Shuxiang Li

Electronic structure and optical gain saturation of InAs1−xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement

Layer thickness and temperature variation of the giant magnetoresistance in Fe/Ag multilayers

The magnetoresistance ratio in Fe/Ag multilayers is increased dramatically with decreasing Fe layer thickness. This behavior can be explained in terms of interference of electronic Bloch waves due to interface roughness and lattice mismatch between Fe and Ag layers. At the same time, the interlayer coupling changes from ferromagnetic to antiferromagnetic when the Fe layer thickness is decreased. An anomalous temperature effect of magnetoresistance is also observed. The magnetoresistance ratio at 4.2 K is smaller than that at 300 K when the Fe layer thickness is larger than about 12 A, which can be attributed to the presence of some superparamagnetic‐like thin pieces at the interfaces.

Influence of microstructure on magnetoresistance of FeAg granular films

The magnetoresistance of FeAg granular films with optimum composition has been systematically studied as a function of film thickness. It was found that the giant magnetoresistance increases rapidly with increasing film thickness in the initial stage, and beyond about 500 A the improvements become limited. The saturation field was also found to rise with increasing film thickness. Transmission electron microscope studies showed that with the increase of film thickness the microstructure becomes more homogeneous, with smaller grains and fewer structural defects such as twins. A discussion of the influence of microstructure on magnetoresistance and saturation field is presented.

Effect of interface on the properties of Ti/NiFe thin films

The microstructure, anisotropic magnetoresistance, and magnetic properties of Ti/Ni81Fe19 thin films have been investigated with respect to annealing temperatures (TA) up to 450u2009°C as well as to anneal times (tA). It has been shown that 120u2009°C is the optimum annealing temperature and that tA has no significant influence on the properties with annealing at 270u2009°C. Auger depth profiling was used to study interdiffusion kinetics. The diffusivity D and activation energy e have been estimated at about 2.0×10−17 cm2/s and 1.69 eV, respectively.

Oscillatory GMR in sputtered Fe/Ag multilayers

Abstract The observation of giant magnetoresistance (GMR) in sputtered Fe Ag multilayers is reported. The maximum GMR reaches −7.3% at 1.5 K. The amplitude of the GMR oscillates with variations in Ag thickness; the oscillation period is about 11 A. An anomaly in the temperature dependence of the saturation field was also observed and is discussed in terms of the interface superparamagnetic state.

Observation of giant magnetoresistance in FeMo multilayers

Abstract The giant magnetoresistance (GMR) in magnetron sputtered Fe Mo multilayers was reported. At 4.2 K, the maximum value of MR reaches 12%. Our present results confirm that the giant magnetoresistance is associated with the existence of antiferromagnetic interlayer coupling in Fe Mo multilayers.

Anisotropic Zeeman splitting and Stark shift of In1−yMnyAs1−xNx oblate quantum dots

The electronic structure, Zeeman splitting, and Stark shift of In1−yMnyAs1−xNx oblate quantum dots are studied using the ten-band k⋅p model including the sp-d exchange interaction between the carriers and the magnetic ion. The Zeeman splitting of the electron ground states is almost isotropic. The Zeeman splitting of the hole ground states is highly anisotropic, with an anisotropy factor of 918 at B=0.1u2002T. The Zeeman splittings of some of the electron and hole excited states are also highly anisotropic. It is because of the spin-orbit coupling which couples the spin states with the anisotropic space-wave functions due to the anisotropic shape. It is found that when the magnetic quantum number of total orbital angular momentum is nearly zero, the spin states couple with the space-wave functions very little, and the Zeeman splitting is isotropic. Conversely, if the magnetic quantum number of total orbital angular momentum is not zero, the space-wave functions in the degenerate states are different, and the ...