of free carriers via defects is dispersive, owing to continued thermalization of excess holes. The slower recombination step is free-hole capture by D^? states, while the decay of the total excess ensemble is controlled by hole release from valence-band tail traps. The index of the excess photoelectron decay provides information on the valence-band tail states, which are exponentially distributed, with a characteristic energy estimated as 0·06 eV.