Lifetime distribution of spontaneous emission from line antennas in two-dimensional quasi-periodic photonic crystals

We investigate the lifetime distribution functions of spontaneous emission from line antennas embedded in finite-size two-dimensional 12-fold quasi-periodic photonic crystals. Our calculations indicate that two-dimensional quasi-periodic crystals lead to the coexistence of both accelerated and inhibited decay processes. The decay behaviors of line antennas are drastically changed as the locations of the antennas are varied from the center to the edge in quasi-periodic photonic crystals and the location of transition frequency is varied.

Neutron irradiation effect in two-dimensional electron gas of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures have been irradiated by neutrons with different influences and characterized by means of temperature-dependent Hall measurements and Micro-Raman scattering techniques. It is found that the carrier mobility of two-dimensional electron gas (2DEG) is very sensitive to neutrons. At a low influence of 6.13 x 10(15) cm(-2), the carrier mobility drops sharply, while the sheet carrier density remains the same as that of an unirradiated sample. Moreover, even for a fluence of up to 3.66 x 10(16) cm(-2), the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of n(s) x mu) of 2DEG to the defects induced by neutron irradiation. Raman measurements show that neutron irradiation does not yield obvious change to the strain state of AlGaN/GaN heterostructures, which proves that degradation of sheet carrier density has no relation to strain relaxation in the present study. The increase of the product of n(s) x mu of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of Ge-Ga transmuted from Ga and the recovery of displaced defects.

Mathematical symbols and computing methods in high dimensional biomimetic informatics and their applications

High dimensional biomimetic informatics (HDBI) is a novel theory of informatics developed in recent years. Its primary object of research is points in high dimensional Euclidean space, and its exploratory and resolving procedures are based on simple geometric computations. However, the mathematical descriptions and computing of geometric objects are inconvenient because of the characters of geometry. With the increase of the dimension and the multiformity of geometric objects, these descriptions are more complicated and prolix especially in high dimensional space. In this paper, we give some definitions and mathematical symbols, and discuss some symbolic computing methods in high dimensional space systematically from the viewpoint of HDBI. With these methods, some multi-variables problems in high dimensional space can be solved easily. Three detailed algorithms are presented as examples to show the efficiency of our symbolic computing methods: the algorithm for judging the center of a circle given three points on this circle, the algorithm for judging whether two points are on the same side of a hyperplane, and the algorithm for judging whether a point is in a simplex constructed by points in high dimensional space. Two experiments in blurred image restoration and uneven lighting image correction are presented for all these algorithms to show their good behaviors.

Surface recombination in GaAs thin films with two-dimensional photonic crystals

The dynamics of spontaneous emission from GaAs slabs with photonic crystals etched into them are investigated both theoretically and experimentally. It is found that the intensity of spontaneous emission decreases significantly and that photonic crystals significantly shorten the lifetime of emission. The mechanics of enhancement and the reduction of emission from photonic crystals are analyzed by considering the surface recombination of GaAs. The measured and calculated lifetimes agree at a surface recombination velocity of 1.88x10(5) cm/s.

Optical response of high-level bandgap in one-dimensional photonic crystal applying in-plane integration

A new broadband filter, based on the high level bandgap in 1-D photonic crystals (PCs) of the form Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si is designed by the plane wave expansion method (PWEM) and the transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-level bandgaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and the PC device. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Optical response of high-order band gap photonic crystal applying in-plane in one-dimensional integration

A new broadband filter, based on the high-order band gap in one-dimensional photonic crystal (PCs) of the form Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si, has been designed by the plane wave expansion method (PWEM) and transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-order band gaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and PC device. (c) 2007 Elsevier B.V. All rights reserved.

Anomalous-circular photogalvanic effect in a GaAs/AlGaAs two-dimensional electron gas

We have studied the circular photogalvanic effect (CPGE) in a GaAs/AlGaAs two-dimensional electron gas excited by near infrared light at room temperature. The anomalous CPGE observed under normal incidence indicates a swirling current which is realized by a radial spin current via the reciprocal spin-Hall effect. The anomalous CPGE exhibits a cubic cosine dependence on the incidence angle, which is discussed in line with the above interpretation.

Strong Spin-Orbit Interactions in an InAlAs/InGaAs/InAlAs Two-Dimensional Electron Gas by Weak Antilocalization Analysis

Spin-orbit interactions in a two-dimensional electron gas were studied in an InAlAs/InGaAs/InAlAs quantum well. Since weak anti localization effects take place far beyond the diffusive regime, (i.e., the ratio of the characteristic magnetic field, at which the magnetoresistance correction maximum occurs, to the transport magnetic field is more than ten) the experimental data are examined by the Golub theory, which is applicable to both diffusive regime and ballistic regime. Satisfactory fitting lines to the experimental data have been achieved using the Golub theory. In the strong spin-orbit interaction two-dimensional electron gas system, the large spin splitting energy of 6.08 meV is observed mainly due to the high electron concentration in the quantum well. The temperature dependence of the phase-breaking rate is qualitatively in agreement with the theoretical predictions. (C) 2009 The Japan Society of Applied Physics

Electric-tunable magneto resistance effect in a two-dimensional electron gas modulated by hybrid magnetic-electric barrier nanostructure

The electric-tunable spin-independent magneto resistance effect has been theoretically investigated in ballistic regime within a two-dimensional electron gas modulated by magnetic-electric barrier nanostructure. By including the omitted stray field in previous investigations oil analogous structures, it is demonstrated based on this improved approximation that the magnetoresistance ratio for the considered structure can be efficiently enhanced by a proper electric barrier up to the maximum value depending on the specific magnetic suppression. Besides, it is also shown the introduction of positive electrostatic modulation can effectively overcome the degradation of magnetoresistance ratio for asymmetric configuration and enhance the visibility of periodic pattern induced by the size effect, while for an opposite modulation the system magnetoresistance ratio concerned may change its sign. (C) 2009 Elsevier B.V. All rights reserved.

Ballistic electron transport in hybrid ferromagnet/two-dimensional electron gas sandwich nanostructure: Spin polarization and magnetoresistance effect

We have theoretically investigated ballistic electron transport through a combination of magnetic-electric barrier based on a vertical ferromagnet/two-dimensional electron gas/ferromagnet sandwich structure, which can be experimentally realized by depositing asymmetric metallic magnetic stripes both on top and bottom of modulation-doped semiconductor heterostructures. Our numerical results have confirmed the existence of finite spin polarization even though only antisymmetric stray field B-z is considered. By switching the relative magnetization of ferromagnetic layers, the device in discussion shows evident magnetoconductance. In particular, both spin polarization and magnetoconductance can be efficiently enhanced by proper electrostatic barrier up to the optimal value relying on the specific magnetic-electric modulation. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3041477]

Tuning of plasmon propagation in two-dimensional electrons

It is shown theoretically that the propagation of plasmons can be tuned by an external electric field via spin-orbit interactions in a two-dimensional electron gas formed in a semiconductor heterostructure. This may provide a manageable way of transmitting quantum information in a quantum device. A possible plasmon field effect transistor is proposed.

Spin precession induced by an effective magnetic field in a two-dimensional electron gas

We theoretically study the spatial behaviors of the spin precession in a two-dimensional electron system with spin-orbit interaction. Through analysis of interaction between the spin and the effective magnetic field in the system, we obtain the general conditions to generate a persistent spin helix and predict a persistent spin helix pattern in [001]-grown quantum wells. Particularly, we demonstrate that the phase of spin can be locked to propagate in a quantum well with SU(2) symmetry.

One-dimensional quantum waveguide theory of Rashba electrons

The ballistic spin transport in one-dimensional waveguides with the Rashba effect is studied. Due to the Rashba effect, there are two electron states with different wave vectors for the same energy. The wave functions of two Rashba electron states are derived, and it is found that their phase depend on the direction of the circuit and the spin directions of two states are perpendicular to the circuit, with the +pi/2 and -pi/2 angles, respectively. The boundary conditions of the wave functions and their derivatives at the intersection of circuits are given, which can be used to investigate the waveguide transport properties of Rashba spin electron in circuits of any shape and structure. The eigenstates of the closed circular and square loops are studied by using the transfer matrix method. The transfer matrix M(E) of a circular arc is obtained by dividing the circular arc into N segments and multiplying the transfer matrix of each straight segment. The energies of eigenstates in the closed loop are obtained by solving the equation det[M(E)-I]=0. For the circular ring, the eigenenergies obtained with this method are in agreement with those obtained by solving the Schrodinger equation. For the square loop, the analytic formula of the eigenenergies is obtained first The transport properties of the AB ring and AB square loop and double square loop are studied using the boundary conditions and the transfer matrix method In the case of no magnetic field, the zero points of the reflection coefficients are just the energies of eigenstates in closed loops. In the case of magnetic field, the transmission and reflection coefficients all oscillate with the magnetic field; the oscillating period is Phi(m)=hc/e, independent of the shape of the loop, and Phi(m) is the magnetic flux through the loop. For the double loop the oscillating period is Phi(m)=hc/2e, in agreement with the experimental result. At last, we compared our method with Koga's experiment. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253752]

Spin dynamics of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system

We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T-2(*)) of electrons decreases monotonically with increasing magnetic field, it has a nonmonotonic dependence on the temperature and reaches a peak value of 596 ps at 36 K, indicating the effect of intersubband electron-electron scattering on the electron-spin relaxation.

Fabrication of high quality two-dimensional photonic crystal mask layer patterns

This work discusses the fabrication of two-dimensional photonic crystal mask layer patterns. Photonic crystal patterns having holes with smooth and straight sidewalls are achieved by optimizing electron beam exposure doses during electron beam lithography process. Thereafter, to precisely transfer the patterns from the beam resist to the SiO2 mask layer, we developed a pulse-time etching method and optimize various reaction ion etching conditions. Results show that we can obtain high quality two-dimensional photonic crystal mask layer patterns.