Investigations on optical properties of AlGaInN epilayers grown by mocvd

Microscopic luminescence and Raman scattering study was carried on AIInGaN quaternary alloy. Based on the analyses of SEM image and cathodoluminescence spectra measured around V-defects, the correlation between V-defect formation and indium segregation was clarified. Raman scattering of thin AlInGaN epilayers was investigated by using the short wavelength excitation of 325nm laser line. The frequency shift of A(1)(LO) phonon induced by the change of Al composition in alloy was observed. The Raman scattering of LO phonons was found to be resonantly enhanced with outgoing resonance, and it is attributed to the cascade-like electron-multiphonon interaction mechanism.

Spontaneous emission lifetime distribution of infinite line antennas in two-dimensional photonic crystals with finite size

The authors calculate the lifetime distribution functions of spontaneous emission from infinite line antennas embedded in two-dimensional disordered photonic crystals with finite size. The calculations indicate the coexistence of both accelerated and inhibited decay processes in disordered photonic crystals with finite size. The decay behavior of the spontaneous emission from infinite line antennas changes significantly by varying factors such as the line antennas' positions in the disordered photonic crystal, the shape of the crystal, the filling fraction, and the dielectric constant. Moreover, the authors analyze the effect of the degree of disorder on spontaneous emission. (c) 2007 American Institute of Physics.

Measurement of a reciprocal four-port transmission line structure using the 16-term error model

A new method to measure reciprocal four-port structures, using a 16-term error model, is presented. The measurement is based on 5 two-port calibration standards connected to two of the ports, while the network analyzer is connected to the two remaining ports. Least-squares-fit data reduction techniques are used to lower error sensitivity. The effect of connectors is deembedded using closed-form equations. (C) 2007 Wiley Periodicals, Inc.

Giant and zero electron g factors of dilute nitride semiconductor nanowires

The electronic structures and electron g factors of InSb1-sNs and GaAs1-sNs nanowires and bulk material under the magnetic and electric fields are investigated by using the ten-band k.p model. The nitrogen doping has direct and indirect effects on the g factors. A giant g factor with absolute value larger than 900 is found in InSb1-sNs bulk material. A transverse electric field can increase the g factors, which has obviously asymmetric effects on the g factors in different directions. An electric field tunable zero g factor is found in GaAs1-sNs nanowires. (C) 2007 American Institute of Physics.

Structure tuning of line-defect waveguides based on silicon-on-insulator photonic crystal slabs

We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a siliconon-insulator substrate and characterize them using a tunable laser source over a wavelength range from 1510nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant. We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.

Application of ICA in on-line verification of the phase difference of the current sensor

The performance of the current sensor in power equipment may become worse affected by the environment. In this paper, based on ICA, we propose a method for on-line verification of the phase difference of the current sensor. However, not all source components are mutually independent in our application. In order to get an exact result, we have proposed a relative likelihood index to choose an optimal result from different runs. The index is based on the maximum likelihood evaluation theory and the independent subspace analysis. The feasibility of our method has been confirmed by experimental results.

Design of two-dimensional photonic crystal edge emitting laser for photonic integrated circuits

An edge emitting laser based on two-dimensional photonic crystal slabs is proposed. The device consists of a square lattice microcavity, which is composed of two structures with the same period but different radius of air-holes, and a waveguide. In the cavity, laser resonance in the inner structure benelits from not only the anomalous dispersion characteristic of the first band-edge at the M point in the first Brillouin-zone but also zero photon states in the outer structure. A line defect waveguide is introduced in the outer structure for extracting photons from the inner cavity. Three-dimensional finite-difference time-domain simulations apparently show the in-plane laser output from the waveguide. The microcavity has an effective mode volume of about 3.2(lambda/eta(slab))(3) for oscillation -mode and the quality factor of the device including line defect waveguide is estimated to be as high as 1300.

Influence of longitudinal electric field on the hot-phonon effect in quantum wells

Using the Huang-Zhu model [K. Huang and B.-F. Zhu, Phys. Rev. B 38, 13377 (1988)] for the optical phonons and associated carrier-phonon interactions in semiconductor superlattices, the effects of longitudinal electric field on the energy-loss rates (ELRs) of hot carriers as well as on the hot-phonon effect (HPE) in GaAs/AlAs quantum wells (QWs) are studied systematically. Contributions of various bulklike and interface phonons to the hot-carrier relaxation are compared in detail, and comprehensively analyzed in relation to the intrasubband and intersubband scatterings for quantum cascade lasers. Due to the broken parity of the electron (hole) states in the electric field, the bulklike modes with antisymmetric potentials are allowed in the intrasubband relaxation processes, as well as the modes with symmetric potentials. As the interface phonon scattering is strong only in narrow wells, in which the electric field affects the electron (hole) states little, the ELRs of hot carriers through the interface phonon scattering are not sensitive to the electric field. The HPE on the hot-carrier relaxation process in the medium and wide wells is reduced by the electric field. The influence of the electric field on the hot-phonon effect in quantum cascade lasers is negligible. When the HPE is ignored, the ELRs of hot electrons in wide QWs are decreased noticeably by the electric field, but slightly increased by the field when considering the HPE. In contrast with the electrons, the ELRs of hot holes in wide wells are increased by the field, irrespective of the HPE. (c) 2006 American Institute of Physics.

New type of Fano resonant tunneling via Anderson impurities in superlattice

The spectrum of differential tunneling conductance in Si-doped GaAs/AlAs superlattice is measured at low electric fields. The conductance spectra feature a zero-bias peak and a low-bias dip at low temperatures. By taking into account the quantum interference between tunneling paths via superlattice miniband and via Coulomb blockade levels of impurities, we theoretically show that such a peak-dip structure is attributed to a Fano resonance where the peak always appears at the zero bias and the line shape is essentially described by a new function \xi\/\xi\+1 with the asymmetry parameter q approximate to 0. As the temperature increases, the peak-dip structure fades out due to thermal fluctuations. Good agreement between experiment and theory enables us to distinguish the zero-bias resonance from the usual Kondo resonance.

Line defect splitters for self-collimated beams in photonic crystals

A one-to-two splitter for self-collimated beams in photonic crystal (PC) is designed by inserting one row of line defects. Finite-difference time-domain (FDTD) method is used to simulate the light propagation process. Our systematical studies show that the splitting ratio is a function of the airholes size of the line defect radius, and stays fairly constant as a function of frequency. Furthermore, it is shown the numerical results can be analyzed by coupled-mode theory. (C) 2005 Elsevier B.V. All rights reserved.

Interdot interaction induced zero-bias maximum of the differential conductance in parallel double quantum dots

We have studied the equilibrium and nonequilibrium electronic transports through a double quantum dot coupled to leads in a symmetrical parallel configuration in the presence of both the inter- and the intradot Coulomb interactions. The influences of the interdot interaction and the difference between dot levels on the local density of states (LDOS) and the differential conductance are paid special attention. We find an interesting zero-bias maximum of the differential conductance induced by the interdot interaction, which can be interpreted in terms of the LDOS of the two dots. Due to the presence of the interdot interaction, the LDOS peaks around the dot levels epsilon(i) are split, and as a result, the most active energy level which supports the transport is shifted near to the Fermi level of the leads in the equilibrium situation. (c) 2006 American Institute of Physics.

Quantum dissipation and broadening mechanisms due to electron-phonon interactions in self-formed InGaN quantum dots

Quantum dissipation and broadening mechanisms in Si-doped InGaN quantum dots are studied via the photoluminescence technique. It is found that the dissipative thermal bath that embeds the quantum dots plays an important role in the photon emission processes. Observed spontaneous emission spectra are modeled with the multimode Brownian oscillator model achieving an excellent agreement between experiment and theory for a wide temperature range. The dimensionless Huang-Rhys factor characterizing the strength of electron-LO-phonon coupling and damping constant accounting for the LO-phonon-bath interaction strength are found to be similar to 0.2 and 200 cm(-1), respectively, for the InGaN QDs. (c) 2006 American Institute of Physics.

Photoluminescence of Mg-doped GaN grown by metalorganic chemical vapor deposition

Two Mg-doped GaN films with different doping concentrations were grown by a metalorganic chemical vapor deposition technique. Photoluminescence (PL) experiments were carried out to investigate the optical properties of these films. For highly Mg-doped GaN, the PL spectra at 10 K are composed of a blue luminescence (BL) band at 2.857 eV and two excitonic luminescence lines at 3.342 eV and 3.282 eV, in addition to a L2 phonon replica at 3.212 eV. The intensity of the L1 line decreases monotonously with an increase,in temperature. However, the intensity of the L2 line first slowly increases at first, and then decreases quickly with an increase in temperature. The two lines are attributed to bound excitonic emissions at extended defects. The BL band is most likely due to the transition from deep donor Mg-V-N complex to Mg shallow acceptor. From the temperature dependence of the luminescence peak intensity of the BL band, the activation energy of acceptor Mg was found to be 290 meV. (C) 2003 American Vacuum Society.

Luminescence study of (11(2)over-bar0) GaN film grown by metalorganic chemical-vapor deposition

Investigations on photoluminescence properties of (11 (2) over bar0) GaN grown on (1 (1) over bar 02) Al2O3 substrate by metalorganic chemical-vapor deposition are reported. Several emission lines not reported before are observed at low temperature. The sharp peak at 3.359 eV is attributed to the exciton bound to the neutral acceptor. Another peak at 3.310 eV represents a free-to-bound, probably a free electron-to-acceptor, transition. The 3.241 and 3.170 eV lines are interpreted as phonon replica lines of the 3.310 eV line. The phonon energy is 70 meV, consistent with the energy of transverse optical E-1 phonon. The optical properties of the lines are analyzed. (C) 2003 American Institute of Physics.

Comparative study on the broadening of exciton luminescence linewidth due to phonon in zinc-blende and wurtzite GaN epilayers

Linewidth broadening of exciton luminescence in wurtzite and zinc-blende GaN epilayers was investigated as a function of temperature with photoluminescence. A widely accepted theoretical model was used to fit the experimental data, so that the coupling parameters between exciton and acoustic and longitudinal optical phonons were obtained for both structures. It was found that the coupling constants of both exciton-acoustic optical phonon coupling and exciton-longitudinal optical phonon coupling for zinc-blende GaN are almost twice as much as the corresponding values of wurtzite GaN. These results show that the relatively strong exciton-phonon scattering seems to be characteristic to zinc-blende GaN film. (C) 2002 American Institute of Physics.