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.

Annihilation of deep level defects in InP through high temperature annealing

Deep level transient spectroscopy (DLTS) and thermally stimulated current spectroscopy (TSC) have been used to investigate defects in semi-conducting and semi-insulating (SI) InP after high temperature annealing, respectively. The results indicate that the annealing in iron phosphide ambient has an obvious suppression effect of deep defects, when compared with the annealing in phosphorus ambient. A defect annihilation phenomenon has also been observed in Fe-doped SI-InP materials after annealing. Mechanism of defect formation and annihilation related to in-diffusion of iron and phosphorus is discussed. Nature of the thermally induced defects has been discussed based on the results. (c) 2007 Elsevier Ltd. All rights reserved.

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.

Proton irradiation-induced defects in undoped GaSb studied by positron lifetime spectroscopy and photoluminescence

Undoped GaSb was irradiated by 2.6 MeV protons. The irradiation-induced defects were studied by positron lifetime spectroscopy (PLS) and photoluminescence (PL). Positron lifetime measurements showed that vacancy-type defects were introduced after irradiation, and divacancies were formed at higher irradiation dose. Annealing experiments revealed there were different annealing steps between the as grown and proton-irradiated samples, the reason for which was tentatively attributed to the formation of divacancies in the proton-irradiated samples during annealing. All the vacancy defects could be annealed out at around 500 degrees C. The PL intensity quickly fell down after proton irradiation and decreased with increasing irradiation dose, indicating that irradiation induced non-irradiative recombination centers, whose candidates were assigned to the vacancy defects induced by proton irradiation.

Decay lifetime and evolution of semiconductor quantum dots in photonic crystals

Spontaneous emission from GaAs/AlGaAs quantum dots (QDs) embedded in photonic crystals with a narrow photonic band gap is studied theoretically. The results show that the decay lifetime is very sensitive to the sizes of QDs, and both inhibited and accelerated emission can occur, which had been indicated in a previous experiment. The Weisskopf-Wigner approximation, good for atoms and molecules, may be incorrect for QDs. A damped Rabi oscillation of the excited state with the transition frequency outside the photonic band gap may appear, which is impossible for atoms and molecules. (c) 2008 Elsevier Ltd. All rights reserved.

Deep level defects in high temperature annealed InP

Deep level defects in high temperature annealed semi-conducting InP have been studied by deep level transient spectroscopy (DLTS). There is obvious difference in the deep defects between as-grown InP, InP annealed in phosphorus ambient and iron phosphide ambient, as far as their quantity and concentration are concerned. Only two defects at 0.24 and 0.64 eV can be detected in InP annealed in iron phosphide ambient, while defects at 0.24, 0.42, 0.54 and 0.64 eV have been detected in InP annealed in phosphorus ambient, in contrast to two defects at 0.49 and 0.64 eV or one defect at 0.13 eV in as-grown InP. A defect suppression phenomenon related to iron diffusion process has been observed. The formation mechanism and the nature of the defects have been discussed.

Method for generating maximally entangled states of multiple three-level atoms in cavity QED

We propose a scheme to generate maximally entangled states (MESs) of multiple three-level atoms in microwave cavity QED based on the resonant atom-cavity interaction. In the scheme, multiple three-level atoms initially in their ground states are sequently sent through two suitably prepared cavities. After a process of appropriate atom-cavity interaction, a subsequent measurement on the second cavity field projects the atoms onto the MESs. The practical feasibility of this method is also discussed.

Photoemission study of chemisorption and Fermi-level pinning at K/GaAs(100) interface with synchrotron radiation

The adsorption of K on the n-GaAs(I 0 0) surface was investigated by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SR-PES). The Ga3d and As3d core level was measured for clean and K adsorbed GaAs(I 0 0) surface. The adsorption of K induced chemical reaction between K and As, and the K-As reactant formed when the K coverage theta > I ML. The chemical reaction between K and Ga did not occur, but Ga atoms were exchanged by K atoms. From the data of band bending, the Schottky barrier is 0.70 eV. The Fermi-level pinning was not caused by defect levels. The probable reason is that the dangling bonds of surface Ga atoms were filled by the outer-shell electrons of K atoms, forming a half-filled surface state. The Fermi-level pinning was caused by this half-filled surface state. (c) 2004 Elsevier B.V. All rights reserved.

Level-oscillation-induced pump effect in a quantum dot with asymmetric constrictions

We have investigated the pump effect induced by the level oscillation in a quantum dot with asymmetric constrictions. The curve of pumped current versus the frequency of level oscillation undulates at zero temperature. The oscillation of the pumped current can be smeared by increasing the temperature and the coupling strength between the quantum dot and the leads. Either the temperature increase or the coupling strength enhancement can lead to a positive or negative effect on the pumped current, depending on the parameters of the quantum dot system. A larger level-oscillation magnitude results in a larger pumped current, especially in the low-frequency case. An analytical expression of the pumped current is obtained in the regime far from adiabatic. A convenient physical picture based on our analytic result is proposed, with which we can explain all the features of the pumped current curves.

Generation of a supersinglet of three three-level atoms in cavity QED

We propose a scheme to generate a supersinglet of three three-level atoms in microwave cavity quantum electrodynamics based on the resonant atom-cavity interaction. In the scheme, three three-level atoms in suitable initial states are sequentially sent through three cavities originally prepared in their vacuum states. After an appropriate atom-cavity interaction process, in the subsequent measurement on the third cavity field the atoms are projected onto the desired supersinglet. The practical feasibility of this method is discussed.

Influence of level filling on optical properties of quantum well

In a specially- designed three-barrier-double-well tunneling structure, electron injecting from the emitter in combination with escaping through a resonant-tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first-excited electron state can result in a suppression to quantum confinement Stark effect. Moreover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the quantum well, that cannot be explained by the theory of hand-to-hand transition in the framework of single electron picture.

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.

Optical properties of the E-0+Delta(0) energy level higher than the bandgap of GaAs studied by micro-photoluminescence technique

Using micro-photoluminescence technique, we observed a new photoluminescence peak about 0.348 eV above the bandgap of GaAs (E-0). By analyzing its optical characteristics, we assigned this peak to the nonequilibrium luminescence emission from the E-0 + Delta(0) bandgap in semi-insulated GaAs, which was further verified by Raman results. The observed polarization, excitation power dependence and temperature dependence of the photoluminescence spectra from the E-0 + Delta(0) energy level were very similar to those from the E-0 of GaAs. This mainly resulted from the common conduction band around Gamma(6) that was involved in the two optical transition processes, and indicated that the optical properties of bulk GaAs were mainly determined by the intrinsic properties of the conduction band. Our results demonstrated that the micro-photoluminescence technique is a powerful tool to investigate the high energy states above the fundamental bandgap in semiconductor materials.

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 x 10(12) cm(-2) was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

Generation and suppression of deep level defects in InP

Deep level defects in as-grown and annealed n-type and semi-insulating InP have been studied. After annealing in phosphorus ambient, a large quantity of deep level defects were generated in both n-type and semi-insulating InP materials. In contrast, few deep level defects exist in InP after annealing in iron phosphide ambient. The generation of deep level defects has direct relation with in-diffusion of iron and phosphorus in the annealing process. The in-diffused phosphorus and iron atoms occupy indium sites in the lattice, resulting in the formation of P anti-site defects and iron deep acceptors, respectively. T e results indicate that iron atoms fully occupy indium sites and suppress the formation of indium vacancy and P anti-site, etc., whereas indium vacancies and P anti-site defects. are formed after annealing in phosphor-us ambient. The nature of the deep level defects in InP has been studied based on the results.